Role Of Microbial Biomass Research Articles

The fate of nitrification and urease inhibitors in simulated bank filtration

The application of nitrification and urease inhibitors (NUI) in conjunction with nitrogen (N) fertilizers improves the efficiency of N fertilizers. However, NUI are frequently found in surface waters through leaching or surface runoff. Bank filtration (BF) is considered as a low-cost water treatment system providing high quality water by efficiently removing large amounts of organic micropollutants from surface water. The fate of NUI in managed aquifer recharge systems such as BF is poorly known. The aim of this work was to investigate sorption and degradation of NUI in simulated BF under near-natural conditions. Besides, the effect of NUI on the microbial biomass of slowly growing microorganisms and the role of microbial biomass on NUI removal was investigated. Duplicate sand columns (length 1.7 m) fed with surface water were spiked with a pulse consisting of four nitrification (1,2,4-triazole, dicyanodiamide, 3,4-dimethylpyrazole and 3-methylpyrazole) and two urease inhibitors (n-butyl-thiophosphoric acid triamide and n-(2-nitrophenyl) phosphoric triamide). The average spiking concentration of each NUI was 5 μg/L. Experimental and modeled breakthrough curves of NUI indicated no retardation for any of the inhibitors. Therefore, biodegradation was identified as the main elimination pathway for all substances and was highest in zones of high microbial biomass. Removal of 1,2,4-triazole was 50% and n-butyl-thiophosphoric acid triamide proved to be highly degradable and was completely removed after a hydraulic retention time (HRT) of 24 h. 50% of the mass recovery for nitrification inhibitors except for 3,4-dimethylpyrazole was observed at the effluent (4 days HRT). In addition, a mild effect of NUI on microbial biomass was noted. This study highlights that the degradation of NUI in BF depends on HRT and microbial biomass.

Short-term mesofauna responses to soil additions of corn stover biochar and the role of microbial biomass

Biochar additions have been suggested to influence soil microbial communities that, through a cascade effect, may also impact soil fauna. In turn, any direct biochar effects on fauna can influence microbial communities through grazing, physical fragmentation of organic debris (and biochar) and modifying soil structure. If biochar creates a favorable environment for soil microorganisms, it is also plausible for fauna to be attracted to such microbially enriched habitats. However, how soil fauna respond to biochar addition to soil and what are the main factors that drive their behavior has rarely been experimentally addressed. Therefore, the behavior of two mesofauna species was assessed as a result of corn stover biochar (slow pyrolysis at 600°C) additions to a loamy temperate soil, after preincubation for 2, 17, 31 and 61d, and related to variations in microbial biomass and activity. Microbial biomass increased by 5–56% and activity by 6–156% with increasing biochar rates for the different preincubation times. Over the incubation time, microbial biomass did not change or increased at most 15% with the different biochar rates, while in turn microbial activity decreased steadily (around 70–80% at day 61). Enchytraeids generally did not show avoidance or preference to biochar when provided with an alternative unamended soil, while collembolans often showed avoidance responses. However, collembolan avoidance to biochar decreased or disappeared in biochar mixtures with higher microbial biomass and water extractable NH4-N content, agreeing with the plausible role of microorganisms to potentially attract soil fauna after biochar applications. Avoidance response was mainly explained by environmental preferences of the test species and not by any toxic effect of the biochar in this study. However, avoidance after the application of biochar may still need to be considered due to the potential negative impacts of individuals’ migration on soil ecosystem functioning.

Soil carbon dioxide flux, carbon sequestration and crop productivity in a tropical dryland agroecosystem: Influence of organic inputs of varying resource quality

