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Correction to: Terrestrial and marine POC export fluxes estimated by 234Th–238U disequilibrium and δ13C measurements in the East China Sea shelf Correction to:东海大陆架 234Th-238U 失衡和 δ13C 测量估算的陆地和海洋 POC 出口通量
IF 3.9 3区 环境科学与生态学 Q2 ENVIRONMENTAL SCIENCES Pub Date : 2024-05-20 DOI: 10.1007/s10533-024-01152-0
Qiangqiang Zhong, Dekun Huang, Qiugui Wang, Jinzhou Du, Fule Zhang, Jing Lin, Tao Yu
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引用次数: 0
Unearthing the legacy of wildfires: post fire pyrogenic carbon and soil carbon persistence across complex Pacific Northwest watersheds 揭示野火的遗产:西北太平洋复杂流域的火成碳和土壤碳持久性
IF 3.9 3区 环境科学与生态学 Q2 ENVIRONMENTAL SCIENCES Pub Date : 2024-05-17 DOI: 10.1007/s10533-024-01151-1
Hayley Peter-Contesse, Kate Lajtha, Aron Boettcher, Regina O’Kelley, Amy Mayedo

Wildfires have the potential to dramatically alter the carbon (C) storage potential, ecological function, and the fundamental mechanisms that control the C balance of Pacific Northwest (PNW) forested ecosystems. In this study, we explored how wildfire influences processes that control soil C stabilization and the consequent soil C persistence, and the role of previous fire history in determining soil C fire response dynamics. We collected mineral soils at four depth increments from burned (low, moderate, and high soil burn severity classes) and unburned areas and surveyed coarse woody debris (CWD) in sites within the footprint of the 2020 Holiday Farm Fire and in surrounding Willamette National Forest and the H.J. Andrews Experimental Forest. We found few changes in overall soil C pools as a function of fire severity; we instead found that unburned sites contained high levels of pyrogenic C (PyC) that were commensurate with PyC concentrations in the high severity burn sites—pointing to the high background rate of fire in these ecosystems. An analysis of historical fire events lends additional support, where increasing fire count is loosely correlated with increasing PyC concentration. An unexpected finding was that PyC concentration was lower in low soil burn severity sites than in control sites, which we attribute to fundamental ecological differences in regions that repeatedly burn at high severity compared with those that burn at low severity. Our CWD analysis showed that high mean fire return interval (decades between fire events) was strongly correlated with low annual CWD accumulation rate; whereas areas that burn frequently had a high annual CWD accumulation rate. Within the first year postfire, trends in soil density fractions demonstrated no significant response to fire for the mineral-associated organic matter pool but slight increases in the particulate pool with increasing soil burn severity—likely a function of increased charcoal additions. Overall, our results suggest that these PNW forest soils display complex responses to wildfire with feedbacks between CWD pools that provide varying fuel loads and a mosaic fire regime across the landscape. Microclimate and historic fire events are likely important determinants of soil C persistence in these systems.

