土地利用方式对白浆土氧化甲烷的影响

Effects of land-use on methane oxidation potential in lessive

白浆土在不同土地利用方式下CH4氧化潜力存在显著差异。天然草甸表层土氧化大气CH4的潜力最大,如果被开垦成人工林、旱田和水田,则氧化潜力分别降低64%、98%和117%。土壤透气性下降,甲烷氧化细菌数量减少以及活性降低,可能是土地利用方式改变后白浆土氧化CH4潜力下降的主要原因。白浆土氧化大气CH4潜力具有明显的垂直分异:草甸和林地土壤氧化大气CH4的潜力随着土壤深度的增加而减小;旱田土壤中耕作层下残存的有机质含量较高的层次仍保留了较强的氧化大气CH4潜力,氧化CH4速率是耕作层的13倍;即使是在大气中培养,水田土壤整个剖面仍排放CH4,最低层CH4排放率最小。供试白浆土氧化大气CH4速率与土壤有机碳、碱解氮和全氮含量显著正相关,与pH和土壤含水量(%WHC)负相关。在一定的温度和水分条件下,土壤有机碳含量是决定白浆土氧化大气CH4速率的一个最重要因素。

Changes in land-use may affect the potential of soils to act as a sink for CH4. Samples of lessive, one of the most important soil types in the Sanjiang Plain （45°01＇-48°28＇N, 130°13＇- 135°05＇E, the largest fresh water wetland area in China）, were incubated to investigate the effect of land-use change on methane oxidation in lessive. Significant differences between CH4 oxidation rates of all topsoils were found under different land-uses. The highest CH4 oxidation rate was found in natural meadow （dominated by Calamagrostisangustifolia） topsoil, but man-made [arch （Larix gmelini） woodland, dry land （wheat or soybean）, and paddy field soils reduced CH4 uptake by 64%, 98% and 117%, respectively, compared with meadow soil. After the natural meadow was reclaimed, the soil water content （percentage WHC） changed, and the soil organic material decreased. So, the diffusiveness of CH4 and Oz into the soil was reduced and the number and activity of methanotrophic bateria was inhibited. These may be the main reasons for the decrease of methane oxidation in lessives after land-use change. Atmospheric CH4 oxidation activity under all four land uses showed a distinct vertical stratification within the soil profiles. Potential CH4 oxidation rates apparently decreased with the depth in meadow soil and woodland soil, indicating a surface maximum for CH4 oxidation capacity in these soils; the methane uptake rate of the buried organic layer in the dry land soil was 13 times higher than that of the plowed layer. The net productivity of methane was observed in samples of all layers of paddy soil incubated under air, indicating that they had no ability to oxidize atmospheric CH4. Correlation analyses of methane oxidation in lessives and physico-chemieal soil parameters yielded significant correlations for the concentrations of organic carbon （r= 0.78, p〈 0.01）, available N （r= 0.71, p〈 0.01） and total N （r= 0.69, p〈 0. 01）, but negative relationships between CH4 uptake rates and pH （r= 0. 69, p〈 0.01） or water content （percentage WHC） （r=0. 60, p〈 0.05） were observed. Linear regression analysis revealed that an individual chemical parameter, soil organic carbon, could be singled out as an indicator for methane oxidation capacity in lessives under certain temperature conditions.