Influence of temperature on CO2 evolution,microbial biomass C and metabolic quotient during the decomposition of two humic forest horizons

The decomposition of the litter layer and the humic mineral horizon from a beech forest site was studied at temperatures of 5, 12, and 22°C for both substrates and additionally at 32°C for beech litter. Weight losses, basal and substrate-induced CO₂ production, and the extractable biomass C were monitored periodically during a 2-year incubation period. Weight losses and microbial activity were controlled by substrate quality and temperature. No significant differences were found between 5 and 12°C in decomposition, biomass C, and the metabolic quotient in the humic mineral horizon. The decay of beech litter and the humic mineral horizon was highest at 22°C but was faster in the litter material by a factor of 2.9 on average. In the glucose-amended samples, the relationship among the CO₂-C fluxes was 1:1:2:3 at temperatures of 5, 12, 22, and 32°C in the litter layer, and 1: 2: 2.4 at 5, 12, and 22°C in the A horizon, respectively. The microbial activity in the humic mineral horizon was only 2–11% of that in the litter layer. The level of biomass C remained constant over 1 year and no significant differences were obtained from the 12 and 22°C treatments in the litter layer.     

Microbial decomposition of skeletal muscle tissue (Ovis aries) in a sandy loam soil at different temperatures

A laboratory experiment was conducted to determine the effect of temperature (2, 12, 22 °C) on the rate of aerobic decomposition of skeletal muscle tissue (Ovis aries) in a sandy loam soil incubated for a period of 42 days. Measurements of decomposition processes included skeletal muscle tissue mass loss, carbon dioxide (CO₂) evolution, microbial biomass, soil pH, skeletal muscle tissue carbon (C) and nitrogen (N) content and the calculation of metabolic quotient (qCO₂). Incubation temperature and skeletal muscle tissue quality had a significant effect on all of the measured process rates with 2 °C usually much lower than 12 and 22 °C. Cumulative CO₂ evolution at 2, 12 and 22 °C equaled 252, 619 and 905 mg CO₂, respectively. A significant correlation (P<0.001) was detected between cumulative CO₂ evolution and tissue mass loss at all temperatures. Q₁₀s for mass loss and CO₂ evolution, which ranged from 1.19 to 3.95, were higher for the lower temperature range (Q₁₀(2-12 °C)>Q₁₀(12-22 °C)) in the Ovis samples and lower for the low temperature range (Q₁₀(2-12 °C)<Q₁₀(12-22 °C)) in the control samples. Metabolic quotient and the positive relationship between skeletal muscle tissue mass loss and cumulative CO₂ evolution suggest that tissue decomposition was most efficient at 2 °C. These phenomena may be due to lower microbial catabolic requirements at lower temperature.     

Application of respiration and FDA hydrolysis measurements for estimating microbial activity during composting processes

Olive-tree leaves (OL) were mixed with olive press cake (OPC) and extracted olive press cake (EPC) at 1:1 dw/dw ratios to prepare two composting mixtures (OL+OPC and OL+EPC). Both CO₂–C evolution and fluorescein diacetate (FDA) hydrolysis, determined as estimates of the microbial activity during composting, were related to temperature fluctuations in the compost piles, showing greater values at the temperature peaks, compared to the end, of each thermophilic phase. This, however, was only shown after handling and incubating samples at the temperatures of the compost mixtures at the sampling times and not at a low standard temperature. Incubating samples from thermophilic phases at low standard temperatures resulted in underestimation of the microbial activity occurring during composting. The effect of incubation temperature was less dramatic for FDA hydrolysis compared to CO₂–C evolution measurements, probably reflecting the reduced dependence of enzymes involved in FDA hydrolysis on the respective temperatures. However, FDA hydrolysis was a less sensitive indicator of microbial activity, probably due to extracellular cleavage of fluorescein by persistent esterases, at lowered microbial activity phases. Total microbial biomass, estimated by the fumigation–extraction method, was not consistently related to temperature fluctuations during composting and showed a clear increase at the end of composting, probably resulting from a large slow-growing mycelial community colonising the end products. Since high temperatures did not induce significant non-microbial CO₂–C release and FDA degradation, we propose the performance of microbial activity measurements during thermophilic composting phases at the actual temperatures evolving in the composts.     

