Statistics for Spatial Data.

I. CONTEXT * The Ecosystem Concept * Earth's Climate System * Geology and Soils * II. MECHANISMS * Terrestrial Water and Energy Balance * Carbon Input to Terrestrial Ecosystems * Terrestrial Production Processes * Terrestrial Decomposition * Terrestrial Plant Nutrient Use * Terrestrial Nutrient Cycling * Aquatic Carbon and Nutrient Cycling * Trophic Dynamics * Community Effects on Ecosystem Processes * III. PATTERNS * Temporal Dynamics * Landscape Heterogeneity and Ecosystem Dynamics * IV. INTEGRATION * Global Biogeochemical Cycles * Managing and Sustaining Ecosystem * Abbreviations * Glossary * References

Principles of Terrestrial Ecosystem Ecology

Although spatial variability in distributions of soil organisms is generally regarded as random noise, this variability often has a predictable spatial structure. Recent studies have provided evidence that a spatially explicit approach to soil ecology can enable identification of factors that drive the spatial heterogeneity of populations and activities of soil organisms, at scales ranging from millimeters to hundreds of meters. Furthermore, there is increasing evidence that spatial soil ecology can yield new insights with regard to understanding the factors that maintain and regulate soil biodiversity, as well as to how the spatial distributions of soil organisms influence both plant growth and plant community structure.

Spatial soil ecology

Inorganic carbonate in soil occurs predominantly as the sparingly soluble alkaline-earth carbonates, calcite (CaCOs) and dolomite (CaMg(CO,),). Calcite is usually the dominant form in active pedogenic environments (Doner & Lynn, 1977; Nelson, 1982). There are only a few reported occurrences of aragonite (CaCOs) and vaterite (CaCOs) in soils. Sodium carbonate and magnesium carbonate and hydroxycarbonate are common in evaporates or in regions of high-salt deposition in soil. Concentration of dissolved carbonate is controlled by equilibrium relations of the solid-phase carbonates and gas-phase CO*. Concentration of dissolved carbonate is likely to be higher in systems with high partial pressures of C02, e.g., in flooded soils or in microenvironments of high microbial activity, or in sodic soils, because of the high solubility of Na&Os. Also, calcite and dolomite usually control the activities of Ca2+(aq) and Mg2+(aq) in soils containing these minerals. Calcium carbonate contents of carbonate-influenced soils range from traces to greater than 80%. Calcite exists in a variety of forms, from nodules of 1 cm or greater diameter to submicrometer particles to well-formed rhomboids. The presence of carbonates is usually associated with neutral to alkaline soils, but solid-

Carbonate and Gypsum

Belowground competition occurs when plants decrease the growth, survival, or fecundity of neighbors by reducing available soil resources. Competition belowground can be stronger and involve many more neighbors than aboveground competition. Physiological ecologists and population or community ecologists have traditionally studied belowground competition from different perspectives. Physiologically based studies often measure resource uptake without determining the integrated consequences for plant performance, while population or community level studies examine plant performance but fail to identify the resource intermediary or mechanism. Belowground competitive ability is correlated with such attributes as root density, surface area, and plasticity either in root growth or in the properties of enzymes involved in nutrient uptake. Unlike competition for light, in which larger plants have a disproportionate advantage by shading smaller ones, competition for soil resources is apparently more symmetric. Below...

Plant competition underground

The degree to which soil resource availability is linked to patterns of microbial activity and plant productivity within ecosystems has important consequences for our understanding of how ecosystems are structured and for the management of systems for agricultural production. We studied this linkage in a 48-ha site in southwest Michigan, USA, that had been cultivated and planted to row crops for decades. Prior to seeding the site to genetically identical soybean plants (Glycine max) in early spring, we removed soil samples from ≈600 locations; plant biomass was harvested from these same locations later in the season. Soil samples were analyzed for physical properties (texture, bulk density), chemical properties (moisture, pH, total C, total N, inorganic N), and biological attributes (microbial biomass, microbial population size, respiration potential, and nitrification and N-mineralization potentials). Plant analyses included biomass and C and N contents. Soil resource variability across this long-cultiva...

