Fumigation-extraction Method Research Articles

Effect of Leaf Litter Treatment on Soil Microbial Biomass

Soil microbial biomass is an active fraction of soil organic matter. It shows quicker response than soil organic matter to any change in the soil environment. Being an index of soil fertility, it plays a key role in the decomposition of litters and fast release of available nutrients. Leaf litters of leguminous and non-leguminous species in alone and mixed form were applied as treatments in the soil to observe the changes in the magnitude of soil microbial biomass. Soil microbial biomass C and N were determined by chloroform fumigation extraction method. Increment in the concentration of microbial biomass C and N was higher in the treatments with leguminous leaf litter (497 - 571 μgCg−1, 48 - 55 μgNg−1) than the non-leguminous one (256 - 414 μgCg−1; 22 - 36 μgNg−1). However, when non-leguminous litters were mixed with leguminous litters then the values increased distinctly (350 - 465 μgCg−1, 28 - 48 μgNg−1). On the basis of increment in soil microbial biomass, leaf litters of the species considered potential to improve soil nutrients are—Cassia siamea and Dalbergia sissoo from leguminous trees, Anthocephalus + Cassia and Shorea + Dalbergia from mixed form of non-leguminous and leguminous one and Eichhornia crassipes, an alien aquatic macrophyte. The leaf litters of these species can be used as source of organic matter to improve the crop yield.

Effects of maize and winter wheat grown under different cultivation techniques on biological activity of soil

The aim of the study was to compare the activity and functional biodiversity in soil under two different cereals: common maize and winter wheat, both grown in the same pattern of cultivation techniques: conventional (to 25 cm depth) and reduced (to 10 cm depth). Soil samples for comparative analysis were collected at the same time (July 2016) at a long-term field experiment, which was carried out in 2013–2016. Soil biological activity was determined by measurement of dehydrogenases activity (DHa) with TTC (2,3,5-triphenyltetrazolium chloride) application, microbial biomass carbon (MBC) and nitrogen (MBN) content by fumigation-extraction method, and functional diversity of soil microorganisms using the Biolog EcoPlate System. The results demonstrated that the cultivation technique had a greater impact on the soil biological activity, compared to the type of cereal. Higher biological activity was found in the soil under reduced tillage in both cereals. Calculated correlations showed that DHa, MBC, MBN and acid phosphatases were positively correlated with each other. The negative correlation obtained between yield and biological parameters of activity in soil was not expected.

Effects of grazing on microbial biomass C, N and respiration in Artemisia frigida rhizosphere soil

Artemisia frigida is a common plant, especially in degraded grasslands, on the Inner Mongolian steppes. To reveal the effects of grazing disturbance on soil microorganisms of the A. frigida rhizosphere, soil microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), and basal respiration and correlation were discussed, by the chloroform fumigation extraction method and the LI-7000 CO2/H2O system. Rhizosphere soil of A. frigida (ARS) and non-rhizosphere soil (NRS) under three grazing intensities, no grazing (CK) plot, light grazing (LG) plot, heavy grazing (HG) plot, were chosen as experimental sites in the Inner Mongolian steppes. Results showed that compared with the control group, the soil microbial biomass carbon, nitrogen and basal respiration after light grazing treatment increased by 22.7%, 45.0%, 17.2%, respectively. These bio-indicators in A. frigida rhizosphere soil were higher than non-rhizosphere soil of A. frigida (P < 0.05). Also, the increasing rate of MBN in rhizosphere and non-rhizosphere soil was higher than that of MBC. In the rhizosphere soil of Artemisia frigida, MBC had a positive correlation with organic matter (r = 0.737), total N (r = 0.798), available N (r = 0.945), and total K (r = 0.697). The MBN had a positive correlation with organic matter (r = 0.906), total N (r = 0.915), available N (r = 0.937), and total K (r = 0.691).The basal respiration had a positive correlation with organic matter (r = 0.507), total N (r = 0.446), available N (r = 0.805), and total K (r = 0.898). The light grazing treatment can contribute to a increase to microbial biomass and basal respiration rate. This study provided a theoretical basis for further exploring of ways that A. frigida could help resist grassland degradation.

