Soil phosphorus cycling across a 100-year deforestation chronosequence in the Amazon rainforest.

Deforestation of tropical rainforests is a major land use change that alters terrestrial biogeochemical cycling at local to global scales. Deforestation and subsequent reforestation are likely to impact soil phosphorus (P) cycling, which in P-limited ecosystems such as the Amazon basin has implications for long-term productivity. We used a 100-year replicated observational chronosequence of primary forest conversion to pasture, as well as a 13-year-old secondary forest, to test land use change and duration effects on soil P dynamics in the Amazon basin. By combining sequential extraction and P K-edge X-ray absorption near edge structure (XANES) spectroscopy with soil phosphatase activity assays, we assessed pools and process rates of P cycling in surface soils (0-10 cm depth). Deforestation caused increases in total P (135-398 mg kg-1 ), total organic P (Po ) (19-168 mg kg-1 ), and total inorganic P (Pi ) (30-113 mg kg-1 ) fractions in surface soils with pasture age, with concomitant increases in Pi fractions corroborated by sequential fractionation and XANES spectroscopy. Soil non-labile Po (10-148 mg kg-1 ) increased disproportionately compared to labile Po (from 4-5 to 7-13 mg kg-1 ). Soil phosphomonoesterase and phosphodiesterase binding affinity (Km ) decreased while the specificity constant (Ka ) increased by 83%-159% in 39-100y pastures. Soil P pools and process rates reverted to magnitudes similar to primary forests within 13 years of pasture abandonment. However, the relatively short but representative pre-abandonment pasture duration of our secondary forest may not have entailed significant deforestation effects on soil P cycling, highlighting the need to consider both pasture duration and reforestation age in evaluations of Amazon land use legacies. Although the space-for-time substitution design can entail variation in the initial soil P pools due to atmospheric P deposition, soil properties, and/or primary forest growth, the trend of P pools and process rates with pasture age still provides valuable insights.

Long-term annual estimation of forest above ground biomass, canopy cover, and height from airborne and spaceborne sensors synergies in the Iberian Peninsula.

The Mediterranean Basin has experienced substantial land use changes as traditional agriculture decreased and population migrated from rural to urban areas, which have resulted in a large forest cover increase. The combination of Landsat time series, providing spectral information, with lidar, offering three-dimensional insights, has emerged as a viable option for the large-scale cartography of forest structural attributes across large time spans. Here we develop and test a comprehensive framework to map forest above ground biomass, canopy cover and forest height in two regions spanning the most representative biomes in the peninsular Spain, Mediterranean (Madrid region) and temperate (Basque Country). As reference, we used lidar-based direct estimates of stand height and forest canopy cover. The reference biomass and volume were predicted from lidar metrics. Landsat time series predictors included annual temporal profiles of band reflectance and vegetation indices for the 1985-2023 period. Additional predictor variables including synthetic aperture radar, disturbance history, topography and forest type were also evaluated to optimize forest structural attributes retrieval. The estimates were independently validated at two temporal scales, i) the year of model calibration and ii) the year of the second lidar survey. The final models used as predictor variables only Landsat based metrics and topographic information, as the available SAR time-series were relatively short (1991-2011) and disturbance information did not decrease the estimation error. Model accuracies were higher in the Mediterranean forests when compared to the temperate forests (R2 = 0.6-0.8 vs. 0.4-0.5). Between the first (1985-1989) and the last (2020-2023) decades of the monitoring period the average forest cover increased from 21 ± 2% to 32 ± 1%, mean height increased from 6.6 ± 0.43 m to 7.9 ± 0.18 m and the mean biomass from 31.9 ± 3.6 t ha-1 to 50.4 ± 1 t ha-1 for the Mediterranean forests. In temperate forests, the average canopy cover increased from 55 ± 4% to 59 ± 3%, mean height increased from 15.8 ± 0.77 m to 17.3 ± 0.21m, while the growing stock volume increased from 137.8 ± 8.2 to 151.5 ± 3.8 m3 ha-1. Our results suggest that multispectral data can be successfully linked with lidar to provide continuous information on forest height, cover, and biomass trends.

Incomplete recovery of tree community composition and rare species after 120 years of tropical forest succession in Panama.

Determining how fully tropical forests regenerating on abandoned land recover characteristics of old-growth forests is increasingly important for understanding their role in conserving rare species and maintaining ecosystem services. Despite this, our understanding of forest structure and community composition recovery throughout succession is incomplete, as many tropical chronosequences do not extend beyond the first 50 years of succession. Here, we examined trajectories of forest recovery across eight 1-hectare plots in middle and later stages of forest succession (40-120 years) and five 1-hectare old-growth plots, in the Barro Colorado Nature Monument (BCNM), Panama. We first verified that forest age had a greater effect than edaphic or topographic variation on forest structure, diversity and composition and then corroborated results from smaller plots censused 20 years previously. Tree species diversity (but not species richness) and forest structure had fully recovered to old-growth levels by 40 and 90 years, respectively. However, rare species were missing, and old-growth specialists were in low abundance, in the mid- and late secondary forest plots, leading to incomplete recovery of species composition even by 120 years into succession. We also found evidence that dominance early in succession by a long-lived pioneer led to altered forest structure and delayed recovery of species diversity and composition well past a century after land abandonment. Our results illustrate the critical importance of old-growth and old secondary forests for biodiversity conservation, given that recovery of community composition may take several centuries, particularly when a long-lived pioneer dominates in early succession. Abstract in Spanish is available with online material.

