An investigation was carried out to assess the effect of Prosopis cineraria on some ecological parameters of soil microfungi in an arid region of western Rajasthan. Nine soil samplings were done from the undercanopy of the tree and from the open areas for 2 years. Undercanopy soil of the tree possessed higher population of fungi and fungal biomass as compared to open field. Fungal parameters varied among different sampling periods. Soil samples analysed during different seasons for soil mycoflora revealed maximum fungal populations in rainy months. Fungal biomass and fungal population are directly proportional to organic matter (r= 0·78;·0·78, respectively). The population of fungi is linearly related to fungal biomass with higher (r= 0·92) correlation at undercanopy as compared to open area (r= 0·72). Soil and climatic factors are responsible for enormous variation in fungal biomass. Organic carbon in the undercanopy is the critical factor that explained 76% variation in fungal biomass. Climatic factors did not affect undercanopy fungal biomass to any measurable extent; however, fungal biomass in the open area varied significantly due to rainfall and the model explained 73% variations in fungal biomass.

Soil microorganisms were metabolically activated by addition of glucose in one large initial ration or eight repeated additions without adding a nitrogen source. We tested whether the adenylate energy charge (AEC = (ATP + 0.5 x ADP)/(AMP + ADP + ATP) reflects this physiological activation. We compared the effects of glucose addition on adenylates with the development of microbial biomass C and biomass N from 6 h onwards during an 8 d incubation at 25 degrees C. Initial addition of 1600 microgram glucose C g(-1) soil increased microbial biomass C within 24 h from 152 to a maximum value of 469, dropping to 291 microgram g(-1) soil. In the treatment with daily addition of glucose, i.e. 8 x 200 microgram glucose C g(-1) soil, microbial biomass C increased within 24 h to roughly constant 325 mg g(-1) soil throughout the experiment. Microbial biomass N showed a smaller increase than biomass C after glucose addition, leading to increased microbial biomass C/N ratios after glucose addition, especially in the treatment with initial glucose addition. The ATP-to-microbial biomass C ratio varied in our treatments between 3.2 and 10.1 micromol g(-1) C and showed a significant negative relationship with the microbial biomass C/N ratio (r = -0.70, P < 0.0001). The average ATP-to-microbial biomass C ratios in the different treatments were 5.1 (initial glucose addition), 6.9 (daily glucose addition) and 8.9 (control) micromol g(-1). It was not possible to increase the AEC with glucose addition. The AEC was very similar in unamended and amended soils, in agreement with previous results.

The turnover times of soil microbial biomass carbon (biomass C) and phosphorus (biomass P) were estimated from the declines in biomass 14C and 32P following the addition to soil of 14C-labelled glucose with added KH2(32)PO4 or with the separate addition of ryegrass which had been doubly labelled with 14CO2 and KH2(32)PO4 (both at 1000 microgram C and about 10 microgram added P g(-1) soil). The labelled substrates were added separately to an UK grassland soil which was then incubated for 60 days at 25 degrees C and 40% water holding capacity. Addition of 32P caused a considerable displacement (up to 60%) of non-labelled P in the biomass of soils also given glucose. There was also significant displacement of non-labelled biomass P in soils given 32P only. With ryegrass, the labelled P addition increased the total biomass P pool size, rather than displacing native biomass P. However, with biomass C the increase in total biomass C pool size was larger than the displacement of original biomass C at this relatively low addition of substrate C. Under the above incubation conditions biomass C had a turnover time of about 82 days for glucose and 95 days for ryegrass. The turnover times of biomass P for glucose was about 37 and 42 days for ryegrass. The much shorter turnover time of biomass P than C may be because P is much more labile within the microbial cell than C. For example, unlike C, little P is generally located in the cell walls of micro-organisms, which turnover more slowly than the cytoplasmic components. These results illustrate the large potential of biomass P turnover as a source of P for plants, particularly in 'low input' systems.

The interrelationships between biomass characteristics and soil properties (including in situ annual nitrogen mineralization) were statistically investigated in a descriptive study using a broad range of plant communities in unfertilized road verges. Not only the dependence of biomass characteristics on soil properties, but also the possibility of inferring soil nutrient availability from biomass characteristics was investigated. Possible effects of vegetation management (mowing) and overstory trees (shading) were accounted for. Annual aboveground biomass production was mainly explained by annual N mineralization, average soil moisture content, shading intensity, and soil pH (optimum at pH-CaCl2 5.7). Average tissue nutrient concentrations were primarily explained by mowing frequency, shading intensity, the availability of the corresponding soil nutrient, and pH (optima between 5.5 and 6.0). Results also implied that making hay twice per year removes more nutrients than a single cut at the end of the season. N mineralization may be inferred from the aboveground biomass production, but only across sites with equal moisture and shading conditions (partial r = 0.74). In general, it is concluded that nutrient availability can only be deduced from biomass characteristics if sites with similar moisture content are compared. The only exception to this general rule is K availability. The latter was mainly indicated by the K concentration in vegetation biomass (partial r = 0.80), and the confounding effect of other factors was small (bivariate r was still 0.71). Soil available P could not be satisfactorily indicated, even across sites with equal moisture and shading conditions. Also, different nutrients appeared to interact, and should not be considered in isolation. K was the only element with a strong relationship between its soil and tissue concentration. For the other nutrients, tissue concentrations did not depend predominantly on the soil availability. It seems most likely that the species occurring in semi-natural vegetation are adapted to the local fertility by means of their physiology or growth rate. It is concluded that, with the possible exception, of K, simple relationships between soil properties and biomass characteristics cannot be expected over wide environmental gradients.