野火有可能极大地改变西北太平洋(PNW)森林生态系统的碳(C)储存潜力、生态功能以及控制碳平衡的基本机制。在这项研究中,我们探讨了野火如何影响控制土壤碳稳定的过程和由此产生的土壤碳持久性,以及以前的火灾历史在决定土壤碳火灾响应动态中的作用。我们采集了 2020 年假日农场大火火场范围内及周边威拉米特国家森林和 H.J. 安德鲁斯实验森林中已烧毁(低、中、高土壤烧毁严重程度等级)和未烧毁地区的矿物土壤,并调查了粗木屑(CWD)。我们发现整体土壤碳库与火灾严重程度的函数关系变化不大;相反,我们发现未被烧毁的地点含有高水平的热源碳(PyC),与严重火灾地点的 PyC 浓度相当,这表明这些生态系统的火灾背景率很高。对历史火灾事件的分析提供了更多支持,火灾次数的增加与 PyC 浓度的增加呈松散相关。一个出乎意料的发现是,土壤燃烧严重程度低的地点的 PyC 浓度低于对照地点,我们将其归因于与燃烧严重程度低的地区相比,重复燃烧严重程度高的地区存在根本性的生态差异。我们的 CWD 分析表明,高平均火灾重现间隔(火灾事件之间的数十年间隔)与低 CWD 年累积率密切相关;而频繁火灾地区的 CWD 年累积率较高。在火灾后的第一年内,土壤密度组分的变化趋势表明,与矿物质相关的有机物库对火灾没有明显的反应,但随着土壤燃烧严重程度的增加,颗粒物库的密度略有增加,这可能是木炭添加量增加的结果。总之,我们的研究结果表明,这些西北太平洋森林土壤对野火的反应很复杂,它们在提供不同燃料负荷的化武分解池之间产生反馈作用,并在整个地貌上形成了马赛克火灾机制。小气候和历史上的火灾事件可能是这些系统中土壤 C 持久性的重要决定因素。
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引用次数: 0
Soil C:N:P stoichiometric signatures of grasslands differ between tropical and warm temperate climatic zones 热带和暖温带气候区草地土壤 C:N:P 的化学计量特征不同
IF 3.9 3区 环境科学与生态学 Q2 ENVIRONMENTAL SCIENCES Pub Date : 2024-05-16 DOI: 10.1007/s10533-024-01143-1
Ángel Héctor Hernández-Romero, Yareni Perroni, Lázaro Rafael Sánchez Velásquez, Sergio Martínez-Hernández, Carlos Héctor Ávila-Bello, Xiaofeng Xu, Lihua Zhang

Climate and land management affect nutrient cycling in grassland ecosystems. We aimed to understand whether temperate and tropical grasslands differ in terms of soil organic carbon (SOC), nitrogen (N), and phosphorus (P) concentrations, and their C:N:P stoichiometric ratios in grazed and ungrazed natural grasslands and pastures. For this, we used a meta-analysis approach (1296 records, 241 papers), and regression models to explain the observed patterns in terms of mean annual precipitation (MAP), mean annual temperature (MAT), altitude, and latitude. SOC, N, and P concentrations were higher in temperate regions than in tropical ones, and they negatively correlated with MAT and MAP. The grassland type effect was more significant for tropical regions. In tropical regions, soil C:N ratios were higher in ungrazed than in grazed pastures, and soil N:P ratios in ungrazed sites were higher in pastures than in natural grasslands. Grazing increases soil N and SOC for natural grasslands in temperate regions. Our findings suggest that soil stoichiometric C:N:P stoichiometric signatures in grasslands differed between tropical and temperate regions on a global scale. P is a key element in regulation and restriction on soil C and N cycling in tropical regions but less in the temperate ones. Our findings suggest the direction of effects of grazing or grassland type on C:N:P stoichiometric signature. Since imbalances in soil stoichiometric ratios may have implications for ecosystem functioning, the assessment of these patterns could serve as a valuable tool for management and conservation of grasslands and pastures in both tropical and temperate regions.

