Grassland degradation levels determine plant eco-physiological properties, and thus influences ecosystem function. However, how land degradation affects the relationship between plant biomass and eco-physiological properties of native and artificially restored grasslands is insufficiently understood. Here, we evaluated aboveground biomass (AGB), plant photosynthetic capacity, as well as soil texture, in a series of native grasslands (non-degraded, slightly degraded, moderately degraded, heavily degraded, and extremely degraded) and artificially restored grasslands with different growth times (5, 9, 11, 14 and 17 years) within the alpine grassland ecosystem of the Qinghai–Tibet Plateau during the plant growing season. Results showed that, in native grasslands, land degradation significantly decreased the nitrogen (N) concentration and AGB of grasses but did not impact the phosphorus (P) concentration. In actively restored grasslands, the AGB, photosynthetic rate (Pn), N and P of grasses decreased significantly after 9 years or longer of replanting time. Furthermore, the AGB of grasses in actively restored grasslands showed stronger association with eco-physiological properties than in native grasslands. In native grasslands, degradation affected AGB directly, but also indirectly through Pn. In actively restored grasslands, degradation affected AGB directly, but also indirectly through Pn, N and P. Our findings suggest that the mechanisms by which grass species respond to degradation differ between native and actively restored grasslands. Also, compared to native grasslands, the eco-physiological properties of grasses are more sensitive to changing environmental conditions in actively restored grasslands. More importantly, the differing response mechanisms are likely to alter the plant community dynamics and future ecosystem stability.

中文翻译：

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与退化的原生草原相比，积极恢复的草原中草的植物生物量与生态生理特性的相关性更强

草地退化程度决定植物的生态生理特性，进而影响生态系统功能。然而，土地退化如何影响植物生物量与原生和人工恢复草地的生态生理特性之间的关系尚不清楚。在这里，我们评估了一系列原生草地（未退化、轻度退化、中度退化、严重退化和极度退化）和人工恢复草地的地上生物量（AGB）、植物光合能力以及土壤质地。青藏高原高寒草原生态系统植物生长季的生长次数（5年、9年、11年、14年和17年）。结果表明，在原生草地上，土地退化显着降低了草的氮（N）浓度和AGB，但不影响磷（P）浓度。在积极恢复的草地中，补种时间9年或更长时间后，草的AGB、光合速率（Pn）、N和P显着下降。此外，与原生草原相比，积极恢复的草原中草的 AGB 显示出与生态生理特性更强的相关性。在原生草原中，退化直接影响 AGB，但也通过 Pn 间接影响。在积极恢复的草原中，退化直接影响AGB，但也通过Pn、N和P间接影响AGB。我们的研究结果表明，原生草原和积极恢复的草原之间草种对退化的反应机制不同。此外，与原生草原相比，积极恢复的草原中草的生态生理特性对环境条件的变化更加敏感。更重要的是，不同的响应机制可能会改变植物群落动态和未来生态系统的稳定性。