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Soil resources, microbial activity, and primary production across an agricultural ecosystem

The spatial distributions of selected soil properties in two adjacent sites in southwest Michigan were examined to evaluate the potential effects of chronic disturbance on resource heterogeneity. One site was a cultivated field that had been cleared, plowed, and cropped annually for decades prior to sampling while the other, uncultivated field was cleared of original forest in 1960 after which it was mown annually but never plowed or cropped. We took replicate samples from a 330-point unaligned grid across the sites for soil pH, gravimetric moisture, inorganic phosphorus, total carbon, and net nitrification and nitrogen mineralization potentials. Soils in the cultivated site contained less than half as much carbon as in the uncultivated site, but had higher levels of inorganic phosphorus and moisture, and higher soil pH. Potential net nitrogen mineralization and nitrification rates did not differ between sites. Geostatistical analysis showed that almost all properties examined were strongly autocorelated within each site; structural variance as a proportion of sample variance ranged from 30–95% for all properties, and for any given property differed little between sites. The distance over which this dependence was expressed, however, was for all properties but pH substantially less in the uncultivated site (7–26 m) as compared to the tilled site (48–108m), especially for total C and net nitrification and N mineralization. These results suggest that the spatial pattern and scale of soil variability can differ markedly among edaphically identical sites and that these differences can be related to disturbance history.

The spatial variability of soil resources following long-term disturbance.

Les ammoniums quaternaires du type [(CH 3 ) 3 NR] + avec R=C 9 a C 16 s'echangent fortement avec des polluants organiques couramment presents dans les eaux souterraines. Les reactions d'echange de cations multiplient par 200 les coefficients de sorption des sols

Enhanced retention of organic contaminants by soils exchanged with organic cations

Research on nitrate-nitrogen (NO 3 -N) leaching in turfgrass indicates that, in most cases, leaching poses little risk to the environment. Most of the research was conducted on sites that were recently established, and the potential for greater NO 3 -N leaching from mature turf sites is unknown. The fate of nitrogen (N) was examined for a 10-yr-old Kentucky bluegrass (Poa pratensis L.) turf using intact monolith lysimeters and microplots. From October 2000 through July 2002, half of the lysimeters and microplots were treated annually with urea at a high rate of 245 kg N ha -1 (49 kg N ha -1 application -1 ). The remaining lysimeters and microplots were treated annually with urea at a low rate of 98 kg N ha -1 (24.5 kg N ha -1 application -1 ). The Oct. 2000 urea application was made with 15 N double-labeled urea to facilitate fertilizer identification among clippings, verdure, thatch, soil, roots, and leachate. The average total recovery of applied labeled fertilizer nitrogen (LFN) for the low and high N rates was 78 and 74%, respectively. NO 3 -N concentrations in leachate for the low N rate were typically below 5 mg L -1 . For the high N rate, NO 3 -N concentrations in leachate were often greater than 20 mg L -1 . Over approximately 2 yr, 1 and 11% of LFN was recovered in leachate for the low and high N rates, respectively. This research indicates that single dose, high rate, water soluble N applications (49 kg N ha -1 application -1 ) to mature turfgrass stands should be avoided to minimize the potential for NO 3 -N leaching.

The Fate of Nitrogen Applied to a Mature Kentucky Bluegrass Turf

Turf management in shaded conditions is difficult in part because the reduced irradiance causes excessive shoot elongation, reduced tillering and root growth, and weak plants exceptionally prone to damage. Successful installation of natural grass athletic fields in covered or shaded stadia require improved management procedures. The objective of this study was to determine if flurprimidol [α-(1- = -methylethyl)-α-[(trifluourmethoxy)phenyl]-5-pyrimidinemethanol], a gibberellic acid (GA)-biosynthesis inhibitor, could be used to increase turf quality for athletic fields in covered stadia and other reduced irradiance situations. Portable plots of Kentucky bluegrass (Poa pratensis L.) were established outdoors and moved inside a covered-stadium simulator facility (CSSF). Four rates of flurprimidol (0.56, 1.12, 1.68, and 2.80 kg ha -1 ) were compared against a control. Studies were conducted under ambient (equivalent to 2-3% full summer sunlight) and supplemental (equivalent to 9-18% full summer sunlight) irradiance. The turf was evaluated with and without simulated soccer traffic. Under ambient irradiance conditions, turf quality generally declined to unacceptable levels within 30 d, although the low rate of flurprimidol extended this period for up to 60 d. Supplemental irradiance provided turf of acceptable quality for up to 70 d and the low rate of flurprimidol extended this period for >100 d. Applications repeated within 30 to 40 d virtually stopped measurable shoot growth under all irradiance and traffic regimes. Flurprimidol did not affect turf shear resistance or rooting but did increase tillering. Low rates of flurprimidol should be useful for maintaining turf in reduced irradiance conditions because turf quality is enhanced with minimal risk of phytotoxicity.

James R. Crum

Papers

Soil resources, microbial activity, and primary production across an agricultural ecosystem

The spatial variability of soil resources following long-term disturbance.

Enhanced retention of organic contaminants by soils exchanged with organic cations

The Fate of Nitrogen Applied to a Mature Kentucky Bluegrass Turf

Flurprimidol Effects on Kentucky Bluegrass under Reduced Irradiance