To assess the recovery trajectory and self-maintenance of restored ecosystems, a successional gradient (1, 3, 5, 15, and 30 years after abandonment) was established in a sub-alpine meadow of the eastern Tibetan Plateau in China. Plant communities and soil carbon and nitrogen properties were investigated and analyzed. Regression analyses were used to assess the models (linear or quadratic) relating measures of species richness, soil carbon and nitrogen properties to fallow time. We found that species richness (S) increased over the first 20 years but decreased thereafter, and aboveground biomass showed a linear increase along the fallow time gradient. The richness of different functional groups (forb, grass and legume) changed little along the fallow time gradient, but their corresponding above ground biomass showed the U-shaped, humped or linear pattern. Soil microbial carbon (MBC) and nitrogen (MBN) in the upper 20 cm showed a U-shaped pattern along the fallow time gradient. However, soil organic carbon (Corg) and total nitrogen (TN) in the soil at depth greater than 20 cm showed significant patterns of linear decline along the fallow time gradient. The threshold models of species richness reflected best the recovery over the 15 year fallow period. These results indicated that fallow time had a greater influence on development of the plant community than soil processes in abandoned fields in sub-alpine meadow ecosystem. These results also suggested that although the succession process did not significantly increase soil C, an increase in microbial biomass at the latter stage of succession could promote the decomposability of plant litter. Therefore, abandoned fields in sub-alpine meadow ecosystem may have a high resilience and strong rehabilitating capability under natural recovery condition.

Over-grazing and large-scale monocultures on the Loess plateau in China have caused serious soil erosion by water and wind. Grassland revegetation has been reported as one of the most effective counter measures. Therefore, we investigated soil aggregation, aggregate stability and soil microbial activities as key parameters for soil remediation through grassland revegetation.The results showed that soil microbial biomass carbon (Cmic) and microbial biomass nitrogen (Nmic) increased under revegetated grass communities compared to cropland and overgrazed pastures and were higher in surface layers (0–10 cm) than in the subsurface (10–20 cm). Although there are variations between the four investigated grassland communities, their values were 10 to 50 times higher in comparison to the cropland and overgrazed pastures, similar to the increase in soil enzyme activities, such as β-glucosidase and β-glucosaminidase.Soil aggregate stability (SAS) showed clear differences between the different land uses with two main soil aggregate fractions measured by ultra sound: < 63 μm and 100–250 μm, with approximately 70% and 10% of the total soil volume respectively. We also found positive correlations between SAS and soil microbial parameters, such as Cmic, Nmic, and soil enzyme activities. From this, we concluded that revegetation of eroded soils by grasses accelerates soil rehabilitation.

The present study was conducted to determine the spatial heterogeneity of bulk density, soil moisture, inorganic N, microbial biomass C, and microbial biomass N in the ridge tillage system of Turiel compared to conventional mouldboard ploughing on three sampling dates in May, July, and August. The soil sampling was carried out under vegetation representing the ridge in a high spatial resolution down the soil profile. Bulk density increased with depth and ranged from 1.3gcm⁻³ at 10cm depth to 1.6gcm⁻³ at 35cm in ploughed plots and from 1.0gm⁻³ at 5cm to 1.4gm⁻³ at 35cm in the ridges. In the ploughed plots, the contents of microbial biomass C and microbial biomass N remained roughly constant at 215 and 33μgg⁻¹ soil, respectively, throughout the experimental period. The microbial biomass C/N ratio varied in a small range around 6.4. In the ridged plots, the contents of microbial biomass C and microbial biomass N were 5% and 6% higher compared to the ploughed plots. Highest microbial biomass C contents of roughly 300μgg⁻¹ soil were always measured in the crowns in July. The lowest contents of microbial biomass C of 85-137μgg⁻¹ soil were measured in the furrows. The ridges showed strong spatial heterogeneity in bulk density, soil water content, inorganic nitrogen and microbial biomass.

Central to soil health and plant productivity in natural ecosystems are in situ soil microbial communities, of which mycorrhizal fungi are an integral component, regulating nutrient transfer between plants and the surrounding soil via extensive mycelial networks. Such networks are supported by plant-derived carbon and are likely to be enhanced under coppiced biomass plantations, a forestry practice that has been highlighted recently as a viable means of providing an alternative source of energy to fossil fuels, with potentially favourable consequences for carbon mitigation. Here, we explore ways in which biomass forestry, in conjunction with mycorrhizal fungi, can offer a more holistic approach to addressing several topical environmental issues, including 'carbon-neutral' energy, ecologically sustainable land management and CO₂ sequestration.

Although belowground ecosystems have been studied extensively and soil biota play integral roles in biogeochemical processes, surprisingly we have a limited understanding of global patterns in belowground biomass and community structure. To address this critical gap, we conducted a meta-analysis of published data (> 1300 datapoints) to compare belowground plant, microbial and faunal biomass across seven of the major biomes on Earth. We also assembled data to assess biome-level patterns in belowground microbial community composition. Our analysis suggests that variation in microbial biomass is predictable across biomes, with microbial biomass carbon representing 0.6-1.1% of soil organic carbon (r² = 0.91) and 1-20% of total plant biomass carbon (r² = 0.42). Approximately 50% of total animal biomass can be found belowground and soil faunal biomass represents < 4% of microbial biomass across all biomes. The structure of belowground microbial communities is also predictable: bacterial community composition and fungal : bacterial gene ratios can be predicted reasonably well from soil pH and soil C : N ratios respectively. Together these results identify robust patterns in the structure of belowground microbial and faunal communities at broad scales which may be explained by universal mechanisms that regulate belowground biota across biomes.

