Comparison of Ecosystem Respiration Components and Carbon Use Efficiency among Different land Use Patterns of Temperate Steppe in the Northern China Pastoral- farming Ecotone

Abstract:

ABSTRACT

The rangeland use/management pattern changes such as cultivation and grazing exclusion, can lead to significant influence on vegetation and soil characteristics, which, in turn, brings changes to the microclimate of community. As a consequences, the carbon budget balance between the grassland ecosystem and the atmosphere may altered. Our research indicated that the GEP of cultivated steppe was enhanced significantly, in comparison with adjacent grazed steppes. However, with a significant rise of the respiration of the crops (Ra) and of heterotrophic respiration of the cultivated ecosystem (Rh), the NEP of the steppes cultivated to cropland is significantly lower than that of the grazed or grazing excluded steppes. The respiration of the aboveground part of ecosystem (Rab) and of the underground part (Rb) both contributes to the dramatic increase of the ecosystem respiration (Re) in cultivated steppe. The steppes under three different management types show a significant difference on the underground root biomass, but the difference on the root respiration (Rr) is not significant. This phenomenon is due to the negative exponential relationship between the root-top ratio and the root respiration activity. The communities on the grazed and grazing excluded steppes have a significantly higher carbon fixation efficiency than the steppes cultivated to cropland (wheat fields). The heterotrophic respiration (Rh) of the ecosystem explains to the maximum extent the carbon use efficiency (CUE) of the vegetation (95%). Long term grazing exclusion or cultivation reduces the net photosynthesis ,NEE and CUE of the steppe ecosystem and weakens the carbon sink function of the vegetation, while enhancing the soil respiration CO₂ release with different respiration sources composition.