CO2 Flush Research Articles

Integrating Soil Biological and Chemical Indices to Predict Net Nitrogen Mineralization across California Agricultural Systems

Core Ideas Agricultural soils with and without a winter cover crop were surveyed. Stronger relationships occurred between soil tests and N mineralization in cover‐cropped fields. Integrated models only improved the variance explained for cover‐cropped fields. Within management systems, preferred predictors varied by climate, independent of soil C. Predicting the capacity of soil to supply crop N (i.e., inorganic N) has proved difficult due to the myriad of interacting soil biophysical factors. We examined soil chemical and biological indices commonly found in commercial soil testing laboratories—total soil C and N, water‐extractable organic C and N, K2SO4–extractable C and N, mineralizable C on rewetting, and permanganate‐oxidizable C—to estimate net N mineralization across a variety of soils from cover‐cropped and non‐cover‐cropped fields in California (47 sites, n = 157). Results show that both biological and chemical indices are variable in their ability to predict N mineralization, with better relationships being shown for cover‐cropped fields. Total C and N contents were the best chemical indicators for both management systems, describing up to 21.8% of the variance. The flush of CO2 measured after capillary rewetting was more variable and had weaker relationships with net N mineralization than respiration measured at 50% water holding capacity. These relationships were only significant in fields that had recently had cover crops and were moderately strong (r = 0.45–0.55), with the strength of the relationship decreasing as the measured interval of the CO2 flush increased. Models were developed for each management system using variables consistently chosen by a partial least squares regression as drivers of N mineralization. These models improved the explained variance in cover‐cropped fields but not in the non‐cover‐cropped fields. The effectiveness of individual predictor variables in these models was inconsistent across climates, illustrating the need for regional and management‐specific tests for predicting N mineralization.

Effects of gamma irradiation on soil biological communities and C and N pools in a clay loam soil

Gamma irradiation is becoming a promising technique in soil ecological studies because it has a particular advantage in selectively eliminating the target organism. But this selective sterilization technique is still in its initial exploratory stage and the subsequent impacts on soil carbon (C) and nitrogen (N) pools are relatively unknown for the majority of soils. Therefore, the responses of soil respiration, soil collembola, nematodes and microbial communities, and soil C and N pools (extracted with KCl, K2SO4 and H2SO4) to a range of gamma irradiation doses (0, 5, 10, 20 and 40kGy) were determined under a clay loam soil in a 4-week incubation study. A flush of CO2 was observed at the beginning of the incubation period (1–2 days) post-irradiation, and then strongly decreased relative to the unirradiated soils. At the middle of incubation period (11–14 days), there was a recovery of CO2 efflux in the 5kGy treatment. The effects of radiation on biological communities were dependent on taxa groups. The majority of collembola (>80%) and nematodes (>90%) were killed immediately in the higher doses (>5kGy), but at lower doses of 5kGy they were killed within 2 weeks after irradiation. The relative abundance of saprophytic fungi and protozoa decreased with increasing irradiation dose throughout the incubation period, while an opposite trend was found for some special bacterial taxa (19:1ω8c and i17:1ω9c). The resistance threshold of the entire microbial community to gamma irradiation was 10kGy. The C and N contents in the KCl/K2SO4-extracted pools (except the dissolved organic C), in the H2SO4-extracted labile pool II (LP II) and in the recalcitrant pool (RP) decreased with increasing irradiation dose across the incubation period. The decreases in LP II and RP were accompanied by the increase in labile pool I. The variation in the level of all soil C and N pools was significantly affected by the radiation doses higher than 5kGy. Our results indicate that the gamma dose between 5 and 10kGy is sufficient to eliminate soil fauna without significant effect on microbial community compared to the unirradiated treatments. Moreover, a radiation dose of 5kGy for selective defaunation has minor impacts on soil C and N pools of a clay loam soil. Our results also suggest that dose optimization is necessary due to high variability associated with irradiation levels effect on biological taxa in different soils.