Effects of nitrogen deposition on soil microbial communities in temperate and subtropical forests in China

Increasing nitrogen (N) deposition has aroused large concerns because of its potential negative effects on forest ecosystems. Although microorganisms play a vital role in ecosystem carbon (C) and nutrient cycling, the effect of N deposition on soil microbiota still remains unclear. In this study, we investigated the responses of microbial biomass C (MBC) and N (MBN) and microbial community composition to 4–5years of experimentally simulated N deposition in temperate needle-leaf forests and subtropical evergreen broadleaf forests in eastern China, using chloroform fumigation extraction and phospholipid fatty acid (PLFA) methods. We found idiosyncratic effects of N addition on microbial biomass in these two types of forest ecosystems. In the subtropical forests, N addition showed a significant negative effect on microbial biomass and community composition, while the effect of N addition was not significant in the temperate forests. The N addition decreased MBC, MBN, arbuscular mycorrhizal fungi, and the F/B ratio (ratio of fungi to bacteria biomass) in the subtropical forests, likely due to a decreased soil pH and changes in the plant community composition. These results showed that microbial biomass and community composition in subtropical forests, compared with the temperate forests, were sensitive to N deposition. Our findings suggest that N deposition may have negative influence on soil microorganisms and potentially alter carbon and nutrient cycling in subtropical forests, rather than in temperate forests.

The high correlation between DNA and chloroform-labile N in various types of soil

Based on the development of a direct DNA extraction method from soil, an estimation of soil microbial biomass by measurement of extracted soil DNA is presented. Chloroform-labile carbon (CLC) and nitrogen (CLN) determined by chloroform fumigation methods have been the major parameters of soil microbial biomass, but to date, there have been few studies of the relationship between DNA and CLN among soils with different characteristics. We applied DNA assays to the estimation of soil microbial biomass in various types of soil in Japan. The quantitative relationships among DNA, CLC and CLN released by the chloroform fumigation–extraction method were examined in 35 soil samples including five different soil types. The amount of DNA was moderately correlated with CLC (r=0.652, n=35), but there was no significant correlation in one of the soil types (fluvisol) representing a typical soil in Japan (r=0.124; n=15). Moreover, there was a strong correlation between DNA and CLN (r=0.887; n=35), and the correlation was high in every major soil type. These findings raise the possibility that DNA could be used to estimate biomass N even among different kinds of soil, with a conversion factor of 2.75 for DNA (μgg−1 soil).

Response of microbial biomass and bacterial community composition to fertilization in a salt marsh in China

The effects of nitrogen (N) addition on microbial biomass, bacterial abundance, and community composition in sediment colonized by Suaeda heteroptera were examined by chloroform fumigation extraction method, real-time quantitative polymerase chain reaction, and denaturing gradient gel electrophoresis (DGGE) in a salt marsh located in Shuangtai Estuary, China. The sediment samples were collected from plots treated with different amounts of a single N fertilizer (urea supplied at 0.1, 0.2, 0.4 and 0.8 g/kg (nitrogen content in sediment) and different forms of N fertilizers (urea, (NH4)2SO4, and NH4NO3, each supplied at 0.2 g/kg (calculated by nitrogen). The fertilizers were applied 1–4 times during the plant-growing season in May, July, August, and September of 2013. Untreated plots were included as a control. The results showed that both the amount and form of N positively influenced microbial biomass carbon, microbial biomass nitrogen, and bacterial abundance. The DGGE profiles revealed that the bacterial community composition was also affected by the amount and form of N. Thus, our findings indicate that short-term N amendment increases microbial biomass and bacterial abundance, and alters the structure of bacterial community.

