Abstract:

Water stress is a frequent and critical limit to wheat (Triticum aestivum L.) production in the North China Plain. It has been shown that photosynthetic active radiation (PAR) has close relation to crop production, and water stress affects the biosynthetic procedure remarkably. However, its mechanism is still not clear. An experiment was conducted at Yucheng ecological station in Shandong Province to investigate the interception and conversion efficiencies of PAR in the canopy from heading to maturity stages, and water use efficiency (WUE) of winter wheat at different soil moisture levels. The relationship between soil moisture level and PAR vertical distribution in wheat canopy, and its influences on grain yield, PAR use efficiency and WUE were evaluated. Different supplemental irrigation amounts from 0 to 180 mm and timings from jointing to grain filling stages were designed to attain various soil moisture levels, which resulted in different wheat populations and canopy structures. These soil moisture levels showed substantial influences on PAR interception and distributions in canopy from heading to maturity stages, and subsequent PAR and water use efficiencies. No great difference (less than 15.7%) in PAR intercepted by the wheat canopies was found between these soil moisture treatments during this period. While great differences in PAR intercepted by the top layer of the canopy (60–80 cm) (100.7%) and in PAR conversion efficiency (63.7%) were found between these treatments (Table 4 and Fig.4). This result was mainly caused by the changes in the vertical distributions of leaf area index (Fig.3) and in leaf photosynthesis capability caused by the different soil moisture levels. Maintaining about 50% PAR rate intercepted by the top canopy layer (60–80 cm) from heading to grain filling stages is very important for obtaining high grain yield and PAR use efficiency for winter wheat. With soil moisture improving, the PAR use efficiency during the late growth stages and grain yield were increased, but WUE decreased prior to the grain yield and PAR use efficiency (Fig.5), which indicated that improving WUE was essential to increasing other natural resources use efficiency in wheat growing season in the North China Plain. In current conditions with well initial soil moisture, two supplemental irrigations with 60 mm at jointing and booting stages could obtain high grain yield and WUE, and additional supplemental irrigations would not increase grain yield greatly but decrease WUE of winter wheat.

Key words: Soil moisture, Winter wheat, Canopy structure, PAR and water use efficiency