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Purpose: Without accurate data on soil carbon (C) components and the relationships between soil C, soil respiration and biological C, it is challenging to produce assessments of the C sequestration rate in the process of soil remediation. Accordingly, it is essential to investigate the variations of soil C sources in different remediation treatments. Methods: To find out the contributors of soil C sequestration, we compared the different forms of soil C and soil respiration in cadmium (Cd)-polluted soil with morning glory, microbes or morning glory + microbe (M + microbe) remediation treatments. Results: Results indicated that (1) M + microbe treatments showed a higher Cd removal rate than microbe treatments; (2) soil C contents in morning glory + Lactobacillus + Saccharomyces (M + I) treatment was highest on day 80, however, soil C contents and soil respiration in other treatments declined with increasing remediation time; (3) soils with microbe application had higher microbial biomass carbon (MBC) compared with soils without microbe application; (4) nematode production C and respiration C increased with remediation duration; (5) the connection between soil organic carbon (SOC) and MBC was not observable; and (6) the disparities in soil C components between day 40 and day 80 were more pronounced compared with those between day 80 and day 120. Conclusion: The paper discusses the strengths and weaknesses of each soil Cd remediation methods, ultimately determining that the integration of morning glory, Bacillus velezensis and Saccharomyces may maximize the rate of soil carbon sequestration. [ABSTRACT FROM AUTHOR]

In order to explore a resource-saving and environmentally friendly approach to reduce nitrogen fertilizer and increase soil carbon pool in crop production. There are 5 treatments in the experiment namely CK: conventional fertilization and irrigation methods (pure nitrogen 30 kg/hm2); T1: drip irrigation fertilization method (pure nitrogen 15 kg/hm2); T2: drip irrigation fertilization method (pure nitrogen 15 kg /hm2), biochar-based fertilizer 600 kg/hm2; T3: drip irrigation method (pure nitrogen 15 kg/hm2), biochar-based fertilizer 1200 kg/hm2; T4: drip irrigation method (pure nitrogen 15 kg/hm2), biochar-based fertilizer is 1800 kg/hm2. The results showed that the microbial carbon content of the biochar-based fertilizer treatment under the condition of drip irrigation to reduce nitrogen was increased by 39.9%-68.4% as compared with the control. All treatments of the biochar-based fertilizer can significantly increase the soil easily oxidizable carbon in the early and mid-term growth. The content of solid carbon and soluble organic carbon increased by 31.3%-148.31% and 12.2%-63.92%, respectively. The application of biochar-based fertilizers significantly increased the net photosynthetic rate and stomatal conductance in the early and mid-transplanting period, as well as the transpiration rate and intercellular CO2 concentration throughout the growth period, and the SPAD, NDVI value, and dry matter accumulation. Under the condition of reducing nitrogen by 50%, drip irrigation combined with biochar-based fertilizer can significantly increase the soil microbial biomass carbon content, oxidizable carbon and soluble carbon content, promote the photosynthetic effect and dry matter accumulation of tobacco plants, and it is beneficial to promote crop planting.

Water-extractable organic matter is the most active and mobile form of soil carbon. The other active fraction and extremely biolabile is the carbon constituent of microorganisms. Both of these fractions play an essential role in agrocenoses and in the global carbon cycle on our planet. The aim of the work was to estimate the carbon content of water-extractable organic matter as well as that of microbial origin in typical chernozems (Protocalcic Chernozems) of different land-use types. Protocalcic Chernozem samples taken from the fields of long-term experiments with different types of land use were investigated: a permanent bare fallow for 55 years (since 1964); conventional tillage – four-field crop rotation, first rotation; direct seeding – crop rotation similar to direct seeding, first rotation; a 21-year fallow (since 1998) after 34 years of bare fallow (since 1964). We determined the carbon content of water-extractable organic matter and the carbon content of microbial origin. In the studied series of variants, the proportion of carbon of water-extractable organic matter in the total amount of organic matter in the upper horizon (0–15 cm) was 0.69, 0.85, 1.01, and 0.98%, respectively, while that of carbon of microbial origin was 0.27, 0.55, 0.53, and 1.52%. It was noted that against the background of increasing the content of total organic carbon in direct seeding variant, compared with the traditional soil treatment, the microbial biomass in this variant does not increase. The fallow variant, unlike all other types of land use, is characterized by a higher proportion of microbial carbon, in contrast to the carbon of water-extractable organic matter.

Climate change causes temperature increase and alteration of precipitation patterns with frequent droughts. These are known to influence soil microorganisms leading to community shifts and physiological adaptations, with consequences for biogeochemical cycles. However, whether soil microbial communities evolved at different average temperature differ in their response to drought is not well understood. Therefore, we collected ten soil samples per site (0–30 cm soil depth) from a walnut-fruit forest at 1000, 1300 and 1600 m above sea level with similar vegetation which represent average temperature differences of 1.3 °C between sites, mimicking potential climate change. We incubated these for 70 days at 22 °C either at (i) constant moisture of 50 % soil water holding capacity, or subjected them to (ii) two or (iii) three drying-rewetting (DRW) cycles. Respiration was measured during the incubation; microbial and chemical properties were determined at the end. No elevation specific or interactive effects with DRW were detected, except for fungal gene abundance, where values were highest at the intermediate elevation level. This reveals that soil microbial communities evolved at different average temperature regimes do not differ in their response to drought. Therefore, data were pooled across all sites and analyzed for the main effects of DRW. Microbial activity increased with DRW as reflected by enhanced net‑nitrogen mineralization and basal respiration. However, microbial biomass carbon and ergosterol were reduced by 20 and 25 % and bacterial gene abundance between 20 and 40 %. This reflects the strong osmotic pressure of DRW causing death of microbial cells. The higher maintenance requirements for cell adjustment to osmotic pressure of surviving microorganisms was revealed by an increase of the metabolic quotient q CO 2 by 60 % and accumulation of potassium in the microbial biomass. Fungi cope better with DRW as shown by higher fungal gene abundance as well as their ratio to ergosterol after DRW, reflecting shifts in cell volume due to community shifts or morphological adaptations. Our findings highlight that soil microbial communities evolved under different average temperature regimes respond similarly to DRW, but overall shift towards fungi as this taxon can potentially physiologically better adapt to osmotic pressure. Consequently, DRW may cause higher organic matter turnover and nutrient release due to higher microbial maintenance costs for osmotic cell adjustments. • Drying-rewetting reduced microbial, in particular bacterial biomass. • Surviving microorganisms adjusted the cell volume and accumulated potassium. • Osmotic adjustments increased metabolic quotient and net N-mineralization. • Microbes adapted to higher temperature did not cope better with drought. [ABSTRACT FROM AUTHOR]