Effect of grazing intensity on protozoan community, microbial biomass, and enzyme activity in an alpine meadow on the Tibetan Plateau

The alpine meadow has received mounting attention due to its degradation resulting from overgrazing on the Tibetan Plateau. However, belowground biotic characteristics under varied grazing stresses in this ecosystem are poorly understood. Here, the responses of soil protozoan abundance, community composition, microbial biomass, and enzyme activity to five grazing patterns including (1) artificial grassland without grazing (AG), (2) winter grazing (WG), (3) grazing for 7 months within a fence (GF), (4) continuous grazing for a whole year (CG), and (5) natural heavy grazing (HG) were investigated for two continuous years. Soil protozoan community composition was investigated using the most possible number (MPN) method, and soil microbial biomass and enzyme activity were analyzed using chloroform fumigation extraction and substrate utilization methods, respectively. Multivariate statistical analysis, the analysis of variance (ANOVA), multiple comparisons, and correlation analysis were together performed. The WG treatment had the highest abundance of total protozoa (2342–2524 cell g−1). Compared with AG treatment, HG treatment significantly reduced the abundance of soil total, flagellate and ciliate protozoa, and protease activities in 2012 and 2013. Significantly, lower soil microbial biomass nitrogen (MBN) was also observed in the HG (6.60 and 14.6 mg N kg−1) than those in other four treatments (22.3–82.9 mg N kg−1) both in 2012 and 2013, whereas significantly higher microbial biomass carbon (MBC) was observed in HG than that in AG treatment in 2012. Moreover, significantly positive correlations were detected between the abundance of soil protozoa and soil moisture, pH, organic C, total N, and MBN. Our results indicated that soil protozoa showed a negative response to increasing grazing intensities and therefore, suggesting that aboveground grazing practices also exerted strong impact on belowground protozoa, not only on soil microbial characteristics. Soil protozoan community composition was apparently different between the HG treatment and other four grazing patterns and was potentially impacted by altered soil properties and MBC and/or MBN. Our results suggested that moderate grazing may sustain better belowground biotic diversity and ecosystem functioning in this alpine meadow on the Tibetan Plateau.

Examination of residual chloroform interference in the measurement of microbial biomass C by fumigation-extraction

Using the chloroform fumigation-extraction (CFE) method for determining microbial biomass in soils, a presumption is followed, i.e., that chloroform becomes fully evacuated from the fumigated soil before extraction. Otherwise, the C-containing fumigant may comprise an unknown part of the extractable C flush, resulting in certain overestimation of soil microbial biomass. A quantitative assessment of extractable residual chloroform levels in fumigated soils was performed, testing soils varying in clay and organic matter contents. The tests were performed over a broad range of soil moisture conditions as to facilitate a mechanistic interpretation of possible chloroform interactions in the studied soils (i.e., dissolution, sorption). The results support the validity of the CFE method's application in agricultural soils, demonstrating the insignificance of biomass overestimation arising from residual chloroform.

Changes in soil microbial biomass and community composition in coastal wetlands affected by restoration projects in a Chinese delta

Severely degraded wetlands due to the lack of freshwater were restored by reintroducing freshwater through the placement of artificial dikes and channels in the Yellow River Delta (YRD) of China. Many studies have evaluated the performances of this restoration projects in aspects of vegetation, soils, hydrology, wildlife, etc. In contrast, limited information was available on the effects of restoration projects on the soil microbial biomass and community composition. To better understand the wetland restoration, differences in soil microbial biomass and community composition between restored tidal wetlands and unrestored wetlands under the disturbance of petroleum exploitation activities or tidal intrusion were assessed. Surface soils (0–10cm) under three different plant covers (Phragmites australis, Suaeda salsa and bare land) were collected from each three wetland zones. Chloroform fumigation-extraction (CFE) method and phospholipid fatty acid (PLFA) analysis were used to characterize soil microbial biomass and community composition. Our results showed significantly elevated microbial biomass in soils of the restoration zone, as indicated by both microbial biomass carbon and total PLFAs. Soil microbial community composition in the restoration zone also differed significantly from those in the petroleum exploitation zone and tidal zone. The freshwater input of restoration projects induced a soil microbial community shift to the increased relative abundance of fungi and decreased relative abundance of Desulfovibrio bacteria. The significantly promoted fungi in soils under P. australis of the restoration zone reflected the necessity of decomposers of the increased surface plant residues after restoration, which in turn contributed to the organic residues accumulation in soils and large aggregates formation by fungal hyphae. Meanwhile the modified soil carbon pool and aggregate structure following restoration of degraded wetland may favor the colonization of soil organisms. These results indicated that freshwater input had strongly altered soil microbial communities in the restored wetland, which may be of great significance in understanding the soil microbial responses to the restoration projects and the underlying mechanisms of wetland restoration.

