Initial soil condition, stand age, and aridity alter the pathways for modifying the soil carbon under afforestation.

Afforestation is a crucial pathway for ecological restoration and has the potential to modify soil microbial community, thereby impacting the cycling and accumulation of carbon in soil across diverse patterns. However, the overall patterns of how afforestation impacts below-ground carbon cycling processes remain uncertain. In this comprehensive meta-analysis, we systematically evaluated 7045 observations from 210 studies worldwide to evaluate the influence of afforestation on microbial communities, enzyme activities, microbial functions, and associated physicochemical properties of soils. Afforestation increases microbial biomass, carbon and nitrogen hydrolase activities, and microbial respiration, but not carbon oxidase activity and nitrogen decomposition rate. Conversely, afforestation leads to a reduction in the metabolic quotient, with significant alteration of bacterial and fungal community structures and positive effects on the fungi: bacteria ratio rather than alpha and beta diversity metrics. We found a total 77 % increase in soil organic carbon (SOC) content after afforestation, which varied depending on initial SOC content before afforestation, afforestation stand age, and aridity index of afforestation sites. The modified SOC is associated with bacterial community composition along with intracellular metabolic quotient and extracellular carbon degrading enzyme activity playing a role. These findings provide insights into the pathways through which afforestation affects carbon cycling via microorganisms, thus improving our knowledge of soil carbon reservoir's responses to afforestation under global climate change.

Short-term effect of reclaimed water irrigation on soil health, plant growth and the composition of soil microbial communities.

The scarcity of freshwater poses significant challenges to agriculture, often necessitating the use of alternative water sources such as reclaimed water. While reclaimed water offers a viable solution by providing water and nutrients to crops, its potential impacts on soil microbial communities remain a subject of investigation. In this investigation, we conducted a field experiment cultivating Maize (Zea mays) and Lavender (Lavandula angustifolia), employing irrigation with reclaimed water originating from domestic wastewater, while control samples were irrigated using freshwater. Utilizing high-throughput sequencing, we assessed the effect of reclaimed water on soil bacteria and fungi. Plant biomass exhibited a significant response to treated wastewater. Alpha diversity metrics of soil microbial communities did not reveal significant changes in soils irrigated with reclaimed water compared to control samples. Reclaimed water, however, demonstrated a selective influence on microorganisms associated with nutrient cycling. Co-occurrence network analysis unveiled that reclaimed water may alter soil microbial community structure and stability. Although our work presents overall positive outcomes, further investigation into the long-term implications of reclaimed water irrigation is warranted.

Can we identify tipping points of resilience loss in Mediterranean rangelands under increased summer drought?

Mediterranean ecosystems are predicted to undergo longer and more intense summer droughts. The mechanisms underlying the response of herbaceous communities to such drier environments should be investigated to identify the resilience thresholds of Mediterranean rangelands. A 5-year experiment was conducted in deep and shallow soil rangelands of southern France. A rainout shelter for 75 days in summer imposed drier and warmer conditions. Total soil water content was measured monthly to model available daily soil water. Aboveground net primary production (ANPP), forage quality, and the proportion of graminoids in ANPP were measured in spring and autumn. Plant senescence and plant cover were assessed in summer and spring, respectively. The experimental years were among the driest ever recorded at the site. Therefore, manipulated summer droughts were drier than long-term ambient conditions. Interactions between treatment, community type, and experimental year were found for most variables. In shallow soil communities, spring plant cover decreased markedly with time. This legacy effect, driven by summer plant mortality and the loss of perennial graminoids, led to an abrupt loss of resilience when the extreme water stress index exceeded 37 mm 10 day-1, characterized by a reduction of spring plant cover below 50% and a decreased ANPP in rainy years. Conversely, the ANPP of deep soil communities remained unaffected by increased summer drought, although the presence of graminoids increased and forage nutritive value decreased. This study highlights the role of the soil water reserve of Mediterranean plant communities in modulating ecosystem responses to chronically intensified summer drought. Communities on deep soils were resilient, but communities on shallow soils showed a progressive, rapid, and intense degradation associated with a loss of resilience capacity. Notably, indexes of extreme stress were a better indicator of tipping points than indexes of integrated annual stress. Considering the role of soil water availability in other herbaceous ecosystems should improve the ability to predict the resilience of plant communities under climate change.

