Ecological Effect Analysis Of Degraded Grassland Fencing In Xinjiang

Grassland rehabilitation and reconstruction is an important issue facing the animal husbandry in Xinjiang. This paper, based on GEF projects, studied biodiversity changes and carbon cycle during the restoration of Xinjiang degraded grassland, made evaluation on the effect of restoration on the basis of grassland ecosystem carbon budget calculations. The main conclusions as follows:1. After construction of pasture fences, the species diversity of plant community outside the fence is obviously higher than that of the plant community low-intensity fooding inside the fence, however, the community evenness index (Alatalo index) of outside fences is lower than that of inside. For microbial community composition of enclosed rotational grazing, enclosed cutting, and inside and outside the fence, the share of fungi is the lowest, basically, less than 1%; bacteria has a share of more than 50% of the total, sometimes even more than 80%; but in the case of grazing-ceasing, the share of actinomycetes basically equal to bacteria, even as high as 61.01%; the order of soil animal diversity index from high to low is cutting >rotative grazing>grazing ceasing. In all of the three fencing methods, the diversity index inside the fence is higher than that outside the fence.Under the conditions of grazing-ceasing treatment, soil organic carbon density inside the fence increase than that inside the fence by 120.66%. Under the grass-cutting condition, soil carbon density inside the fence is lower than that outside the fenced by11.78%; grazing-ceasing treatment and rotative grazing treatment can increase soil organic carbon of 0~20cm by 94.18% and 14.37% respectively; while for grass-cutting processing, there is a decrease of 26.88%; Inside fence, the plant carbon flux are all higher than that outside fence; in mowing, rotational grazing, and grazing-ceasing treatment, plant carbon density inside the fence increased by 344.35%,441.62%. 40.15% than that outside the fence; underground plant carbon deposit accounts for more than 95% of the total plant carbon; In the three encloses, the carbon allocation ratio is slightly different in the various carbon storage of ecological system, but generally soil carbon storage accounts for the largest proportion. Rotational grazing ecosystem has the highest carbon density and the lowest soil carbon storage which only accounts for 66.77%; the highest soil carbon density was found in grazing-ceasing treatment, which can achieve 24.72kg/m2, its soil carbon storage has the highest proportion, reaching 92.21%.Fencing cultivation for five years, underground plant has the largest carbon flux, 8.91kg/m2. While 0-5cm underground plant carbon capacity grows with the increase enclosed years; but with the enclosed time growth, the increment of underground plant carbon capacity will reduce. After enclosing for 25 years, 0-5cm plant underground carbon capacity is 72.78kg/m3. For 0～20cm plant underground carbon capacity, five-years fencing has shown no significant difference with 25 years; Within the first 20 years, plants carbon density grows with the increase of enclosed years, in 20th year, plant carbon density got the largest, reaching 195.71g/m2; plant carbon density in enclosed for 25 years slightly decreased than that in enclosed for 20 years, being 187.13 g/m2. In general, plants carbon density presents the trend of first increasing and then falling as the enclosing years increases. With the growth of enclosed years, allocation ratio of organic carbon of the carbon is slightly different in various carbon storage of ecosystem, but generally speaking, the soil carbon storage accounts for the largest proportion. The share of soil carbon storage in ecosystem's total organic carbon reserve is influenced slightly by enclosing years, with ratio 97.00%~98.00%.CO2 emission is featured with daytime high and night low, the daily change curves for grazing-ceasing and rotative grazing show a single peak curves, the highest rate of CO2 emission for grazing-ceasing appears at 14:00, and rotational grazing occurs in 16:00~18: 00; mowing treatment curve shows the double-peak curve, the peak at about 18:00. With the fencing growth of grazing-ceasing years, single peak curve for daily change has become more indistinct; when enclosing for 10 years, CO2 emission is the weakest, daily change curve appears approximately a straight line and the smallest difference between day and night. The largest CO2 emission rate emerges at 14:00, being 0.64gCO2/m2·h.; In the three kinds of enclosing, daily CO2 emission for mowing and grazing-ceasing treatment are both higher inside the fence than that outside fence, being 127.60% and 107.10% of outside fence respectively; rotational grazing is contrary, daily CO2 emission inside fence is lower than outside the fence, being 88.50%. With the increase of enclosing years, total daily CO2 emission present the trend of first increase then fall; enclosing for 10 years gets the best result, total daily CO2 emission is 9.93g/m2 ? day; it is showed that, only from the point of view for reducing CO2 emission, enclosing grazing-ceasing for 10 years got best results.With the enclosed grazing-ceasing years increasing, grassland ecosystem carbon sink function is continuously strengthened, grassland enclosed for 25 years gets the strongest carbon sink function, fixing additionally 7.08kgC/ m2·a than the comparative grassland. However, only from the view of carbon fixation, the long-term enclosing is beneficial for the increase of ecosystem carbon sink function. Grazing-ceasing treatment gets Net the strongest ability of net fixed carbon, within the fence, it can fixe net carbon 16.21kgC/m2 ? a; the influence of rotational grazing and mowing treatment on ecosystem net carbon fixation capacity is not significantly different, being 7.08 kgC/m2 ? a. 7.11 kgC/m2?a respectively.In the three kinds of enclosing way, the grazing-ceasing treatment gets the largest carbon sink value, 0.1621~0.2431 USD/m2·a; the carbon sink value difference between rotational grazing and mowing treatment is not obvious, both being in 0.0700~0.1100 USD /m2·a. With the increase of enclosing years, enclosed grassland showed an increasing trend of carbon sink value than the comparative grassland, enclose grazing-ceasing for 25 years can increase 0.0708~0.1063USD/m2·a of carbon sink than the comparative grassland. Meanwhile, it can be seen that, during the period of enclosing between 5-10 years, the carbon sink value of enclosed grassland grows faster than the comparative grassland; enclosing for 10-25 years, it shows a slow growth trend. Taking into account the fence maintenance and management cost, it is proposed that enclosing years is about 10 years for the best.