Determinar en que medida los bosques tropicales que se regeneran en tierras abandonadas recuperan las características de los bosques primarios es cada vez más importante para comprender su papel en la conservación de especies raras y el mantenimiento de los servicios ecosistémicos. A pesar de ello, nuestro entendimiento sobre la recuperación de la estructura del bosque y la composición de la comunidad a lo largo de la sucesión es incompleta, ya que muchas cronosecuencias tropicales no van más allá de los primeros 50 años de sucesión. En este estudio, investigamos las trayectorias de recuperación del bosque en ocho parcelas de 1 hectárea en estadíos medios y tardíos de la sucesión forestal (40­120 años) y cinco parcelas de 1 hectárea de bosque primario, en el Monumento Natural Barro Colorado (MNBC), Panamá. En primer lugar, verificamos que la edad del bosque tenía un mayor efecto que la variación edáfica o topográfica en la estructura, diversidad y composición del bosque y luego corroboramos los resultados de parcelas más pequeñas estudiadas 20 años antes. La diversidad de especies arbóreas, pero no la riqueza de especies, y la estructura forestal se habían recuperado completamente hasta alcanzar los niveles de bosque primario a los 40 y 90 años, respectivamente. Sin embargo, los bosques secundarios carecían de especies raras y presentaban una escasa abundancia de especies especialistas del bosque antiguo, lo que condujo a una recuperación incompleta de la composición de especies, incluso a 120 años de sucesión. También encontramos pruebas de que el predominio de un pionero longevo en las primeras etapas de la sucesión provocó una alteración de la estructura forestal y retrasó la recuperación de la diversidad y composición de especies más allá de un siglo después el abandono de las tierras. Nuestros resultados ilustran la importancia crítica de los bosques primarios y secundarios más antiguos para la conservación de la biodiversidad, dado que la recuperación de la composición de la comunidad puede llevar varios siglos, especialmente cuando un pionero longevo domina en la sucesión temprana.

Understanding the influence of soil development on contaminant reactivity along a fluvial chronosequence in the Oregon Coast Range.

Weathering processes are recognized as drivers of soil and water resource sustainability, but how pedogenesis stage impacts contaminant reactivity and mobility in soils has been minimally investigated. The primary goal of this study was to quantify how soil development influences contaminant reactivity. To achieve this goal, soils from two depths (30 and 100 cm) across a chronosequence (ages 3.5, 20, 69, 140, 200, and 908 ky) in the Oregon Coast Range were subjected to arsenic (As) adsorption isotherms, with As removal from solution serving as a proxy for soil-contaminant reactivity. Langmuir models were applied to isotherm data to quantify relationships between contaminant retention capacity, soil age and soil physicochemical properties, and data revealed that 20 ky soils from a 30-cm-depth had the greatest affinity for As sorption (8,474.5 mg kg-1). Chemical extractions revealed that amorphous (oxy)hydroxides were the dominant mineral phases governing As sorption, even in the presence of abundant crystalline oxides. Micro-X-ray fluorescence spectroscopy revealed a strong spatial correlation between As and Fe in reacted soils. The abundance of amorphous minerals within soils is controlled by the balance between their production from weathering of primary minerals and their loss from ripening to crystalline minerals, and because the mode, extent and minerals governing contaminant sorption determine solid-aqueous phase partitioning, this knowledge will assist in improving models for predicting Critical Zone processes that govern the sustainability of soil and water quality.

Compositional changes at neighborhood and stand scales during recovery of a tropical lowland rainforest after shifting cultivation on Hainan Island, China.

Understanding compositional changes during secondary forest recovery is crucial for effective restoration efforts. While previous research has predominantly focused on shifts in species composition at the stand scale, this study delves into the recovery dynamics in three compositional aspects of location (neighbor distances), size (tree diameters), and species (tree species) at both stand and neighborhood scale. The investigation spans nine chronosequence plots within a tropical lowland rainforest ecosystem after shifting cultivation, including three each for young-secondary forests (18-30 years), old-secondary forests (60 years), and old-growth forests (without obvious human interference). The quantification of location, size, and species composition involved categorized neighbor distances (Near, Moderate, Far-distance), tree diameters (Small, Medium, Large-tree), and tree species (Pioneer, Intermediate, Climax-species) into three groups, respectively. Compositional changes at the stand scale (plot) were directly based on these groups, while at the neighborhood scale, assessment involved combination types of these groups within a neighborhood (comprising three adjacent trees). At the stand scale, neighbor distances shifted from Near to Moderate and Far, tree diameters transitioned from Small to Medium and Large, and tree species of Pioneer gave way to Climax. Meanwhile, at the neighborhood scale, there was a notable decline in the aggregations of Near-distance (N), Small-tree (S), and Pioneer-species (P), while the mixtures of Far and Moderate-distance (F-M), Large and Small-tree (L-S), and Climax and Intermediate-species (C-I) experienced a marked increase. The compositional change exhibited a recovery pattern, with the fastest recovery in neighbor distances, followed by tree diameters and tree species. Moreover, compositional recovery in tree diameters and tree species at the neighborhood scale generally lagged behind that at the stand scale. The study suggests that rapid restoration of secondary forest can be achieved by different targeted cutting according to the recovery stages, aimed at reduce the Pioneer-species, Small-tree and Near-distance in neighborhood. Our findings underscore that analyzing the compositional changes in three aspects at two scales not only provides a profound understanding of secondary forest recovery dynamics, but also offers valuable insights for guiding practices in the restoration of degraded forest ecosystems.

