Urban ecosystems are expanding globally, and assessing the ecological consequences of urbanization is critical to understanding the biology of local and global change related to land use. We measured ...carbon (C) fluxes, nitrogen (N) cycling, and soil microbial community structure in a replicated (n=3) field experiment comparing urban lawns to corn, wheat–fallow, and unmanaged shortgrass steppe ecosystems in northern Colorado. The urban and corn sites were irrigated and fertilized. Wheat and shortgrass steppe sites were not fertilized or irrigated. Aboveground net primary productivity (ANPP) in urban ecosystems (383±11 C m−2 yr−1) was four to five times greater than wheat or shortgrass steppe but significantly less than corn (537±44 C m−2 yr−1). Soil respiration (2777±273 g C m−2 yr−1) and total belowground C allocation (2602±269 g C m−2 yr−1) in urban ecosystems were both 2.5 to five times greater than any other land‐use type. We estimate that for a large (1578 km2) portion of Larimer County, Colorado, urban lawns occupying 6.4% of the land area account for up to 30% of regional ANPP and 24% of regional soil respiration from land‐use types that we sampled. The rate of N cycling from urban lawn mower clippings to the soil surface was comparable with the rate of N export in harvested corn (both ∼12–15 g N m−2 yr−1). A one‐time measurement of microbial community structure via phospholipid fatty acid analysis suggested that land‐use type had a large impact on microbial biomass and a small impact on the relative abundance of broad taxonomic groups of microorganisms. Our data are consistent with several other studies suggesting that urbanization of arid and semiarid ecosystems leads to enhanced C cycling rates that alter regional C budgets.
Forest harvesting often increases soil carbon (C) and nitrogen (N) mineralization, and we hypothesized that these increases would be enhanced by predicted climate change. While there are many metrics ...of soil C and N cycling, here we tested our hypothesis using extracellular enzyme activities (EEA) that reflect microbial resource allocation toward C and N acquisition. We monitored soil extracellular enzyme activities for 2.5 years in a whole-tree harvested forest in Pennsylvania with climate manipulations of warming (+2 °C) and wetting (+20% precipitation) implemented in a factorial design. Climate treatments had little effect on soil water-extractable carbon and inorganic N concentrations. Only β-1,4-glucosidase (BG) and N-acetylglucosaminidase (NAG) showed climate treatment effects; evidence suggests warming decreased BG (p = 0.025) and NAG (p = 0.007) relative non-warmed treatments by an average of 19% and 21% respectively. Increased precipitation had no effect on the six soil EEAs. Two commonly used exoenzyme ratios did not vary among treatments. However, the ratio of activity of nitrogen acquiring enzymes (leucine aminopeptidase + NAG) to key C acquiring enzymes (BG + cellobiohydrolase + polyphenol oxydase) was highest in the single-factor warmed (p = 0.023) and wetted (p = 0.025) treatments. Overall, changes in soil EEA ratios were poorly correlated with changes in soil C and N pools, indicating either a strong influence of abiotic controls on EEA or that the particular enzymes we analyzed were not good indicators of microbial supply and demand for C and N.
► We tested climate change interactions on soil enzymes after a forest harvest. ► Climate treatments: ambient, warm (+2 °C), wet (+20% precipitation), and warm+wet. ► Warming decreased soil β-1,4-glucosidase and N-acetyl-glucosaminidase activities. ► Soil DOC, C:N, and total N best predicted variation in exoenzyme activities. ► Climate change had limited effects on soil exoenzymes in a post-harvest forest.
A distinct urban biogeochemistry? Kaye, Jason P.; Groffman, Peter M.; Grimm, Nancy B. ...
