Specific Respiratory Activity Research Articles

Fine-Root Traits Reveal Contrasting Ecological Strategies in European Beech and Norway Spruce During Extreme Drought.

Trees adjust multiple structural and functional organ-specific characteristics, “traits”, to cope with diverse soil conditions. Studies on traits are widely used to uncover ecological species adaptability to varying environments. However, fine-root traits are rarely studied for methodological reasons. We analyzed the adaptability of the fine-root systems of European beech and Norway spruce to extreme drought within species-specific tree groups at Kranzberger Forst (Germany), focusing on the seasonality of morphological, physiological, and biochemical key traits in view of carbon (C) and nitrogen dynamics. We hypothesized that fine roots of both species adjust to seasonal drought: with beech representing a “fast” (i.e. with fast C turnover), and spruce a “slow” (i.e. with long-term C retention) ecological strategy. We identified three functional fine-root categories, based on root function (absorptive or transport fine roots), and mycorrhizal status of the absorptive fine-roots (mycorrhizal or non-mycorrhizal). Solely the non-mycorrhizal absorptive roots adjusted in a species-specific manner supporting fine-root ecological strategy hypothesis. During drought, beech produced thin ephemeral (absorptive non-mycorrhizal) fine roots with high specific fine-root area and high respiratory activity, representing fast C turnover and enabling effective resource exploitation. These adjustments reflect a “fast” ecological strategy. Conversely, spruce absorptive fine roots did not respond to the soil moisture deficit by growth but instead increased root suberization. Drastically lowered respiratory activity of this functional category facilitated C retention and structural persistence during drought, indicating a “slow” ecological strategy in spruce. Absorptive mycorrhizal fine roots maintained respiration throughout the drought event in both tree species, but in spruce this was the only fine-root category with high respiration. This suggests, that spruce relies heavily on mycorrhizal associations as a method of drought resistance. Accumulation of non-structural carbohydrates and high C concentrations were observed in the transport fine roots of both species, indicating drought-induced osmotic protection of these roots. Thus, functional classification enabled us to determine that fine-root branches of each species are not tied to one sole ecological strategy. The suggested approach helps to better understand the complex interplay between structure and function belowground.

Evaluating organic carbon fractions, temperature sensitivity and artificial neural network modeling of CO2 efflux in soils: Impact of land use change in subtropical India (Meghalaya)

The present study investigates the changes in land use pattern from fallow land (control) to fruit orchards on soil organic carbon (SOC) dynamics especially, organic carbon stocks, fractions, and CO2 efflux. The SOC fractions such as total organic carbon (TOC), particulate organic carbon (POC), readily oxidizable carbon (ROC), non-labile carbon (CNL), microbial biomass carbon (MBC), carbon management index (CMI) and their sensitivity to land use change were the focus of this study. The organic carbon fractions showed increasing trend (19.4–46%) under fruit orchards compared to control. Furthermore, the orchard with P. persica recorded the highest mean SOC stocks (59.4 Mg ha−1) and TOC (3.03 g 100 g−1) while orchard with C. reticulata showed the highest ROC (6.11 g kg−1) and MBC (401 mg kg−1). Fruit orchards were characterized by high Cmic:CTOC (microbial quotient; qMIC) and POC: TOC ratios, indicating an increase in substrate availability. Furthermore, the CMI was highest under C. reticulata (226.4) followed by P. guajava (173.3), whereas P. communis showed relatively lower value (160.5). While, upper soil layer (0–15 cm) exhibited higher organic carbon stock and fractions viz., 35.1 % and 58.3%, respectively compared to the subsurface soil (15–75 cm) in all orchards. The labile SOC fractions (POC, ROC, and MBC) showed a positively significant correlation with TOC and CO2 efflux indicating that these labile fractions are the sensitive indicators of soil quality changes and improvements. Soil CO2 efflux exhibited a pronounced variation corresponding to land use change with values ranging from 22.80 µg C g−1 h−1 (fallow land) to 27.39 µg C g−1 h−1 (P. guajava). With temperature increment from 25 to 35 °C, the soil CO2 efflux increased from 55% (P. persica) to 88% (fallow) with an average increase of 72%. However, the microbial metabolic quotient (qCO2), also called as specific respiratory activity (SRA), was relatively lower (40.9 µg CO2 mg MBC−1) in orchards compared to fallow land (50.4 µg CO2 mg MBC−1). A multi-layered Artificial Neural Network model (ANN) was also developed, and the experimental CO2 efflux values obtained from different land uses are in good agreement with the predicted CO2 efflux. We conclude that, labile SOC fractions are highly sensitive to land use change and could be effectively used as the sensitive indicators along with CMI for land use change under mid-altitude subtropical ecosystems. In addition, fruit orchards could store more carbon thus could be a potential option to mitigate global warming.

