Department of Forest Resources, University of Minnesota, St. Paul, MN, USA.
Department of Biology, Behavioral Neuroscience, and Health Sciences, Rider University, Lawrenceville, NJ, USA.
Glob Chang Biol. 2020 Feb;26(2):746-759. doi: 10.1111/gcb.14805. Epub 2019 Sep 18.
Photosynthetic biochemical limitation parameters (i.e., V , J and J :V ratio) are sensitive to temperature and water availability, but whether these parameters in cold climate species at biome ecotones are positively or negatively influenced by projected changes in global temperature and water availability remains uncertain. Prior exploration of this question has largely involved greenhouse based short-term manipulative studies with mixed results in terms of direction and magnitude of responses. To address this question in a more realistic context, we examined the effects of increased temperature and rainfall reduction on the biochemical limitations of photosynthesis using a long-term chamber-less manipulative experiment located in northern Minnesota, USA. Nine tree species from the boreal-temperate ecotone were grown in natural neighborhoods under ambient and elevated (+3.4°C) growing season temperatures and ambient or reduced (≈40% of rainfall removed) summer rainfall. Apparent rubisco carboxylation and RuBP regeneration standardized to 25°C (V and J , respectively) were estimated based on AC curves measured in situ over three growing seasons. Our primary objective was to test whether species would downregulate V and J in response to warming and reduced rainfall, with such responses expected to be greatest in species with the coldest and most humid native ranges, respectively. These hypotheses were not supported, as there were no overall main treatment effects on V or J (p > .14). However, J :V ratio decreased significantly with warming (p = .0178), whereas interactions between warming and rainfall reduction on the J to V ratio were not significant. The insensitivity of photosynthetic parameters to warming contrasts with many prior studies done under larger temperature differentials and often fixed daytime temperatures. In sum, plants growing in relatively realistic conditions under naturally varying temperatures and soil moisture levels were remarkably insensitive in terms of their J and V when grown at elevated temperatures, reduced rainfall, or both combined.
光合生化限制参数（即 V 、 J 和 J : V 比）对温度和水分可用性敏感，但在生物群落边缘的寒冷气候物种中，这些参数是否会受到全球温度和水分可用性变化的正向或负向影响仍不确定。此前对这个问题的探索主要涉及基于温室的短期操纵研究，结果在响应的方向和幅度上存在差异。为了在更现实的背景下解决这个问题，我们在美国明尼苏达州北部的一个长期无室操纵实验中，研究了温度升高和降雨量减少对光合作用生化限制的影响。在自然环境中生长的 9 个来自北方-温带生态交错带的树种，在环境和升高（+3.4°C）的生长季温度以及环境或减少（≈40%的降雨量去除）夏季降雨量下生长。根据三个生长季原位测量的 AC 曲线，估计了表观 Rubisco 羧化和 RuBP 再生标准化到 25°C（分别为 V 和 J ）。我们的主要目标是测试物种是否会响应变暖和减少降雨量而下调 V 和 J ，预计这些响应在最寒冷和最潮湿的原生范围的物种中最大。这些假设没有得到支持，因为 V 或 J 没有总体主要处理效应（p>.14）。然而，J : V 比随着变暖显著下降（p=.0178），而变暖与减少降雨量对 J : V 比的相互作用不显著。光合参数对变暖的不敏感性与许多在更大温度差异下进行的先前研究形成对比，这些研究通常固定日间温度。总的来说，在相对现实的温度和土壤水分条件下生长的植物，在升高温度、减少降雨量或两者结合的情况下，其 J 和 V 表现出惊人的不敏感性。