Aridity regulates the impacts of multiple dimensional plant diversity on soil properties in the drylands of northern China.

Relationships between plant diversity and soil properties are important for restoring ecosystem function to adapt climate change in drylands. Taxonomic, functional and phylogenetic diversity are widely used for understanding community assembly and the responses of plant communities to environmental change. However, one dimension of diversity index is difficult to reflect the multiple dimensional plant diversity, and their effects on soil properties (i.e., moisture, nutrients, and texture characteristics) along aridity gradient in drylands are limitedly understood. In this study, we proposed a holistic biodiversity (HB) index to integrate all the characteristics of plant diversity, and investigated the relationships between plant diversity and soil properties across 41 sites along aridity gradient (from hyperarid to arid and semiarid levels) in drylands of northern China. The results showed that the taxonomic diversity and phylogenetic diversity increased significantly while most of functional diversity indices did not differ significantly along the aridity gradient. The functional diversity was more important than taxonomic and phylogenetic diversity to plant communities, and the importance of taxonomic and phylogenetic diversity varied greatly and inversely along the aridity gradient. The HB index could much better reflect the positive or negative exponential relationships with soil properties compared to the single diversity index. Further, the aridity weakened the positive effects of plant diversity on several soil properties (including soil water content, soil organic carbon and soil total nitrogen), and indirectly strengthened the accumulation of soil total phosphorus, as well as intensified the soil coarsening by limiting the negative effects of plant diversity on soil sand content. Our findings suggest that the holistic biodiversity index can represent the overall traits of plant diversity in drylands, and guide a further step to understand the role of plant diversity in plant-soil relationships of dryland ecosystems.

Interactions between biocrusts and herbaceous communities are divergent in dry and wet semiarid ecosystems.

Biocrusts are a prevalent form of living cover in worldwide drylands, and their presence are intimately associated with herbaceous community, forming a spatially mosaic distribution pattern in dryland ecosystems. The role of biocrusts as modulators of herbaceous community assembly is extensively studied, whereas, less is known whether their interactions are permanent or changeable with various environmental conditions. This study conducted a field survey of herbaceous community accompanied by three types of biocrusts (cyanobacterial, cyanobacterial-moss mixed, and moss crusts) in two contrasting (dry and wet) semiarid climate regions in the Chinese Loess Plateau, to explore whether or not climatic aridity gradient affects the interactions between biocrusts and herbaceous community. Our results showed that in dry semiarid climate, the biomass, species richness, and diversity of herbaceous community from biocrust plots were 89 %, 179 %, and 52 % higher than that from the uncrusted plots, respectively, while in wet semiarid climate, those herbaceous community indices from biocrust plots were 68 %, 43 %, and 23 % lower than that from the uncrusted plots, respectively. The impacts of biocrusts on herbaceous community were highly dependent on the types and coverage of biocrusts. Regardless of aridity gradient, the richness and diversity of herbaceous community were the lowest in the moss-covered plots, followed by the cyanobacteria-covered plots and the plots with a mixed cyanobacteria and moss population. Along with increasing biocrust coverage, the species richness and diversity of herbaceous plants initially increased and then decreased in dry semiarid climate, while in wet semiarid climate they decreased linearly with biocrust coverage. Structural equation modeling revealed that the factors of biocrust types and coverage affected herbaceous community indirectly through soil properties in dry semiarid climate, whereas in wet semiarid climate they directly affected herbaceous community through biotic interactions. Together, our findings indicated that cyanobacterial and moss biocrusts facilitate the development of herbaceous community in dry semiarid climate by increasing soil stability and nutrient levels, but in wet semiarid climate they restrict herbaceous plant growth through competing niche space. These results highlight the divergent relationships between biocrusts and herbaceous community across aridity gradient in dryland ecosystems, and this knowledge may be critically important in light of the projected global climate change which is going to change the aridity of global drylands.

