Soil Microbial Functional Diversity Research Articles

Changes in Transformation of Soil Organic C and Functional Diversity of Soil Microbial Community Under Different Land Uses

Changes in soil biological and biochemical properties under different land uses in the subtropical region of China were investigated in order to develop rational cultivation and fertilization management. A small watershed of subtropical region of China was selected for this study. Land uses covered paddy fields, vegetable farming, fruit trees, upland crops, bamboo stands, and forestry. Soil biological and biochemical properties included soil organic C and nutrient contents, mineralization of soil organic C, and soil microbial biomass and community functional diversity. Soil organic C and total N contents, microbial biomass C and N, and respiration intensity under different land uses were changed in the following order: paddy fields (and vegetable farming) > bamboo stands > fruit trees (and upland). The top surface (0–15 cm) paddy fields (and vegetable farming) were 76.4 and 80.8% higher in soil organic C and total N contents than fruit trees (and upland) soils, respectively. Subsurface paddy soils (15–30 cm) were 59.8 and 67.3% higher in organic C and total N than upland soils, respectively. Soil microbial C, N and respiration intensity in paddy soils (0–15 cm) were 6.36, 3.63 and 3.20 times those in fruit tree (and upland) soils respectively. Soil microbial metabolic quotient was in the order: fruit trees (and upland) > forestry > paddy fields. Metabolic quotient in paddy soils was only 47.7% of that in fruit tree (and upland) soils. Rates of soil organic C mineralization during incubation changed in the order: paddy fields > bamboo stands > fruit trees (and upland) and soil bacteria population: paddy fields > fruit trees (and upland) > forestry. No significant difference was found for fungi and actinomycetes populations. BIOLOG analysis indicated a changing order of paddy fields > fruit trees (and upland) > forestry in values of the average well cell development (AWCD) and functional diversity indexes of microbial community. Results also showed that the conversion from paddy fields to vegetable farming for 5 years resulted in a dramatic increase in soil available phosphorus content while insignificant changes in soil organic C and total N content due to a large inputs of phosphate fertilizers. This conversion caused 53, 41.5, and 41.3% decreases in soil microbial biomass C, N, and respiration intensity, respectively, while 23.6% increase in metabolic quotient and a decrease in soil organic C mineralization rate. Moreover, soil bacteria and actinomycetes populations were increased slightly, while fungi population increased dramatically. Functional diversity indexes of soil microbial community decreased significantly. It was concluded that land uses in the subtropical region of China strongly affected soil biological and biochemical properties. Soil organic C and nutrient contents, mineralization of organic C and functional diversity of microbial community in paddy fields were higher than those in upland and forestry. Overuse of chemical fertilizers in paddy fields with high fertility might degrade soil biological properties and biochemical function, resulting in deterioration of soil biological quality.

Effect of organic, sustainable, and conventional management strategies in grower fields on soil physical, chemical, and biological factors and the incidence of Southern blight

The objectives of our research were to evaluate the impact of organic, sustainable, and conventional management strategies in grower fields on soil physical, chemical, and biological factors including soil microbial species and functional diversity and their effect on the Basidiomycete plant pathogen Sclerotium rolfsii, causal agent of Southern blight. Soils from 10 field locations including conventional, organic and sustainable farms were sampled and assayed for disease suppressiveness in greenhouse assays, and soil quality indicators. Soils from organic and sustainable farms were more suppressive to Southern blight than soils from conventional farms. Soils from organic farms had improved soil chemical factors and higher levels of extractable C and N, higher microbial biomass carbon and nitrogen, and net mineralizable N. In addition, soil microbial respiration was higher in soils from organic than sustainable or conventional farms, indicating that microbial activity was greater in these soils. Populations of fungi and thermophiles were significantly higher in soils from organic and sustainable than conventional fields. The diversity of bacterial functional communities was also greater in soils from organic farms, while species diversity was similar. Soils from organic and sustainable farms had improved soil health as indicated by a number of soil physical, chemical and biological factors and reduced disease.

