Project description:Environmental variation along the geographical space can shape populations by natural selection. In the context of global warming and changing precipitation regimes, it is crucial to understand the role of environmental heterogeneity in tropical trees adaptation, given their disproportional contribution to water and carbon biogeochemical cycles. Here, we investigated how heterogeneity in freshwater availability along tropical wetlands has influenced molecular variations of the black mangrove (Avicennia germinans). A total of 57 trees were sampled at seven sites differing markedly in precipitation regime and riverine freshwater inputs. Using 2,297 genome‐wide single nucleotide polymorphic markers, we found signatures of natural selection by the association between variations in allele frequencies and environmental variables, including the precipitation of the warmest quarter and the annual precipitation. Additionally, we found candidate loci for selection based on statistical deviations from neutral expectations of interpopulation differentiation. Most candidate loci within transcribed sequences were functionally associated with central aspects of drought tolerance or plant response to drought. Moreover, our results suggest the occurrence of the rapid evolution of a population, probably in response to sudden and persistent limitations in plant access to soil water, following a road construction in 1974. Observations supporting rapid evolution included the reduction in tree size and changes in allele frequencies and in transcript expression associated with increased drought tolerance through the accumulation of osmoprotectants and antioxidants, biosynthesis of cuticles, protection against protein degradation, stomatal closure, photorespiration and photosynthesis. We describe a major role of spatial heterogeneity in freshwater availability in the specialization of this typically tropical tree.
Project description:Long-term drought increases soil dark-septate fungi and fungal community turnover, and alters biogeochemical processes in Amazon rain forest
Project description:The photorespiratory pathway, short photorespiration, is an essential process in oxygenic photosynthetic organisms but also reduces the efficiency of photosynthetic carbon assimilation and is hence frequently considered as a wasteful process. By comparing the response of wild-type plants and mutants impaired in photorespiration to a shift in ambient CO2 concentrations, we demonstrate that photorespiration also plays a beneficial role during short-term acclimation to reduced CO2 availability. Wild-type plants responded with few differentially expressed genes, mostly involved in drought stress, which is likely a consequence of enhanced opening of stomata and concomitant water loss upon shift toward low CO2. In contrast, mutants with impaired activity of photorespiratory enzymes were highly stressed and not able to adjust stomatal conductance to reduced external CO2 availability. The mutants´ transcriptional response was congruent, indicating a general reprogramming to deal with the consequences of reduced CO2 availability, signaled by enhanced oxygenation of ribulose-1,5 bisphosphate and amplified by the artificially impaired photorespiratory metabolism. Central in this reprogramming was the pronounced reallocation of resources from growth processes to stress responses. In conclusion, we demonstrate that unrestricted photorespiratory metabolism is a prerequisite for rapid physiological acclimation to a reduction in CO2 availability.
