Environmental Sciences Division and Climate Change Science Institute, Oak Ridge National Laboratory, Oak Ridge, TN, USA.
Department of Forestry and Wood Technology, Linnaeus University, Växjö, Sweden.
Glob Chang Biol. 2021 May;27(9):1820-1835. doi: 10.1111/gcb.15543. Epub 2021 Feb 22.
Boreal peatland forests have relatively low species diversity and thus impacts of climate change on one or more dominant species could shift ecosystem function. Despite abundant soil water availability, shallowly rooted vascular plants within peatlands may not be able to meet foliar demand for water under drought or heat events that increase vapor pressure deficits while reducing near surface water availability, although concurrent increases in atmospheric CO could buffer resultant hydraulic stress. We assessed plant water relations of co-occurring shrub (primarily Rhododendron groenlandicum and Chamaedaphne calyculata) and tree (Picea mariana and Larix laricina) species prior to, and in response to whole ecosystem warming (0 to +9°C) and elevated CO using 12.8-m diameter open-top enclosures installed within an ombrotrophic bog. Water relations (water potential [Ψ], turgor loss point, foliar and root hydraulic conductivity) were assessed prior to treatment initiation, then Ψ and peak sap flow (trees only) assessed after 1 or 2 years of treatments. Under the higher temperature treatments, L. laricina Ψ exceeded its turgor loss point, increased its peak sap flow, and was not able to recover Ψ overnight. In contrast, P. mariana operated below its turgor loss point and maintained constant Ψ and sap flow across warming treatments. Similarly, C. calyculata Ψ stress increased with temperature while R. groenlandicum Ψ remained at pretreatment levels. The more anisohydric behavior of L. laricina and C. calyculata may provide greater net C uptake with warming, while the more conservative P. mariana and R. groenlandicum maintained greater hydraulic safety. These latter species also responded to elevated CO by reduced Ψ stress, which may also help limit hydraulic failure during periods of extreme drought or heat in the future. Along with Sphagnum moss, the species-specific responses of peatland vascular communities to drier or hotter conditions will shape boreal peatland composition and function in the future.
北方泥炭地森林的物种多样性相对较低，因此气候变化对一种或多种优势物种的影响可能会改变生态系统功能。尽管土壤水分丰富，但在干旱或高温事件中，根浅的维管植物可能无法满足叶片对水分的需求，这些事件会增加蒸汽压亏缺，同时减少近地表水的供应，尽管大气 CO2 的同时增加可能会缓冲由此产生的水力压力。我们在整个生态系统升温（0 至+9°C）和升高 CO2 之前以及之后，使用安装在富营养沼泽内的 12.8 米直径开顶罩来评估共同出现的灌木（主要是 Rhododendron groenlandicum 和 Chamaedaphne calyculata）和树木（Picea mariana 和 Larix laricina）物种的植物水分关系。在处理开始之前评估水分关系（水势 [Ψ]、膨压损失点、叶片和根水力传导性），然后在处理 1 或 2 年后评估 Ψ 和峰值液流（仅树木）。在较高温度处理下，L. laricina Ψ 超过其膨压损失点，增加其峰值液流，并且无法在一夜之间恢复 Ψ。相比之下，P. mariana 在膨压损失点以下运行，并且在整个升温处理过程中保持恒定的 Ψ 和液流。同样，C. calyculata Ψ 随着温度的升高而增加，而 R. groenlandicum Ψ 保持在预处理水平。L. laricina 和 C. calyculata 的更异水行为可能会随着升温而增加净 C 吸收，而更保守的 P. mariana 和 R. groenlandicum 则保持更大的水力安全。这些后一种物种也对升高的 CO2 做出反应，降低了 Ψ 压力，这也可能有助于在未来极端干旱或高温期间限制水力故障。与泥炭藓一起，泥炭地维管植物群落对干燥或更热条件的特定物种反应将塑造北方泥炭地的组成和功能。