气候和土地管理会影响草地生态系统的养分循环。我们的目的是了解温带和热带草地的土壤有机碳(SOC)、氮(N)和磷(P)浓度及其 C:N:P 的化学计量比在放牧和未放牧的天然草地和牧场中是否存在差异。为此,我们采用了荟萃分析方法(1296 条记录,241 篇论文)和回归模型,从年平均降水量 (MAP)、年平均气温 (MAT)、海拔高度和纬度等方面解释观察到的模式。温带地区的 SOC、N 和 P 浓度高于热带地区,且与 MAT 和 MAP 负相关。热带地区的草原类型效应更为显著。在热带地区,未放牧草场的土壤碳氮比高于放牧草场,未放牧草场的土壤氮磷比高于天然草场。放牧增加了温带地区天然草地的土壤氮和SOC。我们的研究结果表明,在全球范围内,热带地区和温带地区的草地土壤C:N:P的化学计量特征是不同的。在热带地区,磷是调节和限制土壤碳和氮循环的关键因素,而在温带地区则较少。我们的研究结果表明了放牧或草地类型对 C:N:P 化学计量特征的影响方向。由于土壤化学计量比的失衡可能会对生态系统功能产生影响,因此对这些模式进行评估可作为热带和温带地区草地和牧场管理与保护的重要工具。
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引用次数: 0
Soil gross N2O emission and uptake under two contrasting agroforestry systems: riparian tree buffer versus alley-cropping tree row 两种截然不同的农林系统下的土壤总 N2O 排放量和吸收量:河岸树木缓冲区与巷作树行
IF 3.9 3区 环境科学与生态学 Q2 ENVIRONMENTAL SCIENCES Pub Date : 2024-05-16 DOI: 10.1007/s10533-024-01141-3
Jie Luo, Lukas Beule, Guodong Shao, Dan Niu, Edzo Veldkamp, Marife D. Corre

In addition to the removal of excess mineral nitrogen (N) via root uptake, trees in agroforestry systems may mitigate negative effects of high N fertilization of adjacent crops by enhancing complete denitrification of excess mineral N aside from root uptake. Presently, little is known about the potential for NO3 reduction through denitrification (conversion to greenhouse gas N2O and subsequently to non-reactive N2) in contrasting agroforestry systems: riparian tree buffer versus tree row of an upland alley-cropping system. Our study aimed to (1) quantify gross N2O emissions (both N2O + N2 emissions) and gross N2O uptake (N2O reduction to N2), and (2) determine their controlling factors. We employed the 15N2O pool dilution technique to quantify gross N2O fluxes from 0 to 5 cm (topsoil) and 40 to 60 cm (subsoil) depths with seasonal field measurements in 2019. The riparian tree buffer exhibited higher topsoil gross N2O emissions and uptake than the alley-cropping tree row (P < 0.03). Gross N2O emissions were regulated by N and carbon (C) availabilities and aeration status rather than denitrification gene abundance. Gross N2O uptake was directly linked to available C and nirK gene abundance. In the subsoil, gross N2O emission and uptake were low in both agroforestry systems, resulting from low mineral N contents possibly due to N uptake by deep tree roots. Nonetheless, the larger available C and soil moisture in the subsoil of riparian tree buffer than in alley-cropping tree row (P < 0.05) suggest its large potential for N2O uptake whenever NO3 is transported to the subsoil.

除了通过根部吸收去除多余的矿物氮(N)外,农林系统中的树木还可以通过加强对根部吸收以外的多余矿物氮的完全反硝化作用,减轻邻近作物高氮施肥的负面影响。目前,人们对河岸树木缓冲区与高地小巷种植系统中的树木行通过反硝化作用(转化为温室气体 N2O,然后再转化为非反应性 N2)减少 NO3- 的潜力知之甚少。我们的研究旨在:(1) 量化 N2O 排放总量(N2O + N2 排放)和 N2O 吸收总量(N2O 还原为 N2);(2) 确定其控制因素。我们采用 15N2O 池稀释技术量化了 0 至 5 厘米(表土)和 40 至 60 厘米(底土)深度的 N2O 总通量,并在 2019 年进行了季节性实地测量。河岸树木缓冲区的表土总 N2O 排放量和吸收量均高于小巷种植树木行(P < 0.03)。一氧化二氮总排放量受氮和碳的利用率以及通气状态的影响,而不是受反硝化基因丰度的影响。N2O 总吸收量与可用碳和 nirK 基因丰度直接相关。在两种农林系统中,底土的 N2O 排放总量和吸收总量都很低,这可能是由于树木深根吸收 N 导致矿质 N 含量较低。尽管如此,河岸树木缓冲区底土中的可利用 C 和土壤水分比小巷种植树木行中的大(P < 0.05),这表明只要 NO3- 被运输到底土,其吸收 N2O 的潜力就很大。
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引用次数: 0
Assessing the spatiotemporal variability of dissolved organic matter fluorescence composition in the Lake George, NY watershed 评估纽约州乔治湖流域溶解有机物荧光成分的时空变异性
IF 3.9 3区 环境科学与生态学 Q2 ENVIRONMENTAL SCIENCES Pub Date : 2024-05-15 DOI: 10.1007/s10533-024-01147-x
Aleksandar I. Goranov, Mark W. Swinton, David A. Winkler, Jeremy L. Farrell, Sandra A. Nierzwicki-Bauer, Sasha Wagner