Assessment of Bacterial Communities and Predictive Functional Profiling in Soils Subjected to Short-Term Fumigation-Incubation.

Previous investigations observed that when soil was fumigated with ethanol-free CHCl3 for 24h and then incubated under appropriate conditions, after the initial flush of CO2 was over, soil organic carbon (SOC) mineralization continued at the same rate as in the non-fumigated soil. This indicates that, following fumigation, the much diminished microbial population still retained the same ability to mineralize SOC as the much larger non-fumigated population. We hypothesize that although fumigation drastically alters the soil bacterial community abundance, composition, and diversity, it has little influence on the bacterial C-metabolic functions. Here, we conducted a 30-day incubation experiment involving a grassland soil and an arable soil with and without CHCl3 fumigation. At days 0, 7, and 30 of the incubation, the bacterial abundances were determined by quantitative PCR, and the bacterial community composition and diversity were assessed via the 16S rRNA gene amplicon sequencing. PICRUSt was used to predict the metagenome functional content from the sequence data. Fumigation considerably changed the composition and decreased the abundance and diversity of bacterial community at the end of incubation. At day 30, Firmicutes (mainly Bacilli) accounted for 70.9 and 94.6% of the total sequences in the fumigated grassland and arable soil communities, respectively. The two fumigated soil communities exhibited large compositional and structural differences during incubation. The families Paenibacillaceae, Bacillaceae, and Symbiobacteriaceae dominated the bacterial community in the grassland soil, and Alicyclobacillaceae in the arable soil. Fumigation had little influence on the predicted abundances of KEGG orthologs (KOs) assigned to the metabolism of the main acid esters, saccharides, amino acids, and lipids in the grassland soil community. The saccharide-metabolizing KO abundances were decreased, but the acid ester- and fatty acid-metabolizing KO abundances were elevated by fumigation in the arable soil community. Our study suggests functional redundancy regarding the bacterial genetic potential associated with SOC mineralization.

Should Soil Testing Services Measure Soil Biological Activity?

Core Ideas Soil biological activity is a key indicator for productivity and environmental quality. The flush of CO2 possesses many qualities of a robust soil test. Field calibration is underway to relate the flush of CO2 to nitrogen availability. Health of agricultural soils depends largely on conservation management to promote soil organic matter accumulation. Total soil organic matter changes slowly, but active fractions are more dynamic. A key indicator of healthy soil is potential biological activity, which could be measured rapidly with soil testing services via the flush of CO2 during 1 to 3 d following rewetting of dried soil. The flush of CO2 is related to soil microbial biomass C and has repeatedly been shown strongly related to net N mineralization during standard aerobic incubations. New research is documenting the close association with plant N uptake in semicontrolled greenhouse conditions (r2 = 0.77, n = 36). Field calibrations are underway to relate the flush of CO2 to the need for in‐season N requirement in a variety of crops. An index of soil biological activity can and should be determined to help predict soil health and soil N availability.

Earthworm bioturbation stabilizes carbon in non-flooded paddy soil at the risk of increasing methane emissions under wet soil conditions

Studies on earthworms in rice-based ecosystems tend to focus on some pest species, while the potential of these important soil engineers for beneficially affecting carbon storage and cycling is widely ignored. We carried out a microcosm experiment to quantify the impact of the tropical earthworm Pheretima sp. on the C turnover in paddy soils under different conditions of water saturation and N fertilization. The soil was sampled at the lowland farm of the International Rice Research Institute (Philippines). In the absence of earthworms, soil respiration showed a distinct hump-shaped maximum at intermediate levels of water saturation (4-fold higher than in hand-dry soil) and increased 1.5-fold with increasing amounts of N fertilization. Amounts of CH4 emitted, in contrast, were small at low to moderate soil humidity and became very high under conditions of water saturation (80-fold higher than hand-dry soil). No response to nitrogen addition was observed. Earthworms suppressed both the respiration maximum at intermediate saturation levels (by a factor of 1.4) and the stimulating impact of N fertilization (1.7-fold at maximum fertilizer level). On the other hand, earthworms strongly increased CH4 release under conditions of high water saturation (3-fold). No consistent response of the soil microflora (bacterial abundance, soil enzymes) to earthworm activity could be established. Our findings suggest that the stabilization of soil organic C via earthworm bioturbation is confined to the range of soil humidity that allows high activity of Pheretima sp. Under conditions of intensive agriculture, the stabilizing effect of the worms may even be augmented by the fact that they offset the positive effect of N fertilization on microbial respiration. Earthworms may thus play a vital role in reducing the CO2 flush from paddy soils after the conversion to non-flooded crops such as aerobic rice or maize. Acceleration of methane emission in very humid soils nevertheless points to a certain risk that is associated with increasing earthworm abundance in production systems that are still exposed to temporary flooding during the wet season.

