放牧对呼伦贝尔草地植物和土壤生态化学计量学特征的影响

放牧通过畜体采食、践踏和排泄物归还影响草地群落组成、植物形态和土壤养分,植物通过改变养分利用策略适应环境变化。通过分析呼伦贝尔草原放牧和围封样地中的群落植物和土壤的碳氮磷养分及化学计量比,探讨放牧对生态系统化学计量学特征和养分循环速率的影响机制。结果如下:(1)群落尺度上,放牧和围封草地植物叶片C、N和P的含量没有显著差异;但是在种群尺度上,放牧草地植物叶片N含量显著高于围封草地;(2)放牧草地土壤全C、全N、有机C、速效P含量,低于围封草地,硝态N含量高于围封草地;土壤全P和铵态N指标没有显著差异;(3)放牧草地植物C∶N比显著低于围封草地,植物残体分解速率较快,提高了生态系统养分循环速率。

Grazing effects on eco-stoichiometry of plant and soil in Hulunbeir, Inner Mogolia

The grassland in Inner Mongolia, one of the largest remaining grassland ecosystems in the world, is extensive and covers an area of up to 68% of the entire region. Recently, with the increasing needs of livestock products, the ecological function of the grassland is severely degraded by overgrazing. The effect of grazing has become an urgent and crucial issue in the study of grassland ecology. The early researches mainly focused on the effects of grazing on the productivity, community structure and biodiversity of the grasslands through the browsing, trampling around and excretion of livestock. Focusing on C4 soil or plants, only a few studies have considered the effects of grazing on the stoichiometry traits of soil and plants. The mechanism by which grazing affects the stoichiometry traits of soil and plants is far from clear. For this issue, we carried out a study considering the role of grazing on the stoichiometry traits of soil and plant at both population and community scales. We determined the C, N, P content and the C/N ratios of plant and soil to explore how grazing affects the stoichiometry traits and nutrient cycling rates in an ecosystem. We found that: (1) On community scale, C, N, P content of the leaves had no-significant difference between the grazed and the exclosure grassland; however, on species scale, the N content in the grazed grassland was significantly higher than that in the exclosure.(2) Grazing significantly decreased soil total carbon(TC), total nitrogen(TN), soil organic carbon(SOC) and available phosphorus, increased the nitrate nitrogen, with no effects on total phosphorus (TP) and ammonium nitrogen.(3) The C/N ratio of the plant in grazed grassland was significantly lower than that in the exclosure, suggesting higher decomposition rate of litter and quicker nutrient cycling rate of the ecosystem. In conclusion, our study indicates that plants can adapt to varied environments caused by grazing through choosing suitable strategies of nutrient using.