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Flooding and a rise in soil carbon source do not influence the carbon and nitrogen fractions of the biomass of soil microbial community, whereas the active bacterial population and respiration rate increase. This response does not vary with soil type. But flooding and additional carbon input induce a change in the pattern of utilization of specific carbohydrates in the substrate. This results in a decreased metabolic diversity of the soil microbial community which is corroborated by Biolog microplate analysis.

Toluene functions as a cosubstrate to enhance microbial cometabolism and degradation of trichloroethylene (TCE) in soil. High initial toluene concentrations increase TCE population and the number of toluene degraders. High TCE concentrations decrease the number of TCE degraders and toluene degradation rate.

A comparative analysis of conventional, low-input and organic agricultural systems for a four-year crop rotation indicates similar crop productivity. Fertility maintenance and reduction in weeds are two problems encountered during the first rotation cycle. The analysis also deals with cover crop management, economic conditions, pest control, agronomy and soil microbiology.

A study of three unsaturated soils revealed the biodegradation of trichloroethylene (TCE) and toluene, and measured the sorption and desorption of TCE and toluene. The soils contained various microbial organisms. It was observed that the introduction of phenol increased the rate of degradation of TCE in Rindge and Yolo silt soils whereas the degradation process was slower when methanol and ethylene were introduced in Rindge soil. The introduction of glucose did not affect the soils.

The diffusion-sorption-biodegradation (DSB) model was developed to quantify biodegradation of an organic chemical given the presence of spherical aggregates. The model used Fick's Second Law to measure diffusion, a linear isotherm to measure sorption and rate equations including first order kinetics to measure biodegradation. Sensitivity analyses were done to measure the effectof soil physical and chemical properties on the chemical's half-life. The two-compartment model provided a more adequate measure than the first order model. First order kinetics tend to overestimate chemical degradation when diffusion and sorption were not taken into account.

Root exploitation of soil heterogeneity and microbially mediated rhizosphere nutrient transformations play critical roles in plant resource uptake. However, how these processes change under water-saving irrigation technologies remains unclear, especially for organic systems where crops rely on soil ecological processes for plant nutrition and productivity. We conducted a field experiment and examined how water-saving subsurface drip irrigation (SDI) and concentrated organic fertilizer application altered root traits and rhizosphere processes compared to traditional furrow irrigation (FI) in an organic tomato system. We measured root distribution and morphology, the activities of C-, N-, and P-cycling enzymes in the rhizosphere, the abundance of rhizosphere microbial N-cycling genes, and root mycorrhizal colonization rate under two irrigation strategies. Tomato plants produced shorter and finer root systems with higher densities of roots around the drip line, lower activities of soil C-degrading enzymes, and shifts in the abundance of microbial N-cycling genes and mycorrhizal colonization rates in the rhizosphere of SDI plants compared to FI. SDI led to 66.4% higher irrigation water productivity than FI, but it also led to excessive vegetative growth and 28.3% lower tomato yield than FI. Our results suggest that roots and root-microbe interactions have a high potential for coordinated adaptation to water and nutrient spatial patterns to facilitate resource uptake under SDI. However, mismatches between plant needs and resource availability remain, highlighting the importance of assessing temporal dynamics of root–soil–microbe interactions to maximize their resource-mining potential for innovative irrigation systems. [ABSTRACT FROM AUTHOR]

A molecular genetic system for Methylibium petroleiphilum PM1 is developed to demonstrate the involvement of enzyme MdpA in methyl tert-butyl ether (MTBE) removal. The results showed that MTBE-induced MdpA, constitutively expressed at low levels is involved in the regulation of tert-butyl alcohol (TBA) removal under certain conditions but is not directly responsible for TBA degradation.

The designing of pcrA gene based real-time quantitative PCR assay for detection of perchlorate-reducing bacteria in soil microbial communities is described. Partial sequencing of pcrA gene showed differences in the composition of perchlorate-reducing bacterial communities when exposed to various electron donors.

High-density whole-genome cDNA microarrays are used for examining substrate-dependent gene expression of Methylibium petroleiphilum PM1, one of the aerobic methyl tert-butyl ether (MTBE)-degrading bacteria. The analysis has predicted several unknown enzymes of the upper MTBE degradation pathway in Methylibium petroleiphilum PM1 and the regulation of metabolic processes that might occur in response to pollutant mixtures and perturbations in the environment.