Lake George (LG) is a temperate, oligotrophic, medium-sized lake (114 km2) located in northeastern New York State (U.S.). Lakes are highly understudied environments where extensive dissolved organic matter (DOM) processing occurs. With this study we establish the foundation for researching the organic biogeochemistry of the LG watershed, in particular, the numerous tributaries flowing into the lake. Collected were 213 samples from 64 tributaries and 12 lake locations. Some of the tributaries had unique wastewater, agricultural, or wetland influences. We employed fluorescence spectroscopy, a common biogeochemical technique, to characterize the fluorescent DOM (FDOM) component. We developed a parallel factor analysis (PARAFAC) model for the deconvolution of FDOM data allowing to depict six underlying FDOM constituents, which varied in source and biogeochemical reactivity on spatiotemporal scales. Tributary DOM, in comparison to lake DOM, was much more aromatic, of larger molecular weight, more humic, and contained less protein-like material. The distribution of humic and protein-like PARAFAC components was impacted by land-use and wastewater influences. Supporting characterization of the chromophoric DOM (CDOM) and total DOM (on dissolved organic carbon basis) allowed differentiating the influence of wetlands, which could not be depicted by spatiotemporally assessing the variability of PARAFAC components. Temporal assessment revealed minor variabilities in tributary DOM quantity and quality except in cases of point sources such as wastewater treatment facilities. Overall, this primer study establishes baseline understanding of the baseflow levels of DOM constituents in the LG watershed, and more broadly, presents a PARAFAC model for the deconvolution of fluorescence spectra of DOM from temperate and oligotrophic lake watersheds such as LG.

乔治湖(LG)位于美国纽约州东北部,是一个中型温带寡营养湖泊(114 平方公里)。在湖泊中,大量溶解有机物 (DOM) 被加工处理,但对湖泊的研究却非常不足。通过这项研究,我们为研究 LG 流域(尤其是流入湖泊的众多支流)的有机生物地球化学奠定了基础。我们从 64 条支流和 12 个湖泊地点采集了 213 个样本。其中一些支流受到废水、农业或湿地的独特影响。我们采用荧光光谱(一种常见的生物地球化学技术)来描述荧光 DOM(FDOM)成分的特征。我们建立了一个并行因子分析(PARAFAC)模型,用于对 FDOM 数据进行解卷积,从而描绘出六种基本的 FDOM 成分,它们在时空尺度上的来源和生物地球化学反应性各不相同。与湖泊 DOM 相比,支流 DOM 的芳香烃含量更高、分子量更大、腐殖质更多,蛋白质类物质含量更少。腐殖质和蛋白质类 PARAFAC 成分的分布受到土地利用和废水的影响。色度 DOM(CDOM)和总 DOM(以溶解有机碳为基础)的支持性特征描述可以区分湿地的影响,而 PARAFAC 成分的时空变化评估无法描述湿地的影响。时空评估显示,除了废水处理设施等点源外,支流 DOM 的数量和质量变化不大。总之,这项初步研究建立了对 LG 流域 DOM 成分基流水平的基本认识,并更广泛地提出了一个 PARAFAC 模型,用于解构温带和低营养湖泊流域(如 LG)的 DOM 荧光光谱。
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引用次数: 0
Contribution of marine macrophytes to pCO2 and DOC variations in human-impacted coastal waters 海洋大型藻类对人类影响的沿海水域 pCO2 和 DOC 变化的贡献
IF 3.9 3区 环境科学与生态学 Q2 ENVIRONMENTAL SCIENCES Pub Date : 2024-05-04 DOI: 10.1007/s10533-024-01140-4
Kenta Watanabe, Tatsuki Tokoro, Hirotada Moki, Tomohiro Kuwae