Effect of gold and silver nanoparticles on the growth of the Arabidopsis thaliana cell suspension culture

The addition of 20-nm gold and silver nanoparticles to a growth medium has a positive effect on the growth of biomass of a cell suspension culture of Arabidopsis thaliana (L.) Heynh. Growing the cells with silver and gold nanoparticles causes different changes in the pH of the medium: the culture medium is made markedly acidic by the addition of silver nanoparticles and alkaline by the addition of gold nanoparticles. As is found by the MTT assay, metallic nanoparticles are responsible for a slight but steady decrease in the specific respiratory activity of cells of the A. thaliana suspension culture. Growth with the nanoparticles is accompanied by an increase in the intracellular free amino acid pool (alanine, γ-aminobutyric acid, and valine), which is characteristic of responses to abiogenic stresses. Furthermore, the addition of the nanoparticles changes the composition of extracellular proteins in the A. thaliana cell culture.

Electrochemical detection of specific DNA and respiratory activity of Escherichia coli

We present two rapid and simplified detection methods for Escherichia coli involving the use of a hand-held potentiostat and a disposable screen-printed carbon electrode. E. coli is one of the indicator organisms used to access for food safety. Commonly, microbiological culture techniques take more than one day to yield results and therefore, a simple, cost-effective, in situ detection system is required for testing food safety. This report describes two complementary techniques for high- and low-sensitivity detection of E. coli. High-sensitivity detection relies upon quantification of DNA amplification by using polymerase chain reaction (PCR), while the simplified, low-sensitivity detection can be obtained through measurement of oxygen consumption due to respiration; importantly, both techniques utilize the same type of electrode. The former entails mixing the PCR mixture with Hoechst, an electro-active DNA intercalator, and then, measuring the oxidation current. Binding of Hoechst molecules to the amplified DNA causes the peak current to decrease because of the slow diffusion of the Hoechst-amplified DNA complex to the electrode surface. The results showed that the oxidation peak current of Hoechst decreased depending on the number of E. coli cells added to the PCR mixture as the template for amplification, and the sensitivity of the method was as low as a single bacterium. Oxygen consumption was detected by direct measurement of the cell-containing culture medium. This method required only 10μL to be applied on the screen-printed electrode, and the reduction in oxygen current was clearly observed within 30min when a minimum of 1×105cells were present. These results were obtained without purifying the culture, and the samples were applied onto the electrode without any surface modifications. The techniques describes in this report are versatile, because they require the same type of electrode, have simplistic nature, use a hand-held potentiostat, and have potential to provide an in situ system for assessing food safety.

