Soil Microbial Community Activity Research Articles

Bioremediation of Cesium-Contaminated Soil by Sorghum Bicolor and Soil Microbial Community Analysis

ABSTRACTGrowth and cesium accumulation in Sorghum bicolor was investigated using Cs-spiked soil (0, 40, 100, 200, 400 mg Cs/kg soil) during the entire growth period (139 days). The results showed that higher soil Cs concentrations increased Cs uptake by S. bicolor. The Cs content in stems, leaves and roots correlated well with soil Cs concentration, following an exponential or linear pattern (R2 > 0.92). When the Cs level was 40, 100, 200, 400 mg/kg soil, the average Cs concentration in roots reached 3.84, 43.77, 76.95, 258.49 mg/kg DW, in stems it reached 7.04, 6.12, 27.57, 167.41 mg/kg DW, in leaves it reached 4.23, 4.52, 46.09, 181.70 mg/kg DW, and in shoots it reached 6.09, 5.61, 35.12 and 172.27 mg/kg DW, respectively. The Biolog Eco-plate assay showed that Cs enhanced soil microbial diversity and activity. Microbial community level physiological profiles (CLPPs) were sensitive to Cs and therefore can be used for rapidly assessing soil microbial community activity levels under Cs stress.

Application of mesotrione at different doses in an amended soil: Dissipation and effect on the soil microbial biomass and activity

The aim of this work was to estimate the dissipation of mesotrione applied at three doses (2, 10 and 50mgkg−1 dw) in an unamended agricultural soil, and this same soil amended with two organic residues (green compost (C) and sewage sludge (SS)). The effects of herbicide and organic residue on the abundance and activity of soil microbial communities were also assessed by determining soil microbial parameters such as biomass, dehydrogenase activity (DHA), and respiration. Lower dissipation rates were observed for a higher herbicide dose. The highest half-life (DT50) values were observed in the SS-amended soil for the three herbicide doses applied. Biomass values increased in the amended soils compared to the unamended one in all the cases studied, and increased over the incubation period in the SS-amended soil. DHA mean values significantly decreased in the SS-amended soil, and increased in the C-amended soil compared to the unamended ones, under all conditions. At time 0days, respiration values were significantly higher in SS-amended soils (untreated and treated with mesotrione) than in the unamended and C-amended soils. The effect of mesotrione on soil biomass, DHA and respiration was different depending on incubation time and soil amendment and herbicide dose applied. The results support the need to consider the possible non-target effects of pesticides and organic amendments simultaneously applied on soil microbial communities to prevent negative impacts on soil quality.

Effects of Conservation Agriculture and Fertilization on Soil Microbial Diversity and Activity

Soil microbial communities perform critical functions in ecosystem processes. These functions can be used to assess the impact of agricultural practices on sustainable crop production. In this five-year study, the effect of various agricultural practices on soil microbial diversity and activity was investigated in a summer rainfall area under South African dryland conditions. Microbial diversity and activity were measured in the 0–15 cm layer of a field trial consisting of two fertilizer levels, three cropping systems, and two tillage systems. Using the Shannon–Weaver and Evenness diversity indices, soil microbial species richness and abundance were measured. Microbial enzymatic activities: β-glucosidase, phosphatase and urease, were used to evaluate ecosystem functioning. Cluster analysis revealed a shift in soil microbial community diversity and activity over time. Microbial diversity and activity were higher under no-till than conventional tillage. Fertilizer levels seemed to play a minor role in determining microbial diversity and activity, whereas the cropping systems played a more important role in determining the activity of soil microbial communities. Conservation agriculture yielded the highest soil microbial diversity and activity in diversified cropping systems under no-till.

Effects of GM potato Modena on soil microbial activity and litter decomposition fall within the range of effects found for two conventional cultivars

