Alpine grassland of the Tibetan Plateau has undergone severe degradation, even desertification. However, several questions remain to be answered, especially the response mechanisms of vegetation biomass to soil properties. In this study, an experiment on degradation gradients was conducted in an alpine meadow at the Zoige Plateau in 2017. Both vegetation characteristics and soil properties were observed during the peak season of plant growth. The classification and regression tree model (CART) and structural equation modelling (SEM) were applied to screen the main factors that govern the vegetation dynamics and explore the interaction of these screened factors. Both aboveground biomass (AGB) and belowground biomass (BGB) experienced a remarkable decrease along the degradation gradients. All soil properties experienced significant variations along the degradation gradients at the 0.05 significance level. Soil physical and chemical properties explained 54.78% of the variation in vegetation biomass along the degradation gradients. AGB was mainly influenced by soil water content (SWC), soil bulk density (SBD), soil organic carbon (SOC), soil total nitrogen (STN), and pH. Soil available nitrogen (SAN), SOC and pH, had significant influence on BGB. Most soil properties had positive effects on AGB and BGB, while SBD and pH had a slightly negative effect on AGB and BGB. The correlations of SWC with AGB and BGB were relatively less significant than those of other soil properties. Our results highlighted that the soil properties played important roles in regulating vegetation dynamics along the degradation gradients and that SWC is not the main factor limiting plant growth in the humid Zoige region. Our results can provide guidance for the restoration and improvement of degraded alpine grasslands on the Tibetan Plateau.

中文翻译：

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若尔盖高原高寒草甸沿退化梯度植被生物量对土壤性质的响应

青藏高原高寒草原严重退化，甚至荒漠化。然而，仍有几个问题有待回答，特别是植被生物量对土壤特性的响应机制。本研究于2017年在若尔盖高原的高寒草甸进行了退化梯度试验，在植物生长旺季观察了植被特征和土壤性质。应用分类和回归树模型 (CART) 和结构方程模型 (SEM) 筛选控制植被动态的主要因素，并探索这些筛选因素之间的相互作用。地上生物量 (AGB) 和地下生物量 (BGB) 都沿着降解梯度显着下降。所有土壤特性在 0.05 显着性水平上沿着降解梯度经历了显着变化。土壤物理和化学特性解释了植被生物量沿退化梯度变化的 54.78%。AGB主要受土壤含水量（SWC）、土壤容重（SBD）、土壤有机碳（SOC）、土壤全氮（STN）和pH值的影响。土壤有效氮 (SAN)、SOC 和 pH 值对 BGB 有显着影响。大多数土壤性质对 AGB 和 BGB 有积极影响，而 SBD 和 pH 对 AGB 和 BGB 有轻微的负面影响。SWC与AGB和BGB的相关性与其他土壤性质的相关性相对较小。我们的研究结果强调，土壤特性在沿着退化梯度调节植被动态方面发挥了重要作用，并且 SWC 不是限制潮湿若尔盖地区植物生长的主要因素。研究结果可为青藏高原退化高寒草地的恢复和改善提供指导。