To better understand how soil temperature will influence the responses of boreal trees to increasing atmospheric [CO2], one-year-old jack pine (Pinus banksiana lamb.), black spruce (Picea mariana [Mill.] B.S.P.), white spruce (Picea glauca [Moench] Voss), and current-year white birch (Betula paperifera Mash) seedlings were subjected to two [CO2] (360 versus 720 μmol mol-1) and three soil temperatures (T (soil) = 7, 17, and 27°C initially, increased to 10, 20, and 30°C 3 months later) for 4 months. The low T (soil) significantly suppressed height growth, stem biomass, and total biomass in white birch, black and white spruce, root collar diameter (RCD), and foliage biomass in white birch and white spruce, as well as root biomass in white birch under both ambient and elevated [CO2] and in white spruce under ambient [CO2]. This low T (soil) effect was much more significant in white birch than in the conifers. The [CO2] elevation significantly increased RCD, foliar biomass, and total biomass of the four species at all soil temperatures, stem biomass of all the species at the low T (soil), and the root biomass of white birch at intermediate T (soil). The data suggest that the [CO2] elevation compensated for the negative effects of low T (soil), e.g., the low T (soil) significantly decreased the height and total biomass of black and white spruce at ambient [CO2], but not at elevated [CO2]. The high T (soil) had much smaller negative effects on growth and biomass than did the low T (soil). Jack pine was the least responsive to T (soil) and [CO2]. In general, the ratios of stem, foliage, and root mass to total mass were much less responsive to the treatments than total or component biomass. Neither treatment significantly affected the volume/mass ratio of the stem in any of the four species. The data suggest that white birch and white spruce will benefit the most and jack pine will benefit the least from the increasing atmospheric [CO2].

We report the first attempt to estimate fungal biomass production in soil by correlating relative fungal growth rates (i.e., acetate incorporation into ergosterol) with fungal biomass increase (i.e., ergosterol) following amendments with dried alfalfa or barley straw in soil. The conversion factor obtained was then used in unamended soil, resulting in fungal biomass productions of 10-12 μg C g-1 soil, yielding fungal turnover times between 130 and 150 days. Using a conversion factor from alfalfa-treated soil only resulted in two times higher estimates for biomass production and consequently lower turnover times. Comparing fungal biomass production with basal respiration indicated that these calculations overestimated the former. Still, the turnover times of fungal biomass in soil were in the same range as turnover times estimated in aquatic systems. The slow turnover of fungal biomass contrasts with the short turnover times found for bacteria. The study thus presents empirical data substantiating the theoretical division of bacteria and fungi into a fast and a slow energy channel, respectively, in the soil food web.

Tea (Camellia sinensis) is a globally important crop and is unusual because it both requires an acid soil and acidifies soil. Tea stands tend to be extremely heavily fertilized in order to improve yield and quality, resulting in a great potential for diffuse pollution. The microbial ecology of tea soils remains poorly understood; an improved understanding is necessary as processes affecting nutrient availability and loss pathways are microbially mediated. We therefore examined the relationships between soil characteristics (pH, organic C, total N, total P, available P, exchangeable Al), the soil microbial biomass (biomass C, biomass ninhydrin-N, ATP, phospholipid fatty acids--PLFAs) and its activities (respiration, net mineralization and nitrification). At the Tea Research Institute, Hangzhou (TRI), we compared fields of different productivity levels (low, medium and high) and at Hongjiashan village (HJS) we compared fields of different stand age (9, 50 and 90 years). At both sites tea soils were compared with adjacent forest soils. At both sites, soil pH was highest in the forest soil and decreased with increasing productivity and age of the tea stand. Soil microbial biomass C and biomass ninhydrin-N were significantly affected by tea production. At TRI, microbial biomass C declined in the order forest>low>high>middle production and at HJS in the order stand age 50>age 9>forest>age 90. Soil pH had a strong influence on the microbial biomass, demonstrated by positive linear correlations with: microbial biomass C, microbial biomass ninhydrin-N, the microbial biomass C:organic C ratio, the microbial biomass ninhydrin-N:total N ratio, the respiration rate and specific respiration rate. Above pH(KCl) 3.5 there was net N mineralization and nitrification, and below this threshold some samples showed net immobilization of N. A principal component (PC) analysis of PLFA data showed a consistent shift in the community composition with productivity level and stand age. The ratio of fungal:bacterial PLFA biomarkers was negatively and linearly correlated with specific respiration in the soils from HJS (r2=0.93, p=0.03). Our results demonstrate that tea cultivation intensity and duration have a strong impact on the microbial community structure, biomass and its functioning, likely through soil acidification and fertilizer addition.