Plant roots have a profound effect on soil microbial activity, particularly in the rhizosphere. Hence, it is important to understand the potential effects of genetically modified (GM) crops on soil microbial activity and related processes such as litter decomposition. In this study, we compared the effects of GM potato Modena on soil microbial activity and carbon (C) and nitrogen (N) mineralization to effects induced by Modena’s parental isoline (Karnico) and a conventional potato cultivar (Aventra). A field experiment was conducted at two sites to assess microbial catabolic diversity (using MicroRespTM) in the rhizosphere and in bulk soil, during flowering and senescence of the potato plants. In a laboratory experiment with soil and potato litter from the field experiment, we investigated whether the cultivars had modified the activity of soil microbial communities to such an extent that this affected C and N mineralization. Results of the field experiment showed no GM-induced effects on microbial catabolic diversity, while effects of field site location and sampling date were significant. Multivariate analysis including plant traits and soil characteristics revealed that microbial catabolic activities in rhizosphere soil were strongly correlated with soil organic matter and tuber sucrose content, whereas in bulk soil, they were primarily correlated with soil moisture. In the laboratory experiment, we found that Modena induced a “home-field advantage” in N mineralization, yet this effect was inconsistent across locations and was also observed for other cultivars. Based on our data and results from previous studies, we conclude that the effects of GM cultivar Modena on soil microbial activity and litter decomposition fall within the normal range of effects found for conventional potato cultivars.

Effect of cassava mill effluent on biological activity of soil microbial community.

This study assessed the effect of cassava effluent on soil microbiological characteristics and enzymatic activities were investigated in soil samples. Soil properties and heavy metal concentrations were evaluated using standard soil analytical and spectroscopic methods, respectively. The microbiological parameters measured include microbial biomass carbon, basal soil respiration, catalase, urease, dehydrogenase activities and number of culturable aerobic bacteria, fungi and actinomycetes. The pH and temperature regime vary significantly (p < 0.05) throughout the study period. All other physicochemical parameters studied were significantly different (p < 0.05) higher than the control site. Soil organic carbon content gave significant positive correlations with microbial biomass carbon, basal soil respiration, catalase activity and dehydrogenase activity (r = 0.450, 0.461, 0.574 and 0.591 at p < 0.01), respectively. The quantitative analysis of soil microbial density demonstrates a marked decrease in total culturable numbers of the different microbial groups of the polluted soil samples. Soil contamination decreased catalase, urease and dehydrogenase activities. The findings revealed that soil enzymes can be used as indices of soil contamination and bio-indicator of soil quality.

Microbial models with data‐driven parameters predict stronger soil carbon responses to climate change

Long-term carbon (C) cycle feedbacks to climate depend on the future dynamics of soil organic carbon (SOC). Current models show low predictive accuracy at simulating contemporary SOC pools, which can be improved through parameter estimation. However, major uncertainty remains in global soil responses to climate change, particularly uncertainty in how the activity of soil microbial communities will respond. To date, the role of microbes in SOC dynamics has been implicitly described by decay rate constants in most conventional global carbon cycle models. Explicitly including microbial biomass dynamics into C cycle model formulations has shown potential to improve model predictive performance when assessed against global SOC databases. This study aimed to data-constrained parameters of two soil microbial models, evaluate the improvements in performance of those calibrated models in predicting contemporary carbon stocks, and compare the SOC responses to climate change and their uncertainties between microbial and conventional models. Microbial models with calibrated parameters explained 51% of variability in the observed total SOC, whereas a calibrated conventional model explained 41%. The microbial models, when forced with climate and soil carbon input predictions from the 5th Coupled Model Intercomparison Project (CMIP5), produced stronger soil C responses to 95 years of climate change than any of the 11 CMIP5 models. The calibrated microbial models predicted between 8% (2-pool model) and 11% (4-pool model) soil C losses compared with CMIP5 model projections which ranged from a 7% loss to a 22.6% gain. Lastly, we observed unrealistic oscillatory SOC dynamics in the 2-pool microbial model. The 4-pool model also produced oscillations, but they were less prominent and could be avoided, depending on the parameter values.

Effect of monospecific and mixed sea-buckthorn (Hippophae rhamnoides) plantations on the structure and activity of soil microbial communities.

This study aims to evaluate the effect of different afforestation models on soil microbial composition in the Loess Plateau in China. In particular, we determined soil physicochemical properties, enzyme activities, and microbial community structures in the top 0 cm to 10 cm soil underneath a pure Hippophae rhamnoides (SS) stand and three mixed stands, namely, H. rhamnoides and Robinia pseucdoacacia (SC), H. rhamnoides and Pinus tabulaeformis (SY), and H. rhamnoides and Platycladus orientalis (SB). Results showed that total organic carbon (TOC), total nitrogen, and ammonium (NH4 +) contents were higher in SY and SB than in SS. The total microbial biomass, bacterial biomass, and Gram+ biomass of the three mixed stands were significantly higher than those of the pure stand. However, no significant difference was found in fungal biomass. Correlation analysis suggested that soil microbial communities are significantly and positively correlated with some chemical parameters of soil, such as TOC, total phosphorus, total potassium, available phosphorus, NH4 + content, nitrate content (NH3 −), and the enzyme activities of urease, peroxidase, and phosphatase. Principal component analysis showed that the microbial community structures of SB and SS could clearly be discriminated from each other and from the others, whereas SY and SC were similar. In conclusion, tree species indirectly but significantly affect soil microbial communities and enzyme activities through soil physicochemical properties. In addition, mixing P. tabulaeformis or P. orientalis in H. rhamnoides plantations is a suitable afforestation model in the Loess Plateau, because of significant positive effects on soil nutrient conditions, microbial community, and enzyme activities over pure plantations.

