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1. Multiple Element Limitation in Northern Hardwood Ecosystems (MELNHE): Leaf Litter Decomposition 2012-2014

   https://doi.org/10.6073/pasta/704c062966f0289818e438bee78a71fe  

   Biche, Richard; Innusa, Brianne N; Zukswert, Jenna M; Gilcrist, Gracie; Young, Alex; Yanai, Ruth D (January 2024, Environmental Data Initiative)

   Decomposition of leaf litter is a major source of nutrient transfer from vegetation to soils and an important carbon flux. In northern hardwood forests, litter decomposition might be affected by nutrient availability, species composition, stand age or structure, or access by soil decomposers. We investigated these factors in four stands at the Bartlett Experimental Forest in New Hampshire that have had nitrogen and phosphorus added in full factorial design since 2011. Leaf litter of early and late successional species was collected in 2012 and deployed in bags of two mesh sizes (63 µm and 2 mm) in two young and two mature stands and collected three times over the next 2 years. Decomposition was evaluated by fitting mass loss as an exponential function of time represented by growing degree days. Litter decomposed more quickly in the small mesh bags (p < 0.001), which excluded mesofauna. This result was surprising, but might be explained by the greater rigidity of the large mesh material making poor contact with the soil. The litter with a species composition characteristic of our young stands decomposed more quickly than the litter representing mature stands (p = 0.01 for species mix in the full model). The environment in which is was placed was not as important: Neither the age of the stand in which it was placed (p = 0.31), nor N addition (p = 0.59), P addition (p = 0.41), or the interaction of N and P addition (p = 0.13) were significant predictors of the decomposition rate, defined by fitting an exponential decay constant. Additional detail on the MELNHE project, including a datatable of site descriptions and a pdf file with the project description and diagram of plot configuration can be found in this data package: https://portal.edirepository.org/nis/mapbrowse?scope=knb-lter-hbr&identifier=344 Litter was collected by Rick Bicher and sorted by species by middle school students. Litterbags were made, filled, and weighed by middle school students. Gracie Gilcrist and Jeff Merriam generated data for the chemical analyses. 

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2. Nitrogen and phosphorus additions affect fruiting of ectomycorrhizal fungi in a temperate hardwood forest

   https://doi.org/10.1016/j.funeco.2024.101388  

   Bashian-Victoroff, Claudia; Yanai, Ruth D; Horton, Thomas R; Lamit, Louis J (February 2025, Fungal Ecology)

   The functioning of mycorrhizal symbioses is tied to soil nutrient status, suggesting that nutrient availability should influence the reproduction of mycorrhizal fungi. To quantify the effects of nitrogen (N) and phosphorus (P) availability on ectomycorrhizal fungal fruiting, we collected >4000 epigeous sporocarps representing 19 families during the course of a season in a full factorial NxP addition experiment in six replicate forest stands. Nutrient effects on fruiting shifted as the season progressed, with early fruiting species responding more to P and late-fruiting species responding more to N. The composition of species fruiting in young successional forests differed more with nutrient addition than in mature forests. Sporocarp abundance and species richness were suppressed by N addition. This work shows that N and P availability affect ectomycorrhizal fungal fruiting, with these effects taking place within a context defined by stand age and the progression of fruiting across the season. 

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3. Foliar nutrient concentrations of six northern hardwood species responded to nitrogen and phosphorus fertilization but did not predict tree growth

   https://doi.org/10.7717/peerj.13193  

   Hong, Daniel S.; Gonzales, Kara E.; Fahey, Timothy J.; Yanai, Ruth D. (January 2022, PeerJ)