Soil microbial organisms are central to carbon (C) and nitrogen (N) transformations in soils, yet not much is known about the stable isotope composition of these essential regulators of element cycles. We investigated the relationship between C and N availability and stable C and N isotope composition of soil microbial biomass across a three million year old semiarid substrate age gradient in northern Arizona. The δ15N of soil microbial biomass was on average 7.2[per thousand] higher than that of soil total N for all substrate ages and 1.6[per thousand] higher than that of extractable N, but not significantly different for the youngest and oldest sites. Microbial 15N enrichment relative to soil extractable and total N was low at the youngest site, increased to a maximum after 55,000 years, and then decreased slightly with age. The degree of 15N enrichment of microbial biomass correlated negatively with the C:N mass ratio of the soil extractable pool. The δ13C signature of soil microbial biomass was 1.4[per thousand] and 4.6[per thousand] enriched relative to that of soil total and extractable pools respectively and showed significant differences between sites. However, microbial 13C enrichment was unrelated to measures of C and N availability. Our results confirm that 15N, but not 13C enrichment of soil microbial biomass reflects changes in C and N availability and N processing during long-term ecosystem development.

Because soil CO₂ efflux or soil respiration (R S) is the major component of forest carbon fluxes, the effects of forest management on R S and microbial biomass carbon (C), microbial respiration (R H), microbial activity and fine root biomass were studied over two years in a loblolly pine (Pinus taeda L.) plantation located near Aiken, SC. Stands were six-years-old at the beginning of the study and were subjected to irrigation (no irrigation versus irrigation) and fertilization (no fertilization versus fertilization) treatments since planting. Soil respiration ranged from 2 to 6μmolm⁻² s⁻¹ and was strongly and linearly related to soil temperature. Soil moisture and C inputs to the soil (coarse woody debris and litter mass) which may influence R H were significantly but only weakly related to R S. No interaction effects between irrigation and fertilization were observed for R S and microbial variables. Irrigation increased R S, fine root mass and microbial biomass C. In contrast, fertilization increased R H, microbial biomass C and microbial activity but reduced fine root biomass and had no influence on R S. Predicted annual soil C efflux ranged from 8.8 to 10.7MgCha⁻¹ year⁻¹ and was lower than net primary productivity (NPP) in all stands except the non-fertilized treatment. The influence of forest management on R S was small or insignificant relative to biomass accumulation suggesting that NPP controls the transition between a carbon source and sink in rapidly growing pine systems.

The effect of integrated nutrient management (INM) on active pools of soil organic matter (SOM) under maize-wheat cropping sequence of a Typic Haplustept was studied in a long-term field experiment initiated during kharif 1997 at the Instructional Farm of Rajasthan College of Agriculture, Udaipur. Effect of varying doses of N, NP, NPK with FYM, Zn, S and Azotobacter on active pools of SOM viz., soil microbial biomass carbon, nitrogen and phosphorus; water soluble carbon; water soluble carbohydrates and dehydrogenase activity after 9th year of maize-wheat crop rotation was studied. Application of FYM @ 20 t ha-1 significantly increased the microbial biomass carbon (SMB-C), water soluble carbon (WS-OC) and water soluble carbohydrates (WS-CHO), whereas maximum amount of soil microbial biomass nitrogen (SMB-N) and dehydrogenase activity (DHA) was found in 100; NPK + 10 t FYM ha-1 treatment and maximum soil microbial biomass phosphorus (SMB-P) was observed in 150; NPK treatment compared to sole use of chemical fertilizers. Integrated use of FYM with chemical fertilizers or use of FYM alone exerted significant effect on the active pools of soil carbon. The C/N ratio was highly and significantly correlated with soil microbial biomass carbon (SMB-C), soil microbial biomass nitrogen (SMB-N), water soluble carbon (WS-OC), water soluble carbohydrates (WS-CHO) and dehydrogenase activity (DHA) under maize crop.

Intensive greenhouse vegetable-production systems commonly utilize excessive fertilizer inputs that are inconsistent with sustainable production and may affect soil quality. Soil samples were collected from 15 commercial greenhouses used for tomato production and from neighboring fields used for wheat cropping to determine the effects of intensive vegetable cultivation on soil microbial biomass and community structure. Soil total nitrogen (N) and organic-matter contents were greater in the intensive greenhouse tomato soils than the open-field wheat soils. Soil microbial carbon (C) contents were greater in the greenhouse soils, and soil microbial biomass N showed a similar trend but with high variation. The two cropping systems were not significantly different. Soil microbial biomass C was significantly correlated with both soil total N and soil organic matter, but the relationships among soil microbial biomass N, soil total N, and organic-matter content were not significant. The Biolog substrate utilization potential of the soil microbial communities showed that greenhouse soils were significantly higher (by 14%) than wheat soils. Principal component (PC) analysis of soil microbial communities showed that the wheat sites were significantly correlated with PC1, whereas the greenhouse soils were variable. The results indicate that changes in soil microbiological properties may be useful indicators for the evaluation of soil degradation in intensive agricultural systems.