To study the influences of gap size on the variation in soil nutrients, soil microbial carbon (micro-C), soil samples from Pinus massoniana forests were collected in and around different forest gaps with size ranging from 40.38 to 1321.40 m2 in Guizhou Province. The soil nutrients (include SOC, TP, TK, TKN, valid-P, valid-K and hydro-N) and micro-C in soil samples were analyzed, and the artificial neural networks was employed to explore the importance of different soil nutrients and gap size concerning micro-C. The results indicate that the micro-Cgap ranged from 38.00 to 660.32 mg kg-1 with a mean value of 221.24 mg kg-1, and the micro-Cforest ranged from 110.70 to 685.62 mg kg-1 with a mean value of 356.16 mg kg-1. The micro-Cgap/micro-Cforest values increased with the increase of gap size in the range from 40 to 600 m2, and this trend inversed when gap size was greater than 600 m2. Micro-C was mainly associated with valid-P for both gaps and surrounding forests, large gap may lead to the loss of soil N. The results suggested that: (a) SOC, TK, TKN, hydro-N and valid-P are important factors to microbial in forest soils; (b) TP, valid- K, TKN, TK, valid-P and SOC are important factors to microbial in gap soils. In summary, gaps can increase the heterogeneity of soil nutrients and soil microbial, valid-P is a key factor affecting microbial abundance for Pinus massoniana forest. These promote the preservation of biodiversity and pedodiversity. [ABSTRACT FROM AUTHOR]

Future climate scenarios indicate increasing drought intensity that threatens ecosystem functioning. However, the behavior of ecosystems during intense drought, such as the 2018 drought in Northern Europe, and their respective response following rewetting is not fully understood. We investigated the effect of drought on four different vegetation types in a temperate climate by analyzing dissolved organic matter (DOM) concentration and composition present in soil leachate, and compared it to two accompanying years. DOM is known to play an important role in ecosystem recovery and holds information on matter flows between plants, soil microorganisms and soil organic matter. Knowledge about DOM opens the possibility to better disentangle the role of plants and microorganisms in ecosystem recovery. We found that the average annual DOM concentration significantly decreased during the 2018 drought year compared to the normal year. This suggests a stimulation of DOM release under normal conditions, which include a summer drought followed by a rewetting period. The rewetting period, which holds high DOM concentrations, was suppressed under more intense drought. Our detailed molecular analysis of DOM using ultrahigh resolution mass spectrometry showed that DOM present at the beginning of the rewetting period resembles plant matter, whereas in later phases the DOM molecular composition was modified by microorganisms. We observed this pattern in all four vegetation types analyzed, although vegetation types differed in DOM concentration and composition. Our results suggest that plant matter drives ecosystem recovery and that increasing drought intensity may lower the potential for ecosystem recovery. [ABSTRACT FROM AUTHOR]

To fulfill sustainability principles, a three-site field experiment was conducted to screen suitably mixed passivators from lime + biochar (L + C, 9000 kgha−1 with a rate of 1:1) and lime + biochar + sepiolite (L + C + S, 9000 kg ha−1 with a rate of 1:1:1), in Yuecheng (YC), Zhuji (ZJ), and Fuyang (FY), where there are typical contaminated soils, in South China. Treated with passivators in soil, DTPA-extractable Cd, Cr and Pb in soil were decreased by 9.87–26.3%, 37.2–67.5%, and 19.0–54.2%, respectively; Cd, Cr, and Pb in rice were decreased by 85.9–91.5%, 40.0–76.5%, and 16.4–45.4%, respectively; and these were followed by slightly higher efficacy of L + C + S than L + C. The differences between L + C and L + C + S mainly lie in soil microbial communities, enzymes, and fertility. In YC, treatment with L + C + S increased microbial carbon and activities of urease (EC3.5.1.5) and phosphatase (EC3.1.3.1) by 21.0%, 85.5%, and 22.3%; while treatment with L + C decreased microbial carbon and activities of phosphatase and sucrose (EC3.2.1.26) by 1.31%, 34.9%, and 43.4%, respectively. Moreover, the treatment of FY soils with L + C + S increased microbial carbon and activities of urease, phosphatase, and sucrase by 35.4%, 41.6%, 27.9%, and 7.37%; and L + C treatment only increased the microbial carbon and the activity of phosphatase by 3.14% and 30.3%, respectively. Furthermore, the organic matter and available nitrogen were also increased by 8.8–19.0% and 7.4–14.6% with L + C + S treatments, respectively. These suggested that the combination of L + C + S stimulated the growth of soil microbial communities and increased the activity of soil enzymes. Therefore, the L + C + S strategy can be a practical and effective measure for safe rice production as it was more suitable for the remediation of heavy metals in our experimental sites. [ABSTRACT FROM AUTHOR]

Recently, the eastern region of the Maranhão state (Northeastern Brazil) became a hotspot of land‐use change (LUC) directly from native vegetation to soybean cultivation, but due to the soil characteristics, LUC has caused substantial soil organic carbon (SOC) and nitrogen depletion. Therefore, we quantified these impacts arising from two factors: (i) different timeframes after LUC and (ii) contrasting soil management practices. For the first study, soil samples (0–30 cm; six replicates) were taken on soybean fields year one, year eight and 15 years after LUC. It the second study, another area was sampled, of which part was managed under no‐tillage (NT) and the other using a mouldboard plough (MP). For both studies, native vegetation (NV) was sampled as the control. NV stored about 50 Mg of carbon (C) ha−1; but LUC reduced C stocks by 35% (after 8 and 15 years); moreover, labile‐C decreased between 20% and 45%, while, microbial‐C decreased between 20% and 60%, considering the interval between year one and 15 years. Regarding soil management, the MP did not cause differences on C stock (24 Mg C ha−1) in comparison to NT; however, both labile‐C and microbial‐C decreased by 15% to NT, while, decreased by 40% to MP. These results lead us to believe that, since LUC is inevitable, we suggested the adoption of the best agricultural management practices, in order to preserve/increase the SOC, reducing the impacts on GHG emissions and, thus, achieving sustainability and profitability. [ABSTRACT FROM AUTHOR]

Future climate scenarios indicate increasing drought intensity that threatens ecosystem functioning. However, the behavior of ecosystems during intense drought, such as the 2018 drought in Northern Europe, and their respective response following rewetting is not fully understood. We investigated the effect of drought on four different vegetation types in a temperate climate by analyzing dissolved organic matter (DOM) concentration and composition present in soil leachate, and compared it to two accompanying years. DOM is known to play an important role in ecosystem recovery and holds information on matter flows between plants, soil microorganisms and soil organic matter. Knowledge about DOM opens the possibility to better disentangle the role of plants and microorganisms in ecosystem recovery. We found that the average annual DOM concentration significantly decreased during the 2018 drought year compared to the normal year. This suggests a stimulation of DOM release under normal conditions, which include a summer drought followed by a rewetting period. The rewetting period, which holds high DOM concentrations, was suppressed under more intense drought. Our detailed molecular analysis of DOM using ultrahigh resolution mass spectrometry showed that DOM present at the beginning of the rewetting period resembles plant matter, whereas in later phases the DOM molecular composition was modified by microorganisms. We observed this pattern in all four vegetation types analyzed, although vegetation types differed in DOM concentration and composition. Our results suggest that plant matter drives ecosystem recovery and that increasing drought intensity may lower the potential for ecosystem recovery.

