Synergistic effects of planting density and nitrogen fertilization on chlorophyll degradation and leaf senescence after silking in maize

Regulating planting density and nitrogen (N) fertilization could delay chlorophyll (Chl) degradation and leaf senescence in maize cultivars. This study measured changes in ear leaf green area (GLAear), Chl content, the activities of Chl a-degrading enzymes after silking, and the post-silking dry matter accumulation and grain yield under multiple planting densities and N fertilization rates. The dynamic change of GLAear after silking fitted to the logistic model, and the GLAear duration (GLADear) and the GLAear at 42 d after silking were affected mainly by the duration of the initial senescence period (T1) which was a key factor of the leaf senescence. The average chlorophyllase (CLH) activity was 8.3 times higher than pheophytinase activity and contributed most to the Chl content, GLAear at 42 d after silking, and GLADear, indicating that CLH is a key enzyme for degrading Chl a in maize. Increasing density increased the CLH activity and decreased the Chl content, GLAear, GLADear and T1. Under high density, appropriate N application prolonged T1, reduced CLH activity, increased Chl content, alleviated high-density-induced leaf senescence, and increased post-silking dry matter accumulation and grain yield.