Carbon cycles in coastal waters are highly sensitive to human activities and play important roles in global carbon budgets. CO2 sink–source behavior is regulated by spatiotemporal variations in net biological productivity, but the contribution of macrophyte habitats including macroalgae aquaculture to atmospheric CO2 removal has not been well quantified. We investigated the variations in the carbonate system and dissolved organic carbon (DOC) in human-impacted macrophyte habitats and analyzed the biogeochemical drivers for the variations of these processes. Cultivated macroalgal metabolism (photosynthesis, respiration, calcification, and DOC release) was quantified by in situ field-bag experiments. Cultivated macroalgae took up dissolved inorganic carbon (DIC) (16.2–439 mmol-C m−2 day−1) and released DOC (1.2–146 mmol-C m−2 day−1). We estimated that seagrass beds and macroalgae farming contributed 0.8 and 0.4 mmol-C m−2 day−1 of the in situ total CO2 removal (5.7 and 6.7 mmol-C m−2 day−1, respectively) during their growing period in a semi-enclosed embayment but efficient water exchange (i.e., short residence time) in an open coastal area precluded detection of the contribution of macrophyte habitats to the CO2 removal. Although hydrological processes, biological metabolism, and organic carbon storage processes would contribute to the net CO2 sink–source behavior, our analyses distinguished the contribution of macrophytes from other factors. Our findings imply that macroalgae farming, in addition to restoring and creating macrophyte habitats, has potential for atmospheric CO2 removal.

沿岸水域的碳循环对人类活动非常敏感,在全球碳预算中发挥着重要作用。二氧化碳的汇-源行为受净生物生产力时空变化的调控,但大型藻类养殖等大型生物栖息地对大气二氧化碳去除的贡献尚未得到很好的量化。我们研究了受人类影响的大型藻类生境中碳酸盐系统和溶解有机碳(DOC)的变化,并分析了这些过程变化的生物地球化学驱动因素。通过现场袋式实验对人工养殖的大型藻类的新陈代谢(光合作用、呼吸作用、钙化和溶解有机碳释放)进行了量化。培养的大型藻类吸收溶解无机碳(DIC)(16.2-439 mmol-C m-2 day-1)并释放 DOC(1.2-146 mmol-C m-2 day-1)。据估计,海草床和大型藻类养殖在半封闭海湾的生长期对二氧化碳原位总去除量(分别为 5.7 和 6.7 mmol-C m-2 day-1)的贡献分别为 0.8 和 0.4 mmol-C m-2 day-1,但在开阔的沿海地区,高效的水交换(即停留时间短)使得无法检测到大型藻类生境对二氧化碳去除量的贡献。尽管水文过程、生物新陈代谢和有机碳储存过程都会对二氧化碳的净汇-源行为作出贡献,但我们的分析将大型藻类的贡献与其他因素区分开来。我们的研究结果表明,大型藻类养殖除了能恢复和创造大型藻类栖息地外,还具有去除大气中二氧化碳的潜力。
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引用次数: 0
Has nitrogen availability decreased over much of the land surface in the past century? A model-based analysis 上个世纪大部分陆地表面的氮供应量是否有所下降?基于模型的分析
IF 3.9 3区 环境科学与生态学 Q2 ENVIRONMENTAL SCIENCES Pub Date : 2024-05-03 DOI: 10.1007/s10533-024-01146-y
Peter M. Vitousek, Xiaoyu Cen, Peter M. Groffman