Effect of forest and soil type on microbial biomass carbon and respiration

The aim of study was to evaluate the variation of soil microbial biomass carbon (Cmic) and microbial respiration (MR) in three types soil (Chromic Cambisols, Chromic Luvisols and Eutric Leptosols) of mixed beech forest (Beech- Hornbeam and Beech- Maple). Soil was randomly sampled from 0–10 cm layer (plant litter removed), 90 soil samples were taken. Cmic determined by the fumigation-extraction method and MR by closed bottle method. Soil Corg, Ntot and pH were measured. There are significant differences between the soil types concerning the Cmic content and MR. These parameters were highest in Chromic Cambisols following Chromic Luvisols, while the lowest were in Eutric Leptosols. A similar trend of Corg and Ntot was observed in studied soils. Two-way ANOVA indicated that soil type and forest type have significantly effect on the most soil characteristics. Chromic Cambisols shows a productive soil due to have the maximum Cmic, MR, Corg and Ntot. In Cambisols under Beech- Maple forest the Cmic value and soil C/N ratio were higher compared to Beech-Hornbeam (19.5 and 4.1 mg C g–1, and 16.3 and 3.3, respectively). This fact might be indicated that Maple litter had more easy decomposable organic compounds than Hornbeam. According to regression analysis, 89 and 68 percentage of Cmic variability could explain by soil Corg and Ntot respectively.

Contrastive effects of inorganic phosphorus addition on soil microbial respiration and microbial biomass in tropical monoculture tree plantation soils in Thailand

An incubation experiment was conducted to test the effects of inorganic phosphorus (P) addition on soil microbial activities in tropical monoculture tree plantation soils. The soils taken from an experimental tree plantation site in Nakhon Ratchasima, Thailand were incubated for 48 h with and without adding 100 μg of P (KH2PO4) per gram soil after adjusting the water holding capacity to 80%. During the incubation period, the microbial biomass carbon (MBC) contents determined using the chloroform fumigation extraction method decreased and P addition stimulated the decreased rate significantly. On the other hand, the P addition increased the dissolved organic carbon (DOC) contents and CO2 emissions. The study suggested that P addition had changed soil microbial activities, possibly including a soil microbial community change. Furthermore, the study showed that the stimulated soil respiration by P addition is not necessarily accompanied by increased MBC. The assessment of the effects of P limitation on soil microbial activities should measure at least the effects of P addition on both soil respiration and MBC, possibly combined with soil microbial community analyses.

Microbial communities and residues in robinia- and poplar-based alley-cropping systems under organic and integrated management

Organic farming and agroforestry are considered as sustainable alternative agricultural practices for intensive agriculture. In a long-term field trial in Scheyern Germany, we evaluated the effects of 21-year organic farming and 4-year agroforestry (robinia and poplar) on microbial community and microbial residues. Microbial biomass and microbial community were determined by fumigation–extraction method and the analysis of phospholipid fatty acid (PLFA), respectively. Microbial residues were evaluated by the measurement of amino sugars. The results showed that organic farming had significantly positive effect on soil organic carbon (SOC) but that it tended to decrease microbial biomass C (MBC), PLFA functional guilds, muramic acid (MurN), and glucosamine (GlcN). Robinia system, however, significantly increased SOC and had the potential to enhance MBC, PLFA functional guilds especially Gram (+), but it tended to decrease MurN and GlcN, in comparison with poplar system. The hedgerow tree did not show significantly positive effect on SOC and microbial properties except the abundance of fungi and Gram (+) bacterial, after 4-year establishment period. The principal component analysis of the PLFA profile showed that in comparison with other investigated treatments, robinia system under organic farming had significantly a different microbial community structure. It also indicated tree species-specific effect on microbial community in the organic farming was stronger than that in the integrated farming. In summary, the short-term introduction of trees into an existing agricultural system will not substantially change the microbial biomass, but it has certain influence on the abundance of specific microbial groups in the hedgerow. Although organic farming did not show positive effect on overall microbial indices, we still see positive effect on SOC after 21-year organic farming and its additive effect with robinia on SOC in current study. We expect that alley-cropping agroforestry system that combines organic farming and robinia hedgerow has a great potential for sequestering SOC and developing sustainable agroecosystems with time.

