Soil respiration dynamics and its response to soil temperature and water content of Pinus tabulaeformis and Hippophae rhamnoides plantations in the Loess Hilly region
[Background]As an essential component of the carbon flux in terrestrial ecosystems,soil respiration plays a critical role in maintaining global carbon cycling and the carbon balance. Exploring the process of soil respiration and its influencing factors is conducive to understanding ecosystem carbon emissions and regulation mechanisms. [Methods]In order to analyze the dynamic characteristics of soil respiration rate ( R_s) and its response to the main environmental factors in the dominant plantations in the hilly Loess Plateau region,the R_s of Pinus tabulaeformis and Hippophae rhamnoides plantations were measured using a LI - 8100 soil carbon flux measurement system from June 2015 to May 2016. Soil temperature ( T) and soil water content ( W) were simultaneously monitored. At seasonal and daily scales,there were significant differences in R_s and significant effects of T and W on R_s in the two plantations. In addition,temperature sensitivities of R_s were investigated using the Q_(10) function at the seasonal scale. [Results] 1 ) The seasonal dynamic patterns of R_s in P. tabulaeformis and H. rhamnoides plantations were similar,with the respective maxima ( 2. 31 and 2. 89 mumol CO_2·m~(-2)·s~(-1) ) in summer ( June-August) and minima ( 0. 60 and 0. 65 mumol CO_2·m~(-2)·s~(-1) ) in winter ( December- February) ; the annual mean R_s in the plantations was 1. 36 mumol CO_2·m~(-2)·s~(-1) ( P. tabulaeformis) and 1. 64 mumol CO_2·m~(-2)·s~(-1) ( H. rhamnoides) ,with corresponding annual total R_s emissions of 18. 90 and 22. 81 t CO_2·hm~(-2)·a~(-1) . The R_s emission during winter accounted for 14. 67% and 12. 65% of the annual total emission in P. tabulaeformis and H. rhamnoides,respectively. In addition,the R_s maxima of P. tabulaeformis and H. rhamnoides appeared during 10: 00 - 16: 00,and the minima at 06: 00 in the diurnal dynamic. 2) At the seasonal scale,at 5 cm depth,R_s was significantly exponentially related with T and negatively linearly related with W ( both P < 0. 01 ) in the two plantations. Moreover,the temperature sensitivity of R_s in H. rhamnoides ( Q_(10) = 1. 40) was significantly ( P < 0. 01) higher than that in the P. tabulaeformis plantation ( Q_(10) = 1. 34) . 3) . At the daily scale,the contribution of T to R_s increased when W exceeded 13% and 12% for P. tabulaeformis and H. rhamnoides,respectively.[Conculsions]The results indicate that the response of R_s to T is mainly affected by W in this region. Therefore,to ensure accuracy of the carbon balance budget and improve the regional carbon cycle model for the loess hilly region under conditions of climate change,we should fully consider the effects of T and W on R_s and strengthen observations of soil respiration in winter in future research.