Long-term Consequences on Soil Fungal Community Structure: Monoculture Planting and Natural Regeneration.

Understanding the regeneration and succession of belowground communities, particularly in forests, is vital for maintaining ecosystem health. Despite its importance, there is limited knowledge regarding how fungal communities change over time during ecosystem development, especially under different forest restoration strategies. In this study, we focused on two restoration methods used in northern Japan: monoculture planting and natural regeneration. We examined the responses of the fungal community to monoculture plantations (active tree planting) and naturally regenerated (passive regeneration) forests over a 50-year chronosequence, using natural forests as a reference. Based on DNA metabarcoding, we assessed the richness of fungal Operational Taxonomic Units (OTUs) and their dissimilarity. Our findings revealed that soil fungal richness remained stable after natural regeneration but declined in monoculture plantations, from 354 to 247 OTUs. While the compositional dissimilarity of fungal assemblages between monoculture plantations and natural forests remained consistent regardless of the time since tree planting, it significantly decreased after natural regeneration, suggesting recovery to a state close to the reference level. Notably, the composition of key functional fungal groups-saprotrophic and ectomycorrhizal- has increasingly mirrored that of natural forests over time following passive natural regeneration. In summary, our study suggests that monoculture plantations may not be effective for long-term ecosystem function and service recovery because of their limited support for soil fungal diversity. These results underscore the importance of natural regeneration in forest restoration and management strategies.

Host-virus coevolution drives soil microbial function succession along a millennium land reclamation chronosequence.

INTRODUCTION: Gene exchange between viruses and hosts plays an important role in driving virus-host coevolution, enabling adaptation of both viruses and hosts to environmental changes. However, the mechanisms and functional significance of virus-host gene exchanges over long-term scales remain largely unexplored. OBJECTIVE: The present study aimed to gain insights into the role of viruses in virus-host interactions and coevolution by monitoring virome dynamics along a millennium-long land reclamation chronosequence. METHODS: We collected 24 soil samples from 8 stages of a millennium-long land reclamation chronosequence, including non-reclamation, and reclamation periods of 10, 50, 100, 300, 500, 700, and 1000 years. We characterized their metagenomes, and identified DNA viruses within these metagenomes. RESULTS: Our findings reveal a significant shift in viral community composition after 50 years of land reclamation, but soil viral diversity reached a stable phase approximately 300 years after the initial reclamation. Analysis of the virus-host network showed a scale-free degree distribution and a reduction in complexity over time, with generalist viruses emerging as key facilitators of horizontal gene transfer. CONCLUSION: These findings highlight the integral role of viruses, especially generalist types, in mediating gene exchanges between viruses and hosts, thereby influencing the coevolutionary dynamics in soil ecosystems over significant timescales. This study offers novel insights into long-term virus-host interactions, showing how the virome responds to environmental changes, driving shifts in various microbial functions in reclaimed land.

Long-term paddy use influences response of methane production, arsenic mobility and speciation to future higher temperatures.

Anaerobic microbial metabolisms make flooded paddy soils a major source of the greenhouse gas methane (CH4) and mobilize toxic arsenic (As), threatening rice production and consumption. Increasing temperatures due to climate change enhance these microbially mediated processes, increasing their related threats. Chronosequence studies show that long-term paddy use ("age") changes soil properties and redox biogeochemistry through soil organic carbon (SOC) accumulation, its association to amorphous iron (Fe) phases, and increased microbial activity. Using paddy and non-paddy soils from a chronosequence as proxies of soil development and incubating them at different temperatures, we show that paddy soil age influences the response of paddies to changes in temperature. Older paddies showed up to a 6-fold higher CH4 production with increasing temperature, compared to a 2-fold increase in young ones. Contrarily, changes in As mobility were higher in non-paddies and young paddies due to a lack of Fe-SOC-sorption sites. Temperature increased the formation of phytotoxic methylated As in all paddies, posing a risk for rice production. Mitigation strategies for future maintenance, abandonment, or management of paddy soils should include the consideration that history of use shapes the soils' biogeochemistry and microbiology and can influence the response of paddy soils to future temperature increases.

Dryland soil recovery after disturbance across soil and climate gradients of the Colorado Plateau.

