塔克拉玛干沙漠南缘荒漠绿洲过渡带不同土地利用影响下土壤化学计量特征

荒漠绿洲过渡带在维护绿洲生态安全和绿洲稳定上具有重要作用。垦荒等土地利用的增强使得荒漠绿洲过渡带的健康稳定受到了巨大的挑战。以塔克拉玛干沙漠南缘典型荒漠绿洲过渡带为研究对象,系统分析了不同土地利用方式(桑田、半自然柽柳林、瓜地、棉花-玉米地)对土壤养分化学计量特征的影响。土壤取样沿农田到荒漠方向进行,分5层进行。研究发现,土壤各养分指标均受土地利用方式(4种)、土层(5层)和与农田边缘垂直距离(4梯度)的显著影响,且存在一定的交互作用。土地利用方式显著影响土壤各养分元素含量。随土层由浅到深,有机碳(C)、有效氮(N)和有效磷(P)基本呈下降趋势,全N具有波动变化,而全P变化不显著。随与农田边缘垂直距离的增加,各养分含量基本呈递减趋势。对同一土层(共选择三层)不同土地利用方式下土壤养分具体分析表明,棉花-玉米地这一利用方式在农田内部具有最高的土壤有机C和全N含量,其次为桑田。随着与农田边缘垂直距离的增加,土壤C、N含量优势减弱。除农田内部样地(0 m)外,三层土壤全P含量基本呈桑田柽柳林棉花-玉米地趋势。表层有效N含量在农田内部样地(0 m)瓜地最高,其他距离处(大于等于20 m)棉花-玉米地高,下层土壤有效氮含量在农田内部各土地利用方式间无差异。在各距离样点处不同土地利用类型间土壤有效P含量的变化无明显规律,在农田内部以瓜地有效P含量最高。棉花-玉米地土壤全量N/P在农田内部和与农田边缘垂直距离20 m处含量最高。三土层土壤有效N/P在农田内部以柽柳林最高,随着与农田边缘垂直距离增加,土壤有效N/P显著改变。综合来看,土地利用对荒漠绿洲过渡带土壤营养含量的增加具有正向作用,由土壤养分变化带来的生态效应值得关注。

Soil stoichiometry in different land-use categories in desert-oasis ecotones of the southern Taklimakan Desert

Desert-oasis ecotones play a crucial role in the ecological security and stability of oases. The health and stability of desert-oasis ecotones are continuously challenged by increasing land use intensity, particularly the conversion of desert to farmland. Typical desert-oasis ecotones of the southern Taklimakan Desert were selected to study changes in soil nutrients in response to different types of land use:mulberry fields; Tamarix forests; melon fields; and cotton-corn fields. Plots were established along transects set out from farmland across the ecotones into the desert, and five soil depths were analyzed. All nutrient indexes were significantly affected by the type of land use, soil depth, and distance from farmland. Soil organic carbon (C), available nitrogen (N) and phosphorus (P) generally decreased with increasing soil depth. No trend was observed for total N, and total P did not vary significantly with increasing soil depth. Most nutrient concentrations decreased with increasing distance from farmlands. In exploring soil nutrients at three different depths in different land use types, we found that soil organic C and total N were the highest in cotton-corn fields, followed by mulberry fields. Organic C and total N decreased with increasing distance from farmland. With the exception of plots located within farmland (0 m), all plots along the transects from all three depths showed a total P trend as follows:mulberry field > Tamarix forest > cotton-corn field. In the farmland plots, soil available N from the uppermost depth was the highest in melon field plots, whereas topsoil available N at all other points along the transect was the highest in cotton-corn fields (>=20 m). Soil available N from lower soil depths did not differ significantly among land use types at any distance along the transect. Despite trends in total P, there were no trends in soil available P from plots at different distances from farmland. However, available P did vary with land use types, with the highest value recorded for farmland melon field plots. For cotton-corn field plots, soil total N/P ratios were the highest in farmlands and in the adjacent to farmland (20 m distance) plots. The highest available N/P ratios were found in farmland plots of Tamarix forest. Soil available N/P ratios changed significantly with increased distance from farmland. These results indicate that land use activity, specifically farming, can result in positive effects on soil nutrient levels. Further research should be conducted on the ecological effects of soil nutrient variations in desert-oasis ecotones.