Decomposition of pea and maize straw in Pakistani soils along a gradient in salinity

Maize straw and pea straw were added to five Pakistani soils from a gradient in salinity to test the following hypotheses: Increasing salinity at high pH decreases proportionally (1) the decomposition of added straw and (2) the resulting net increase in microbial biomass. In the non-amended control soils, salinity had depressive effects on microbial biomass C, biomass N, but not on biomass P and ergosterol. The ratios microbial biomass C-to-N and biomass C-to-P decreased consistently with increasing salinity. In contrast, the ergosterol-to-microbial biomass C ratio was constant in the four soils at pH>8.9, but nearly doubled in the most saline, but least alkaline, soil (pH 8.2). The addition of the maize and pea straw always increased the contents of microbial biomass C, biomass N, biomass P and ergosterol, but without clear effects of salinity. Highest mean contents of microbial biomass C and biomass N were measured at day 0, immediately after the straw was added. Straw amendments increased the CO₂ evolution rates of all five soils without any effect of salinity. The same was true for total C and total N in the two fractions of particulate organic matter (POM) 63–400 μm and >400 μm. Lowest percentage of straw-derived CO₂-C and highest recoveries of POM-C and POM-N were observed in the maize straw treatment and the reverse in the pea straw treatment. Yield coefficients were calculated for maize and pea straw based on the assumption that the balance gap between CO₂ and the amount of POM can be fully assigned to microbial products.     

Developmental patterns of lamellae and stroma fractions of chloroplasts in rice plants

On examining the changes in lamellae and stroma nitrogen during leaf development, it is demonstrated that the lamellae and stroma fractions ofrice chloroplasts develop in quite different ways. In the case of stroma, the stroma materials existing in the leaf section which has just emerged from a leaf sheath are quite limited and the major part of this fraction is derived from the successive protein synthesis, i.e., the synthesis of this fraction was markedly increased during leaf expansion. This developmental pattern of the stroma coincided with the changes in the high-molecular-weight water soluble leaf protein, which seemed to be mainly composed of Fraction I protein. A rapid increase in stroma nitrogen was found to be a major cause for an increase in the leaf nitrogen content during leaf development.

On the other hand, the developmental pattern of the lamellae fraction was characterized by the fact that a considerable amount of this fraction had already been prepared when a leaf emerged from a leaf sheath and thereafter, no outstanding increase was seen compared to that of the stroma. This developmental pattern of the lamellae fraction resulted in a lowering of the proportion of lamellae nitrogen to the total leaf nitrogen during leaf development.

A great change in the lamellae-stroma composition of chloroplasts was observed. The proportion of stroma nitrogen to the total chloroplast nitrogen tended to increase as a leaf develops. Since the developmental stage varied according to the regions of a leaf, variation of the lamellaestroma composition was seen even within a leaf, i.e., the proportion of stroma nitrogen increased from base to tip.

In order to compare the synthetic rate of chlorophyll with those of the stroma and lamellae fractions, the changes in the ratios of stroma nitrogen/chlorophyll and lamellae nitrogen/chlorophyll were examined. The lamellae nitrogen/chlorophyll ratio decreased as a leaf developed, whereas the stroma nitrogen/chlorophyll ratio increased. Then the synthetic rates of these fractions during leaf development turned out to be of the same order as the stroma fraction, chlorophyll, lamellae fraction.     

Effects of manure quality and application forms on soil C and N turnover of a subtropical oasis soil under laboratory conditions

Our knowledge of the agricultural sustainability of the millennia-old mountain oases in northern Oman is restricted in particular with respect to C and N turnover. A laboratory study was conducted (1) to analyse the effects of rewetting and drying on soil microorganisms after adding different manures, (2) to investigate the effects of mulching or incorporating of these manures, and (3) to evaluate the relationships between C and N mineralisation rates and manure quality indices. During the first 9-day rewetting and drying cycle, i.e. the mulch period, the content of extractable organic C decreased by approximately 40% in all four treatments. During the second 9-day rewetting and drying cycle, i.e. the incorporation period, this fraction decreased insignificantly in almost all treatments. The control and mature manure treatments form the first pair with a low percentage of total organic C evolved as CO₂ (0.3% in 18 days) and a considerable percentage of total N mineralised as NH₄ and NO₃ (1% in 18 days), the fresh and immature manure treatments form the second pair with a higher amount of total organic C evolved as CO₂ (0.5% in 18 days) and no net N mineralisation. During the first 9-day rewetting and drying cycle, the contents of microbial biomass C and biomass N increased by approximately 150% in all four treatments. During the second 9-day rewetting and drying cycle, no further increase was observed in the control and immature manure treatments and a roughly 30% increase in the other two treatments.     

