Ecophysiology of fabaceae tree species during forest restoration in the balbina hydroeletric dam in Amazonas state

Abstract

Plants can adjust functional traits according to the variations in the availability of resources. Under low soil water and nutrient availability, as found in degraded areas, the growth of tree species can be drastically reduced. Tree legumes evolved different strategies to efficiently uptake and use nutrients, securing high survival and growth rates, thus facilitating the restoration of important biogeochemical cycles during forest restoration. Early successional species may increase fast (aquisitive) traits under high resources, while slow (conservative) traits can be enhanced under limited resources and for late successional species. Variations in functional traits such as growth, gas exchange, water potential, nutrients, non-structural carbohydrates (soluble sugars and starch) (NSC), photosynthetic pigments and chlorophyll fluorescence of six tree legumes species were studied according with low vs. high water and nutrient availabilities during a forest restoration plantation in Hydroelectric dam Balbina. The species selected were five native species from Amazonia Cenostigma tocantinum, Senna reticulata, Dipteryx odorata, Clitoria fairchildiana and Inga edulis, and one alien species from Australia Acacia sp.. The individuals were either fertilized or remain unfertilized throughout the 24 month experiment. Three main hypotheses were tested: a) economics spectrum; b) functional equilibrium; and c) NSC dynamics and source-sink allocations. Economics spectrum was mostly confirmed under high water and nutrient availabilities increasing transpiration (E), photosynthesis (P n ), relative growth rates in diameter and performance index of chlorophyll fluorescence (PI ABS ). Traits from the slow spectrum such as dissipation energy flux (DI 0 /RC), intrinsic water use efficiency (IWUE) and root mass fraction (RMF) were enhanced under limited conditions. Functional equilibrium hypothesis was also confirmed as unfertilized plants increased twice the RMF as compared with high nutrient plants. Further RMF was positively correlated with starch and soluble sugars in root tissues indicating an active process of increased root fraction involving energy costs. Acacia sp. which respond differently than economics spectrum had significant growth under severe nutrient limitations, increasing nutrient and energy use efficiency, and the pool of NSC in leaf biomass. S. reticulata also diverge from economics assumptions being unable to adjust traits such as gas exchange and showing responses to drought stress which were related with increased leaf calcium and starch content. The fast acquisition of resources according (increased E and P n ) was considered the main strategy of species in a degraded and fertilized environment, as adjustments in energy use efficiency and NSC pools were essential for plants acclimation. Tree legumes especially N 2 -fixing species are proven to be well succeeded in forest restoration plantations producing eight times more biomass than non N 2 -fixing. Photosynthesis was the most responsive variable to evaluate species responses to resource variations in our study, nonetheless chlorophyll fluorescence appears to be an alternative efficient technique to evaluate the performance and responses to abiotic stress factors. This study makes a significant contribution to the understanting of the ecophysiology of tropica tree legumes and also to provide data to enhance Dynamic Global Vegetation Models. Additionally, from the conceptual view this thesis provide data to enhance climate change predictions models on the interface of soil-plant-atmosphere (during 2015/16 El Niño event) in Amazon forest. In conclusion, the mixing of different successional cological groups and including biological N 2 fixation process appears to be an efficient way to achieve ecological forest restoration goals in nutrient limited soils such as in Amazon basin.