Soil provides ecosystem services, including storage of CO2 and protection against global warming. The Ouargla region is characterized by high temperatures, low and irregular rainfall, sparse vegetation and soils poor in organic matter. Nevertheless, the soil remains a favorable environment for macros and microorganisms, which tolerate this deficit, even if this microbial biomass represents only 2 to 4% on average of organic carbon. It intervenes for the renewal of organic matter in the soil. The aim of this work is to study the impact of microorganisms on organic carbon storage in different soil landscapes of the Ouargla region. For this study, 7 stations of different pedo-sequences were chosen (saline soil, reg soil, clay soil…etc). After taking a soil sample at 30 cm, the samples underwent microbiological analyzes for the enumeration of bacteria and fungi, fumigationextraction, and physicochemical analyzes. The results of enumeration of the main microbial groups in bacteria and fungi showed the predominance of bacterial microflora, followed by fungal microflora at higher values in cultivated soil and those of Sebkhat. The identification of fungal species according to the determination keys allowed us to identify Alternaria alternata, Rhizopus sp, and Aspergillus niger, as well as yeasts. The fumigation-extraction results show that the microbial carbon values are higher in Sebkhat N’Goussa, gypsum soil of Frane and in cultivated soils. It is at these stations where high levels of organic carbon and organic matter are recorded. We can say that microorganisms play an important role in carbon sequestration. They mineralize microbial residues and provide carbon to the stable organic matter fraction of soil. [ABSTRACT FROM AUTHOR]

To fulfill sustainability principles, a three-site field experiment was conducted to screen suitably mixed passivators from lime + biochar (L + C, 9000 kgha−1 with a rate of 1:1) and lime + biochar + sepiolite (L + C + S, 9000 kg ha−1 with a rate of 1:1:1), in Yuecheng (YC), Zhuji (ZJ), and Fuyang (FY), where there are typical contaminated soils, in South China. Treated with passivators in soil, DTPA-extractable Cd, Crand Pb in soil were decreased by 9.87–26.3%, 37.2–67.5%, and 19.0–54.2%, respectively; Cd, Cr, and Pb in rice were decreased by 85.9–91.5%, 40.0–76.5%, and 16.4–45.4%, respectively; and these were followed by slightly higher efficacy of L + C + S than L + C. The differences between L + C and L + C + S mainly lie in soil microbial communities, enzymes, and fertility. In YC, treatment with L + C + S increased microbial carbon and activities of urease (EC3.5.1.5) and phosphatase (EC3.1.3.1) by 21.0%, 85.5%, and 22.3%; while treatment with L + C decreased microbial carbon and activities of phosphatase and sucrose (EC3.2.1.26) by 1.31%, 34.9%, and 43.4%, respectively. Moreover, the treatment of FY soils with L + C + S increased microbial carbon and activities of urease, phosphatase, and sucrase by 35.4%, 41.6%, 27.9%, and 7.37%; and L + C treatment only increased the microbial carbon and the activity of phosphatase by 3.14% and 30.3%, respectively. Furthermore, the organic matter and available nitrogen were also increased by 8.8–19.0% and 7.4–14.6% with L + C + S treatments, respectively. These suggested that the combination of L + C + S stimulated the growth of soil microbial communities and increased the activity of soil enzymes. Therefore, the L + C + S strategy can be a practical and effective measure for safe rice production as it was more suitable for the remediation of heavy metals in our experimental sites.

Microbial communities in soil A horizons derive their carbon from several potential sources: organic carbon (C) transported down from overlying litter and organic horizons, root-derived C, or soil organic matter. We took advantage of a multi-year experiment that manipulated the 14C isotope signature of surface leaf litter inputs in a temperate forest at the Oak Ridge Reservation, Tennessee, USA, to quantify the contribution of recent leaf litter C to microbial respiration and biomarkers in the underlying mineral soil. We observed no measurable difference (4 years) old (which fell after (or prior to) the manipulation and therefore did not differ between plots) are not supported because the 14C signatures of the PLFA compounds (averaging 200-220‰) is much higher that of the 2004-5 leaf litter (115‰) or pre-2000 litter. A mesocosm experiment further demonstrated that C leached from 14C-enriched surface litter or the O horizon was not a detectable C source in underlying mineral soil microbes during the first eight months after litter addition. Instead a decline in the 14C of PLFA over the mesocosm experiment likely reflected the loss of a pre-existing substrate not associated with added leaf litter. Measured PLFA Δ14C signatures were higher than those measured in bulk mineral soil organic matter in our experiments, but fell within the range of 14C values measured in mineral soil roots. Together, our experiments suggest that root-derived C is the major (>60%) source of C for microbes in these temperate deciduous forest soils. © 2010 Elsevier Ltd.

There is insufficient information about the dynamics of soil organic matter in integrated production systems. Therefore, we aimed to evaluate the variations in soil C and N stocks and microbial attributes as a function of the distances apart from the eucalyptus double rows within a silvopastoral system in the Brazilian Cerrado. Four treatments were considered, consisting of four distances (0.5 m, 1.6 m, 3.8 m and 6 m) apart from the double rows of eucalyptus for soil sampling within the silvopastoral system. The soil C and N contents and stocks, C/N ratio, microbial C (Cmic), soil basal respiration, metabolic quotient and microbial quotient were evaluated. Our results showed that soil C contents and stocks were significantly higher near the eucalyptus trees. Soil C stocks ranged from 99.91 (6.0 m) to 119.64 Mg ha−1 (0.5 m) up to 100 cm soil depth, with an increase of 19.73 Mg ha−1 nearest of the forest component. The same pattern was observed for N stocks, with values ranging from 9.52 (0.5 m) to 7.95 Mg ha−1 (6.0 m) and representing an increase of 1.57 Mg ha−1 near the eucalyptus. We also found an increase of 51.32% in the Cmic at 0.5 m apart from the forest component. Thus, we can infer that the presence of eucalyptus improved the soil quality within the silvopastoral system, indicating that the correct soil sampling and measurements must be performed considering all the transect cultivated with forage grass and double rows of eucalyptus. [ABSTRACT FROM AUTHOR]

