Department of Environmental Science, Policy, and Management, University of California, Berkeley, CA, 94720, USA.
Institute of Integrative Biology, ETH Zürich, 8092, Zurich, Switzerland.
Oecologia. 2020 May;193(1):1-13. doi: 10.1007/s00442-020-04624-w. Epub 2020 Feb 20.
Recent observational evidence suggests that nighttime temperatures are increasing faster than daytime temperatures, while in some regions precipitation events are becoming less frequent and more intense. The combined ecological impacts of these climatic changes on crassulacean acid metabolism (CAM) plants and their interactions with other functional groups (i.e., grass communities) remain poorly understood. Here we developed a growth chamber experiment to investigate how two CAM-grass communities in desert ecosystems of the southwestern United States and northern Mexico respond to asymmetric warming and increasing rainfall variability. Grasses generally showed competitive advantages over CAM plants with increasing rainfall variability under ambient temperature conditions. In contrast, asymmetric warming caused mortality of both grass species (Bouteloua eriopoda and Bouteloua curtipendula) in both rainfall treatments due to enhanced drought stress. Grass mortality indirectly favored CAM plants even though the biomass of both CAM species Cylindropuntia imbricata and Opuntia phaeacantha significantly decreased. The stem's volume-to-surface ratio of C. imbricata was significantly higher in mixture than in monoculture under ambient temperature (both P < 0.0014); however, the difference became insignificant under asymmetric warming (both P > 0.1625), suggesting that warming weakens the negative effects of interspecific competition on CAM plant growth. Our findings suggest that while the increase in intra-annual rainfall variability enhances grass productivity, asymmetric warming may lead to grass mortality, thereby indirectly favoring the expansion of co-existing CAM plants. This study provides novel experimental evidence showing how the ongoing changes in global warming and rainfall variability affect CAM-grass growth and interactions in dryland ecosystems.
最近的观测证据表明，夜间温度的上升速度快于白天温度，而在一些地区，降水事件变得越来越不频繁，强度却越来越大。这些气候变化对景天酸代谢（CAM）植物的综合生态影响及其与其他功能群（即草群落）的相互作用仍知之甚少。在这里，我们开发了一个生长室实验，以研究美国西南部和墨西哥北部沙漠生态系统中的两种 CAM-草群落如何应对非对称升温以及增加的降雨变异性。在环境温度条件下，随着降雨变异性的增加，草类通常对 CAM 植物表现出竞争优势。相比之下，由于干旱胁迫加剧，非对称升温导致两种草种（Bouteloua eriopoda 和 Bouteloua curtipendula）在两种降雨处理下均死亡。即使两种 CAM 物种（Cylindropuntia imbricata 和 Opuntia phaeacantha）的生物量明显减少，草类的死亡也间接有利于 CAM 植物。在环境温度下（均 P<0.0014），C.imbricata 的茎体积与表面积比在混合物中明显高于单培养物；然而，在非对称升温下，差异变得不显著（均 P>0.1625），这表明升温削弱了种间竞争对 CAM 植物生长的负面影响。我们的研究结果表明，虽然年内降雨变异性的增加提高了草类的生产力，但非对称升温可能导致草类死亡，从而间接有利于共存的 CAM 植物的扩张。本研究提供了新的实验证据，表明全球变暖和降雨变异性的持续变化如何影响旱地生态系统中 CAM-草类的生长和相互作用。
