小麦/玉米/大豆三熟套作体系中小麦根系分泌特性及氮素吸收研究
摘要
Root exudates play a role in adjusting physical and chemical characteristics of soil, improving soil fertility, and facilitating nutrient uptake. Thus, they are used to explaining the mechanism of high nutrient utilization efficiency for plants. In the relay cropping system of wheat/maize/soybean, nitrogen use efficiency appears higher than that in the cropping system of wheat/maize/sweet potato. For explaining the relationship between the high use efficiency of nitrogen and the effects of rhizosphere microenvironment in the wheat/maize/soybean cropping system, the characteristics of wheat root exudates as well as its effects on wheat roots, wheat rhizosphere soil, and nitrogen uptake in wheat were studied in a two-year continuous experiment from 2006 to 2008 with four cropping systems, including two sole cropping systems (wheat-soybean and wheat-sweet potato) and two rely cropping systems (wheat/maize/soybean and wheat/maize/sweet potato). In the wheat/maize/soybean system, the soil moisture, soil pH and soil quick-acting N (NO3(superscript -)N and NH4(superscript +)-N) content at wheat rhizosphere reduced at both flowering and ma-turity stages, and the total nitrogen uptake in shoots, root activity, root dry matter weight and soil total nitrogen content of wheat increased. At flowering stage, the total amount of organic acids and the content of soluble sugar of wheat rhizosphere increased in the wheat/maize/soybean system. The total amount of organic acid and the content of soluble sugar of wheat were higher in relay cropping system than in sole cropping system. In the two sole cropping systems, the wheat-soybean mode had higher amount of organic acid and higher content of soluble sugar than wheat-sweet potato. Wheat plants from fringe rows could exude organic acids and higher soluble sugar content than those from central rows, and the amount of root exudates in fringe rows was the high-est among all the cropping systems. At jointing stage, the content of acetic a