Abstract Many studies have focused on the responses of phenophases to warming in natural, non-degraded grasslands. However, degraded grasslands widely distribute in the world due to climate change and overgrazing. So far, a comprehensive understanding of how plant phenology responds to warming, degradation and their interactions remains elusive. Here, the relative effects of warming and degradation on the phenological sequences of two dominant plant species were tested using a two factorial experiment of warming and moderate degradation (i.e., four treatments: NWND, WND, NWD and WD) during three successive years. We found that WND significantly delayed the onsets of early phenophases (i.e., leaf-out, booting-set, flowering and fruiting-set) and shortened the total activity period (TAP) only for the early spring flowering Kobresia pygmaea compared with NWND. NWD generally did not significantly affect the timing or duration of all phenophases for the two plant species depending on year relative to NWND. Interaction between warming and moderate degradation significantly delayed leaf-out and shortened total activity period of the two plant species. There were negative correlations between plant species richness and onset of vegetation after fruiting-set for K. pygmaea and the duration of fruiting-set for Potentilla multifida (a dominant mid-summer flowering species in degraded plots), but there were positive correlations between plant species richness and leafing duration for P. multifida. Positive correlations were found between first leaf-out and NO3−-N in soils for both species but negative correlations were found between first leaf-out and NH4−-N in soils for P. multifida. There were positive and negative correlations between TAP of P. multifida and NH4−-N and NO3−-N in soils, respectively. Therefore, our results suggest that moderate degradation could weaken the negative effects of warming on reproductive phenophases of K. pygmaea, and that we should take into account grassland degradation and its associated changes in plant species richness and soil inorganic nitrogen when we predict the response of plant phenology to future warming.

中文翻译：

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升温和退化对青藏高原高粱和多裂草的物候期的影响

摘要 许多研究集中在自然、非退化草地物候期对变暖的响应。然而，由于气候变化和过度放牧，退化的草原在世界范围内广泛分布。到目前为止，对植物物候学如何响应变暖、退化及其相互作用的全面了解仍然难以捉摸。在这里，使用连续三年变暖和中度退化（即四种处理：NWND、WND、NWD 和 WD）的两个因子实验测试了变暖和退化对两种优势植物物种物候序列的相对影响。我们发现 WND 显着延迟了早期物候期（即叶出、启动期、开花和坐果），并且与 NWND 相比，仅对早春开花的 Kobresia pygmaea 缩短了总活动期（TAP）。NWD 通常不会显着影响两个植物物种的所有物候期的时间或持续时间，这取决于相对于 NWND 的年份。变暖和适度退化之间的相互作用显着延迟了两种植物的落叶并缩短了总活动期。K. pygmaea 的植物物种丰富度与坐果后植被开始与 Potentilla multifida（退化地块中盛夏开花的优势种）的坐果持续时间呈负相关，但植物之间呈正相关。 P. multifida 的物种丰富度和生叶持续时间。在两个物种的土壤中第一次脱叶和 NO3--N 之间发现了正相关，但在 P. multifida 的土壤中第一次脱叶和 NH4--N 之间发现了负相关。P. multifida的TAP与土壤中的NH4--N和NO3--N分别呈正相关和负相关。因此，我们的研究结果表明，适度退化可以减弱变暖对 K. pygmaea 繁殖物候期的负面影响，并且在预测 K. pygmaea 的响应时，应考虑草地退化及其在植物物种丰富度和土壤无机氮方面的相关变化。植物物候对未来变暖的影响。multifida 和 NH4--N 和 NO3--N 分别在土壤中。因此，我们的研究结果表明，适度退化可以减弱变暖对 K. pygmaea 繁殖物候期的负面影响，并且在预测 K. pygmaea 的响应时，应考虑草地退化及其在植物物种丰富度和土壤无机氮方面的相关变化。植物物候对未来变暖的影响。multifida 和 NH4--N 和 NO3--N 分别在土壤中。因此，我们的研究结果表明，适度退化可以减弱变暖对 K. pygmaea 繁殖物候期的负面影响，并且在预测 K. pygmaea 的响应时，应考虑草地退化及其在植物物种丰富度和土壤无机氮方面的相关变化。植物物候对未来变暖的影响。