Aridity affects soil organic carbon concentration and chemical stability by different forest types and soil processes across Chinese natural forests.

Forest soils play a critical role in carbon (C) reservoirs and climate change mitigation globally. Exploring the driving factors of soil organic carbon (SOC) concentration and stability in forests on a large spatial scale can help us evaluate the role of forest soils in regulating C sequestration. Based on SOC quantification and solid-state 13C nuclear magnetic resonance spectroscopy, we investigated the SOC concentration and SOC chemical stability (indicated by alkyl-to-O-alkyl ratio and hydrophobic-to-hydrophilic ratio) in top 0-5 and 5-10 cm soils from 65 Chinese natural forest sites and explored their driving factors. Results showed that SOC concentration in 0-5 cm soils were highest in mixed forests but SOC chemical stability in 0-5 cm soils were highest in coniferous forests, while SOC concentration and chemical stability in 5-10 cm soil layers did not differ across forest types. SOC concentration in 0-5 cm was directly related to soil pH and soil bacterial diversity. Structural equation models showed that aridity indirectly affected SOC concentration in 0-5 cm by directly affecting soil pH. While SOC chemical stability in 0-5 cm soils was higher with increased aridity. According to the correlations, the potential mechanisms could be attributed to higher proportion of coniferous forests in more arid forest sites, lower relative abundance of O-alkyl C, higher MgO and CaO contents, and higher bacterial diversity in soils from more arid forest sites. Our study reveals the important role of aridity in mediating SOC concentration and chemical stability in top 0-5 cm soils in Chinese natural forests on a large-scale field investigation. These results will help us better understand the different mechanisms underlying SOC concentration and stability in forests and assess the feedback of forest SOC to future climate change.

Shared xerophytic genes and their re-use in local adaptation to aridity in the desert plant Gymnocarpos przewalskii.

In order to thrive and survive, plant species need to combine stability in the long term and rapid response to environmental challenges in the short term. The former would be reflected by parallel or convergent adaptation across species, and the latter by pronounced local adaptation among populations of the same species. In the present study, we generated a high-quality genome and re-sequenced 177 individuals for Gymnocarpos przewalskii, an important desert plant species from North-West China, to detect local adaptation. We first focus on ancient adaptation to aridity at the molecular level by comparing the genomic data of 15 species that vary in their ability to withstand aridity. We found that a total of 118 genes were shared across xerophytic species but absent from non-xerophytic species. Of the 65 found in G. przewalskii, 63 were under purifying selection and two under positive selection. We then focused on local adaptation. Up to 20% of the G. przewalskii genome showed signatures of local adaptation to aridity during population divergence. Thirteen of the selected shared xerophytic genes were reused in local adaptation after population differentiation. Hence, only about 20% of the genes shared and specific to xerophytic species and associated with adaptation to aridity were later recruited for local adaptation in G. przewalskii.

Long-term climate and hydrologic regimes shape stream invertebrate community responses to a hurricane disturbance.

Disturbances can produce a spectrum of short- and long-term ecological consequences that depend on complex interactions of the characteristics of the event, antecedent environmental conditions, and the intrinsic properties of resistance and resilience of the affected biological system. We used Hurricane Harvey's impact on coastal rivers of Texas to examine the roles of storm-related changes in hydrology and long-term precipitation regime on the response of stream invertebrate communities to hurricane disturbance. We detected declines in richness, diversity and total abundance following the storm, but responses were strongly tied to direct and indirect effects of long-term aridity and short-term changes in stream hydrology. The amount of rainfall a site received drove both flood duration and flood magnitude across sites, but lower annual rainfall amounts (i.e. aridity) increased flood magnitude and decreased flood duration. Across all sites, flood duration was positively related to the time it took for invertebrate communities to return to a long-term baseline and flood magnitude drove larger invertebrate community responses (i.e. changes in diversity and total abundance). However, invertebrate response per unit flood magnitude was lower in sub-humid sites, potentially because of differences in refuge availability or ecological-evolutionary interactions. Interestingly, sub-humid streams had temporary large peaks in invertebrate total abundance and diversity following recovery period that may be indicative of the larger organic matter pulses expected in these systems because of their comparatively well-developed riparian vegetation. Our findings show that hydrology and long-term precipitation regime predictably affected invertebrate community responses and, thus, our work underscores the important influence of local climate to ecosystem sensitivity to disturbances.

