Nitrogen fixation rates in forested mountain streams: Are sediment microbes more important than previously thought?

Biological nitrogen (N) fixation, the microbial conversion of N2 gas to ammonia, makes N available to food webs. Low-N streams often have a high relative abundance of N-fixing taxa, suggesting that N fixation is an important N source in these systems. Despite this potential, stream N fixation has not been well-characterised, particularly compared to lakes and marine environments. One unknown is the relative contributions of various N-fixing organisms, particularly heterotrophic microbes. In low-N streams in the Cascade Mountains (Washington, USA), three groups of N-fixers predominate: cyanobacteria (Nostoc paramelioides) colonies that house a midge symbiont (Cricotopus spp.), cyanobacteria without a midge symbiont, and heterotrophic sediment microbes. In seven streams, we measured N fixation rates in each group with the acetylene reduction assay and a 15N2 calibration. Cyanobacteria N fixation rates were relatively low (7.9 ± 8.9 μg N m−2 hr−1, mean ± SD) compared to other mountain streams. Although rates were comparable among types of N-fixers, our sediment conversion ratio (moles of ethylene produced:moles of N fixed) was 0.16:1, much lower than our cyanobacteria conversion ratio of 1.72:1 and the commonly used theoretical ratio of 3:1. Sediment N fixation rates (5.7 ± 4.0 μg N m−2 hr−1) were higher than previously reported rates measured only with acetylene reduction. The midge symbiosis did not greatly impact N fixation rates; however, owing to their prevalence, colonies with the midge probably contributed more total N to streams than colonies without the midge. Additionally, N fixation by sediment heterotrophs was comparable to that of cyanobacteria colonies on an areal basis. Our study demonstrated that the contribution of sediment heterotrophs previously may have been underestimated in streams, especially considering that sediment heterotrophs are probably present for a longer portion of the growing season than cyanobacteria in temperate and boreal ecosystems

Goal attainment scaling as a measure of meaningful outcomes for children with sensory integration disorders.

Goal attainment scaling (GAS) is a methodology that shows promise for application to intervention effectiveness research and program evaluation in occupational therapy (Dreiling & Bundy, 2003; King et al., 1999; Lannin, 2003; Mitchell & Cusick, 1998). This article identifies the recent and current applications of GAS to occupational therapy for children with sensory integration dysfunction, as well as the process, usefulness, and problems of application of the GAS methodology to this population. The advantages and disadvantages of using GAS in single-site and multisite research with this population is explored, as well as the potential solutions and future programs that will strengthen the use of GAS as a measure of treatment effectiveness, both in current clinical practice and in much-needed larger, multisite research studies

N and P constrain C in ecosystems under climate change: role of nutrient redistribution, accumulation, and stoichiometry

© The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Rastetter, E., Kwiatkowski, B., Kicklighter, D., Plotkin, A., Genet, H., Nippert, J., O’Keefe, K., Perakis, S., Porder, S., Roley, S., Ruess, R., Thompson, J., Wieder, W., Wilcox, K., & Yanai, R. N and P constrain C in ecosystems under climate change: role of nutrient redistribution, accumulation, and stoichiometry. Ecological Applications, (2022): e2684, https://doi.org/10.1002/eap.2684.We use the Multiple Element Limitation (MEL) model to examine responses of 12 ecosystems to elevated carbon dioxide (CO2), warming, and 20% decreases or increases in precipitation. Ecosystems respond synergistically to elevated CO2, warming, and decreased precipitation combined because higher water-use efficiency with elevated CO2 and higher fertility with warming compensate for responses to drought. Response to elevated CO2, warming, and increased precipitation combined is additive. We analyze changes in ecosystem carbon (C) based on four nitrogen (N) and four phosphorus (P) attribution factors: (1) changes in total ecosystem N and P, (2) changes in N and P distribution between vegetation and soil, (3) changes in vegetation C:N and C:P ratios, and (4) changes in soil C:N and C:P ratios. In the combined CO2 and climate change simulations, all ecosystems gain C. The contributions of these four attribution factors to changes in ecosystem C storage varies among ecosystems because of differences in the initial distributions of N and P between vegetation and soil and the openness of the ecosystem N and P cycles. The net transfer of N and P from soil to vegetation dominates the C response of forests. For tundra and grasslands, the C gain is also associated with increased soil C:N and C:P. In ecosystems with symbiotic N fixation, C gains resulted from N accumulation. Because of differences in N versus P cycle openness and the distribution of organic matter between vegetation and soil, changes in the N and P attribution factors do not always parallel one another. Differences among ecosystems in C-nutrient interactions and the amount of woody biomass interact to shape ecosystem C sequestration under simulated global change. We suggest that future studies quantify the openness of the N and P cycles and changes in the distribution of C, N, and P among ecosystem components, which currently limit understanding of nutrient effects on C sequestration and responses to elevated CO2 and climate change.This material is based on work supported by the National Science Foundation under Grant No. 1651722 as well through the NSF LTER Program 1637459, 2220863 (ARC), 1637686 (NWT), 1832042 (KBS), 2025849 (KNZ), 1636476 (BNZ), 1637685 (HBR), 1832210 (HFR), 2025755 (AND). We also acknowledge NSF grants 1637653 and 1754126 (INCyTE RCN), and DOE grant DESC0019037. We also acknowledge support through the USDA Forest Service Hubbard Brook Experimental Forest, North Woodstock, New Hampshie (USDA NIFA 2019-67019-29464) and Pacific Northwest Research Station, Corvallis, Oregon

