Department of Natural Resources and the Environment, College of Life Science and Agriculture, University of New Hampshire, Durham, NH, USA.
Earth Systems Research Center, Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, Durham, NH, USA.
Glob Chang Biol. 2020 Mar;26(3):1519-1531. doi: 10.1111/gcb.14850. Epub 2019 Oct 21.
Northern temperate ecosystems are experiencing warmer and more variable winters, trends that are expected to continue into the foreseeable future. Despite this, most studies have focused on climate change impacts during the growing season, particularly when comparing responses across different vegetation cover types. Here we examined how a perennial grassland and adjacent mixed forest ecosystem in New Hampshire, United States, responded to a period of highly variable winters from 2014 through 2017 that included the warmest winter on record to date. In the grassland, record-breaking temperatures in the winter of 2015/2016 led to a February onset of plant growth and the ecosystem became a sustained carbon sink well before winter ended, taking up roughly 90 g/m more carbon during the winter to spring transition than in other recorded years. The forest was an unusually large carbon source during the same period. While forest photosynthesis was restricted by leaf-out phenology, warm winter temperatures caused large pulses of ecosystem respiration that released nearly 230 g C/m from February through April, more than double the carbon losses during that period in cooler years. These findings suggest that, as winters continue to warm, increases in ecosystem respiration outside the growing season could outpace increases in carbon uptake during a longer growing season, particularly in forests that depend on leaf-out timing to initiate carbon uptake. In ecosystems with a perennial leaf habit, warming winter temperatures are more likely to increase ecosystem carbon uptake through extension of the active growing season. Our results highlight the importance of understanding relationships among antecedent winter conditions and carbon exchange across land-cover types to understand how landscape carbon exchange will change under projected climate warming.
北方温带生态系统正经历着更温暖和多变的冬季，预计这种趋势将持续到可预见的未来。尽管如此，大多数研究都集中在生长季节的气候变化影响上，特别是在比较不同植被覆盖类型的反应时。在这里，我们研究了美国新罕布什尔州的一个多年生草原和相邻的混合林生态系统如何应对 2014 年至 2017 年期间高度多变的冬季，其中包括迄今为止有记录以来最温暖的冬季。在草原上，2015/2016 年冬季创纪录的高温导致植物生长在 2 月开始，生态系统在冬季结束前成为一个持续的碳汇，在冬季到春季的过渡期间吸收了大约 90 克/平方米的碳，比其他有记录的年份多。同期森林是一个异常大的碳源。虽然森林光合作用受到展叶物候的限制，但温暖的冬季温度导致了生态系统呼吸的大量脉冲，从 2 月到 4 月释放了近 230 克/平方米的碳，比在较冷年份同期的碳损失多出两倍多。这些发现表明，随着冬季继续变暖，生长季节以外的生态系统呼吸增加可能超过更长生长季节的碳吸收增加，特别是在依赖展叶时间开始碳吸收的森林中。在具有多年生叶习性的生态系统中，温暖的冬季温度更有可能通过延长活跃生长季节来增加生态系统的碳吸收。我们的研究结果强调了理解不同土地覆盖类型之间的前冬条件和碳交换关系的重要性，以了解在预计的气候变暖下景观碳交换将如何变化。
