Truong Anthony T, Edwards Matthew S, Long Jeremy D
Department of Biology San Diego State University San Diego California USA.
Ecol Evol. 2024 Feb 13;14(2):e10947. doi: 10.1002/ece3.10947. eCollection 2024 Feb.
Understory assemblages associated with canopy-forming species such as trees, kelps, and rockweeds should respond strongly to climate stressors due to strong canopy-understory interactions. Climate change can directly and indirectly modify these assemblages, particularly during more stressful seasons and climate scenarios. However, fully understanding the seasonal impacts of different climate conditions on canopy-reliant assemblages is difficult due to a continued emphasis on studying single-species responses to a single future climate scenario during a single season. To examine these emergent effects, we used mesocosm experiments to expose seaweed assemblages associated with the canopy-forming golden rockweed, , to elevated temperature and pCO conditions reflecting two projected greenhouse emission scenarios (RCP 2.6 [low] & RCP 4.5 [moderate]). Assemblages were grown in the presence and absence of , and in two seasons. Relative to ambient conditions, predicted climate scenarios generally suppressed biomass and photosynthetic efficiency. However, these effects varied seasonally-both future scenarios reduced biomass in summer, but only the moderate scenario did so in winter. These reductions shifted the assemblage, with more extreme shifts occurring in summer. Contrarily, future scenarios did not shift assemblages within Absent treatments, suggesting that climate primarily affected assemblages indirectly through changes in . Mesocosm experiments were coupled with a field removal experiment to simulate the effects of climate-mediated loss on natural assemblages. Consistent with the mesocosm experiment, loss resulted in season-specific assemblage shifts, with weaker effects observed in winter. Together, our study supports the hypotheses that climate-mediated changes to canopy-forming species can indirectly affect the associated assemblage, and that these effects vary seasonally. Such seasonality is important to consider as it may provide periods of recovery when conditions are less stressful, especially if we can reduce the severity of future climate scenarios.
与树冠形成物种（如树木、海带和墨角藻）相关的林下组合，由于树冠与林下之间强烈的相互作用，应该会对气候压力源产生强烈反应。气候变化可以直接和间接地改变这些组合，特别是在压力更大的季节和气候情景下。然而，由于一直强调研究单一物种在单一季节对单一未来气候情景的反应，因此很难全面了解不同气候条件对依赖树冠的组合的季节性影响。为了研究这些新出现的影响，我们使用了中宇宙实验，将与树冠形成物种金色墨角藻相关的海藻组合暴露在反映两种预测温室气体排放情景（RCP 2.6[低]和RCP 4.5[中]）的升高温度和pCO₂条件下。组合在有和没有金色墨角藻的情况下生长，并在两个季节中进行。相对于环境条件，预测气候情景通常会抑制金色墨角藻的生物量和光合效率。然而，这些影响随季节而变化——两种未来情景在夏季都会降低金色墨角藻的生物量，但只有中等情景在冬季会这样做。这些减少改变了组合，夏季发生的变化更为极端。相反，未来情景在没有金色墨角藻的处理中没有改变组合，这表明气候主要通过金色墨角藻变化间接影响组合。中宇宙实验与一项实地金色墨角藻去除实验相结合，以模拟气候介导的金色墨角藻损失对自然组合的影响。与中宇宙实验一致，金色墨角藻损失导致特定季节的组合变化，冬季观察到的影响较弱。总之，我们的研究支持以下假设：气候介导的对树冠形成物种的变化会间接影响相关组合，并且这些影响随季节而变化。考虑到这种季节性很重要，因为当条件压力较小时，它可能会提供恢复时期，特别是如果我们能够降低未来气候情景的严重程度。
