Centre for Functional Ecology, Department of Life Sciences, University of Coimbra, Calçada Martim de Freitas, 3000-456 Coimbra, Portugal.
Cardiff School of Biosciences, Cardiff University, Cardiff, Wales, UK.
Sci Total Environ. 2022 Jul 10;829:154666. doi: 10.1016/j.scitotenv.2022.154666. Epub 2022 Mar 18.
Stream intermittency - periodic sequences of water flow cessation and resumption - occurs throughout the year, across seasons. Even though temperature is a known regulator of litter decomposition in both terrestrial and aquatic environments, comparative experiments on drought durations at distinct temperatures on microbial-mediated decomposition in streams experiencing intermittency are still lacking. Here, three drought temperatures (5, 15 and 25 °C) and two durations (short: 2.5 weeks; long: 5 weeks) were applied in a microcosm study to oak leaf discs colonized in a reference stream; mass loss and associated microbial parameters (fungal biomass, microbial activity, and sporulation rates) were evaluated following re-submersion for 2 weeks. Higher mass loss was found at 15 °C than 25 °C. A prolongation of the drought exposure period had no effect on mass loss, suggesting an early (≤ 2.5 weeks) inhibitor effect of drought on microbial-mediated leaf degradation. Fungal biomass was highest at 25 °C following a short drought, and decreased with a longer drought period at both 15 °C and 25 °C. Microbial activity was not affected by either drought duration or temperature. Sporulation rates and fungal diversity were significantly reduced by the longer drought period; in the short treatment, maximum values were found at 15 °C. In contrast to longer droughts, aquatic fungal communities during short dry periods seem to invest in energetically-expensive physiological responses to desiccation (e.g., ergosterol production) promoting biomass accrual at the expense of mass loss and reproductive output. Under more severe desiccation (higher duration and temperature), the lower diversity of fungal communities seem to result in negative legacy effects for fungal growth and reproductive capacity after flow resumption. These results suggest that native riparian vegetation, through its ability to regulate temperature in streams, may be critical in protecting freshwaters from intensified severity of drought periods in streams experiencing intermittency.
水流间歇性 - 水流停止和恢复的周期性序列 - 全年、跨季节都在发生。尽管温度是陆地和水生环境中凋落物分解的已知调节剂，但在经历间歇性的溪流中，针对不同温度下的干旱持续时间对微生物介导的分解的比较实验仍然缺乏。在这里，在一个微宇宙研究中，三个干旱温度（5、15 和 25°C）和两个持续时间（短：2.5 周；长：5 周）应用于在参考溪流中定殖的栎树叶片；在重新淹没 2 周后评估质量损失和相关的微生物参数（真菌生物量、微生物活性和孢子形成率）。在 15°C 时发现更高的质量损失，而在 25°C 时则较低。干旱暴露时间的延长对质量损失没有影响，这表明干旱对微生物介导的叶片降解有早期（≤2.5 周）的抑制作用。在短期干旱后，真菌生物量在 25°C 时最高，并且在 15°C 和 25°C 时随着干旱期的延长而减少。微生物活性不受干旱持续时间或温度的影响。孢子形成率和真菌多样性因较长的干旱期而显著降低；在短期处理中，最大值出现在 15°C。与较长的干旱期相比，在短的干旱期内，水生真菌群落似乎会投入大量的能量来应对干燥（例如，麦角固醇的产生），从而在牺牲质量损失和生殖输出的情况下促进生物量的积累。在更严重的干旱（更高的持续时间和温度）下，真菌群落的较低多样性似乎会导致水流恢复后真菌生长和生殖能力的负面遗留效应。这些结果表明，原生河岸植被通过其调节溪流温度的能力，可能对保护淡水免受间歇性溪流中干旱期强度加剧至关重要。
