Photosynthesis, crop growth, and respiration of a tall and short rice varieties

Abstract

Abstract The crop growth rate (CGR) of IRS and Peta increased as leaf area index (LAI) increased up to certain values. Beyond these values, the CGR was almost constant. The plateau value of CGR was greater for IRS than for Peta. The respiration of the crop for both varieties did not increase linearly but asymptotically with increase in LAI. The gross photosynthesis was estimated from (CGRx0.9)+respiration. The gross photosynthesis of both varieties increased with increasing LAI up to about 6, then showed little further increase. The maximum gross photosynthesis of IRS was greater than that of Peta. The respiration of both varieties was approximately 40 percent of gross photosynthesis over a wide range of values for LAI and leaf area ratio. The similar relationship was also found for 6 varieties of different plant type. These data suggest that the balance between photosynthesis and respiration is relatively stable over a broad range of photosynthetic rates for all varieties tested. Thus, it is unlikely that optimum LAI occurs due to an imbalance between photosynthesis and respiration. An optimum LAI value may occur when heavy application of nitrogen markedly increases the droopiness of leaves at high LAI values, thereby decreasing gross photosynthesis.