贡嘎山树线过渡带土壤有机碳矿化和温度敏感性

Soil organic carbon mineralization and its temperature sensitivity of the alpine treeline ecotone in the Gongga Mountain,China

树线过渡带作为高山地区重要的生态过渡带之一,是响应温度变化的敏感区域。树线过渡带内土壤碳储量丰富,其碳周转在全球碳循环方面扮演着重要角色。探究树线过渡带土壤有机碳矿化及其温度敏感性,对于预测气候变化背景下高山地区土壤碳循环过程具有重要的指导意义。为此以青藏高原东南部贡嘎山树线过渡带(森林、树线、灌丛)的土壤为对象,在室内开展90 d不同温度(15℃和20℃)的培养实验,测定土壤有机碳矿化速率,计算单位土壤有机碳累积矿化量、温度敏感性,并分析影响它们的相关因素。结果表明:土壤有机碳矿化速率受温度和样地类型的显著影响。升温显著增加土壤有机碳矿化速率,而不同样地类型间矿化速率差异显著,矿化速率大小表现为森林>树线>灌丛。本研究用单位土壤有机碳累积矿化量表征土壤有机碳的稳定性,经90 d的培养,15℃下树线过渡带从森林、树线到灌丛单位土壤有机碳累积矿化量分别为12.33 mg/g、12.99 mg/g和10.53 mg/g,20℃下则分别为19.16 mg/g、21.14 mg/g和16.26 mg/g,灌丛土壤单位土壤有机碳累积矿化量显著低于森林和树线土壤,这表明灌丛土壤具备更高的稳定性。单位土壤有机碳累积矿化量与土壤颗粒有机碳占比呈显著正相关关系,与土壤矿物结合有机碳占比呈显著负相关,但与酸解性碳组分无显著相关关系,说明土壤有机碳与矿物结合形成的化学保护作用显著影响贡嘎山树线过渡带土壤有机碳稳定性。树线过渡带土壤有机碳矿化的温度敏感性系数Q_(10)为2.45±0.25,表现出较高的温度敏感性。相关性分析结果表明土壤pH值和C:N是影响树线过渡带土壤温度敏感性大小的主要因素,而树线过渡带内相似的土壤pH值和C:N可能是导致不同样地类型间Q_(10)值无显著差异的重要原因。

As one of the important ecological ecotones in alpine regions,the treeline ecotone is a sensitive area in response to climate change.Soil carbon stock is abundant within the treeline ecotone and its carbon turnover plays an important role in the global carbon cycle.Exploring soil organic carbon mineralization and its temperature sensitivity in the treeline ecotone is important for predicting soil carbon cycling processes in alpine regions under the background of climate change.In this study,we performed an incubation experiment at different temperatures(15℃and 20℃)for 90 days based on soils from the treeline ecotone(forest,treeline,shrub)in the Gongga Mountain on southeastern Qinghai-Tibet Plateau.Soil organic carbon mineralization rates were measured,cumulative mineralization per unit of soil organic carbon and temperature sensitivity were calculated.At the same time,we analyzed the relevant factors affecting them.The results showed that the soil organic carbon mineralization rates were significantly influenced by temperature and vegetation types.Warming significantly increased soil organic carbon mineralization rates,while the mineralization rates also had significant differences among vegetation types,the values showed that forest>treeline>shrub.We used the cumulative mineralization per unit of soil organic carbon to characterize the soil organic carbon stability.After 90 days of incubation,the cumulative mineralization per unit of soil organic carbon from forest,treeline to shrub was 12.33 mg/g,12.99 mg/g,and 10.53 mg/g at 15℃,while 19.16 mg/g,21.14 mg/g,and 16.14 mg/g at 20℃,respectively.The values for shrub soils were significantly lower than forest and treeline soils,indicating that shrub soils had higher stability.The cumulative mineralization per unit of soil organic carbon was significantly positively correlated with the percentage of particulate organic carbon and negatively correlated with the percentage of mineral-bound organic carbon,but had no significant correlation with acid hydrolysable carbon fractions,indicating that the chemical protection formed by the combination of soil organic carbon and minerals significantly affected the stability of soil organic carbon in the treeline ecotone in the Gongga Mountain.The temperature sensitivity coefficient Q_(10) of soil organic carbon mineralization in the treeline ecotone was 2.45±0.25,showing a high temperature sensitivity.The results of correlation analysis indicated that soil pH and C:N were the main factors to influence temperature sensitivity,while similar soil pH and C:N within the treeline ecotone might be an important reason for the lack of significant differences in Q_(10) values between different vegetation types.