Population differentiation and dynamics of five pioneer species of Gaultheria from the secondary forests in subtropical China.

BACKGROUND: The influence of native secondary succession associated with anthropogenic disturbance on the biodiversity of the forests in subtropical China remains uncertain. In particular, the evolutionary response of small understory shrubs, particularly pioneer species inhabiting continuously disturbed habitats, to topographic heterogeneity and climate change is poorly understood. This study aimed to address this knowledge gap by focusing on the Gaultheria crenulata group, a clade of small pioneer shrubs in subtropical China. RESULTS: We examined the genetic structure and demographic history of all five species of the G. crenulata group with two maternally inherited chloroplast DNA (cpDNA) fragments and two biparentally inherited low-copy nuclear genes (LCG) over 89 natural populations. We found that the genetic differentiation of this group was influenced by the geomorphological boundary between different regions of China in association with Quaternary climatic events. Despite low overall genetic diversity, we observed an isolation-by-distance (IBD) pattern at a regional scale, rather than isolation-by-environment (IBE), which was attributed to ongoing human disturbance in the region. CONCLUSION: Our findings suggest that the genetic structure of the G. crenulata group reflects the interplay of geological topography, historical climates, and anthropogenic disturbance during the Pliocene-Pleistocene-Holocene periods in subtropical China. The observed IBD pattern, particularly prominent in western China, highlights the role of limited dispersal and gene flow, possibly influenced by physical barriers or decreased connectivity over geographic distance. Furthermore, the east-to-west trend of gene flow, potentially facilitated by the East Asian monsoon system, underscores the complex interplay of biotic and abiotic factors shaping the genetic dynamics of pioneer species in subtropical China's secondary forests. These findings can be used to assess the impact of environmental changes on the adaptation and persistence of biodiversity in subtropical forest ecosystems.

Integrating traditional ecological knowledge into habitat restoration: implications for meeting forest restoration challenges.

BACKGROUND: Traditional ecological knowledge (TEK) helps tribal communities adapt to socio-ecological changes, improving the long-term sustainability of their livelihood strategies and fostering social-ecological resilience. TEK provides thorough understanding of ecosystem dynamics, as well as how they relate to societal norms, practices, and resource use patterns. The integrity of TEK is often in jeopardy due to changes in belief systems, regional languages, traditional ways of subsistence, and disruption of traditional social-ecological systems. Landscape restoration has the ability to promote self-determination while safeguarding the livelihoods, beliefs, cultural, and biodiversity of indigenous peoples. However, there is a substantial knowledge gap on how TEK might aid ecosystem restoration, particularly in elephant corridors. METHODS: The current study focused on gathering traditional ecological knowledge on the woody tree species from the Dering-Dibru Saikhowa Elephant Corridor using semi-structured interviews, group discussions, and direct observations. The acquired data were applied to heat map cluster analysis and ordination techniques using R software version 4.0.0. RESULTS: Traditional usage information of 31 tree species utilized for food, fodder, timber, fuelwood, medicinal, and livelihood by local people was gathered. Most of the species utilized locally belonged to the families Combretaceae and Fabaceae. The species were classified into single, double, or multi-uses based on the extent of utilization. Azadirachta indica, Phyllanthus emblica, and Syzygium cumini (six each) had the highest utilization, while Mesua ferrea had the lowest. Chionanthus ramiflorus, Artocarpus heterophyllus, and Dillenia indica were among the plants valuable to wildlife, providing both forage and habitat for a wide variety of birds and animals. Artocarpus heterophyllus, Averrhoa carambola, Mangifera indica, P. emblica, Psidium guajava, and S. cumini were among the plants important for the livelihoods of the local community. Our findings demonstrated that local people were knowledgeable about the plant species to use as pioneer species, such as Bombax ceiba, Albizia lebbeck, D. indica, S. cumini, P. emblica, Lagerstroemia speciosa, and Alstonia scholaris, for habitat restoration in a diverse habitat. We classified the habitat of the enlisted species into different categories, and two clusters (clusters 1 and 2) were identified based on the similarity of woody species in different habitats. We prioritized multiple tree species for eco-restoration using the information collected through TEK. We planted 95,582 saplings on 150 hectares in the Dering-Dibru Saikhowa Elephant Corridors' degraded habitat patches, which will serve as future reference site for landscape rehabilitation. Out of total saplings planted, 56% of the species were linked to native communities through ethnobotanical uses, as well as providing connectivity and habitat for elephant movement, 16% of all woody species are pioneer species to colonize a degraded habitat, 15% of all woody species are preferred food and foraging by wildlife, and 13% of the species as a source of livelihood for local people, incorporating social, economic, cultural, and biodiversity benefits into the restoration framework. CONCLUSION: The current study also provides insights how the TEK can assist with aspects of ecological restoration, from reference ecosystem reconstruction and adaptive management through species selection for restoration, monitoring, and evaluation of restoration effectiveness.

