| Soybean is grain and oil crop in China. Nitrogen nutrition was provided for soybean growth by soybean-rhizobium symbiosis, studying on characteristics of nodule nitrogen fixation and influencing factors-fertility and moisture conditions are profound implications for appropriate application of fertilizer, increasing yield, improving quality, reduction in production costs and alleviation of environmental pollution.This work was conducted from2009to2011, using15N tracer technique with frame tests (pot without bottom) and sand culture. In frame experiment, DGGE and AFLP methods were used to study differences of rhizobium and nodule nitrogen fixation among different soybean varieties; effect of fertility factors and moisture conditions on nodule nitrogen fixation and yield were studied with SN14by15N tracer technique. In sand culture, effect of phosphorus nutrient and potassium nutrient on nodule nitrogen fixation and yield were researched with SN14by15N tracer technique. The results showed that:Symbiotic rhizobium with tested soybean varieties were mainly uncultured bacterium. DGGE method was used to research differences of R4rhizobium among LX1, FS10, SN14, XJH and MSD, the number and brightness of bands were different; sequence analysis of the bands with NCBI stated that the similarity was94%-100%with uncultured bacterium from environmental samples.AFLP results of HH41, SN14, HN40and MSD showed that there were578bands with5primer combinations, the percentage of polymorphic loci was68.86%; Rhizobium could be divided into two clusters, rhizobium of SN14R2and SN14R6were one kind, others were another kind; there was no difference of rhizobium under the condition of drought at different growth stages.Soybean varieties with the long growth period had obvious advantages on nodule nitrogen fixation, the accumulation and ratio of nodule nitrogen fixation of tested varieties both showed that late varieties>medium varieties>early varieties, and the accumulation of nodule nitrogen fixation had significant difference.The effect of nitrogen levels on nodule nitrogen fixation of soybean was different because of soil fertility. The accumulation and ratio of nodule nitrogen fixation of soybean presented a single peak curve with nitrogen levels when the available nitrogen content of soil was18.17mg·kg-1, nodule nitrogen fixation was the highest when the amount of (NH4)2SO4was225kg/hm2(pure N:47.73kg/hm2); nodule nitrogen fixation was the highest when the amount of (NH4)2SO4was75kg/hm2(pure N:15.91kg/hm2) under the condition of available nitrogen content of soil was 50.38mg·kg-1, nodule nitrogen fixation was significantly inhibited with the nitrogen levels increasing.There was significant effect of phosphorus nutrient on nodule nitrogen fixation of soybean. With sand culture, the accumulation and ratio of nodule nitrogen fixation of soybean presented a single peak curve with phosphorus levels, when phosphorus concentration was11mg/L, increasing phosphorus concentration again had no obvious promotion of ratio of nodule nitrogen fixation, when phosphorus concentration was21mg/L, increasing phosphorus concentration again had no obvious promotion of accumulation of nodule nitrogen fixation; accumulation and ratio of nodule nitrogen fixation decreased significantly when interruption of phosphorus supply during V3-R1and R1-R5period, while interruption of phosphorus supply during R5-R7period had no significant effect on those, which means that nitrogen metabolism of soybean was sensitive to phosphorus requirement during V3-R5period and not sensitive after R5; with frame, phosphate application could improve the accumulation of nodule nitrogen fixation of soybean when available phosphorus content of soil was26.31mg·kg-1, while the promotion effect on accumulation of nodule nitrogen fixation of soybean was not significant with phosphate fertilizer increasing when the amount of triple superphosphate was150kg/hm2(P2O5:69kg/hm2); the ratio of nodule nitrogen fixation of soybean showed an increasing tendency with phosphate fertilizer increasing, the ratio of nodule nitrogen fixation of whole plant and seeds was significantly increased when the amount of triple superphosphate was450kg/hm2(P2O5:207kg/hm2).There was effect of potassium nutrient on nodule nitrogen fixation of soybean. With sand culture, the accumulation and ratio of nodule nitrogen fixation of soybean presented a single peak curve with potassium levels, nodule nitrogen fixation could be satisfied when potassium levels was21mg/L; there was no significant effect of interruption of potassium supply during different periods on the accumulation and ratio of nodule nitrogen fixation; potassium fertilizer could improve the accumulation and ratio of nodule nitrogen fixation of soybean when available potassium content of soil was174.75mg·kg-1, potassium could satisfy the need of nodule nitrogen fixation when the amount of K2SO4was90kg/hm2(K2O:45kg/hm2).The accumulation and ratio of nodule nitrogen fixation showed an increasing tendency with moisture increasing in HN60, NF18and SN14, the sensitivity of the ratio of nodule nitrogen fixation to moisture was lower than the accumulation of nodule nitrogen fixation; there was no obvious rules of nodule nitrogen fixation under the condition of phased drought during growth period.Fertility and moisture factors could influence soybean yield.(1) Soybean yield presented a single peak curve with the increase of nitrogen rate under the condition of two soil treatments, which showed that the yield decreased either too high or too low.(2) With sand culture, soybean yield presented a single peak curve with phosphorus levels, the yield reached its maximum when phosphorus concentration was31mg/L, while increasing phosphorus concentration again had no obvious promotion of yield when phosphorus concentration was21mg/L; soybean yield decreased significantly when interruption of phosphorus supply during V3-R1and R1-R5period, while interruption of phosphorus supply during R5-R7period had no significant effect on yield; soybean yield was not significantly increased with phosphate application when available phosphorus content of soil was26.31mg·kg-1.(3) Soybean yield presented a single peak curve with potassium levels increasing with sand culture, the yield reached its maximum when potassium concentration was64mg/L, while increasing potassium concentration again had no obvious promotion of yield when potassium concentration was52mg/L; soybean yield decreased significantly when interruption of potassium supply during V3-R1and R1-R5period, while interruption of potassium supply during R5-R7period had no significant effect on yield; soybean yield showed an increasing tendency with potassium levels increasing when available potassium content of soil was174.75mg·kg-1.(4) The yield of HN60, NF18and SN14was increased with moisture improving, which showed that improving precipitation was beneficial to yield; podding-seed filling period of soybean was the most sensitive to drought, and the yield was significantly decreased. |
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