Data_Sheet_1_Species-Specific Trait Responses of Three Tropical Seagrasses to Multiple Stressors: The Case of Increasing Temperature and Nutrient Enrichment.docx

Seagrass meadows are declining globally. The decrease of seagrass area is influenced by the simultaneous occurrence of many factors at the local and global scale, including nutrient enrichment and climate change. This study aims to find out how increasing temperature and nutrient enrichment affect the morphological, biochemical and physiological responses of three coexisting tropical species, Thalassia hemprichii, Cymodocea serrulata and Halophila stipulacea. To achieve these aims, a 1-month experiment under laboratory conditions combining two temperature (maximum ambient temperature and current average temperature) and two nutrient (high and low N and P concentrations) treatments was conducted. The results showed that the seagrasses were differentially affected by all treatments depending on their life-history strategies. Under higher temperature treatments, C. serrulata showed photo-acclimation strategies, while T. hemprichii showed decreased photo-physiological performance. In contrast, T. hemprichii was resistant to nutrient over-enrichment, showing enhanced nutrient content and physiological changes, but C. serrulata suffered BG nutrient loss. The limited response of H. stipulacea to nutrient enrichment or high temperature suggests that this seagrass is a tolerant species that may have a dormancy state with lower photosynthetic performance and smaller-size individuals. Interaction between both factors was limited and generally showed antagonistic effects only on morphological and biochemical traits, but not on physiological traits. These results highlight the different effects and strategies co-inhabiting seagrasses have in response to environmental changes, showing winners and losers of a climate change scenario that may eventually cause biodiversity loss. Trait responses to these stressors could potentially make the seagrasses weaker to cope with following events, due to BG biomass or nutrient loss. This is of importance as biodiversity loss in tropical seagrass ecosystems could change the overall effectiveness of ecosystem functions and services provided by the seagrass meadows.

全球海草床（Seagrass meadows）正面临全球性衰退。海草面积的缩减受局地与全球尺度下多重因素共同作用影响，其中包括营养富集与气候变化。本研究旨在明确升温与营养富集对三种共域热带海草物种（Thalassia hemprichii、Cymodocea serrulata、Halophila stipulacea）的形态、生化及生理响应的影响。为达成上述研究目标，本研究在实验室条件下开展了为期1个月的控制实验，设置两类温度处理（环境最高温度与当前平均温度）以及两类营养盐处理（高低氮[N]、磷[P]浓度）。研究结果显示，所有处理对海草的影响存在物种特异性，这取决于各物种的生活史策略。在高温处理下，C. serrulata展现出光适应策略，而T. hemprichii的光生理性能则出现下降。与之相反，T. hemprichii对营养盐过度富集具有耐受性，其营养含量与生理活动均有所增强，而C. serrulata则出现地下（BG）营养流失的现象。H. stipulacea对营养富集与高温的响应较为有限，这表明该海草物种具有较强耐受性，可能通过进入休眠状态以维持较低的光合性能，并形成个体小型化的特征。两类胁迫因子的交互作用影响有限，且仅在形态与生化性状上表现出拮抗效应，对生理性状则无显著影响。上述研究结果揭示了共域海草物种对环境变化的不同响应效应与适应策略，明确了气候变化情景下的优胜与劣势物种，这一情景最终可能引发生物多样性丧失。海草对这些胁迫因子的性状响应可能会因地下生物量或营养流失，而削弱其应对后续环境事件的能力。这一结论具有重要意义，因为热带海草生态系统的生物多样性丧失可能会改变海草床所提供的生态系统功能与服务的整体效能。