Trends in ecology & evolution (Amsterdam),
04/2006, Letnik:
21, Številka:
4
Journal Article
Recenzirano
Most of the global human population lives in urban areas where biogeochemical cycles are controlled by complex interactions between society and the environment. Urban ecology is an emerging ...discipline that seeks to understand these interactions, and one of the grand challenges for urban ecologists is to develop models that encompass the myriad influences of people on biogeochemistry. We suggest here that existing models, developed primarily in unmanaged and agricultural ecosystems, work poorly in urban ecosystems because they do not include human biogeochemical controls such as impervious surface proliferation, engineered aqueous flow paths, landscaping choices, and human demographic trends. Incorporating these human controls into biogeochemical models will advance urban ecology and will require enhanced collaborations with engineers and social scientists.
Data for 479 patients were analyzed to assess the impact of methicillin resistance on the outcomes of patients with Staphylococcus aureus surgical site infections (SSIs). Patients infected with ...methicillin-resistant S. aureus (MRSA) had a greater 90-day mortality rate than did patients infected with methicillin-susceptible S. aureus (MSSA; adjusted odds ratio, 3.4; 95% confidence interval, 1.5–7.2). Patients infected with MRSA had a greater duration of hospitalization after infection (median additional days, 5; P < .001), although this was not significant on multivariate analysis (P = .11). Median hospital charges were $29,455 for control subjects, $52,791 for patients with MSSA SSI, and $92,363 for patients with MRSA SSI (P < .001 for all group comparisons). Patients with MRSA SSI had a 1.19-fold increase in hospital charges (P = .03) and had mean attributable excess charges of $13,901 per SSI compared with patients who had MSSA SSIs. Methicillin resistance is independently associated with increased mortality and hospital charges among patients with S. aureus SSI.
The fluorescent nature of aerosol at a high-altitude Alpine site was studied using a wide-band integrated bioaerosol (WIBS-4) single particle multi-channel ultraviolet – light-induced ...fluorescence (UV-LIF) spectrometer. This was supported by comprehensive cloud microphysics and meteorological measurements with the aims of cataloguing concentrations of bio-fluorescent aerosols at this high-altitude site and also investigating possible influences of UV–fluorescent particle types on cloud–aerosol processes. Analysis of background free tropospheric air masses, using a total aerosol inlet, showed there to be a minor increase in the fluorescent aerosol fraction during in-cloud cases compared to out-of-cloud cases. The size dependence of the fluorescent aerosol fraction showed the larger aerosol to be more likely to be fluorescent with 80 % of 10 μm particles being fluorescent. Whilst the fluorescent particles were in the minority (NFl∕NAll = 0.27 0.19), a new hierarchical agglomerative cluster analysis approach, Crawford et al. (2015) revealed the majority of the fluorescent aerosols were likely to be representative of fluorescent mineral dust. A minor episodic contribution from a cluster likely to be representative of primary biological aerosol particles (PBAP) was also observed with a wintertime baseline concentration of 0.1 0.4 L−1. Given the low concentration of this cluster and the typically low ice-active fraction of studied PBAP (e.g. pseudomonas syringae), we suggest that the contribution to the observed ice crystal concentration at this location is not significant during the wintertime.
Disturbances alter ecosystem carbon dynamics, often by reducing carbon uptake and stocks. We compared the impact of two types of disturbances that represent the most likely future conditions of ...currently dense ponderosa pine forests of the southwestern United States: (1) high-intensity fire and (2) thinning, designed to reduce fire intensity. High-severity fire had a larger impact on ecosystem carbon uptake and storage than thinning. Total ecosystem carbon was 42% lower at the intensely burned site, 10 years after burning, than at the undisturbed site. Eddy covariance measurements over two years showed that the burned site was a net annual source of carbon to the atmosphere whereas the undisturbed site was a sink. Net primary production (NPP), evapotranspiration (ET), and water use efficiency were lower at the burned site than at the undisturbed site. In contrast, thinning decreased total ecosystem carbon by 18%, and changed the site from a carbon sink to a source in the first post-treatment year. Thinning also decreased ET, reduced the limitation of drought on carbon uptake during summer, and did not change water use efficiency. Both disturbances reduced ecosystem carbon uptake by decreasing gross primary production (55% by burning, 30% by thinning) more than total ecosystem respiration (TER; 33-47% by burning, 18% by thinning), and increased the contribution of soil carbon dioxide efflux to TER. The relationship between TER and temperature was not affected by either disturbance. Efforts to accurately estimate regional carbon budgets should consider impacts on carbon dynamics of both large disturbances, such as high-intensity fire, and the partial disturbance of thinning that is often used to prevent intense burning. Our results show that thinned forests of ponderosa pine in the southwestern United States are a desirable alternative to intensively burned forests to maintain carbon stocks and primary production.