In view of the significance of agricultural soils in affecting global C balance, the impact of manipulation of the quality of exogenous inputs on soil CO 2–C flux was studied in rice–barley annual rotation tropical dryland agroecosystem. Chemical fertilizer, Sesbania shoot (high quality resources), wheat straw (low quality resource) and Sesbania + wheat straw (high + low quality), all carrying equivalent recommended dose of N, were added to soil. A distinct seasonal variation in CO 2–C flux was recorded in all treatments, flux being higher during rice period, and much reduced during barley and summer fallow periods. During rice period the mean CO 2–C flux was greater in wheat straw (161% increase over control) and Sesbania + wheat straw (+129%) treatments; however, during barley and summer fallow periods differences among treatments were small. CO 2–C flux was more influenced by seasonal variations in water-filled pore space compared to soil temperature. In contrast, the role of microbial biomass and live crop roots in regulating soil CO 2–C flux was highly limited. Wheat straw input showed smaller microbial biomass with a tendency of rapid turnover rate resulting in highest cumulative CO 2–C flux. The Sesbania input exhibited larger microbial biomass with slower turnover rate, leading to lower cumulative CO 2–C flux. Addition of Sesbania to wheat straw showed higher cumulative CO 2–C flux yet supported highest microbial biomass with lowest turnover rate indicating stabilization of microbial biomass. Although single application of wheat straw or Sesbania showed comparable net change in soil C (18% and 15% relative to control, respectively) and crop productivity (32% and 38%), yet they differed significantly in soil C balance (374 and −3 g C m −2 y −1 respectively), a response influenced by the recalcitrant and labile nature of the inputs. Combining the two inputs resulted in significant increment in net change in soil C (33% over control) and crop yield (49%) in addition to high C balance (152 g C m −2 y −1). It is suggested that appropriate mixing of high and low quality inputs may contribute to improved crop productivity and soil fertility in terms of soil C sequestration.

Microbial biomass and size-density fractions differ between soils of organic and conventional agricultural systems

Agricultural production systems have to combine management practices in order to sustain soil quality and also profitability. We investigated microbial biomass and size-density fractions of soils from a long-term field trial set up in 1978 at Therwil, Switzerland. It compares the economic and ecological performance of organic and conventional agricultural systems. Main differences of the systems were the amount and form of fertiliser as well as the plant protection strategy, whilst crop rotation and soil tillage were the same. Microbial biomass C and N as well as their ratios to the total and light fraction C and N pools in soils of the organic systems were higher than in conventional systems. This is interpreted as an enhanced decomposition of the easily available light fraction pool of soil organic matter (SOM) with increasing amounts of microbial biomass. The role of microbial biomass as a regulator and light fraction organic matter as an indicator of decomposition is discussed. The presented results indicate that labile pools of SOM are distinctly affected by long-term management practices.

Remineralization of nitrogen immobilized by soil microorganisms and effect of drying and rewetting of soils

Abstract Microbial biomass is considered to act as one of the major sources of inorganic N pool in soil. Many investigators indicated that significant portions of the flux of inorganic N in soil originated from the mineralization of dead microbial biomass (Ladd et al. 1977; Powlson 1980; Marumoto et al. 1982a, b). However, their findings were based in experiments in which the nitrogen flux from the microbial biomass increased by the addition of dead microbial biomass and/or by the pre-treatment of soils under artificial conditions such as oven-drying, grinding, fumigation. Thus, to determine the nitrogen flux from the microbial biomass in natural soil ecosystems and to analyze the quantitative role of microbial biomass in the nitrogen cycle, it is necessary to determine the flux of inorganic N from microbial biomass under natural field conditions.

Mobilization and turnover of soil phosphorus in the rhizosphere

AbstractRecent progress in methods enables a better understanding of the turnover of P in the rhizosphere. Examples of this progress are the separation of soil layers differing in proximity to the roots, improved methods for extraction and fractionation of soil P, application of 32P isotope dilution analysis to follow P fluxes between various fractions and direct determination of microbially bound P and of root phosphatases. These methods were combined to investigate the following aspects –labile P pools, the P fluxes between these pools and their contribution to the P supply to growing maize roots –the role of microbial biomass in these interactions and the partition of mobilized P between plants and microorganisms –modifications of sorption and transport of P in the rhizosphere –plant availability of native and added organic phosphates, and the relative significance of root and soil phosphatases. There is a significant transformation of P in the rhizosphere with a corresponding redistribution among fractions of different plant availability. About 9% of the inorganic 32P added to soil were incorporated within 2 weeks into microbial and organic fractions. The transfer of P from non‐exchangeable forms exceeded the depletion of the exchangeable P by a factor of 5. About 53% of the mobilized P originated from inorganic, the remaining 47% from organic fractions. Of the mobilized P 80% was taken up by the plants and 20% was found in the microbial biomass. Up to 90% of the P in the rhizosphere soil solution was organic with a maximum just outside the root zone. Soluble inositol hexaphosphate modified the sorption of inorganic P, thus shifting its equilibrium solution concentration. The phosphatase activity of the roots is considerable. Both root phosphatase activity and the utilization of inositol hexaphosphate depend on the P supply and nutritional status of plants with regard to P.It is concluded that the rhizosphere is a key site of P transformation with a significant mobilization of P from the non‐exchangeable inorganic and organic fractions. Organic P fractions not only play a significant role as a P source but also modify important soil parameters related to the sorption and transport of P in the rhizosphere.