Climatic regulation of the non-structural and structural carbon in the pioneer Senna multijuga and non-pioneer Hymenaea aurea trees of a humid tropical rainforest

Key message

Structural and non-structural carbon pools of Senna multijuga and Hymenaea aurea provide future projections on carbon dynamics in other pioneer and non-pioneer tree species of tropical rainforests in a scenario of global climate change.

Abstract

The knowledge of carbon dynamics in tropical rainforests is still incipient, especially regarding the strategies of carbon allocation and mobilization in species from diverging functional group. Literature shows that rainforest pioneers invest more in soluble sugar to meet their high-energy demand for metabolism and growth than in cell-wall polymers compared to non-pioneers. Recent studies also point to a substantial investment in soluble sugars and starch in pioneer tropical trees during the dry season. Therefore, we hypothesize that the carbon reservoirs of pioneer species are more susceptible to climate variations than those of the non-pioneers. To test this hypothesis, we determined the levels of non-structural (soluble sugars and starch) and structural (cellulose, hemicelluloses, and lignin) carbon on the leaves and stem of the pioneer species Senna multijuga and of the non-pioneer Hymenaea aurea, in an altitudinal contrast of a humid tropical rainforest in southeastern Brazil. The results showed that the energy-rich compounds of the pioneer species accumulated in the winter and declined in the summer. Contrary to expectations, the starch in leaves and stem of the non-pioneer species also followed the same pattern. Another interesting result was the similar pattern of species responses under the altitudinal contrast, where strategies are rather conservative within each functional group regardless the environmental conditions. We conclude that the allocation and usage of non-structural and structural carbon play an important ecological role in pioneer and non-pioneer trees of a humid tropical rainforest in southeastern Brazil.