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Item type:Publication, Variation of non-structural carbohydrates across the fast-slow continuum in Amazon forest canopy trees(Wiley, 2021-11-20)Tropical tree species span a range of life‐history strategies within a fast–slow continuum. The position of a species within this continuum is thought to reflect a negative relationship between growth and storage, with fast‐growing species allocating more carbon to growth and slow‐growing species investing more in storage. For tropical species, the relationship between storage and life‐history strategies has been largely studied on seedlings and less so in adult trees. We evaluated how stored non‐structural carbohydrates (NSC) vary across adult trees spanning the fast–slow continuum in the Peruvian Amazon by: (a) analysing whole‐tree NSC in two species of contrasting growth and (b) investigating the relationships with key life‐history traits across a broader set of species. Our results are consistent with a growth–storage trade‐off. The analysis of whole‐tree NSC revealed that the slow‐growing Eschweilera coriacea stored about 2.7 times as much NSC as the fast‐growing Bixa arborea due to markedly higher storage in woody stems and roots. B. arborea also had higher seasonality in NSC, reflecting its strong seasonality in stem growth. Across a range of species, stem starch was negatively related to species growth rate and positively related to wood density. Given the role of NSC in mediating plants' response to stress, our results suggest that slow‐growing species with greater storage reserves may be more resilient to drought than fast‐growing species. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Non-structural carbohydrates mediate seasonal water stress across Amazon forests(Nature Research, 2021-12-01)Non-structural carbohydrates (NSC) are major substrates for plant metabolism and have been implicated in mediating drought-induced tree mortality. Despite their significance, NSC dynamics in tropical forests remain little studied. We present leaf and branch NSC data for 82 Amazon canopy tree species in six sites spanning a broad precipitation gradient. During the wet season, total NSC (NSCT) concentrations in both organs were remarkably similar across communities. However, NSCT and its soluble sugar (SS) and starch components varied much more across sites during the dry season. Notably, the proportion of leaf NSCT in the form of SS (SS:NSCT) increased greatly in the dry season in almost all species in the driest sites, implying an important role of SS in mediating water stress in these sites. This adjustment of leaf NSC balance was not observed in tree species less-adapted to water deficit, even under exceptionally dry conditions. Thus, leaf carbon metabolism may help to explain floristic sorting across water availability gradients in Amazonia and enable better prediction of forest responses to future climate change. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Amazonian and Andean tree communities are not tracking current climate warming(EarthArXiv, 2024-12-18)Climate change is shifting species distributions, leading to changes in community composition and novel species assemblages worldwide. However, the responses of tropical forests to climate change across large-scale environmental gradients remain largely unexplored. Using long-term data over 66,000 trees of more than 2,500 species occurring over 3,500 m elevation along the hyperdiverse Amazon-to-Andes elevational gradient, we assessed community-level shifts in species composition through a 44-year time span. We tested for the predicted increase in relative abundances of species from warmer climates (thermophilization) along the Amazon-to-Andes elevational gradients in Peru and Bolivia. Additionally, we examined the relative contributions of tree mortality, recruitment, and growth to observed compositional changes. Mean thermophilization rates across the Amazon-to-Andes gradient were slow relative to concordant changes in regional temperatures. Thermophilization rates were positive and more variable among Andean forest plots compared to Amazonian plots but were fastest at mid-elevations around the cloud base. Across all elevations, thermophilization rates were driven primarily by tree mortality and decreased growth of highland species rather than an influx of lowland species with higher thermal optima. Given the high variability of community-level responses to warming along the elevational gradients and the generally slower-than-warming rates of compositional change, we conclude that most tropical tree species, and especially Amazonian tree species, will not be able to escape current or future climate change through upward range shifts.1 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Wood density variation across an Andes-to-Amazon elevational gradient(2024-12-18)1. Understanding how functional traits are related to species diversity and ecosystem properties is a central goal of ecology. Wood density is a trait that integrates many aspects of plant form and function and is highly variable among species. Previous studies of wood density across elevational gradients have been based on limited sampling and have reported declines with increasing elevation, though even this simple pattern remains unknown, much less its underlying functional and evolutionary relationships. 2. Here, we use one of the longest and most speciose elevational gradients in the world, extending from the Andean tree line to the Amazon basin, to test the extent to which elevation, species composition, phylogenetic affinity, and forest structure determine variation in wood density. Using field-collected wood samples and global databases, we assigned wood density to 1231 species and 31,330 stems across 41 (47.5 ha) mature forest plots arrayed across a 3,500 m vertical gradient. 