东北黑土农田侵蚀沟的氮磷“源-汇”功能机制

Gullies as the popular landscape elements are broadly distributed in Mollisols field. They are the main channels for soil and water transportation, and highly connected to under- and above- ground water. Nitrogen (N) and Phosphorus(P) condensed in the gullies are the sink or source to the environment, and correlate to the health of agroecosystem and the security of the environment, however, the mechanism of gullies on source and sink functions is poorly understood. In this study, gullies in landscape field are focused on, and the methods of field investigation, fixed point observation, laboratory simulation and incubation, and model building are included. Geostatistics and traditional statistics combining with penetration theory, hierarchy theory, landscape indexes and location-weighted landscape contrast index are also used to analyze the distribution of N and P at watershed, sub-watershed and intra-gully scale, respectively. The project is mainly focused on: (1) the functions of sink and source and its driving mechanisms of gullies for the N and P at the three scales; (2) the functions of sink and source and its driving mechanisms among the kind types of gullies for the N and P coming from the up slope during crop growing season and freezing-thawing season; (3) the influencing of the N and P condensed in gullies on the recovery of ecosystem, biodiversity, gas releasing, and quality of the water above- and under- ground. The results of the study is beneficial to understand of the mechanism of sink and source function, landscape process of agricultural field, and can provide the reference for gully controlling, planning, development and utilization.

侵蚀沟是东北黑土农田中常见的景观要素，是水土流失的重要通道，与地表水和地下水紧密相连，其对农田土壤氮磷的“源-汇”作用直接关系到农业生态系统健康和环境质量安全，但有关侵蚀沟对土壤氮磷的“源-汇”作用解析还缺乏报道。本项目采用野外调查、定点观测、室内模拟和建模的方法，借助等级理论和渗透理论，结合经典统计学、地统计学、景观指数和景观负荷空间对比指数等，从流域侵蚀沟网、子流域侵蚀沟和侵蚀沟内3个尺度重点开展：（1）不同时空尺度下侵蚀沟对氮磷的“源-汇”功能作用机制；（2）作物生长季和冻融期不同类型侵蚀沟对坡面氮磷的“源-汇”功能作用机制；（3）侵蚀沟截留的氮磷对侵蚀沟内生态恢复、生物多样性、温室气体排放的影响，以及对河流、地下水安全的潜在威胁。项目预期结果有助于深入认识侵蚀沟的“源-汇”功能机制和农田景观生态过程，可为侵蚀沟的综合治理、规划、开发和利用等提供理论依据和技术支撑。

侵蚀沟是东北黑土农田中常见的景观要素，其对农田土壤氮磷（N、P）的“源-汇”作用直接关系到农业生态系统健康和环境质量，但有关侵蚀沟对土壤N、P的“源-汇”作用解析还缺乏报道。项目采用野外调查结合室内模拟的方法，重点研究了典型黑土区（1）侵蚀沟对土壤N、P的“源-汇”作用机制，（2）N、P对侵蚀沟植被恢复的影响机制。研究发现：.（1）黑土耕地景观中，不同类型侵蚀沟对土壤N、P的“源汇”作用不同，且随季节变化，主要受耕地作物生长和侵蚀沟植被恢复过程中施肥、侵蚀、淋溶等因素程影响。空间上，稳定型侵蚀沟沟底表土层（0-20 cm）通常对N表现汇作用（3.6-41.3%）；沉积区对表土层P起到汇作用（22.4-140.3%），深土层（20-100 cm）对N表现出汇作用（21.0-233.1%）。发展型侵蚀沟表土层对P表现出汇作用（8.7-43.9%），沉积区深土层是N的汇。时间上，稳定型侵蚀沟沟底与沉积区表土层N随季节变化降低（4.7-30.1%）；侵蚀沟内土壤P先降低后升高，沉积区土壤P逐渐升高。冻融后不同类型侵蚀沟土壤N、P均下降，沉积区下降幅度最大（N 23.2%，P 275%），相当于“源”的作用。.（2）侵蚀沟沟壁侵蚀是沟底N、P的源，发生沟壁侵蚀的坡度和频度均为沟中>沟头>沟尾；发展型侵蚀沟沟壁侵蚀从上到下受壁上径流影响增大，而稳定型侵蚀沟相反。植被覆盖对沟壁侵蚀影响最大，然后为壁上径流和坡度；沟壁侵蚀临界坡度与坡向有关，临界覆盖度与侵蚀沟类型有关，沟中段沟壁中部乔木加速沟壁侵蚀。沟壁冻融侵蚀主要多生在早期（约80%），主要受融雪径流的影响，发展型侵蚀沟的侵蚀模数约是稳定型侵蚀沟的7.3-9.8倍。.（3）水分、有机质和N是影响侵蚀沟植被恢复关键因子。N能显著增加草本植物的地上生物量，其中非禾本科植物生物量对N添加响应更敏感；N显著降低了植物群落的生物多样性，增加披碱草（Elymus dahuricus）多度。N、P对植物群落生物量和多样性存在交互作用。增施N对黑土农田侵蚀沟植被恢复有重要的促进作用，增施P肥可加快N影响下植被恢复的速度。