Simon K S, Simon M A, Benfield E F
School of Biology and Ecology, University of Maine, Orono, Maine 04469-5722, USA.
Ecol Appl. 2009 Jul;19(5):1147-60. doi: 10.1890/08-0571.1.
Acidification is a widespread phenomenon that damages aquatic systems, and it has been the focus of intensive management efforts. While most management has focused on community structure as an endpoint, ecosystem function is also sensitive to acidification and important in stream health. We examined how a key ecosystem function in streams, leaf breakdown, varied along a gradient of pH resulting from acid deposition, natural conditions, and liming. We also measured how invertebrate and microbial assemblage structure and microbial function were related to altered leaf breakdown rates. Leaf breakdown rates declined more than threefold along a gradient of stream acidity from pH 6.8 to 4.9. The diversity of leaf-shredding invertebrates, bacteria, and fungi showed little response to variation in pH. The abundance of one acid-sensitive caddisfly, Lepidostoma, declined with acidification, and Lepidostoma abundance explained 37% of the variation in leaf breakdown rates among sites. Microbial respiration was suppressed along the acidity gradient, although the pattern was weaker than that for breakdown rate. In short-term laboratory incubations, microbes at acidic and circumneutral sites demonstrated adaptation to ambient pH. The activity of microbial extracellular enzymes was strongly influenced by pH. In particular, the pattern of activity of phosphatase indicated increasing P limitation of microbes with increasing acidification. Our results show that leaf breakdown is a sensitive tool for examining the response of stream function to acidification and also for defining the mechanisms that drive functional response. Future management efforts should focus on key taxa that are particularly sensitive and effective at shredding leaves and also the role of shifting acidity in mediating the availability of phosphorus to microbial films that are important for stream function.
酸化是一种广泛存在的现象，会损害水生系统，一直是密集管理工作的重点。虽然大多数管理工作都将群落结构作为终点，但生态系统功能对酸化也很敏感，并且在溪流健康中很重要。我们研究了溪流中的一项关键生态系统功能——树叶分解，在由酸沉降、自然条件和石灰处理导致的pH梯度上是如何变化的。我们还测量了无脊椎动物和微生物群落结构以及微生物功能与树叶分解速率变化之间的关系。沿着溪流酸度从pH 6.8到4.9的梯度，树叶分解速率下降了三倍多。撕食树叶的无脊椎动物、细菌和真菌的多样性对pH变化几乎没有反应。一种对酸敏感的毛翅目昆虫——鳞石蛾的丰度随着酸化而下降，鳞石蛾的丰度解释了各站点树叶分解速率变化的37%。沿着酸度梯度，微生物呼吸受到抑制，尽管这种模式比分解速率的模式要弱。在短期实验室培养中，酸性和近中性站点的微生物表现出对环境pH的适应性。微生物胞外酶的活性受到pH的强烈影响。特别是，磷酸酶的活性模式表明，随着酸化程度的增加，微生物对磷的限制也在增加。我们的结果表明，树叶分解是检验溪流功能对酸化反应以及确定驱动功能反应机制的一个敏感工具。未来的管理工作应关注对撕食树叶特别敏感且有效的关键分类群，以及酸度变化在调节对溪流功能重要的微生物膜可利用磷方面的作用。
