Centre for Functional Ecology, Department of Life Sciences, University of Coimbra, Calçada Martim de Freitas, 3000-456 Coimbra, Portugal.
Centre for Functional Ecology, Department of Life Sciences, University of Coimbra, Calçada Martim de Freitas, 3000-456 Coimbra, Portugal.
Sci Total Environ. 2017 Dec 1;599-600:1638-1645. doi: 10.1016/j.scitotenv.2017.05.101. Epub 2017 May 19.
Salinization is of major global concern due to its effect on stream biota, and ecosystem functions and services. In small streams, litter decomposition is a key ecosystem-level process driven by decomposers, mainly fungi (aquatic hyphomycetes), which link litter and invertebrates. Here we assessed the effects of an environmentally relevant range of salt additions (0, 2, 4, 8, 16gL NaCl) on (1) fungal growth and species-specific reproductive output and (2) fungal mediated-decomposition of Quercus robur leaves. Growth rates of eight out of nine species of aquatic hyphomycetes were negatively affected by salinity at concentrations ≥4gL. EC50s were species-specific and ≥7.80gL. Distinct thresholds were observed for reproduction: only five species sporulated at 2gL, and a single one (Flagellospora curta) sporulated at 4 and 8gL NaCl. Based on these results, we evaluated if tolerant fungal assemblages, with increasingly fewer species (9, 5, 1), were able to maintain similar functional functions and processes at the different salt levels. No significant differences were found in oak mass loss or sporulation rates at 0 or 2gL NaCl; a clear inhibition of both parameters was observed at the highest concentrations (i.e., 4 and 8gL NaCl). Different dominance patterns in multi-species fungal assemblages may determine bottom-up impacts on the stream food webs through effects on detritivore feeding preferences. Specific growth rate, characterized by RNA concentration, was higher in the single species, at the highest salt-concentration, and lower in the 9-species assemblage. Respiration was almost 2-times higher in mixed assemblages without added salt. Under salt-contamination, trade-offs between growth and sporulation seem to guarantee high levels of fungal growth and decomposition, particularly in multi-species assemblages. In the presence of salt contamination, aquatic hyphomycetes, even at reduced diversity, remain important drivers of leaf decomposition and ensure organic matter recycling.
盐化作用是一个全球性的主要问题，因为它会影响溪流生物群、生态系统功能和服务。在小溪流中，凋落物分解是由分解者（主要是真菌，即水生真菌）驱动的关键生态系统级过程，它将凋落物和无脊椎动物联系起来。在这里，我们评估了环境相关范围内的盐分添加（0、2、4、8、16gL NaCl）对（1）真菌生长和种特异性生殖产量和（2）真菌介导的栎树叶分解的影响。在浓度≥4gL 的盐度下，有 8 种水生真菌中有 9 种的生长速度受到负面影响。EC50 是种特异性的，≥7.80gL。生殖也有明显的阈值：只有 5 种物种在 2gL 时产生孢子，只有一种（Flagellospora curta）在 4 和 8gL NaCl 时产生孢子。基于这些结果，我们评估了在不同盐度下，具有越来越少物种（9、5、1）的耐受真菌组合是否能够维持类似的功能和过程。在 0 或 2gL NaCl 时，栎树叶的质量损失或孢子产生率没有显著差异；在最高浓度（即 4 和 8gL NaCl）时，这两个参数都明显受到抑制。在多物种真菌组合中不同的优势模式可能通过对碎屑食性者摄食偏好的影响，决定对溪流食物网的底栖影响。以 RNA 浓度为特征的特定生长率在最高盐浓度下的单一物种中较高，而在 9 种物种组合中较低。在没有添加盐的情况下，混合组合中的呼吸作用几乎高出 2 倍。在盐分污染下，生长和生殖之间的权衡似乎保证了真菌生长和分解的高水平，特别是在多物种组合中。在盐分污染的情况下，水生真菌即使在多样性降低的情况下，仍然是叶片分解的重要驱动因素，并确保有机物质的再循环。