Long-term effects of cropping system on N2O emission potential

The potential for N2O emissions outside the main growing season may be influenced by long-term effects of cropping system. This was investigated by collecting intact soil cores (100 cm3, 0–4 cm depth) under winter wheat in three organic cropping systems and a conventional reference within a long-term crop rotation experiment. Average annual inputs of C in crop residues and manure ranged from 1.7 to 3.3 Mg ha−1. A simulated freeze–thaw cycle resulted in a flush of CO2 during the first 48 h, which could be mainly from microbial sources. Other samples were adjusted to approximately −10, −30 or −100 hPa and amended with excess 15NO3− prior to freezing and thawing. Denitrification was the main source of N2O during a 72-h incubation at 22 °C, as judged from N2O and total 15N evolution. Although the input of C in the conventionally managed cropping system was significantly less than in the organic cropping systems, it showed higher N2O evolution at all three matric potentials. Estimates of relative gas diffusivity (DP/D0) in soil from the four cropping systems indicated that C input affected soil aeration. Soil from the two cropping systems with highest C input showed N2O evolution at DP/D0 in excess of 0.02, which is normally considered a threshold for development of anaerobic sites in the soil, presumably because the oxygen demand was also high. The study shows that cropping system affects both soil gas diffusivity and C availability, and that both characteristics significantly influence the N2O emission potential.

Preparation of the Drager Fabius CE and Drager Zeus anaesthetic machines for patients susceptible to malignant hyperthermia

Malignant hyperthermia may follow exposure to trace quantities of inhalational anaesthetics. In susceptible patients, the complete avoidance of these triggers is advised when possible; however, failing this, it is essential to washout or purge the anaesthesia machine of residual inhalational anaesthetics. This study examined the washout profile of sevoflurane from the Drager Fabius CE and the Drager Zeus machines. The washout profile of sevoflurane was measured from the Fabius CE and Zeus anaesthesia machines following a standard period of exposure. The disposable tubing, CO2 absorber and other components of each machine were then replaced to examine their impact on the retention of sevoflurane. The effect of autoclaving the ventilator diaphragm and non-disposable ventilator tube or substituting for a new diaphragm and ventilation tube were examined in later parts of this study. University teaching hospital. Time taken to reach 5 parts per million of sevoflurane when machines underwent standard washout with fresh gas flush. The concentration of sevoflurane reached 5 parts per million in the Fabius CE machines after an mean (SD) of 140 min (46) at a fresh gas flow (FGF) of 10 l min(-1). The time taken for sevoflurane to reach 5 parts per million was significantly reduced when the ventilator diaphragm and non-disposable tube were replaced with either new or autoclaved components [14 or 22 min, respectively (P = 0.017, P = 0.031)]. The concentration of sevoflurane reached 5 parts per million in the Zeus machines after an mean (SD) of 85 min (6) at a fresh gas flow of 10 l min(-1). When the fresh gas flow was increased to 18 l min(-1) (the maximum allowable), the time to reach 5 parts per million was reduced to 16 min. When preparing the Fabius CE for the malignant hyperthermia susceptible patient, remove the vaporiser, replace the disposable tubing, the reservoir bag and the CO2 absorber. Replace the ventilator diaphragm and non-disposable ventilator tube with new or autoclaved components and flush the machine at 10 l min(-1) for at least 36 min. When preparing the Zeus, remove the vaporiser, replace the disposable tubing, the reservoir bag and CO2 absorber and flush at a fresh gas flow of 10 l min(-1) for at least 90 min. In both the Fabius and Zeus, continue at a fresh gas flow of 10 l min(-1) for the duration of the operation.