Limosilactobacillus reuteri inhibits the acid tolerance response in oral bacteria.

Probiotic bacteria show promising results in prevention of the biofilm-mediated disease caries, but the mechanisms are not fully understood. The acid tolerance response (ATR) allows biofilm bacteria to survive and metabolize at low pH resulting from microbial carbohydrate fermentation. We have studied the effect of probiotic strains: Limosilactobacillus reuteri and Lacticaseibacillus rhamnosus on ATR induction in common oral bacteria. Communities of L. reuteri ATCC PTA5289 and Streptoccus gordonii, Streptococcus oralis, Streptococcus mutans or Actinomyces naeslundii in the initial stages of biofilm formation were exposed to pH 5.5 to allow ATR induction, followed by a low pH challenge. Acid tolerance was evaluated as viable cells after staining with LIVE/DEAD®BacLight™. The presence of L. reuteri ATCC PTA5289 caused a significant reduction in acid tolerance in all strains except S. oralis. When S. mutans was used as a model organism to study the effects of additional probiotic strains (L. reuteri SD2112, L. reuteri DSM17938 or L. rhamnosus GG) as well as L. reuteri ATCC PTA5289 supernatant on ATR development, neither the other probiotic strains nor supernatants showed any effect. The presence of L. reuteri ATCC PTA5289 during ATR induction led to down-regulation of three key genes involved in tolerance of acid stress (luxS, brpA and ldh) in Streptococci. These data suggest that live cells of probiotic L. reuteri ATCC PTA5289 can interfere with ATR development in common oral bacteria and specific strains of L. reuteri may thus have a role in caries prevention by inhibiting development of an acid-tolerant biofilm microbiota.

Pioneer tree species accelerate restoration of tree-related microhabitats in 50-year-old reserves of Bialowieza Forest, Poland.

Retention of structural elements such as deadwood and habitat trees at the level of forest stands has been promoted to integrate biodiversity conservation into multiple-use forest management. The conservation value of habitat trees is largely determined by the presence, richness, and abundance of tree-related microhabitats (TreMs). Since TreMs are often lacking in intensively managed forests, an important question of forest conservation is how the abundance and richness of TreMs may be effectively restored. Here, we investigated whether the strict protection of forest through cessation of timber harvesting influenced TreM occurrence at tree and stand levels. For that purpose, we compared four managed and four set-aside stands (0.25 ha each) in the Bialowieza Forest, with identical origin following clear-cuts approximately 100 years ago. We found that the abundance and richness of TreMs on living trees were not significantly different between stands that were either conventionally managed or where active forest management ceased 52 years ago. Yet, our analysis of TreMs on tree species with contrasting life-history traits revealed that short-lived, fast-growing species (pioneers) developed TreMs quicker than longer-lived, slower-growing species. Hence, tree species such as Populus or Betula, which supply abundant and diverse TreMs, can play an important role in accelerating habitat restoration.

Contrasting sap flow characteristics between pioneer and late-successional tree species in secondary tropical montane forests of Eastern Himalaya, India.

