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a b s t r a c tUrban forests play an important role in mitigating climate change in urban ecosystems. In order to obtain greater carbon sequestration benefits, it is crucial to advance the understanding of soil CO 2 efflux from urban forests. This study was undertaken to identify biotic and abiotic parameters that explained spatial variation in soil respiration, especially the effect of forest stand structure. To this aim, we measured soil respiration at 44 points in a 30 m × 50 m plot in an urban forest in Beijing over a 10 month period. The spatial variations of soil respiration were investigated, relating to soil climate, soil nutrients, root biomass and forest structural traits. The highest spatial variation in soil respiration was observed during the summer dry period, and similar degrees of variability were shown both in the growing and dormant season. Vegetation area index, soil moisture and nitrate nitrogen were the determinable parameters that influenced the spatial variation in soil respiration in the growing season, while nitrate nitrogen and soil temperature in the dormant season. Soil temperature, sulfur and roots biomass also affected the soil respiration during the growing season. Moreover, mean DBH and tree number within a 6-m radius had a significant influence on the spatial pattern of soil respiration at sub-plot level. Our results suggest that decreasing the soil CO 2 efflux might be an optional way to increase carbon sequestration potential for urban forest. This can be achieved by regulating forest stand structure and applying appropriate maintenance practices.

In this paper, we establish a finiteness theorem for $L^{p}$ L p harmonic 1-forms on a locally conformally flat Riemannian manifold under the assumptions on the Schrödinger operators involving the squared norm of the traceless Ricci form. This result can be regarded as a generalization of Han’s result on $L^{2}$ L 2 harmonic 1-forms.