Divergent driving mechanisms of community temporal stability in China's drylands.

Climate change and anthropogenic activities are reshaping dryland ecosystems globally at an unprecedented pace, jeopardizing their stability. The stability of these ecosystems is crucial for maintaining ecological balance and supporting local communities. Yet, the mechanisms governing their stability are poorly understood, largely due to the scarcity of comprehensive field data. Here we show the patterns of community temporal stability and its determinants across an aridity spectrum by integrating a transect survey across China's drylands with remote sensing. Our results revealed a U-shaped relationship between community temporal stability and aridity, with a pivotal shift occurring around an aridity level of 0.88. In less arid areas (aridity level below 0.88), enhanced precipitation and biodiversity were associated with increased community productivity and stability. Conversely, in more arid zones (aridity level above 0.88), elevated soil organic carbon and biodiversity were linked to greater fluctuations in community productivity and reduced stability. Our study identifies a critical aridity threshold that precipitates significant changes in community stability in China's drylands, underscoring the importance of distinct mechanisms driving ecosystem stability in varying aridity contexts. These insights are pivotal for developing informed ecosystem management and policy strategies tailored to the unique challenges of dryland conservation.

Impact of aridity rise and arid lands expansion on carbon-storing capacity, biodiversity loss, and ecosystem services.

Drylands, comprising semi-arid, arid, and hyperarid regions, cover approximately 41% of the Earth's land surface and have expanded considerably in recent decades. Even under more optimistic scenarios, such as limiting global temperature rise to 1.5°C by 2100, semi-arid lands may increase by up to 38%. This study provides an overview of the state-of-the-art regarding changing aridity in arid regions, with a specific focus on its effects on the accumulation and availability of carbon (C), nitrogen (N), and phosphorus (P) in plant-soil systems. Additionally, we summarized the impacts of rising aridity on biodiversity, service provisioning, and feedback effects on climate change across scales. The expansion of arid ecosystems is linked to a decline in C and nutrient stocks, plant community biomass and diversity, thereby diminishing the capacity for recovery and maintaining adequate water-use efficiency by plants and microbes. Prolonged drought led to a -3.3% reduction in soil organic carbon (SOC) content (based on 148 drought-manipulation studies), a -8.7% decrease in plant litter input, a -13.0% decline in absolute litter decomposition, and a -5.7% decrease in litter decomposition rate. Moreover, a substantial positive feedback loop with global warming exists, primarily due to increased albedo. The loss of critical ecosystem services, including food production capacity and water resources, poses a severe challenge to the inhabitants of these regions. Increased aridity reduces SOC, nutrient, and water content. Aridity expansion and intensification exacerbate socio-economic disparities between economically rich and least developed countries, with significant opportunities for improvement through substantial investments in infrastructure and technology. By 2100, half the world's landmass may become dryland, characterized by severe conditions marked by limited C, N, and P resources, water scarcity, and substantial loss of native species biodiversity. These conditions pose formidable challenges for maintaining essential services, impacting human well-being and raising complex global and regional socio-political challenges.

Cyanobacterial and moss biocrusts shape soil nematode community in dryland mountain ecosystems with increasing aridity.

