Department of Biology, University of North Florida, 1 UNF Drive, Jacksonville, FL 32224, USA.
School of Forestry and Wildlife Sciences, Auburn University, 602 Duncan Drive, Auburn, AL 36849, USA.
Tree Physiol. 2021 Jan 9;41(1):103-118. doi: 10.1093/treephys/tpaa107.
Temperature and salinity are important regulators of mangrove range limits and productivity, but the physiological responses of mangroves to the interactive effects of temperature and salinity remain uncertain. We tested the hypothesis that salinity alters photosynthetic responses to seasonal changes in temperature and vapor pressure deficit (D), as well as thermal acclimation _of leaf respiration in black mangrove (Avicennia germinans). To test this hypothesis, we grew seedlings of A. germinans in an outdoor experiment for ~ 12 months under four treatments spanning 0 to 55 ppt porewater salinity. We repeatedly measured seedling growth and in situ rates of leaf net photosynthesis (Asat) and stomatal conductance to water vapor (gs) at prevailing leaf temperatures, along with estimated rates of Rubisco carboxylation (Vcmax) and electron transport for RuBP regeneration (Jmax), and measured rates of leaf respiration at 25 °C (Rarea25). We developed empirical models describing the seasonal response of leaf gas exchange and photosynthetic capacity to leaf temperature and D, and the response of Rarea25 to changes in mean daily air temperature. We tested the effect of salinity on model parameters. Over time, salinity had weak or inconsistent effects on Asat, gs and Rarea25. Salinity also had little effect on the biochemical parameters of photosynthesis (Vcmax, Jmax) and individual measurements of Asat, gs, Vcmax and Jmax showed a similar response to seasonal changes in temperature and D across all salinity treatments. Individual measurements of Rarea25 showed a similar inverse relationship with mean daily air temperature across all salinity treatments. We conclude that photosynthetic responses to seasonal changes in temperature and D, as well as seasonal temperature acclimation of leaf R, are largely consistent across a range of salinities in A. germinans. These results might simplify predictions of photosynthetic and respiratory responses to temperature in young mangroves.
温度和盐度是调节红树林分布范围和生产力的重要因素，但红树林对温度和蒸汽压差（D）季节变化以及叶片呼吸热驯化的生理响应仍不确定。我们检验了这样一个假设，即盐度改变了光合作用对温度和蒸汽压差季节性变化的响应，以及黑榄（Avicennia germinans）叶片呼吸的热驯化。为了检验这一假设，我们在一个户外实验中，将黑榄幼苗在 0 至 55 ppt 孔隙水盐度的四个处理中生长了约 12 个月。我们反复测量了幼苗的生长和原位叶片净光合速率（Asat）和蒸腾速率（gs），同时还测量了 Rubisco 羧化（Vcmax）和 RuBP 再生电子传递（Jmax）的估计速率，以及在 25°C 时的叶片呼吸速率（Rarea25）。我们开发了经验模型，描述了叶片气体交换和光合能力对叶片温度和 D 的季节性响应，以及 Rarea25 对平均日气温变化的响应。我们测试了盐度对模型参数的影响。随着时间的推移，盐度对 Asat、gs 和 Rarea25 的影响较弱或不一致。盐度对光合作用的生化参数（Vcmax、Jmax）也几乎没有影响，而 Asat、gs、Vcmax 和 Jmax 的个别测量值对所有盐度处理下温度和 D 的季节性变化表现出相似的响应。Rarea25 的个别测量值在所有盐度处理中与平均日气温呈相似的反比关系。我们得出结论，在黑榄中，光合作用对温度和 D 季节性变化的响应以及叶片 R 的季节性温度驯化在很大程度上是一致的，跨越了一系列盐度范围。这些结果可能会简化对幼红树林光合作用和呼吸作用对温度响应的预测。