Fidelity in sensory integration intervention research.

OBJECTIVE: We sought to assess validity of sensory integration outcomes research in relation to fidelity (faithfulness of intervention to underlying therapeutic principles). METHOD: We identified core sensory integration intervention elements through expert review and nominal group process. Elements were classified into structural (e.g., equipment used, therapist training) and therapeutic process categories. We analyzed 34 sensory integration intervention studies for consistency of intervention descriptions with these elements. RESULTS: Most studies described structural elements related to therapeutic equipment and interveners\u27 profession. Of the 10 process elements, only 1 (presentation of sensory opportunities) was addressed in all studies. Most studies described fewer than half of the process elements. Intervention descriptions in 35% of the studies were inconsistent with one process element, therapist-child collaboration. CONCLUSION: Validity of sensory integration outcomes studies is threatened by weak fidelity in regard to therapeutic process. Inferences regarding sensory integration effectiveness cannot be drawn with confidence until fidelity is adequately addressed in outcomes research

Pore water physicochemical constraints on the endangered clubshell mussel (Pleurobema clava)

Freshwater mussels are in decline worldwide, but it remains challenging to link specific stressors to mussel declines. The clubshell mussel (Pleurobema clava) is a federally endangered species that spends most of its life completely buried beneath stream sediments. We tested the hypothesis that clubshell’s decline stems, in part, from low pore water dissolved oxygen (DO) concentrations and toxic ammonia (NH3) levels, resulting from sedimentation of interstitial pore spaces. We measured pore water DO, NH3, interstitial sedimentation rates, and sediment organic matter content in the Tippecanoe River (Indiana, USA) at sites that spanned a range of clubshell populations, including two sites devoid of clubshell. We found little evidence for pore water NH3 stress, but pore water DO generally declined with clubshell population and dipped below stress thresholds more frequently at non-clubshell sites than at sites with clubshell. In addition, interstitial sedimentation rates generally increased as clubshell populations declined, suggesting that the low DO concentrations were the result of decreased pore water – surface water exchange. As a result, we conclude that maintaining or improving habitat for clubshell mussels will require the reduction of riverine sediment loading

How cost-effective are cover crops, wetlands, and two-stage ditches for nitrogen removal in the Mississippi River Basin?

Excess nitrogen (N) causes numerous water quality problems, and in the upper Mississippi River Basin, much of the excess N results from landscape modifications necessary for row crop agriculture. Several conservation practices reduce N export, but cost estimates for these practices are often lacking, which can inhibit decisions by farmers and policy-makers. Many practices are eligible for cost-share funds from the United States Department of Agriculture (USDA), but these programs do not usually cover the full cost, and so farmers need to be able to approximate their share of costs. In addition, cost estimates may help the USDA to set priorities and make programmatic decisions. We address lack of cost information by estimating the direct implementation costs and USDA program costs for three agricultural conservation practices: wetlands, cover crops, and two-stage ditches, over 10 and 50 year time horizons. We then compare these costs to the N removal effectiveness of each practice, in $kg N−1 removed. Wetlands were the most cost-effective practice (in$ kg N−1 removed) over both time horizons. Over 50 years, the two-stage ditch ranked second in cost-effectiveness and cover crops were least cost-effective, while over 10 years, cover crops were second and two-stage ditches were least cost-effective. Finally, we note that these practices need not be used in isolation, but can be implemented simultaneously to maximize N removal. Overall, our analysis suggests that careful implementation can cost-effectively mitigate N pollution

