We tested whether and how functional composition changes with succession in dry deciduous and wet evergreen forests of Mexico. We hypothesized that compositional changes during succession in dry ...forest were mainly determined by increasing water availability leading to community functional changes from conservative to acquisitive strategies, and in wet forest by decreasing light availability leading to changes from acquisitive to conservative strategies. Research was carried out in 15 dry secondary forest plots (5-63 years after abandonment) and 17 wet secondary forest plots (<1-25 years after abandonment). Community-level functional traits were represented by community-weighted means based on 11 functional traits measured on 132 species. Successional changes in functional composition are more marked in dry forest than in wet forest and largely characterized by different traits. During dry forest succession, conservative traits related to drought tolerance and drought avoidance decreased, as predicted. Unexpectedly acquisitive leaf traits also decreased, whereas seed size and dependence on biotic dispersal increased. In wet forest succession, functional composition changed from acquisitive to conservative leaf traits, suggesting light availability as the main driver of changes. Distinct suites of traits shape functional composition changes in dry and wet forest succession, responding to different environmental filters.
Mechanistic models of community assembly state that biotic and abiotic filters constrain species establishment through selection on their functional traits. Predicting this assembly process is ...hampered because few studies directly incorporate environmental measurements and scale up from species to community level and because the functional traits' significance is environment dependent. We analyzed community assembly by measuring structure, environmental conditions, and species traits of secondary forests in a species-rich tropical system. We found, as hypothesized, that community structure shaped the local environment and that strong relationships existed between this environment and the traits of the most successful species of the regeneration communities. Path and multivariate analyses showed that temperature and leaf traits that regulate it were the most important factors of community differentiation. Comparisons between the trait composition of the forest's regeneration, juvenile, and adult communities showed a consistent community assembly pattern. These results allowed us to identify the major functional traits and environmental factors involved in the assembly of dry-forest communities and demonstrate that environmental filtering is a predictable and fundamental process of community assembly, even in a complex system such as a tropical forest.
Aim: Tropical forests account for a quarter of the global carbon storage and a third of the terrestrial productivity. Few studies have teased apart the relative importance of environmental factors ...and forest attributes for ecosystem functioning, especially for the tropics. This study aims to relate aboveground biomass (AGB) and biomass dynamics (i.e., net biomass productivity and its underlying demographic drivers: biomass recruitment, growth and mortality) to forest attributes (tree diversity, community-mean traits and stand basal area) and environmental conditions (water availability, soil fertility and disturbance). Location: Neotropics. Methods: We used data from 26 sites, 201 1-ha plots and >92,000 trees distributed across the Neotropics. We quantified for each site water availability and soil total exchangeable bases and for each plot three key community-weighted mean functional traits that are important for biomass stocks and productivity. We used structural equation models to test the hypothesis that all drivers have independent, positive effects on biomass stocks and dynamics. Results: Of the relationships analysed, vegetation attributes were more frequently associated significantly with biomass stocks and dynamics than environmental conditions (in 67 vs. 33% of the relationships). High climatic water availability increased biomass growth and stocks, light disturbance increased biomass growth, and soil bases had no effect. Rarefied tree species richness had consistent positive relationships with biomass stocks and dynamics, probably because of niche complementarity, but was not related to net biomass productivity. Community-mean traits were good predictors of biomass stocks and dynamics. Main conclusions: Water availability has a strong positive effect on biomass stocks and growth, and a future predicted increase in (atmospheric) drought might, therefore, potentially reduce carbon storage. Forest attributes, including species diversity and community-weighted mean traits, have independent and important relationships with AGB stocks, dynamics and ecosystem functioning, not only in relatively simple temperate systems, but also in structurally complex hyper-diverse tropical forests.
Vegetation and environment change mutually during secondary succession, yet the idiosyncrasies of the vegetation effect on the understorey environment are poorly understood. To test whether the ...successional understorey environment changes predictably and is shaped by the structure and seasonality of tropical dry forests, we estimated basal area and vegetation cover, and measured understorey temperature, light and moisture conditions, in 17 plots forming a 60-y chronosequence and a mature forest. Light and air and soil temperature decreased with time (75−15% of open-sky radiation, 31.7−29.3 °C, and +2.5 °C to −0.5 °C relative to ambient, respectively), whereas relative humidity increased (67−74%). Soil water availability increased with early-successional development (−45 to −1 kPa) but decreased afterwards (to −18 kPa). The first axis of a PCA of the rainy-season environment explained 60% of the variation and was strongly related to air temperature and relative humidity. During tropical dry-forest succession, such factors may be more important than light, the reduction in which is not extreme compared with taller and more vertically stratified wet forests. Seasonality significantly affected the successional environmental gradients, which were marked mainly during the wet season. Environmental heterogeneity was higher in the wet than in the dry season, and larger for resources (light and water) than for conditions (temperature and humidity). The wet-season increase in environmental heterogeneity potentially creates differential growing scenarios; the environmental harshness of the dry season would mostly challenge seedling survival.