Drylands impacted by energy development often require costly reclamation activities to reconstruct damaged soils and vegetation, yet little is known about the effectiveness of reclamation practices in promoting recovery of soil quality due to a lack of long-term and cross-site studies. Here, we examined paired on-pad and adjacent undisturbed off-pad soil properties over a 22-year chronosequence of 91 reclaimed oil or gas well pads across soil and climate gradients of the Colorado Plateau in the southwestern United States. Our goals were to estimate the time required for soil properties to reach undisturbed conditions, examine the multivariate nature of soil quality following reclamation, and identify environmental factors that affect reclamation outcomes. Soil samples, collected in 2020 and 2021, were analyzed for biogeochemical pools (total nitrogen, and total organic and inorganic carbon), chemical characteristics (salinity, sodicity, pH), and texture. Predicted time to recovery across all sites was 29 years for biogeochemical soil properties, 31 years for soil chemical properties, and 6 years for soil texture. Ordination of soil properties revealed differences between on- and off-pad soils, while site aridity explained variability in on-pad recovery. The predicted time to total soil recovery (distance between on- and off-pad in ordination space) was 96 years, which was longer than any individual soil property. No site reached total recovery, indicating that individual soil properties alone may not fully indicate recovery in soil quality as soil recovery does not equal the sum of its parts. Site aridity was the largest predictor of reclamation outcomes, but the effects differed depending on soil type. Taken together, results suggest the recovery of soil quality - which reflects soil fertility, carbon sequestration potential, and other ecosystem functions - was influenced primarily by site setting, with soil type and aridity major mediators of on-pad carbon, salinity, and total soil recovery following reclamation.

Microbial composition and function in reclaimed mine sites along a reclamation chronosequence become increasingly similar to undisturbed reference sites.

Mine reclamation historically focuses on enhancing plant coverage to improve below and aboveground ecology. However, there is a great need to study the role of soil microorganisms in mine reclamation, particularly long-term studies that track the succession of microbial communities. Here, we investigate the trajectory of microbial communities of mining sites reclaimed between three and 26 years. We used high-throughput amplicon sequencing to characterize the bacterial and fungal communities. We quantified how similar the reclaimed sites were to unmined, undisturbed reference sites and explored the trajectory of microbial communities along the reclamation chronosequence. We also examined the ecological processes that shape the assembly of bacterial communities. Finally, we investigated the functional potential of the microbial communities through metagenomic sequencing. Our results reveal that the reclamation age significantly impacted the community compositions of bacterial and fungal communities. As the reclamation age increases, bacterial and fungal communities become similar to the unmined, undisturbed reference site, suggesting a favorable succession in microbial communities. The bacterial community assembly was also significantly impacted by reclamation age and was primarily driven by stochastic processes, indicating a lesser influence of environmental properties on the bacterial community. Furthermore, our read-based metagenomic analysis showed that the microbial communities' functional potential increasingly became similar to the reference sites. Additionally, we found that the plant richness increased with the reclamation age. Overall, our study shows that both above- and belowground ecological properties of reclaimed mine sites trend towards undisturbed sites with increasing reclamation age. Further, it demonstrates the importance of microbial genomics in tracking the trajectory of ecosystem reclamation.

Amino acid-sulphur decomposition in agricultural soil profile along a long-term recultivation chronosequence.

The significance of sulphur (S) availability for crop yield and quality is highlighted under the global S deficiency scenario. However, little is known about the temporal trend in belowground organic S mineralisation when restoring land to productive agricultural systems, particularly for the deeper soil parts. Therefore, we investigated the decomposition of 35S-labelled methionine in surface (0-30 cm) and subsurface soil (30-60 cm and 60-90 cm) over a 48-year recultivation chronosequence (sampled after1, 8, 14, 24 and 48 years). Soil total sulphur (TS) significantly (p < 0.05) increased in surface soil but not in subsurface soils after 48 years of recultivation. Overall, the immobilisation of 35S-methionine (35S-MB) in subsurface soils relative to year 1 significantly decreased over the chronosequence but did not change in the surface samples. The 35S-MB values in subsurface soils were positively corrected with soil carbon (C) stoichiometry (Pearson correlation, p < 0.05), suggesting the immobilisation of methionine was likely constrained by microbial C demand in deep soil. Compared to year 1, 35S-SO42- released from 35S-methionine significantly declined throughout the older (≥ 8 years) soil profiles. Significant (p < 0.05) changes in the organic 35S partition (35S immobilisation and 35S released as sulphate) were observed in year 8 after the soil was recultivated with N-fixing alfalfa or fertilisers. Whereas, after that (≥ 14 years), soil organic S partition remained affected when conventional tillage and agricultural crops dominated this site. Indicating that the effect of recultivation on organic S decomposition depends on the manner of recultivation management. Our study contributes to an improved understanding of amino acid S and organic S mineralisation under severe anthropogenic disturbance.

Fungal community determines soil multifunctionality during vegetation restoration in metallic tailing reservoir.

Microorganisms are pivotal in sustaining soil functions, yet the specific contributions of bacterial and fungal succession on the functions during vegetation restoration in metallic tailing reservoirs remains elusive. Here, we explored bacterial and fungal succession and their impacts on soil multifunctionality along a ∼50-year vegetation restoration chronosequence in China's largest vanadium titano-magnetite tailing reservoir. We found a significant increase in soil multifunctionality, an index comprising factors pertinent to soil fertility and microbially mediated nutrient cycling, along the chronosequence. Despite increasing heavy metal levels, both bacterial and fungal communities exhibited significant increase in richness and network complexity over time. However, fungi demonstrated a slower succession rate and more consistent composition than bacteria, indicating their relatively higher resilience to environmental changes. Soil multifunctionality was intimately linked to bacterial and fungal richness or complexity. Nevertheless, when scrutinizing both richness and complexity concurrently, the correlations disappeared for bacteria but remained robust for fungi. This persistence reveals the critical role of the fungal community resilience in sustaining soil multifunctionality, particularly through their stable interactions with powerful core taxa. Our findings highlight the importance of fungal succession in enhancing soil multifunctionality during vegetation restoration in metallic tailing reservoirs, and manipulating fungal community may expedite ecological recovery of areas polluted with heavy metals.

