US Geological Survey, Southwest Biological Science Center, Moab, Utah, USA.
USDA-ARS Rangeland Resource and Systems Research Unit, Crops Research Laboratory, Fort Collins, Colorado, USA.
Glob Chang Biol. 2023 Jun;29(12):3364-3377. doi: 10.1111/gcb.16681. Epub 2023 Apr 11.
Global dryland vegetation communities will likely change as ongoing drought conditions shift regional climates towards a more arid future. Additional aridification of drylands can impact plant and ground cover, biogeochemical cycles, and plant-soil feedbacks, yet how and when these crucial ecosystem components will respond to drought intensification requires further investigation. Using a long-term precipitation reduction experiment (35% reduction) conducted across the Colorado Plateau and spanning 10 years into a 20+ year regional megadrought, we explored how vegetation cover, soil conditions, and growing season nitrogen (N) availability are impacted by drying climate conditions. We observed large declines for all dominant plant functional types (C and C grasses and C and C shrubs) across measurement period, both in the drought treatment and control plots, likely due to ongoing regional megadrought conditions. In experimental drought plots, we observed less plant cover, less biological soil crust cover, warmer and drier soil conditions, and more soil resin-extractable N compared to the control plots. Observed increases in soil N availability were best explained by a negative correlation with plant cover regardless of treatment, suggesting that declines in vegetation N uptake may be driving increases in available soil N. However, in ecosystems experiencing long-term aridification, increased N availability may ultimately result in N losses if soil moisture is consistently too dry to support plant and microbial N immobilization and ecosystem recovery. These results show dramatic, worrisome declines in plant cover with long-term drought. Additionally, this study highlights that more plant cover losses are possible with further drought intensification and underscore that, in addition to large drought effects on aboveground communities, drying trends drive significant changes to critical soil resources such as N availability, all of which could have long-term ecosystem impacts for drylands.
随着持续的干旱条件将区域气候向更干旱的未来转变，全球旱地植被群落可能会发生变化。旱地的进一步干旱化会影响植物和地被物、生物地球化学循环和植物-土壤反馈，但这些关键生态系统组成部分将如何以及何时对干旱加剧做出响应仍需要进一步研究。本研究使用了横跨科罗拉多高原的长期降水减少实验（减少 35%），该实验持续了 10 年，并跨越了 20 多年的区域特大干旱，我们探讨了植被覆盖、土壤条件和生长季节氮（N）供应如何受到干燥气候条件的影响。我们观察到，在整个测量期间，所有主要植物功能类型（C 和 C 禾本科植物和 C 和 C 灌木）的覆盖度都大幅下降，无论是在干旱处理和对照小区，这可能是由于持续的区域特大干旱条件。在实验干旱小区，我们观察到植物覆盖度更低、生物土壤结皮覆盖度更低、土壤温度更高且更干燥，以及土壤树脂可提取氮更多，而对照小区则没有这种情况。无论处理方式如何，观察到的土壤 N 有效性增加都与植物覆盖度呈负相关，这表明植被 N 吸收的减少可能导致可用土壤 N 的增加。然而，在经历长期干旱化的生态系统中，如果土壤水分始终过于干燥，无法支持植物和微生物 N 固定和生态系统恢复，那么增加的 N 有效性最终可能导致 N 损失。这些结果表明，长期干旱会导致植物覆盖度急剧下降，令人担忧。此外，本研究强调，随着干旱加剧，可能会有更多的植物覆盖损失，并且强调，除了干旱对地上社区的巨大影响外，干燥趋势还会导致关键土壤资源（如 N 有效性）发生重大变化，这对旱地的生态系统都可能会产生长期影响。
