How do fertilized and unfertilized Fabaceae trees respond to seasonal variation in Amazonian reforestation?

Plants adjust traits such as stomatal conductance ( g s ) and leaf area (LA) to cope with resource fluctuations, and while species differ in their responses to water scarcity, fertilization can enhance resilience. This study assessed how seasonal variation, fertilization, and their interaction influence functional adjustments in tree legumes: three non-N-fixers ( Cenostigma tocantinum , Senna reticulata and Dipteryx odorata ), one N fixer ( Clitoria fairchildiana ), and two facultative N fixers ( Inga edulis and Acacia mangium ). The experiment included six species with nine replicates per treatment, monitored over a 25-month period. Gas exchange, nutrient and carbohydrate concentrations, and leaf area were measured on fertilized and unfertilized plants under both drought and wet conditions, enabling analysis of both physiological and biochemical responses across different environmental and nutritional scenarios. All species reduced their g s , photosynthetic performance, and transpiration rates during drought, and fertilization imposed little effect on these seasonal changes. However, fertilization increased LA in D. odorata and C. fairchildiana , but not in A. mangium . Seasonal changes and fertilization also influenced macro (P, K, Ca) and micronutrients (Fe, Zn), with responses differing significantly among species. Most species, particularly those that were fertilized, exhibited lower concentration of carbohydrates (starch and soluble sugars) during drought but restored these reserves upon recovery. These functional acclimations allow species to adjust more effectively and optimize resource use in degraded Amazonian environments. These results suggest that selecting tree legumes with greater functional plasticity may enhance reforestation success and ecosystem resilience in degraded Amazonian landscapes, subsidizing restoration strategies and policy decisions for tropical forest management.