Soil Organic C:N vs. Water-Extractable Organic C:N

Traditionally, soil-testing laboratories have used a variety of methods to determine soil organic matter, yet they lack a practical method to predict potential N mineralization/immobilization from soil organic matter. Soils with high micro-bial activity may experience N immobilization (or reduced net N mineralization), and this issue remains unresolved in how to predict these conditions of net mineralization or net immobilization. Prediction may become possible with the use of a more sensitive method to determine soil C:N ratios stemming from the water-extractable C and N pools that can be readily adapted by both commercial and university soil testing labs. Soil microbial activity is highly related to soil organic C and N, as well as to water-extractable organic C (WEOC) and water-extractable organic N (WEON). The relationship between soil respiration and WEOC and WEON is stronger than between respiration and soil organic C (SOC) and total organic N (TON). We explored the relationship between soil organic C:N and water-extractable organic C:N, as well as their relationship to soil microbial activity as measured by the flush of CO2 following rewetting of dried soil. In 50 different soils, the relationship between soil microbial activity and water-extractable organic C:N was much stronger than for soil organic C: N. We concluded that the water-extractable organic C:N was a more sensitive measurement of the soil substrate which drives soil microbial activity. We also suggest that a water-extractable organic C:N level > 20 be used as a practical threshold to separate those soils that may have immobilized N with high microbial activity.

Autotrophic and heterotrophic contributions to short-term soil CO2efflux following simulated summer precipitation pulses in a Mediterranean dehesa

[1] Autotrophic and heterotrophic components of soil CO2 efflux may have differential responses to environmental factors, so estimating the relative contribution of each component during summer precipitation pulses is essential to predict C balance in soils experiencing regular drought conditions. As even small summer rains induced high instantaneous soil respiration rates in Mediterranean wooded grasslands, we hypothesized that standing dead mass, surface litter, and topsoil layer could play a dominant role in the initial flush of CO2 produced immediately after soil rewetting; in contrast, soil CO2 effluxes during drought periods should be mostly derived from tree root activity. In a grazed dehesa, we simulated four summer rain events and measured soil CO2 efflux discontinuously, estimating its δ13C through a Keeling plot nonsteady state static chamber approach. In addition, we estimated litter contribution to soil CO2 efflux and extracted soil available C fractions (K2SO4-extracted C and chloroform-fumigated extracted C). The δ13C-CO2 from in-tube incubated excised tree roots and rewetted root-free soil was −25.0‰ (±0.2) and −28.4‰ (±0.2), respectively. Assuming those values as end-members' sources, the autotrophic component of soil CO2 efflux was dominant during the severe drought, whereas the heterotrophic contribution dominated from the very beginning of precipitation pulses. As standing dead mass and fresh litter contribution was low (<25%) in the first day and negligible after, we concluded that CO2 efflux after rewetting was mostly derived from microbial mineralization of available soil organic C fractions.