Changes in bryophyte functional composition during post-fire succession.

Climate and land-use changes are altering fire regimes in many regions around the world. To date, most studies have focused on the effects of altered fire regimes on woody and herbaceous communities, while the mechanisms driving post-fire bryophyte succession remain poorly understood, particularly in Mediterranean-type ecosystems. Here, we examined changes in bryophyte functional composition along a post-fire chronosequence (ranging from 1 to 20+ years) in Pyrenean oak woodlands (northeastern Portugal). To do so, we defined bryophyte functional groups based on seven morphological, reproductive, and life history traits. Then, we fitted linear and structural equation models to disentangle the direct and indirect effects of fire (time since fire and fire intensity), vegetation structure, climate, topography, and edaphic conditions on the abundance of each group. We identified two main functional groups: early colonizers (species with traits associated with strong colonization ability and desiccation tolerance) and perennial stayers (species with high competitive ability, i.e., large perennial mosses). Overall, the abundance of early colonizer species decreased with time since fire and increased with fire intensity, while the opposite was observed for perennial stayers. Thus, successional dynamics reflected a trade-off between species' competitive and colonization abilities, highlighting the role of biotic interactions later in succession. Patterns of functional composition were also consistent with changes in environmental conditions during succession, suggesting that species may experience stressful conditions (i.e., high radiation and low water availability) in early stages of post-fire succession. Our results also indicate that increased fire intensity may alter successional trajectories, leading to long-term changes in bryophyte communities. By understanding the response of bryophyte communities to fire, we were able to identify species with potential use as soil restoration materials.

[Soil Carbon Pool Allocation Dynamics During Soil Development in the Lower Yangtze River Alluvial Plain].

The allocation dynamics of soil carbon pools during soil development and land use are the key to revealing the carbon cycle process. To clarify the distribution of the soil carbon pool and its change trend, a soil reclamation chronosequence (0 a, 60 a, 160 a, 280 a, 1 000 a, and 1 500 a reclamation) was established in a typical alluvial plain in the Lower Yangtze River, and the content and density of soil organic carbon (SOC), soil inorganic carbon (SIC), particulate organic carbon (POC), and mineral-associated organic carbon (MAOC), along with carbon sequestration potential (CSP) indicators of topsoil under different land use types were measured and analyzed. The results showed that after approximately 1 500 a reclamation, the SOC content developed from the Yangtze River alluvial deposits generally increased by 4.9% after the initial decline, whereas the SIC content decreased to 0.2% from 25.8% of the total carbon content due to its rapid leaching. The MAOC content was normally higher than that of POC, and MAOC was contributing 48.0%-79.7% of the SOC accumulation. In this region, the soil organic carbon density (SOCD) accounted for 57.4%-100% of the total carbon density, the soil carbon sequestration levels (CSL) ranged from 18.6% to 56.1%, and CSP under paddy-dryland rotation increased by 20.8% compared to that under dryland. The C/N ratio and total nitrogen content are key factors in explaining soil carbon accumulation processes, and the reclamation year plays an important role in evaluating soil carbon sequestration levels. After long-term utilization, the cultivated soil in the Yangtze River floodplain must be carefully managed through balanced fertilization to maintain soil productivity, promote the accumulation of SOC, and avoid the decline in soil carbon sequestration capacity.

Soil heavy metal pollution promotes extracellular enzyme production by mediating microbial community structure during vegetation restoration of metallic tailing reservoir.

Vegetation restoration in metallic tailing reservoirs is imperative to restore the post-mining degraded ecosystems. Extracellular enzymes determine microbial resource acquisition in soils, yet the mechanisms controlling the enzyme activity and stoichiometry during vegetation restoration in metallic tailing reservoirs remain elusive. Here, we investigated the variations and drivers of C-, N- and P-acquiring enzymes together with microbial community along a 50-year vegetation restoration chronosequence in the China's largest vanadium titano-magnetite tailing reservoir. We found a parabolic pattern in the enzyme activity and efficiency along the chronosequence, peaking at the middle restoration stage (∼30 years) with approximately six-fold increase relative to the initial 1-year site. The enzyme ratios of C:P and N:P decreased by 33 % and 68 % along the chronosequence, respectively, indicating a higher microbial demand of C and N at the early stage and a higher demand of P at the later stage. Soil nutrients directly determined the enzyme activities and stoichiometry, whereas microbial biomass and community structure regulated the temporal pattern of the enzyme efficiency. Surprisingly, increased heavy metal pollution imposed a positive effect on the enzyme efficiency indirectly by altering microbial community structure. This was evidenced by the increased microbial diversity and the conversion of copiotrophic to oligotrophic and stress-tolerant taxa along the chronosequence. Our findings provide new insights into microbial functioning in soil nutrient dynamics during vegetation restoration under increasing heavy metal pollution.

Deciphering factors driving soil microbial life-history strategies in restored grasslands.

