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1. Saltwater and phosphorus drive unique soil biogeochemical processes in freshwater and brackish wetland mesocosms

   https://doi.org/10.1002/ecs2.3704  

   Servais, Shelby; Kominoski, John S.; Fernandez, Marco; Morales, Kristina (August 2021, Ecosphere)

   Abstract Coastal ecosystems are exposed to saltwater intrusion but differential effects on biogeochemical cycling are uncertain. We tested how elevated salinity and phosphorus (P) individually and interactively affect microbial activities and biogeochemical cycling in freshwater and brackish wetland soils. In experimental mesocosms, we added crossed gradients of elevated concentrations of soluble reactive P (SRP) (0, 20, 40, 60, 80 μg/L) and salinity (0, 4, 7, 12, 16 ppt) to freshwater and brackish peat soils (10, 14, 17, 22, 26 ppt) for 35 d. We quantified changes in water chemistry [dissolved organic carbon (DOC), ammonium (), nitrate + nitrite (N + N), SRP concentrations], soil microbial extracellular enzyme activities, respiration rates, microbial biomass C, and soil chemistry (%C, %N, %P, C:N, C:P, N:P). DOC, , and SRP increased in freshwater but decreased in brackish mesocosms with elevated salinity. DOC similarly decreased in brackish mesocosms with added P, and N + N decreased with elevated salinity in both freshwater and brackish mesocosms. In freshwater soils, water column P uptake occurred only in the absence of elevated salinity and when P was above 40 µg/L. Freshwater microbial EEAs, respiration rates, and microbial biomass C were consistently higher compared to those from brackish soils, and soil phosphatase activities and microbial respiration rates in freshwater soils decreased with elevated salinity. Elevated salinity increased arylsulfatase activities and microbial biomass C in brackish soils, and elevated P increased microbial respiration rates in brackish soils. Freshwater soil %C, %N, %P decreased and C:P and N:P increased with elevated salinity. Elevated P increased %C and C:N in freshwater soils and increased %P but decreased C:P and N:P in brackish soils. Freshwater soils released more C and nutrients than brackish soils when exposed to elevated salinity, and both soils were less responsive to elevated P than expected. Freshwater soils became more nutrient‐depleted with elevated salinity, whereas brackish soils were unaffected by salinity but increased P uptake. Microbial activities in freshwater soils were inhibited by elevated salinity and unaffected by added P, but brackish soil microbial activities slightly increased with elevated salinity and P. 

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2. Soil Quality as a Key Factor in Producing Vegetables for Home Consumption—A Case Study of Urban Allotments in Gorzów Wielkopolski (Poland)

   https://doi.org/10.3390/agronomy11091836  

   Bosiacki, Maciej; Bednorz, Leszek; Fedeńczak, Konstancja; Górecki, Tomasz; Mizgajski, Andrzej; Poniży, Lidia; Spiżewski, Tomasz (September 2021, Agronomy)

   The aim of the study was to analyse the quality of soil in urban allotment gardens in the context of the production of home-grown vegetables. The study was conducted on six allotment gardens (31 individual plots) in Gorzów Wielkopolski, a medium-sized Polish city with an average level of industrialisation. The following soil characteristics were analysed: pH, electric conductivity, organic matter, organic carbon, humus, total nitrogen, C:N ratio, NH4+-N, NO3-N−, P, K, Ca, Mg, SO4−-S, Cl, Na, Fe, Cu, Zn, Mn, Ni, Cr, Cd, Pb. The analyses showed that the soils were abundant in necessary nutrients for vegetable growing. They had high content of calcium, magnesium, and phosphorus. However, the soil pH in areas of vegetable cropping was too high. The content of toxic heavy metals—cadmium (0.22–0.59 mg∙kg−1 d.m.) and lead (3.46–16.89 mg∙kg−1 d.m.)—was within the acceptable limits. Nevertheless, the chemical analysis of carrots used as test vegetables showed that the permissible limits of cadmium and lead content in their roots were exceeded. The excessive uptake of these toxic metals can be reduced by lowering the soil pH and applying organic carbon to the soil. 

