Department of Biology, Duke University, Durham, North Carolina, United States of America.
Department of Forestry and Environmental Resources, North Carolina State University, Raleigh, North Carolina, United States of America.
PLoS One. 2023 Dec 21;18(12):e0296128. doi: 10.1371/journal.pone.0296128. eCollection 2023.
Salinization of coastal freshwater wetlands is an increasingly common and widespread phenomenon resulting from climate change. The ecosystem consequences of added salinity are poorly constrained and highly variable across prior observational and experimental studies. We added 1.8 metric tons of marine salts to replicated 200 m2 plots within a restored forested wetland in Eastern North Carolina over the course of four years. Based on prior small-scale experiments at this site, we predicted that salinization would lead to slower tree growth and suppressed soil carbon cycling. Results from this large-scale field experiment were subtle and inconsistent over space and time. By the fourth year of the experiment, we observed the predicted suppression of soil respiration and a reduction of water extractable carbon from soils receiving salt treatments. However, we found no cumulative effects of four years of salinization on total soil carbon stocks, tree growth, or root biomass. We observed substantial variation in soil solution chemistry (notably, pH and base saturation) across replicated treatment blocks; the effective salt levels, ionic composition, and pH varied following treatment depending upon pre-existing differences in edaphic factors. Our multi-year monitoring also revealed an underlying trend of wetland acidification across the entire site, a suspected effect of ecosystem recovery following wetland restoration on former agricultural land. The overwhelming resistance to our salt treatments could be attributed to the vigor of a relatively young, healthy wetland ecosystem. The heterogeneous responses to salt that we observed over space and time merits further investigation into the environmental factors that control carbon cycling in wetlands. This work highlights the importance of multi-year, large-scale field experiments for investigating ecosystem responses to global environmental change.
滨海淡水湿地的盐渍化是气候变化导致的一种日益普遍和广泛的现象。由于先前的观测和实验研究，添加盐分对生态系统的影响受到很大的限制，而且变化很大。我们在北卡罗来纳州东部一个已恢复的森林湿地内的 200 平方米复制地块中，在四年的时间里添加了 1.8 公吨的海水盐。基于该地点之前的小规模实验，我们预测盐渍化会导致树木生长缓慢和土壤碳循环受到抑制。这项大规模野外实验的结果在空间和时间上都很细微且不一致。到实验的第四年，我们观察到了预期的土壤呼吸抑制和盐处理土壤中可提取水碳的减少。然而，我们没有发现四年盐渍化对土壤总碳储量、树木生长或根系生物量的累积效应。我们观察到土壤溶液化学性质（特别是 pH 值和基础饱和度）在重复处理区块之间存在很大差异；有效盐分水平、离子组成和 pH 值在处理后会根据土壤因素的先前差异而变化。我们多年的监测还揭示了整个场地湿地酸化的潜在趋势，这是湿地恢复后对前农业用地的生态系统恢复的一种怀疑效应。我们的盐分处理受到强烈抵制，可以归因于相对年轻、健康的湿地生态系统的活力。我们在空间和时间上观察到的盐分反应的异质性值得进一步研究控制湿地碳循环的环境因素。这项工作强调了进行多年、大规模野外实验对于研究生态系统对全球环境变化的响应的重要性。
