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We are conducting nutrient manipulations in three study sites in the White Mountain National Forest in New Hampshire: Bartlett Experimental Forest, Hubbard Brook Experimental Forest, and Jeffers Brook. We monitored foliar chemistry in 13 of our stands (including HBCa and excluding C3) pre-treatment (2008-2010) and post-treatment (2014-2016 and 2021-22). In 2021-22, we also measured specific leaf area, leaf dry matter content, carbon isotope composition, and stomatal density. We found that foliar N concentrations were higher with N addition and foliar P concentrations were higher with P addition. More interestingly, P addition reduced foliar N concentrations and N addition reduced foliar P concentrations. Some interactive effects were observed (i.e. NxP, Species x N, Species x P, Species x N x P). This dataset contains pre- and post- treatment foliar chemistry and trait data, and data from the analysis of quality control standard samples. Changes to pre-treatment data from version 1 include switching white birch trees #8272 and #8252 in stand JBM plots 2 and 3 (8272 is now in the nitrogen plot and 8252 is now in the control plot), correcting the species of tree #1628 in stand HBCa plot 1 (changed from red maple to sugar maple) and tree #8457 in stand HBO plot 3 (changed from sugar maple to red maple), and updating nutrient concentrations for C8 plot 3 sugar maple trees #28 and #30 to include averages of subsamples re-run in 2022. Tree tags were also updated to the tag ID present during the 2023 tree inventory. 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 These data were gathered as part of the Hubbard Brook Ecosystem Study (HBES). The HBES is a collaborative effort at the Hubbard Brook Experimental Forest, which is operated and maintained by the USDA Forest Service, Northern Research Station. 

Summary Coarse roots represent a globally important belowground carbon pool, but the factors controlling coarse root decomposition rates remain poorly understood relative to other plant biomass components. We compiled the most comprehensive dataset of coarse root decomposition data including 148 observations from 60 woody species, and linked coarse root decomposition rates to plant traits, phylogeny and climate to address questions of the dominant controls on coarse root decomposition.We found that decomposition rates increased with mean annual temperature, root nitrogen and phosphorus concentrations. Coarse root decomposition was slower for ectomycorrhizal than arbuscular mycorrhizal associated species, and angiosperm species decomposed faster than gymnosperms. Coarse root decomposition rates and calcium concentrations showed a strong phylogenetic signal.Our findings suggest that categorical traits like mycorrhizal association and phylogenetic group, in conjunction with root quality and climate, collectively serve as the optimal predictors of coarse root decomposition rates.Our findings propose a paradigm of the dominant controls on coarse decomposition, with mycorrhizal association and phylogeny acting as critical roles on coarse root decomposition, necessitating their explicit consideration in Earth‐system models and ultimately improving confidence in projected carbon cycle–climate feedbacks. 

Abstract Fungal necromass is increasingly recognized as a key component of soil carbon (C) and nitrogen (N) cycling. However, how C and N loss from fungal necromass during decomposition is impacted by global change factors such as anthropogenic N addition and changes to soil C supply (e.g. via changing root exudation and rhizosphere priming) remains unclear and understudied relative to plant tissues.To address these gaps, we conducted a year‐long decomposition experiment with four species of fungal necromass incubated across four forested sites in plots that had received inorganic N and/or labile C fertilization for two decades in Minnesota, USA.We found that necromass chemistry was the primary driver of C and N loss from fungal necromass as well as the response to fertilization. Specifically, N addition suppressed late‐stage decomposition, but this effect was weaker in melanin‐rich necromass, contrary to the hypothesis based on plant litter dynamics that N addition should suppress the decomposition of more complex organic molecules. Labile C addition had no effect on either the early or late stages of necromass decomposition.Nitrogen release from necromass also varied among species, with N‐poor necromass having lower N release after controlling for differences in mass loss via regression. The relatively minor effects of N fertilization on the proportion of initial necromass N released suggest that N demand by decomposers is the primary control on N loss during fungal necromass decomposition.Synthesis. Together, our results stress the importance of the afterlife effects of fungal chemical composition to forest soil C and N cycles. Further, they demonstrate that C and N release from this critical pool can be reduced by ongoing anthropogenic N addition. 

This dataset describes litterfall mass collected in the Multiple Element Limitation in Northern Hardwood Ecosystems (MELNHE) study in New Hampshire from fall 2009 through summer 2022. Litter was collected three times per year: fall (late October or early November), spring (June), and summer (August). Fall litter was sorted by species in a subset of stands. This data package also includes the R code used to impute missing data for analysis, a manually edited data file used in the R code flow, and a file matching the labels for litterfall collectors from the original (pre Fall 2011) and current (Fall 2011 and onwards) labeling systems. All collectors have the most current label if known for all years of data. Additional detail on MELNHE, including a table of stand descriptions, project description, and a diagram of plot configuration can be found in this data package: Yanai, R.D., M. Fisk, and T.J. Fahey. 2024. Multiple Element Limitation in Northern Hardwood Ecosystems (MELNHE): Project description, plot characteristics and design ver 2. Environmental Data Initiative. https://doi.org/10.6073/pasta/6cc8a39d052834c030650fb29937bf4f (Accessed 2024-10-17). Litterfall chemistry data for a subset of these samples can be found in the following data package: Fisk, M.C., R.D. Yanai, S.D. Hong, C.R. See, and S. Goswami. 2022. Litter chemistry and masses for the MELNHE NxP fertilization experiment ver 1. Environmental Data Initiative. https://doi.org/10.6073/pasta/8b2975a3a02cbcfb1b0a12ac954576d4 (Accessed 2024-06-09). These data were gathered as part of the Hubbard Brook Ecosystem Study (HBES). The HBES is a collaborative effort at the Hubbard Brook Experimental Forest, which is operated and maintained by the USDA Forest Service, Northern Research Station. 