Organic amendments change soil organic C structure and microbial community but not total organic matter on sub-decadal scales

Organic C has many benefits for soil, but it is depleted by tillage and crop harvest, and especially so for biofuel crops. Accordingly, strategies such as partially retaining stover or planting a cover crop can help ameliorate the negative effect of C removal. We used a long-term field experiment to study the impacts of stover retention and planting a cover crop on soil organic matter (SOM), its extractable components, and the soil microbial community. SOM chemical composition characterization was determined by electrospray ionization (ESI) coupled with Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) in sequential water, methanol (MeOH), and chloroform (CHCl3) extracts. The characteristics of the soil bacterial community were measured by phospholipid fatty acid (PLFA), real-time quantitative PCR, and 16S rRNA gene sequence. The variations in total SOM content, total microbial biomass, and bacterial population were slight among treatments, but SOM chemical compounds, arbuscular mycorrhizal fungi (AMF) biomass, and bacterial structure changed significantly, and especially so in the coupled application of stover retention and cover crop. Specifically, stover retention enriched more lignin-like compounds in soil, whereas cover crop enriched more condensed hydrocarbons, and had more compounds with an aromaticity index (AI) > 0.5. The bacterial community was not altered by the cover crop, but the corn stover retention increased the relative abundances of Myxococcales (Deltaproteobacteria) and decreased that of Actinobacteria. Redundancy analysis (RDA) further revealed that the bacterial community in the stover treatments had a significant positive association with CHCl3-extracted chemical classes, i.e. unsaturated hydrocarbons and lipids, with the coupled application (stover and cover crop), and lignin and proteins with the corn stover only treatment. Taken together, our study shows how different C addition practices influence the molecular composition of SOM and the structure of soil microbial communities.24 month embargo; published online 5 September 2020This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Data from: Associative nitrogen fixation (ANF) in switchgrass (Panicum virgatum) across a nitrogen input gradient

Associative N fixation (ANF), the process by which dinitrogen gas is converted to ammonia by bacteria in casual association with plants, has not been well-studied in temperate ecosystems. We examined the ANF potential of switchgrass (Panicum virgatum L.), a North American prairie grass whose productivity is often unresponsive to N fertilizer addition, via separate short-term 15N2 incubations of rhizosphere soils and excised roots four times during the growing season. Measurements occurred along N fertilization gradients at two sites with contrasting soil fertility (Wisconsin, USA Mollisols and Michigan, USA Alfisols). In general, we found that ANF potentials declined with long-term N addition, corresponding with increased soil N availability. Although we hypothesized that ANF potential would track plant N demand through the growing season, the highest root fixation rates occurred after plants senesced, suggesting that root diazotrophs exploit carbon (C) released during senescence, as C is translocated from aboveground tissues to roots for wintertime storage. Measured ANF potentials, coupled with mass balance calculations, suggest that ANF appears to be an important source of N to unfertilized switchgrass, and, by extension, to temperate grasslands in general

Roley_etal_2018_Nfix_SG_roots

During 2015, net nitrogen mineralization, net nitrification, soil nitrogen fixation, and root nitrogen fixation was measured in the Switchgrass Nitrogen Rate Experiment, at both Kellogg Biological Station (MI, USA) and Arlington Agricultural Research Station (WI, USA). All replicates of 3 fertilizer treatments (0 kg N/ha/yr, 56 kg N/ha/yr, and 196 kg N/ha/yr) were measured 4 times: pre-fertilizer (May), post-fertilizer (June), at peak biomass (late July) and post-senescence (October). This data file contains the data on root N fixation, measured with 7-day lab incubations with 15N2 and glucose