Department of Biology, Virginia Commonwealth University, 1000 W Cary Street, Richmond, VA, 23284, USA.
Glob Chang Biol. 2014 Apr;20(4):1351-62. doi: 10.1111/gcb.12431. Epub 2014 Jan 13.
Climate change-associated sea level rise is expected to cause saltwater intrusion into many historically freshwater ecosystems. Of particular concern are tidal freshwater wetlands, which perform several important ecological functions including carbon sequestration. To predict the impact of saltwater intrusion in these environments, we must first gain a better understanding of how salinity regulates decomposition in natural systems. This study sampled eight tidal wetlands ranging from freshwater to oligohaline (0-2 ppt) in four rivers near the Chesapeake Bay (Virginia). To help isolate salinity effects, sites were selected to be highly similar in terms of plant community composition and tidal influence. Overall, salinity was found to be strongly negatively correlated with soil organic matter content (OM%) and C : N, but unrelated to the other studied environmental parameters (pH, redox, and above- and below-ground plant biomass). Partial correlation analysis, controlling for these environmental covariates, supported direct effects of salinity on the activity of carbon-degrading extracellular enzymes (β-1, 4-glucosidase, 1, 4-β-cellobiosidase, β-D-xylosidase, and phenol oxidase) as well as alkaline phosphatase, using a per unit OM basis. As enzyme activity is the putative rate-limiting step in decomposition, enhanced activity due to salinity increases could dramatically affect soil OM accumulation. Salinity was also found to be positively related to bacterial abundance (qPCR of the 16S rRNA gene) and tightly linked with community composition (T-RFLP). Furthermore, strong relationships were found between bacterial abundance and/or composition with the activity of specific enzymes (1, 4-β-cellobiosidase, arylsulfatase, alkaline phosphatase, and phenol oxidase) suggesting salinity's impact on decomposition could be due, at least in part, to its effect on the bacterial community. Together, these results indicate that salinity increases microbial decomposition rates in low salinity wetlands, and suggests that these ecosystems may experience decreased soil OM accumulation, accretion, and carbon sequestration rates even with modest levels of saltwater intrusion.
预计气候变化引起的海平面上升将导致许多历史上的淡水生态系统受到海水入侵。特别令人关注的是潮汐淡水湿地，它们具有包括碳封存在内的多种重要生态功能。为了预测这些环境中的海水入侵的影响，我们必须首先更好地了解盐分如何调节自然系统中的分解作用。本研究在切萨皮克湾（弗吉尼亚州）附近的四条河流中，从淡水到寡盐水域（0-2 ppt）的八个潮汐湿地进行了采样。为了帮助隔离盐分的影响，选择了在植物群落组成和潮汐影响方面高度相似的地点。总的来说，盐分与土壤有机质含量（OM%）和 C:N 呈强烈负相关，但与其他研究的环境参数（pH 值、氧化还原电位、地上和地下植物生物量）无关。偏相关分析，在控制这些环境协变量的情况下，支持盐分对碳降解细胞外酶（β-1,4-葡萄糖苷酶、1,4-β-纤维二糖酶、β-D-木糖苷酶和酚氧化酶）以及碱性磷酸酶活性的直接影响，使用每单位 OM 为基础。由于酶活性是分解的假定限速步骤，因此盐分增加引起的酶活性增强可能会极大地影响土壤 OM 的积累。盐分也与细菌丰度（16S rRNA 基因的 qPCR）呈正相关，并与群落组成紧密相关（T-RFLP）。此外，还发现细菌丰度和/或组成与特定酶（1,4-β-纤维二糖酶、芳基硫酸酯酶、碱性磷酸酶和酚氧化酶）的活性之间存在很强的关系，这表明盐分对分解的影响可能至少部分是由于其对细菌群落的影响。综上所述，这些结果表明盐分增加了低盐湿地中微生物的分解速率，并表明这些生态系统即使受到适度的海水入侵，也可能会经历土壤 OM 积累、堆积和碳封存速率的降低。