Relationship between plant species diversity and soil microbial functional diversity along a longitudinal gradient in temperate grasslands of Hulunbeir, Inner Mongolia, China

AbstractNumerous experiments have been established to examine the effect of plant diversity on the soil microbial community. However, the relationship between plant diversity and microbial functional diversity along broad spatial gradients at a large scale is still unexplored. In this paper, we examined the relationship of plant species diversity with soil microbial biomass C, microbial catabolic activity, catabolic diversity and catabolic richness along a longitudinal gradient in temperate grasslands of Hulunbeir, Inner Mongolia, China. Preliminary detrended correspondence analysis (DCA) indicated that plant composition showed a significant separation along the axis 1, and axis 1 explained the main portion of variability in the data set. Moreover, DCA‐axis 1 was significantly correlated with soil microbial biomass C (r= 0.735,P= 0.001), microbial catabolic activity (average well color development;r= 0.775,P< 0.001) and microbial functional diversity (catabolic diversity:r= 0.791,P< 0.001 and catabolic richness:r= 0.812,P< 0.001), which suggested thatsome relationship existed between plant composition and the soil microbial community along the spatial gradient at a large scale. Soil microbial biomass C, microbial catabolic activity, catabolic diversity and catabolic richness showed a significant, linear increase with greater plant species richness. However, many responses that we observed could be explained by greater aboveground plant biomass associated with higher levels of plant diversity, which suggested that plant diversity impacted the soil microbial community mainly through increases in plant production.

Relationship between Mikania micrantha invasion and soil microbial biomass, respiration and functional diversity

The relationship between Mikania micrantha invasion and soil microbial communities was studied across the invasive gradients varying from 0 to 38, 80, and 100% coverage of M. micrantha. The results showed microbial biomass C, N, and P all increased as the cover of M. micrantha increased. Soil microbial quotient Cmic/Corg (microbial biomass C/organic C) tended to increase linearly with the cover of M. micrantha. Basal respiration (BR) also showed a similar trend. The respiratory quotient qCO2 decreased with M. micrantha invasion, and remained at quite a constantly low level in the invasive soils. Community level physiological profiles (CLPP) analyses indicated that M. micrantha invasion tended to result in higher average well color development, substrate richness, and functional diversity. Average utilization of specific substrate guilds was highest in M. micrantha monoculture. Principle component analysis of CLPP further indicated that M. micrantha monoculture was distinctly separated from the native area and the ecotones. In conclusion, M. Mikania invasion improved soil microbial biomass, respiration and utilization of carbon sources, and decreased qCO2, thus created better soil conditions, which in turn were more conducive to the growth of M. micrantha.

Soil microbial biomass, functional diversity and enzyme activity in glyphosate-resistant wheat–canola rotations under low-disturbance direct seeding and conventional tillage

As glyphosate-resistant (GR) crops are becoming common in agro-ecosystems, their effects on non-target soil organisms need to be monitored. We evaluated soil microbial biomass C (MBC), bacterial functional diversity and community structure, and dehydrogenase enzyme activity in a field experiment conducted at six sites on the Canadian prairies. Treatments consisted of a factorial arrangement of three GR wheat and GR canola crop frequencies and two tillage systems. GR crop frequencies were arranged in 4-yr wheat-canola-wheat-pea rotations, with GR wheat and GR canola in zero of four, two of four, or three of four possible GR crop frequencies. The two tillage systems were either low soil-disturbance direct-seeding (LDS) or conventional tillage (CT). MBC increased with increasing frequency of GR crops in two of 20 site-years in the rhizosphere, and had no effects in bulk soil. Depending on tillage, GR crop frequency also affected the functional diversity of rhizosphere soil bacteria in only two of 20 site-years, and had no effects in bulk soil. Shifts in the structures of bacterial communities related to GR crop frequency were detected, but they were few and inconsistent. In three of 22 cases (10 in rhizosphere+12 in bulk soil), the activity of dehydrogenase enzyme decreased with increasing frequency GR crops in both the rhizosphere and bulk soil. In five of 20 site-years, soil MBC in the rhizosphere was greater under CT than under LDS, regardless of GR crop frequency. In bulk soil, tillage affected soil MBC in five site-years, three of which had greater MBC under CT than LDS, and vice versa in the other two. Tillage affected the functional diversity of soil bacteria in the rhizosphere in three site-years, but the effects were not consistent. Similar inconsistent tillage-related patterns were observed in the community structures of bacteria. There were no tillage effects on bacterial diversity in bulk soil. Dehydrogenase enzyme activity was greater under LDS than under CT in three of four cases in which tillage had significant effects. Overall, GR crop frequency effects on soil microorganisms were minor and inconsistent over a wide range of growing conditions and crop management.