We analyzed successional patterns in a very dry tropical deciduous forest by using 15 plots differing in age after abandonment and contrasted them to secondary successions elsewhere in the tropics. ...We used multivariate ordination and nonlinear models to examine changes in composition and structure and to estimate forest recovery rates and resilience. A shrub phase characterized early succession (0-3 yr); afterwards, the tree Mimosa acantholoba became dominant. Below its canopy, sprouts and seed-regenerated individuals of mature forest species slowly accumulated. Canopy height, plant density, and crown cover stabilized in less than 15 yr, whereas species richness, diversity, and basal area continued to increase. The pioneer species group has very low diversity and the long-lived pioneer phase typical of humid forests is absent; species composition may therefore recover soon as suggested by convergence toward mature forest species composition. The time trend of plant density also differed from humid forests for it lacked its characteristic density decline, presumably because of differences in regeneration mechanisms between very dry and other less water-stressed forest types. As opposed to the prevailing hypothesis, resilience was not higher than in moister forests, and thus factors other than structure relative simplicity must be accounted for when assessing resilience.
Biodiversity conservation and ecosystem-service provision will increasingly depend on the existence of secondary vegetation. Our success in achieving these goals will be determined by our ability to ...accurately estimate the structure and diversity of such communities at broad geographic scales. We examined whether the texture (the spatial variation of the image elements) of very high-resolution satellite imagery can be used for this purpose. In 14 fallows of different ages and one mature forest stand in a seasonally dry tropical forest landscape, we estimated basal area, canopy cover, stem density, species richness, Shannon index, Simpson index, and canopy height. The first six attributes were also estimated for a subset comprising the tallest plants. We calculated 40 texture variables based on the red and the near infrared bands, and EVI and NDVI, and selected the best-fit linear models describing each vegetation attribute based on them. Basal area (R(2) = 0.93), vegetation height and cover (0.89), species richness (0.87), and stand age (0.85) were the best-described attributes by two-variable models. Cross validation showed that these models had a high predictive power, and most estimated vegetation attributes were highly accurate. The success of this simple method (a single image was used and the models were linear and included very few variables) rests on the principle that image texture reflects the internal heterogeneity of successional vegetation at the proper scale. The vegetation attributes best predicted by texture are relevant in the face of two of the gravest threats to biosphere integrity: climate change and biodiversity loss. By providing reliable basal area and fallow-age estimates, image-texture analysis allows for the assessment of carbon sequestration and diversity loss rates. New and exciting research avenues open by simplifying the analysis of the extent and complexity of successional vegetation through the spatial variation of its spectral information.
The magnitude of the carbon sink in second-growth forests is expected to vary with successional biomass dynamics resulting from tree growth, recruitment, and mortality, and with the effects of ...climate on these dynamics. We compare aboveground biomass dynamics of dry and wet Neotropical forests, based on monitoring data gathered over 3–16 years in forests covering the first 25 years of succession. We estimated standing biomass, annual biomass change, and contributions of tree growth, recruitment, and mortality. We also evaluated tree species’ contributions to biomass dynamics. Absolute rates of biomass change were lower in dry forests, 2.3 and 1.9 Mg ha⁻¹ y⁻¹, after 5–15 and 15–25 years after abandonment, respectively, than in wet forests, with 4.7 and 6.1 Mg ha⁻¹ y⁻¹, in the same age classes. Biomass change was largely driven by tree growth, accounting for at least 48% of biomass change across forest types and age classes. Mortality also contributed strongly to biomass change in wet forests of 5–15 years, whereas its contribution became important later in succession in dry forests. Biomass dynamics tended to be dominated by fewer species in early-successional dry than wet forests, but dominance was strong in both forest types. Overall, our results indicate that biomass dynamics during succession are faster in Neotropical wet than dry forests, with high tree mortality earlier in succession in the wet forests. Long-term monitoring of second-growth tropical forest plots is crucial for improving estimates of annual biomass change, and for enhancing understanding of the underlying mechanisms and demographic drivers.
