Effects of leaf area index on photosynthesis and yield of winter wheat after anthesis

Leaf is the main tissue of photosynthesis for green plant. Leaf area is closely correlated with the grain yield of crops. To make clear the effects of leaf area index on photosynthesis and yield of winter wheat after anthesis, and to provide a theoretical basis for winter wheat cultivation with high and stable grain yield, Tainong18 (T18), a winter wheat cultivar with multi-grain number per spike, and Shannong15 (S15), a winter wheat cultivar with middle grain number per spike, were used as experimental materials. The two cultivar were both widely grown. Field trials were carried out from 2008 to 2010 in two successive growth seasons in a split plot design, with 2 nitrogen rates (180 kg/ha and 240 kg/ha of pure nitrogen) being in the main plot and 3 plant densities (0.75, 1.50 and 2.25 million basic seedlings per hectare) representing in the subplots. The results showed that lower leaf area index (LLAI, the third leaves and the forth leaves under the flag leaves on the stems) is positively and significantly correlated with canopy apparent photosynthesis (CAP) and grain yields during the lower leaf stay-green stage, and the top leaf area index (TLAI, flag leaves, the first leaves and the second leaves under the flag leaves on the stems) and whole leaf area index (WLAI) which consists of all of the leaves on the stems are positively significantly correlated with CAP and grain yield for T18 but not for S15 so the relationships are not certain within 14 days after anthesis. TLAI and WLAI are positively and significantly correlated with CAP and grain yields for two kind of wheat from 14 days after anthesis to maturity. There is a significant interaction between nitrogen rate and plant density on grain yield. Being reducing nitrogen amount from 240 kg/ha to 180 kg/ha of pure nitrogen, both T18 which adopts 2.25 million basic seedlings per hectare and S15 which adopts 1.50 million basic seedlings per hectare could gain high grain yields.