Climate change impacts on overstory Desmarestia spp. from the western Antarctic Peninsula

This study examines climate change impacts (increased temperature and pCO2) on canopy-forming Desmarestia anceps and D. menziesii from the western Antarctic Peninsula during the austral summer–winter of 2013. These are ecologically important species that play a role functionally equivalent to kelp forests in this region. Two-way factorial microcosm experiments with treatments reflecting near-future ocean conditions were run with these species and include increased temperature alone (3.5 °C × pH 8.0), reduced pH alone (1.5 °C × pH 7.6), and both factors combined (3.5 °C × pH 7.6). Phlorotannin concentration, chlorophyll a concentration, growth, and photosynthetic parameters (slope to saturation of photo centers (α), saturating irradiance (E k), maximum electron transport rate (ETRmax), and maximum quantum yield of photosystem II (F v/F m)) were used to assess the physiological responses of the individuals to the different climate change treatments. Few significant impacts were observed: In D. menziesii, E k at the midpoint (after 39 days) was significantly higher in the 3.5 °C × pH 7.6 treatment and phlorotannin concentration was significantly higher in the 1.5 °C × pH 7.6 treatment than others at the end point of the experiment (79 days). All individuals in the experiment grew quickly through the midpoint, but growth declined thereafter. The photosynthetic apparatus of these species acclimated to microcosm conditions, and photo-physiological parameters changed between initial, midpoint, and end point measurements. Results indicate that D. menziesii is the more sensitive of the two species and that climate change factors can have a synergistic effect on this species. However, neither species responds negatively to climate change factors at the level of change used in this study, though the observed shifts in phlorotannin concentration and photosynthetic characteristics may have an unforeseen impact on the community dynamics in this geographic area.

本研究探究了2013年南半球夏冬季节，气候变化（升温与二氧化碳分压升高（pCO₂））对南极半岛西部冠层形成类群安氏网胰藻（Desmarestia anceps）与曼氏网胰藻（D. menziesii）的影响。这两个物种均为具有重要生态意义的类群，在该区域发挥着与海藻林功能等同的生态作用。本研究针对这两个物种开展了反映近未来海洋环境的双因子析因微宇宙实验，共设置3种处理：单独升温组（3.5 ℃ × pH 8.0）、单独降pH组（1.5 ℃ × pH 7.6）以及双因子协同组（3.5 ℃ × pH 7.6）。本研究通过测定褐藻多酚浓度、叶绿素a浓度、生长速率以及光合参数（包括光中心饱和斜率（α）、饱和光强（E_k）、最大电子传递速率（ETRmax）与光系统II最大量子产额（F_v/F_m）），评估了个体对不同气候变化处理的生理响应。本研究仅观测到少量显著影响：在曼氏网胰藻中，实验中期（39天后）的饱和光强（E_k）在3.5 ℃ × pH 7.6处理组中显著更高，而实验终点（79天）的褐藻多酚浓度在1.5 ℃ × pH 7.6处理组中显著高于其余组别。实验所有个体在实验中期阶段均快速生长，但在此之后生长速率出现下降。这两个物种的光合机构均适应了微宇宙实验环境，且光合生理参数在初始、中期与终点测定节点间发生了变化。研究结果表明，曼氏网胰藻是两个物种中更为敏感的类群，且气候变化因子可对该物种产生协同效应。但在本研究采用的变化幅度下，两个物种均未对气候变化因子产生负面响应；不过观测到的褐藻多酚浓度与光合特性变化，可能会对该区域的群落动态产生难以预测的影响。