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3. Relationship of Atmospheric Nitrogen Deposition to Soil Nitrogen Cycling Along an Elevation Gradient in the Colorado Front Range

   https://doi.org/10.1029/2024EF005356  

   Repert, Deborah A; Heindel, Ruth C; Murphy, Sheila F; Jeanis, Kaitlyn M (January 2025, Earth's Future)

   Abstract Microbial processing of atmospheric nitrogen (N) deposition regulates the retention and mobilization of N in soils, with important implications for water quality. Understanding the links between N deposition, microbial communities, N transformations, and water quality is critical as N deposition shifts toward reduced N and remains persistently high in many regions. Here, we investigated these connections along an elevation transect in the Colorado Front Range. Although rates of N deposition and pools of extractable N increased down the elevation transect, soil microbial communities and N transformation rates did not follow clear elevational patterns. The subalpine microbial community was distinct, corresponding to a high C:N ratio and low pH, while the microbial communities at the lower elevation sites were all very similar. Net nitrification, mineralization, and nitrification potential rates were highest at the Plains (1,700 m) and Montane (2,527 m) sites, suggesting that these ecosystems mobilize N. In contrast, the net immobilization of N observed at the Foothills (1,978 m) and Subalpine (3,015 m) sites suggests that these ecosystems retain N deposition. The contrast in N transformation rates between the plains and foothills, both of which receive elevated N deposition, may be due to spatial heterogeneity not captured in this study and warrants further investigation. Stream N concentrations from the subalpine to the foothills were consistently low, indicating that these soils are currently able to process and retain N deposition, but this may be disrupted if drought, wildfire, or land‐use change alter the ability of the soils to retain N. 

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4. Links between litter quality and nitrogen oligotrophication in a northern hardwood forest

   https://doi.org/10.1139/cjfr-2025-0037  

   Caron, Stephen B; Bailey, Amey; Cleavitt, Natalie; Driscoll, Charles; Fahey, Timothy; Groffman, Peter M; Leonardi, Brendan; Rustad, Lindsey; Wilson, Geoffrey; Templer, Pamela H (August 2025, Canadian Journal of Forest Research)

   Declining nitrogen (N) availability relative to plant demand, known as N oligotrophication, is a widespread phenomenon that has been particularly well documented in northern hardwood forests of the northeast U.S. It is hypothesized that later fall senescence contributes to this trend by increasing tree resorption of N, resulting in higher carbon:nitrogen ratios (C:N) in litterfall and reduced N availability in soil. To examine the effects of litterfall C:N on soil N cycling, we conducted a litter quality manipulation experiment comparing low C:N and high C:N litter with native litter along an elevation and aspect gradient at Hubbard Brook Experimental Forest, NH, USA. We found that potential net ammonification and mineralization rates were positively correlated with litter N and negatively correlated with litter C:N under high C:N litter, but these relationships were not present under native or low C:N litter. Differences in nitrate pools and net mineralization rates between high- and low-quality litter treatments were greater at colder sites, where native litterfall tends to have lower C:N than at low-elevation sites. Together, these results demonstrate that higher C:N litter and a warming climate may contribute to N oligotrophication through effects on microbially driven N cycling rates in organic soils. 

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5. Distinct microbial communities alter litter decomposition rates in a fertilized coastal plain wetland

   https://doi.org/10.1002/ecs2.3619  

   Koceja, Megan_E; Bledsoe, Regina_B; Goodwillie, Carol; Peralta, Ariane_L (June 2021, Ecosphere)

   Abstract Human activities have led to increased deposition of nitrogen (N) and phosphorus (P) into soils. Nutrient enrichment of soils is known to increase plant biomass and rates of microbial litter decomposition. However, interacting effects of hydrologic position and associated changes to soil moisture can constrain microbial activity and lead to unexpected nutrient feedbacks on microbial community structure–function relationships. Examining feedbacks of nutrient enrichment on decomposition rates is essential for predicting microbial contributions to carbon (C) cycling as atmospheric deposition of nutrients persists. This study explored how long‐term nutrient addition and contrasting litter chemical composition influenced soil bacterial community structure and function. We hypothesized that long‐term nutrient enrichment of low fertility soils alters bacterial community structure and leads to higher rates of litter decomposition especially for low C:N litter, but low‐nutrient and dry conditions limit microbial decomposition of high C:N ratio litter. We leveraged a long‐term fertilization experiment to test how nutrient enrichment and hydrologic manipulation (due to ditches) affected decomposition and soil bacterial community structure in a nutrient‐poor coastal plain wetland. We conducted a litter bag experiment and characterized litter‐associated and bulk soil microbiomes using 16S rRNA bacterial sequencing and quantified litter mass losses and soil physicochemical properties. Results revealed that distinct bacterial communities were involved in decomposing higher C:N ratio litter more quickly in fertilized compared to unfertilized soils especially under drier soil conditions, while decomposition rates of lower C:N ratio litter were similar between fertilized and unfertilized plots. Bacterial community structure in part explained litter decomposition rates, and long‐term fertilization and drier hydrologic status affected bacterial diversity and increased decomposition rates. However, community composition associated with high C:N litter was similar in wetter plots with available nitrate detected, regardless of fertilization treatment. This study provides insight into long‐term fertilization effects on soil bacterial diversity and composition, decomposition, and the increased potential for soil C loss as nutrient enrichment and hydrology interact to affect historically low‐nutrient ecosystems. 

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