The deposition of volcanic ash into the ocean initiates a range of chemical and biological reactions. During diagenesis, these reactions may enhance the preservation of organic carbon (OC) in marine sediments, which ultimately promotes CO 2 sequestration from the ocean-atmosphere system. However, this interpretation is reliant on a small number of studies that make a link between tephra and OC burial. Here, we compare organic and inorganic geochemical data from tephra-bearing marine sediments from three sites that differ widely in their location, age, and composition. We show that OC is buried in, and proximal to, tephra layers, in proportions higher than would be expected via simple admixture of surrounding sediment. Our data indicate that this OC is preserved primarily through interactions with reactive iron phases, which act to physically protect the carbon from oxidation. Analysis of the composition of the OC associated with reactive iron indicates it is isotopically (consistently more negative δ13C than sediment) and chemically (comprised of compounds not found in the sediment) distinct from OC in the background sediments. We interpret this signal as indicating a microbial source of OC, with autochthonous OC production resulting from autotrophic microbial exploitation of nutrients supplied from tephra. This finding has implications for our understanding of carbon cycling on Earth, and possibly for the emergence of life in terrestrial and perhaps even extra-terrestrial environments. • Organic carbon (OC) is buried in and around tephra layers in high proportions. • OC is preserved through interactions with reactive iron and manganese phases. • Tephra-hosted OC is different from OC in surrounding sediments. • This difference in OC composition suggests in situ, autochthonous OC production by microbes. [ABSTRACT FROM AUTHOR]

Highlights • Future changes in the global SOC and MBC pools are simulated using TRIPLEX-MICROBE. • SOC simulated by TRIPLEX-MICROBE in the Arctic decreases in 21st under three RCPs. • Tropical and temperate vegetation expand northward along with radiation increase. Abstract Microbial physiology is very important in the biogeochemical cycles of the Earth system. Considerable uncertainty exists in the responses of global soil organic and microbial carbon to future climate change. In this study, future changes in the global soil organic carbon (SOC) and microbial carbon (MBC) pools are simulated using TRIPLEX-MICROBE, which considers and predicts microbial activity, under three future representative concentration pathways (RCPs) in the 21st century. Between 2013 and 2100, TRIPLEX-MICROBE simulates decreases in SOC from 1099 Pg (petagrams, 1012 kg) to 1032 Pg, 996 Pg and 924 Pg under RCP scenarios RCP2.6, RCP4.5 and RCP8.5, respectively, representing reductions of approximately 6.1%, 9.4% and 15.9%, respectively. The MBC reaches a stable state after 2030 under RCP2.6, and it increases from 20.89 Pg to 23.78 Pg between 2013 and 2100. Under RCP4.5 and RCP8.5, MBC increases by 20.3% and 39.6%, respectively, between 2013 and 2100. The SOC stored in the Arctic declines under the priming effect; however, as the climate gradually warms from the equator to the mid-latitudes, the Northern Hemisphere becomes a larger carbon sink, which could offset the carbon losses from high-latitude and high-altitude regions. The latitude where the MBC reaches its maximum during the coldest season of a year in the Northern Hemisphere moves northward approximately 10 degrees under the three RCPs from the latitude in the historical period. Tropical and temperate vegetation expand northward gradually with warming, and vegetation fixes more carbon as it migrates northward to offset the increase in atmospheric CO 2. [ABSTRACT FROM AUTHOR]

Highlights: • A pronounced effect of Pheidole ants on soil was observed in a tropical forest. • Ants increased spatial variability of soil microbial and physicochemical properties. • Different feeding habits contributed to explanation of the diverse effect on soil. • The species Pheidole capellini usually had the greatest impact on soil parameters. Abstract The research about the effect of ants on soils is generally focused on the aboveground-nesting ant species in temperate soils. Little is known about the potential of belowground nesting ants in regulating soil properties in tropical forests. In this study, three belowground-nesting Pheidole ant species with different feeding habits were surveyed to explore the nesting effects on microbial carbon and physicochemical properties in tropical forest soils. We found that Pheidole ants with high-density nests can induce a pronounced effect on the concentration and vertical variability of microbial carbon and physicochemical properties in soils. Pheidole capellini as a honeydew harvester elevated the levels of soil microbial carbon, soil temperature, total organic carbon, readily oxidizable carbon, and total nitrogen and NO 3 −, but decreased soil bulk density. Whereas, the highest increase in soil moisture and NH 4 + was observed in the nests of P. noda ants (seed predator), and the greatest decrease of dissolved organic nitrogen was in the nests of P. spathifera ants (scavenger). Pheidole capellini ants inputted more materials into the nests, thus they had the greatest modification on the concentration and vertical change in soil properties. We conclude that Pheidole ant species differ in the direction and power of their effect on soil heterogeneity and soil fertility, which may be mainly attributed to different feeding strategies in the tropical forests. [ABSTRACT FROM AUTHOR]

Abstract This work assessed the role of mangrove vegetation on soil characteristics of mangrove sediment and barren sandy soil in order to assess the impact of mangrove vegetation on the coastal soil. The soil samples were obtained from three sites (natural mangroves, planted mangroves, and non-mangrove sandy shore) located in the Vellar-coleroon estuarine complex for four seasons at three different soil depths (0–10, 10–50 and 50–100 cm). The samples were analyzed for microbial counts, nutrients and trace elements. The total fungal count was 42.5-fold higher in natural mangrove sediment than sandy soil as against the total heterotrophic bacterial count which was only 1.9-fold higher. Notably, planted mangrove sediment had higher total organic carbon, microbial carbon, N, P and K than the sandy soil. There was a significant correlation between soil temperature and microbial counts revealing that the temperature rise may be favorable for soil biospheres such as heterotrophs, saprophytes, and parasites. Remarkably, boron, cadmium, and cobalt were many folds greater in the natural mangrove sediments than that in planted mangrove sediment. This work has suggested that an amendment of sandy soil with nutrients nitrogen and microbial biomass is likely to transform the barren soil into carbon-rich mangroves. Graphical abstract Image 1 Highlights • Analysis of microbial, and physicochemical properties of mangrove and sandy habitat. • Microbiome, clay and silt was higher in natural mangrove habitat than the sandy habitat. • Mangrove habitat had higher TOC, microbial carbon, N, P and K than the sandy habitat. • Amendment of sandy habitat with microbial fertilizer can convert it into rich mangroves. • Thereby mangrove forest can automatically establish and act as green wall in coasts. [ABSTRACT FROM AUTHOR]