The interactive role of life-history traits and environmental factors on plant water relations is crucial for understanding the responses of species to climate change, but it remains poorly understood in secondary tropical montane forests (TMFs). In this study, we examined differences in sap flow between the pioneer species Symplocos racemosa and Eurya acuminata, and the late-successional species Castanopsis hystrix that co-occur in a biodiverse Eastern Himalayan secondary broadleaved TMF. The fast-growing pioneers had sap flux densities that were 1.6-2.1 times higher than the late-successional species, and exhibited characteristics of long-lived pioneer species. Significant radial and azimuthal variability in sap flow (V) between species was observed and could be attributed to the life-history trait and the access of the canopy to sunlight. Nocturnal V was 13.8% of the daily total and was attributable to stem recharge during the evening period (18.00-23.00 h) and to endogenous stomatal controls during the pre-dawn period (00.00-05.00 h). The shallow-rooted pioneer species both exhibited midday depression in V that was attributable to photosensitivity and diel moisture stress responses. In contrast, the deep-rooted late-successional species showed unaffected transpiration across the dry season, indicating their access to groundwater. Thus, our results suggest that secondary broadleaved TMFs, with a dominance of shallow-rooted pioneers, are more prone to the negative impacts of drier and warmer winters than primary forests, which are dominated by deep-rooted species. Our study provides an empirical understanding of how life-history traits coupled with microclimate can modulate plant water use in the widely distributed secondary TMFs in Eastern Himalaya, and highlights their vulnerability to warmer winters and reduced winter precipitation due to climate change.

Photosynthetic Properties of Co-Occurring Pioneer Species on Volcanically Devastated Sites in Miyake-jima Island, Japan.

Pioneer species differing in their inherent ecological characteristics (e.g., N-fixing ability, photosynthetic pathway) can have a large impact on local ecosystems in the early stages of volcanic succession. However, it remains unclear as to how these pioneer species adapt to the extreme environment of volcanically devastated sites in terms of ecophysiological leaf traits. In this study, we compared the leaf traits (including morphological, physiological) of three co-occurring pioneer species, including a C4 non-N-fixing grass, a C3 N-fixing tree, and a C3 non-N-fixing herb from a newly created (18 years after eruption) volcanically devastated site in Miyake-jima, Japan. Our results showed that three pioneer species have different sets of leaf traits that are associated with their ecophysiological growth advantages, respectively. Miscanthus condensatus shows the highest light-saturated photosynthetic rate (Amax). The higher Amax were partially the result of higher water use efficiency (WUE) and photosynthetic N-use efficiency (PNUE). The PNUE in M. condensatus appears to be high, even for a C4 grass. Alnus sieboldiana rely on its N-fixing ability, has a higher leaf N content (Narea) that compensates for its photosynthetic machinery (Rubisco), and further ensures its photosynthetic capacity. Fallopia japonica var. hachidyoensis has a higher leaf mass per area (LMA), chlorophyll content (Chl), and maximum quantum yield of PSII (Fv/Fm), demonstrating its higher light capturing ability. These results make it possible to predict certain ecological processes that take place in the early stages of volcanic succession resulting from ecological characteristics and from some key leaf traits of pioneer species. It also provides a theoretical basis for species selection and species combination for volcanic ecological restoration.

Large tree mortality leads to major aboveground biomass decline in a tropical forest reserve.

Humans are transforming the ecology of the Earth through rapid changes in land use and climate. These changes can affect tropical forest structure, dynamics and diversity. While numerous studies have focused on diversity metrics, other aspects of forest function, such as long-term biomass dynamics, are often less considered. We evaluated plant community structure change (i.e., abundance, diversity, composition, and aboveground biomass) in a 2.25 ha forest dynamics plot located within a ~ 365 ha reserve in southern Costa Rica. We censused, mapped and identified to species all plants ≥ 5 cm diameter at breast height (DBH) in three surveys spanning 2010-2020. While there were no changes in late-successional species diversity, there were marked changes in overall species composition and biomass. Abundance of large (≥ 40 cm DBH) old-growth dense-wooded trees (e.g., Lauraceae, Rosaceae) decreased dramatically (27%), leading to major biomass decline over time, possibly driven by recent and recurrent drought events. Gaps created by large trees were colonized by early-successional species, but these recruits did not make up for the biomass lost. Finally, stem abundance increased by 20%, driven by increasing dominance of Hampea appendiculata. While results suggest this reserve may effectively conserve overall plant diversity, this may mask other key shifts such as large aboveground biomass loss. If this pattern is pervasive across tropical forest reserves, it could hamper efforts to preserve forest structure and ecosystem services (e.g., carbon storage). Monitoring programs could better assess carbon trends in reserves over time simply by tracking large tree dynamics.

Morphological Features of Plants on Ash Settling Ponds. Case Study.

