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1. Transport of N and P in U.S. streams and rivers differs with land use and between dissolved and particulate forms

   https://doi.org/10.1002/eap.2130  

   Manning, David W. P. ; Rosemond, Amy D. ; Benstead, Jonathan P. ; Bumpers, Phillip M. ; Kominoski, John S. ( May 2020 , Ecological Applications)

   We used a recently published, open‐access data set of U.S. streamwater nitrogen (N) and phosphorus (P) concentrations to test whether watershed land use differentially influences N and P concentrations, including the relative availability of dissolved and particulate nutrient fractions. We tested the hypothesis that N and P concentrations and molar ratios in streams and rivers of the United States reflect differing nutrient inputs from three dominant land‐use types (agricultural, urban and forested). We also tested for differences between dissolved inorganic nutrients and suspended particulate nutrient fractions to infer sources and potential processing mechanisms across spatial and temporal scales. Observed total N and P concentrations often exceeded reported thresholds for structural changes to benthic algae (58, 57% of reported values, respectively), macroinvertebrates (39% for TN and TP), and fish (41, 37%, respectively). The majority of dissolved N and P concentrations exceeded threshold concentrations known to stimulate benthic algal growth (85, 87%, respectively), and organic matter breakdown rates (94, 58%, respectively). Concentrations of both N and P, and total and dissolved N:P ratios, were higher in streams and rivers with more agricultural and urban than forested land cover. The pattern of elevated nutrient concentrations with agricultural and urban land use was weaker for particulate fractions. The % N contained in particles decreased slightly with higher agriculture and urbanization, whereas % P in particles was unrelated to land use. Particulate N:P was relatively constant (interquartile range = 2–7) and independent of variation in DIN:DIP (interquartile range = 22–152). Dissolved, but not particulate, N:P ratios were temporally variable. Constant particulate N:P across steep DIN:DIP gradients in both space and time suggests that the stoichiometry of particulates across U.S. watersheds is most likely controlled either by external or by physicochemical instream factors, rather than by biological processing within streams. Our findings suggest that most U.S. streams and rivers have concentrations of N and P exceeding those considered protective of ecological integrity, retain dissolved N less efficiently than P, which is retained proportionally more in particles, and thus transport and export high N:P streamwater to downstream ecosystems on a continental scale.

    

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2. Leaf NPK stoichiometry, δ15N , and apparent nutrient limitation of co‐occurring carnivorous and noncarnivorous plants

   https://doi.org/10.1002/ecy.3825  

   Givnish, Thomas J. ; Shiba, Zackary W. ( October 2022 , Ecology)

   Previous meta‐analyses suggested that carnivorous plants—despite access to N, P, and K from prey—have significantly lower leaf concentrations of these nutrients than noncarnivores. Those studies, however, largely compared carnivores in nutrient‐poor habitats with noncarnivores in more nutrient‐rich sites, so that the differences reported might reflect habitat differences as much as differences in nutrient‐capture strategy. Here we examine three carnivorous and 12 noncarnivorous plants in the same nutrient‐poor bog to compare their foliar nutrient concentrations, assess their patterns of nutrient limitation using leaf NPK stoichiometry, and estimate percentage N derived from prey by carnivores using a mixing model for stable N isotopes. We hypothesized that (1) carnivore leaf nutrient concentrations approach or exceed those of noncarnivores in the same nutrient‐poor habitat; (2) species in different functional groups show different patterns of stoichiometry and apparent nutrient limitation; and (3) noncarnivores might show evidence of using other means of nutrient acquisition or conservation to reduce nutrient limitation. At Fallison Bog in northern Wisconsin, carnivorous plants (Drosera rotundifolia,Sarracenia purpurea,Utricularia macrorhiza) showed significantly lower leaf percentage C and N:P ratio, higher δ¹⁵N, and no difference from noncarnivores in leaf N, P, K, and δ¹³C. Sedges had significantly lower leaf percentage P, percentage C, and N:K ratio, and higher K:P ratio than nonsedges restricted to theSphagnummat, and may tap peat N via aerenchyma‐facilitated peat oxidation (oxipeditrophy). Evergreen ericaceous shrubs exhibited significantly higher levels of percentage C and lower values of δ¹⁵N than mat nonericads.Calla palustris—growing in the nutrient‐rich moat at the bog's upland edge—had very high values of leaf N, K, δ¹⁵N, and N:P ratio, suggesting that it may obtain nutrients from minerotrophic flows from the adjacent uplands and/or rapidly decaying peat. Stoichiometric analyses indicated that most species are N limited. A mixing model applied to δ¹⁵N values for carnivores, noncarnivores, and insects produced an estimate of 50% of leaf N derived from prey forUtricularia, 42% forSarracenia, and 41% forDrosera.

