羟氨苄青霉素引起大疱性类天疱疮样疹

Although it is generally accepted that plant community composition is key for predicting rates of ecosystem processes in the face of global change, microbial community composition is often ignored in ecosystem modeling. To address this issue, we review recent experiments and assess whether microbial community composition is resistant, resilient, or functionally redundant in response to four different disturbances. We find that the composition of most microbial groups is sensitive and not immediately resilient to disturbance, regardless of taxonomic breadth of the group or the type of disturbance. Other studies demonstrate that changes in composition are often associated with changes in ecosystem process rates. Thus, changes in microbial communities due to disturbance may directly affect ecosystem processes. Based on these relationships, we propose a simple framework to incorporate microbial community composition into ecosystem process models. We conclude that this effort would benefit from more empirical data on the links among microbial phylogeny, physiological traits, and disturbance responses. These relationships will determine how readily microbial community composition can be used to predict the responses of ecosystem processes to global change.

https://www.pnas.org/content/pnas/105/Supplement_1/11512.full.pdf

Resistance, resilience, and redundancy in microbial communities

Vesicular-arbuscular mycorrhizal fungi can affect the water balance of both amply watered and droughted host plants. This review summarizes these effects and possible causal mechanisms. Also discussed are host drought resistance and the influence of soil drying on the fungi.

Water relations, drought and vesicular-arbuscular mycorrhizal symbiosis

(1991). Applied Linear Regression Models. Journal of Quality Technology: Vol. 23, No. 1, pp. 76-77.

Applied Linear Regression Models

Positive ions that are available in soils absorb on grain surfaces. The total sum of cations that can be absorbed bij a soil/sediment at a certain PH is defined by the cation-exchange capacity (CEC, in meq g-1: mol equivalents per gram). The uptake of cations is an important parameter in agriculture and the larger the CEC, the more cations can be absorbed to the soil. The CEC depends highly on the pH of soil and sediments, where the CEC decreases with decreasing PH (increasing acidity). The exchange of ions on sediments occurs commonly fast on geological time scales, but the kinetics of adsorption in natural environments is still poorly understood. The strength of the bonding between the cations and the sediments varies from weak Van der Waals bondings (physical adsorption) to strong chemical bonds. The CEC is widely used for agricultural assessment because it is a measure of general soil fertility as well as an indicator of structural stability because CED is capabel of enhancing development of shrinkage cracks. The list below shows the CEC for different types of minerals. The data indicate that the CEC can vary over 2 orders of magnitude for various types of , minerals and can vary one order of magnitude within one soil type. Cation exchange capacity for different types of sediment (Eisma, 1992; Locher and de Bakker, 1990):

Cation exchange capacity.

We assessed the direct and indirect effect of the herbicide glyphosate on soil microbial communities from ponderosa pine ( Pinus ponderosa ) plantations of varying site quality. Direct, toxic effects were tested using culture media and soil bioassays at glyphosate concentrations up to 100-fold greater than expected following a single field application. Indirect effects on microbial biomass, respiration, and metabolic diversity (Biolog and catabolic response profile) were compared seasonally after 9–13 years of vegetation control using repeated glyphosate applications in a replicated field study. Three pine plantations were selected to provide a range of soil characteristics associated with glyphosate binding (clay, Fe and Al oxide content) and site growing potential from the lowest to the highest in northern California. Glyphosate was toxic to bacteria and fungi from each plantation when grown in soil-free media. Culturable populations were reduced, as was the growth rate and metabolic diversity of surviving bacteria, by increasing concentrations of glyphosate. This toxicity was not expressed when glyphosate was added directly to soil, however. Microbial respiration was unchanged at expected field concentrations (5–50 μg g −1 ), regardless of soil, and was stimulated by concentrations up to 100-fold greater. Increased microbial activity resulted from utilization of glyphosate as an available carbon substrate. Estimated N and P inputs from glyphosate were inconsequential to microbial activity. Long-term, repeated applications of glyphosate had minimal affect on seasonal microbial characteristics despite substantial changes in vegetation composition and growth. Instead, variation in microbial characteristics was a function of time of year and site quality. Community size, activity, and metabolic diversity generally were greatest in the spring and increased as site quality improved, regardless of herbicide treatment. Our findings suggest that artificial media assays are of limited relevance in predicting glyphosate toxicity to soil organisms and that field rate applications of glyphosate should have little or no affect on soil microbial communities in ponderosa pine plantations.

