Department of Earth and Environmental Sciences, The University of Manchester, Manchester, UK.
Biological & Environmental Sciences, Faculty of Natural Sciences, University of Stirling, Stirling, UK.
Glob Chang Biol. 2024 Mar;30(3):e17245. doi: 10.1111/gcb.17245.
The seasonal coupling of plant and soil microbial nutrient demands is crucial for efficient ecosystem nutrient cycling and plant production, especially in strongly seasonal alpine ecosystems. Yet, how these seasonal nutrient cycling processes are modified by climate change and what the consequences are for nutrient loss and retention in alpine ecosystems remain unclear. Here, we explored how two pervasive climate change factors, reduced snow cover and shrub expansion, interactively modify the seasonal coupling of plant and soil microbial nitrogen (N) cycling in alpine grasslands, which are warming at double the rate of the global average. We found that the combination of reduced snow cover and shrub expansion disrupted the seasonal coupling of plant and soil N-cycling, with pronounced effects in spring (shortly after snow melt) and autumn (at the onset of plant senescence). In combination, both climate change factors decreased plant organic N-uptake by 70% and 82%, soil microbial biomass N by 19% and 38% and increased soil denitrifier abundances by 253% and 136% in spring and autumn, respectively. Shrub expansion also individually modified the seasonality of soil microbial community composition and stoichiometry towards more N-limited conditions and slower nutrient cycling in spring and autumn. In winter, snow removal markedly reduced the fungal:bacterial biomass ratio, soil N pools and shifted bacterial community composition. Taken together, our findings suggest that interactions between climate change factors can disrupt the temporal coupling of plant and soil microbial N-cycling processes in alpine grasslands. This could diminish the capacity of these globally widespread alpine ecosystems to retain N and support plant productivity under future climate change.
植物和土壤微生物养分需求的季节性耦合对于高效的生态系统养分循环和植物生产力至关重要，特别是在强季节性高山生态系统中。然而，气候变化如何改变这些季节性养分循环过程，以及对高山生态系统中养分损失和保留的后果仍不清楚。在这里，我们探讨了两种普遍存在的气候变化因素（积雪减少和灌木扩张）如何相互作用，改变了高山草原中植物和土壤微生物氮（N）循环的季节性耦合，而高山草原的升温速度是全球平均水平的两倍。我们发现，积雪减少和灌木扩张的组合破坏了植物和土壤 N 循环的季节性耦合，在春季（雪融后不久）和秋季（植物衰老开始时）的影响尤为明显。这两个气候变化因素共同使植物有机 N 吸收减少了 70%和 82%，土壤微生物生物量 N 减少了 19%和 38%，并分别使春季和秋季的土壤反硝化菌丰度增加了 253%和 136%。灌木扩张也单独改变了土壤微生物群落组成和化学计量在春季和秋季向更受 N 限制的条件和更缓慢的养分循环的季节性。在冬季，除雪显著降低了真菌与细菌生物量比、土壤 N 库，并改变了细菌群落组成。总之，我们的研究结果表明，气候变化因素的相互作用可以破坏高山草原中植物和土壤微生物 N 循环过程的时间耦合。这可能会降低这些在全球广泛分布的高山生态系统在未来气候变化下保留 N 和支持植物生产力的能力。
