Wendy H. Yang

Beyond carbon and nitrogen: how the microbial energy economy couples elemental cycles in diverse ecosystems

Microbial metabolism couples elemental reactions, driving biogeochemical cycles. Assimilatory coupling of elemental cycles, such as the carbon (C), nitrogen (N), and phosphorus cycles, occurs when these elements are incorporated into biomass or released through its decomposition. In addition, many microbes are capable of dissimilatory coupling, catalyzing energy-releasing reactions linked to transformations in the oxidation state of elements, and releasing the transformed elements to the environment. Different inorganic elements provide varying amounts of energy yield, and the interaction of these processes creates a microbial energy economy. Dissimilatory reactions involving C, N, iron, and sulfur provide particularly important examples where microbially mediated oxidation–reduction (redox) transformations affect nutrient availability for net primary production, greenhouse-gas emissions, levels of contaminants and natural toxic factors, and other ecosystem dynamics. Recent discoveries of previously unrec...

High potential for iron reduction in upland soils

Changes in the redox state of iron (Fe) can be coupled to the biogeochemical cycling of carbon (C), nitrogen, and phosphorus, and thus regulate soil C, ecosystem nutrient availability, and greenhouse gas production. However, its importance broadly in non-flooded upland terrestrial ecosystems is unknown. We measured Fe reduction in soil samples from an annual grassland, a drained peatland, and a humid tropical forest We incubated soil slurries in an anoxic glovebox for 5.5 days and added sodium acetate daily at rates up to 0.4 mg C x (g soil)(-1) x d(-1). Soil moisture, poorly crystalline Fe oxide concentrations, and Fe(II) concentrations differed among study sites in the following order: annual grassland < drained peatland < tropical forest (P < 0.001 for all characteristics). All of the soil samples demonstrated high Fe reduction potential with maximum rates over the course of the incubation averaging 1706 ± 66, 2016 ± 12, and 2973 ± 115 μg Fe x (g soil)(-1) x d(-1) (mean ± SE) for the tropical forest, annual grassland, and drained peatland, respectively. Our results suggest that upland soils from diverse ecosystems have the potential to exhibit high short-term rates of Fe reduction that may play an important role in driving soil biogeochemical processes during periods of anaerobiosis.

Microbially mediated nitrogen retention and loss in a salt marsh soil

Salt marshes currently play an important role as filters for upslope nitrogen (N) inputs. This could change in the future with sea level rise, warming and eutrophication, which are expected to favor monocultures over diverse plant communities. We explored patterns in gross N cycling, dissimilatory nitrate (NO3−) reduction to ammonium (NH4+) (DNRA), and denitrification in a salt marsh soil under two typical redox conditions (aerobic and anaerobic), and in soils under plant communities manipulated to simulate potential future composition (forb and graminoid monocultures). Natural salt marsh soils exhibited high potential gross N mineralization rates, averaging 50.4 ± 5.7 μg N g−1 d−1 under aerobic conditions; rates declined to 23.6 ± 3.4 μg N g−1 d−1 under an N2 headspace. Microbial NH4+ uptake and gross nitrification together accounted for only 14 % of gross N mineralization. Nitrogen retention via DNRA and microbial uptake greatly exceeded N losses via denitrification. Gross nitrification rates were great...

Application of the N(2)/Ar technique to measuring soil-atmosphere N(2) fluxes.

RATIONALE The emission of dinitrogen (N(2) ) gas from soil is the most poorly constrained flux in terrestrial nitrogen (N) budgets because the high background atmospheric N(2) concentration makes soil N(2) emissions difficult to measure. In this study, we tested the theoretical and analytical feasibility of using the N(2) /Ar technique to measure soil-atmosphere N(2) fluxes. METHODS Dual inlet isotope ratio mass spectrometry was used to measure δAr/N(2) values of gas sampled from surface flux chambers. In laboratory experiments using dry sand in a diffusion box, we induced a known steady-state flux of N(2) , and then measured the change in the N(2) /Ar ratio of chamber headspace air samples to test our ability to reconstruct this flux. We m\odeled solubility, thermal, and water vapor flux fractionation effects on the N(2) /Ar ratio to constrain physical effects on the measured N(2) flux. RESULTS In dry sand, an actual N(2) flux of 108 mg N m(-2)  day(-1) was measured as 111 ± 19 mg N m(-2)  day(-1) (± standard error (SE)). In wet sand, an actual N(2) flux of 160 mg N m(-2)  day(-1) was measured as 146 ± 20 mg N m(-2)  day(-1) when solubility and water vapor flux fractionation were taken into account. Corrections for thermal fractionation did not improve estimates of N(2) fluxes. CONCLUSIONS We conclude that our application of the N(2) /Ar technique to soil surface fluxes is valid only above a detection limit of approximately 108 mg N m(-2)  day(-1) . The N(2) /Ar method is currently best used as a validation tool for other methods in ecosystems with high soil N(2) fluxes, but, with future improvements, it holds promise to provide high-resolution measurements in systems with low soil N(2) fluxes.

Frontiers in alley cropping: Transformative solutions for temperate agriculture

Annual row crops dominate agriculture around the world and have considerable negative environmental impacts, including significant greenhouse gas emissions. Transformative land-use solutions are necessary to mitigate climate change and restore critical ecosystem services. Alley cropping (AC)-the integration of trees with crops-is an agroforestry practice that has been studied as a transformative, multifunctional land-use solution. In the temperate zone, AC has strong potential for climate change mitigation through direct emissions reductions and increases in land-use efficiency via overyielding compared to trees and crops grown separately. In addition, AC provides climate change adaptation potential and ecological benefits by buffering alley crops to weather extremes, diversifying income to hedge financial risk, increasing biodiversity, reducing soil erosion, and improving nutrient- and water-use efficiency. The scope of temperate AC research and application has been largely limited to simple systems that combine one timber tree species with an annual grain. We propose two frontiers in temperate AC that expand this scope and could transform its climate-related benefits: (i) diversification via woody polyculture and (ii) expanded use of tree crops for food and fodder. While AC is ready now for implementation on marginal lands, we discuss key considerations that could enhance the scalability of the two proposed frontiers and catalyze widespread adoption.

Evaluating the Classical Versus an Emerging Conceptual Model of Peatland Methane Dynamics

We appreciate discussions with M. Firestone and S. Blazewicz. We received assistance in the field and lab from K. Smetak, H. Dang, and A. McDowell. This research was funded by grants to W.L.S. from the U.S. National Science Foundation (ATM-0842385 and DEB-0543558) and the California Department of Fish and Wildlife (CDFW) and California Department of Water Resources (DWR) contract 4600011240. The data used are listed in the references, tables, supporting information, and the Illinois Digital Environment for Access to Learning and Scholarship (IDEALS) repository at https://www.ideals.illinois.edu/.