Microbial response to high severity wildfire in the southwest United States

Southwest United States ponderosa pine (Pinus ponderosa Dougl. ex Laws) ecosystems have received great attention due to fuel conditions that increase the likelihood of large-scale wildfires with severe fire behavior. The fire season of 2002 demonstrated these extreme fuel load conditions with the largest fires in southwest history. The Jemez District of the Santa Fe National Forest, New Mexico experienced a wildfire (Lake Fire Complex 08/26/02 to 09/01/02)) that consumed one complete replicate block that was part of the nationwide Fire/ Fire Surrogate (FFS) project. This event provided a unique opportunity to investigate wildfire effects on soil, and associated microbial populations. Pre-treatment sampling completed prior to the wildfire allowed resampling of the exact sites to investigate immediate post-fire effects. Soil microbial functional diversity and biomass were determined from the top 5 cm of mineral soil. Virgin Mesa and Tusa Tank FFS control and burn only blocks were used as controls since they had not been treated. We predicted that due to the direct impact of heating, that the high severity wildfire would reduce the size of the microbial biomass and possibly favor bacteria over fungi because of the apparent greater sensitivity of fungi to heat. We also expected that wildfire would not only alter the quantity of available C, but it would also change the quality of C remaining in the soil, and these two factors would alter the physiological capacity of the microbial community. Community level physiological profiles (Biolog), and laboratory estimates of C and N transformations suggest that there was a large change in the function of the soil microflora following a high-severity burn. Phospholipid fatty acid (PLFA) analysis of the microbial population shows significant decrease in the fungal and bacterial populations in the 0-5 cm layer of soil immediately following the fire. Wildfire resulted in a reduction in the size of the microbial biomass and a change in its functional and structural composition.

Functional Diversity and Size of Soil Microbial Communities Induced by Different Land Management Systems

Soil microorganisms drive nutrients cycling to a great extent, and they play an essential role in maintaining a stable soil ecosystem and ensuring sustainable forestry development. Land management has been proven to be a real factor in influencing soil quality. The purpose of this study was to investigate the effects of different land management techniques on soil microbial communities. There were four types of land management systems selected for this study: natural masson pine, Phyllostachy pubescens, Phyllostachys praecox, and vegetable. Soils were sampled from these four systems and assayed for soil microbial biomass carbon (MBC), community level substrate utilization pattern, functional diversity, and principle component analysis. Values of MBC were significantly different (P<0.05) from one another in the order of masson pine>Phyllostachy pubescens>Phyllostachys Praecox>vegetable. Analysis of community level substrate utilization pattern indicated that carbon source utilization and total activity by soil microorganisms were greater under the masson pine system than the other three systems (P<0.01). The functional diversities of soil microbial communities characterized as Shannon and McIntosh indexes were much richer in soil under masson pine system; Shannon index was 4.483, 4.241, 4.224, and 3.938 and McIntosh index was 13.51, 7.332, 6.272, and 6.261 for natural masson pine, Phyllostachy pubescens. Phyllostachys praecox, and vegetable systems, respectively. The results from the principle components analysis (PCA), based on the data of optical density (OD) at 120 h of incubation, showed that the value of the first principal component (PC1) of soil for natural masson pine was greater (P<0.05) than those for the other three systems. The difference in scores of the second principal component (PC2) between Phyllostachy pubescens, Phyllostachys praecox, and vegetable were not statistically different. The size and activity of soil microbial communities generally decreased with soil depth, with significant differences in soil MBC, community level substrate utilization pattern, and functional diversity indexes found between A and C horizons (P<0.01). It was concluded that land management systems had a great influence on soil microbial biomass, activity, and functional diversity.

Effects of continuous cucumber cropping and alternative rotations under protected cultivation on soil microbial community diversity

The diversity of soil microbial communities as affected by continuous cucumber cropping and alternative rotations under protected cultivation were evaluated using community level physiological profiles (CLPP) and random amplified polymorphic DNA (RAPD) analysis. The soils were selected from six cucumber cropping systems, which cover two cropping practices (rotation and continuous cropping) and a wide spectrum for cucumber cropping history under protected cultivation. Shannon–Weaver index and multivariate analysis were performed to characterize variations in soil microbial communities. Both CLPP and RAPD techniques demonstrated that cropping systems and plastic-greenhouse cultivation could considerably affect soil microbial functional diversity and DNA sequence diversity. The open-field soil had the highest Shannon–Weaver index (3.27 for CLPP and 1.50 for RAPD), whereas the lowest value occurred in the 7-year continuous protected cultivation soil (3.27 for CLPP and 1.50 for RAPD). The results demonstrated that continuous plastic-greenhouse cultivation and management can cause the reduction in the species diversity of the biota. Higher Shannon–Weaver index and coefficients of DNA sequence similarity were found in soils under rotation than those under continuous cropping. Cluster analysis also indicated that microbial community profiles of continuous cultivation soils were different from profiles of rotation soils. The reduction in diversity of microbial communities found in continuous cultivation soils as compared with rotation soils might be due to the differences in the quantity, quality and distribution of soil organic matter.

