Effects Of Litter Removal And Addition On Ecosystem Carbon Flux In A Typical Steppe

Grassland ecosystem is the most widely distributed ecosystem type, accounting for 41% of the total area of the land ecosystem. The Inner Mongolia grassland plays an important role in the carbon balance of grassland in China. Typical grassland is an important component of Inner Mongolia grassland, which has crucial effects on the developments of agriculture and animal husbandry in the Inner Mongolia. Litter is an important organic matter input source of grassland ecosystem, and also an vital indicator for grassland health assessment. This paper discusses the effects of litter quantity on plant community composition, aboveground biomass, soil physicochemical property and carbon flux, which provide theory basis for the maintenance of ecosystem stability, the sustainable development and scientific management of grassland.The field experiment was carried out at the Inner Mongolia Grassland Ecosystem Research Station of the Chinese Academy of Sciences, which is located in the Xilin River Basin of Inner Mongolia.In order to reveal the effects of the litter removal and addition on carbon flux in grassland ecosystem, we conducted the litter removal(control、-50%、-100%)in mature community and the litter addition(control、+50%、+100%) experiments in degraded community in continuous two years(year 2013 and 2014).At the same time, we carried out another experiment in consideration of the effects of the litter removal and addition on carbon flux which might vary with the different seasons in which we began to conduct the litter removal and addition experiment.We investigated the aboveground biomass, soil moisture, soil temperature and the net ecosystem carbon exchange(NEE) in annual growth season.The main results obtained are as follows:1. The results of the effects of different gradients of litter removal and addition on carbon fluxes showed that there were obvious seasonal changes of NEE in mature and degraded communities. In the litter removal treatment of the mature community, the net ecosystem carbon exchange(NEE) and ecosystem gross primary productivity(GEP) changed in the same way, both increased in the 50% removal treatment,and decreased in the 100% removal. In the litter addition treatment of the degraded community, the changes of NEE and GEP had a similar trend that both increased with the increase of the litter addition amounts. Meanwhile, both litter removal and addition had no significant effect on the total ecosystem respiration(ER). In both communities, the correlation between NEE and soil temperature was positive(P<0.05). However, the change of GEP and NEE was contrary to the soil temperature, and the same with 10 cm soil moisture content. It was concluded that the mechanism of litter removal and addition to affect the carbon flux of ecosystem was mainly affect the GEP by changing the soil water content, thus affecting the carbon flux of the ecosystem.2. As for the effects of litter removal and addition on carbon fluxes in different seasons, the effect of the autumn litter removal on the GEP and NEE was positive in mature communities and it was much greater than that in the spring. The litter removal in autumn influenced the soil temperature, and then affected the GEP and NEE. Excessive accumulation of litter might affect the productivity of the grassland, and the litter removal in autumn might remove the limits that the excessive litter accumulation on the effective radiation and soil temperature.In degraded communities, the effect of the spring litter addition on the GEP and NEE was positive andit was much greater than that in the autumn. The litter could not be accumulated effectively in degraded communities and the plant growth was restricted by the factors such as soil nutrients and soil moisture.The spring litter addition might remove the limits discussed above so that the plants could grow rapidly.It provides a theoretical basis for understanding the rational use of litter for the improvement of grassland ecosystem management, the promotion of the restoration of grassland, and theprediction for the future carbon cycle.