Abstract

High latitude forests cope with considerable variation in moisture and temperature at multiple temporal scales. To assess how their photosynthetic physiology responds to short- and long-term temperature variation, we measured photosynthetic capacity for four tree species growing in an open-air experiment in the boreal-temperate ecotone `Boreal Forest Warming at an Ecotone in Danger' (B4WarmED). The experiment factorially manipulated temperature above- and below-ground (ambient, +3.2 °C) and summer rainfall (ambient, 40% removal). We measured A/C_i curves at 18, 25 and 32 °C for individuals of two boreal (Pinus banksiana Lamb., Betula papyrifera Marsh.) and two temperate species (Pinus strobus L., Acer rubrum L.) experiencing the long-term warming and/or reduced-rainfall conditions induced by our experimental treatments. We calculated the apparent photosynthetic capacity descriptors V_Cmax,Ci and J_max,Ci and their ratio for each measurement temperate. We hypothesized that (i) V_Cmax,Ci and J_max,Ci would be down-regulated in plants experiencing longer term (e.g., weeks to months) warming and reduced rainfall (i.e., have lower values at a given measurement temperature), as is sometimes found in the literature, and that (ii) plants growing at warmer temperatures or from warmer ranges would show greater sensitivity (steeper slope) to short-term (minutes to hours) temperature variation. Neither hypothesis was supported as a general trend across the four species, as there was not a significant main effect (across species) of either warming or rainfall reduction on V_Cmax,Ci and J_max,Ci. All species markedly increased V_Cmax,Ci and J_max,Ci (and decreased their ratio) with short-term increases in temperature (i.e., contrasting values at 18, 25 and 32 °C), and those responses were independent of long-term treatments and did not differ among species. The J_max,Ci:V_Cmax,Ci ratio was, however, significantly lower across species in warmed and reduced rainfall treatments. Collectively, these results suggest that boreal trees possess considerable short-term plasticity that may allow homeostasis of V_Cmax,Ci and J_max,Ci to a longer term temperature treatment. Our results also caution against extrapolating results obtained under controlled and markedly contrasting temperature treatments to responses of photosynthetic parameters to more modest temperature changes expected in the near-term with climate warming in field conditions.

中文翻译：

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自由空气增温和降雨控制实验中四种北方树种光合能力对温度的短期和长期响应。

摘要

高纬度森林在多个时间尺度上应对相当大的湿度和温度变化。为了评估它们的光合生理对短期和长期温度变化的反应，我们测量了在北方温带交错带“处于危险的交错带的北方森林变暖”（B4WarmED）的露天实验中生长的四种树种的光合能力）。该实验对地上和地下温度（环境，+3.2 °C）和夏季降雨（环境，40% 去除）进行了因子控制。我们在 18、25 和 32 °C 下测量了两种北方物种（ Pinus _bankiana Lamb.、Betula papyrifera Marsh.）和两种温带物种（Pinus strobus L., Acer rubrum L. ) 经历由我们的实验处理引起的长期变暖和/或减少降雨条件。我们计算了每个测量温度的表观光合能力描述符V _{C max,Ci}和J _max,Ci及其比率。我们假设 (i) V _{C max,Ci}和J _max,Ci在经历较长时间（例如，数周至数月）变暖和降雨减少（即在给定测量温度下具有较低值）的植物中会被下调，正如文献中有时发现的那样，并且（ii）植物生长在较高的温度或较高的范围将对短期（几分钟到几小时）温度变化表现出更大的敏感性（更陡的斜率）。这两种假设都没有作为四个物种的总体趋势得到支持，因为变暖或降雨减少对V _{C max,Ci}和J _max,Ci没有显着的主要影响（跨物种）。所有物种均显着增加V _{C max,Ci}和J _max,Ci（并降低它们的比率）随着温度的短期升高（即，在 18、25 和 32°C 的对比值），并且这些反应与长期处理无关，并且在物种之间没有差异。然而，在变暖和减少降雨处理中，物种间的J _max,Ci : V _{C max,Ci比率显着降低。}总的来说，这些结果表明北方树木具有相当大的短期可塑性，可以使V _{C max,Ci}和J _{max,Ci保持平衡。}到更长时间的温度处理。我们的结果还告诫不要将在受控和明显对比的温度处理下获得的结果外推到光合参数对预期在短期内随着气候变暖在田间条件下更温和的温度变化的响应。