Soil sampling based on field spatial variability of soil microbial indicators

Microbial indicators exhibit a high spatial heterogeneity which often masks comparison of the effects of different soil management treatments. It is therefore desirable to use a proper sampling design which integrates spatial heterogeneity at field level. Thus, the objectives were: (1) to study the spatial heterogeneity of biological and chemical soil variables, and (2) with obtained maps of spatial variability to test different sampling strategies to assess the usefulness of this ‘new’ soil map unit. 63 soil samples were collected according to a 10 m × 10 m grid on a 0.48 ha plot. On each of these samples, 10 variables were measured: soil water content, cation exchange capacity (CEC), organic carbon (OC) and total nitrogen (N), C/N, soil microbial biomass (SMB), labile soil organic matter (LOM), mineralisable C (C min) and N (N min), inverse of specific respiratory activity (1/SRA = SBM/C min). The spatial heterogeneity of each variable was charted with geostatistics. The biological variables exhibited spatial variability of the same order of magnitude as physicochemical parameters. From the maps, zones with different levels of organic matter, microbial biomass and specific respiratory activity were identified. The spatial patterns of SMB and SRA were related to CEC (positively for SMB and negatively for SRA), pointing out the effects of soil protection on microbial biomass and availability of organic substrates. The definition of these zones for a pool of variables (OC, N, SMB, LOM, CEC) is useful at 3 levels: (1) to record the initial values of the measured variables for each plot, (2) to integrate these zones as blocks in experimental design for future experiments, and (3) to focus analysis of specific biological mechanisms such as activity of micro-organisms.

Analysis of bacterial activity, biomass and diversity during windrow composting

Two contrasting compost windrows were monitored for various physical, chemical and microbiological parameters for a period of 106 days. The different input materials and management practises gave rise to different temperature, moisture, and oxygen consumption profiles as composting proceeded. However, despite the different composting conditions, the specific respiratory activity, as determined by oxygen consumption per bacterial cell, was remarkably similar for both windrows. Further investigations into diversity dynamics were done through DGGE and cloning and sequencing of bacterial 16S rDNA PCR products. Although sequence analysis showed differing bacterial communities across time and between the different windrows, similarities in the progression were noted. The majority of sequences recovered from the first sampling period (day 1) were highly similar to previously isolated organisms. The clone libraries from the last sampling period (day 106) contained organisms that showed lower homology to their closest relatives, often with other uncultured organisms, and in phyla that contain few cultured representatives. These data suggest that specific respiratory activity may be an important driver of bacterial diversity in composting environments.

Performance of Direct Biofiltration of Surface Water for Reduction of Biodegradable Organic Matter and Biofilm Formation Potential

Direct biofiltration of surface water may be considered as pre-treatment for membrane filtration, in order to reduce fouling. The biofiltration process was investigated with regard to biodegradable organic matter and biofilm formation, covering the annual variations under moderately cold climate conditions. Granular activated carbon (GAC) and two types of crushed expanded clay (EC) were compared as filter media. To assess the biological properties of the biofilters, viable biomass and respiratory activity was examined. Biofiltration removed assimilable organic carbon (AOC) and biodegradable dissolved organic carbon (BDOC) by about 30% and also reduced the bacterial concentration in the water phase. Also, biofilm formation in the treated water was reduced by 80-90% during summer and winter conditions. The reductions in the investigated parameters were similar in the biofilters with GAC and EC. Likewise, a similar amount and development of biomass was found in the GAC and EC biofilters of comparable grain size with a pronounced stratification from top to bottom of the filter bed. The specific respiratory activity of the biofilter biomass was dependent on raw water temperature. Even though slight correlations between BDOC removal and temperature or respiratory activity were observed, AOC and BDOC removals were mainly dependent on the feed water concentrations of these compounds. The results indicate that direct biofiltration of surface water, by reducing AOC, BDOC and biofilm formation in the water, may be an advantageous pre-treatment for membrane filtration processes.

