黄土丘陵区油松、沙棘人工林土壤呼吸动态及其对土壤温度和水分的响应

Soil respiration dynamics and its response to soil temperature and water content of Pinus tabulaeformis and Hippophae rhamnoides plantations in the Loess Hilly region

作为陆地生态系统碳通量的重要组成部分,土壤呼吸在维持全球碳循环及碳平衡中具有重要作用。以黄土丘陵区油松、沙棘人工林为研究对象,于2015年6月至2016年5月,采用LI-8100土壤碳通量测量系统,分别观测二者的土壤呼吸(Rs)、5 cm土壤温度(T)和水分(W),分析2种人工林Rs的动态特征及其对T和W的响应。结果表明:1)季节尺度油松、沙棘人工林Rs夏季(6—8月)最高(2.31和2.89μmol CO_2/m^2·s),冬季(12—2月)最低(0.60和0.65μmol CO_2/m^2·s),年均值分别为1.51和1.92μmol CO_2/m^2·s,年呼吸总量分别为18.90和22.81t CO2/hm2·a,冬季呼吸量占年呼吸总量比例分别为14.67%和12.65%;日尺度最高值出现在10:00—16:00,最低值均出现在6:00。2)季节尺度2种林分Rs与T均呈显著指数关系(P<0.01),与W则呈显著线性负相关(P<0.01),且沙棘林全年尺度土壤呼吸Q10值(1.40)显著高于油松林(1.34,P<0.01)。3)日尺度上,油松、沙棘人工林W分别大于13%和12%时,T对Rs的解释量(R2)均有所提高。因此,在充分考虑温度和水分对土壤呼吸影响的同时,加强冬季土壤呼吸的观测,对未来气候变化条件下,区域碳循环估算模型的完善具有重要意义。

[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（ Rs） and its response to the main environmental factors in the dominant plantations in thehilly Loess Plateau region,the Rsof 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 Rsand significant effects of T and W on Rs in the two plantations. In addition,temperature sensitivities of Rswere investigated using the Q10 function at the seasonal scale. [Results] 1） The seasonal dynamic patterns of Rsin P. tabulaeformis and H.rhamnoides plantations were similar,with the respective maxima（ 2. 31 and 2. 89 μmol CO2·m^（-2）·s^（-1））in summer（ June-August） and minima（ 0. 60 and 0. 65 μmol CO2·m^（-2）·s^（-1）） in winter（ DecemberFebruary）; the annual mean Rsin the plantations was 1. 36 μmol CO2·m^（-2）·s^（-1）（ P. tabulaeformis） and1. 64 μmol CO2·m^（-2）·s^（-1）（ H. rhamnoides）,with corresponding annual total Rsemissions of 18. 90 and22. 81 t CO2·hm- 2·a- 1. The Rsemission during winter accounted for 14. 67% and 12. 65% of the annual total emission in P. tabulaeformis and H. rhamnoides,respectively. In addition,the Rsmaxima 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,Rswas significantly exponentially related with T and negatively linearly related with W（ both P〈0. 01） in the two plantations. Moreover,the temperature sensitivity of Rs in H. rhamnoides（ Q10= 1. 40） was significantly（ P〈0. 01） higher than that in the P. tabulaeformis plantation（ Q10= 1. 34）. 3）. At the daily scale,the contribution of T to Rs increased when W exceeded 13% and 12% for P. tabulaeformis and H. rhamnoides,respectively.[Conculsions]The results indicate that the response of Rsto 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 Rsand strengthen observations of soil respiration in winter in future research.