Advances in the study of photosynthate allocation and its controls.

Abstract

Photosynthate allocation is influenced by both environmental and biological factors. This paper reviews recent advances in the mechanism of photosynthate allocation and its controls at individual and community/ecosystem levels in order to improve understanding of plant responses to global change. At the individual level, more photosynthate will be allocated to roots under conditions of high light, low water and low nutrient availabilities. The effect of increased atmospheric carbon dioxide concentration on photosynthate allocation depends on soil nitrogen availability. The root mass fraction (RMF) will increase under low nitrogen and is unchanged under high nitrogen. At the community/ecosystem levels, photosynthate allocation is insensitive to environmental change. The RMF decreases with increasing stand age. The functional equilibrium hypothesis (optimal partitioning) can explain the regulation of photosynthate allocation in response to environmental change, the source-sink relationship can reflect the effect of ontogeny on photosynthate allocation and the allometric relationship provides an important theoretical baseline prediction to disentangle the effects of plant size and environmental variation on photosynthate allocation. Research is needed on 1) the fraction of photosynthate allocated to respiration at the ecosystem level, 2) accurate estimation of belowground biomass and belowground net primary productivity (BNPP), 3) comparative study of photosynthate allocations between young and mature forests and between field and greenhouse experiments, 4) effects of multiple factors and their interactions on photosynthate allocation at the ecosystem level and 5) cooperative effects of ontogeny and environmental factors on the regulation of photosynthate allocation.