College of Life Sciences, Nankai University, Tianjin, 300071, China.
State Environmental Protection Key Laboratory of Regional Eco-process and Function Assessment, State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing, 100012, China.
Sci Rep. 2017 Mar 27;7:44525. doi: 10.1038/srep44525.
Enclosures (fenced, grazing or clipping) within a certain period of years are the most common tools for restoration of degraded grasslands in temperate regions. Short-term enclosures can improve biodiversity and productivity by effectively relieving grazing pressure, while long-term enclosures can reduce species diversity. We therefore carried out a field experiment to investigate the specific causes of the reduced species diversity in Hulunbeier grassland of northern China. After eight years of enclosure, the significantly increased soil available nitrogen (AN) and available phosphorus (AvP) in enclosure community reduced nitrogen (N) limitation but most vegetation was still N limited. Many environmental factors led to decreased species richness, but increased soil AN and decreased light intensity at the community bottom were the most significant ones. Community density decreased independently of soil nutrition but significantly related to decreased species richness. Density of dominant canopy species increased, while dominant understory species decreased during assemblage-level thinning; therefore, the random-loss hypothesis was not supported. The dominant understory species responded to lower light availability by increasing their height, leaf area, and chlorophyll content. Moreover, our results were expected to provide some specific guidance for the restoration mode selection of degraded grasslands in northern China.
在温带地区，围封（围栏、放牧或刈割）是恢复退化草地最常用的工具之一。短期围封可以通过有效缓解放牧压力来提高生物多样性和生产力，而长期围封会降低物种多样性。因此，我们进行了一项野外实验，以调查中国北方呼伦贝尔草原物种多样性降低的具体原因。经过八年的围封，围封群落中土壤有效氮（AN）和有效磷（AvP）的显著增加减轻了氮（N）限制，但大多数植被仍受到 N 限制。许多环境因素导致物种丰富度降低，但增加的土壤 AN 和群落底部降低的光强度是最显著的因素。群落密度独立于土壤养分而减少，但与物种丰富度的减少显著相关。优势冠层物种的密度增加，而在组装级别的稀疏化过程中，优势林下物种减少；因此，随机损失假说不成立。林下优势物种通过增加其高度、叶面积和叶绿素含量来应对较低的光照条件。此外，我们的结果有望为中国北方退化草地的恢复模式选择提供一些具体指导。