To assess the effect of long-term fertilization on labile organic matter fractions, we analyzed the C and N mineralization and C and N content in soil, particulate organic matter (POM), light fraction organic matter (LFOM), and microbial biomass. Results showed that fertilizer N decreased or did not affect the C and N amounts in soil fractions, except N mineralization and soil total N. The C and N amounts in soil and its fractions increased with the application of fertilizer PK and rice straw. Generally, there was no significant difference between fertilizer PK and rice straw. Furthermore, application of manure was most effective in maintaining soil organic matter and labile organic matter fractions. Soils treated with manure alone had the highest microbial biomass C and C and N mineralization. A significant correlation was observed between the C content and N content in soil, POM, LFOM, microbial biomass, or the readily mineralized organic matter. The amounts of POM-N, LFOM-N, POM-C, and LFOM-C closely correlated with soil organic C or total N content. Microbial biomass N was closely related to the amounts of POM-N, LFOM-N, POM-C, and LFOM-C, while microbial biomass C was closely related to the amounts of POM-N, POM-C, and soil total N. These results suggested that microbial biomass C and N closely correlated with POM rather than SOM. Carbon mineralization was closely related to the amounts of POM-N, POM-C, microbial biomass C, and soil organic C, but no significant correlation was detected between N mineralization with C or N amounts in soil and its fractions.

M.W Baaru, 'Soil microbial biomass carbon and nitrogen as influenced by organic and inorganic inputs at Kabete, Kenya', In: Bationo, A., Waswa, B., Kihara, J. and Kimetu, J. (eds). Advances in integrated soil fertility management in sub Saharan Africa: challenges and opportunities. Berlin: Springer, pp.827-832, 2007 | Soil microbial biomass is the main driving force in the decomposition of organic materials and is frequently used as an early indicator of changes in soil properties resulting from soil management and environment stresses in agricultural ecosystems This study was designed to assess the effects of organic and inorganic inputs on soil microbial biomass carbon and nitrogen overtime at Kabete, Kenya. Tithonia diversifolia, Cassia spectabilis, Calliandra calothyrsus were applied as organic resources, and Urea as inorganic source. Soil was sampled at 0â??10 cm depth before incorporating the inputs and every two months thereafter and at harvesting in a maize-cropping season. Soil microbial biomass carbon and nitrogen was determined by Fumigation Extraction method (FE) while carbon evolution was measured by Fumigation Incubation (FI) method. The results indicated a general increase in soil microbial biomass carbon and nitrogen in the season with the control recording lower values than all the treatments. Microbial biomass carbon, nitrogen and carbon dioxide evolution was affected by both quality of the inputs added and the time of plant growth. Tithonia recorded relatively higher values of microbial biomass carbon, nitrogen and carbon evolution than all the other treatments. A significant difference was recorded between the control and the organically treated soils at the of the season for the microbial biomass nitrogen and carbon dioxide evolution. Both the microbial biomass C and N showed a significance difference (P $⩽0.05) in the different months of the season

