Coastal freshwater and brackish wetlands are exposed to pulses of saltwater during times of reduced freshwater flows (i.e., dry seasons, droughts), periodic storm surges, and increased tidal extent associated with rising seas. The effects of saltwater pulses on belowground processing rates of detrital organic matter as mediated by microbial activities are uncertain. Our objectives were to quantify whether and how pulses of saltwater (i) change soil porewater physicochemistry, (ii) change soil microbial extracellular enzyme activities, and (iii) change root litter breakdown over time in freshwater and brackish marshes. From 2014 to 2016, we simulated saltwater intrusion as monthly in situ pulsed additions of artificial seawater in experimental dosing chambers (1.4 m diameter) within freshwater and brackish marshes of Everglades National Park. At monthly intervals, we collected soil porewater chemistry, and measured microbial extracellular enzymes, elemental stoichiometric ratios, and breakdown rates (k) of incubated (0–30 cm depth) root litter and compared these responses over time. Saltwater pulses increased sulfate and nitrogen concentrations in porewater at the freshwater site. However, saltwater pulses generally decreased porewater constituents (e.g., dissolved organic carbon, dissolved nitrogen and phosphorus species) at the brackish site. One saltwater pulse increased root litter k by 1.25-fold in the brackish marsh. However, long-term (740 days) k in brackish wetlands, and both short- and long-term k in freshwater wetlands, were not affected by 24 monthly pulses of saltwater. Enzyme activities fluctuated with time and did not respond to multiple saltwater pulses. Our results suggest that detrital organic matter stocks and associated soil microbial activities are relatively resistant to single and multiple (n = 24) pulses of saltwater.

中文翻译：

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咸水脉冲对淡水和咸淡滨海湿地土壤微生物酶和有机质分解的影响

在淡水流量减少（即干旱季节，干旱），周期性风暴潮以及与海平面上升有关的潮汐范围增加的时间段内，沿海淡水和咸淡的湿地暴露于盐水的脉冲中。由微生物活动介导的盐水脉冲对碎屑有机物地下加工速率的影响尚不确定。我们的目标是量化盐水脉冲是否以及如何改变（i）改变土壤孔隙水的物理化学，（ii）改变土壤微生物的细胞外酶活性，以及​​（iii）随时间改变淡水和微咸沼泽中的凋落物分解。从2014年到2016年，我们模拟了盐水入侵，即在Everglades国家公园的淡水和咸淡沼泽中的实验配液室（直径1.4 m）中按月原位脉冲添加人造海水。k）培养的（0-30厘米深）根凋落物，并随时间比较这些响应。盐水脉冲增加了淡水站点孔隙水中硫酸盐和氮的浓度。但是，咸水脉冲通常会使微咸点的孔隙水成分减少（例如，溶解的有机碳，溶解的氮和磷物质）。在咸淡水沼泽中，一个盐水脉冲使根凋落物k增加1.25倍。但是，在半咸湿地中长期（740天）k，短期和长期k在淡水湿地中，不受24个每月脉冲盐水的影响。酶活性随时间波动，并且不响应多个盐水脉冲。我们的结果表明，碎屑有机物储量和相关的土壤微生物活动 对盐水的单个和多个（n = 24）脉冲具有相对的抵抗力。