中国北方温带草原植被恢复的氮限制

Vegetation restoration constrained by nitrogen availability in temperate grasslands in northern China

围栏禁牧被认为是退化草原植被恢复的有效手段。在植被的恢复过程中,植物需要从土壤中吸收更多的氮。氮素也是中国北方温带草原植被生长的一个主要限制因素。目前尚不清楚该地区的土壤氮素供应是否能够支持长期的植被恢复。本研究在植被的生长季期间对我国北方7个温带草原进行了野外调查。其中,围栏外侧草地保持持续放牧状态,围栏内侧草地保持完全禁牧状态。研究结果表明,禁牧显著提高了草地地上生物量、物种丰富度和香农-维纳多样性指数,其分别提高了126.2%、42.6%和18.8%。禁牧使土壤硝态氮和总无机氮浓度分别降低了51.9%和21.0%,这表明生长季氮素供应与植物需求可能存在错配现象。同时,围封草地地上生物量、物种丰富度和香农-维纳多样性指数与豆科植物群落优势度呈正相关。这些结果表明,温带草原植被恢复受土壤无机氮限制。群落中豆科植物的生物固氮可能缓解植被恢复的氮限制。

Grazing exclusion using fencing has been considered an effective means of vegetation restoration in degraded grasslands.Increased plant growth during recovery requires more nitrogen(N),which is a major limiting factor in northern China.It remains unclear whether soil N supply in this region can support long-term vegetation restoration.In this study,a field inventory was conducted in seven temperate grasslands in northern China.At each site,grassland outside of the fencing experienced continuous grazing,whereas that within the fencing was protected.Results showed that grazing exclusion significantly increased aboveground biomass,species richness and the Shannon–Wiener diversity index by 126.2%,42.6%and 18.8%,respectively.Grazing exclusion reduced the concentrations of nitrate and total inorganic N by 51.9%and 21.0%,respectively,suggesting that there may be a mismatch between N supply and plant demand during the growing season.The aboveground biomass,species richness and Shannon–Wiener diversity index in the restored grasslands were positively correlated with legume dominance within the community.These results indicate that the vegetation restoration in temperate grasslands could be constrained by soil N availability,which may be supplemented through biological N fixation.