A recent publication (Mason et al. in Science 376:261, 2022a) suggested that nitrogen (N) availability has declined as a consequence of multiple ongoing components of anthropogenic global change. This suggestion is controversial, because human alteration of the global N cycle is substantial and has driven much-increased fixation of N globally. We used a simple model that has been validated across a climate gradient in Hawai ‘i to test the possibility of a widespread decline in N availability, the evidence supporting it, and the possible mechanisms underlying it. This analysis showed that a decrease in δ15N is not sufficient evidence for a decline in N availability, because δ15N in ecosystems reflects both the isotope ratios in inputs of N to the ecosystem AND fractionation of N isotopes as N cycles, with enrichment of the residual N in the ecosystem caused by greater losses of N by the fractionating pathways that are more important in N-rich sites. However, there is other evidence for declining N availability that is independent of 15N and that suggests a widespread decline in N availability. We evaluated whether and how components of anthropogenic global change could cause declining N availability. Earlier work had demonstrated that both increases in the variability of precipitation due to climate change and ecosystem-level disturbance could drive uncontrollable losses of N that reduce N availability and could cause persistent N limitation at equilibrium. Here we modelled climate-change-driven increases in temperature and increasing atmospheric concentrations of CO2. We show that increasing atmospheric CO2 concentrations can drive non-equilibrium decreases in N availability and cause the development of N limitation, while the effects of increased temperature appear to be relatively small and short-lived. These environmental changes may cause reductions in N availability over the vast areas of Earth that are not affected by high rates of atmospheric deposition and/or N enrichment associated with urban and agricultural land use.

最近发表的一篇文章(Mason 等人,载于《科学》376:261, 2022a)认为,氮(N)的可利用性已经下降,这是全球人为变化的多个持续组成部分造成的结果。这一观点存在争议,因为人类对全球氮循环的改变是巨大的,并已在全球范围内大大增加了氮的固定。我们使用了一个简单的模型,该模型已在夏威夷的气候梯度上得到了验证,以检验氮供应量普遍下降的可能性、支持这种可能性的证据以及可能的内在机制。该分析表明,δ15N 的减少不足以证明氮的可用性下降,因为生态系统中的δ15N 既反映了输入生态系统的氮的同位素比率,也反映了氮循环过程中氮同位素的分馏。不过,也有其他证据表明氮的可用性在下降,这些证据与 15N 无关,而且表明氮的可用性在普遍下降。我们评估了全球人为变化是否以及如何导致氮的可用性下降。早先的研究表明,气候变化导致的降水变异性增加和生态系统层面的干扰都可能导致无法控制的氮损失,从而降低氮的可用性,并可能在平衡状态下造成持续的氮限制。在这里,我们模拟了气候变化导致的温度上升和大气中二氧化碳浓度的增加。我们的研究表明,大气中二氧化碳浓度的增加会导致氮供应量的非平衡减少,并造成氮限制的发展,而温度升高的影响似乎相对较小且持续时间较短。这些环境变化可能会导致地球上未受大气沉降率高和/或与城市和农业用地相关的氮富集影响的广大地区的氮可用性降低。
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引用次数: 0
Bison and cattle grazing increase soil nitrogen cycling in a tallgrass prairie ecosystem 野牛和牛的放牧增加了高草草原生态系统的土壤氮循环
IF 3.9 3区 环境科学与生态学 Q2 ENVIRONMENTAL SCIENCES Pub Date : 2024-04-30 DOI: 10.1007/s10533-024-01144-0
Nicholas Vega Anguiano, Kiona M. Freeman, Janaye D. Figge, Jaide H. Hawkins, Lydia H. Zeglin

