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Shifts in plant community structure in shrub and grass-dominated ecosystems are occurring over large land areas in the western US. It is not clear what effect this vegetative change will have on rates of carbon and nitrogen cycling, and thus long-term ecosystem productivity. To study the effect of different plant species on the decomposability of soil organic substrates and rates of C- and N-cycling, we conducted laboratory incubations of soils from a 15-yr-old experimental plot where big sagebrush (Artemisia tridentata Nutt.) and crested wheatgrass (Agropyron desertorum [Fisch.] Schult.) plants had been planted in a grid pattern. Soil samples collected from beneath crested wheatgrass had significantly greater total...
Abstract The importance of snow and related cryospheric processes as an ecological factor has been recognized since at least the beginning of the twentieth century. Even today, however, many observations remain anecdotal. The research to date on cold-lands ecosystems results in scientists being unable to evaluate to what extent changes in the cryosphere will be characterized by abrupt changes in local and global biogeochemical cycles, and how these changes in seasonality may affect the rates and timing of key ecological processes. Studies of gas exchanges through snow have revealed that snow plays an important role in modulating wintertime soil biogeochemical processes, and that these can be the driving processes...
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To assess the distribution, frequency, and global extent of riverine hypoxia, we compiled 118 million paired dissolved oxygen (DO) and water temperature measurements from 125,158 unique locations in rivers in 93 countries and territories across the globe. The dataset also includes site characteristics derived from StreamCat, the National Hydrography and HydroAtlas datasets and proximal land cover derived from MODIS-based IGBP land cover types compiled using Google Earth Engine (GEE).
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Predicted changes in climate may affect key soil processes such as respiration and net nitrogen (N) mineralization and thus key ecosystem functions such as carbon (C) storage and nutrient availability. To identify the sensitivity of shrubland soils to predicted climate changes, we have carried out experimental manipulations involving ecosystem warming and prolonged summer drought in ericaceous shrublands across a European climate gradient. We used retractable covers to create artificial nighttime warming and prolonged summer drought to 20-m 2 experimental plots. Combining the data from across the environmental gradient with the results from the manipulation experiments provides evidence for strong climate controls...
In semiarid ecosystems, physiography (landscape setting) may interact with woody-plant and soil microbe communities to constrain seasonal exchanges of material and energy at the ecosystem scale. In an upland and riparian shrubland, we examined the seasonally dynamic linkage between ecosystem CO2 exchange, woody-plant water status and photosynthesis, and soil respiration responses to summer rainfall. At each site, we compared tower-based measurements of net ecosystem CO2 exchange (NEE) with ecophysiological measurements among velvet mesquite (Prosopis velutina Woot.) in three size classes and soil respiration in sub-canopy and inter-canopy micro-sites. Monsoonal rainfall influenced a greater shift in the magnitude...
In the arid and semiarid regions of North America, discrete precipitation pulses are important triggers for biological activity. The timing and magnitude of these pulses may differentially affect the activity of plants and microbes, combining to influence the C balance of desert ecosystems. Here, we evaluate how a "pulse" of water influences physiological activity in plants, soils and ecosystems, and how characteristics, such as precipitation pulse size and frequency are important controllers of biological and physical processes in arid land ecosystems. We show that pulse size regulates C balance by determining the temporal duration of activity for different components of the biota. Microbial respiration responds...
? The influences of prior monsoon-season drought (PMSD) and the seasonal timing of episodic rainfall (?pulses?) on carbon and water exchange in water-limited ecosystems are poorly quantified. ? In the present study, we estimated net ecosystem exchange of CO2 (NEE) and evapotranspiration (ET) before, and for 15 d following, experimental irrigation in a semi-arid grassland during June and August 2003. Rainout shelters near Tucson, Arizona, USA, were positioned on contrasting soils (clay and sand) and planted with native (Heteropogon contortus) or non-native invasive (Eragrostis lehmanniana) C4 bunchgrasses. Plots received increased (?wet?) or decreased (?dry?) monsoon-season (July?September) rainfall during 2002 and...