   Foliar chemistry can be useful for diagnosing soil nutrient availability and plant nutrient limitation. In northern hardwood forests, foliar responses to nitrogen (N) addition have been more often studied than phosphorus (P) addition, and the interactive effects of N and P addition have rarely been described. In the White Mountains of central New Hampshire, plots in ten forest stands of three age classes across three sites were treated annually beginning in 2011 with 30 kg N ha −1 y −1 or 10 kg P ha −1 y −1 or both or neither–a full factorial design. Green leaves of American beech ( Fagus grandifolia Ehrh.), pin cherry ( Prunus pensylvanica L.f.), red maple ( Acer rubrum L.), sugar maple ( A. saccharum Marsh.), white birch ( Betula papyrifera Marsh.), and yellow birch ( B. alleghaniensis Britton) were sampled pre-treatment and 4–6 years post-treatment in two young stands (last cut between 1988–1990), four mid-aged stands (last cut between 1971–1985) and four mature stands (last cut between 1883–1910). In a factorial analysis of species, stand age class, and nutrient addition, foliar N was 12% higher with N addition ( p < 0.001) and foliar P was 45% higher with P addition ( p < 0.001). Notably, P addition reduced foliar N concentration by 3% ( p = 0.05), and N addition reduced foliar P concentration by 7% ( p = 0.002). When both nutrients were added together, foliar P was lower than predicted by the main effects of N and P additions ( p = 0.08 for N × P interaction), presumably because addition of N allowed greater use of P for growth. Foliar nutrients did not differ consistently with stand age class ( p  ≥ 0.11), but tree species differed ( p  ≤ 0.01), with the pioneer species pin cherry having the highest foliar nutrient concentrations and the greatest responses to nutrient addition. Foliar calcium (Ca) and magnesium (Mg) concentrations, on average, were 10% ( p < 0.001) and 5% lower ( p = 0.01), respectively, with N addition, but were not affected by P addition ( p = 0.35 for Ca and p = 0.93 for Mg). Additions of N and P did not affect foliar potassium (K) concentrations ( p = 0.58 for N addition and p = 0.88 for P addition). Pre-treatment foliar N:P ratios were high enough to suggest P limitation, but trees receiving N ( p = 0.01), not P ( p = 0.64), had higher radial growth rates from 2011 to 2015. The growth response of trees to N or P addition was not explained by pre-treatment foliar N, P, N:P, Ca, Mg, or K. 

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4. Nitrogen and Phosphorus Addition Affect Soil Respiration in Northern Hardwood Forests

   https://doi.org/10.1007/s10021-024-00912-1  

   Mann, T A; Yanai, R D; Fahey, T J; Reinmann, A B (September 2024, Ecosystems)

   Soil respiration is the largest single efflux in the global carbon cycle and varies in complex ways with climate, vegetation, and soils. The suppressive effect of nitrogen (N) addition on soil respiration is well documented, but the extent to which it may be moderated by stand age or the availability of soil phosphorus (P) is not well understood. We quantified the response of soil respiration to manipulation of soil N and P availability in a full-factorial N x P fertilization experiment spanning 10 years in 13 northern hardwood forests in the White Mountains of New Hampshire, USA. We analyzed data for 2011 alone, to account for potential treatment effects unique to the first year of fertilization, and for three 3-year periods; data from each 3-year period was divided into spring, summer, and fall. Nitrogen addition consistently suppressed soil respiration by up to 14% relative to controls (p £ 0.01 for the main effect of N in 5 of 10 analysis periods). This response was tempered when P was also added, reducing the suppressive effect of N addition from 24 to 1% in one of the ten analysis periods (summer 2012–2014, p = 0.01 for the interaction of N and P). This interaction effect is consistent with observations of reduced foliar N and available soil N following P addition. Mid-successional stands (26–41 years old at the time of the first nutrient addition) consistently had the lowest rates of soil respiration across stand age classes (1.4–6.6 lmol CO2 m-2 s-1), and young stands had the highest (2.5–8.5 lmol CO2 m-2 s-1). In addition to these important effects of treatment and stand age, we observed an unexpected increase in soil respiration, which doubled in 10 years and was not explained by soil temperature patterns, nutrient additions, or increased in fine-root biomass. 

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5. Elevated P availability slows N recycling in northern hardwood forests

   https://doi.org/10.1016/j.foreco.2024.122203  

   Goswami, Shinjini; Fisk, Melany C (October 2024, Forest Ecology and Management)

   Nutrient cycling in forest ecosystems can be sensitive to disturbances that change the availability of one nutrient relative to others, altering the synchrony in nutrient cycles that is expected to develop in undisturbed systems. We asked whether the relative availabilities of nitrogen (N) and phosphorus (P) differ with forest successional age after harvest, and tested effects of adding one nutrient on availability and recycling of the other, in a factorial nitrogen (N) × phosphorus (P) fertilization study in multiple early- and mid-successional and mature northern hardwood forest stands in central NH, USA. We did not find effects of forest age on resin-available N:P ratios, which varied widely among successional forest stands and were related to net N mineralization potentials in the forest floor of each stand. P addition suppressed resin-N availability by 31 % and lowered litterfall N recycling by 10 %, but we detected no effects on net N mineralization potentials. P addition also increased nitrification potentials in the organic horizon by up to 60 %, mostly in combination with added N. The effects of added N depended on P; lower resin-P in mature stands and lower litterfall P recycling in stands of all ages were detected only when P was added with N. We conclude that P limitation influences N recycling across forest age classes in these northern hardwoods, with some indication of stronger effects in successional stands. However, net N mineralization potentials better predicted the resin-N response to added P than did stand age. Our results suggest that alleviating P limitation promotes N limitation over time, especially in more rapidly growing successional forests, by increasing biotic demand for N, reducing its recycling in litterfall, and potentially by reducing net N mineralization. 

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