Coordinated adjustments of carbohydrates and growth of tree legumes under different fertilization regimes in degraded areas in Amazonia

Abstract

Soil fertility management and N-fixing species can support the ecosystem-level restoration of disrupted biogeochemical cycles in tropical degraded environments. However, the effectiveness of N-fixers during tropical forest restoration remains unclear. We hypothesized that tree legumes adjust growth, nonstructural carbohydrate allocation and foliar nutrients under different fertilization regimes. We compared the following six tree legume species: three native nonfixers (Cenostigma, Senna and Dipteryx), two native N-fixers (Clitoria and Inga) and an introduced N-fixer (Acacia). Twenty-four months after the experiment was established, fertilized plants increased growth rates and starch allocation to leaves, whereas unfertilized plants primarily increased their biomass and starch allocation to roots. The greater tolerance to nutrient deficiency of the Acacia than other native tree legumes was due to Acacia’s ability to adjust carbohydrate pools. N-fixers adjusted the shoot-to-root ratio and soluble sugar allocation to leaves, increasing biomass growth. The three N-fixing species were especially suitable for restoration because Acacia had tolerance of nutrient deficiencies, Clitoria and Inga had fast growth and biomass production. Hence, fertilization management and N-fixing species may have a considerable impact on C stocks in different plant compartments. Overall non-structural carbohydrate adjustments influence growth responses of species, especially the ratio between leaf and root tissues. Our findings suggest that this aspect should be considered as a tree species selection criterion for forest restoration programs in the Amazon region.