Aims Exotic fast-growing tree species have been commonly planted as pioneer species to facilitate ecological restoration in South China.Their growth and resource utilization behavior related to intrinsic physiology and structural properties have profound influences on forest ecosystem.However,the contrastive research focusing on water utilization features along with xylem anatomical properties between native and exotic species is scarce in South China.The objective of this study is to investigate the sapwood anatomical characteristics and water utilization conditions of native and exotic fast-growing species,and to elucidate the relationship between sap-flux density and conduit features.Methods We measured sap-flux density,conduit length,diameter and density of four native species(Schima superba,Michelia mac-clurei,Castanopsis hystrix and Castanopsis fissa)and four exotic species(Eucalyptus citriodora,Eucalyptus urophylla×grandis,Acacia auriculaeformis and Acacia mangium).Sap flux density was measured based on the Granier’s thermal dissipation probe method.The whole-tree water transport was quantified by mul-tiplying sap-flux density by sapwood area.The measurements of conduit characteristics were conducted by using segregation and slice method.Important Findings Sapwood area increased with the growing diameter at breast height(DBH)as a power function.Native species had a larger water-conducting tissue area than exotic species at the same DBH value when trees grew to a size with a certain value of DBH.The con-duit diameter of exotic species was significantly larger than that of native species.Conversely,native species,such as S.superba and M.macclurei,had longer conduit length and higher conduit den-sity than other tree species.Based on a physiological interpretation of the measured conduit characteristics,native tree species devel-oped a safe water transport system while exotic fast-growing tree species come into being an efficient system instead.Water trans-port increased with the growing DBH as a power func
Introduction:Soil heterotrophic respiration(Rh,an indicator of soil organic carbon decomposition)is an important carbon efflux of terrestrial ecosystems.However,the dynamics of soil Rh and its empirical relations with climatic factors have not been well understood.Methods:We incubated soils of three subtropical forests at five temperatures(10,17,24,31,and 38°C)and five moistures(20,40,60,80,and 100%water holding capacity(WHC))over 90 days.Rh was measured throughout the course of the incubation.Three types of models(log-linear,exponential,and power model)were fitted to the measurements and evaluated based on the coefficient of determination(r2)and Akaike Information Criterion(AIC)of the model.Further regression analysis was used to derive the empirical relations between model parameters and the two climatic factors.Results:Among the three models,the power function model(Rh=R1 t−k)performed the best in fitting the descending trend of soil Rh with incubation time(r2>0.69 for 26 of 30 models).Both R1 and k generally increased linearly with soil temperature but varied quadratically with soil moisture in the three forest soils.Conclusions:This study demonstrated that the power function model was much more accurate than the exponential decay model in describing the decomposition dynamics of soil organic carbon(SOC)in mineral soils of subtropical forests.The empirical relations and parameter values derived from this incubation study may be incorporated into process-based ecosystem models to simulate Rh responses to climate changes.