Porcine liver has a high nutritional value and is rich in proteins, minerals, and vitamins, making it an interesting co-product to alleviate the growing global demand for protein. The objective of ...this study was to analyze how the drying and defatting processes of porcine liver affect the physicochemical and techno-functional properties of its proteins. Two drying temperatures (40 and 70 °C) were studied, and dried samples were defatted using organic solvents. The drying process turned out to be an effective method for the stabilization of the protein fraction; however, when the drying temperature was high (70 °C), greater protein degradation was found compared to drying at a moderate temperature (40 °C). Regarding the defatting stage, it contributed to an improvement in certain techno-functional properties of the liver proteins, such as the foaming capacity (the average of the dried and defatted samples was 397% higher than the dried samples), with the degree of foaming stability in the liver dried at 40 °C and defatted being the highest (13.76 min). Moreover, the emulsifying capacity of the different treatments was not found to vary significantly (p > 0.05). Therefore, the conditions of the drying and defatting processes conducted prior to the extraction of liver proteins must be properly adjusted to maximize the stability, quality, and techno-functional properties of the proteins.
QUESTION: Niche differentiation may promote species co‐existence because it precludes competitive exclusion. However, in stressful environments, facilitation may predominate, and large niche overlaps ...may result from niche widening and positive spatial associations. We analysed the niche structure of a species‐rich system over a soil depth gradient (a niche axis positively correlated with water availability) and tested for various patterns expected from competition or facilitation. LOCATION: Semi‐arid grassland, Oaxaca, Mexico. METHODS: We recorded species abundance and soil depth in 1200 0.1 × 0.1 m quadrats from four sites. Community structure was described through correspondence analysis and correlated with soil depth. We measured niche breadth (Levine's index), position (mean depth) and overlap (Hurlbert's index). We used a null model to estimate the expected overlap if interactions play no role in determining community structure. We tested whether overlap changed along the depth gradient. We also analysed if niches become narrow with higher competition. RESULTS: Data supported three predictions derived from competition: most species’ niches were relatively narrow and differed in their position along the gradient, a pattern reflected in a changing community structure; realized niches became narrower where competition was stronger; and niche overlap was smaller than expected by chance. Facilitation had no support: large niche overlaps expected from stress amelioration were as frequent as predicted by chance. Overlap increased in the most stressful (shallow) soils, as expected if facilitation predominates there, but also in the deepest ones where evidence for competition was strong, suggesting an artifact at the extremes of the gradient. CONCLUSIONS: In this grassland, competition seems to restrict species distribution, abating richness in the deepest soils and relegating poor competitors (succulent and poikilohydric species) to the shallow soils. There, drought tolerance rather than facilitation determined community composition and richness. Our results support the idea that hydrological niches play an important role in maintaining plant diversity because (1) differentiation in hydrological requirements (small niche overlaps over the water‐use axis) reduces competition, and (2) spatial heterogeneity and stress create competition‐free patches. Our results also support the hypothesis that facilitation is rare when stress is caused by resource (in this case, water) scarcity.
Regulatory T cells (Tregs) are considered key players in the prevention of allograft rejection in transplanted patients. Belatacept (BLT) is an effective alternative to calcineurin inhibitors that ...appears to preserve graft survival and function; however, the impact of this drug in the homeostasis of Tregs in transplanted patients remains controversial. Here, we analyzed the phenotype, function, and the epigenetic status of the Treg-specific demethylated region (TSDR) in FOXP3 of circulating Tregs from long-term kidney transplant patients under BLT or Cyclosporine A treatment. We found a significant reduction in the proportion of CD4
CD25
CD127
FOXP3
T cells in all patients compared to healthy individual (controls). Interestingly, only BLT-treated patients displayed an enrichment of the CD45RA
"naïve" Tregs, while the expression of Helios, a marker used to identify stable FOXP3
thymic Tregs remained unaffected. Functional analysis demonstrated that Tregs from transplanted patients displayed a significant reduction in their suppressive capacity compared to Tregs from controls, which is associated with decreased levels of FOXP3 and CD25. Analysis of the methylation status of the FOXP3 gene showed that BLT treatment results in methylation of CpG islands within the TSDR, which could be associated with the impaired Treg suppression function. Our data indicate that analysis of circulating Tregs cannot be used as a marker for assessing tolerance toward the allograft in long-term kidney transplant patients. Trial registration number IM103008.
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