In macroecology, the concept of r- and K-strategy has been widely applied, yet, there have been limited studies on microbial life-history strategies in temperate grasslands using multiple sequencing approaches. Total phospholipid fatty acid (PLFA) analysis, high-throughput meta-genomic sequencing, and GeoChip technologies were used to examine the changes in microbial life-history traits in a chronosequence of restored grasslands (1, 5, 10, 15, 25, and 30 years since restoration). Grassland restoration increased the relative abundances of Actinobacteria, Proteobacteria, and Bacteroidetes but reduced the relative abundances of Acidobacteria, Planctomycetes, and Chloroflexi. PLFA analysis revealed that grassland restoration reduced the fungi:bacteria and Gram-positive:Gram-negative bacteria ratios. Combined with the meta-genomic data, we found that grassland restoration shifted microorganisms from oligotrophic (K-) to copiotrophic (r-) groups, consistent with the increased rRNA operon copy number of the microbial community. Structural equation modeling showed that soil properties positively (p < 0.05) while plant properties negatively (p < 0.05) affected microbial life-history traits. We built a framework to highlight the importance of plant and soil properties in driving microbial life-history traits during grassland restoration. Finally, by incorporating meta-genomic and other microbiological data, this study showed that microbial life-history traits support the idea that rRNA operon copy number is a trait that reflects resource availability to soil microorganisms.

Changes in Diversity and Abundance of Ammonia-Oxidizing Archaea and Bacteria along a Glacier Retreating Chronosequence in the Tianshan Mountains, China.

Glaciers retreating due to global warming create important new habitats, particularly suitable for studying ecosystem development where nitrogen is a limiting factor. Nitrogen availability mainly results from microbial decomposition and transformation processes, including nitrification. AOA and AOB perform the first and rate-limiting step of nitrification. Investigating the abundance and diversity of AOA and AOB is essential for understanding early ecosystem development. The dynamics of AOA and AOB community structure along a soil chronosequence in Tianshan No. 1 Glacier foreland were analyzed using qPCR and clone library methods. The results consistently showed low quantities of both AOA and AOB throughout the chronosequence. Initially, the copy numbers of AOB were higher than those of AOA, but they decreased in later stages. The AOB community was dominated by "Nitrosospira cluster ME", while the AOA community was dominated by "the soil and sediment 1". Both communities were potentially connected to supra- and subglacial microbial communities during early stages. Correlation analysis revealed a significant positive correlation between the ratios of AOA and AOB with soil ammonium and total nitrogen levels. These results suggest that variations in abundance and diversity of AOA and AOB along the chronosequences were influenced by ammonium availability during glacier retreat.

Seasonal microclimatic variation in a succession gradient of low thorn forest in Northeastern Mexico / Variación microclimática estacional en un gradiente sucesional de selva baja espinosa en el Noreste de México

Abstract Global increase in land cover change and deforestation bring about fragmentation of a high proportion of native vegetation areas. Microclimate is among the first modified factors after vegetation loss, effects of such disturbances are critical for species performance. However, both secondary succession and seasonality provoke further modifications in abiotic environment after disturbances. Although microclimate patterns during succession are well studied for several ecosystems, they are practically unknown for low thorn forests. In Northern Mexico, this is an endangered ecosystem characterized by harboring a high percentage of endemics. Measurement of microclimatic factors is crucial for understanding possible consequences of post-disturbance time on species inhabiting this ecosystem. This work aimed to assess seasonal variation of microclimatic patterns in a succession gradient of four categories (conserved areas, 31, 17 and four years of succession). The study area was delimited using Landsat satellite images (1973, 1986, 2000, 2005, and 2013) in a fragment of low thorn forest in Northeastern Mexico. For microclimate characterization we studied wind speed, temperature, relative humidity, heat index, dew point, and evapotranspiration. Variables were measured monthly on eight plots, in each of the four successional categories, during two different seasons: wet (May through October 2016) and dry season (November 2016 through April 2017). A multivariate discriminant function analysis showed that microclimate differs among successional stages. In the wet season, early succession areas were characterized by higher values of heat index and wind speed, contrary to conserved areas. In the dry season, successional differences were attributed to wind speed and relative humidity. Moreover, microclimate differences between categories and importance of variables measured were both higher only during the dry season. Our results show that seasonality influences greatly microclimatic patterns during secondary succession. In addition, each one of the successional categories exhibited unique microclimatic conditions. Remarkably, four, 17, and even 31 years succession categories differed from conserved areas. This work provides evidence on the great relevance of seasonality and microclimate for studying secondary succession. It is suggested to take both factors into consideration when implementing conservation programs concerning endangered habitats such as low thorn forests. As an ecosystem poorly studied, microclimate characterization provided herein, shall help to a better understanding and management of these areas.(AU)

