Simulation on Photosynthetically Active Radiation Distributing in Rice Canopy With Rolled Leaves and Its Optimum Leaf Rolling Index

By replacing leaf area index(LAI)with effective leaf area index(ELAI)through introduction of leaf rolling index(LRI),the distribution of photosynthetically active radiation(PAR)in the canopy of three hybrid rice combinations,Liangyou E32 with high leaf rolling index,Liangyoupeijiu with medium leaf rolling index and Shanyou 63 with non-rolled(normal)leaves,was simulated.The results showed that the model based on ELAI could predict more accurately than that based on LAI.PAR interception,conversion and utilization efficiency of the three combinations were studied and their each optimal LRI and LAI were evaluated.The PAR utilization efficiency of Liangyou E32 was lower due to excessive rolled leaves and less ELAI,and that of Shanyou 63 was also lower because of the faulty PAR interception and lower photosynthetic rate and saturation point at lower layer in the canopy.Compared with the other two combinations,Liangyoupeijiu showed more appropriate distribution of PAR interception conversion efficiency in canopy with higher PAR utilization efficiency.The optimal LRI and LAI for Liangyoupeijiu were 0.11 and 7.6,respectively,which were close to the observed values,0.11 and 7.9,respectively.However,the optimum LAI of 9.8 for Liangyou E32 and 6.2 for Shanyou 63 were larger or smaller than those under the current plant density,which led to lower PAR utilization efficiency.The optimum LRI of the three hybrids was concluded as 0.08-0.12,close to the actual LRI of Liangyoupeijiu.