Relationship between presence of the desert shrub Haloxylon ammodendron and microbial communities in two soils with contrasting textures

Shrubs are usually dominated species for desert ecosystems, and resource islands often occurred around shrubs. It is widely considered that soils beneath shrub canopy have higher microbial diversity and biomass than those outside of the canopy. However, it remains poorly understood how shrubs affect this resource islands along soil profile and functional consequence on soil microbial community changes. Here, we showed distinct patterns of soil physiochemical properties and microbial communities along a soil profile outward from the taproot of Haloxylon ammodendron (C.A.Mey.) in two soils with contrasting textures: Torripsamments and Haplocalcids (USDA Soil Taxonomy). Soil samples were collected in circles with radii of 5, 40, 100 and 200cm respectively around the taproot in four randomly selected horizontal directions, and from respective depths of 0–20, 20–60 and 60–100cm. Microbial biomass and community composition were examined using a chloroform fumigation extraction and phospholipid fatty acids method. Redundancy analysis showed that the spatial variability of soil microbial communities was closely correlated with that of soil water and nutrients in both soils. Soil microbial biomass, soil water and nutrient contents had a similar decreasing trend along the increasing distance from the taproot. The coarse-textured Torripsamments showed stronger variability of soil water and nutrient contents than the fine-textured Haplocacids within the resource islands, and similar results were observed for soil microbial biomass. A clear trend of spatial variability (outward from taproot) for various microbial groups was observed in Torripsamments, but not in Haplocalcids. The biomass decreased to a lesser extent for total fungi than bacteria, and for Gram-positive than Gram-negative bacteria in Torripsamments. Our results suggest that the presence of H. ammodendron plays an important role in shaping the spatial variability of microbial communities in these desert ecosystems. Soil texture may determine the intensity of their spatial variability.

Decomposition, Nitrogen Release and Soil Fertility of Plant Residues Incorporation from Different Pre- Sugarcane Planting Management

The effect of decomposition, nitrogen release and soil fertility of upland rice-legume residues incorporation before sugarcane planting was investigated. The experimental design was randomized complete block design (RCBD) with 4 replications. The following residue and control treatments were implemented: i.e. i) control; no residues incorporation, ii) weed, iii) soybean (Glycine max), iv) sunn hemp (Crotalaria juncea) and v) upland rice. Soil samples and litter bags were collected at 1, 2, 4, 8, 12, 16, 24 and 32 weeks after incorporation. Soil mineral N was analyzed by Flow Injection Analyzer (FIA) and remaining dry weights of litter bag were recorded. Soil microbial biomass was measured by chloroform fumigation extraction method. The results revealed that weed residues treatment had the highest of remaining dry weight and % N remaining in litter bag in most sampling dates. Sunn hemp residues treatment had the highest soil mineral N and was significantly different from the other treatments (p < 0.01) at 4, 8, 12 and 16 weeks after residues incorporation. At final sampling date, the upland rice residues treatment gave the highest microbial biomass N and was significantly different from the other treatments (p < 0.01) and provided the highest relative microbial biomass N but not significantly different from soybean residues treatment. Moreover, soil organic matter could be improved by all residue treatments. However, sunn hemp may be a potential crop for soil N release but upland rice could support rice consumption demand. Thus, the effect of legume-upland rice residue incorporation on sugarcane yield should be further investigated under field conditions.