Resumen El aumento global en el cambio de cobertura vegetal y la deforestación han fragmentado una elevada proporción de áreas de vegetación nativa. El microclima es un factor que se modifica después de la pérdida de vegetación, y los efectos de tales perturbaciones son trascendentales para las especies. Sin embargo, tanto la sucesión secundaria como la estacionalidad implican modificaciones adicionales en el medio abiótico después del disturbio. Aunque los patrones microclimáticos durante la sucesión son conocidos en varios ecosistemas, no se han evaluado en áreas de selva baja espinosa, que constituye un ecosistema amenazado en el norte de México. La medición de tales factores microclimáticos es crucial para comprender las consecuencias de la recuperación post-disturbio en las especies. Por lo tanto, el objetivo del estudio fue evaluar la variación estacional del microclima en un gradiente de sucesión de cuatro categorías (áreas conservadas, 31, 17 y cuatro años de sucesión), delimitadas mediante imágenes de satélite LANDSAT (1973, 1986, 2000, 2005 y 2013) en un fragmento de selva baja espinosa en el noreste de México. Para caracterizar el microclima se consideraron la velocidad del viento, temperatura, humedad relativa, índice de calor, punto de rocío y evapotranspiración. Las variables se midieron de forma mensual, durante un año, en ocho sitios de muestreo en cada una de las cuatro categorías sucesionales, durante dos estaciones diferentes: húmeda (mayo a octubre 2016) y seca (noviembre 2016 hasta abril 2017). A través de un análisis multivariado de funciones discriminantes, se determinó que las categorías sucesionales en la selva baja espinosa son diferentes dependiendo del microclima. En la estación húmeda, las áreas con poco tiempo de sucesión se caracterizaron por valores más altos de índice de calor y velocidad del viento, al contrario de las áreas conservadas. En la estación seca, las diferencias sucesionales se atribuyeron a la velocidad del viento y la humedad relativa. Además, tanto la discriminación entre categorías como la importancia de las variables fueron mayores solo durante la estación seca. Por lo tanto, la estacionalidad determina los patrones microclimáticos durante la sucesión secundaria. Además, cada categoría sucesional representa condiciones microclimáticas únicas, pero difieren de las áreas conservadas incluso después de 31 años de sucesión. De acuerdo con nuestros resultados, la estacionalidad y el microclima son de gran relevancia para el estudio de la sucesión secundaria. Se sugiere considerar ambos factores cuando se implementan programas de conservación de ecosistemas en riesgo, como la selva baja espinosa en el noreste de México. Al ser este un ecosistema poco estudiado, la caracterización microclimática que aquí se proporciona, ayudará a un mejor entendimiento y manejo forestal de dichas áreas.(AU)

Efecto de los estadios sucesionales del bosque tropical seco sobre el microhábitat usado por Agalychnis dacnicolor (Anura: Phyllomedusidae) y Smilisca fodiens (Anura: Hylidae) / Effect of tropical dry forest succesional stages on microhabitat use by Agalychnis dacnicolor (Anura: Phyllomedusidae) and Smilisca fodiens (Anura: Hylidae)

ResumenLa perturbación del hábitat puede modificar los microhábitats y por lo tanto tener un marcado efecto en la abundancia y distribución de especies de anuros, en particular en aquellas asociadas a microhábitats específicos. En el presente estudio evaluamos cambios en el uso del microhábitat de dos especies sintópicas de ranas arborícolas, Agalychnis dacnicolor y Smilisca fodiens a lo largo de un gradiente sucesional del bosque tropical seco (BTS). Nuestra hipótesis fue que debido a que estas dos especies son generalistas de hábitat, modificarían el uso del microhábitat en respuesta a la sucesión secundaria del BTS y la temporada climática (TC). Aunque ambas especies se registraron en los bosques secundarios y en los bosques maduros, A. dacnicolor prefirió el bosque maduro mientras que S. fodiens prefirió los lugares perturbados. Ninguna de las dos especies presentaron diferencias en biomasa entre los estadios sucesionales (ES), ni entre temporadas climáticas. A diferencia de S. fodiens la rana A. dacnicolor presentó mayores tallas durante la temporada de lluvias. La temperatura corporal de ambas especies varió entre ES y temporada climática. S. fodiens presentó una temperatura mas constante entre individuos en los pastizales, mientras que A. dacnicolor en los bosques maduros. Las variables ambientales y estructurales del hábitat que influyeron en la presencia de ambas especies dentro de los diferentes ES fueron la temperatura del sustrato, altura del árbol o arbusto donde se encontraba perchando el individuo y los porcentajes de cobertura de hojarasca, herbáceas, arbustos, árboles y suelo desnudo. Las variables que mejor explicaron la biomasa, la longitud hocico-cloaca (LHC) y la temperatura corporal de S. fodiens fueron las ramas secas y la temperatura del sustrato y en A. dacnicolor la biomasa estuvo mejor explicada por las herbáceas, LHC, la altura del árbol o arbusto donde la rana perchaba, y la temperatura corporal por la temperatura del sustrato. Ambas especies usaron de manera diferencial las variables ambientales y estructurales del microhábitat conforme los ES aumentaron en edad. Las variables que separaron a las especies fueron la altura del refugio o percha y el porcentaje de árboles en los diferentes ES. A. dacnicolor mantuvo preferencia por los estratos mas bajos de la vegetación, mientras que S. fodiens mostró una amplia plasticidad en el uso del microhábitat, en particular modificó el uso en la altura del refugio o percha. Nuestros resultados sugieren que aunque ambas especies han sido consideradas generalistas de hábitat, en los paisajes antropizados A. dacnicolor es una especie especialista del microhábitat y S. fodiens es una especie con mayor plasticidad ecológica en el uso del microhábitat. Estas diferencias en el uso del microhábitat en respuesta a la perturbación del hábitat pueden ayudar a explicar el éxito de las especies en estos nuevos paisajes, así como la importancia de los bosques secundarios en distintas etapas de sucesión para mantener microhábitats adecuados para la permanencia de las especies en los paisajes antropizados.