Owing to variable water conditions, chemical conditions of water or ash substrate, ash settling ponds belong to anthropogenic objects which do not easily undergo plant succession. However, there are plants exhibiting biological traits allowing colonisation of a substrate characterised by variability in terms of acidity and heavy metal content. The aim of the study was to determine differences in morphology of plants colonising spontaneous surfaces of ash settling ponds with variability moisture level. We identified also differences in morphology of the plants. Identified: Agrostis stolonifera, Atriplex patula, Juncus bufonius, Phragmites australis, Poa pratensis and Ranunculus sceleratus. The obtained results broaden the knowledge on the bioremediation of degraded areas, indicate species that inhabit the surface of ash settlers. Lower water level in ash settling pond I created more favourable conditions for growth of the aboveground parts of plants, and higher waterlevel in ash settling pond II contributed to a more intensive development of the root part of plants. Considering the generative factors and measurement values of the aboveground part of plants, the best adapted species were Juncus bufonius and Atriplex patula. Due to changing water level in ash settling ponds, the species to be monitored is Phragmites australis-most deeply colonising the surface of ash settling ponds.

Exceptional nitrogen-resorption efficiency enables Maireana species (Chenopodiaceae) to function as pioneers at a mine-restoration site.

Tailings are among the most challenging mined substrates for plant re-establishment, in particular because of a lack of soil-like structure and nitrogen. Potential pioneer plants are sometimes found in such disturbed and infertile sites. We present a group of pioneer species from the genus Maireana (Chenopodiaceae) that are promising candidates for the restoration of magnetite tailings. We found that these Maireana species did not rely on biologically fixed N from the atmosphere, but exhibited an exceptionally high leaf N-resorption efficiency (about 95%) during leaf senescence, at the same time effectively scavenging trace amount of N from the substrate, in part through rapid transpiration.

[Structure and dynamic characteristics of Betula luminifera populations in different regions of Southwest Hubei Province, China]. / 鄂西南不同区域亮叶桦种群结构与动态特征.

We investigated Betula luminifera populations in three regions (Mulinzi, Qizimei Mountains, and Jinzi Mountains) in the southwest Hubei Province, China. Population structure was divided by age classes and height classes. Population structure figures were drawn. The static life tables of B. luminifera populations in different regions were analyzed using the method of substitution of space for time. The survival curve, mortality rate curve and disappearance rate curve were created. Four functions of survival analysis were used to analyze the dynamics of B. luminifera population in different regions. The results showed that the B. luminifera populations in three regions were the increasing type. The height class structures were relatively complete. Some age classes were absent from the age structures of B. luminifera populations in Qizimei Mountains and Jinzi Mountains. Although the dynamic index of trees number Vpi＞0, but it was sensitive to external disturbance. The survival of B. luminifera of different age classes varied greatly in static life table, which gradually decreased with increasing age class, with Deevey-type 2 survival curve. The trend of mortality rate changed similarly to the disappearance rate, but fluctuated differently. All B. luminifera populations in different regions appeared to decrease in the early stage and keep dynamically stable in the medium-late stage.

When the Ice Has Gone: Colonisation of Equatorial Glacier Forelands by Ground Beetles (Coleoptera: Carabidae).

Ground beetles (Coleoptera: Carabidae) are among the early colonisers of recently deglaciated terrains. While patterns of carabid colonisation along forelands of retreating glaciers have been thoroughly investigated in temperate climates, information remains scarce in tropical mountains. This study aimed to describe for the first time the carabid beetle species assemblages along the chronosequence of two tropical Andean glaciers (Antisana and Carihuairazo, Ecuador). Shannon index, taxonomic distinctness and species assemblage composition did not reveal deterministic and directional patterns. Only the principal coordinate analysis performed on the Antisana dataset showed that some species had a clear preference for terrains deglaciated for more than 200 years. Our results showed that equatorial glacier forelands are colonised by pioneer species that persist from the recently deglaciated terrains (less than 25 years) to terrains deglaciated since more than 200 years. This pattern fits the 'addition and persistence model' of high-latitude glacier forelands, rather than the 'species replacement model' of the Alps. The pioneer species observed are high-altitude specialists adapted to constantly cold environments, but not specifically ice-related. In the current context of climate warming, pioneer and cold-adapted species living near the glaciers of equatorial mountains are therefore only threatened by the 'summit trap' risk, unlike in temperate regions, as they are not strictly linked to the glacier microclimate.