C and N mineralization and microbial biomass in heavy-metal contaminated soil

Heavy metals such as arsenic (As), lead (Pb), copper (Cu) and zinc (Zn) can be found in large concentrations in mine spills in Mexico. Interest in contamination by these heavy metals has increased recently as they can change the functioning of soil ecosystems qualitatively and quantitatively. They disturb the activities of soil fauna and contaminate drinking water in large parts of the world, which severely affects human health. Little, however, is known how heavy metals might affect the biological functioning of a soil. Soil was sampled from eight locations along a gradient of heavy-metal contamination with distance from a mine in San Luis Potosí (Mexico) active since about 1800 AD. Microbial biomass was determined with the original chloroform fumigation incubation (CFI) as well as extraction (CFE) techniques and the substrate induced respiration (SIR) technique while C and N mineralization were measured. Total concentrations of As in the top 0–10 cm soil layer ranged from 8 to 22992 mg kg –1, from 31 to 1845 mg kg –1 for Pb, from 27 to 1620 mg kg –1 for Cu and from 81 to 4218 mg kg –1 for Zn. There was a significant negative correlation ( P < 0.0001) between microbial biomass, soil organic carbon, total N and C mineralization and the heavy metal content of the soil. The microbial biomass C to organic C ratio, which varied from 0.4 to 1.9%, specific respiratory activity ( qCO 2), and oxidation of NO 2 – were not affected by heavy metals. It was found that long-term contamination of soil with heavy metals had an adverse effect on the amount of soil microorganisms as evidenced by a marked decrease in microbial biomass C, but not some of their characteristics. According to principal components analysis (PCA), the correlation matrix showed three distinct factors explaining 71% of the variance. A first factor including heavy metals (As, Pb, Cu and Zn) with a negative loading and total N, organic C, soil microbial biomass with a positive loading characterized the soil organic matter and contamination status. Loam and sand combined for the second factor characterizing the textural classification while the third factor was loaded by CEC and clay content.

Determination of organophosphorus aromatic nitro insecticides and p-nitrophenol by microbial-cell respiratory activity

We examined the possibility of measuring the organophosphorus aromatic nitro insecticides metaphos and sumithion as well as their hydrolysis product p-nitrophenol (PNP) by the specific respiratory activity (SRA) of Pseudomonas putida C-11, P. putida BA-11, and Acinetobacter calcoaceticum A-122. The plots of cellular SRA against the two insecticides and PNP were linear over the ranges of 0.5–2.5 mM for P. putida C-11 and BA-11 and 0.5–1.0 mM for A. calcoaceticum A-122. P. putida BA-11 showed the greatest respiratory-response selectivity in the determination of the test substrates. We made comparison studies of the SRA of cells immobilised by two methods: carrier-surface adsorption and inclusion in various gels. We discuss the feasibility of developing a microbial sensor system for the determination of metaphos, sumithion, and PNP in aqueous media.

Relationships of soil respiration to microbial biomass, substrate availability and clay content

The roles of microbial biomass (MBC) and substrate supply as well as their interaction with clay content in determining soil respiration rate were studied using a range of soils with contrasting properties. Total organic C (TOC), water-soluble organic carbon, 0.5 M K 2SO 4-extractable organic C and 33.3 mM KMnO 4-oxidisable organic carbon were determined as C availability indices. For air-dried soils, these indices showed close relationship with flush of CO 2 production following rewetting of the soils. In comparison, MBC determined with the chloroform fumigation–extraction technique had relatively weaker correlation with soil respiration rate. After 7 d pre-incubation, soil respiration was still closely correlated with the C availability indices in the pre-incubated soils, but poorly correlated with MBC determined with three different techniques—chloroform fumigation extraction, substrate-induced respiration, and chloroform fumigation–incubation methods. Results of multiple regression analyses, together with the above observations, suggested that soil respiration under favourable temperature and moisture conditions was principally determined by substrate supply rather than by the pool size of MBC. The specific respiratory activity of microorganisms (CO 2-C/MBC) following rewetting of air-dried soils or after 7 d pre-incubation was positively correlated with substrate availability, but negatively correlated with microbial pool size. Clay content had no significant effect on CO 2 production rate, relative C mineralization rate (CO 2-C/TOC) and specific respiratory activity of MBC during the first week incubation of rewetted dry soils. However, significant protective effect of clay on C mineralization was shown for the pre-incubated soils. These results suggested that the protective effect of clay on soil organic matter decomposition became significant as the substrate supply and microbial demand approached to an equilibrium state. Thereafter, soil respiration would be dependent on the replenishment of the labile substrate from the bulk organic C pool.