Soil Respiration, Climate Change and the Role of Microbial Communities

The CO2 flush is recommended as an indicator of soil biological health. We conducted field and greenhouse experiments to evaluate the effect of several factors likely to influence C mineralization (presence/absence of plants, plant species, time of season, N fertility) on the CO2 flush. The field experiment was conducted with barley grown in 2017 (two sampling times) and 2018 (three sampling times). In greenhouse experiments, barley was grown for 4, 6, or 8 weeks; barley, corn, crimson clover, soybean, and ryegrass were grown for 4 weeks; and corn and barley were grown for 5 weeks at 4 levels of N. All had unplanted controls. Root biomass, microbial biomass carbon (MBC), dissolved organic carbon (DOC), and the amount of CO2-C released during 24 h after rewetting dried soil were measured. MBC was determined by the microwave method, and DOC was extracted by water with C quantified using a Shimadzu TOC-VCPH. A LI-COR infrared gas analyzer was used to quantify CO2. We found that planted soil had a greater CO2 flush than bare or unplanted soil, but the difference was not large, ranging between 15 and 40%. Root biomass did not consistently correlate with the CO2 flush. In unfertilized soils, the CO2 flush was not influenced by plant species. In fertilized soils, the CO2 flush was significantly higher in soils planted to corn than soils planted to barley at the two highest nitrogen levels. We found strong correlations between DOC and the CO2 flush, and inconsistent correlations between MBC and the CO2 flush. Because the CO2 flush was not strongly influenced by collection time, plant species, or N fertility, the CO2 flush may be a robust soil health indicator among different crops and sampling times.

Assessing Indices for Predicting Potential Nitrogen Mineralization in Soils under Different Management Systems

A reliable laboratory index of N availability would be useful for making N recommendations, but no single approach has received broad acceptance across a wide range of soils. We compared several indices over a range of soil conditions to test the possibility of combining indices for predicting potentially mineralizable N (N0). Soils (0–5 and 5–15 cm) from nine tillage studies across the southern USA were used in the evaluations. Long‐term incubation data were fit to a first‐order exponential equation to determine N0, k (mineralization rate), and N0* (N0 estimated with a fixed k equal to 0.054 wk−1). Out of 13 indices, five [total C (TC), total N (TN), N mineralized by hot KCl (Hot_N), anaerobic N (Ana_N), and N mineralized in 24 d (Nmin_24)] were strongly correlated to N0 (r &gt; 0.85) and had linear regressions with r2 &gt; 0.60. None of the indices were good predictors of k Correlations between indices and N0* improved compared with N0, ranging from r = 0.90 to 0.95. Total N and flush of CO2 determined after 3 d (Fl_CO2) produced the best multiple regression for predicting N0 (R2 = 0.85) while the best combination for predicting N0* (R2 = 0.94) included TN, Fl_CO2, Cold_N, and NaOH_N. Combining indices appears promising for predicting potentially mineralizable N, and because TN and Fl_CO2 are rapid and simple, this approach could be easily adopted by soil testing laboratories.

Impact of manipulated drought and heavy rainfall events on peat mineralization processes and source‐sink functions of an acidic fen

Climate change models predict changes in precipitation patterns over the next several decades for northern temperate regions. Resulting fluctuations of the water level may drastically affect the source‐sink functions of peatlands. Here, we manipulated the water table level in an acidic, minerotrophic fen using drying and rewetting experiments to simulate summer drought and heavy rainfalls to estimate changes in peat decomposition and source‐sink functions. We found that carbon dioxide (CO2) formation rates and exoenzymatic activities increased in the most active surface layer during the initial water table drawdown; however, extreme drying did not further increase these activities. Activity stimulated in deeper oxygenated peat layers did not substantially contribute to CO2 emissions. Additionally, no phenol oxidase activity was determined. Rewetting of peat after drying did not lead to a CO2 flush like in mineral soils. Water table manipulations yielded a higher availability of nitrate, ferric iron, and sulfate and prolonged the onset of methane formation. Sulfate was exported to a nearby stream. We concluded that the increasing frequency of extreme weather conditions like summer droughts and heavy rainfalls might not affect carbon storage but instead strengthen the sink function for nitrate and ferrous iron and the source function for sulfate in peatlands.