    

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3. Patterns and controls of foliar nutrient stoichiometry and flexibility across United States forests

   https://doi.org/10.1002/ecy.3909  

   Dynarski, Katherine A. ; Soper, Fiona M. ; Reed, Sasha C. ; Wieder, William R. ; Cleveland, Cory C. ( January 2023 , Ecology)

   Plant element stoichiometry and stoichiometric flexibility strongly regulate ecosystem responses to global change. Here, we tested three potential mechanistic drivers (climate, soil nutrients, and plant taxonomy) of both using paired foliar and soil nutrient data from terrestrial forested National Ecological Observatory Network sites across the USA. We found that broad patterns of foliar nitrogen (N) and foliar phosphorus (P) are explained by different mechanisms. Plant taxonomy was an important control over all foliar nutrient stoichiometries and concentrations, especially foliar N, which was dominantly related to taxonomy and did not vary across climate or soil gradients. Despite a lack of site‐level correlations between N and environment variables, foliar N exhibited intraspecific flexibility, with numerous species‐specific correlations between foliar N and various environmental factors, demonstrating the variable spatial and temporal scales on which foliar chemistry and stoichiometric flexibility can manifest. In addition to plant taxonomy, foliar P and N:P ratios were also linked to soil nutrient status (extractable P) and climate, especially actual evapotranspiration rates. Our findings highlight the myriad factors that influence foliar chemistry and show that broad patterns cannot be explained by a single consistent mechanism. Furthermore, differing controls over foliar N versus P suggests that each may be sensitive to global change drivers on distinct spatial and temporal scales, potentially resulting in altered ecosystem N:P ratios that have implications for processes ranging from productivity to carbon sequestration.

    

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4. Ontogenetic variation in the ecological stoichiometry of 10 fish species during early development

   https://doi.org/10.1002/ecy.4176  

   Downs, Kelsea N. ; Kelly, Patrick T. ; Ascanio, Alfredo ; Vanni, Michael J. ( October 2023 , Ecology)

   The chemical composition and stoichiometry of vertebrate bodies changes greatly during ontogeny as phosphorus‐rich bones form, but we know little about the variation among species during early development. Such variation is important because element ratios in animal bodies influence which element limits growth and how animals contribute to nutrient cycling. We quantified ontogenetic variation from embryos through 2–3 months of age in 10 species of fish in six different families, ranging in adult size from 73 to 720 mm in length. We measured whole‐body concentrations (percentage of dry mass) and ratios of carbon (C), nitrogen (N), and phosphorus (P) as fish developed. We also quantified whole‐body concentrations of calcium (Ca), because Ca should reflect bone development, and RNA, which can be a major pool of body P. To account for interspecific differences in adult size, we also examined how trends changed with relative size, defined as body length divided by adult length. Ontogenetic changes in body composition and ratios were relatively similar among species and were more similar when expressed as a function of relative size compared to age. Body P increased rapidly in all species (likely because of bone development) from embryos until individuals were ~5%–8% of adult size. Body N also increased, while body C, C:N, C:P, and N:P all decreased over this period. Body Ca increased with development but was more variable among species. Body RNA was low in embryos, increased rapidly in young larvae, then decreased as fish reached 5%–8% of adult size. After fish were about 5%–8% of adult size, changes in body composition were relatively slight for all elements and ratios. These results reveal a consistency in the dynamics of body stoichiometry during early ontogeny, presumably because of similar constraints on the allocation of elements to bones and other body pools. Because most changes occur when individuals are <1 month old (<10% of adult size for that species), early ontogenetic variation in body stoichiometry may be especially important for growth limitation of individuals and ecosystem‐level nutrient cycling.