Prolonged irrigation with municipal wastewater promotes a persistent and active soil microbial community in a semiarid agroecosystem

The use of treated wastewater (WW) for irrigation is a common practice, especially in arid and semiarid agroecosystems. We aimed to evaluate the influence of long-term (up to 45 years) irrigation with WW on the soil microbial community structure, microbial activity and physicochemical properties, in comparison with soil irrigated with fresh water (FW), in a semiarid orange-tree orchard. Phospholipid fatty acid (PLFA) analysis was used to assess the shifts in the soil microbial community in response to the application of WW. Total organic carbon and available P increased significantly, by about 49% and 37%, respectively, due to WW irrigation. The urease, β-glucosidase, alkaline phosphatase and dehydrogenase activities and aggregate stability were higher in the soil irrigated with WW than in that irrigated with FW. The PLFA analysis showed a significant increase in bacterial abundance, particularly in G+ bacteria. The relative abundances of fungi, G− bacteria and actinobacteria were similar in the two soils. Principal components analysis of the PLFAs showed discrimination between the FW-irrigated soil and the WW-irrigated soil, which was enriched in actinobacterial PLFA 10Me18:0. The prolonged use of treated WW for irrigation in a semiarid agroecosystem promoted the establishment of a specific and persistent microbial community that was functionally more active.

Soil volatile analysis by proton transfer reaction-time of flight mass spectrometry (PTR-TOF-MS)

We analyzed the volatile organic compounds (VOCs) emitted from different soils by using the PTR-MS-TOF technique under laboratory conditions and compared them with soil chemical biochemical activities. The emitted VOCs were related to soil microbial biomass, soil respiration and some soil enzyme activities so as to evaluate if size and activity of soil microbial communities influenced the soil VOCs profiles. Our results showed that the emitted VOCs discriminated between soils with different properties and management, and differences in the VOCs emission profiles were likely related to the active metabolic pathways in the microbial communities of the three studied soil. Our results also showed that some soil enzyme activities such as β-glucosidase and arylsulfatase were possibly involved in the release of compounds fueling microbial metabolic pathways leading to the production of specific VOCs. It was concluded that the PTR-MS-TOF technique is suitable for analyze VOCs emission from soil and that studies comparing soil enzyme activities and soil volatile profiles can reveal the origin of VOCs and give further insights on microbial activity and soil functionality.

Soil biochemical alterations and microbial community responses under Acacia dealbata Link invasion

A critical outcome of the invasive processes of exotic plants is the impact on soil microbial communities and chemical parameters. We studied the impact of Acacia dealbata on soils of mixed forests and shrublands. We hypothesized that A. dealbata can alter soil microbial community function and soil chemical profile in invaded ecosystems. Two sampling dates were selected depending on the phenological stage of A. dealbata (vegetative vs. reproductive).Soil chemical parameters were deeply modified in the invaded sites. Total C and N, P, K, Ca, Mg, NO3− and NH4+ content and available P, were significantly higher in invaded soils of both mixed forests and shrublands. Soil microbial community activities were affected by the sampling date, soil type and ecosystem. Enzymatic activities mainly varied in soils collected during the vegetative stage of A. dealbata in mixed forests and during both vegetative and reproductive stages in shrublands. Soils invaded by A. dealbata showed increased acid phosphatase, β-glucosidase and N-acetyl glucosaminidase activities and the geometrical mean of these activities. Soil basal respiration was significantly reduced in invaded patches of mixed forests. Our results showed an alteration of soil chemistry and microbial community function related to A. dealbata presence, probably leading to acceleration in the decomposition and mineralization rates.

The availability of mineral nitrogen in Mediterranean open steppe dominated by Stipa tenacissima L.