Soil nematodes are the most abundant animals on Earth and play critical roles in regulating numerous ecosystem processes, from enhancing primary productivity to mineralizing multiple nutrients. In dryland soils, a rich community of microphyte organisms (biocrusts) provide critical habitats for soil nematodes, but their presence is being threatened by increasing aridity induced by global climate change. Despite its importance, how types of biocrusts and aridity index influence soil nematode community in dryland mountain ecosystems remains largely unknown. To fill these knowledge gaps, we conducted a field survey with contrasting aridity indexes (0.2, 0.4, and 0.6) and three types of biocrusts (cyanobacterial, cyanobacterial-moss mixed, and moss crusts) in the topsoil (0-5 cm) from the northern Chinese Loess Plateau. We found that the abundance (number of individuals per gram of soil), richness (number of Operational Taxonomic Units; OTUs), and diversity (number of different species) of soil nematodes were remarkably higher under biocrusts than in bare soils, regardless of aridity index and types of biocrusts. Our results also showed that the same variables had the highest values in moss crusts compared to cyanobacterial and cyanobacterial-moss mixed crusts. Structural equation modelling further revealed that biocrust types and traits (i.e., biocrust thickness, chlorophyll content, shear force, and penetration resistance) are the most important factors associated with both nematode abundance and richness. Together, our findings indicate that biocrusts, especially moss cover, and less stressful aridity conditions favor soil nematodes community in dryland mountain regions. Such knowledge is critical for anticipating the distribution of these animals under climate change scenarios and, ultimately, the numerous ecosystem services supported by soil nematodes.

Different responses of oxygen and hydrogen isotopes in leaf and tree-ring organic matter to lethal soil drought.

The oxygen and hydrogen isotopic composition (δ18O, δ2H) of plant tissues are key tools for the reconstruction of hydrological and plant physiological processes and may therefore be used to disentangle the reasons for tree mortality. However, how both elements respond to soil drought conditions before death has rarely been investigated. To test this, we performed a greenhouse study and determined predisposing fertilization and lethal soil drought effects on δ18O and δ2H values of organic matter in leaves and tree rings of living and dead saplings of five European tree species. For mechanistic insights, we additionally measured isotopic (i.e. δ18O and δ2H values of leaf and twig water), physiological (i.e. leaf water potential and gas-exchange) and metabolic traits (i.e. leaf and stem non-structural carbohydrate concentration, carbon-to-nitrogen ratios). Across all species, lethal soil drought generally caused a homogenous 2H-enrichment in leaf and tree-ring organic matter, but a low and heterogenous δ18O response in the same tissues. Unlike δ18O values, δ2H values of tree-ring organic matter were correlated with those of leaf and twig water and with plant physiological traits across treatments and species. The 2H-enrichment in plant organic matter also went along with a decrease in stem starch concentrations under soil drought compared with well-watered conditions. In contrast, the predisposing fertilization had generally no significant effect on any tested isotopic, physiological and metabolic traits. We propose that the 2H-enrichment in the dead trees is related to (i) the plant water isotopic composition, (ii) metabolic processes shaping leaf non-structural carbohydrates, (iii) the use of carbon reserves for growth and (iv) species-specific physiological adjustments. The homogenous stress imprint on δ2H but not on δ18O suggests that the former could be used as a proxy to reconstruct soil droughts and underlying processes of tree mortality.

Global patterns and drivers of plant-soil microbe interactions.

Plant-soil feedback (PSF) is an important mechanism determining plant community dynamics and structure. Understanding the geographic patterns and drivers of PSF is essential for understanding the mechanisms underlying geographic plant diversity patterns. We compiled a large dataset containing 5969 observations of PSF from 202 studies to demonstrate the global patterns and drivers of PSF for woody and non-woody species. Overall, PSF was negative on average and was influenced by plant attributes and environmental settings. Woody species PSFs did not vary with latitude, but non-woody PSFs were more negative at higher latitudes. PSF was consistently more positive with increasing aridity for both woody and non-woody species, likely due to increased mutualistic microbes relative to soil-borne pathogens. These findings were consistent between field and greenhouse experiments, suggesting that PSF variation can be driven by soil legacies from climates. Our findings call for caution to use PSF as an explanation of the latitudinal diversity gradient and highlight that aridity can influence plant community dynamics and structure across broad scales through mediating plant-soil microbe interactions.

Dominance of soil moisture over aridity in explaining vegetation greenness across global drylands.