https://www.fs.fed.us/psw/publications/busse/psw_2001_busse001_sbb.pdf

Glyphosate toxicity and the effects of long-term vegetation control on soil microbial communities.

https://www.fs.fed.us/psw/publications/busse/psw_2006_busse(ratcliff)001.pdf

Changes in microbial community structure following herbicide (glyphosate) additions to forest soils

Downed Bole-Wood Decomposition in Lodgepole Pine Forests of Central Oregon

Mastication of woody shrubs is used increasingly as a management option to reduce fire risk at the wildland-urban interface. Whether the resulting mulch layer leads to extreme soil heating, if burned, is unknown. We measured temperature profiles in a clay loam soil during burning of Arctostaphylos residues. Four mulch depths were burned (0, 2.5, 7.5 and 12.5 cm), spanning typical conditions at forested sites in northern California with dense pre-mastication shrub cover. Two soil moisture contents were compared at each fuel depth to simulate spring prescribed burning (moist soil) and late-season wildfire (dry soil). Maximum temperatures reached 600 ◦ C on the surface of dry soils and were 100-200 ◦ C lower for moist soil. Heating was extensive in dry soil for the two deepest mulch depths, exceeding the lethal threshold for plants (60 ◦ C) for a minimum of 7 h throughout the 10-cm soil profile. Minimal heat pulse was found with less mulch. Moist soil also dampened heat penetration; peak temperatures exceeded 60 ◦ C only to 2.5 cm in the soil profile for all but the deepest mulch layer. No adverse effects of burning on water repellency were found in dry or moist soil. The potential for biological damage from soil heating during fire exists following mastication, particularly in dry soil with a mulch depth of 7.5 cm or greater. Field projections indicate that up to one-fourth of treated areas with dense pre-mastication vegetation would surpass lethal soil temperatures during a surface wildfire.

https://www.fs.fed.us/psw/publications/busse/psw_2005_busse001_ijwf.pdf

Lethal soil temperatures during burning of masticated forest residues

Current management and harvesting practices can compact forest soils and degrade soil health. However, effects of soil compaction on microbial processes and composition are poorly understood. We measured microbial community responses to compaction in a sandy loam and a clay loam soil under laboratory and field conditions. Treatments of no, moderate (approximately 20% increase in bulk density), and severe (approximately 40% increase) compaction were manually applied to intact soil cores. A 67-d laboratory experiment, punctuated by four sampling dates, was used to evaluate microbial indices (biomass, respiration, total and culturable bacteria and fungi, N mineralization, surface CO 2 efflux, C use (Biolog), and phospholipid fatty adds [PLFA]) and their relationship to soil physical properties (bulk density, pore-size distribution, water-holding capacity [WHC], gas diffusion). Macropores (>30 μm diam.) were reduced 50 to 90% in compacted samples. In contrast, habitable-sized pores for microorganisms (0.2-30 μm diam.) increased at least 40% in both soils with compaction. Despite these changes, microbial measures were either unaffected by compaction or showed inconsistent increases (e.g., fungal hyphae, C use, total PLFA) across sampling periods and soil types. Surface CO 2 efflux was reduced 34 to 51% in severe compaction samples. Minimal changes in microbial respiration indicate that reduced efflux was due to restricted gas diffusion. Microbial indifference to compaction also was verified at two mixed-conifer plantations in northern California. Soil strength values, ranging from 75 to 3800 kPa (no to severe compaction), were unrelated to either microbial respiration or biomass. The results show broad tolerance of microbial communities from contrasting soil textures to compaction, and indicate a poor link between physical and biological indices of soil health.

https://www.fs.fed.us/psw/publications/busse/psw_2005_busse(shestak)003.pdf

Matt D. Busse

Papers

Glyphosate toxicity and the effects of long-term vegetation control on soil microbial communities.

Changes in microbial community structure following herbicide (glyphosate) additions to forest soils

Downed Bole-Wood Decomposition in Lodgepole Pine Forests of Central Oregon

Lethal soil temperatures during burning of masticated forest residues

Compaction Alters Physical but Not Biological Indices of Soil Health