Effects of stem fraction on the optimization of biomass allocation and maximum photosynthetic capacity

Abstract

SummaryA model was developed to examine effects of the stem biomass fraction on the optimal responses of plants to soil nitrogen availability.Our model predicts that the optimal leaf : root ratio and optimal photosynthetic capacity (Pmax) increase with soil N availability. For a given N availability, the optimal leaf : root ratio decreases and the optimalPmaxincreases with increasing stem fraction. As a result, the increase in optimal leaf : root ratio is smaller, and that in optimalPmaxis greater, in response to increasing N availability when stem fraction is large.To test these predictions we grew two herbs with different stem fractions:Polygonum cuspidatumSieb. et Zucc. andChenopodium albumL.Showing excellent agreement with the simulation results, the leaf N concentration and leaf : root ratio of the two herbs increased with increasing N availability, and leaf N concentration was larger forC. albumwith higher stem fraction thanP. cuspidatum.The general tendency for plants with larger stem fractions also to have greater leaf N concentrations andPmaxwas demonstrated for a wide range of temperate herbs. This suggests that stem fraction may be a source of variation inPmaxamong plants in the same functional group.