Effects of Plant Density and Soil Moisture on Photosynthetic Characteristics of Flag Leaf and Accumulation and Distribution of Dry Matter in Wheat

Water shortage is one of the major problems in wheat (Triticum aestivum L.) production in northern plain in China, and water-saving technique is of great importance in wheat cultivation in this area. A water-controlled irrigation strategy based on measuring soil moisture at jointing and anthesis stages (SMJ+SMA) was adopted in a 2-year field experiment in Shandong Province, China from October 2008 to June 2010, using the famous commercial wheat cultivar Jimai 22. The dynamics of photosynthetic parameters and dry matter accumulation were determined during grain filling period. In the 2008–2009 growing season, 3 irrigation treatments were designed under the plant densities of 150 (M1) and 225 seedlings m⁻² (M2), whose SMJ+SMA percentages were 65%+60% (W0), 75%+75% (W1), and 75%+75% at 7 d after jointing or anthesis (W2). In the 2009–2010 growing season, the irrigation treatments were conducted under only M1 density because M1 showed higher yield and water use efficiency (WUE) than M2 density in last season. The SMJ+SMA percentages in the 3 irrigation treatments of 2009–2010 were adjusted to 75%+60% (W'0), 85%+75% (W'1), and 85%+75% at 7 d after jointing or anthesis (W'2). Under the same irrigation condition, the maximal photochemical efficiency of PSII (F_v/F_m) and actual photochemical efficiency of PSII (ϕ_PSII) in M1 treatment were higher than those in M2 treatment from middle to late grain-filling stage, and the dry matter accumulation amount after anthesis and dry matter translocation to grains in M1 treatment were significantly higher than those in M2 treatment. Under the same plant density condition, the F_v/F_m and ϕ_PSII values were significantly higher in W2 treatment than in W1 treatment from middle to late grain-filling stage; and the photosynthetic rate (P_n), evapotranspiration (T_r), leaf WUE, and stomatal conductance (G_s) were higher in W'2 treatment than in W'1 treatment. The management of soil moisture to 75–85% at 7 d after jointing or anthesis showed the largest dry matter accumulation amount after anthesis and its contribution to grains, grain yield, and WUE under the M1 density. In the practical point of view, plant density of 150 m⁻² and the SMJ+SMA percentages of 75%+75% at 7 d after jointing or anthesis are proposed in water-saving wheat production with environment similar to this experiment.