Nitrogen (N) is a necessary element of soil fertility and a limiting nutrient in tallgrass prairie but grazers like bison and cattle can also recycle N. Bison and cattle impact the nitrogen (N) cycle by digesting forage that is consumed, and recycled back to the soil in a more available forms stimulating soil microbial N cycling activities. Yet we do not know how both grazers comparatively affect N cycling in tallgrass prairie. Thus, we investigated if bison and cattle had similar impacts on N cycling in annually burned tallgrass prairie relative to ungrazed conditions over a 3-year period (2020–2022) at the Konza Prairie Biological Station. We examined: soil pH, soil water content, mineralized N, nitrification potential, denitrification potential and extracellular enzyme assays. Interannual variability in precipitation controlled soil water and N cycling microbial activities but grazing effects had a stronger influence on N cycling. We found significant differences and increased soil pH, nitrification and denitrification potential and less N limitation in bison vs cattle grazed soils where bison grazed soils exhibited faster N cycling. Differences between the grazers may be attributed to the different management of bison and cattle as both can impact N cycling. Overall, these data provide some evidence that bison and cattle affect N cycling differently at this study site, and improve the ecological understanding of grazer impacts on N cycling dynamics within the tallgrass prairie ecosystem.

氮(N)是土壤肥力的必要元素,也是高草草原的一种限制性养分,但野牛和牛等食草动物也可以循环利用氮。野牛和牛通过消化消耗掉的草料影响氮(N)循环,并以更多的形式循环回土壤,刺激土壤微生物的氮循环活动。然而,我们并不知道这两种食草动物是如何对高草草原的氮循环产生相对影响的。因此,我们在康萨草原生物站进行了为期 3 年(2020-2022 年)的调查,研究野牛和牛是否对每年焚烧的高草草原的氮循环产生了类似于未放牧条件下的影响。我们研究了:土壤 pH 值、土壤含水量、矿化氮、硝化潜力、反硝化潜力和细胞外酶测定。降水量的年际变化控制着土壤水分和氮循环微生物活动,但放牧效应对氮循环的影响更大。我们发现,野牛放牧的土壤与牛放牧的土壤在土壤 pH 值、硝化和反硝化潜力以及氮限制方面存在明显差异,且野牛放牧的土壤氮循环速度更快。放牧者之间的差异可能归因于对野牛和牛的不同管理,因为两者都会影响氮循环。总之,这些数据提供了一些证据,证明野牛和牛对该研究地点的氮循环有不同的影响,并提高了生态学对高草草原生态系统中放牧者对氮循环动态影响的认识。
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引用次数: 0
Terrestrial and marine POC export fluxes estimated by 234Th–238U disequilibrium and δ13C measurements in the East China Sea shelf 通过 234Th-238U 失衡和 δ13C 测量估算东海大陆架陆地和海洋 POC 出口通量
IF 3.9 3区 环境科学与生态学 Q2 ENVIRONMENTAL SCIENCES Pub Date : 2024-04-29 DOI: 10.1007/s10533-024-01136-0
Qiangqiang Zhong, Dekun Huang, Qiugui Wang, Jinzhou Du, Fule Zhang, Jing Lin, Tao Yu