ANALISIS KESUBURAN TANAH DENGAN INDIKATOR MIKROORGANISME TANAH PADA BERBAGAI SISTEM PENGGUNAAN LAHAN DI PLATEAU DIENG

&lt;p&gt;Dieng is a plateau region, with an altitude about ± 2095 meters above sea level. Dieng Plateau is unique land because that has low air temperature and soil dominated Andisol and has various land slope from 0 percent until &amp;gt;40 percent. Therefore, Dieng Plateau is ideal land for horticultural cultivations. The serious problem in Dieng Plateau was conducted intensively conversion the forest area to the various land use system, to example for land potatoes cultivation, settlements and tourist activity. These conditions increasing hazard for the rate soil erosion. High soil erosion rate will decrease the soil fertility.&lt;/p&gt;&lt;p&gt;This study aims to determine the level of soil fertility with indicators of soil microorganisms in a various of land use, given the high levels of soil erosion. The layout design of the research used is a Randomized Complete Block Design (RCBD). Analysis of the data used is Analysist of Variance – ANOVA (F test), Honestly Significant Analysis (5%) and Stepwise Regressiont. To determination the number of carbon biomass of microorganisms is applied with fumigation-extraction method. For&lt;br /&gt;determination of total soil microorganisms using NA media, where as the determination of soil respiration using Verstraete method.&lt;/p&gt;&lt;p&gt;The results showed that the land is sloping physiography (tourist land and residential) have higher fertility than high physiographic area, as a result of soil erosion. Different case for protected forests, although a high physiographic land, forests have higher fertility than the land potatos cultivation. Forest area are still natural, and its has a vegetation litter and diversity of vegetations, therefor the forest area has good barrier water runoff that carries organik material and soil salts.&lt;/p&gt;

Potential nitrogen immobilization as influenced by available carbon in Japanese arable and forest soils

Microbial nitrogen (N) immobilization following the addition of organic materials to soils regulates soil N availability, which affects plant growth and N leaching from soils. In this study, the potential for microbial N immobilization was evaluated by short-term incubation experiments following the addition of available carbon (C) under non-limiting conditions of N and phosphorus (P) to seven Japanese arable and forest soils. Glucose was added as a model substrate at concentrations close to microbial biomass C. The forest soils had lower pH and smaller increases in respiration rates after the glucose addition, and higher organic and biomass C compared to the arable soils. Microbial N immobilization, estimated by net decreases in extractable N, was significantly correlated with the concentrations of added glucose and was on average 43 mg N g−1 glucose C during 3- and 7-day incubation for all soils. Net increases in biomass N measured by the chloroform fumigation-extraction method using the common conversion factor of 0.54 at 3 and 7 days after the glucose addition were lower than the microbial N immobilization for all soils, and the biomass N accounted for a smaller portion of immobilized N in the arable soils than in the forest soils. Therefore, the present study suggests that microbial N immobilization would be dependent on the concentrations of available C in organic materials and higher than the increases in biomass N, especially for arable soils when organic materials are added to soils under non-limiting conditions of N and P.

Spatial variability of soil microbial biomass and its relationships with edaphic, vegetational and climatic factors in the Three-River Headwaters region on Qinghai-Tibetan Plateau

This study aims to investigate the level of soil microbial biomass (MB) and analyze the relationships between soil MB and edaphic, vegetational and climatic factors at high elevation sites (>3000m). We collected soil samples from 0 to 10cm soil depth in 259 plots at 55 sites across 6 biomes in Three-River Headwaters (TRH) region at 3280–5127m elevation. Soil microbial biomass carbon and nitrogen (MBC and MBN) were measured with the chloroform fumigation–extraction method. Multivariate stepwise regression analyses were used to analyze the combined effects of edaphic, vegetational and climatic factors on soil MB. We found: (1) soil MBC and MBN had an average of 30.95mmol C/kg dry soil and 5.84mmol N/kg dry soil in TRH, respectively, and their values were found to be negatively correlated with elevation; (2) soil MB was found to be significantly different among different biomes, and this spatial variation could be explained by the levels of soil organic carbon and belowground plant biomass. Our results indicate that the MB at high elevation region might be very low, and the increasing trend of soil microbial biomass with elevation could reverse at higher elevations.