Climatic influences on active fractions of soil organic matter

Biologically active fractions of soil organic matter are important in understanding decomposition potential of organic materials, nutrient cycling dynamics, and biophysical manipulation of soil structure. We evaluated the quantitative relationships among potential C and net N mineralization, soil microbial biomass C (SMBC), and soil organic C (SOC) under four contrasting climatic conditions. Mean SOC values were 28±11mgg−1 (n=24) in a frigid–dry region (Alberta/British Columbia), 25±5mgg−1 (n=12) in a frigid–wet region (Maine), 11±4mgg−1 (n=117) in a thermic–dry region (Texas), and 12±5mgg−1 (n=131) in a thermic–wet region (Georgia). Higher mean annual temperature resulted in consistently greater basal soil respiration (1.7 vs 0.8mgCO2–Cg−1 SOC d−1 in the thermic compared with the frigid regions, P<0.001), greater net N mineralization (2.8 vs 1.3mg inorganic Ng−1 SOC 24d−1, P<0.001), and greater SMBC (53 vs 21mg SMBC g−1 SOC, P<0.001). Specific respiratory activity of SMBC was, however, consistently lower in the thermic than in the frigid regions (29 vs 34mgCO2–Cg−1 SMBC d−1, P<0.01). Higher mean annual precipitation resulted in consistently lower basal soil respiration (1.1 vs 1.3mgCO2–Cg−1 SOC d−1 in the wet compared with the dry regions, P<0.01) and lower SMBC (31 vs 43mg SMBCg−1 SOC, P<0.001), but had inconsistent effects on net N mineralization that depended upon temperature regime. Specific respiratory activity of SMBC was consistently greater in the wet than the dry regions (≈33 vs 29mgCO2–Cg−1 SMBC d−1, P<0.01). Although the thermic regions were not able to retain as high a level of SOC as the frigid regions, due likely to high annual decomposition rates, biologically active soil fractions were as high per mass of soil and even 2–3-times greater per unit of SOC in the thermic compared with the frigid regions. These results suggest that macroclimate has a large impact on the portion of soil organic matter that is potentially active, but a relatively small impact on the specific respiratory activity of SMBC.

Soil carbon, microbial activity and nitrogen availability in agroforestry systems on moderately alkaline soils in northern India

The present investigation aimed to analyze the role of agroforestry systems in improving soil organic matter status, microbial activity and nitrogen availability with a view to effective management of the fertility of moderately alkaline soils. The study site was located at Karnal (29°59′N, 76°51′E, 250 m.s.l.) and the systems were characterized by a rice–berseem crop rotation; agrisilvicultural systems of Acacia, Eucalyptus and Populus along with rice–berseem and single species tree plantations. Soil microbial biomass was measured using the fumigation extraction technique and nitrogen mineralization using the aerobic incubation method. Microbial biomass carbon was low in rice–berseem crops (96.14 μg g −1 soil) and increased in soils under tree plantations (109.12–143.40 μg g −1 soil) and agrisilvicultural systems (133.80–153.40 μg g −1 soil). Microbial biomass was higher by 42% (microbial C) and 13% (microbial N) in tree-based systems as compared to monocropping. Microbial biomass immobilized 2.32–2.57% of the soil carbon and 4.08–4.48% of the soil nitrogen in tree-based systems. Soil carbon increased by 11–52% due to integration of trees along with the crops for 6–7 years. Cropland management practices and tree species influenced CO 2-C production, biomass specific respiratory activity, and nitrogen mineralization rates. In tree-based systems, soil inorganic N levels were higher by 8–74% and nitrogen mineralization by 12–37% as compared to monocropping. On the basis of increased soil organic matter content, enlarged soil microbial biomass pool and greater soil N availability, agrisilvicultural systems have been found to be ecologically sustainable land-use systems for utilizing moderately alkaline soils.

