The Soil Nutrition And Dynamic Features Of Carbon Fixation In Leymus Secalinus Communities

We selected Leymus secalinus communities of fenced and grazed plots of grassland ecosystem research station in Shanxi northwest. During the growing season, we studied the dynamic variation of aboveground and underground biomass in fenced and grazed plots. At the same time, we determined the content of organic carbon in aboveground and underground biomass, the content of organic carbon, total nitrogen, total potassium, total phosphorus, alkali solution nitrogen potassium, and rapidly available phosphorus of soil were also determined. We are analyzed the dynamic characteristics of grassland soil nutrients in the growing season and effect on biomass and carbon fixation of Leymus secalinus communities. The research will provide theoretical basis for research the nitrogen fixation and carbon budget mechanism. The results were summarized as following:1.The soil content of total nitrogen, alkali solution nitrogen, total phosphorus, apidly available phosphorus and rapidly-available potassium in the fenced and grazed plots of grassland were present obvious vertical distribution characteristics, the trend was top-down decreased. The minimum value was appears different part in growing season. The content of total potassium was evenly distributed, but there was an obvious effect of the surface in the five and six month. The soil total nitrogen content of fenced grassland in the whole growing season was changed quite gentle (238.59g/m2-277.61g/m2), and was decreased to 151.03 g/m2 in the late growing season. While the soil total nitrogen content of grazed grassland was presented "W" type dynamic change characteristics, in the five month it was reached the maximum value 390.49 g/m2, the minimum value 183.97 g/m2 was at the six month. The change trends of alkaline hydrolysis nitrogen content both fenced and grazed grassland was presented a single peak curve, and the maximum value was present in the eight and seven month, respectively 26.83g/m2 and 27.20 g/m2. The change of total potassium content in the whole growing season was quite gentle, fall in between 626.99 ～711.70g/m2 in fenced grassland and 637.28～808.22 g/m2 in grazed grassland. The change trends of rapidly available potassium content both fenced and grazed grassland was presented a single peak curve, and the maximum value was present in the eight and nine month, respectively 137.71g/m2 and 178.25 g/m.2.The aboveground biomass of fenced plots fall in between 567.19～673.1 g/m2 has significantly higher than graced plots fall in between 239.99～302.50 g/m2. The living biomass showed unimodal curve of fenced plots and the peak values appeared in July for 406.10 g/m2, while the graced plots changed was gentle and the peak values also appeared in July for 100.63 g/m2. The change trend of litter biomass was contrary to living biomass. The underground biomass variation of Leymus secalinus communities showed unimodal curve and the peak values appeared in August at fenced and grazed plots, respectively 3736.64g/m2 and 3331.51 g/m2. The underground biomass in 0-30cm was accounted for 88.54% in fenced plots total biomass and 89.03% in graced plots total biomass.3.The correlation analysis of soil nutrient and grassland biomass showed that the soil alkali solution nitrogen content, total nitrogen content in 10-20cm were significantly correlation with aboveground biomass; the total potassium content in 20-30cm, total nitrogen content in 10-20cm were significantly correlation with aboveground living biomass; the alkali solution nitrogen content in 5-10cm was significantly correlation with aboveground biomass of fenced plots; the total potassium content was significantly correlation with aboveground living biomass of fenced plots.4.The total carbon library in the growing season was remained in a stable level, but the living biomass of fenced plots (192.56-238.37g/m2) was significantly higher than graced plots (65.02-92.41 g/m2). The living biomass of fenced plots was showed a single peak changed and the peak value 238.37 g/m2 appeared in the seven month, while the graced plots were small fluctuation and fall in between 65.02～92.41 g/m2. The carbon library of litter was reached to the maximum in late of growing season at fenced and graced plots, respectively 190.51 g/m2 and 49.21 g/m2. The change trend of carbon library in decomposition layer was gentled.5.The carbon library of underground biomass was higher than aboveground biomass, was account for 9.37%-11.40% of carbon library in Leymus secalinus communities. The soil carbon library was account for the most portion of total carbon library, and showed the trend of rendering first after reduction increased, the minimum value of graced plots appeared in nine month for 6671.24 g/m2 and fenced plots was in seven month for 6715.50 g/m2. The carbon library of graced plots in growing season showed a increased trend, the maximum value was in the nine month (993.61g/m2),while the fenced plots was in the seven month (1025.33g/m2).6.The carbon fixation of Leymus secalinus ecosystem in growing season was showed decreased, the consuming of breathe is significantly greater than the accumulation of photosynthetic in the late growing season, and then it becomes the pure carbon source. The total nitrogen in 20-30cm was significantly correlation with carbon fixation of Leymus secalinus ecosystem. The available nitrogen content in 70-100cm was correlation with carbon fixation of graced plots, The total phosphorus in 10-20cm was significantly correlation with carbon fixation of fenced plots, the apidly available phosphorus in 10-20cm was significantly correlation with carbon fixation of graced plots, the apidly available phosphorus in 20-30cm was significantly correlation with carbon fixation of fenced plots. The effects of potassium content on carbon fixation was the most significantly, in 0-10cm,0-20cm,0-30cm were significantly correlation with carbon fixation of fenced plots.