Soil microbial biomass is considered as an important early indicator of changes that may occur in the long term with regard to soil fertility and constitutes an important source and sink of nutrients. In South Africa, rangeland monitoring has mostly focused on assessing changes of aboveground vegetation in response to land uses effects, but the associated changes at belowground soil level remain a topic of further research. The aim of this study was to explore soil microbial biomass at three sites under communal grazing management. Soils from grazed and adjacent ungrazed rangeland plots were collected at a depth of 0-25 cm towards the end of the rainy season in April 2005. The soil microbial biomass was characterized by analyzing the phospholipids ester-linked fatty acids. Soils were also analyzed for organic carbon, pH, and total phosphorus. Results showed no statistically significant differences in organic carbon and soil microbial biomass between the grazed and ungrazed plots at any of the sites. Both organic carbon and soil microbial biomass were low, ranging from 0.06 to 0.11% and 489.28 pmol g-1 to 1823.04 pmol g- 1 , respectively. Fourteen grass species were recorded during the vegetation surveys, and most occurred in low abundance. Plants supply organic materials as energy sources for microbial growth, so the low soil microbial biomass could be a reflection of the low vegetation abundance. This study provides essential baseline information regarding soil microbial activity never reported before in these rangelands. Further investigations are required for in-depth understanding of the underlying processes that regulate soil microbial biomass dynamics at these sites.

The influence of the earthworm Aporrectodea caliginosa on the biomass and the proportion of active and dormant soil microorganisms after the addition of cut perennial ryegrass (Lolium perenne) to upper soil from agricultural field was studied in a microcosm experiment. During a 2-month period, soil samples were taken 1, 8, 22, 36, 50, and 64 days after cut grass addition. A substrate-induced respiration (SIR) method was used to analyse the samples for total microbial biomass and the distribution of active and dormant microbial biomass. It was found that the addition of grass increased the microbial biomass (SIR) because of an increase in the active microbial biomass. After the initially high values, the active microbial biomass decreased slowly, and at day 64, it was still higher in the grass-amended soils than in the control treatment without grass addition. After 1 day, the active microbial biomass was higher in the soil with A. caliginosa than without the earthworm. At the subsequent samplings, there were no differences in microbial biomass or the proportion of dormant vs active microorganisms between the grass-amended soils. The average from all sampling occasions of SIR was higher in earthworm-treated soil.

A study was performed selecting one protected forest and an adjacent degraded forest ecosystem to quantify the impact of forest degradation on soil inorganic nitrogen, fine root production, nitrification, N-mineralization and microbial biomass N. There were marked seasonal variations of all the parameters in the upper 0-10 and lower 10-20 cm depths. The seasonal trend of net nitrification and net N-mineralization was reverse of that for inorganic nitrogen and microbial biomass N. Net nitrification, net N-mineralization and fine root biomass values were highest in both forests during rainy season. On contrary, inorganic nitrogen and microbial biomass N were highest during summer season. There was a marked impact of forest degradation on inorganic nitrogen, fine root production nitrification, N-mineralization and microbial biomass observed. Soil properties also varied with soil depth. Fine root biomass, nitrification, N-mineralization and microbial biomass N decreased significantly in higher soil depth. Degradation causes decline in mean seasonal fine root biomass in upper layer and in lower depth by 37% and 27%, respectively. The mean seasonal net nitrification and N-mineralization in upper depth decreased by 42% and 37%, respectively and in lower depth by 42.21% and 39% respectively. Similarly microbial biomass N also decreased by 31.16% in upper layer 33.19% in lower layer.

Microbial biomass and community catabolic diversities at three depths (0-10 cm, 20-30 cm, and 40-50 cm) in Chinese Mollisols as influenced by long-term managements of natural restoration (R), cropping (C) and bare fallow (F) were investigated. Microbial biomass was estimated from chloroform fumigation-extraction and substrate-induced respiration, and catabolic diversity was determined by using Biolog EcoPlate. Microbial biomass significantly declined with soil depth in R and C systems, but not in F, where the microbial biomass had a positive relationship with the total soil C content. R had a relatively stronger metabolic ability than C and F systems. Shannon's diversity index, substrate richness and substrate evenness calculated from the Biolog data were higher in R and C than in F. The catabolic profiles of the three treatments were similar to each other in the soil depth of 0-10 cm and distinctly different in the soil depths of 20-30 cm and 40-50 cm. These results suggest that it was microbial biomass rather than community function that was influenced by the different soil management in the top soil (0-10 cm), whereas in deeper layers, the soil microbial community function was more easily influenced than microbial biomass.