Felton Andrew J, Goldsmith Gregory R
Schmid College of Science and Technology, Chapman University, Orange, California, USA.
Department of Land Resources and Environmental Sciences, Montana State University, Bozeman, Montana, USA.
Glob Chang Biol. 2023 May;29(10):2790-2803. doi: 10.1111/gcb.16637. Epub 2023 Feb 26.
Although drought is known to negatively impact grassland functioning, the timing and magnitude of these impacts within a growing season remain unresolved. Previous small-scale assessments indicate grasslands may only respond to drought during narrow periods within a year; however, large-scale assessments are now needed to uncover the general patterns and determinants of this timing. We combined remote sensing datasets of gross primary productivity and weather to assess the timing and magnitude of grassland responses to drought at 5 km temporal resolution across two expansive ecoregions of the western US Great Plains biome: the C -dominated shortgrass steppe and the C -dominated northern mixed prairies. Across over 700,000 pixel-year combinations covering more than 600,000 km , we studied how the driest years between 2003-2020 altered the daily and bi-weekly dynamics of grassland carbon (C) uptake. Reductions to C uptake intensified into the early summer during drought and peaked in mid- and late June in both ecoregions. Stimulation of spring C uptake during drought was small and insufficient to compensate for losses during summer. Thus, total grassland C uptake was consistently reduced by drought across both ecoregions; however, reductions were twice as large across the more southern and warmer shortgrass steppe. Across the biome, increased summer vapor pressure deficit (VPD) was strongly linked to peak reductions in vegetation greenness during drought. Rising VPD will likely exacerbate reductions in C uptake during drought across the western US Great Plains, with these reductions greatest during the warmest months and in the warmest locations. High spatiotemporal resolution analyses of grassland response to drought over large areas provide both generalizable insights and new opportunities for basic and applied ecosystem science in these water-limited ecoregions amid climate change.
尽管干旱会对草地功能产生负面影响，但在生长季节内这些影响的时间和程度仍未得到解决。先前的小规模评估表明，草地可能仅在一年中的狭窄时期对干旱作出反应；然而，现在需要进行大规模评估以揭示这种时间的一般模式和决定因素。我们结合了总初级生产力和天气的遥感数据集，以5公里的时间分辨率评估美国西部大平原生物群落两个广阔生态区域（以C为主的矮草草原和以C为主的北部混合草原）对干旱的草地响应时间和程度。在涵盖超过600,000平方公里的700,000多个像素 - 年组合中，我们研究了2003 - 2020年期间最干旱的年份如何改变草地碳（C）吸收的每日和每两周动态。在干旱期间，碳吸收的减少在初夏加剧，并在两个生态区域的6月中旬和下旬达到峰值。干旱期间春季碳吸收的刺激很小，不足以弥补夏季的损失。因此，两个生态区域的干旱都持续减少了草地的总碳吸收；然而，在更南部和温暖的矮草草原，减少幅度是前者的两倍。在整个生物群落中，夏季水汽压差（VPD）的增加与干旱期间植被绿度的峰值降低密切相关。VPD的上升可能会加剧美国西部大平原干旱期间碳吸收的减少，在最温暖的月份和最温暖的地区，这些减少最为明显。对大面积草地对干旱响应的高时空分辨率分析为这些水资源有限的生态区域在气候变化背景下的基础和应用生态系统科学提供了可推广的见解和新机会。