AbstractHabitat disturbance can modify microhabitats and therefore have a significant effect on the abundance and distribution of anurans species, particularly those associated to specific microhabitats. In this study we evaluated changes in the use of microhabitat by two syntopic species of tree frogs, Agalychnis dacnicolor and Smilisca fodiens along a successional gradient of Tropical Dry Forest in the region of the Biosphere Reserve of Chamela-Cuixmala at the coast of Jalisco, Mexico. We hypothesized that because these two species are habitat generalists, microhabitat use would change in response to secondary forest succession and to the climatic season of the year. Although both species were registered in both secondary and mature forests, A. dacnicolor was associated to mature forest, whereas S. fodiens was more associated to disturbed sites. Neither species showed differences in biomass among successional stages (ES) or between climatic seasons. Unlike S. fodiens, A. dacnicolor presented larger sizes during the rainy season. Body temperature of both species varied between ES and climatic season. S. fodiens presented a more constant temperature among individuals in pastures, while A. dacnicolor in mature forests. Environmental and structural habitat variables that influenced the presence of both species in ES were substrate temperature, height of tree or shrub where the frog was perching and percentage cover of litter, grasses, shrubs, trees and bare soil. The variables that best explained biomass, snout-vent length (LHC) and body temperature of S. fodiens were cover of dry branches and substrate temperature, whereas biomass of A. dacnicolor was better explained by cover of herbs, LHC, height of the tree or shrub where the frog was perching, body temperature and the substrate temperature. Both species used differentially environmental and structural variables of microhabitats along the gradient of initial to late ES. The variables that separated the species were the height of the shelter or perch and the percentage of trees in different ES. Whereas A. dacnicolor was more associated to the lowest strata of vegetation, S. fodiens showed plasticity in microhabitat use, especially in height of shelter or perch. Our results suggested that even when both species are considered habitat generalists, in anthropic landscapes, A. dacnicolor is specialist in microhabitat use, whereas S. fodiens is a species with greater ecological plasticity in microhabitat use. These differences in microhabitat use in response to habitat disturbance may help explain the success of these species in these new landscapes, as well as the importance of secondary forests in different stages of succession to maintain adequate microhabitats for the permanence of species in anthropogenic landscapes.

Forest structure and species composition along a successional gradient of Lowland Atlantic Forest in Southern Brazil / Estrutura e composição ao longo de um gradiente sucessional de Floresta de Terras Baixas no sul do Brasil

The Lowland Forest is one of the most disturbed and fragile ecosystems in the Atlantic Forest biome, yet little is known regarding its successional trajectory and resilience. We evaluated changes in species assemblages and forest structure of the canopy and understory along a successional gradient (young 21-yrs old forest, immature 34-yrs old forest and late successional 59-yrs old forest) aiming to assess changes in species composition and successional trajectory of different strata of secondary forests. A 0.1 ha plot (ten 10x10 m sub-plots) from each forest stand was surveyed for trees and shrubs with a diameter at breast height (DBH) ≥ 4.8 cm (canopy) and for individuals with heights ≥ 1 m and DBH < 4.8 cm (understory). A total of 3,619 individuals from 82 plant species were sampled. The successional gradient was marked by a unidirectional increase in species richness and a bidirectional pattern of density changes (increasing from young to immature forest and decreasing from immature to late successional forest). Community assemblages were distinct in the three forests and two strata; indicator species were only weakly shared among stands. Thus, each successional forest and stratum was observed to be a unique plant community. Our results suggest slight predictability of community assemblages in secondary forests, but a relatively fast recovery of forest structure.

As Florestas de Terras Baixas constituem um dos ecossistemas mais perturbados e frágeis no bioma Mata Atlântica, mas ainda pouco se sabe sobre sua trajetória sucessional e resiliência. Foram avaliadas alterações na composição de espécies e a estrutura florestal do dossel e sub-bosque ao longo de um gradiente sucessional (floresta jovem-21 anos, floresta imatura-34 anos, floresta madura-59 anos) com o objetivo de verificar as mudanças na composição de espécies e a trajetória sucessional de diferentes estratos destas florestas secundárias. Uma parcela de 0,1 ha (dez sub-parcelas de 10x10 m) foi estabelecida em cada floresta, amostrando-se árvores e arbustos com um diâmetro è altura do peito (DAP) ≥ 4,8 cm (dossel) e para indivíduos com altura > 1 m e DAP < 4,8 cm (sub-bosque). Um total de 3.619 indivíduos de 82 espécies de plantas foram amostrados. O gradiente sucessional foi marcado por um aumento unidirecional na riqueza de espécies com o tempo, e um padrão bidirecional de mudanças de densidade (aumentando da floresta jovem para a imatura e diminuindo da imatura para a madura). As assembléias de plantas eram distintas nas três florestas e nos dois estratos; espécies indicadoras foram pouco compartilhadas entre as florestas. Portanto, cada estádio da cronosequência e cada estrato representam uma comunidade única de plantas. Nossos resultados sugerem pouca previsibilidade das assembleias de plantas destas florestas secundárias, mas uma recuperação relativamente rápida da estrutura da floresta.