Cover crops may enhance soil organic carbon (SOC) sequestration, but the links among SOC fractions, microbial necromass carbon (C), and SOC sequestration potential in legume and non-legume cover-cropped orchards are unclear. We leveraged data from seven orchards with varying climatic and edaphic properties in China to assess the effects of legume and non-legume cover crops on SOC and microbial necromass C in bulk soil, particulate organic matter (POM), and mineral-associated organic matter (MAOM). Legume cover crops led to a significantly greater increase in SOC than non-legumes (23 % vs. 2 %), compared with no cover crops. The MAOM-C with legumes and non-legumes were similar but were both significantly greater than the control plots without cover crops. Legume cover crops positively influenced bacterial and fungal necromass C in all SOC fractions, while non-legume cover crops only affected fungal necromass C in bulk soil and MAOM. The effect of cover crops on the microbial necromass C to SOC ratio was negligible. Fungal necromass contributed most of the microbial necromass C to SOC accumulation, particularly in MAOM. Linear regression showed SOC, POM-C, and MAOM-C accumulated with increasing microbial necromass C. Microbial necromass C was the key factor explaining the variation in POM-C and MAOM-C compared to other climatic and edaphic factors. Partial least squares path modeling showed a causal relationship among cover crops, climate, soil substrates, soil properties, microbial necromass, and SOC and SOC fractions. Our study suggests that changes in microbial necromass C and composition may explain most of the increase in SOC in cover-cropped orchards and that MAOM-C is the principal sink of microbial necromass. This information is valuable for improving our understanding of the potential impact of microbial necromass C on enhancing SOC sequestration potential in orchard soils under cover crop management. [Display omitted] • Cover crop impacts on SOC and microbial necromass were tested in seven orchards. • Legume cover crops increased: SOC by 23 %, POM-C by 24 %, and MAOM-C by 25 %. • Non-legume cover crops increased: SOC by 2 % and MAOM-C by 9 %. • Changes in SOC content and stability were linked to microbial necromass carbon. • Cover crops increased SOC most via fungal necromass carbon accumulation in MAOM-C. [ABSTRACT FROM AUTHOR]

Frequent periods of low rainfall accompanying climate change are expected to affect many aspects of agricultural production and greenhouse gas emissions. In this work, we conducted field experiments on soil CO 2 efflux and soil microbial activity using two precipitation treatments and two crop management technologies. While the control treatment was exposed to natural precipitation, the reduced water availability was induced during the early stages of crop growth using rain-exclusion shelters within the water deficit treatment. We aimed to test the difference in the response to water deficit between two management technologies: conventional tillage (CT - ploughed without cover crops) and adaptation technology (AT - no-till with species rich cover crops). After a month of simulated water deficit, the soil CO 2 efflux under a regime of adaptation technology was essentially the same as that under the conventional technology, and the decrease in soil CO 2 efflux ranged between 22 % and 55 %. The water deficit had a technology-specific effect on microbes. While no effect on the microbial carbon under CT was observed, the water deficit decreased Cmic under AT. In contrast, the opposite pattern was observed for DHA. When a normal soil water regime was restored, CO 2 efflux recovered rapidly while recovery of microbial biomass and dehydrogenase activity was more variable. Generally, the soil microbial biomass and activity recovered better under AT. The results show that while the reduction in Rs during water deficit and its recovery after the restoration of the ambient precipitation regime were not affected by the technology, the response of microbial biomass and activity to water deficit depended on the technology with better recovery under AT. [Display omitted] • One-month simulated drought resulted in a decrease in soil CO 2 efflux by 22–55 %. • CO 2 efflux recovered after the end of the water deficit period. • Response of microbial carbon and DHA to water deficit depended on the tillage. • Adaptation tillage technology showed better post-drought recovery of soil activity. [ABSTRACT FROM AUTHOR]

ABSTRACT Discovered in 1980 and unleashed an utter gold rush of the modern era, Serra Pelada was the largest open-air mine in Brazil. About 80,000 gold prospectors worked there until 1984, when the gold pits were flooded. The environmental impact caused by mining inflicted irreversible damage to the ecosystem, with the formation of a large lake and piles of waste rock and sterile overburden, still evident 28 years after the mine was closed. This study aimed to evaluate the available and pseudo total contents of potentially toxic elements (PTEs), the contamination and pollution levels, and to understand how the biological soil factors are related to the chemical properties of the soil and the available PTE contents in the Serra Pelada - Amazônia, Brazil. Soil was collected from seven areas around the lake: Area 1 - margin of the mine without waste and/or sterile deposits; Area 2 - margin with waste and/or sterile deposits; Area 3 - area with sterile deposit; Area 4 - mine tailings, denominated curimã by the prospectors, from which gold had been extracted; Area 5 - sediment dredged from the lake in the mine pit; Area 6 - area with agroforestry system; Area 7 - riparian forest, unaffected by the artisanal gold extraction process (control treatment). Apart from selenium (Se), all evaluated elements, in at least one of the studied areas, exceeded the contents of the investigation values (defined as the content of a given substance in soil or groundwater above which the human health is under potential direct or indirect risks, considering a standardized exposure scenario) in agricultural areas in Brazil, as determined by the National Council of the Environment. Soil enrichment and contamination with Co, Ba, Mn, and Hg were investigated. Principal component analysis showed that the available levels of PTEs influenced the soil biological properties, in particular basal respiration, indicating that important ecosystem processes are being affected by PTE contamination.

Integrated crop-livestock systems (ICLs) are a viable strategy for the recovery and maintenance of soil characteristics. In the present study, an ICL experiment was conducted by the Instituto Agronômico do Paraná in the municipality of Xambre, Parana (PR), Brazil, to evaluate the effects of various grazing intensities. The objective of the present study was to quantify the levels of microbial biomass carbon (MBC) and soil enzymatic activity in an ICL of soybean (summer) and Brachiaria ruziziensis (winter), with B. ruziziensis subjected to various grazing intensities. Treatments consisted of varying pasture heights and grazing intensities (GI): 10, 20, 30, and 40 cm (GI-10, GI-20, GI-30, and GI-40, respectively) and a no grazing (NG) control. The microbial characteristics analysed were MBC, microbial respiration (MR), metabolic quotient (qCO2), the activities of acid phosphatase, β-glucosidase, arylsuphatase, and cellulase, and fluorescein diacetate (FDA) hydrolysis. Following the second grazing cycle, the GI-20 treatment (20-cm - moderate) grazing intensity) contained the highest MBC concentrations and lowest qCO2 concentrations. Following the second soybean cycle, the treatment with the highest grazing intensity (GI-10) contained the lowest MBC concentration. Soil MBC concentrations in the pasture were favoured by the introduction of animals to the system. High grazing intensity (10-cm pasture height) during the pasture cycle may cause a decrease in soil MBC and have a negative effect on the microbial biomass during the succeeding crop. Of all the enzymes analyzed, only arylsuphatase and cellulase activities were altered by ICL management, with differences between the moderate grazing intensity (GI-20) and no grazing (NG) treatments.