Effects of Folsomia candida (Collembola) on the microbial biomass in a grassland soil

Summary The effects of the presence of Folsomia candida on substrate-induced respiration, CO₂-C evolution, bacterial count and NH ₄ ⁺ -N were investigated in a grassland soil. Differences in these parameters, with the exception of NH ₄ ⁺ , were correlated with the age of the collembolan Folsomia candida. In the presence of juvenile animals total CO₂-C evolution was enhanced, but substrate-induced respiration and the bacterial count were unchanged. In fumigated soil with imagos, substrate-induced respiration and the number of bacteria were increased, but total CO₂-C evolution was unaltered. Different food selection strategies between adults and juvenile animals may explain the results.     

Availability of CO2 as a factor affecting the rate of nitrification in soil

A laboratory incubation experiment was conducted to demonstrate that reduced availability of CO₂ in soil may be an important factor limiting nitrification. Soil samples were incubated at 30±2 °C for 20 days using vessels with or without the arrangement for trapping CO₂ in sodium hydroxide. This arrangement led to a decrease of ca. 96% in the CO₂ concentration of the headspace, with a range of 95.7-97.5 at different sampling intervals. In the absence of trapping arrangement, CO₂ concentration of the headspace varied from 580 to 859 ppm, i.e. 62-140% higher than that of the outside atmosphere (358 ppm). The nitrification process was significantly retarded under conditions of reduced CO₂ concentration; reduction varied from 8 to 62% at different incubation intervals. The results of the study led to the inference that decreased availability of CO₂ in closed vessels (with arrangement for trapping CO₂) will have a significant bearing on the process of nitrification and hence on the overall dynamics of N transformations.     

Reaction of microorganisms to rewetting in continuous cereal and legume rotation soils of semi-arid Sub-Saharan Africa

A 20-day incubation experiment with continuous cereal (CC) versus cereal legume (CL) rotation soils of two semi-arid Sub-Saharan sites (Fada-Kouaré in Burkina Faso, F, and Koukombo in Togo, K) were carried out to investigate the effects of rewetting on soil microbial properties. Site- and system-specific reactions of soil microorganisms were observed on cumulative CO₂ production, adenylates (ATP, ADP, and AMP), microbial biomass C and N, ergosterol, muramic acid and glucosamine. Higher values of all parameters were found in the CL rotation soils and in both soils from Fada-Kouaré. While the inorganic N concentration showed only a system-specific response to rewetting, the adenylate energy charge (AEC) showed only a site-specific response. ATP recovered within 6 h after rewetting from ADP and AMP due to rehydration of microorganisms and not due to microbial growth. Consequently, no N seemed to be immobilized by microorganisms and all NO₃ in the soil was immediately available to the plants. The fungal cell-membrane component ergosterol was three (CC) and five (CL) times larger at Fada than in the respective soils at Koukombo. The concentrations of the bacterial cell-wall component muramic acid were by 20% and of mainly fungal glucosamine by 10% larger in the CL rotation soils than in the CC soils. This indicates long-shifts in the microbial community structure.     

A simple gas chromatographic approach to evaluate CO2 release,N2O evolution,and O2 uptake from soil

Summary We have developed a simple method for the determination of gaseous compounds that reflect microbial activity in soil, as affected by factors such as the presence of an organic amendment (peat) or a variation in soil moisture. The method is based on a gas chromatographic analysis of the headspace of vials containing the soil under examination. A single gas chromatograph can detect up to 10 different gases. As expected, after peat was added to the soil, CO₂ evolution and O₂ uptake increased significantly. Positive relationships were found between the evolution of N₂O, and soil moisture and the amount of peat added to the soil. Both the these variables influenced the CO₂:O₂ ratio. The results given by this method show high reproducibility.     

Immobilization and mineralization of nitrogen in a saline and alkaline soil during microbial use of sugarcane filter cake amended with glucose

