Jeffrey M. Klopatek

THE EFFECTS OF LITTER QUALITY AND CLIMATE ON DECOMPOSITION ALONG AN ELEVATIONAL GRADIENT

The process of decomposition is controlled by both biotic and abiotic factors. While it has been widely hypothesized that litter quality and climatic conditions regulate decomposition, the relative importance of these factors appears to vary across biomes. This study examines the decomposition of native plant litter along an elevational gradient in northern Arizona to determine the influence of litter quality and climate on the rate of decomposition in semiarid communities. A litter-bag experiment was performed using needle/leaf litter from Pinus ponderosa, Pinus edulis, Juniperus monosperma, Gutierrezia sarothrae, and Bouteloua gracilis. The five litter types are representative of the dominant local vegetation and offer a range of litter qualities. The bags were placed along a gradient, running from Great Basin Desert scrub (1960 m) through a pinyon-juniper woodland (2100 m) and up into a ponderosa pine forest (2280 m). Samples were collected and analyzed over a period of 2 yr. Decomposition was closely correlated with the relative proportion of easily decomposed carbon fractions to recalcitrant fractions for the first year. Litter from G. sarothrae and B. gracilis contained relatively low levels of lignin and high levels of cellulose and carbohydrates, and these litter types exhibited significantly faster rates of decay than the highly lignified pine and juniper litter. The order of the relative rates of decomposition was G. sarothrae k B. gracilis . J. monosperma . P. ponderosa 5 P. edulis. There was no correlation between initial litter nitrogen content and the rate of decomposition, suggesting that decomposition is limited by carbon substrates rather than by nutrient content. Decomposition rates were significantly greater at the upper elevation sites, which were colder and wetter. Evidence strongly suggests that decomposition is limited by moisture in these ecosystems. Warmer temperatures resulting from climate change may not increase the rate of decomposition in the Southwest unless accompanied by increases in available moisture.

Anthropogenic and natural CO2 emission sources in an arid urban environment

Recent research has shown the Phoenix, AZ metropolitan region to be characterized by a CO2 dome that peaks near the urban center. The CO2 levels, 50% greater than the surrounding non-urban areas, have been attributed to anthropogenic sources and the physical geography of the area. We quantified sources of CO2 emissions across the metropolitan region. Anthropogenic CO2 emission data were obtained from a variety of government and NGO sources. Soil CO2 efflux from the dominant land-use types was measured over the year. Humans and automobile activity produced more than 80% input of CO2 into the urban environment. Soil CO2 efflux from the natural desert ecosystems showed minimal emissions during hot and dry periods, but responded rapidly to moisture. Conversely, human maintained vegetation types (e.g. golf courses, lawns, irrigated agriculture) have greater efflux and are both temperature and soil moisture dependent. Landfills exhibited the most consistent rates, but were temperature and moisture independent. We estimate the annual CO2 released from the predominant land-use types in the Phoenix region and present a graphical portrayal of soil CO2 emissions and the total natural and anthropogenic CO2 emissions in the metropolitan region using a GIS-based approach. The results presented here do not mimic the spatial pattern shown in previous studies. Only, with sophisticated mixing models will we be able to address the total effect of urbanization on CO2 levels and the contribution to regional patterns.

Potential contribution of carbon by microphytic crusts in pinyon‐juniper woodlands

Abstract We examined the possibility that microphytic crusts (terrestrial algae, cyanobacteria, lichens, and mosses) contribute organ carbon fixed in photosynthesis directly to the soil ecosystem. Microphytic crusts and their underlying soils were collected from pinyon‐juniper woodlands in the fall and in spring. Samples of these crusts were exposed to 14 CO2‐labeled atmosphere. In general, a downward translocation of photosynthate over time from the crust was demonstrated by an increase in 14C content in the soils beneath the crusts. Following a 30‐min exposure to labeled atmosphere, the crusts accumulated as much as 55 × 103 disintegrations per minute (dpm) for a 0.1‐mL subsample volume (in the spring), leveling off about 25 × 103 dpm 10 and 21 days later. The crusts respired from 34 to 36% of the initial fixed carbon. The underlying soils accumulated significant 14C (relative to background) in both fall and spring samples. The source of this increase in 14C radiation in the soil is attributable to carb...

Effects of simulated fire on vesicular-arbuscular mycorrhizae in pinyon-juniper woodland soil

Effects of fire on vesicular-arbuscular mycorrhizal fungi were tested using microcosms constructed from soil, litter, and duff collected beneath canopies of pinyon pine, Utah juniper, and in the open space (interspace). Burning was conducted over wet and dry soils. Soil temperatures were monitored continuously throughout the microcosms during burning. Plants grown in soils burned when dry had a lower VAM colonization than soils burned when wet. Juniper soils demonstrated the greatest reduction, over 95%, compared to their respective controls. Plants grown in interspace soils burned when wet were least affected. There was a positive correlation (r2=0.90) between the decrease in VAM colonization and the soil temperature as a result of the fire. Temperature effects, and associated reductions in VAM, were related to amount of litter burned in each microcosm and the moisture content of the soils.

Impacts of land degradation on historical temperature records from the sonoran desert

Previous research revealed that severe overgrazing and resultant land degradation in the semiarid areas of northern Mexico created significantly higher temperatures in the border area. In this investigation, the temperature and precipitation records from ten ‘homogeneous’ stations are identified in the arid and hyperarid areas of northwest Sonora and are compared with the records from ten stations in southwestern Arizona. Our data show that the Mexican stations are again consistently warmer than the Arizona stations when statistical controls are applied to correct for the linear or non-linear effects of latitude and/or elevation. The stations in Sonora warm at a statistically significantly faster pace than the stations in Arizona during the study period. Furthermore, and consistent with other dryland areas undergoing land degradation, the stations in Sonora reveal a significant increase in the diurnal temperature range during the summer season. Local precipitation reduces the temperature differential between nations on the time scale of days, but enhances the differential on the time scale of months and seasons. Among other findings, the results show how land degradation in dryland areas appears to influence local historical temperature records.