Mineral protection is known as an important mechanism stabilizing soil organic carbon (SOC). However, the composition, sources, and variations of mineral-protected SOC remain poorly constrained. To fill this knowledge gap, we used hydrofluoric acid to demineralize soil matrix and compared the sources and distribution of mineral-protected lipids (ML) versus hydrolyzable lipids (HL) of four typical Chinese shrubland soils. ML was found to represent a sizable fraction (9-32%) of total aliphatic lipids (including n-alkanols; n-alkanoic acids; α, ω-alkanedioic acids; hydroxyalkanoic acids; and midchain-substituted acids) in all soils. Based on carbon chain length and branch positions, microbe- and plant-derived lipids were distinguished. No significant difference was found in the ratio of microbe- to plant-derived lipids in ML versus HL, implying that plant and microbial inputs are equally important for the mineral-associated soil lipids. However, ML contained a higher proportion of nonspecific lipids, especially at depths. Furthermore, to evaluate key environmental variable(s) controlling the distribution of different lipid components, a multiple stepwise regression analysis was conducted. Notably, ML was mainly affected by SOC-to-nitrogen ratio instead of mineralogical properties, implying that the accrual of mineral-associated soil lipids relies strongly on organic matter properties. Collectively, our findings provide novel insights on sources and accumulation mechanisms of mineral-protected soil lipids. SOC decomposition and subsequent accretion of degradation products appear to be vital for the sequestration of mineral-associated soil lipids and warrant better recognition in the investigations of stable soil carbon accumulation mechanisms. [ABSTRACT FROM AUTHOR]

The aim of this study was to evaluate the sustainability of an agro-industry sludge as a nitrogen (N) fertilizer in perennial crops by assessing its dynamics of release of: 1) N as ammonium (NH4+)- and nitrate (NO3−)-N, and 2) carbon as soil respiration. In incubation assay, application of agro-industry sludge promoted the maximum NH4+-N concentration (50 mg kg−1) 2 h after application, then it decreased with time until day 26. NO3−-N increased, reaching the maximum between day 60 and day 100, according to a second degree function. Agro-industry sludge showed a slower release of NO3−-N compared with urea. Soil basal respiration and cumulative amount of carbon dioxide were higher in sludge from day 71 on. In field, soil NO3−-N increased after fertilization treatments and was higher in Calcari Stagnic Cambisols soil. Sludge showed a potential lower environment impact in terms of mineral N release, than urea. [ABSTRACT FROM AUTHOR]

The use of mulching is an alternative to control weeds but there are few studies on its effect on soil quality. In this sense, this study aimed to evaluate the effect of types of mulching on the attributes of microbial carbon, nitrogen and phosphorus in a Typic Hapludox with production of integrated apples in southern Brazil. The experiment was conducted in randomized blocks in the Vacaria, state of Rio Grande do Sul, southern Brazil. The soil mulch types studied were: pine needle, sawdust, black plastic and a control. The soil samples were collected in February (summer) and August (winter) of 2006, and the attributes related to total organic and microbial carbon, nitrogen and phosphorus were determined. Organic mulchings (pine needle and sawdust) promoted lower soil temperature, and greater moisture, microbial carbon (Cmic), microbial nitrogen (Nmic), and the ratios Cmic:Corg, Nmic:Norg and microbial C:N than black plastic. Microbial phosphorus was greater in winter. Sawdust mulching promoted the best conditions to microbial biomass in winter. The mulch types increased the microbial compartment in winter as compared to the nonweeded control .O uso da cobertura do solo é alternativa para o controle de plantas daninhas. Entretanto há poucos estudos sobre seu efeito na qualidade do solo. Avaliou-se, em duas estações do ano, o efeito de tipos de cobertura do solo nos atributos microbianos de um Latossolo com produção integrada de maçãs no sul do Brasil. O experimento foi conduzido em blocos ao acaso em Vacaria, RS. As coberturas estudadas foram: acícula, serragem e plástico preto comparativamente ao tratamento controle (infestado). As amostras de solo foram coletadas em fevereiro e agosto de 2006, sendo avaliados atributos relacionados ao carbono, ao nitrogênio e ao fósforo. As coberturas orgânicas (acícula e pínus) promoveram no solo menor temperatura e maior umidade, além de maiores teores de carbono e nitrogênio microbiano, relação Cmic:Corg, Nmic:Norg e Cmic:Nmic quando comparadas ao solo sob plástico preto; já o fósforo microbiano foi maior no inverno. A cobertura com serragem promoveu as melhores condições para os compartimentos microbianos no inverno, sendo que nessa mesma estação, as coberturas incrementaram o compartimento microbiano comparativamente ao tratamento controle, infestado com plantas daninhas.

A biomassa e a atividade microbiana têm sido apontadas como indicadores adequados de alterações provocadas por diferentes sistemas de uso e manejo do solo. O objetivo deste trabalho foi avaliar as alterações na biomassa e na atividade microbiana de um Latossolo Vermelho-Amarelo ácrico típico, sob Cerrado nativo e diferentes sistemas de manejo, na região fisiográfica Campos das Vertentes, Minas Gerais. Os sistemas avaliados foram: cultivo convencional com batata (CCB); cultivo com batata, sucedido por aveia e rotação com milho (CBAM); cultivo convencional com milho (CCM); plantio direto com milho (PDM); cultivo convencional com eucalipto (CCE); e o Cerrado nativo (CN) como referência. Foram coletadas amostras de solo nas profundidades de 0-10, 10-20 e 20-30 cm, analisados o C microbiano (Cmic) e a respiração basal e calculados o quociente metabólico (qCO2) e a relação Cmic/C orgânico. A biomassa e a atividade microbiana foram influenciadas pelos diferentes sistemas de manejo do solo, e as condições mais satisfatórias para a microbiota do solo ocorreram no Cerrado nativo. O manejo mais intensivo do solo e o uso frequente de agrotóxicos, característicos dos sistemas CCB e CBAM, determinaram redução nos teores de Cmic, menores valores da relação Cmic/C orgânico e maiores valores de qCO2, indicando uma provável condição de estresse para a biomassa microbiana.Biomass and microbial activity have been suggested as appropriate indicators of changes caused by different land use and management systems. The objective of this study was to evaluate alterations in biomass and microbial activity of a typic acric Red-Yellow Latosol (Oxisol), under native Cerrado and different management systems, in the physiographic region Campos das Vertentes, state of Minas Gerais. The evaluated systems were: conventional tillage with potato (CCB); potato followed by oat in rotation with corn (CBAM); conventional tillage with corn (CCM); no-till with corn (PDM); conventional tillage with eucalyptus (CCE); and native Cerrado (CN) as reference. Soil samples were collected in the layers 0-10, 10-20 and 20-30 cm. The microbial carbon (Cmic) and basal respiration were analyzed, and the metabolic quotient (qCO2) and Cmic/organic carbon ratio were calculated. The biomass and microbial activity were influenced by the different soil management systems and the conditions for soil microbiota were most adequate under NC. The most intensive soil managements with frequent pesticide use, as in the CCB and CBAM systems, resulted in lower amounts of Cmic, lower Cmic/TOC ratio and higher qCO2 values, indicating a probable stress condition for microbial biomass.

