Leaf protein allocation across the canopy and during senescence in earlier and later senescing maize hybrids, and implications for the use of chlorophyll as a proxy of leaf N

Abstract

Leaf chlorophyll (chl) and protein distribution were analyzed throughout grain flling in four modern maize hybrids with contrasting senescence behavior, at three diferent canopy levels and at low-N (LN, 18 kg N ha−1) and high-N (HN, 218 kg N ha−1) fertilization levels. Chl content assessed by SPAD resembled protein content only at LN, with delayed senescing genotypes having more leaf protein content than reference genotypes. Across N levels, relative chl content negatively related to light intensity (r 2=0.59, P<0.001), while relative protein content did only for the lowest part of the canopy (r2=0.54, P<0.001), suggesting protein distribution in the canopy could be further improved. Relative Rubisco/LHCII partitioning increased from lower to upper leaves (P<0.09) and difered among genotypes (P<0.05) with no link to senescence behavior. Photosynthetic electron transport rates were lower at LN and difered between genotypes (P<0.05) including those with similar leaf protein contents. Chl and protein contents were related across the entire dataset (r 2=0.53, P<0.001) but the slope (b) of this relationship varied widely depending on the leaf position (b=0.026–0.019), the senescence stage (b=0.014–0.020), the N level (b=0.035–0.026) and the hybrid (b=0.016–0.033). Our results suggest that in modern maize hybrids, leaf N utilization can be further improved and that genotypic together with other sources of variation should be included as specifc variables in SPAD-based predictions of leaf N content.