A multi-scale model for CO2 sequestration enhanced coalbed methane recovery

This paper presents a multi-scale model to simulate the multicomponent gas diffusion and flow in bulk coals for CO2 sequestration enhanced coalbed methane recovery. The model is developed based on a bi-dispersed structure model by assuming that coal consists of microporous micro-particles, meso/macro-pores and open microfractures. The bi-disperse diffusion theory and the Maxwell-Stefan approach were incorporated in the model, providing an improved simulation of the CH4-CO2/CH4-N2 counter diffusion dynamics. In the model, the counter diffusion process is numerically coupled with the flow of the mixture gases occurring within macro-pores or fractures in coal so as to account for the interaction between diffusion and flow in gas transport through coals. The model was validated by both experimental data from literature and our CO2 flush tests, and shows an excellent agreement with the experiments. The results reveal that the gas diffusivities, in particular the micro-pore diffusivities are strongly concentration-dependent.

Organic Amendments Affect Soil Parameters in Two Long‐Term Rice‐Wheat Experiments

The impacts of continuous applications of an organic manure (farmyard manure [FYM], green manure [GM], and wheat straw [WS]) combined with inorganic fertilizers (N, P, and K) on soil parameters and productivity of rice (Oryza sativa L.)–wheat (Triticum aestivum L.) systems were investigated in two long‐term experiments under conventional tillage in Ludhiana, India, and Bhairahawa, Nepal. Changes in total and labile soil C and N, and microbiological parameters relative to unfertilized and inorganically fertilized controls were measured. Organic amendments had positive but variable effects. In Ludhiana, FYM application increased total C and N, permanganate‐oxidizable C, and hot‐water‐extractable C (HWEC) by 40 to 70% relative to the control after 20 yr and maintained HWEC and total N with time. In the other treatments, HWEC and total N showed declining trends with time, whereas total C increased by 17% on average. In Bhairahawa, although total organic C and N increased with organic amendments after 15 yr, HWEC did not. Increases in C and N, respectively, as fractions of the applied organic fertilizers were 11 to 23 and 37 to 39% from FYM, 4 to 21 and 19 to 41% from GM, and 3 and 24% from WS. The FYM improved available P, cation exchange capacity, potential mineralizable N, and dehydrogenase activity, but microbial biomass C, basal respiration, flush of CO2 after rewetting dried soil, and metabolic quotient remained unchanged. The current practice of inorganic fertilization alone cannot maintain the soil quality needed to sustain crop productivity. Amounts of organic manures to supplement inorganic fertilizers must be optimized to increase C and N accumulations in the soil without negative effects on crop yield.

Enhancing Soil Quality through Residue Management in a Rice-Wheat System in Fukuoka, Japan

A long-term experiment (LTE) on a rice-wheat system was initiated in 1963 at the Kyushu National Agricultural Experiment Station, in Fukuoka, Japan, to determine the effects of continuous application of rye grass/wheat straw, rice straw and rice straw compost, alone or in combination with inorganic N on crop yields. Increase in rice yields and enhancement of total soil C and N contents with the application of organic residues in this LTE have been reported earlier. However, evaluation of the changes in the soil microbiological properties and the decomposable C fraction of soil organic matter that is needed for soil quality assessment is still lacking. Soil samples were collected after rice harvest in 2003 from the organic residue treatments and unfertilized control, air-dried and incubated for 1 month under aerobic [50% water-filled pore space (WFPS)] and flooded conditions prior to the analysis of the amount of microbial biomass C (MBC), soil respiration and the amount of potential mineralizable N (PMN). The contents of total C (TC), total N (TN), organic C (OC), hot water-extractable C (HWEC) and permanganate-oxidizable C (POC) were determined from air-dried soils. Organic residue incorporation brought about significant increases in the contents of TC, TN, OC, POC, HWEC and PMN. The largest accumulation of total C (23%) and N (72%) in the soil was from rice straw compost, compared with that from rice straw (C, 7% and N, 33%) and rye grass/wheat straw (C, 9% and N, 29%). Incorporation of rice straw compost also increased the amount of MBC under both aerobic and flooded conditions and basal soil respiration under aerobic conditions only. An efficient utilization of C by microorganisms was indicated by a significantly lower metabolic quotient (qCO2) in the composted and uncomposted rice straw treatments compared with the control in the “-” N treatment under aerobic conditions. Similarly, the flush of CO2 after rewetting of dry soil per unit of HWEC was lower in the organic matter treatments, indicating a more efficient C utilization and lower C losses per unit of available C. The content of HWEC was significantly correlated with the basal soil respiration (at 50% WFPS), the amounts of MBC, PMN and with the increase in the content of soil organic C in the residuetreated soils. In the treatments without inorganic N fertilizer, grain yield was significantly correlated with the amounts of total organic C, HWEC, MBC (at 50% WFPS), basal soil respiration (at 50% WFPS) and the amount of PMN.

