Subsidy-stress responses of ecosystem functions along experimental freshwater salinity gradients

IF 3.9 3区 环境科学与生态学 Q2 ENVIRONMENTAL SCIENCES Biogeochemistry Pub Date : 2024-04-26 DOI:10.1007/s10533-024-01131-5
Stephen E. DeVilbiss, Brian D. Badgley, Erin R. Hotchkiss, Meredith K. Steele
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Abstract

Human activity is increasing salt concentrations in freshwaters worldwide, but effects of freshwater salinity gradients on biogeochemical cycling are less understood than in saline, brackish, or marine environments. Using controlled microcosm experiments, we characterized (1) short-term (one to five days) biogeochemical responses and (2) water column metabolism along a freshwater salinity gradient of multiple salt types. After one day, microcosms were oxic (4.48–7.40 mg O2 L−1) but became hypoxic (1.20–3.31 mg L−1) by day five. After one day in oxic conditions, microbial respiration in magnesium-, sodium-, and sea salt-based salinity treatments showed a subsidy-stress response, with respiration increasing by over 100% as salinity increased from 30 to 350–800 µS cm−1. Conversely, respiration consistently increased along a calcium-based salinity gradient, peaking at 1500 µS cm−1. By day five, an inverse subsidy-stress response was observed with elevated respiration at upper or lower ends of the gradient except for the magnesium treatment, which had the lowest respiration at the highest salinity. Calcium- and magnesium-based salinity treatments also caused considerable changes in phosphorus concentrations and C:P and N:P. In a separate experiment, microbial respiration and water column primary production also displayed subsidy-stress responses, but imbalances in effect sizes caused consistently declining net community production with increasing salinity. Collectively, our results establish that short-term exposure to different salt ion concentrations can enhance freshwater biogeochemical cycling at relatively low concentrations and alter resource stoichiometry. Furthermore, the nature of effects of freshwater salinization may also change with oxygen availability.

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实验性淡水盐度梯度生态系统功能的补贴-压力反应
人类活动正在增加全球淡水中的盐浓度,但人们对淡水盐度梯度对生物地球化学循环的影响的了解还不如对盐水、咸水或海洋环境的了解。利用受控微生态系统实验,我们描述了(1)短期(一至五天)生物地球化学反应和(2)多种盐类淡水盐度梯度的水体代谢。一天后,微观世界处于缺氧状态(4.48-7.40 毫克氧气/升),但到第五天,微观世界变得缺氧(1.20-3.31 毫克氧气/升)。在缺氧条件下一天后,镁、钠和海盐盐度处理中的微生物呼吸作用显示出一种补助应激反应,当盐度从 30 µS cm-1 增加到 350-800 µS cm-1 时,呼吸作用增加超过 100%。相反,呼吸作用沿着以钙为基础的盐度梯度持续增加,在 1500 µS cm-1 时达到峰值。到第五天,除了镁处理在最高盐度时呼吸作用最低外,在梯度的上端或下端都出现了反向的补贴压力反应,呼吸作用升高。以钙和镁为基础的盐度处理也会导致磷浓度以及碳:磷和氮:磷发生很大变化。在另一项实验中,微生物呼吸作用和水体初级生产力也显示出补贴应激反应,但效应大小的不平衡导致群落净生产力随着盐度的增加而持续下降。总之,我们的研究结果表明,短期暴露于不同浓度的盐离子可在相对较低的浓度下促进淡水生物地球化学循环,并改变资源的化学计量。此外,淡水盐碱化的影响性质也会随着氧气供应量的变化而改变。
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来源期刊
Biogeochemistry
Biogeochemistry 环境科学-地球科学综合
CiteScore
7.10
自引率
5.00%
发文量
112
审稿时长
3.2 months
期刊介绍: Biogeochemistry publishes original and synthetic papers dealing with biotic controls on the chemistry of the environment, or with the geochemical control of the structure and function of ecosystems. Cycles are considered, either of individual elements or of specific classes of natural or anthropogenic compounds in ecosystems. Particular emphasis is given to coupled interactions of element cycles. The journal spans from the molecular to global scales to elucidate the mechanisms driving patterns in biogeochemical cycles through space and time. Studies on both natural and artificial ecosystems are published when they contribute to a general understanding of biogeochemistry.
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