Soil microbial functional diversity response following nematocide and biocide amendments in a desert ecosystem

The aim of the current study was to gain a better understanding of the changes that occur in soil microbial community and in its functional diversity as a result of the use of nematocide and biocide inhibitors in natural ecosystems. Both inhibitors are known to have a great effect on the nematode community and total biota, playing an important role in soil food web and biota interactions. The experiment was set up in the Negev Desert using sixteen 1×1 m soil plots, to which two chemical inhibitors were applied: (a) a biocide, to eliminate the whole biotic community; and (b) a nematocide, to eliminate the nematode community in soil. In addition, water treatment was applied to the same soil plots, while untreated soil plots were used as control. Microbial functional diversity, together with abiotic parameters such as soil moisture and total organic carbon, was tested monthly in soil samples collected from the 0–10 and 10–20 cm soil layers. The results of the abiotic parameters showed similar patterns in the two soil layers regardless of the inhibitor treatments. An increase in soil water content followed rainfall patterns. Total organic carbon was low during the wet season and increased during the dry seasons. The Shannon–Weaver index value for microbial functional diversity was found to increase in spring after the wet season in both soil layers. In the upper soil layer, an increase was observed both in the inhibitor and water treatments. However, the increase in the water treatment lasted longer compared to the increase observed in the inhibitor-treated soil plots. In the 10–20 cm soil layer, a different pattern was observed: an increase in microbial functional diversity was observed in the inhibitor-treated soil plots, while an increase in the water-treated soil plots was seen at a later stage. Principal Component Analysis was also conducted, revealing different patterns between inhibitors and water treatments on both a temporal scale, when changes from a homogeneous to heterogeneous consumption pattern were observed, and in the nature of communities that proliferate in the soil. Differences were also observed in the microbial community between the upper 0–10 and the lower 10–20 cm soil layers, where an opposite pattern of substrate consumption was observed. This study emphasizes the important role the biotic component plays in the soil of an arid climate, studying the long-term effects of key species elimination on the microbial community in desert soil.

Pilot-scale electrokinetic treatment of a Cu contaminated red soil

A pilot-scale experiment for electrokinetic treatment of 700 kg of copper contaminated red soil was conducted using a constant voltage of 80 V. Dynamic removal percentages of Cu from the soil and energy consumption during the treatment were evaluated together with changes of soil pH, electrical conductivity and soil microbial functional diversity before and after the electrokinetic treatment. The results indicate that 76% of Cu was successfully removed from the soil after 140 d of treatment when lactic acid was used as enhancing reagent for adjusting the catholyte pH and dissolving soil Cu by complexation, and the pilot-scale electrokinetic experiment consumed electric energy of 224 kW h t −1 soil. The post-treatment soil pH values decreased about 0.1–1.6 units compared with the initial value (pH 4.8), and soil electrical conductivities in most of soil sections also significantly decreased. Soil microbial functional diversity varied after the electrokinetic treatment, particularly the increase of substrate richness index, which is possibly due to the stimulation of lactic acid that was introduced into the soil column during the experiment.

Effects of Irrigation and Fertilization on Soil Microbial Biomass and Functional Diversity

Optimal water and nutrient treatment effects on soil mi-crobial characteristics, including microbial functional diversity and mi-crobial biomass carbon (C) and nitrogen (N) were assessed at a loblolly pine plantation on a Sandhills site after 6 years of continuous fertilization and irrigation. Fertilization significantly increased soil C and N and microbial C and N. Irrigation significantly increased soil C and N, and microbial C. Fertilization, irrigation, and their interaction changed soil microbial selection of carbon compounds, but did not influence the numbers of carbon compounds utilized by soil microbes, as measured by the BIOLOG method suggesting that soil microbial species may have changed. The increases in soil microbial biomass and soil C and N indicate that the fertilization and irrigation treatments have had a positive effect on soil productivity on this very sandy site.