The soil nutrient status and microbial biomass at three stages of first year cropping in an 8-year jhum (slash-and-burn agriculture) cycle system were determined and compared to an adjacent humid tropical forest in Arunachal Pradesh, north-eastern India. Soil pH increased after burning and decreased as the cultivation progressed in the jhum field. Soil organic carbon, available-P,total Kjeldahl nitrogen, ammonium-N and nitrate-N decreased as the duration of cultivation increased. Microbial biomass C, N, and P were high in the forest stand. Microbial biomass C increased gradually as cultivation progressed, while microbial biomass N and P showed a post-burn decreasing trend. Bacterial and fungal populations were drastically reduced following slash burning. The study indicates that first-year cropping may result in temporary pattern homogenization of soil nutrient cycling, but can have drastic effects with continued slashing and burning for long-term agriculture.

We evaluated the temporal variation of microbial biomass C, beta-glucosidase, acid phosphomonoesterase (acP), alkaline phosphomonoesterase (alP), and protease activity over 18 consecutive months. The likely causes for the seasonal variability at a non-degraded and a degraded site in south-western Nigeria were identified. Microbial biomass, alP, and beta-glucosidase activity were sensitive indicators of soil quality changes over time. Microbial biomass C correlated significantly with soil moisture conditions and soil organic matter-related parameters. AlP and beta-glucosidase activities were not controlled by climatic conditions over the course of two rainy seasons and one dry season but were temporally related to microbial biomass C and total C and N. Due to the steadiness of the alP activity over time the enzyme is considered a suitable indicator with which to monitor long-term changes of soil quality. Single sampling during the course of a year is adequate. Both microbial biomass and beta-glucosidase activity fluctuated highly. They were sensitive indicators to monitor short-term variations of soil quality with. Sampling for microbial biomass ought to be limited to the rainy seasons, whereas the measurement of beta-glucosidase activity need not be restricted seasonally. Due to the short-term variability found, sampling should be repeated. AcP and protease activity fluctuated highly during the course of a year and exhibited pronounced inter-seasonal differences. The marked seasonal changes could not be ascribed to soil moisture conditions and only poorly to major ecological soil processes. This was more pronounced for acP than for protease. Hence, neither parameter was considered a sensitive and meaningful indicator of soil quality changes over time.

Spatial characteristics of soil microbial community structure and selected soil chemical factors were analyzed in soil surrounding Agropyron smithii (Western wheatgrass) and Artemisia tridentata (Wyoming big sagebrush) plants in sites reclaimed after surface mining and adjacent undisturbed sites in Wyoming. Microbial biomass C (MBC) and fatty acid methyl ester (FAME) biomarkers for total biomass, bacteria, and fungi were used as indicators of soil microbial community abundance and structure. In soil 20 years after reclamation FAME total microbial biomass, bacterial and fungal biomarkers, MBC and soil organic matter (SOM) averaged only 20, 16, 28, 44 and 36% of values found in undisturbed soils. In contrast to undisturbed soils, FAME biomarkers and MBC of reclaimed soils exhibited spatial correlation up to 42 cm. Reclaimed soils also exhibited localized enrichment of bacterial, fungal, and total microbial biomass, as well as depletion of inorganic N concentrations, around plant bases (<10 cm), suggesting relatively poor soil exploration by roots and microorganisms compared to the undisturbed ecosystem. Strong spatial stratification of undisturbed SOM and soil NH4(+) pools was found with highest concentrations on the leeward side of shrubs, likely due to localized changes in microclimate and plant litter deposition. This indicates that shrub cover plays a central role in the establishment of site heterogeneity and regulation of ecological processes, such as C and N mineralization and immobilization, which has important implications for reclamation.

In arable systems, seasonal fluctuations of microbiological properties can be significant. We hypothesized that adaptation to soil environmental conditions may contribute to the variation observed, and this was examined by characterization of different microbial community attributes under a range of soil conditions. Soil was sampled from no-till and chisel-tilled fields within a long-term experiment in eastern Washington during growth of spring wheat (Triticum aestivum). The range of soil environmental conditions covered was extended by amendment of crop residues. Soil samples were characterized with respect to biomass N and biomass P, substrate utilization dynamics, phospholipid fatty acid (PLFA) profiles and whole-soil fatty acid (MIDI-FA) profiles, and with respect to soil environmental variables (bulk density, soil organic C [SOC], temperature, moisture, and inorganic N and P). Bacterial and fungal lipid biomarkers were negatively correlated (P < 0.001), confirming that these subsets of fatty acids are associated with contrasting components of the microbial biomass. Biomass N was closely associated with soil conditions, notably N availability. The proportion of substrates used with no apparent lag phase decreased during summer and was negatively correlated with lipid stress indicators. Cyclopropyl fatty acids accounted for more than 60% of the variation in bacterial PLFA. These observations suggest that adaptation to environmental stresses was partly responsible for the microbial dynamics observed. Tillage practice had little effect on the relationships between soil conditions and microbiological properties. The results showed that MIDI-FA included a significant background of nonmicrobial material and was less sensitive to soil environmental conditions than PLFA.