Cloud cover and delayed herbivory relative to timing of spring onset interact to dampen climate change impacts on net ecosystem exchange in a coastal Alaskan wetland
Cloud cover and delayed herbivory relative to timing of spring onset interact to dampen climate change impacts on net ecosystem exchange in a coastal Alaskan wetland
复制标题
DOI：
10.1088/1748-9326/ab1c91
复制
发表时间：
2019-08-01
影响因子：
6.7
通讯作者：
Welker, Jeffrey M.
中科院分区：
文献类型：
--
作者：
Leffler, A. Joshua;Beard, Karen H.;Welker, Jeffrey M.
在过去的40年里，北方生态系统的快速变暖导致了更早的春季，降水增加，并改变了动植物相互作用的时间，如食草动物。提前的春季物候期可以导致更长的生长季节和更多的碳(C)吸收。更大的降雨量与更大的云量相吻合，可能会抑制光合作用。与春季物候相关的食草性时间影响植物生物量。所有这些变化都不是相互排斥的，它们的相互作用可能会给北极生态系统功能带来意想不到的后果。我们用三年的时间研究了春季提前物候、云量和放牧时间对阿拉斯加西部育空-库斯科维姆三角洲碳交换的影响。我们结合了使用被动升温开放式箱体(OTC)的生长季提前，以及控制放牧(早期、典型和后期)和取消放牧的时间安排。我们还监测了入射太阳光的自然变化，以检查这些相互作用的作用力的C交换结果。我们使用自动室系统每小时监测一次C(NEE)的净生态系统交换。数据被用来构建每个实验区的每日光照曲线，阳光数据与晴空模型相结合被用来量化一系列入射阳光条件下的每日和季节性NEE。阴天对NEE的抑制最大，无论季节或放牧时间如何，碳吸收都减少了约2gCm(-2)d(-1)。延迟放牧使土壤对碳的吸收增加约3gCm(-2)d(-1)。春季提前使C吸收减少了约1.5g Cm(-2)d(-1)，但仅当样地受到OTCs的直接增温时；春季推进对NEE没有长期影响。因此，净需求的两个最大驱动因素--云量和放牧--可能产生相反的影响，因此未来生长季节净需求将取决于放牧和入射阳光时间的变化幅度。
Rapid warming in northern ecosystems over the past four decades has resulted in earlier spring, increased precipitation, and altered timing of plant-animal interactions, such as herbivory. Advanced spring phenology can lead to longer growing seasons and increased carbon (C) uptake. Greater precipitation coincides with greater cloud cover possibly suppressing photosynthesis. Timing of herbivory relative to spring phenology influences plant biomass. None of these changes are mutually exclusive and their interactions could lead to unexpected consequences for Arctic ecosystem function. We examined the influence of advanced spring phenology, cloud cover, and timing of grazing on C exchange in the Yukon-Kuskokwim Delta of western Alaska for three years. We combined advancement of the growing season using passive-warming open-top chambers (OTC) with controlled timing of goose grazing (early, typical, and late season) and removal of grazing. We also monitored natural variation in incident sunlight to examine the C exchange consequences of these interacting forcings. We monitored net ecosystem exchange of C (NEE) hourly using an autochamber system. Data were used to construct daily light curves for each experimental plot and sunlight data coupled with a clear-sky model was used to quantify daily and seasonal NEE over a range of incident sunlight conditions. Cloudy days resulted in the largest suppression of NEE, reducing C uptake by approximately 2 g C m(-2 )d(-1) regardless of the timing of the season or timing of grazing. Delaying grazing enhanced C uptake by approximately 3 g C m(-2) d(-1). Advancing spring phenology reduced C uptake by approximately 1.5 g C m(-2) d(-1), but only when plots were directly warmed by the OTCs; spring advancement did not have a long-term influence on NEE. Consequently, the two strongest drivers of NEE, cloud cover and grazing, can have opposing effects and thus future growing season NEE will depend on the magnitude of change in timing of grazing and incident sunlight.