Spatial variation of soil enzyme activities and microbial functional diversity in temperate alley cropping systems

Spatially dependent patterns in microbial properties may exist in temperate alley cropping systems due to differences in litter quality and microclimate in areas under trees compared to those in the alleys. The effect of tree row location was evaluated for its impact on soil enzyme activities and Biolog substrate use patterns. Soils were sampled to a depth of 30 cm at the tree row and at the middle of the alley at two sites: a 21-year-old pecan (Carya illinoinensis)/bluegrass (Poa trivials) intercrop (Pecan site) and a 12-year-old silver maple (Acer saccharinum)/soybean (Glycine max)–maize (Zea mays) rotation (Maple site). Sampling was done in fall 2001 and summer 2002. β-Glucosidase activities, Biolog patterns expressed as average well color (AWC), substrate richness, and Shannon diversity index, and total Kjeldahl nitrogen (TKN) were significantly higher (P<0.05) in the tree row than at the middle of the alley for surface soils at the Pecan site. Fluorescein diacetate (FDA) hydrolytic activity was also higher at the tree row for soils sampled in the fall, but did not differ significantly for soils sampled in the summer. At the Maple site, AWC and substrate richness were significantly higher at the tree row for soils sampled in 2001. Soil volumetric water content and temperature were generally lower in the tree row at the Maple site. The results of this study suggest that functionally different microbial populations may be present under pecan trees compared to cropped alleys which may promote disparities in nutrient availability necessitating differential long-term nutrient management in such alley cropping systems.

Biodiversity of indigenous tussock grassland sites in Otago, Canterbury and the central North Island of New Zealand III. Soil microorganisms

Bacterial and fungal communities in indigenous tussock grassland soils were studied at four locations, Mt Benger and Deep Stream (Otago), Cass (Canterbury) and Tukino (central North Island). Soil samples collected from inter‐tussock and tussock areas were used to enumerate total culturable bacteria (colony forming units (CFU)) as well as a number of specific groups of bacteria, fungal types and diversity, and soil microbial functional diversity. Soil microbial biomass carbon (C) and nitrogen (N) as well as extractable C and N were also determined. Fungal populations were lowest at Mt Benger while fluorescent Pseudomonas was lowest at Cass. In these indigenous soils, bacterial CFU were c. 30 times lower and fungal populations c. 10 times greater than in developed New Zealand pastoral soils. CFU of bacteria in complex media (r‐strategists) were similar in magnitude to bacteria growing on weak CA medium (K‐strategists). The microbial biomass C in indigenous grassland soils were also significantly greater than that found in developed pastoral soils, possibly due to dominance of fungi in indigenous soils. Microbial C and N were lower in Cass and Tukino sites compared to Mt Benger and Deep Stream sites. Microbial nitrogen was also significantly greater (P < 0.001) in inter‐tussock than under tussock samples. The functional diversity of soil microbes, was significantly greater (P< 0.01) in inter‐tussock samples compared to tussock samples at all sites except Mt Benger. The total microbial activity, as measured by the colour development in Biolog plates (Average Well Colour Development (AWCD)), was low in Cass soil compared to others. Eighty‐three types of fungi belonging to 30 genera were recovered from the four sites. The diversity of fungi found in Otago sites was greater than in the other two sites (P < 0.001). Fusarium spp. that are often common in pastoral soils were conspicuous by their rarity in indigenous soils.

Soil microbial biomass, functional diversity and crop yields following application of cattle manure, hog manure and inorganic fertilizers

Soil biological properties can be significantly impacted by land management. Cattle manure, hog manure or inorganic fertilizers were applied annually or triennially in field trials conducted at two sites over 3 yr. A control treatment without manure or fertilizer was also included. Canola (Brassica napus) was grown in year 1, hulless barley (Hordeum vulgare) in year 2, and wheat (Triticum aestivum) in year 3. Where effects were significant, cattle manure increased soil microbial biomass C (MBC) by 26% to three-fold, hog manure by 31% to two-fold, and inorganic fertilizers reduced MBC by 20–64%. Similar effects, except the reduction by inorganic fertilizers, were observed for functional diversity of soil bacteria (Shannon index, H′ ). At one site, where crop yields were recorded for 3 yr, hog manure produced greater grain yields (75% increase over the control) than the rest of the treatments (49% increase by cattle manure) in year 1, but cattle manure out-yielded other treatments thereafter, when it increased yields by 25–50%. Cattle manure out-yielded other treatments even when nutrient uptake from inorganic fertilizers was the highest, implying that other factors also influenced crop yields. At the other site, crop yields were recorded only in year 1, and all soil amendments increased canola yields about three-fold relative to the control. Frequency of application usually had no effects on MBC or H′, but the triennial application rate of inorganic fertilizers or hog manure produced lower crop yields than annual applications in year 1. Key words: Functional diversity, Gray Luvisol, manure quality, NPK fertilizers, soil microbial communities

