University of Maine School of Forest Resources, 5755 Nutting Hall, Orono, ME 04469, United States.
University of Maine School of Biology and Ecology, Hitchner Hall, 7 Portage Road, Orono, ME 04469, United States.
Tree Physiol. 2024 Sep 3;44(9). doi: 10.1093/treephys/tpae095.
Climate change is raising concerns about how forests will respond to extreme droughts, heat waves and their co-occurrence. In this greenhouse study, we tested how carbon and water relations relate to seedling growth and mortality of northeastern US trees during and after extreme drought, warming, and combined drought and warming. We compared the response of our focal species red spruce (Picea rubens Sarg.) with a common associate (paper birch, Betula papyrifera Marsh.) and a species expected to increase abundance in this region with climate change (northern red oak, Quercus rubra L.). We tracked growth and mortality, photosynthesis and water use of 216 seedlings of these species through a treatment and a recovery year. Each red spruce seedling was planted in containers either alone or with another seedling to simulate potential competition, and the seedlings were exposed to combinations of drought (irrigated, 15-d 'short' or 30-d 'long') and temperature (ambient or 16 days at +3.5 °C daily maximum) treatments. We found dominant effects of the drought reducing photosynthesis, midday water potential, and growth of spruce and birch, but that oak showed considerable resistance to drought stress. The effects of planting seedlings together were moderate and likely due to competition for limited water. Despite high temperatures reducing photosynthesis for all species, the warming imposed in this study minorly impacted growth only for oak in the recovery year. Overall, we found that the diverse water-use strategies employed by the species in our study related to their growth and recovery following drought stress. This study provides physiological evidence to support the prediction that native species to this region like red spruce and paper birch are susceptible to future climate extremes that may favor other species like northern red oak, leading to potential impacts on tree community dynamics under climate change.
气候变化引发了人们对于森林如何应对极端干旱、热浪及其同时发生的担忧。在这项温室研究中，我们测试了在极端干旱、增温以及干旱和增温共同作用期间及之后，碳和水分关系如何与美国东北部树种的幼苗生长和死亡率相关。我们比较了我们的研究重点物种红云杉（Picea rubens Sarg.）与一种常见伴生种（纸皮桦，Betula papyrifera Marsh.）以及一种预计在该地区由于气候变化而增加丰度的物种（北方红栎，Quercus rubra L.）的响应。我们通过处理和恢复年跟踪了这些物种的 216 株幼苗的生长和死亡率、光合作用和水分利用。每株红云杉幼苗单独或与另一株幼苗一起种植在容器中，以模拟潜在的竞争，幼苗暴露于干旱（灌溉、15 天“短”或 30 天“长”）和温度（环境或 16 天每天最高温度+3.5°C）处理的组合中。我们发现干旱会显著降低云杉和桦木的光合作用、中午水分势和生长，但栎属树种对干旱胁迫具有相当大的抵抗力。将幼苗一起种植的影响是适度的，可能是由于对有限水分的竞争。尽管高温降低了所有物种的光合作用，但本研究中施加的增温在恢复年仅对栎属树种的生长产生了轻微影响。总体而言，我们发现研究中物种多样化的水分利用策略与其在干旱胁迫后的生长和恢复有关。这项研究提供了生理证据，支持了这样一种预测，即该地区的本地物种，如红云杉和纸皮桦，容易受到未来气候极端事件的影响，而其他物种，如北方红栎，可能会受益，这可能会对气候变化下的树木群落动态产生潜在影响。