ABSTRACT Microbial necromass contributes significantly to both soil carbon (C) persistence and ecosystem nitrogen (N) availability, but quantitative estimates of C and N movement from necromass into soils and decomposer communities are lacking. Additionally, while melanin is known to slow fungal necromass decomposition, how it influences microbial C and N acquisition as well as elemental release into soils remains unclear. Here, we tracked decomposition of isotopically labeled low and high melanin fungal necromass and measured¹³C and¹⁵N accumulation in surrounding soils and microbial communities over 77 d in a temperate forest in Minnesota, USA. Mass loss was significantly higher from low melanin necromass, corresponding with greater¹³C and¹⁵N soil inputs. A taxonomically and functionally diverse array of bacteria and fungi was enriched in¹³C and/or¹⁵N at all sampling points, with enrichment being consistently higher on low melanin necromass and earlier in decomposition. Similar patterns of preferential C and N enrichment of many bacterial and fungal genera early in decomposition suggest that both microbial groups co-contribute to the rapid assimilation of resource-rich soil organic matter inputs. While overall richness of taxa enriched in C was higher than in N for both bacteria and fungi, there was a significant positive relationship between C and N in co-enriched taxa. Collectively, our results demonstrate that melanization acts as a key ecological trait mediating not only fungal necromass decomposition rate but also necromass C and N release and that both elements are rapidly co-utilized by diverse bacterial and fungal decomposers in natural settings. IMPORTANCERecent studies indicate that microbial dead cells, particularly those of fungi, play an important role in long-term carbon persistence in soils. Despite this growing recognition, how the resources within dead fungal cells (also known as fungal necromass) move into decomposer communities and soils are poorly quantified, particularly in studies based in natural environments. In this study, we found that the contribution of fungal necromass to soil carbon and nitrogen availability was slowed by the amount of melanin present in fungal cell walls. Further, despite the overall rapid acquisition of carbon and nitrogen from necromass by a diverse range of both bacteria and fungi, melanization also slowed microbial uptake of both elements. Collectively, our results indicate that melanization acts as a key ecological trait mediating not only fungal necromass decomposition rate, but also necromass carbon and nitrogen release into soil as well as microbial resource acquisition. 

The Multiple Element Limitation in Northern Hardwood Ecosystems (MELNHE) project studies N, P, and Ca acquisition and limitation of forest productivity through a series of nutrient manipulations in northern hardwood forests. This data set includes litterfall chemistry and mass for litter collected approximately weekly through the fall litterfall season, either composited over the entire fall season or selected from individual collection times, pre-treatment (2009), and post-treatment (2012, 2014, 2016, 2018). 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 These data were gathered as part of the Hubbard Brook Ecosystem Study (HBES). The HBES is a collaborative effort at the Hubbard Brook Experimental Forest, which is operated and maintained by the USDA Forest Service, Northern Research Station. 

Abstract The Arctic–Boreal Zone is rapidly warming, impacting its large soil carbon stocks. Here we use a new compilation of terrestrial ecosystem CO₂fluxes, geospatial datasets and random forest models to show that although the Arctic–Boreal Zone was overall an increasing terrestrial CO₂sink from 2001 to 2020 (mean ± standard deviation in net ecosystem exchange, −548 ± 140 Tg C yr⁻¹; trend, −14 Tg C yr⁻¹;P < 0.001), more than 30% of the region was a net CO₂source. Tundra regions may have already started to function on average as CO₂sources, demonstrating a shift in carbon dynamics. When fire emissions are factored in, the increasing Arctic–Boreal Zone sink is no longer statistically significant (budget, −319 ± 140 Tg C yr⁻¹; trend, −9 Tg C yr⁻¹), and the permafrost region becomes CO₂neutral (budget, −24 ± 123 Tg C yr⁻¹; trend, −3 Tg C yr⁻¹), underscoring the importance of fire in this region. 

We are conducting nutrient manipulations in three study sites in the White Mountain National Forest in New Hampshire: Bartlett Experimental Forest, Hubbard Brook Experimental Forest, and Jeffers Brook. We monitored foliar chemistry in 12 of our stands (excluding C3) pre-treatment (2008-2010) and post-treatment (2014-2016). In general, we found that foliar N concentrations were higher with N addition and foliar P concentrations were higher with P addition. More interestingly, P addition reduced foliar N concentrations and N addition reduced foliar P concentrations. Some interactive effects were observed (i.e. NxP, Species x N, Species x P, Species x N x P). This dataset contains pre- and post- treatment foliar chemistry data, and data from the analysis of quality control standard samples. These data were gathered as part of the Hubbard Brook Ecosystem Study (HBES). The HBES is a collaborative effort at the Hubbard Brook Experimental Forest, which is operated and maintained by the USDA Forest Service, Northern Research Station. 

Abstract Tundra and boreal ecosystems encompass the northern circumpolar permafrost region and are experiencing rapid environmental change with important implications for the global carbon (C) budget. We analysed multi-decadal time series containing 302 annual estimates of carbon dioxide (CO₂) flux across 70 permafrost and non-permafrost ecosystems, and 672 estimates of summer CO₂flux across 181 ecosystems. We find an increase in the annual CO₂sink across non-permafrost ecosystems but not permafrost ecosystems, despite similar increases in summer uptake. Thus, recent non-growing-season CO₂losses have substantially impacted the CO₂balance of permafrost ecosystems. Furthermore, analysis of interannual variability reveals warmer summers amplify the C cycle (increase productivity and respiration) at putatively nitrogen-limited sites and at sites less reliant on summer precipitation for water use. Our findings suggest that water and nutrient availability will be important predictors of the C-cycle response of these ecosystems to future warming.