青藏高原泥炭地水位下降促进土壤碳积累的影响机制

Abstract

酚类物质作为泥炭地重要的碳分解抑制剂, 植被作为泥炭地关键的碳输入来源, 它们在土壤碳(可溶性有机碳(DOC)等)周转过程中都发挥着重要作用。然而, 目前关于植被群落结构、酚类物质以及DOC含量对水位波动的响应存在较大争议。因此, 为明确泥炭地水位下降对植被群落结构、酚类物质以及DOC含量的影响并探明三者间的潜在联系, 以若尔盖高原泥炭地作为研究对象, 选取红原县日干乔地区3处不同地下水位泥炭地(水位由高到低依次为S1(-1.9 cm)、S2(-10 cm)、S3(-19 cm)样地), 调查不同水位条件下植被群落结构特征, 并探究酚类物质及土壤碳含量对水位波动的响应。结果表明：(1)从S1到S3样地水位下降促进土壤DOC显著增加(P < 0.05), 土壤总碳从S1到S2显著增加(P < 0.05), 而从S2到S3无显著差异；(2)泥炭地水位下降促使禾本科(发草Deschampsia cespitosa)、莎草科(木里薹草Carex muliensis、乌拉草Carex meyeriana)植物大量出现, 植被群落高度显著增加(P < 0.05)。植被群落地上生物量由153.67 g/m²增加至649.22 g/m², 地下生物量由1067.52 g/m²增加至3424.78 g/m², 植物体地上地下部总酚分别增加34.58%和13.17%(P < 0.05)。这将有可能促进植物输入更多碳进入土壤系统；(3)随水位下降, 土壤总酚、水溶性酚以及多元酚分别增加29.06%、542.87%和110.56%(P < 0.05)。一元酚呈先增加后减少, 但总体仍表现为增加, 二元酚无明显变化；(4)结构方程模型分析发现, 一元酚和多元酚能显著促进DOC和总碳积累(P < 0.05), 二元酚对DOC和总碳的积累影响不显著。以往的研究认为水位下降会加速碳流失, 但本研究发现这样的流失似乎被植物以及酚酸的作用所抵消。故此, 对泥炭地碳循环的研究应关注土壤－植物整个系统并考虑土壤中酚类物质的影响。;Phenolic substances, as important carbon decomposition inhibitors in peatlands, and vegetation, as a key carbon input source in peatlands, play an important role in soil carbon (Dissolved organic carbon (DOC)) cycle. However, the response of vegetation community structure, phenolic substances and DOC content to water level fluctuations has been controversial. Therefore, in order to elucidate the effects of water table drawdown on vegetation community structure, phenolic substances and DOC content, and explore the potential relationship among them in peatland. Taking the Zoige Plateau peatland as the research object, three peatlands with different groundwater levels in Riganqiao of Hongyuan County were selected (The order of water table from high to low: S1 (-1.9 cm), S2 (-10 cm), S3 (-19 cm) sample plot). To explore the characteristics of vegetation community structure under different water tables and to explore the response of phenolic substances and soil carbon content to water table fluctuations. The results showed that: (1) The decrease of water table from S1 to S3 promoted the soil DOC to increase significantly (P < 0.05), and soil total carbon was significantly increased from S1 to S2 (P < 0.05), but had no significant difference from S2 to S3.; (2) The decrease of water table in peatland has led to the emergence of large amounts of Gramineae (Deschampsia cespitosa) and Cyperaceae (Carex muliensis and Carex meyeriana), and the height of vegetation community was significantly increased (P < 0.05). Aboveground biomass increased from 153.67 g/m² to 649.22 g/m² (P < 0.05), and underground biomass increased from 1067.52 g/m² to 3424.78 g/m² (P < 0.05). Total phenols in aboveground and underground parts of plants increased by 34.58% and 13.17%, respectively (P < 0.05). And this may promoted more plant carbon to enter the soil system. (3) With the decrease of water table, soil total phenols, water-soluble phenols and polyphenols increased by 29.06%, 542.87% and 110.56%, respectively (P < 0.05). The content of monophenol first increased and then decreased, but the overall content still showed an increasing trend, and the change of diphenol content was not obvious; (4) Structural equation model analysis shows that monophenol and polyphenols can significantly promote DOC and total carbon accumulation (P < 0.05), while diphenol had no significant effects on soil DOC and total carbon accumulation. Previous studies have shown that falling water table accelerate carbon losses, but this study found that this loss appears to be offset by the effects of plants and phenolic acids. Therefore, the study of carbon cycle in peatland should focus on the whole soil-plant system and consider the effect of phenolic substances in soil.