Drylands are one of the most sensitive areas to climate change. Despite being characterized by water scarcity and low precipitation, drylands support a wide range of green biodiversity and nearly 40 % of the global population. However, the climate change impacts on dryland characteristics and vegetation dynamics are debatable as the reasons remain poorly understood. Here, we use hydro-meteorological variables from ERA5 reanalysis and GIMMS-NDVI to analyze the changes in dryland aridity and vegetation greenness in the eight selected global dryland regions. The total dryland area (excluding hyperarid) has increased by 12 %, while arid, semiarid, and dry sub-humid areas have increased by 10.5 %, 8 %, and 25 %, respectively. We find a significant increase in aridity in drylands across the globe, except for South Asia. A decrease (increase) in precipitation is the major driver for a significant increase (decrease) in dryland aridity, with a notable contribution from climate warming. Despite decreasing trends in precipitation, vegetation greenness has significantly increased in most dryland regions due to increased soil moisture. Cropland expansion in Europe, Asia, and Australia resulted in the maximum increase in NDVI (Normalized Difference Vegetation Index) in dryland regions. The highest increase, with a ΔNDVI of 0.075, was observed in South Asia. The enhanced vegetation greenness observed is attributed to the expansion of croplands in recent decades, which has increased soil moisture. Overall, we show that monitoring soil moisture variability can provide a more robust explanation for vegetation greenness in the global drylands than aridity change. Moreover, human interventions of climatic alteration through land use change practices, such as cropland expansion, cannot be ignored while explaining the ecosystem dynamics of the drylands.

Effects of aridification on soil total carbon pools in China's drylands.

Drylands are important carbon pools and are highly vulnerable to climate change, particularly in the context of increasing aridity. However, there has been limited research on the effects of aridification on soil total carbon including soil organic carbon and soil inorganic carbon, which hinders comprehensive understanding and projection of soil carbon dynamics in drylands. To determine the response of soil total carbon to aridification, and to understand how aridification drives soil total carbon variation along the aridity gradient through different ecosystem attributes, we measured soil organic carbon, inorganic carbon and total carbon across a ~4000 km aridity gradient in the drylands of northern China. Distribution patterns of organic carbon, inorganic carbon, and total carbon at different sites along the aridity gradient were analyzed. Results showed that soil organic carbon and inorganic carbon had a complementary relationship, that is, an increase in soil inorganic carbon positively compensated for the decrease in organic carbon in semiarid to hyperarid regions. Soil total carbon exhibited a nonlinear change with increasing aridity, and the effect of aridity on total carbon shifted from negative to positive at an aridity level of 0.71. In less arid regions, aridification leads to a decrease in total carbon, mainly through a decrease in organic carbon, whereas in more arid regions, aridification promotes an increase in inorganic carbon and thus an increase in total carbon. Our study highlights the importance of soil inorganic carbon to total carbon and the different effects of aridity on soil carbon pools in drylands. Soil total carbon needs to be considered when developing measures to conserve the terrestrial carbon sink.

Fog controls biological cycling of soil phosphorus in the Coastal Cordillera of the Atacama Desert.

Soils in hyper-arid climates, such as the Chilean Atacama Desert, show indications of past and present forms of life despite extreme water limitations. We hypothesize that fog plays a key role in sustaining life. In particular, we assume that fog water is incorporated into soil nutrient cycles, with the inland limit of fog penetration corresponding to the threshold for biological cycling of soil phosphorus (P). We collected topsoil samples (0-10 cm) from each of 54 subsites, including sites in direct adjacency (<10 cm) and in 1 m distance to plants, along an aridity gradient across the Coastal Cordillera. Satellite-based fog detection revealed that Pacific fog penetrates up to 10 km inland, while inland sites at 10-23 km from the coast rely solely on sporadic rainfall for water supply. To assess biological P cycling we performed sequential P fractionation and determined oxygen isotope of HCl-extractable inorganic P δ 18 O HCl - P i $$ \mathrm{P}\ \left({\updelta}^{18}{\mathrm{O}}_{\mathrm{HCl}-{\mathrm{P}}_{\mathrm{i}}}\right) $$ . Total P (Pt ) concentration exponentially increased from 336 mg kg-1 to a maximum of 1021 mg kg-1 in inland areas ≥10 km. With increasing distance from the coast, soil δ 18 O HCl - P i $$ {\updelta}^{18}{\mathrm{O}}_{\mathrm{HCl}-{\mathrm{P}}_{\mathrm{i}}} $$ values declined exponentially from 16.6‰ to a constant 9.9‰ for locations ≥10 km inland. Biological cycling of HCl-Pi near the coast reached a maximum of 76%-100%, which could only be explained by the fact that fog water predominately drives biological P cycling. In inland regions, with minimal rainfall (<5 mm) as single water source, only 24 ± 14% of HCl-Pi was biologically cycled. We conclude that biological P cycling in the hyper-arid Atacama Desert is not exclusively but mainly mediated by fog, which thus controls apatite dissolution rates and related occurrence and spread of microbial life in this extreme environment.

