Relative growth rate, biomass partitioning and nutrient allocation in seedlings of two threatened trees grown under different light conditions

Abstract

The present study investigates the variation in the relative growth, biomass and nutrient allocation in two threatened tree species viz. Magnolia punduana Hook.f. & Th. and Elaeocarpus prunifolius Wall. ex Müll. Berol. grown under three different levels of irradiance. The irradiance ranged between 1 and 12molm−2d−1. Results showed that the highest relative growth rate (RGR) was achieved under the intermediate light treatment for both the species (mean: 0.005mgmg−1d−1). The growth response coefficient (GRC) model revealed that net assimilation rate (NAR) was the factor driving the RGR in both species. A significant positive correlation was found between NAR and RGR (R2=0.33, p=0.000) whereas specific leaf area (SLA) and leaf mass fraction (LMF) was negatively correlated to RGR. Overall, multiple regression of the studied species based on the independent variables viz. NAR, SLA, and LMF showed a significant relation with RGR (F(3,50,53=13.001, p=0.000, R2=0.43). The biomass distribution in the studied species is in agreement with the “balanced-growth hypothesis” where high irradiance increased allocation to below ground biomass fraction and decreased irradiance increased allocation to the above ground fraction. The highest nitrogen concentration in leaves was observed under the intermediate light treatment. Overall seedlings growth under intermediate light had a higher mean RGR indicating the species' preference for partial light conditions. Long-term experiments under varied light conditions as in the present study would provide useful insight into plant growth strategies in varied environmental conditions.