Sexual differences in morphology and aboveground biomass allocation in relation to branch number in Morus alba saplings

Abstract

The effect of branch number on crown size and biomass accumulation has been reported for many trees, but knowledge about sexual differences in growth and aboveground biomass allocation related to branch number is still limited. Morus alba L. is a dioecious plant of economic importance, and was employed as a model species in our study. Thirty male and 30 female 1-month-old M. alba saplings with single or multiple (five) primary branches were cultivated for one growing season. Sexual differences in gas exchange, morphology, biomass accumulation and allocation, and relationships among morphological and biomass traits were investigated. Branch multiplication significantly increased the total leaf number, total leaf area, total leaf mass, aboveground mass, leaf : stem biomass ratio and specific leaf area at the plant level but decreased net photosynthetic rate (Pn), leaf number, mean single-leaf area, stem length, basal diameter and branch biomass at the branch level. Five-branch male saplings exhibited a significantly higher Pn, total leaf number, total leaf area, total leaf mass and aboveground biomass than did female ones. No such between plant sex differences were found in single-branch saplings. Further, branch number was positively correlated with aboveground mass in male saplings only. Our results demonstrate that branch multiplication might result in sexual differences in morphology and biomass accumulation and male saplings may allocate greater resources than females to aboveground parts for vegetative growth.