Abstract: The allocation of annual growth in biomass to primary plant organs is a central theme in ecology due to its role in developing ecological theories and agricultural applications. Classic theories have significantly improved our understanding of biomass allocation patterns influenced by various factors. However, increasing contrasting observations cannot be explained by classic theories. Recently, transient dynamic theory can resolve the problem. Here, we provide empirical evidence describing transient variations of biomass allocated to stems for four crop species (i.e., corn, soybean, flax, and wheat) in single and mixed systems. We show that plant ontogeny and increasing intraspecific competition promote variations in stem mass fractions. However, variations in stem mass fractions are reduced under strong interspecific competition. Plants with large total biomass have relatively stable stem mass fractions. These findings provide empirical foundations for integrating transient dynamics into general theoretical frameworks of biomass allocation patterns and may stabilize agricultural crop yields.

Key words: stem mass fraction, biomass allocation, transient dynamics, competition, ontogeny.