Biomass Allocation and C-N-P Stoichiometry in C3 and C4 Crops Under Abiotic Stress.

Biomass allocation to structural, metabolic and reproductive organs as well as their carbon, nitrogen and phosphorus (C-N-P) profiles and ratios (C:N, C:P, and N:P) were estimated in C3 and C4 crop plants subjected to multiple abiotic stresses (i.e., combination of temperature and water stress levels; CO2 enrichment of 400 micromole mol-1 was used for C3 crop species) under controlled growth chamber conditions. The reduced major axis (RMA) or Model Type II regression was used to estimate the mean and 95% bootstrapped confidence intervals of constants (a) and scaling coefficients (beta) for biomass, nutrients, and nutrient ratios. Isometric and allometric constants and scaling coefficients estimated for these variables, as well as adjusted coefficients of determination (R2), were used to explore differences between and within C3 and C4 crop species in biomass and nutrient allocations to structural, metabolic and reproductive organs in response to abiotic stress. Results of the standardized major axis analyses suggested that biomass partitioning to structural, metabolic and reproductive organs, in decreasing order, were positively correlated with C:N ratio; while N:P, but not C:P ratio, was positively correlated with allometric biomass allocation to metabolic and reproductive organs. The level of deviation from the expected balanced or functional partitioning of biomass and nutrients to different plant organs differed between and within C3 and C4 crop species and was dependent on abiotic stress factors and their interactions.