Late-vegetative and reproductive-stage nitrogen determinants of kernel weight in maize

Abstract

Differences in maize kernel weight (KW) due to soil N availability have usually been associated with the indirect role that N plays in the prevailing source-sink balance for carbon at the canopy level during reproductive development. Additionally, KW changes have also been described in response to N assimilate supply to the reproductive tissues (i.e., direct N role). Our objective was to determine the most important source factors driving KW gains with varying N and dry matter supply via the multivariate study of pertinent phenotypic relationships during late vegetative and reproductive growth. Maize responses to N rate plus N timing and(or) plant density treatments were followed in five field experiments. Principal component analyses (PCA) and partial least square (PLS) regressions explored the relationships between final KW, plant-component biomass (DM), plant-component N concentrations, N uptake at V12, R1, R3, and R6 stages, plus specific grain-filling parameters including effective grain-filling rate (EGFR), grain-filling duration (GFD), and the kernel N accumulation features of rate and duration (KNAR and KNAD, respectively). Across experimental sites, grain yields at the highest N rate were 93–196 % above those with zero N. These yield increases coincided with incremental gains in both kernel number and KW at maturity. Via PCA, final KW was more positively correlated with vegetative-tissue N concentrations (stem N % at V12 and R1, leaf N % at R1 and R3) than with biomass during the critical period. In addition, final KW was more correlated with stem biomass at R6 than at V12, R1 or R3 stages. Via PLS, the majority of KW variability was explained by critical-period N contents, either in leaf (V12 and R1) or stem (R3), while at R6 stem DM was more important in KW determination. Finally, when tested against its physiological determinants, KW at maturity was largely associated with KNAR (via PCA) and EGFR (via PLS) during the grain-filling period. Overall, these results suggest the dual importance of N in determining KW at maturity through both leaf and stem N supply during the critical period and through dry matter allocation during the effective grain filling period.