Warmer and drier ecosystems select for smaller bacterial genomes in global soils.

Bacterial genome size reflects bacterial evolutionary processes and metabolic lifestyles, with implications for microbial community assembly and ecosystem functions. However, to understand the extent of genome-mediated microbial responses to environmental selections, we require studies that observe genome size distributions along environmental gradients representing different conditions that soil bacteria normally encounter. In this study, we used surface soils collected from 237 sites across the globe and analyzed how environmental conditions (e.g., soil carbon and nutrients, aridity, pH, and temperature) affect soil bacterial occurrences and genome size at the community level using bacterial community profiling. We used a joint species distribution model to quantify the effects of environments on species occurrences and found that aridity was a major regulator of genome size with warmer and drier environments selecting bacteria with smaller genomes. Drought-induced physiological constraints on bacterial growth (e.g., water scarcity for cell metabolisms) may have led to these correlations. This finding suggests that increasing cover by warmer and drier ecosystems may result in bacterial genome simplifications by a reduction of genome size.

Cambio climático y recursos hídricos en Colombia / Climate change and water resources in Colombia

RESUMEN La presente investigación tuvo por objeto evaluar los posibles impactos que habría en la distribución espacial del recurso hídrico sobre el territorio colombiano, bajo dos escenarios de cambio climático, a mediados del siglo XXI. Para el efecto, se utilizaron dos indicadores hídricos ambientales (Índice de Aridez y Balance Hídrico), con los cuales, se estima y se cuantifica la oferta hídrica del territorio colombiano, a partir de datos climatológicos del período de referencia 1976-2005 y, posteriormente, utilizando los datos de las variables climatológicas de los escenarios RCP 4,5 y 6,0, de la tercera comunicación nacional de Colombia ante la convención marco de cambio climático. Los resultados de esta modelación arrojaron los siguientes resultados: el régimen hidrológico del país, se caracteriza por tener una escorrentía promedio de 1.644mm, con valores que van desde una escorrentía promedio de 100mm al año, en la península de la Guajira, hasta escorrentías mayores de 6.000mm, en el Pacífico. El índice de aridez modelado arrojó un valor promedio de 0,23, ubicando a Colombia en condiciones Moderadas y Excedentes de agua. Se presentarían reducciones significativas en el volumen de escorrentía hasta en un 18% en promedio para los dos escenarios. La menor reducción se daría en el escenario RCP 4,5, con un 12% de la escorrentía actual y la reducción más drástica, se presentaría en el RCP 6,0, hasta en un 18%. En cuanto al Índice de Aridez, se sugiere que el escenario más fuerte es el RCP 6,0, con un valor promedio de 0,50 lo que significa una mderada situación deficitaria de agua.