Soil Carbon and Nitrogen Dynamics Following Application of Pig Slurry for the 19th Consecutive Year I. Carbon Dioxide Fluxes and Microbial Biomass Carbon

Agricultural soils often receive annual applications of manure for long periods. The objective of this study was to quantify the effects of 19 consecutive years of pig (Sus scrofa) slurry (PS) application on CO2 emissions and soil microbial biomass. Soil temperature, soil moisture, and extractable soil C were also determined to explain the variations in CO2 emissions and soil microbial biomass. Long‐term (19 yr) treatments were 60 (PS60) and 120 Mg ha−1 yr−1 (PS120) of pig slurry and a control receiving mineral fertilizers at a dose of 150 kg ha−1 yr−1 each of N, P2O5, and K2O. Very high CO2 emissions (up to 1.5 mg CO2 m−2 s−1) occurred during the first 2 d after PS application. Following that peak, decomposition of PS was rapid, with one‐half the total emissions occurring during the first week after slurry application. The rapid initial decomposition was exponential and was attributed to the decomposition of the labile fraction of the slurry C. The second phase was linear and much slower and probably involved more recalcitrant C material. Cumulative annual decomposition was proportional to the application rate, with 769 and 1658 kg C ha−1 lost from the 60 and 120 Mg ha−1 doses, respectively. Pig slurry application caused a rapid increase in soil microbial biomass (from ≈100 to up to 370 mg C kg−1 soil), which coincided with a peak in the concentration of extractable C and in CO2 emissions. Field estimates of the microbial specific respiratory activity suggested that the difference in soil respiration between the two slurry treatments was due to differences in the size of the induced microbial biomass rather than to differences in specific activity.

Comparison of the electrooptical properties and specific respiratory activity of Acinetobacter calcoaceticum A-122.

The electrooptical (EO) properties of a cell suspension and the specific respiratory activity of cells towards p-nitrophenol (PNP) were compared during PNP metabolism in Acinetobacter calcoaceticum strain A-122. The frequency dependence of the suspension's turbidity changes due to cellular orientation (orientational spectra) at frequencies of an orienting electric field of 10-10,000 kHz was determined. Orientational spectral changes observed during PNP incubation of the cells were followed over the range of 10-502 kHz. There were linear relationships between the magnitude of the EO effect at a 502-kHz frequency and the concentration of PNP over the range of 0.1-0.8 mM, and between the specific respiratory activity of the cells and the concentration of PNP over the range of 0.1-1.0 mM. The knowledge gained from these studies suggests a direct relationship between alterations in the cellular EO properties and PNP metabolism.

Comparison of the electrooptical properties and specific respiratory activity of Acinetobacter calcoaceticum A-122

The electrooptical (EO) properties of a cell suspension and the specific respiratory activity of cells towards p-nitrophenol (PNP) were compared during PNP metabolism in Acinetobacter calcoaceticum strain A-122. The frequency dependence of the suspension's turbidity changes due to cellular orientation (orientational spectra) at frequencies of an orienting electric field of 10–10 000 kHz was determined. Orientational spectral changes observed during PNP incubation of the cells were followed over the range of 10–502 kHz. There were linear relationships between the magnitude of the EO effect at a 502-kHz frequency and the concentration of PNP over the range of 0.1–0.8 mM, and between the specific respiratory activity of the cells and the concentration of PNP over the range of 0.1–1.0 mM. The knowledge gained from these studies suggests a direct relationship between alterations in the cellular EO properties and PNP metabolism.