O potencial de medidas de biomassa microbiana do solo como indicadoras da bioatividade e das interferências nesse ambiente pode ser verificado pela quantidade de trabalhos publicados a esse respeito. Entretanto, a comparação entre dados de diferentes autores, localidades e solos só é possível quando o método de determinação é o mesmo. No entanto, há numerosos trabalhos que propõem diferentes métodos e cálculos. Este trabalho avaliou resultados de determinação de C microbiano obtidos por diferentes métodos de extração e digestão de amostras de dois solos e cálculos de biomassa; além de diferentes cálculos para transformação indireta de CO2 produzido por respiração basal e induzida em C microbiano, nos dois diferentes solos. Os resultados variaram bastante entre métodos e cálculos e concluiu-se que o método de Vance et al. (1987), mais freqüentemente citado na literatura, deve ser a opção para boa comparação da quantidade de C microbiano entre solos e dados da literatura.The potential of soil microbial biomass measurements as indicators of soil bioactivity and interferences in this environment can be verified by the amount of published papers on the subject. Nevertheless, a comparison among data from different authors, regions, and soils is only possible when the methodology employed in the determinations is the same. Several papers, however, propose different methodologies and calculations. This study evaluated the results of microbial carbon determination by different extraction and digestion methodologies in two distinct soils. It was also performed biomass calculations, besides calculations for indirect transformation of CO2 from basal and induced respiration into microbial carbon in the two soils. Results varied greatly among methods and calculations, and the conclusion was drawn that the most frequently used methodology (Vance et al., 1987) should be adopted for a valid comparison of the amount of microbial carbon among soils and literature data.

The soils of the studied area function in different temperature regimes: under the influence of permafrost (Turbic Histic Cryosol and Cryic Eutric Histosol) and long-term seasonal freezing (Albic Podsol). Sporadic permafrost defines the differences in temperature regimes. All soils are characterized by the low production of carbon dioxide (an average of 160 mg CO/(m h)), indicating their low biological activity. The lack of easily available carbon for microorganisms is detected in all investigated soils by the C: C ratio despite the high reserves of organic matter. The value of CO emission and the C: C ratio are 'site-specific' for the region of investigation and may be used as indicators of environmental changes. Cryogenic peat soils represent a unique natural object and ensure the functional diversity and integrity of northern taiga ecosystems in Western Siberia. [ABSTRACT FROM AUTHOR]

Avaliou-se, em um Latossolo Roxo, o efeito de diferentes formas de manejo do solo sobre a matéria orgânica do solo e na biomassa microbiana. Os tratamentos usados foram: mata natural; mata natural até 1976 e café até 1994 (amostragem na projeção da copa e na entrelinha); mata natural até 1976, café até 1991 e milho até 1994; mata natural até 1940, café até 1960, citros até 1978, e cana-de-açúcar até 1994 (amostragem na linha e na entrelinha). A mata natural apresentou os maiores valores de C orgânico no solo e na fração humina e os menores valores foram obtidos nas áreas com cana-de-açúcar, que apresentaram os maiores valores de C microbiano em relação à mata natural. O uso agrícola do solo aumentou a porcentagem de C orgânico na forma de ácidos húmicos e fúlvicos, em relação à mata natural. Em geral, o solo apresentou mais de 74% do C orgânico na forma de húmus residual.The effect of soil management on forms of carbon and microbial biomass was studied in a Typic Euthortox soil. The treatments tested were: natural forest; natural forest till 1976 and coffee till 1994 (sampling on the shoot projection and between lines ); natural forest till 1976, coffee till 1991 and corn till 1994; natural forest till 1940, coffee till 1960, citrus till 1978 and sugar cane till 1994 (sampling on the planting line and between lines ). The treatment with sugar cane presented the largest values of microbial carbon in relation to the natural forest. The agricultural management of soil increased the percentage of organic carbon in humic and fulvic acids forms. The soil presented more than 74% of organic carbon in the form of residual humus.

In mountainous areas of Europe, the abandonment of grasslands followed by forest expansion is the dominant land-use change. Labile (i.e. easily decomposable) litter represents the major source for soil microbial products, which promote soil aggregation and long-term C stabilization. Our objective was to investigate changes in the content and origin of soil C components involved into aggregate stabilization (i.e. carbohydrates) following forest expansion on abandoned grassland in the Alps, where only few studies have been conducted. Changes in carbohydrates and thermally labile C were assessed along a land-use gradient in the Southern Alps (Italy) following analysis of carbohydrate monomers and thermal analysis of mineral soil and physical soil fractions. The land-use gradient comprised managed grassland, two transitional phases in which grassland abandonment led to colonization by Picea abies (L.) Karst., and an old forest dominated by Fagus sylvatica L. and P. abies. Grassland abandoned for 10 years tended to have higher levels of carbohydrate and thermally labile soil C than managed grassland and old forest, presumably caused by differences in the quality and amount of litter input. Carbohydrates and thermally labile C showed similar patterns in bulk soil, suggesting that thermal analysis can be used to complement chemical analysis although a straightforward relationship could not be established. Following forest expansion on abandoned grassland, ratios of microbially to plant-derived carbohydrates and thermally labile to resistant components decreased in bulk soil and soil fractions. Forest expansion entailed decreasing amounts of microbially derived compounds known to be important for aggregate stability, and corresponded to decreased soil C allocation to stable aggregates. The combination of carbohydrate and thermal analyses revealed a lower abundance of microbially derived C components after forest colonization on abandoned grasslands, thus resulting in lower physical protection of soil C considering that carbohydrates of microbial origin actively promote soil aggregation. [ABSTRACT FROM AUTHOR]

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In grassland soils, the temporal dynamics in different fractions of soil organic carbon (SOC) is not completely understood. We investigated the temporal variations of water-stable aggregates, microbial biomass C (C mic ) and ergosterol concentrations (as a proxy for fungal biomass) in loamy sandy soils under grassland (north of Kiel, Germany). Samples were taken six times between October 2010 and October 2011 from i) a permanent grassland, ii) an arable plot converted to grassland and iii) a grassland with a one-time tillage operation (both in September 2010). Water-stable aggregate concentrations were determined by a wet-sieving procedure, C mic concentrations by chloroform-fumigation-extraction and ergosterol concentrations by ethanol extraction. Temporal variation in aggregate distribution of soil samples from the permanent grassland was considerable: the large macroaggregate (> 2000 μm) concentrations (mean ± standard error, n = 3) in the surface soil (0–10 cm) were highest in October 2011 (666 ± 12 g kg − 1 ) and lowest in May (206 ± 49 g kg − 1 ). The tillage operation in grassland led to lower concentrations of large macroaggregates, ergosterol and C mic in the surface soil than in the permanent grassland. The conversion of arable land into grassland did not affect macroaggregate concentrations, despite an increase in C mic (1.4-fold) and ergosterol concentration (3.3-fold) in the surface soil. Multiple linear regression analysis described the variations in the large macroaggregate concentration satisfactorily (R 2 = 0.60) and indicated that the gravimetric moisture content and the C mic concentration had positive effects and the pH a negative effect. While ergosterol concentrations (mean ± standard error) showed some temporal variations (values for the surface soil in the grassland ranged from 0.5 ± 0.1 to 1.5 ± 0.1 mg kg − 1 ), C mic concentrations varied much less, indicating a higher sensitivity of ergosterol to soil cultivation or changing environmental conditions. [ABSTRACT FROM AUTHOR]