Microbial community changes in heathland soil communities along a geographical gradient: interaction with climate change manipulations

Climate change constitutes a serious threat for European heathlands as unlike other sources of damage, such as over-grazing, local remediation is not a possibility. Within the large pan-European projects, CLIMOOR and VULCAN, the effect of periodic drought and increased temperature were investigated in four heathland ecosystems along a geographical and climatic gradient across Europe. Fluorogenically labelled substrates for four enzymes (glucosidase, sulphatase, phosphatase, leucine amino peptidase) were used to measure extra-cellular enzyme activity in soil samples from each of the CLIMOOR sites. Microbial extra-cellular enzyme production is linked to microbial activity as well as soil physico-chemical properties, making soil enzymes one of the more reactive components of terrestrial ecosystems and potentially excellent indicators of soil microbial functional status and diversity. Across all sites and over all the substrates, organic matter content was exponentially, inversely related to enzyme activity. Although the increase in temperature produced by the CLIMOOR roofs was small (on average 0.9 °C), this was sufficient to increase enzyme activity in all sites (on average by 45%). The increase was within the range of seasonal variability at each of the sites. The effect of drought on enzyme activity was more pronounced in the Northern European sites than the southern European, and most moisture limited, site. This suggests that the effect of temperature increases may be observed across all regions; however, the soils of northern Europe may be more sensitive to changes in rainfall patterns than more moisture limited Southern European soils.

Microbial biomass and bacterial functional diversity in forest soils: effects of organic matter removal, compaction, and vegetation control

The effects of organic matter removal, soil compaction, and vegetation control on soil microbial biomass carbon, nitrogen, C-to-N ratio, and functional diversity were examined in a 6-year loblolly pine plantation on a Coastal Plain site in eastern North Carolina, USA. This experimental plantation was established as part of the US Forest Service's Long Term Soil Productivity Study. Sampling was undertaken on eight treatments within each of three blocks. Treatments sampled included main 2×2 factorial treatments of organic matter removal (stem-only or complete tree plus forest floor) and compaction (none or severe) with split-plot treatment of vegetation control (none or total vegetation control). Two blocks were located on a somewhat poorly drained, fine-loamy, siliceous, thermic aeric Paleaquult (Lynchburg soil) and one on a moderately well drained, fine-loamy, siliceous, thermic aquic Paleudult (Goldsboro soil). Soil microbial C and N were positively related with soil C and N, respectively. Microbial C and N on the Lynchburg soil were higher than those on the Goldsboro soil. Organic matter removal decreased microbial N. Compaction reduced microbial C-to-N ratio. Vegetation control decreased microbial C and C-to-N ratio. The number of C compounds utilized by bacteria was not affected by soil type or treatment. However, soil types and treatments changed bacterial selections for a few C compounds on BIOLOG plates. Soil microbial properties varied more due to the natural soil differences (soil type) as compared with treatment-induced differences.

Kemira broadens Ecocat operations

The use of soil microbial and biochemical parameters could play an important role in monitoring effects of shrub encroachment in grasslands due to their rapid reaction to environmental fluctuations. We compared total organic carbon (Corg), soil total nitrogen (TON), microbial biomass, basal respiration, soil microbial quotient (Cmic/Corg) species and functional diversity between pairs of neighbouring, leguminous shrub-encroached and open grassland plots along a rainfall gradient (300 mm to 1500 mm mean annual precipitation (MAP)) in South Africa. "In semi-arid regions, soil Corg was higher in shrub-encroached grasslands than in open grasslands while the reverse was true in humid regions (1500 mm MAP)". Soil total nitrogen was generally higher in the shrub-encroached grasslands compared to open grasslands. Soil microbial biomass and basal respiration was higher in shrub-encroached grassland across the precipitation gradient. There was also a difference in microbial functional diversity between the encroached and adjacent open grasslands, which was most evident in the semi-arid regions. Our results suggest that land-cover change might influence microbial properties along the rainfall gradient.

