呼伦贝尔草原土壤养分及生物学特性对氮沉降的响应

针对在我国开展的草地生态系统氮沉降的研究主要集中在内蒙古温带草原,以及氮沉降模拟与真实的氮沉降输入存在较大差异这些问题,本研究于2014年在内蒙古呼伦贝尔草原设置双因素模拟氮沉降试验平台,包括普通尿素与缓释尿素两种氮沉降模拟方式和8个氮沉降水平(0、25、50、75、100、150、200与300 kg N·hm^-2·a^-1),试验开展3年后,于地上植被生长旺盛时期(2016年8月)采集土壤样品,考察土壤养分及生物学特性对不同氮沉降模拟方式及氮沉降水平的响应.结果表明: 氮沉降对呼伦贝尔草原土壤化学性质、生物学性质和酶活性均产生了显著影响.随着氮沉降水平的增加,土壤pH最高下降约0.2个单位,可溶性全氮(TDN)最高增长5～7倍,可溶性有机碳(DOC)增加了12%～36%,土壤全磷含量出现了降低的趋势;微生物量和代谢活性先增加后降低;与土壤碳氮磷转化相关的酶活性在中等氮沉降水平下显著增加.相对于普通尿素,缓释尿素模拟氮沉降减缓了土壤pH下降与可溶性养分增加的程度;使微生物量和代谢活性,以及与氮转化相关的酶活性的变化趋势相对平缓.该区域研究结果印证了氮持续输入造成土壤pH下降、生物有效性养分增加,从而对微生物量与活性、酶活性产生影响的结果.

Responses of soil nutrients and biological characteristics to nitrogen deposition in Hulun Buir Grassland,China

Studies on effects of nitrogen deposition were mainly focused on temperate grasslands in Inner Mongolia of China. In addition, there are substantial differences between the present simulation methods and the natural nitrogen deposition. A three-year experiment was carried out to compare the effects of simulation methods (common urea and slow-released urea) and nitrogen deposition rates (0, 25, 50, 75, 100, 150, 200 and 300 kg N·hm^-2·a^-1) on soil nutrients and biological characteristics in Hulun Buir Grassland. We found that simulated nitrogen deposition had significant influences on soil chemical properties, biological properties and enzyme activities. With the increases of nitrogen deposition, soil pH declined with the greatest extent of 0.2 units, while the highest concentrations of total dissolved nitrogen (TDN) and dissolved organic carbon (DOC) increased by 5-7 times and 12%-36%, respectively. There was a decline trend for soil total phosphorus (TP) and organic phosphorus (TOP). Microbial biomass and metabolic activity increased firstly and then decreased. Moderate simulated nitrogen deposition rates significantly increased soil carbon, nitrogen and phosphorus related enzyme activities. Compared to common urea, using slow-released urea to simulate nitrogen deposition decelerate the decline of soil pH and the increase of dissolved nutrients, and smoothed the change of microbial biomass, metabolic activity, and nitrogen hydrolyzed enzyme activities. Overall, the results confirmed that continuous nitrogen input caused the decline of soil pH and the increase of bioavailable carbon and nitrogen, and then changed microbial biomass and activity.