ABSTRACT The possible impacts from the spatial distribution of the water resource over the Colombian territory are analyzed under two scenarios of climate change in the middle of the 21st century. For the effect, two environmental water indicators were used (Aridity index and Water Balance) to estimate, quantify and water supply of the Colombian territory, from the climate data during the period of reference 1976-2005 in spatial resolution of 900 meters. In this modeling, the water regimen of the country is characterized by its average runoff of 1644mm, with values that are between an annual average runoff of 100mm in the Guajira peninsula until higher runoffs of 6000 millimeters in the Pacific. The aridity index in such modeling generated an average of 0,37, putting Colombia in moderate conditions of aridity, which shows sectors with a high-water deficit such as the Guajira peninsula and in the north of Magdalena and Atlántico regions. Additionally, the climate variables for Colombia were taken by a regional climate modeling in two scenarios RCP 4,5 and 6,0 for the period 2011-2040 and the environmental water indicators were generated. Across a comparison between the indicators of the current (1976-2005) and future period 2011-2040, the changes that would appear in the water availability towards those periods in both scenarios were established. The results are summarized in: substantial reductions in the runoff volume in respect to the current values in an 18% average for all scenarios, the lowest reduction would appear in 4,5 with 12% of the current runoff and the most drastic reduction presents in 6,0 in the middle of the century until 18%. Regarding the aridity index, the most aggressive scenario is 6.0 with an average value of 0,50, which refers to a water deficit, while by the middle of the century 6,0 and 4,5 would locate the country in a moderate condition of water deficit.

Abundancia altitudinal de Dendroctonus frontalis (Coleoptera: Curculionidae) en relación a variables climáticas en Hidalgo, México

Los descortezadores Dendroctonus frontalis (Coleoptera: Scolytidae) son un grupo de coleópteros estrechamente ligado a las masas forestales y son una de las plagas más dañinas en México, ocasionando que la cobertura forestal se reduzca considerablemente. Adicionalmente factores como el cambio climático, favorecen el aumento en las poblaciones de escarabajos descortezadores del género Dendroctonus. Por lo anterior es conveniente conocer la variación poblacional de descortezadores, particularmente de Dendroctonus frontalis, cuyas poblaciones dependen de la variabilidad climática que influye en su abundancia. Teniendo como hipótesis que la altitud y las variables ambientales afectan el comportamiento en la abundancia de D. frontalis, se planteó como objetivo estimar la variación espacio-temporal de poblaciones de D. frontalis en bosques de pino a diferentes altitudes. El estudio se realizó en la comunidad de Durango, Zimapán, Hidalgo, México. Se utilizó un diseño experimental de parcelas apareadas con dos tratamientos, de feromona y testigo. Se colocaron siete trampas con ambos tratamientos en un rango de 1 568 a 2 117 m.s.n.m. para determinar la abundancia altitudinal de D. frontalis. El muestreo se llevó a cabo de enero a diciembre 2015. Se obtuvo una relación positiva entre la abundancia de D. frontalis y el gradiente altitudinal y respecto a la abundancia de D. frontalis y la temperatura se observó una relación moderada, pero no significativa; de la misma forma para la precipitación media anual. La relación con la temperatura media máxima y el balance de precipitación de primavera/verano fueron estadísticamente significativos. Se presentó una tendencia positiva en la abundancia de D. frontalis de acuerdo al índice anual de aridez, por lo cual se espera que con el aumento de las temperaturas el estrés en la vegetación de los bosques sea mayor, favoreciendo el incremento de las poblaciones de escarabajos descortezadores.

The bark beetles Dendroctonus frontalis (Coleoptera: Scolytidae) are a group of coleoptera closely linked to forest masses, and one of the most harmful pests in Mexico, causing the forest cover to be considerably reduced. Additionally factors such as climate change, favor the increase in populations of bark beetles of the genus Dendroctonus. Taking as a hypothesis that altitude and environmental variables affect the behavior in the abundance of D. frontalis, the objective was to estimate the temporary-spatial variation of D. frontalis populations in pine forests at different altitudes. The study was conducted in the community of Durango, Zimapán, Hidalgo, Mexico. An experimental design of paired plots with two treatments was used, pheromone and control. Seven traps were placed with both treatments in a range of 1 568 to 2 117 m.a.s.l. to determine the altitudinal abundance of D. frontalis. The sampling was realized from January to December 2015. A positive relationship was observed between the abundance of D. frontalis and the altitudinal gradient. About the abundance of D. frontalis and the temperature, a moderate but not significant relationship was observed in the same way for the average annual precipitation. The relation with the maximum average temperature and the spring summer precipitation balance were statistically significant. There was a positive trend on the abundance of D. frontalis according to the annual aridity index, which is why it is expected that the increase of temperatures the stress in the vegetation of the forests will be greater, favoring the increase of bark beetles populations.