Abstract:

【Objective】 The amount of photosynthetically active radiation (PAR) interception and distribution within canopy affects crop photosynthesis and biomass production. The primary objective of this study was to elucidate the relationship of PAR interception of canopy to leaf area and yield of rice (Oryza sativa L.) under different nitrogen rates for different cultivar types.【Method】 Two field experiments were conducted at Nanjing in 2007 and 2008 rice growing seasons, involving two rice cultivars and three nitrogen rates. The amount of PAR interception and its distribution at different canopy heights, leaf area and yield of two cultivars were measured from jointing to maturity. 【Result】 The results indicated that the vertical distribution of upward cumulative leaf area index (LAI) followed a sigmoid curve, which could be described well with Logistic equation (R2＞0.99). The maximum leaf area density in heading, 17 days after heading and maturity stages appeared at 0.53, 0.56 and 0.60 of relative canopy height, respectively. The relative leaf area density of upper and middle canopy increased with rice development progress, but the relative leaf area density of basal canopy decreased with rice development progress. The relationship between fraction of PAR interception (FIPAR) and downward cumulative LAI could be described with a negative exponential equation as FIPAR=α×(1-e-K×LAI) (R2＞0.86). Diurnal variation of extinction coefficient (K) at noon was smaller than in the morning and afternoon, and the value of K decreased with rice development progress. The amount of PAR interception (AIPAR) showed multi-peaks distribution during rice development period, and the maximum peak appeared at 58-70 d after transplanting, around booting to heading stages. The AIPAR increased with increasing nitrogen application rate. Diurnal variation of AIPAR showed one peak distribution on the clear days, and the maximum AIPAR appeared at 11:00-13:00 in rice canopy. 【Conclusion】 The vertical distribution of leaf area affects PAR interception within rice canopy. The grain yield of rice was positively related to the PAR use efficiency, while PAR conversion efficiency first increased and then decreased with increasing PAR interception, thus it is benefit to have some penetration loss of PAR in rice canopy for high grain yield.

Key words: rice (Oryza sativa L.), canopy, photosynthetically active radiation (PAR), light interception, leaf area, yield