Short-term changes in microbial biomass and activity in soils under black locust trees (Robinia pseudoacacia L.) in the northwest of Turkey

The literature indicates that the presence and activity of microbial biomass could be potential indicators of other changes in mineral soils, making it useful for monitoring and assessing the relationships between plants and soil and their effects on the health and quality of the soil. Therefore, the aim of the study was to determine whether if there were any changes in the C and N content or the basal respiration of microbial biomass in soils under black locust trees (Robinia pseudoacacia L.) between 2013 and 2014. Samples of topsoil (0–6.5 cm) under the black locust were collected randomly from 12 different locations in 2013, and 12 samples were taken from the same locations in 2014. The C and N contents of the microbial biomass were determined by the chloroform fumigation extraction method. Basal respiration was determined by the sodium hydroxide (NaOH) trap method. The results demonstrated that the average C content of microbial biomass (Cmic) increased by about 55 % in soils under black locust and that the average N content (Nmic) of microbial biomass N increased by about 59 %. Both the Cmic and Nmic values were significantly affected by the temporal variation (P 0.05). Thus, it was concluded that the effect of black locust on the C and N content and basal respiration of the microbial biomass was due to the combined result of changing microclimatic conditions and soil characteristics, including the temperature, moisture content, pH, organic C, and total N in the soil. Therefore, this tree is an appropriate and valuable species where poor ecological conditions exist because of its rapid growth rate and its positive effect on the health and quality of soil.

Soil microbial community composition rather than litter quality is linked with soil organic carbon chemical composition in plantations in subtropical China

Purpose Native broadleaf plantations are increasingly being developed as an alternative to coniferous plantations. This studyexaminedtherelationshipsamonglittercarbon(C)quality, soil microbial community composition, and soil organic C (SOC) chemical properties in plantations and how they were affected by tree species. Materials and methods The solid-state 13 C nuclear magnetic resonance spectroscopy (NMR) technique was used to examine SOC chemical composition, and litter and fine root C quality in four plantations of native tree species (Pinus massoniana, Castanopsis hystrix, Michelia macclurei, and Mytilaria laosensis) in Pingxiang, Guangxi Zhuang AutonomousRegion,insubtropicalChina.Soilmicrobialbiomass C and nitrogen (N) were determined by the chloroform fumigation-extraction method and soil bacterial and fungal biomass were measured with the phospholipid fatty acid (PLFA) technique. Results and discussion The proportions of O-alkyl C, alkyl C, aromatic C, and carbonyl C in SOC and the alkyl/O-alkyl C ratio (A/O-A) in litter and fine root samples, soil microbial C and N, microbial C/N ratios, and the amount of PLFAs were significantly different among the four plantations of different species. SOC in the 0–10-cm layer had 43–49 % O-alkyl C, 24–34 % alkyl C, 14–17 % aromatic C, and 9–11 % carbonyl C in SOC. The microbial C/N ratio, the amount of total PLFAs, and bacterial and Gram-positive bacterial population sizes were linked to the proportion of alkyl C in SOC and the A/O-A ratio in soil. The proportion of alkyl C in SOC was not related to the proportion of alkyl C in litter or fine root samples. Conclusions The microbial community composition rather than plant litter or fine root quality was linked to chemical composition of SOC in the studied subtropical plantations. Future research should place more emphasis on the processes involved in the formation of SOC and their association with the microbial community.

EFFECT OF WATER AVAILABILITY ON SOIL MICROBIAL BIOMASS IN SECONDARY FOREST IN EASTERN AMAZONIA

Soil microbial biomass (SMB) plays an important role in nutrient cycling in agroecosystems, and is limited by several factors, such as soil water availability. This study assessed the effects of soil water availability on microbial biomass and its variation over time in the Latossolo Amarelo concrecionário of a secondary forest in eastern Amazonia. The fumigation-extraction method was used to estimate the soil microbial biomass carbon and nitrogen content (SMBC and SMBN). An adaptation of the fumigation-incubation method was used to determine basal respiration (CO2-SMB). The metabolic quotient (qCO2) and ratio of microbial carbon:organic carbon (CMIC:CORG) were calculated based on those results. Soil moisture was generally significantly lower during the dry season and in the control plots. Irrigation raised soil moisture to levels close to those observed during the rainy season, but had no significant effect on SMB. The variables did not vary on a seasonal basis, except for the microbial C/N ratio that suggested the occurrence of seasonal shifts in the structure of the microbial community.