A 42-day incubation was conducted to study the effect of glucose and ammonium addition adjusted to a C/N ratio of 12.5 on sugarcane filter cake decomposition and on the release of inorganic N from microbial residues formed initially. The CO₂ evolved increased in comparison with the non-amended control from 35% of the added C with pure +5 mg g⁻¹ soil filter cake amendment to 41% with +5 mg g⁻¹ soil filter cake +2.5 mg g⁻¹ soil glucose amendment to 48% with 5 mg g⁻¹ soil filter cake +5 mg g⁻¹ soil glucose amendment. The different amendments increased microbial biomass C and microbial biomass N within 6 h and such an increase persisted. The fungal cell-membrane component ergosterol initially showed a disproportionate increase in relation to microbial biomass C, which completely disappeared by the end of the incubation. The cellulase activity showed a 5-fold increase after filter cake addition, which was not further increased by the additional glucose amendment. The cellulase activity showed an exponential decline to values around 4% of the initial value in all treatments. The amount of inorganic N immobilized from day 0 to day 14 increased with increasing amount of C added, in contrast to the control treatment. After day 14, the immobilized N was re-mineralized at rates between 1.3 and 1.5 μg N g⁻¹ soil d⁻¹ in the treatments being more than twice as high as in the control treatment. This means that the re-mineralization rate is independent of the actual size of the microbial residues pool and also independent of the size of the soil microbial biomass.     

Absorption and emission of CO2 by ponded water of a paddy field

In the daytime, the CO₂ concentration in the air close to the water surface of a ponded paddy field was lowest and it increased with the distance above the water surface, while an inverse relation was observed in the nighttime. On the other hand, the pH of the ponded water changed significantly throughout a day and was expected to affect atmospheric CO₂ in the vicinity of the water surface, because the solubility of CO₂ in water depends on the pH. In this study, we investigated the relationship between the changes in the pH of the ponded water and the response of the CO₂ concentration in the air above the water. The pH of the ponded water of the paddy field increased in the daytime and decreased in the nighttime, so that the water was alkaline in the daytime and weakly acidic in the nighttime. We found that the daily changes in the atmospheric CO₂ concentration gradient almost corresponded to the daily changes in pH. The increase of the pH of the ponded water in the daytime was due to the absorption of dissolved CO₂ by photosynthetic bacteria and micro-algae within the ponded water. Furthermore, we compared the pH with RpH, defined as the pH at which the CO₂ concentration of the water is in equilibrium with that of the air, to determine whether CO₂ was absorbed by or emitted from the ponded water. In the daytime, the pH value of the ponded water was higher than that of the RpH, and the water could therefore absorb CO₂ , whereas during the nighttime, since the pH value of the ponded water was lower than that of the RpH, the water was expected to emit CO₂. These results show that the ponded water absorbed CO₂ from the air above the water surface in the daytime and emitted CO₂ in the nighttime.     

几种主要CO2施肥肥源性能的比较与评价

在空闲拱棚和黄瓜日光温室内,分别研究了化学反应法(H₂SO₄+NH₄HCO₃）、煤球燃烧法和颗粒CO₂气肥3种肥源的性能,并与液体CO₂进行成本比较,结果表明：化学反应法产气迅速,设备折旧成本较低;煤球燃烧法产气速度中等,原料成本最低;颗粒CO₂气肥产气速度较慢且不易调控,原料成本最高。考虑化学反应产物的再利用因素,化学反应法、煤球燃烧法和液体CO₂ 3种肥源总成本接近,但从生态、节能、成本和效果等方面综合评价,煤球燃烧法原料丰富、成本低廉,较符合我国目前的设施、经济、资源和技术条件。     

Enchytraeids in a changing climate: A mini-review

The climate is undergoing rapid changes with rising atmospheric CO₂ concentration, increasing temperatures and changes in the hydrological regimes resulting in more frequent and intense drought periods. These three climate change factors will, separately and in combination, affect the biotic and abiotic components of soil communities. This paper reviews the impact of climate change on field communities of enchytraeids with special emphasis on Cognettia sphagnetorum because most relevant studies have involved this species. C. sphagnetorum prefers cold and wet environments and several studies suggest that reductions of soil moisture may have dramatic consequences for C. sphagnetorum and other enchytraeid species. Effects of changing temperatures are less clear partly because thermal conditions influence soil moisture, which complicate the predictions of the outcome from such changes. The predicted increasing annual mean temperature may be stimulating and expand the season for growth and reproduction of enchytraeids; on the other hand, an increased frequency of extreme weather events, with heat waves during summer and bare soil freezes during autumn and spring, may occasionally cause severe mortality. Stimulating effects of increased atmospheric CO₂ have been observed, perhaps due to increased food availability via root and litter production. However, effects of CO₂ are also influenced by moisture and temperature. Generally, there is a lack of research looking into the complicated interactions between various climate change factors, and little is known about the potential of enchytraeids to adapt to a changing climate. Existing data suggest that C. sphagnetorum is not capable of adapting to a drier climate, thus, a decline in abundance and distribution of this species is possible. Since enchytraeids are of ecological significance in some types of habitats, a reduction may result in serious disruption in the functioning of these decomposer communities.