Decomposition rate of organic substrates in relation to the species diversity of soil saprophytic fungi.

Despite the great interest concerning the relationship between species diversity and ecosystem functioning, there is virtually no knowledge as to how the diversity of decomposer microbes influences the decomposition rate of soil organic matter. We established a microcosm study in which the number of soil fungi was investigated in relation to the system's ability to (i) degrade raw coniferous forest humus, and (ii) use resources that were either added to the systems or released into the soils after a disturbance (drought). With the exception of the most diverse treatment, in each of the six replicates of each of the six diversity treatments (1, 3, 6, 12, 24 or 43 taxa), fungal taxa were randomly chosen from a pool of 43 commonly isolated fungal species of raw humus. Two months after initiation of the study CO2 production increased as fungal diversity increased, but in the species-poor end of the diversity gradient only. Addition of various energy resources to the microcosms generally increased the level of soil respiration but did not affect the shape of the diversity-CO2-production curve. Rewetting the soil after severe drought resulted in a rapid flush of CO2, particularly in the most diverse communities. The biomass of the fungi in the non-disturbed soils, and soil NH4-N concentration and soil pH in both disturbed and non-disturbed systems were slightly but significantly higher in the diverse than in the simple systems. Fungal species richness had no influence on the organic matter content of the humus at the end of the experiment. The results suggest that the functional efficiency of fungal communities can increase with the number of fungal taxa. This diversity effect was, however, significant at the species-poor end of the diversity gradient only, which implies considerable functional equivalency (redundancy) among the decomposer fungi.

A Rapid Method to Estimate Potentially Mineralizable Nitrogen in Soil

Rapid estimates of mineralizable N in soil are important for management decisions and soil quality assessments. We adapted and evaluated a rapid method based on measuring the gas pressure generated when soil is treated with Ca(ClO)2 in a closed vessel. An experiment was conducted to determine the effects of reaction time, soil/reagent, and soil/water ratios on the gas pressure generated by the method. Based on this experiment, 5 g of soil, 5 mL of deionized water, 0.3 g Ca(ClO)2, and a reaction time of 25 min were selected as optimum conditions. The method was evaluated with 60 Cecil (fine, kaolinitic, thermic Typic Kanhapludults) sandy loam samples ranging in organic C from 4 to 16 g C kg−1 Nitrogen mineralized in 24 d and soil microbial biomass C (SMBC) were measured and related to the Ca(ClO)2 method and to two other rapid methods, the flush of CO2 during 3 d following rewetting of a dry soil, and the NH4–N extractable with hot 2 M KCl. The Ca(ClO)2 method (mmol kg−1) was strongly correlated with net N mineralized in 24 d (r = 0.77) and with microbial biomass C (r = 0.90). The method was also correlated with the flush of CO2 during 3 d following rewetting of dried soil (r = 0.85) and with the NH4–N extractable with hot 2 M KCl (r = 0.86). These results indicate that the Ca(ClO)2 method may be useful to make rapid estimates of mineralizable N and microbial biomass C in soil. Additional work is needed to investigate the nature of the compounds oxidized by the method.