Agroforestry system effects on soil characteristics of the Sarapiquı́ region of Costa Rica

Agroforestry systems have been considered sustainable land-use alternatives for the humid tropics because they may imitate characteristics of natural ecosystems – notably those that have beneficial effects on soil properties. The objective of this study was to compare the effects of agroforestry systems on selected soil properties of Haplic Acrisols and Dystic Fluvisols, in the Atlantic Region of Costa Rica, approximately five years after their establishment. The agroforestry systems were established on unmanaged pastures near the La Selva Biological Station in 1989 and 1990. The original forest had been removed on most of these areas at least 25 years earlier. Tree components of the agroforestry systems were the tropical hardwoods Vochysia ferruginea (Botarrama), V. guatemalensis (Chancho), Stryphnodendron microstachyum (Vainello) and Hieronyma alchorneoides (Pilón). The soil properties studied included physical (soil bulk density; 0–10 cm), chemical [pH, exchangeable bases, extractable P, soil organic C (SOC) and total soil N; 0–50 cm] and biological parameters (mineralizable C and N and microbial biomass C and N; 0–15 cm). Soils were sampled in August 1995. Lower exchangeable bases and soil pH were noted in agroforestry treatments as compared to pastures. Extractable P was higher in the surface 25 cm of agroforestry plots. Total soil N, soil organic C and soil C : N ratios were not influenced by agroforestry systems. Higher mineralizable C levels were observed in pasture surface soils, but no differences in mineralizable N in soils under pasture and agroforestry systems were observed. Soil microbial biomass C and N and specific respiratory activity were not significantly different in pastures and agroforestry systems. Agroforestry systems did not appear to improve soils in this study compared to pasture.

Microbial activity in response to water-filled pore space of variably eroded southern Piedmont soils

Potential C and N mineralization and soil microbial biomass C (SMBC) are soil biological properties important in understanding nutrient and organic matter dynamics. Knowledge of soil water content at a matric potential near field capacity is needed to determine these biological properties. The objective of this study was to examine whether adjustment of soil water content to a common level of water-filled pore space (WFPS) may be an acceptable alternative that would require little prior analysis in comparison with adjustment based on matric potential. Potential C and N mineralization and SMBC were determined from 15 variably eroded soils of the Madison–Cecil–Pacolet association (clayey, kaolinitic, thermic Typic Kanhapludults) in response to WFPS. The levels of WFPS to achieve maximum activity and biomass under naturally settled conditions were unaffected by clay content and occurred at 0.42±0.03 m 3 m −3 for net N mineralization during 24 days of incubation, 0.51±0.22 m 3 m −3 for specific respiratory activity of SMBC, 0.60±0.07 m 3 m −3 for cumulative C mineralization during 24 d of incubation, and 0.76±0.27 m 3 m −3 for SMBC. Selecting a common WFPS level of 0.5 m 3 m −3 resulted in 96±2%, 97±5%, 97±4%, and 88±10% of the maximum for these four properties, respectively, and was a reasonable compromise when attempting to estimate these properties during simultaneous incubations. Adjusting soil water content based on WFPS was simpler and nearly as reliable as based on matric potential, in which soil water content at −33 kPa varied from 0.16 to 0.30 g g −1.

Long-term effects of tillage and fallow-frequency on soil quality attributes in a clay soil in semiarid southwestern saskatchewan

Reduced tillage management is being adopted at an accelerated rate on the Canadian prairies. This may influence soil quality and productivity. A study conducted on a clay soil (Udic Haplustert) in southwestern Saskatchewan, Canada, to determine the effects of fallow frequency [fallow-wheat (F-W) vs. continuous wheat (Cont W)] and tillage [no-tillage (NT) vs. conventional (CT) or minimum tillage (MT)] on yields of spring wheat ( Triticum aestivum L.), was sampled after 3, 7 and 11 years to assess changes in selected soil quality attributes. Tillage had no effect on amount of crop residues returned to the land, but the tilled systems had significantly ( P<0.05) lower total organic C and N in the 0–7.5 cm soil depth, though not in the 7.5–15 cm depth. Further, these differences were observed after only 3 years and persisted for the entire 11 years of the study. For example, in the 0–7.5 cm depth, organic C in F-W (MT) after 3 years was 10 480 kg ha −1 and in F-W (NT) 13 380 kg ha −1, while in Cont W (CT) and Cont W (NT) corresponding values were 11 310 and 13 400 kg ha −1, respectively. After 11 years, values for F-W (MT) and F-W (NT) were 11 440 and 14 960 kg ha −1, respectively, and for Cont W (CT) and Cont W (NT), 12 970 and 16 140 kg ha −1, respectively. In contrast to total organic matter, two of the more labile soil quality attributes [i.e., C mineralization (C min) and N mineralization (N min)] did not respond to fallow frequency until after 7 years and only in the 0–7.5 cm depth. Microbial biomass (MB) and the ratio of C min to MB [specific respiratory activity (SRA)], two attributes also regarded as labile, were not influenced by the treatments even after 11 years. After 11 years, only C min and N min among the labile soil quality attributes responded to the treatments. Surprisingly, the labile attributes were no more sensitive to the treatments than was total organic C or N. More research is required to determine why responses in this soil differed from those reported elsewhere.