3. Our results show that mean wood density, either weighted by abundance, basal area, or species, was highly variable but tended to decline from low to middle elevations and increase again from mid-elevations to the tree line. As a result of this non-linearity, forests at the Andean tree line had higher wood density than their lowland Amazon counterparts. We observed an abrupt transition in wood density at the lower limit of persistent cloud formation (cloud base), where the lowest wood density values were found. The decline of wood density is attributed to a significant shift in life forms, with an abundance of tree ferns at middle elevations and a higher probability of landslides and disturbances favoring a suite of traits associated with low wood density, such as softer wood and higher elasticity. Species turnover explained most of the among-species variation across the gradient, with elevation having no consistent effect on within-species variation in wood density. 4. Together, both gradual compositional changes and sharp local changes in the importance of non-dicot life forms, such as arborescent ferns and palms, define patterns of forest-level carbon density, with wood density per se controlling ecosystem properties across the Andes-to-Amazon elevational gradient. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Tropical Forest Lianas Have Greater Non-Structural Carbohydrate Concentrations in the Stem Xylem Than Trees(Oxford University Press, 2023-08-16)Lianas (woody vines) are important components of tropical forests and are known to compete with host trees for resources, decrease tree growth and increase tree mortality. Given the observed increases in liana abundance in some forests and their impacts on forest function, an integrated understanding of carbon dynamics of lianas and liana-infested trees is critical for improved prediction of tropical forest responses to climate change. Non-structural carbohydrates (NSC) are the main substrate for plant metabolism (e.g. growth, respiration), and have been implicated in enabling tree survival under environmental stress, but little is known of how they vary among life-forms or of how liana infestation impacts host tree NSC. We quantified stem xylem total NSC concentrations and its fractions (starch and soluble sugars) in trees without liana infestation, trees with ˃50% of the canopy covered by lianas, and the lianas infesting those trees. We hypothesized that (i) liana infestation depletes NSC storage in host trees by reducing carbon assimilation due to competition for resources; (ii) trees and lianas, which greatly differ in functional traits related to water transport and carbon uptake, would also have large differences in NSC storage. As water availability has a significant role in NSC dynamics of Amazonian tree species, we tested these hypotheses within a moist site in western Amazonia and a drier site in southern Amazonia. We did not find any difference in NSC, starch or soluble sugar concentrations between infested and non-infested trees, in either site. This result suggests that negative liana impact on trees may be mediated through mechanisms other than depletion of host tree NSC concentrations. We found lianas have higher stem NSC and starch than trees in both sites. The consistent differences in starch concentrations, a long-term NSC reserve, between life forms across sites reflect differences in lianas and trees carbon gain and use. Soluble sugar concentrations were higher in lianas than in trees in the moist site but indistinguishable between life forms in the dry site. The lack of difference in soluble sugars between trees and lianas in the dry site emphasizes the importance of this NSC fraction for the metabolism of plants occurring in water limited environments. Abstracts in Portuguese and Spanish are available in the supplementary material. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Basin-Wide Variation in Tree Hydraulic Safety Margins Predicts the Carbon Balance of Amazon Forests(Nature Research, 2023-05-04)Tropical forests face increasing climate risk1,2, yet our ability to predict their response to climate change is limited by poor understanding of their resistance to water stress. Although xylem embolism resistance thresholds (for example, Ψ50) and hydraulic safety margins (for example, HSM50) are important predictors of drought-induced mortality risk3–5, little is known about how these vary across Earth’s largest tropical forest. Here, we present a pan-Amazon, fully standardized hydraulic traits dataset and use it to assess regional variation in drought sensitivity and hydraulic trait ability to predict species distributions and long-term forest biomass accumulation. Parameters Ψ50 and HSM50 vary markedly across the Amazon and are related to average long-term rainfall characteristics. Both Ψ50 and HSM50 influence the biogeographical distribution of Amazon tree species. However, HSM50 was the only significant predictor of observed decadal-scale changes in forest biomass. Old-growth forests with wide HSM50 are gaining more biomass than are low HSM50 forests. We propose that this may be associated with a growth–mortality trade-off whereby trees in forests consisting of fast-growing species take greater hydraulic risks and face greater mortality risk. Moreover, in regions of more pronounced climatic change, we find evidence that forests are losing biomass, suggesting that species in these regions may be operating beyond their hydraulic limits. Continued climate change is likely to further reduce HSM50 in the Amazon6,7, with strong implications for the Amazon carbon sink.