小流域土壤有机碳的分布和积累及土壤水分的影响

Soil Organic Carbon Accumulation and Distribution in a Small Watershed and the Effects of Soil Water

地形和土地利用决定的土壤水分和土壤有机碳(Soil Organic Carbon,SOC)的空间分布格局为研究水碳关系提供了重要的线索,但土壤水分的强变异性和SOC的相对稳定性对土壤水碳关系的研究提出了挑战。研究基于陆地水量平衡角度,选择雨季后土壤水分恢复期在晋西黄土丘陵小流域尺度进行了重复采样,按照3种地貌类型(沟底、沟坡、峁坡)和3种土地利用方式(农地、林地、草地)共布置37个样点,采集0～100 cm土壤样品测定土壤水分和SOC,探讨土壤水分与SOC分布特征及其相互关系。结果表明:同一土地利用方式下,土壤水分和SOC总体上沟底>沟坡>峁坡;同一地貌类型下,土壤水分农地>草地>林地,SOC农地<草地<林地。SOC与土壤水分呈现正相关关系,二者符合指数增长(y=y0+log a×ax,y为SOC,x为土壤水分)关系,因地貌部位和土地利用方式的不同决定系数在7%～37%之间变化。这一结果为基于土壤水分变化预测SOC积累和分布提供了参考。

The spatial distribution patterns of soil water and Soil Organic Carbon（SOC） caused by topography and land use provide opportunities to study the coupling of water and carbon of the ter restrial ecosystem. It can help us better understand the contribution of soil water to SOC accumu lation and distribution at a watershed scale, but the strong variability of soil water and relative sta bility of SOC bring new challenges for the work. Thereafter, a resampling approach was used to assess soil water and SOC after rainy season based on the continental water balance. Totally 37 plots covering three different landfornls and three different land uses were sampled 100 cm below surface soil using a 3 cm diameter auger. When compared under the same land use, generally soil water and SOC of valley bottom was higher than ridge slope, while gully slope was intermediate; but the water carbon transferring efficiency presented an inverse order. Under the same land form, soil water and SOC of different land uses had the opposite order, when farmland owned the highest water content, its SOC was the lowest; the same occurred at grassland and woodland. Both the woodland and grassland could transfer water to carbon faster compared to farmland. ／ There was a positive relationship fitted well by an exponential growth model （y = Y0 ＋ log a x ax ） between SOC and soil water. Soil water could partially （7% 37% ） explain SOC accumulation and distribution in the small watershed. This would be very crucial for the prediction of SOC ac cumulation and distribution based on soil water variability.