Soil quality—Effect of tillage and fallow frequency. Soil organic matter quality as influenced by tillage and fallow frequency in a silt loam in southwestern Saskatchewan

Characterization of organic matter is valuable for identifying the overall quality of soils. Management will influence soil quality. The rate at which quality attributes change may depend upon soil texture and environmental conditions. We assessed the effects of tillage (no-tillage (NT) vs conventional mechanical tillage (CT)) and fallow frequency (continuous wheat ( Triticum aestivum L.) (Cont W) vs fallow-wheat (F-W)) on selected soil quality attributes for a silt loam in semiarid southwestern Saskatchewan. Measurements were made in the 0–7.5 and 7.5–15 cm depths after 4, 8 and 12 y of study. After 4 and 8 y, only C mineralization (C min) and N mineralization (N min) showed significant treatment effects, but after 12 y specific respiratory activity (SRA) was also significant ( P<0.05). Total organic C and N and microbial biomass (MB) were not affected significantly by treatments ( P<0.05) even after 12 y. Cropping more frequently resulted in higher C min, N min and SRA, likely associated with higher crop residue production (e.g., correlation of C min and N min with mean annual straw production was 0.95, significant at P=0.05). Tillage did not influence straw production nor any of the soil quality attributes assessed. The labile attributes were more sensitive than total organic C and N to fallow frequency, but they were generally less sensitive to method of tillage management.

The influence of acid irrigation and liming on the soil microbial biomass in a Norway spruce (Picea abies [L.] K.) stand

Over a period of three years (1990–1992) microbial biomass-C (Cmic), CO2 evolution, the Cmic:Corg ratio and the metabolic quotient for CO2 (qCO2) were determined in a Norway spruce stand (Hoglwald) with experimentally acid-irrigated and limed plots since 1984. A clear relationship between soil pH and the level of microbial biomass-(Cmic) was noted, Cmic increasing with increasing soil pH in Oh or Ah horizons. More microbial biomass-C per unit C{org} (Cmic:Corg ratio) was detected in limed plots with elevated pH of Oh or Ah horizons as compared to unlimed plots with almost 3 times more Cmic per unit Corg in the limed Oh horizon. Differences here are significant at least at the p=0.05 level. The positive effects of liming (higher pH) on the Cmic:Corg ratio was more pronounced in the upper horizon (Oh)). The total CO2 evolution rate of unlimed plots was only half of that noted for limed plots which corresponded to the low microbial biomass levels of unlimed plots. The specific respiratory activity, qCO2, was similar and not significantly different between the unlimed control plot and the limed plot. Acid irrigation of plots with already low pH did not significantly affect the level of microbial biomass, the Cmic:Corg ratio or qCO2. An elevated qCO2 could be seen, however, for the limed + acid irrigated plot. The biomass seemed extremely stressed, showing with 3.8 µg CO2-C mg-1 Cmic h-1 (Oh) the highest qCO2 value of all treatments. This was interpreted as a reflection of the continuous adaptation processes to the H+ ions by the microflora. The negative effect of acid irrigation of limed plots was also manifested in a decreased Cmic:Corg ratio.