    

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5. Nutrient and stoichiometric time series measurements of decomposing coarse detritus in freshwaters

   https://doi.org/10.1002/ecy.4114  

   Robbins, Caleb J. ; Norman, Beth C. ; Halvorson, Halvor M. ; Manning, David W. P. ; Bastias, Elliot ; Biasi, Cristiane ; Dodd, Allyn K. ; Eckert, Rebecca A. ; Gossiaux, Alice ; Jabiol, Jérémy ; et al ( June 2023 , Ecology)

   Decomposition of coarse detritus (e.g., dead organic matter larger than ~1 mm such as leaf litter or animal carcasses) in freshwater ecosystems is well described in terms of mass loss, particularly as rates that compress mass loss into one number (e.g., a first‐order decay coefficient, or breakdown rate, “k”); less described are temporal changes in the elemental composition of these materials during decomposition, with important implications for elemental cycling from microbes to ecosystems. This stands in contrast with work in the terrestrial realm, where a focus on detrital elemental cycling has provided a sharper mechanistic understanding of decomposition, especially with specific processes such as immobilization and mineralization. Notably, freshwater ecologists often measure carbon (C), nitrogen (N), and phosphorus (P), and their stoichiometric ratios in decomposing coarse materials, including carcasses, wood, leaf litter, and more, but these measurements remain piecemeal. These detrital nutrients are measurements of the entire detrital–microbial complex and are integrative of numerous processes, especially nutrient immobilization and mineralization, and associated microbial growth and death. Thus, data relevant to an elemental, mechanistically focused decomposition ecology are available in freshwaters, but have not been fully applied to that purpose. We synthesized published detrital nutrient and stoichiometry measurements at a global scale, yielding 4038 observations comprising 810 decomposition time series (i.e., measurements within a defined cohort of decomposing material through time) to build a basis for understanding the temporality of elemental content in freshwater detritus. Specifically, the dataset focuses on temporally and ontogenetically (mass loss) explicit measurements of N, P, and stoichiometry (C:N, C:P, N:P). We also collected ancillary data, including detrital characteristics (e.g., species, lignin content), water physiochemistry, geographic location, incubation system type, and methodological variables (e.g., bag mesh size). These measurements are important to unlocking mechanistic insights into detrital ontogeny (the temporal trajectory of decomposing materials) that can provide a deeper understanding of heterotroph‐driven C and nutrient cycling in freshwaters. Moreover, these data can help to bridge aquatic and terrestrial decomposition ecology, across plant or animal origin. By focusing on temporal trajectories of elements, this dataset facilitates cross‐ecosystem comparisons of fundamental decomposition controls on elemental fluxes. It provides a strong starting point (e.g., via modeling efforts) for comparing processes such as immobilization and mineralization that are understudied in freshwaters. Time series from decomposing leaf litter, particularly in streams, are common in the dataset, but we also synthesized ontogenies of animal‐based detritus, which tend to decompose rapidly compared with plant‐based detritus that contains high concentrations of structural compounds such as lignin and cellulose. Although animal‐based data were rare, comprising only three time series, their inclusion in this dataset underscores the opportunities to develop an understanding of decomposition that encompasses all detrital types, from carrion to leaf litter. There are no copyright or proprietary restrictions on the dataset; please cite this data paper when reusing these materials.

    

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