Comparative phylogeography of five widespread tree species: Insights into the history of western Amazonia.

Various historical processes have been put forth as drivers of patterns in the spatial distribution of Amazonian trees and their population genetic variation. We tested whether five widespread tree species show congruent phylogeographic breaks and similar patterns of demographic expansion, which could be related to proposed Pleistocene refugia or the presence of geological arches in western Amazonia. We sampled Otoba parvifolia/glycycarpa (Myristicaceae), Clarisia biflora, Poulsenia armata, Ficus insipida (all Moraceae), and Jacaratia digitata (Caricaceae) across the western Amazon Basin. Plastid DNA (trnH-psbA; 674 individuals from 34 populations) and nuclear ribosomal internal transcribed spacers (ITS; 214 individuals from 30 populations) were sequenced to assess genetic diversity, genetic differentiation, population genetic structure, and demographic patterns. Overall genetic diversity for both markers varied among species, with higher values in populations of shade-tolerant species than in pioneer species. Spatial analysis of molecular variance (SAMOVA) identified three genetically differentiated groups for the plastid marker for each species, but the areas of genetic differentiation were not concordant among species. Fewer SAMOVA groups were found for ITS, with no detectable genetic differentiation among populations in pioneers. The lack of spatially congruent phylogeographic breaks across species suggests no common biogeographic history of these Amazonian tree species. The idiosyncratic phylogeographic patterns of species could be due instead to species-specific responses to geological and climatic changes. Population genetic patterns were similar among species with similar biological features, indicating that the ecological characteristics of species impact large-scale phylogeography.

Germinación de Phacelia secunda (Boraginaceae) y Eryngium paniculatum (Apiaceae), hierbas perennes de la Patagonia Argentina

El objetivo fue evaluar los requerimientos de germinación de Phacelia secunda J.F. Gmel. y Eryngium paniculatum Cav. y Dombey ex F. Delaroche, herbáceas perennes colonizadoras de ambientes degradados del noroeste patagónico argentino y de interés para la restauración ecológica. Se evaluó el porcentaje, tiempo medio e inicio de germinación en un control (C) y dos tratamientos pre-germinativos: escarificación mecánica con bisturí (EM) y estratificación húmeda fría durante 45 días (EHF). En P. secunda, el porcentaje de germinación en el tratamiento EHF (2%) fue menor que en el C (24%) y el tratamiento EM (16%). En E. paniculatum se encontraron diferencias entre el C (94%) y el tratamiento EHF (82%), pero no entre el C y EM (91%). El tratamiento EHF aceleró el inicio de la geminación en ambas especies. Las semillas de P. secunda mostraron baja capacidad de germinación siendo necesario evaluar nuevos tratamientos. Eryngium paniculatum mostró alta capacidad germinativa aún en el control, lo que evidencia que no requiere tratamientos pregerminativos específicos.

The aim was to evaluate the seed germination requirements of Phacelia secunda J.F. Gmel. and Eryngium paniculatum Cav. y Dombey ex F. Delaroche, perennial herbaceous colonizers of degraded environments of northwest Argentinian Patagonia and of interest for ecological restoration. The germination percentage, mean germination time and time until initiation of germination of a control (C) and two pre-germination treatments: mechanical scarification with a scalpel (EM) and 45 days cold moist stratification (EHF) were evaluated. In P. secunda, the germination percentage in EHF treatment (2%) was lower than in C (24%) and EM (16%) treatment. In E. paniculatum, differences between C (94%) and EHF (82%) were found, but not between C and EM (91%). EHF treatment accelerated the germination initiation in both species. Seeds of P. secunda showed low germination capacity being necessary to evaluate new treatments. Eryngium paniculatum showed high germination capacity in the control. Thus this species does not require specific pre-germination treatments.

Growth evaluation of several types of energy crops from tropical shrubs species.

Background: Few species of tropical shrubs potentially produce biomass to replace fossil fuels for heat production and electricity. The aims of this study were to determine the growth and nutrient status of leaves of several types of energy crops from tropical shrub species with NPK fertilizer application. Methods: Randomized block design was used with ten replications of four levels of fertilizer treatment: T0 = 40 g, T1 = 80 g, T2 = 120 g and T4 = 160 g per plant. Results: The results indicated that fertilization increased plant growth and the quantity of nutrients in leaves. The plants accumulated a lot of potassium, followed by nitrogen and phosphorus. The species of tropical shrubs with the best growth were Vernonia amygdalina, Calliandra calothyrsus and Gliricidia sepium, which are all potentially cultivated as sustainable energy crops. Conclusions: Serious attention must be paid to the availability of soil nutrients in order to sustain the cultivation of these plants.

