Abstract: To study the roles of nitrogen fertilization in regulating the physiological bases of fiber specific strength formation in cotton bolls bloomed at different dates (July 15, July 25, and September 10; expressed as PSB, SB, and AB, respectively), field experiments were conducted in two sites with different ecological conditions, i.e., Nanjing (middle lower reach of Yangtze River Valley) and Xuzhou (Yellow River Valley). Three treatments (0, 240, and 480 kg N·hm^-2) were installed. The results showed that comparing with applying optimum nitrogen (240 kg N·hm^-2), no N application decreased the N content and increased the C/N in the leaves subtending cotton bolls significantly, and the effects increased with postponing blooming date, which, to a great extent, led to the decreases of the capabilities of the leaves subtending cotton bolls bloomed at SB and AB in the accumulation and transportation of photosynthetic products, the relative growth rate of fiber in cotton bolls, and the activities of key enzymes (sucrose synthetase and β-1,3-glucanase) during the middle-later period of fiber development, and also, the decline of cellulose speedily accumulating duration in cotton fiber and of the fiber specific strength in the bolls bloomed at SB and AB. On the contrary, applying high nitrogen (480 kg N·hm^-2) increased the N content but decreased the C/N in the leaves subtending cotton bolls significantly, and the effects decreased with postponing blooming date, which decreased the distribution proportion of photosynthetic products to fiber, the key enzyme activities during the early-middle period of fiber development, and the momentary rate of cellulose accumulation in the fiber of the bolls blooming at PSB and SB, resulting in a significant decrease of the fiber specific strength. It was suggested that appropriate N application could regulate the ‘source-sink’ relation of cotton, and benefit the high fiber specific strength formation in cotton bolls bloomed at different dates.

Key words: soil nematode, community structure, humus layer, high-throughput sequencing, soil surface layer