The area of interest is located in the Sierra de los Filabres in semi-arid steppe of the province of Almeria in Spain. The amount of water in the soil is a limiting factor and its availability affects the structure and species composition of ecosystem. On the other hand, the type of vegetation affects the water loss via evapotranspiration and thus the soil microclimate. It has a great influence on the growth and activity of soil microbial communities and hence the dynamics of decomposition of organic matter and nutrient availability. The aim of this study was to assess the intensity of microbial transformations of soil organic nitrogen and describe changes in the content of nitrogen mineral forms at different depths in the semi-arid climate soil in the Mediterranean region. Availability and movement of nitrogen was monitored by capturing the mineral nitrogen into the structures of ion exchange resin applied to the soil in three different variants (control variant, a variant with the addition of cellulose, and the variant with the addition of raw silk). Ion exchange resins have been installed into soil profile in 2008, 2009, and 2010. After the in situ exposure the ion exchange resins were removed from the soil profile and the quantity of captured mineral N was determined by distillation titration method. The availability of ammonia-nitrogen was significantly affected by the addition of different substrates mainly by the additions of the raw silk, where the availability was regularly the highest. However, the availability of ammonia-nitrogen form was generally higher than the availability of nitrate form.

Imidacloprid induces changes in the structure, genetic diversity and catabolic activity of soil microbial communities

This is the first report describing the effect of imidacloprid applied at field rate (FR, 1 mg/kg of soil) and 10 times the FR (10*FR, 10 mg/kg of soil) on the structural, genetic and physiological diversity of soil bacterial community as determined by the phospholipid fatty acid (PLFA), the denaturing gradient gel electrophoresis (DGGE), and the community level physiological profile (CLPP) approaches. PLFA profiles showed that imidacloprid significantly shifted the microbial community structure and decreased the biomass of the total, bacterial and fungal PLFAs, however, this effect was transient at the FR dosage. The alterations in DGGE patterns caused by imidacloprid application, confirmed considerable changes in the overall richness and diversity of dominant bacteria. Although, as a result of imidacloprid application, the metabolic activity of microbial communities was generally lower, the richness and functional biodiversity of the soil microbial community were not negatively affected. In general, the analysis of the variance indicated that the measured parameters were significantly affected by treatment and the incubation time, however, the incubation time effect explained most of the observed variance. Imidacloprid degradation and the appearance of some new bands in DGGE profiles suggest the evolution of bacteria capable of degrading imidacloprid among indigenous microflora.

Utilizing earthworm and microbial assays to assess the ecotoxicity of chromium mine wastes

Mining plays an important role in the South African economy which results in environmental impacts. This holds a potential hazard for ecosystems surrounding mining areas and also for public health in the surrounding communities. The aim of this study was to use soil enzymatic analyses and earthworm (Eisenia andrei) responses viz. growth, reproduction, lysosomal membrane stability and tissue metal concentrations to determine the effect caused by chromium mine waste on the activity of soil microbial community and soil invertebrates. Results indicated that chromium mining did have an ecotoxic effect on enzymatic activity, as the material which exceeded the Cr benchmark for microorganisms showed the least amount of enzymatic activity. Significant differences in enzymatic activity were observed between the different samples. Earthworm biomass increases were low in the mining material exposed worms and might have been correlated with the low enzymatic activities in the materials. Biomass was however not considered a sensitive endpoint. Lysosomal membrane stability, measured as NRRT, proved to be a sensitive endpoint, showing the same pattern from day 7 up to day 28. Hatching success of cocoons was not considered a sensitive endpoint, due to the low cocoon production in the mining material exposed worms. Since mine waste materials often contain complex mixtures of metals that might be toxic on their own or in combination with other factors, it is difficult to attribute any observed effect to any of the specific metals analyzed. The metal concentrations were however compared to benchmarks in order to determine which of the metals could have had a toxic effect on the soil organisms. The only benchmark exceeded, was the PNEC for microorganisms, for Cr in the unrehabilitated silt (TDF1) material. None of the other benchmarks were exceeded, indicating that perhaps granular composition of the materials might have had a greater influence than the metals.