Factors influencing the natural regeneration of the pioneering shrub Calligonum mongolicum in sand dune stabilization plantations in arid deserts of northwest China.

Calligonum mongolicum is a successful pioneer shrub to combat desertification, which is widely used for vegetation restoration in the desert regions of northwest China. In order to reveal the limitations to natural regeneration of C. mongolicum by asexual and sexual reproduction, following the process of sand dune stabilization, we assessed clonal shoots, seedling emergence, soil seed bank density, and soil physical characteristics in mobile and stabilized sand dunes. Controlled field and pot experiments were also conducted to assess germination and seedling emergence in different dune soil types and seed burial depths. The population density of mature C. mongolicum was significantly different after sand dune stabilization. Juvenile density of C. mongolicm was much lower in stabilized sand dunes than mobile sand dune. There was no significant difference in soil seed bank density at three soil depths between mobile and stabilized sand dunes, while the emergence of seedlings in stabilized dunes was much lower than emergence in mobile dunes. There was no clonal propagation found in stabilized dunes, and very few C. mongolicum seedlings were established on stabilized sand dunes. Soil clay and silt content, air-filled porosity, and soil surface compaction were significantly changed from mobile sand dune to stabilized dunes. Seedling emergence of C. mongolicm was highly dependent on soil physical condition. These results indicated that changes in soil physical condition limited clonal propagation and seedling emergence of C. mongolicum in stabilized sand dunes. Seed bank density was not a limiting factor; however, poor seedling establishment limited C. mongolicum's further natural regeneration in stabilized sand dunes. Therefore, clonal propagation may be the most important mode for population expansion in mobile sand dunes. As a pioneer species C. mongolicum is well adapted to propagate in mobile sand dune conditions, it appears unlikely to survive naturally in stabilized sand dune plantations.

Unravelling the core microbiome of biofilms in cooling tower systems.

In this study, next generation sequencing and catalyzed reporter deposition fluorescence in situ hybridization, combined with confocal microscopy, were used to provide insights into the biodiversity and structure of biofilms collected from four full-scale European cooling systems. Water samples were also analyzed to evaluate the impact of suspended microbes on biofilm formation. A common core microbiome, containing members of the families Sphingomonadaceae, Comamonadaceae and Hyphomicrobiaceae, was found in all four biofilms, despite the water of each coming from different sources (river and groundwater). This suggests that selection of the pioneer community was influenced by abiotic factors (temperature, pH) and tolerances to biocides. Members of the Sphingomonadaceae were assumed to play a key role in initial biofilm formation. Subsequent biofilm development was driven primarily by light availability, since biofilms were dominated by phototrophs in the two studied 'open' systems. Their interactions with other microbial populations then shaped the structure of the mature biofilm communities analyzed.

Soilborne fungi have host affinity and host-specific effects on seed germination and survival in a lowland tropical forest.

The Janzen-Connell (JC) hypothesis provides a conceptual framework for explaining the maintenance of tree diversity in tropical forests. Its central tenet-that recruits experience high mortality near conspecifics and at high densities-assumes a degree of host specialization in interactions between plants and natural enemies. Studies confirming JC effects have focused primarily on spatial distributions of seedlings and saplings, leaving major knowledge gaps regarding the fate of seeds in soil and the specificity of the soilborne fungi that are their most important antagonists. Here we use a common garden experiment in a lowland tropical forest in Panama to show that communities of seed-infecting fungi are structured predominantly by plant species, with only minor influences of factors such as local soil type, forest characteristics, or time in soil (1-12 months). Inoculation experiments confirmed that fungi affected seed viability and germination in a host-specific manner and that effects on seed viability preceded seedling emergence. Seeds are critical components of reproduction for tropical trees, and the factors influencing their persistence, survival, and germination shape the populations of seedlings and saplings on which current perspectives regarding forest dynamics are based. Together these findings bring seed dynamics to light in the context of the JC hypothesis, implicating them directly in the processes that have emerged as critical for diversity maintenance in species-rich tropical forests.