Flush of Carbon Dioxide Following Rewetting of Dried Soil Relates to Active Organic Pools

Soil quality assessment could become more standardized with the development of a simple, rapid, and reliable method for quantifying potential soil biological activity. We evaluated the flush of CO2 following rewetting of dried soil under standard laboratory conditions as a method to estimate an active organic matter fraction. The flush of CO2 following rewetting of dried soil (3 d incubation at ≈50% water‐filled pore space and 25°C) was assessed for 20 soil series containing a wide range of organic C (20 ± 13 g kg−1) from Alberta–British Columbia, Maine, Texas, and Georgia. This flush of CO2 explained 97% of the variability in cumulative C mineralization during , 86% of the variability in soil microbial biomass , and 67% of the variability in net N mineralization during Accounting for geographical differences in mean annual temperature and precipitation, which could affect soil organic matter quality, further improved relationships between the flush of CO2 and active, passive, and total C and N pools. Measuring the flush of CO2 following rewetting of dried soil may have value for routine soil testing of biological soil quality because it (i) is an incubation procedure patterned after natural occurrences in most soils, (ii) exhibits strong overall relationships with active organic pools, (iii) shows relatively minor changes in relationships with active organic pools that may be due to climatic variables, (iv) has a simple setup with minimal equipment requirements, and (v) has rapid analysis time.

A Climate Change Scenario for Carbon Dioxide and Dissolved Organic Carbon Fluxes from a Temperate Forest Soil Drought and Rewetting Effects

Our objective was to assess the effect of changes in rainfall amount and distribution on CO2 emissions and dissolved organic C (DOC) leaching. We manipulated soil moisture, using a roof constructed below the canopy of a 65‐yr‐old Norway spruce plantation [Picea abies (L.) Karst.] at Solling, Germany. We simulated two scenarios: a prolonged summer drought of 172 d followed by a rewetting period of 19 d and a shorter summer drought of 108 d followed by a rewetting period of 33 d. Soil CO2 emission, DOC, soil matric potential, and soil temperature were monitored in situ for 2 yr. On an annual basis no significant influence of the droughts on DOC leaching rates below the rhizosphere was observed. Although not significantly, the droughts tended to reduce soil respiration. Rewetting increased CO2 emissions in the first 30 d by 48% (P &lt; 0.08) in 1993 and 144% (P &lt; 0.01) in 1994. The CO2 flush during rewetting was highest at high soil temperatures and strongly affected the annual soil respiration rate. The annual emission rate from the drought plot was not affected by the drought and rewetting treatments in 1993 (2981 kg C ha−1 yr−1), but increased by 51% (P &lt; 0.05) to 4813 kg C ha−1 yr−1 in 1994. Our results suggest that reduction of rainfall or changes in rainfall distribution due to climate change will affect soil CO2 emissions and possibly C storage in temperate forest ecosystems.

Process variable implications for residual solvent removal and polymer morphology in the formation of gentamycin-loaded poly (L-lactide) microparticles.

The purpose was to determine the influence of process parameters in the precipitation with a compressed antisolvent (PCA) process on the morphology and residual dichloromethane (DCM) levels in gentamycin-loaded PLA microparticles. The three variables studied were the rate of CO2 co-flowed during the polymer and drug post-precipitation, the post-precipitation pure CO2 flush rate, and the post-precipitation CO2 flush volume. Residual DCM levels were determined from headspace gas chromatography-mass spectroscopy (GC-MS) with single ion monitoring. X-ray diffraction (XRD) and differential scanning calorimetry (DSC) were used to estimate the crystallinity within microparticles. DCM was extracted from drug-loaded microparticles by both supercritical CO2 extraction and vacuum drying for up to two days to determine a lower limit for solvent removal. Increasing either the post-precipitations CO2 flow rate or flush volume resulted in lower residual DCM levels in the microparticle. The CO2 co-flow rate showed an opposite trend. Increasing in value resulted in a higher DCM value after precipitation. XRD and DSC analysis on these samples suggest that those produced at lower CO2 co-flow rates have a higher degree of crystallinity, which increases the diffusivity of DCM through the polymer matrix. Finally, samples subjected to extended (48 hr) CO2 extraction resulted in DCM levels on the order of one to three ppm. Specific PCA process conditions during microparticle formation have a strong influence on the residual solvent levels within the microparticles. Polymer morphology affects the diffusivity of solvent through the polymer matrix, which in turn determines the solvent removal rates.