Impact of Super Absorbent Polymer and Plants on Microbial Community and Petroleum Hydrocarbon Degradation in Contaminated Soil

A greenhouse pot test, in which wheat, cabbage, spinach were cultivated separately in petroleum contaminated soil with and without super absorbent polymer (SAP), was conducted to evaluated the effect of plants and SAP on soil microbiological properties. phospholipid fatty acids (PLFAs) profiles were analyzed to reveal the microbial communities. As a measure of the functional activity of soil microbial community, the ratio of degraded to total petroleum hydrocarbon (TPH) in soil was estimated. The results indicated that SAP had an important effect on the soil microbial community and its degrading TPH activities. First, the principal component analysis (PCA) of the PLFA signatures revealed marked changes between soil with SAP and without SAP. In addition, the total amount and the profile of PLFA were significantly different between the untreated and SAP-amended soils. Using PLFA patterns as a biomarker, it was found that gram-positive bacteria (G+) were more sensitive to SAP than gram-negative bacteria (G-), and the biomass of G+ was higher in soil with SAP than in that without SAP. Second, the crop could stimulate the growth of soil microorganisms; however, the differences depended clearly on the crop species. The G+ and G- biomass was increased in cabbage, spinach soil containing SAP, but was decreased in wheat soils. The population of fungi was increased in cabbage and spinach soils containing SAP, but was decreased in wheat soil with SAP. The population of actinomycetes was decreased in all soils with SAP. Third, the ratio of degraded to TPH was slightly increased in soil with SAP treatment, but a significant change depended on the crop species. In total, 12 different PLFAs were identified, including saturated, monounsaturated, branched, and polyunsaturated species. There was a clear difference in the PLFAs composition between soils with and without SAP.

Impact of Humics and Plants on Microbial Community and Petroleum Hydrocarbon Degradation in Contaminated Soil

A greenhouse pot experiment, in which 3 different crops (wheat, cabbage, spinach) were cultivated in soil with and without humics (HS), was conducted to evaluate the effect of HS on soil microbiological properties. Phospholipid fatty acid (PLFA) profiles were analyzed to reveal the microbial community structure. As a measure of the functional activity of soil microbial community, the ratio of degraded to total petroleum hydrocarbon in soil was estimated. The results indicated that HS had an important effect on the soil microbial community and its functional activities. First, the principal component analysis (PCA) of the PLFA signatures revealed marked changes between soil with HS and without HS. In addition, the total amount and the profile of PLFA were significantly different between the untreated and HS-amended soils. Using PLFA patterns as a biomarker, it was found that gram-positive bacteria (G+) were more sensitive to HS than gram-negative bacteria (G-), and the biomass of G+ was higher in soil with HS than in that without HS. Second, the crop could stimulate the growth of soil microorganisms; however, the differences depended clearly on the crop species. The G+ and G- biomass was increased in spinach soil containing HS, but was decreased in wheat and cabbage soils. The population of fungi was increased in wheat and spinach soils containing HS, but was decreased in cabbage soil. The population of actinomycetes was increased in cabbage soil, but was decreased in wheat and spinach soils containing HS. Third, the ratio of degraded to total petroleum hydrocarbon was also affected by the HS treatment. It was slightly increased in soil with HS treatment, but a significant change depended on the crop species. In general, fatty acids ranged from C13 to C19. In total, 25 different PLFAs were identified, including saturated (SAT), monounsaturated (MUFA), branched (BR), and polyunsaturated (PUFA) species. There was a clear difference in the PLFA composition between soils with and without HS.

Soil Microbial Biomass, Basal Respiration and Enzyme Activity of Main Forest Types in the Qinling Mountains

Different forest types exert essential impacts on soil physical-chemical characteristics by dominant tree species producing diverse litters and root exudates, thereby further regulating size and activity of soil microbial communities. However, the study accuracy is usually restricted by differences in climate, soil type and forest age. Our objective is to precisely quantify soil microbial biomass, basal respiration and enzyme activity of five natural secondary forest (NSF) types with the same stand age and soil type in a small climate region and to evaluate relationship between soil microbial and physical-chemical characters. We determined soil physical-chemical indices and used the chloroform fumigation-extraction method, alkali absorption method and titration or colorimetry to obtain the microbial data. Our results showed that soil physical-chemical characters remarkably differed among the NSFs. Microbial biomass carbon (Cmic) was the highest in wilson spruce soils, while microbial biomass nitrogen (Nmic) was the highest in sharptooth oak soils. Moreover, the highest basal respiration was found in the spruce soils, but mixed, Chinese pine and spruce stands exhibited a higher soil qCO2. The spruce soils had the highest Cmic/Nmic ratio, the greatest Nmic/TN and Cmic/Corg ratios were found in the oak soils. Additionally, the spruce soils had the maximum invertase activity and the minimum urease and catalase activities, but the maximum urease and catalase activities were found in the mixed stand. The Pearson correlation and principle component analyses revealed that the soils of spruce and oak stands obviously discriminated from other NSFs, whereas the others were similar. This suggested that the forest types affected soil microbial properties significantly due to differences in soil physical-chemical features.

