放牧强度对高寒草甸土壤理化性状和植物功能群的影响

为明晰放牧强度对植物功能群落的物种分布特征和土壤理化性状的影响。在青藏高原东北缘高寒草甸设置6块放牧强度样地开展试验。采用多元排序和方差分解等方法,分析放牧强度作用下植物功能群落物种分布与土壤物理结构和化学养分因子的定量关系。结果表明:(1)随放牧强度增加,禾本科、莎草科和多年生杂类草植物群落的物种丰富度、盖度和实际重要值均显著降低,而一年生杂类草无显著变化。(2)对于土壤化学养分,不同放牧强度区,土壤速效钾、全氮和有机质含量均随土层深度的增加而降低,土壤速效磷在不同放牧强度区变化规律不一致。随放牧强度增加,土壤速效钾和全氮含量增加,而土壤速效磷和有机质含量无明显变化。(3)对于土壤物理性状,不同放牧强度区,随土层深度增加,土壤紧实度和容重均增加,而土壤含水量和通气孔隙度均降低。随放牧强度增加,0—30 cm各土层深度的土壤紧实度和容重均增加,土壤含水量和通气孔隙度均降低。(4)以功能群为基本单元对植物群落进行方差分解得出,土壤物理性状可单独解释群落功能群分布总方差的58.10%。(5)基于物种尺度对不同功能群落与环境因子进行定量研究表明,土壤紧实度是决定每种功能群物种分布格局的最主要因子。禾本科、莎草科和多年生草本植物均受土壤物理性状的显著影响,贡献率分别为26.3%、31.0%和16.5%。而一年生草本植物不受土壤物理和化学性状的显著影响。综上所述,放牧强度对土壤化学性状的影响具有不确定性,而对土壤物理性状和群落特征的影响具有确定性。土壤物理结构性状主导了高寒草甸植物功能群落的物种分布格局。

Effects of grazing disturbance on soil properties and plant functional groups and their relationships in an alpine meadow on the Tibetan Plateau, China

Our goal was to understand the effect of grazing intensities on the characteristics of plant species distribution in functional communities and soil physical and chemical properties. This study consisted of a controlled grazing trail with six grazing intensities on an alpine meadow located in the northeastern Qinghai-Tibetan Plateau. We used multivariate analysis and the variance decomposition method and studied the quantitative relationships between plant species distribution of plant functional groups and soil physical and chemical properties. The results showed that:(1) The richness, coverage, and real importance value of plant species in Gramineae, sedge, and perennial herb communities significantly decreased with increasing grazing intensity, whereas annual forbs exhibited no significant change. (2) For soil chemical properties, the soil available K, total N, and organic C contents decreased with soil depth and increased in plots with different grazing intensity, although soil available P changed inconsistently in different grazing intensity plots. With the increase of grazing intensity, the soil available P and total N content increased, whereas soil available P and organic C content did not change significantly. (3) For soil physical properties, the soil compaction and bulk density increased with soil depth and increased with grazing intensity in different plots, whereas the soil moisture and ventilation porosity decreased. With the increase in grazing intensity, the soil compaction and bulk density increased at 0-30 cm depth, and soil moisture and ventilation porosity decreased. (4) Based on the variance decomposition of plant communities obtained using plant functional groups as the basic unit, the soil physical properties could explain 58.10% of the total variance of plant functional group distribution. (5) Quantitative multivariate analysis between different functional groups and soil factors based on plant species scales indicated that soil compaction was the most important factor determining the distribution pattern of each functional group. The distribution of Gramineae, sedges, and perennial herb plants were influenced by soil physical properties, and the contribution rates were 26.3%, 31.0%, and 16.5%, respectively. However, the annual herbaceous plants were not significantly affected by soil physical and chemical properties. In conclusion, the effect of grazing intensity on soil chemical properties was uncertain, but the effect on plant community characteristics and soil physical properties was certain. Soil physical properties dominated the species distribution pattern of functional groups in the alpine meadow.