The use of 234Th–238U disequilibrium has been widely employed to estimate the sinking flux of particulate organic carbon (POC) from the upper sea and ocean. Here, the deficits of 234Th relative to 238U in the water column and the carbon isotope signature (δ13C) of POC in the East China Sea (ECS) Shelf were measured, which was used to distinguish the fraction of marine and terrestrial POC export fluxes. In the ECS Shelf, very strong deficits of 234Th relative to 238U were observed throughout the water column, with 234Th/238U activity ratios ranging from 0.158 ± 0.045 to 0.904 ± 0.068 (averaging 0.426 ± 0.159). The residence times of particle reactive radionuclide 234Th (τTh–T) in the ECS shelf water varied between 9 and 44 days, which is significantly shorter than that in the continental slope area or the basin area. This phenomenon indicates that there is a more rapid particle scavenging process in the ECS shelf water compared to the continental slope and basin upper water. By applying a two-end-member mixing model based on the δ13C, the fraction of terrestrial POC was estimated to be 0 to 74% (mean: 30 ± 22%) and the fraction of marine POC was in the range of 25% to 100% (mean: 70 ± 22%). Fluxes of marine and terrestrial POC settling to the seafloor exhibited significant spatial differences among different stations, ranging from 11 to 129 mmol C/m2/day and from 2.6 to 38 mmol C/m2/day, respectively. The averaged terrestrial POC fluxes in the southern and northern ECS Shelf were similar (~ 21 to 24 mmol C/m2/day), while the marine POC fluxes in the north (86 ± 37 mmol C/m2/day) were approximately four times higher than those in the south (26 ± 20 mmol C/m2/day). Interestingly, the estimated export flux of both marine and terrestrial POC were approximately one order of magnitude higher than the previously reported burial fluxes of POC (ranging from 1.1 ± 0.1 to 11.4 ± 1.1 mmol C/m2/day) in the underlying bottom sediments, indicating that the majority (> 90%) of both terrestrial and marine POC exported from the upper water column are degraded in the sediments of the ECS Shelf. This “carbon missing” phenomenon can greatly be attributed to rapid decomposition by other processes (including microbial reworking, cross-shelf transport, and possible consumption by benthic organisms). Our findings highlight the dynamic nature of carbon cycling in the continental shelf and the need for further research to understand these processes and improve carbon budget assessments.

利用234Th-238U不平衡来估算上层海洋颗粒有机碳(POC)的下沉通量已被广泛采用。本文测定了东海大陆架水体中234Th相对于238U的缺失和POC的碳同位素特征(δ13C),并以此区分海洋和陆地POC输出通量的比例。在东海大陆架的整个水体中,观察到 234Th 相对于 238U 的极度缺乏,234Th/238U 放射性活度比在 0.158 ± 0.045 到 0.904 ± 0.068 之间(平均值为 0.426 ± 0.159)。颗粒活性放射性核素234Th(τTh-T)在大陆架水体中的停留时间为9-44天,明显短于大陆坡区和海盆区。这一现象表明,与大陆坡和盆地上层水相比,ECS 陆架水的颗粒物清除过程更为迅速。通过应用基于 δ13C 的两端成员混合模型,估计陆地 POC 的比例为 0-74%(平均值:30±22%),海洋 POC 的比例为 25%-100%(平均值:70±22%)。沉降到海底的海洋和陆地 POC 通量在不同站点之间存在显著的空间差异,分别为 11 至 129 毫摩尔碳/平方米/天和 2.6 至 38 毫摩尔碳/平方米/天。南部和北部大陆架的平均陆地 POC 通量相似(约 21 至 24 毫摩尔碳/平方米/天),而北部的海洋 POC 通量(86 ± 37 毫摩尔碳/平方米/天)约为南部的四倍(26 ± 20 毫摩尔碳/平方米/天)。有趣的是,海洋和陆地 POC 的估计出口通量比以前报告的 POC 在底层沉积物中的埋藏通量(从 1.1 ± 0.1 到 11.4 ± 1.1 毫摩尔碳/平方米/天)高出约一个数量级,这表明从上层水体出口的陆地和海洋 POC 大部分(90%)在大陆架沉积物中降解。这种 "碳缺失 "现象在很大程度上可归因于其他过程(包括微生物再加工、跨大陆架迁移以及底栖生物可能的消耗)的快速分解。我们的研究结果突显了大陆架碳循环的动态性质,以及进一步研究了解这些过程和改进碳预算评估的必要性。
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引用次数: 0
Subsidy-stress responses of ecosystem functions along experimental freshwater salinity gradients 实验性淡水盐度梯度生态系统功能的补贴-压力反应
IF 3.9 3区 环境科学与生态学 Q2 ENVIRONMENTAL SCIENCES Pub Date : 2024-04-26 DOI: 10.1007/s10533-024-01131-5
Stephen E. DeVilbiss, Brian D. Badgley, Erin R. Hotchkiss, Meredith K. Steele

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.

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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引用次数: 0
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Biogeochemistry
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