Active and total prokaryotic communities in dryland soils

The relationship between total and metabolically active soil microbial communities can change drastically with environment. In dry lands, water availability is a key factor limiting cells' activity. We surveyed the diversity of total and active Archaea and Bacteria in soils ranging from arid desert to Mediterranean forests. Thirty composited soil samples were retrieved from five sites along a precipitation gradient, collected from patches located between and under the dominant perennial plant at each site. Molecular fingerprinting was used to site-sort the communities according of their 16S rRNA genes (total community) and their rRNA (active community) amplified by PCR or RT-PCR from directly extracted soil nucleic acids. The differences between soil samples were much higher in total rather than active microbial communities: differences in DNA fingerprints between sites were 1.2 and 2.5 times higher than RNA differences (for Archaea and Bacteria, respectively). Patch-type discrepancies between DNA fingerprints were on average 2.7-19.7 times greater than RNA differences. Moreover, RNA-based community patterns were highly correlated with soil moisture but did not necessarily follow spatial distribution pattern. Our results suggest that in water-limited environments, the spatial patterns obtained by the analysis of active communities are not as robust as those drawn from total communities.

Effectiveness of management strategies in Acacia dealbata Link invasion, native vegetation and soil microbial community responses

Acacia dealbata Link is an aggressive invasive tree currently widely distributed but little information concerning its management is available. To our knowledge, this paper presents the first approach to its control in Europe. Presented assay was carried out in an invaded area in the NW of Spain using direct herbicide (triclopyr) spraying and herbicide application after cutting of saplings and adult plants. Biometrical measurements were periodically carried out and soil microbial community activity, plant diversity and species composition were monitored. A. dealbata individuals were severely affected by treatments, causing all of the treated individuals to die. Enzymatic activities and soil respiration were significantly enhanced when cutting and herbicide were applied in combination but not after herbicide application on its own. Species richness, diversity, evenness and cover were significantly reduced in the sprayed herbicide treatment one year after the last herbicide application, but the differences disappeared in the following spring. Plant species and functional group distribution were conditioned due to the treatment. This study provides the first approach to A. dealbata management in Europe. Due to the effectiveness of treatments and the absence of long-term effects, further application of triclopyr would seem to be feasible to reduce A. dealbata spreading.

Responses of ecosystem respiration and its components to fertilization in an alpine meadow on the Tibetan Plateau

Nitrogen (N) deposition alters composition and productivity of plant community, plant litter quality and quantity, composition and activity of soil microbial community. All these changes would influence ecosystem and soil CO2 emissions. We established a fertilization experiment in an alpine meadow in hinterland of the Tibetan Plateau to detect the responses of ecosystem and soil respiration to fertilization and further explore forces driving changes of CO2 fluxes. The fertilization experiment was conducted in 2008, in which five treatments were manipulated, i.e. three N levels of 0, 5, 10 g N m−2 yr−1 (coded as Control, LN and HN, respectively), and two N levels combined with constant level of 5 g phosphorus (P) m−2 yr−1, respectively (coded as LN + P and HN + P, respectively). Ecosystem respiration (Rec), aboveground plant respiration (Ra), and soil respiration (Rs) were measured in growing season of 2010 the third year of the experiment. N addition alone did not affect Rec, Ra or Rs. However, combination of N and P increased Rec, Ra and Rs mainly in later period of the growing season. Similarly, N addition did not affect aboveground biomass, but combination of N and P increased aboveground biomass. Rec, Ra and Rs were positively correlated with aboveground biomass, but were not correlated with belowground biomass, indicates enhancement of aboveground biomass by nutrient enrichment could contribute a large part of variation of ecosystem and soil respiration, especially at the end of the growing season. It is suggested that apparent negative effect of soil temperature on ecosystem and soil respiration could be confounded by the effect of aboveground biomass, especially under nutrient enrichment.

Non-linear impacts of Eucalyptus plantation stand age on soil microbial metabolic diversity

Purpose Although it is generally accepted that planting exotic plant species alters metabolic function of soil microbial communities, its temporal dynamic is often ignored when evaluating ecological effects of associated land use changes. To investigate the dynamic impacts of successive Eucalyptus planting on carbon metabolic activities of soil microbial communities, we studied community-level physiological profiles of soil microbial communities in different generations of Eucalyptus plantations.