Early-successional ectomycorrhizal fungi effectively support extracellular enzyme activities and seedling nitrogen accumulation in mature forests.

After stand-replacing disturbance, regenerating conifer seedlings become colonized by different ectomycorrhizal fungi (EMF) than the locally adapted EMF communities present on seedlings in mature forests. We studied whether EMF species that colonized subalpine fir (Abies lasiocarpa) seedlings in clearcuts differed from those that colonized seedlings in adjacent mature forests with respect to mycorrhizoplane extracellular enzyme activities (EEAs) and N status of the seedlings. We tested two alternate hypotheses: (1) that EEAs would differ between the two EMF communities, with higher activities associated with forest-origin communities, and (2) that acclimation to soil environment was considerable enough that EEAs would be determined primarily by the soil type in which the ectomycorrhizas were growing. Naturally colonized fir seedlings were reciprocally transplanted between clearcuts and forests, carrying different EMF communities with them. EEAs were influenced more by destination environment than by EMF community. EEAs were as high in early-successional as in late-successional communities in both destination environments. Buds of clearcut-origin seedlings had the same or higher N contents as forest seedlings after a growing season in either environment. These results indicate that (i) symbiotic EMF and/or their associated microbial communities demonstrate substantial ability to acclimate to new field environments; (ii) the ability to produce organic matter-degrading enzymes is not a trait that necessarily distinguishes early- and late-successional EMF communities in symbiosis; (iii) early-successional EMF are as capable of supporting seedling N accumulation in forest soils as late-successional EMF; and (iv) disturbed ecosystems where early-successional EMF are present should have high resilience for organic matter degradation.

Germinación y latencia de semillas de Miconia chartacea (Melastomataceae), en respuesta a luz, temperatura y hormonas vegetales

Miconia chartacea es un árbol con amplia distribución altitudinal y latitudinal en Brasil, que se encuentra desde formaciones vegetales estacionales xerofíticas como Caatinga y Cerrado hasta bosques pluviales como Mata Atlántica, en pastizales con árboles aislados hasta interior de bosques maduros. Fue descrita la respuesta germinativa de las semillas de M. chartacea a la luz, temperatura, hormonas vegetales y posmaduración a baja temperatura. Los frutos se recolectaron en la reserva de Cerrado "Prof. Karl Arens", en el municipio Corumbataí (San Paulo, Brasil), la cual presenta una estación seca y fría desde abril hasta septiembre y una estación húmeda y caliente de octubre a marzo. Las semillas se dispersaron durante la estación seca, son fotoblásticas positivas bajo temperaturas constantes y variables, la germinación disminuye bajo irradiaciones de luz blanca inferiores a 17 umol/m2s, la razón rojo/rojo lejano (R/RL) no afectó el porcentaje de germinación, pero la velocidad de germinación aumentó a partir de razones R/ RL > 0.4. Las semillas germinaron en el intervalo térmico de 15 a 35 °C, la temperatura optima esta entre 20 y 25 °C, la alternancia de temperatura no estimuló la germinación respecto a las temperaturas constantes. Las semillas presentaron latencia fisiológica no profunda, la cual fue rota mediante posmaduración durante 93 días a 7 °C y el etileno estimuló la germinación. La gama de temperaturas en la cual germinan las semillas fue menor en las semillas maduradas bajo las condiciones más calientes de la transición de la estación lluviosa a seca que las semillas maduradas en la estación seca. El requerimiento de un periodo frío para romper latencia disminuye la probabilidad de que las semillas germinen durante el invierno, quedando listas para germinar en el verano. Así, la detección de cambios estacionales de temperatura del suelo y el aumento de sensibilidad a la temperatura después de un periodo de frío son responsables por el control temporal de la germinación de M. chartacea, mientras que la respuestas a luz permite que solo germinen las semillas que están en la superficie del suelo, y favorece la germinación en claros de bosque pequeños a grandes.

