Department of Ecology and Evolutionary Biology, School for Environment and Sustainability, University of Michigan, Ann Arbor, Michigan, 48109, USA.
School of Forest Resources and Environmental Science, Michigan Technological University, Houghton, Michigan, 49937, USA.
Ecology. 2018 Feb;99(2):411-420. doi: 10.1002/ecy.2095. Epub 2018 Jan 17.
Most forest ecosystems are simultaneously affected by concurrent global change drivers. However, when assessing these effects, studies have mainly focused on the responses to single factors and have rarely evaluated the joined effects of the multiple aspects of environmental change. Here, we analyzed the combined effects of anthropogenic nitrogen (N) deposition and climatic conditions on the radial growth of Acer saccharum, a dominant tree species in eastern North American forests. We capitalized on a long-term N deposition study, replicated along a latitudinal gradient, that has been taking place for more than 20 yr. We analyzed tree radial growth as a function of anthropogenic N deposition (ambient and experimental addition) and of summer temperature and soil water conditions. Our results reveal that experimental N deposition enhances radial growth of this species, an effect that was accentuated as temperature increased and soil water became more limiting. The spatial and temporal extent of our data also allowed us to assert that the positive effects of growing under the experimental N deposition are likely due to changes in the physiological performance of this species, and not due to the positive correlation between soil N and soil water holding capacity, as has been previously speculated in other studies. Our simulations of tree growth under forecasted climate scenarios specific for this region also revealed that although anthropogenic N deposition may enhance tree growth under a large array of environmental conditions, it will not mitigate the expected effects of growing under the considerably drier conditions characteristic of our most extreme climatic scenario.
大多数森林生态系统同时受到多种全球变化驱动因素的影响。然而，在评估这些影响时，研究主要集中在对单一因素的响应上，很少评估环境变化多个方面的综合影响。在这里，我们分析了人为氮 (N) 沉积和气候条件对北美东部森林优势树种糖枫径向生长的综合影响。我们利用了一项长期的、沿纬度梯度进行的人为氮沉积研究，该研究已经进行了 20 多年。我们分析了树木径向生长与人为氮沉积（背景和实验添加）以及夏季温度和土壤水分条件的关系。研究结果表明，实验性氮沉积促进了该物种的径向生长，这种效应随着温度升高和土壤水分变得更加有限而加剧。我们数据的空间和时间范围也使我们能够断言，在实验性氮沉积下生长的积极影响可能是由于该物种生理性能的变化，而不是由于土壤氮和土壤持水能力之间的正相关关系，如以前在其他研究中推测的那样。我们根据该地区特定的预测气候情景对树木生长进行的模拟也表明，尽管人为氮沉积可能会在多种环境条件下促进树木生长，但在我们最极端气候情景下典型的干燥条件下，它不会减轻生长的预期影响。