Research has been conducted on methyl tert-butyl ether-contaminated groundwater. The authors report the discovery of bacterial strain discovered in this groundwater which is identical to the native strain PM1, degrading methyl tert-butyl ether, in its ribosomal 16S DNA sequence.

Increasing soil organic carbon (SOC) via organic inputs is a key strategy for increasing long‐term soil C storage and improving the climate change mitigation and adaptation potential of agricultural systems. A long‐term trial in California's Mediterranean climate revealed impacts of management on SOC in maize‐tomato and wheat–fallow cropping systems. SOC was measured at the initiation of the experiment and at year 19, at five depth increments down to 2 m, taking into account changes in bulk density. Across the entire 2 m profile, SOC in the wheat–fallow systems did not change with the addition of N fertilizer, winter cover crops (WCC), or irrigation alone and decreased by 5.6% with no inputs. There was some evidence of soil C gains at depth with both N fertilizer and irrigation, though high variation precluded detection of significant changes. In maize‒tomato rotations, SOC increased by 12.6% (21.8 Mg C/ha) with both WCC and composted poultry manure inputs, across the 2 m profile. The addition of WCC to a conventionally managed system increased SOC stocks by 3.5% (1.44 Mg C/ha) in the 0–30 cm layer, but decreased by 10.8% (14.86 Mg C/ha) in the 30–200 cm layer, resulting in overall losses of 13.4 Mg C/ha. If we only measured soil C in the top 30 cm, we would have assumed an increase in total soil C increased with WCC alone, whereas in reality significant losses in SOC occurred when considering the 2 m soil profile. Ignoring the subsoil carbon dynamics in deeper layers of soil fails to recognize potential opportunities for soil C sequestration, and may lead to false conclusions about the impact of management practices on C sequestration. [ABSTRACT FROM AUTHOR]

Nitrogen is a critical component of the economy, food security, and planetary health. Many of the world's sustainability targets hinge on global nitrogen solutions, which, in turn, contribute lasting benefits for (i) world hunger; (ii) soil, air, and water quality; (iii) climate change mitigation; and (iv) biodiversity conservation. Balancing the projected rise in agricultural nitrogen demands while achieving these 21st century ideals will require policies to coordinate solutions among technologies, consumer choice, and socioeconomic transformation. Key Points: Global nitrogen solutions generate cobenefits for (i) world hunger, (ii) pollution, (iii) climate change, and (iv) biodiversityWe provide the most comprehensive, solutions‐focused strategy for global nitrogen to dateWe call for an IPCC‐type organization focused on global nitrogen issues and public‐private partnerships to scale solutions [ABSTRACT FROM AUTHOR]

Little is known about the short-term effects (hours to days) of tillage on labile pools of C and N, or microbial activity and community composition. We examined the effects of rototillage on microbial biomass C (MBC) and N (MBN), respiration (i.e., soil [CO.sub.2] production in 1-h incubations), [CO.sub.2] efflux from the soil surface, inorganic N, nitrification potential, denitrification rate, and phospholipid fatty acids (PLFA). A fallow silt loam soil was rototilled in the field and soil cores were immediately obtained from tilled and adjacent control soils. The soil cores were then incubated at constant temperature and sampled throughout a 2-wk period. Tilled soil had higher [CO.sub.2] efflux than the control soil. This increase occurred immediately after tillage and lasted for 4 d. Respiration was similar in both soils until the fourth day after tillage, and then declined in the tilled soil. Tilled soil showed increases in MBN, nitrate, and denitrification rates, suggesting that tillage makes available previously protected organic N. The overall reduction in respiration together with the lack of response in MBC, however, suggests that tillage did not make available significant amounts of readily decomposable C. These combined C and N dynamics suggest that low C/N ratio compounds may have been mineralized following tillage. Denitrification rates increased in the tilled soil even though the bulk of the soil had reduced respiration and bulk density. Tillage caused temporary changes in PLFA profiles, suggesting changes in soil microbial community structure. Phospholipid fatty acid 18:1 [Omega]7t, which marks the presence of eubacteria, decreased in the tilled soil. In contrast, 19:0 cy, a marker for anaerobic eubacteria, increased in the tilled soil. Our results show that tillage causes short-term changes in nutrient dynamics that may potentially result in N losses through denitrification and nitrate leaching, as well as C losses through degassing of dissolved [CO.sub.2]. These changes are accompanied by concomitant shifts in microbial community structure, suggesting a possible relationship between microbial composition and ecosystem function.