Shifts in plant community structure in shrub and grass-dominated ecosystems are occurring over large land areas in the western US. It is not clear what effect this vegetative change will have on rates of carbon and nitrogen cycling, and thus long-term ecosystem productivity. To study the effect of different plant species on the decomposability of soil organic substrates and rates of C- and N-cycling, we conducted laboratory incubations of soils from a 15-yr-old experimental plot where big sagebrush (Artemisia tridentata Nutt.) and crested wheatgrass (Agropyron desertorum [Fisch.] Schult.) plants had been planted in a grid pattern. Soil samples collected from beneath crested wheatgrass had significantly greater total...
Carbon gain depends on efficient photosynthesis and adequate respiration. The effect of temperature on photosynthetic efficiency is well understood. In contrast, the temperature response of respiration is based almost entirely on short-term (hours) measurements in mature organisms to develop Q(10) values for maintenance and whole-plant respiration. These Q(10) values are then used to extrapolate across whole life cycles to predict the influence of temperature on plant growth. Published in Annals of Botany, volume 94, issue 1, on pages 155 - 66, in 2004.
This study is part of an assessment of potential effects of climate change on the St. Lawrence Great Lakes. Its purpose is to investigate potential future lake mixing patterns and primary production. Nested physical and biological models were applied to seasonal mixed layer depth, heat content, primary productivity, and to algal biomass measured as particulate chlorophyll. Two independent second generation General Circulation Models provided scenarios for future conditions of cloud cover, air temperature, humidity, and winds. The climate variables were used to force heat balance and surface mixed layer models for Lakes Superior, Michigan, Huron, Erie, and Ontario. Physical models of heat balance and mixed layer...
Coleogyne ramosissima Torr. (blackbrush) and Atriplex confertifolia [Torr. & Frem.] Wats. (shadscale) are cold desert shrubs from different families. Despite very different life histories they often grow in close geographic proximity in the Great Basin and the Colorado Plateau between 800 and 2000 m elevation. The purpose of this study is to compare the ecophysiology of slow growing and reproducing blackbrush with the ecophysiology of faster growing and reproducing shadscale. Metabolic heat and carbon dioxide production rates were measured on leaf tissue from wild plants and on lab-grown seedlings at temperatures from 10 to 35 °C at 5 °C intervals. Heat of combustion, ash content, and carbon and nitrogen contents...
Cheatgrass (Bromus tectorum L.) is a dominant weed that has increased the frequency of wildfire in the Great Basin since its introduction about 100 yr ago. This study examines characteristics of respiratory metabolism in several different populations. Seeds from 6 populations were germinated and metabolic heat rates (q) and dark respiration rates (Rco2) of all seedlings were measured calorimetrically at 15° and 25° C or (for 3 populations) at 5° intervals from 5° to 35° C. Growth rates, substrate carbon conversion efficiencies, and Arrhenius temperature coefficients were calculated from the data. Results show that cheatgrass metabolism is most efficient at temperatures near 0° C; at temperatures above 20-25°...
Eddy covariance measures net ecosystem exchange of CO2 (NEE) at a scale between chamber-based measurements of CO2 exchange processes and large-scale models of CO2 flux dynamics. As the intermediate, it represents a link between small and large-scale estimates of NEE. Accuracy is therefore critical. However, estimates of nighttime ecosystem respiration based on scaled-up measurements of soil and leaf CO2 exchange are most often larger than from eddy covariance. Identifying the source of the discrepancy is difficult due to large measurement uncertainties associated with high variability of fluxes in complex ecosystems. This study compared measurements in a simple system that allowed for minimal uncertainty. We compared...
Determining the relative temperature sensitivities of the decomposition of the different soil organic matter (SOM) pools is critical for predicting the long-term impacts of climate change on soil carbon (C) storage. Although kinetic theory suggests that the temperature sensitivity of SOM decomposition should increase with substrate recalcitrance, there remains little empirical evidence to support this hypothesis. In the study presented here, sub-samples from a single bulk soil sample were frozen and sequentially defrosted to produce samples of the same soil that had been incubated for different lengths of time, up to a maximum of 124 days. These samples were then placed into an incubation system which allowed CO2...
    map background search result map search result map The Response of Soil Processes to Climate Change: Results from Manipulation Studies of Shrublands Across an Environmental Gradient The Response of Soil Processes to Climate Change: Results from Manipulation Studies of Shrublands Across an Environmental Gradient