内蒙古克氏针茅草原土壤异养呼吸对土壤温度和水分变化的响应

Responses of soil heterotrophic respiration to changes in soil temperature and moisture in a Stipa krylovii grassland in Nei Mongol

土壤异养呼吸在野外自然条件下除受温湿度影响外,还受其他多种因子的综合影响,很难利用野外观测数据确定土壤异养呼吸对温湿度变化的响应方程形式,以及温湿度间是否存在交互作用。该研究在严格控制温湿度的条件下对内蒙古克氏针茅(Stipa krylovii)(西北针茅(Stipa sareptana var.krylovii))草原土样进行室内培养实验,旨在解决上述问题。该研究的正交实验包括5个温度梯度(9、14、22、30、40℃)和5个湿度梯度(土壤持水力(water holding capacity,WHC)分别为20%、40%、60%、80%、100%)。室内培养实验持续71天,土壤异养呼吸速率测定为2天(后期为1周)一次,土壤可溶性有机碳和微生物生物量碳含量测定约为18天一次。研究结果显示:土壤异养呼吸与温度呈显著正相关(p<0.001)且温度间差异显著(p=0.001),呼吸温度敏感性(Q10)与土壤水分含量呈正相关(p<0.001);呼吸与土壤水分二项式拟合效果较好,在80%WHC时呼吸速率最大,且最适湿度随温度上升而增加。土壤温度和水分的交互作用显著(p<0.05),土壤异养呼吸最适响应方程为lnRh=0.914+0.098T+0.046M+0.001TM–0.002T2–0.001M2(Rh为异养呼吸,T为温度,M为湿度),这说明加和形式的温湿度响应模型可能优于乘积形式。微生物生物量碳与土壤异养呼吸的相关性随培养时间发生变化,土壤可溶性有机碳与土壤异养呼吸无显著相关(培养第20天除外),原因可能是培养期间微生物死亡或群落结构改变导致微生物总体代谢活性的变化。

Aims Due to concurrent variations of multiple factors influencing soil heterotrophic respiration （Rh）, it is difficult to determine the responses of Rh to changes in individual factors and their interactive effects under field conditions. In this study, we conducted a laboratory incubation experiment with controlled temperature and water levels to determine the responses of Rh to changes in soil temperature and moisture using soil samples collected from an Stipa krylovii （Stipa sareptana var. krylovii） grassland in Nei Mongol. Methods The incubation experiment consisted of five temperature treatments （9, 14, 22, 30, and 40℃） and five water treatments （20%, 40%, 60%, 80%, and 100% of water holding capacity （WHC））, with a full factorial arrangement. We measured Rh at an interval varying from every two days to once a week, and soil dissolved organic carbon （DOC） and microbial biomass carbon （MBC） at an 18-day interval during the 71 days of incubation period. lmportantfindings The results showed that Rh differed significantly among different temperature treatments （p 〈 0.001） and was positively related to temperature （p = 0.001）; the temperature sensitivity of Rh （Q10） also increased with increasing moisture level. The relationship between Rh and water was best fitted using quadratic equations, and the optimal moisture condition increased when temperature rose. There existed significant interactions between soil temperature and moisture （p 〈 0.001） and their interactions could be best fitted using the function InRh = 0.914 ＋ 0.098T ＋ 0.046M＋ 0.001TM- 0.002T2 - 0.001M2, it suggested that the models in additive form could explain the Rh response better than those in multiple form. Our results also showed that the relationship between Rh and MBC varied during incubation, and DOC was not significantly related to Rh （except for the 20th incubation day）, suggesting that microbial turnover and community transformation could lead to the changes of gross microbial activity.