Potential variation of nitrogen transformations in pinyon-juniper ecosystems resulting from burning

SummaryForest floor litter, duff, and underlying soils were assembled in laboratory microcosms representing pinyon, juniper, and interspace field conditions. Burning removed more than 95% of both N and C from the litter, with losses from the duff dependent on soil moisture conditions. No significant changes in total N or C were noted in the soil. Immediate increases were observed in soil NHinf4sup+, decreasing with depth and related to soil heating. The greatest increases were noted in both the pinyon and juniper soils that were dry at the time of the burn, with interspace soils exhibiting the least changes. Soil NHinf4sup+closely approximated the controls on day 90 after the burns in all treatments. Ninety days after the burn microbial biomass N was highest in the controls, followed by the wet and then the dry-burned soils, in both the pinyon and juniper microcosms. This was inversely related to the levels of accumulated NOinf3sup-. Nitrifying bacteria populations were indirectly correlated to soil temperatures during the burn. Population levels 90 days after the burn showed increases in both the wet- and the dry-burn treatments, with those in the pinyon treatments exceeding those found in the nitial controls of pinyon soils.

Carbon fluxes and nitrogen availability along an urban-rural gradient in a desert landscape

Urbanization is increasing in arid and semi-arid regions of the world and impacting native ecosystems through disturbance, climatic modification, and pollution deposition. Arid ecosystems often exhibit a mosaic of shrub/tree canopy covered and non-canopy covered patches that differ in elemental pools and processes. We measured belowground ecosystem attributes and processes in native Larrea tridentata {(D.C.) Cov} dominated communities along an urban–rural gradient in Phoenix, Arizona. Organic carbon (C), total nitrogen (N), and nitrate levels were significantly greater in the urban locations, but soil respiration rates (Rs) were higher at the rural sites. Urban sites exhibited no difference in Rs and N between the canopy and interplant patches while both the rural and suburban sites had significantly greater N and higher Rs under the canopy than in the interplant spaces. Soil respiration rates at the urban locations were not correlated with either soil moisture or temperature individually. These data suggest that urbanization has caused a disconnect of ecological pattern and processes in L. tridentata ecosystems within the urban setting such that water and N limitations no longer explain expected spatial Rs patterns, or elemental pools.

Cryptogamic Crusts as Potential Indicators of Disturbance in Semi-Arid Landscapes

Cryptogamic crusts,† consisting of nonvascular photosynthetic plants (primarily algae, lichens, and mosses) that live on the soil surface, are important elements of arid and semi-arid ecosystems worldwide (Cameron and Fuller, 1960; Shtina and Bolyshev, 1963; Snyder and Wullstein, 1973; Johansen et al., 1984; Harper and Marble, 1988). Because of a deficiency of available moisture, arid and semi-arid regions of the world are characterized by a lack of significant vegetative cover. Cryptogamic crusts, which often occur alone and mixed with grasses in the interspaces between woody plants, can perform critical functions of protecting the soil from erosion (Bailey et al., 1973), aiding in water infiltration, augmenting sites for seed germination (St. Clair et al., 1984; Harper and Marble, 1988), and increasing the soil’s supply of nutrients (Shields and Durrell, 1964; Loope and Gifford, 1972; Rychert and Skujins, 1974; Brotherson and Rushforth, 1983; Jeffries, 1989; Beymer and Klopatek, 1991).

Nitrifiers and mycorrhizae in pristine and grazed pinyon‐juniper ecosystems

We compared soils from grazed and pristine pinyon‐juniper ecosystems for the numbers of chemoautotrophic nitrifying bacteria and determined the distribution of vesicular‐arbuscular (VA) mycorrhizae and ectomycorrhizae (EM). Additionally, we report on the presence of allelopathic substances in organic horizons. Ammonium (NH4+)‐oxidizing bacteria were in greater numbers in the interspaces between the trees, ranging from 9.60 × 104 to 2.13 × 105 bacteria‐1 soil, than under canopies, 3.5 × 104 to 4.8 × 104 bacteria‐1 soil. Grazed interspace soils had over twice the number of NH4+oxidizing bacteria than any other location. There were no differences in the numbers of nitrite‐oxidizing bacteria between either vegetative covers or sites. The rate of nitrate production did not correlate with the number of nitrifiers. However, there was a significant correlation (r2 = 0.85) between mineralization coefficients of total nitrogen and the total number of nitrifiers. Fourteen known and ten unknown monoterpenes were foun...

Some thoughts on using a landscape framework to address cumulative impacts on wetland food chain support

Problems of using food chain support as a functional attribute of a wetland are discussed. It is suggested that primary production may not be the metric that best evaluates food chain support. Environmental constructs of the wetland and resultant habitat variables appear to yield more information on life-support functions. A landscape-oriented approach is derived to separate hierarchically the wet-lands into ecological regions and landscape elements. This classification scheme allows for predetermination of environmental constraints and the possible natural limits of wetland food chain support. It is proposed that models derived from spatial location theory be used to determine the movement of animals from wetland patches experiencing impacts on food chain support. Patch size, distance between patches, habitat diversity, and environmental constraints are incorporated in these models.