Forest disturbances, including whole-tree harvest, will increase with a growing human population and its rising affluence. Following harvest, forests become sources of C to the atmosphere, partly ...because wetter and warmer soils (relative to pre-harvest) increase soil CO₂ efflux. This relationship between soil microclimate and CO₂ suggests that climate changes predicted for the northeastern US may exacerbate post-harvest CO₂ losses. We tested this hypothesis using a climate-manipulation experiment within a recently harvested northeastern US forest with warmed (H; +2.5 °C), wetted (W; +23 % precipitation), warmed + wetted (H+W), and ambient (A) treatments. The cumulative soil CO₂ effluxes from H and W were 35 % (P = 0.01) and 22 % (P = 0.07) greater than A. However, cumulative efflux in H+W was similar to A and W, and 24 % lower than in H (P = 0.02). These findings suggest that with higher precipitation soil CO₂ efflux attenuates rapidly to warming, perhaps due to changes in substrate availability or microbial communities. Microbial function measured as CO₂ response to 15 C substrates in warmed soils was distinct from non-warmed soils (P < 0.001). Furthermore, wetting lowered catabolic evenness (P = 0.04) and fungi-to-bacteria ratios (P = 0.03) relative to non-wetted treatments. A reciprocal transplant incubation showed that H+W microorganisms had lower laboratory respiration on their home soils (i.e., home substrates) than on soils from other treatments (P < 0.01). We inferred that H+W microorganisms may use a constrained suite of C substrates that become depleted in their “home” soils, and that in some disturbed ecosystems, a precipitation-induced attenuation (or suppression) of soil CO₂ efflux to warming may result from fine-tuned microbe-substrate linkages.
Whole-tree forest harvest can increase soil nitrous oxide (N₂O) effluxes and leaching of nitrogen (N) from soils. These altered N dynamics are often linked to harvesting effects on microclimate, ...suggesting that this “hot moment” for N cycling may become hotter with climate change. We hypothesized that increases in temperature and precipitation during this post-harvest period would increase availability of soil mineral N and soil-atmosphere N₂O efflux. To test this hypothesis we implemented a climate manipulation experiment after a forest harvest, and measured soil N₂O fluxes and inorganic N accumulating on ion exchange resins. Climate treatments were: control (A, ambient), heated (H, +2.5 °C), wetted (W, +23 % precipitation), and a two-factor treatment (H+W). For all treatments, the first year after harvest had highest N₂O efflux and resin N. Wetting significantly increased cumulative soil N₂O fluxes, but only when soils were not heated too. The cumulative soil-to-atmosphere N₂O efflux from W (5.8 mg N₂O–N m⁻²) was significantly higher than A (−1.9 mg N₂O–N m⁻²), but H+W (~0 mg N₂O–N m⁻²) was similar to A. Regardless of wetting, heating increased resin N, but only on certain dates. Cumulative resin N was on average 125 % greater in the H plots than non-heated plots. Thus, changes in temperature and precipitation each impart distinct changes to the soil N cycle. Heating increased resin N regardless of water inputs, while wetting increasing N₂O but not when combined with heating. Our results suggest that climate change may exacerbate soil N losses from whole-tree harvest in the future, but the form and quantity of N loss will depend on how the future climate changes.
The temperature sensitivity of soil respiration will largely determine the effects of a warmer world on net carbon flux from soils to the atmosphere. CO2 flux from soils to the atmosphere is ...estimated to be 50-70 petagrams of carbon per year and makes up 20-38% of annual inputs of carbon (in the form of CO2) to the atmosphere from terrestrial and marine sources.
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