Miconia chartacea is a widely distributed tree along both altitudinal and latitudinal gradients in Brazil, and it can be found in seasonal xerophytic vegetation, e.g. Caatinga and Cerrado, and tropical rainforest (e.g. Mata Atlantica), from grassland with scattered trees to mature forest. We studied the germination response of M. chartacea seeds to light, temperature, plant hormones and after-ripening at low temperature. Seeds were collected from a Cerrado reserve located in Corumbataí, Sao Paulo State, which characterizes to have a cool dry season from April to September, and a warm wet season from October to March. M. chartacea seeds are dispersed in the dry season and exhibited a photoblastic behavior both at constant and alternating temperatures. The germination was decreased at irradiances below 17 umol / m2s, whereas R: FR ratios below 0.4 reduced the germination rate, but not the germination capacity. The germination-permissive temperatures range from 15 to 35 °C, with an optimum interval from 20 to 25 °C. Germination is not improved by alternating temperature regimes as compared to isothermal treatments. The seeds have a non-deep physiological dormancy, which can be partially overcame either by dry after-ripening at 7 °C for 93 days, or by the 2-chloroethylphosphonic acid treatment. The thermal window within which the seeds germinate was narrower for seeds matured in the rainy to dry season transition period, under warmer conditions, than in the dry season. Cold requirement for dormancy break in seeds of M. chartacea can prevent the germination in the winter, allowing the seeds to germinate in the summer under more favorable conditions. The results suggest that seed response to temperature accounts for temporal distribution of germination, of M. chartacea, while light predominantly influences the spatial distribution of seedlings, precluding the germination of buried seeds and affecting the germination response to gap size.

Sucesión de micooalgas perifíticas en tributaris del río gaira, sierra nevada de santa marta, Colomiia / Succession of Microalgae Periphytic in Tributaries the Gaira River, Sierra Nevada de Santa Marta, Colombia

Las microalgas poseen atributos para la bioindicación, el estudio de algas perifíticas en ecosistemas fluviales tropicales, es de vital importancia ya que permite interpretar la dinámica de estos ecosistemas con importancia ecológica y con vocación para ofrecer servicios de abastecimiento. Para este estudio se seleccionaron tributarios de la cuenca media del río Gaira (SNSM), se evaluó el proceso sucesional de microalgas perifíticas, siguiendo el avance de la comunidad desde enero hasta abril de 2012, mediante la metodología de sustratos artificiales. El propósito fue analizar la variación en la estructura de la comunidad, durante el proceso de sucesión y evaluar los factores ambientales que determinan esta variación en un rio tropical. Los resultados destacan caudal, luz y oxígeno disuelto los cuales presentaron los valores más altos para el tributario C (Jabalí); el pH fue ligeramente básico para todos los sitios, la temperatura y conductividad presentaron valores más altos en el tributario A (Honduras). Durante las primeras semanas de exposición del sustrato Melosira varians y Lyngbya sp. fueron dominantes para los tributarios A y B (La Picúa), mientras que para el tributario C lo fueron Fragilaria sp., Nitzschia sp. y Melosira varians. Después de la cuarta semana de colecta se registraron los mayores valores de diversidad y riqueza de especies. Fueron más notorios los cambios en densidad que en composición de especies, a pesar de esto el proceso de sucesión fue completo y se evidenció la presencia de especies pioneras (Lyngbya sp., Nitzschia sp.), intermedias (Melosira varians, Cocconeis placentula) y tardías (Surirella sp.).

Microalgae have attributes for bioindication, the study of periphytic algae in tropical river ecosystems, is vital as it allows interpreting the dynamics of these ecosystems and ecological importance vocation to offer catering services. For this study were selected tributaries of the middle basin of Gaira (SNSM) River, the successional process periphytic microalgae was evaluated following the progress of the community from January to April 2012, using the methodology of artificial substrates. The purpose was to analyze the variation in community structure during the succession process and assess environmental factors that determine this variation in a tropical river. The results highlight flow, light and dissolved oxygen which presented the highest for tax C (Jabalí) values; the pH was slightly basic for all sites, temperature and conductivity showed the highest values in the tax A (Honduras). During the first weeks of exposure of the substrate Melosira varians and Lyngbya sp. were dominant for tributary A and B (La Picúa), while for the tributary C they were Fragilaria sp, Nitzschia sp and Melosira varians. After the fourth week of collecting the highest values of diversity and species richness recorded. Were greatest density changes in species composition, despite this the succession process was complete and the presence of pioneer species (Lyngbya sp, Nitzschia sp), intermediate (Melosira varians, Cocconeis placentula) and late (Surirella sp).