Soil microbial biomass and diversity respond to tillage and sulphur fertilizers

There is little information on the effects of S management strategies on soil microorganisms under zero tillage systems o n the North American Prairies. Experiments were conducted to examine the effects of tillage and source and placement of S on soil microbial biomass (substrate induced respiration) and functional diversity (substrate utilization patterns) in a canola-wheat rotation under conventional and zero tillage systems at three sites in Gray Luvisolic and Black Chernozemic soils. Conventional tillage significantly reduced microbial biomass and diversity on an acidic and C-poor Luvisolic soil, but it had mostly no significant effects on the near-neutral, C-rich Luvisolic and Chernozemic soils, which underlines the importance of soil C in maintaining a healthy soil. Sulphur had no significant effects on soil microbial biomass, and its effects on microbial diversity were more frequent on the near-neutral Luvisol, which was more S-deficient, than on the acidic Luvisol or the Chernozem. Significant S effects on microbial diversity were observed both in the bulk soil (negative effects, compared with the control) and rhizosphere (positive effects) of the acidic Luvisol, but all significant effects (positive) were observed in root rhizospheres in the other soils. Sulphur by tillage interactions on acidic Luvisolic soil indicated that the negative effects of S in bulk soil occurred mostly under zero tillage, presumably because the fertilizer is concentrated in a smaller volume of soil than under conventional tillage. Sulphate S effects, either negative or positive, on microbial diversity were usually greater than elemental S effects. Therefore, S application can have direct, deleterious effects on soil microorganisms or indirect, beneficial effects through crop growth, the latter presumably due to increased root exudation in the rhizosphere of healthy crops. Key Words: Biolog, conservation tillage, microbial biodiversity, rhizosphere, soil biological quality, S fertilizer type and placement

Soil microbial community and bacterial functional diversity at Machu Picchu, King George Island, Antarctica

The objective of this study was to evaluate the potential contribution of the soil microbial community in the vicinity of two plant covers, Sanionia uncinata and Deschampsia antarctica, at Machu Picchu Station, King George Island, Antarctica. Soil samples were collected at the study site during the southern (pole) summer period from 0–5 cm and 5–10 cm depths, for chemical and biological analyses. Soil microbial biomass reached a maximal value of 144 µg g–1 in soil samples taken from under the S. uncinata upper layer plant. qCO2 ranged from 167 to 239 µg CO2.mgCmic.h–1 at the 0–5 and 5–10 cm depths, respectively. CO2 evolution showed values of 54.3 mg.m–2 h–1 beneath plant cover and 55.9 mg.m–2 h–1 in the open space. CO2 evolved by substrate induced respiration in the soil samples taken under the plant cover in the summer period, oscillated between 0.25 and 4.78 µg CO2 g–1 h–1. The data obtained from this short study may provide evidence that both activity and the composition and substrate utilization of the microbial community appear to change substantially across the moisture level and sample location.

Decreases in Soil Microbial Function and Functional Diversity in Response to Depleted Uranium

AbstractA soil microcosm experiment was used to analyze effects of depleted uranium (DU) on soil function, and the concomitant changes in bacterial functional diversity. Uranium treatment levels were 0, 50, 500, 5000, 10 000, and 25 000 mg DU kg−1 soil. Three measures of soil function were made. Overall soil biological activity was assessed via measurement of soil respiration. Decomposition was assessed by measurement of mass loss of four different plant litter types: wood sticks, cellulose paper, high‐N grass, and low‐N grass. Mineral N availability in the microcosms was estimated using ion‐exchange resin bags. Functional diversity of the microcosms was analyzed through the use of the Biolog‐system of sole‐C‐utilization patterns. Soil respiration was the most sensitive measure of functional changes, with significant decreases observed starting at the 500 mg kg−1 treatment. No differences in N availability were observed across the U treatments. Litter decomposition was significantly decreased (P &lt; 0.05) at the 25 000 mg kg−1 level relative to the control for all litter types except the high‐N grass. Wood decomposition was reduced by 84% at the 25 000 mg kg−1 treatment, cellulose paper by 68%, and low‐N grass by 15%. Decreases in the functional diversity of the bacterial community were related to the observed decrease in soil respiration, and to the greater effect on decomposition of the lower‐quality litter types.