Aims: We assessed the temporal changes on microbial biomass in relation to changes in soil moisture, dissolved organic carbon and plant biomass during the summer season in a Mediterranean high-mountain grassland. Methods: Temporal variations were tested by two-way ANOVA. The relationships among microbial biomass, plant biomass, soil water content, soil organic carbon, dissolved organic carbon and total soil nitrogen during the summer season were assessed by means of structural equation modeling. Results: Microbial biomass did not show variation, while dissolved organic carbon and root biomass decreased throughout the summer. Aboveground plant biomass peaked in the middle of the summer, when soil water content was at its minimum. Soil water content directly and negatively affected soil microbial biomass, and positively affected dissolved organic carbon. Moreover soil microbial biomass and dissolved organic carbon were negatively related. Plant biomass effects on soil microbial biomass were driven by root biomass, which indirectly affected soil microbial biomass through effects on soil organic carbon and soil nitrogen. Conclusions: The temporal dynamic of microbial biomass during the summer season appeared to differ from previous observations in temperate alpine communities, and indicated the drought resistance of the microbial community during the summer in Mediterranean high-mountain grasslands. During the dry period, microbial biomass may play an alternative role in soil carbon conservation. [ABSTRACT FROM AUTHOR]

Soil microorganisms are critical to carbon and nutrient fluxes in terrestrial ecosystems. Understanding the annual pattern of soil microbial community structure and how it corresponds to soil nutrient availability and plant production is a fundamental first step towards being able to predict impacts of environmental change on ecosystem functioning. We investigated the composition, structure and nutrient stoichiometry of the soil microbial community in mesic arctic tundra on 9 sample dates in 6 months from winter to fall using phospholipid fatty acid analysis (PLFA), quantitative polymerase chain reaction (qPCR), epifluorescent microscopy and chloroform-fumigation–extraction (CFE). PLFA analysis indicates that the winter microbial community was fungal-dominated, cold-adapted and associated with high C, N and P in the soil solution and microbial biomass. The microscopy data suggest that both bacteria and fungi were active and growing in soils between −5 °C and 0 °C. A significant shift occurred in the PLFA data, qPCR patterns, microscopy and microbial biogeochemistry after the thaw period, resulting in a distinct community that persisted through our spring, summer and fall sample dates, despite large changes in plant productivity. This shift was characterised by increasing relative abundances of certain bacteria (especially Gram +ves) as well as a decline in fungal biomass, and corresponded with decreasing C, N and P in the soil solution. The summer period of low substrate availability (plant–microbe competition) was associated with microbial indicators of nutritional stress. Overall, our results indicate that tundra microbial communities are clearly differentiated according to the changes in soil nutrient status and environmental conditions that occur between winter and post-thaw, and that those changes reflect functionally important adaptations to those conditions. [ABSTRACT FROM AUTHOR]

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Abstract: Sustainability of dryland cropping is a major issue in the typical Mediterranean climatic environment of West Asia and North Africa. Management of crop residues and soil organic matter (SOM) and its interrelationship with tillage and crop rotation is of central importance for maintaining soil quality and sustaining crop yields. We examined the medium-term influence of conventional moldboard plowing compared with shallow tillage, under barley-vetch and barley-vetch–wheat-vetch rotation, with different levels of straw management (burned, removed, or incorporated) and compost addition (10Mgha−1 every 2 or 4 years) on the distribution with soil depth (0–30cm) of SOM, total organic nitrogen (Ntot), and labile as well as microbial carbon (C) and nitrogen (N). Shallow tillage increased SOM in 0–20cm across all residue management treatments by on average 2.7gkg−1. Compost addition every 2 years instead of burning or removing residues significantly increased Ntot in 0–20cm by 0.22gkg−1, doubled labile N and C in 0–5 cm depth, and increased the ratio of labile N to Ntot in 0–20cm by 4%. Consequently, SOM accumulated in the labile pool, which reacts readily to changes in soil management practice, but which may also be depleted as quickly. Thus, shallow tillage in combination with compost addition can help build-up of SOM, and therefore soil quality. Under conditions of intensive cultivation, where crop residues are not in demand for livestock fodder, the system assessed constitutes a new agronomic direction under dryland agriculture in the Mediterranean region. [Copyright &y& Elsevier]

Terrestrial ecosystems are exposed to atmospheric and climatic changes including increases in atmospheric CO concentration, temperature and alterations of precipitation patterns, which are predicted to continue with consequences for ecosystem services and functioning in the future. In a field scale experiment on temperate heathland, manipulation of precipitation and temperature was performed with retractable curtains, and atmospheric CO concentration was increased by FACE. The combination of elevated CO and warming was expected to affect belowground processes additively, through increased belowground sequestration of labile carbohydrates due to elevated CO in combination with temperature increased process rates. Together, these changes might increase microbial activity and availability of plant nutrients. Two years after the start of the experiment, belowground processes responded significantly to the treatments. In the combined temperature and CO treatment the dissolved organic nitrogen concentration decreased and the ammonium concentration increased, but this release of nutrients was not mirrored by plant parameters. Microbial biomass carbon and microbial enrichment with C and N (1 year after CN-glycine was injected into the soil) increased in warmed plots and in elevated CO plots, but not when these treatments were combined. Furthermore, drought led to an increase in Calluna biomass and total plant nitrogen pool. The full combination of warming, elevated CO and periodic drought did not unambiguously express the ecosystem responses of single factors additively, which complicates predictions of ecosystem responses to multifactor climate change. [ABSTRACT FROM AUTHOR]

In order to monitor changes in the concentrations of metals in the soil, different microbial indices such as BIOLOG®, microbial carbon (Cmic), basal respiration, and culturable microbe’s most probable number were used. We compared these methods and wanted to discover which method was the best at measuring slight changes in the amounts of heavy metals. Factor analyses were applied to the BIOLOG® data and metal concentrations so the combined effects of heavy metals on microbes could be analyzed via statistical data reduction and the distribution patterns of metal concentration could also be revealed. The results showed that the BIOLOG® method could barely detect subtle characteristic changes in the soil samples, while the Cmic method was more sensitive. Furthermore, different heavy metals did not have the same origin/source, and their effects on microbial indices should be analyzed separately. Significant positive correlations between Cmic and metals were observed and suggested the limitation of using traditional microbial parameters as metal pollution indicators. Among all the soil characteristics in our study, pH seemed to be the most active abiotic factor that affected microorganisms. [ABSTRACT FROM AUTHOR]

Abstract: Cover crops may influence soil carbon (C) sequestration and microbial biomass and activities by providing additional residue C to soil. We examined the influence of legume [crimson clover (Trifolium incarnatum L.)], nonlegume [rye (Secale cereale L.)], blend [a mixture of legumes containing balansa clover (Trifolium michelianum Savi), hairy vetch (Vicia villosa Roth), and crimson clover], and rye+blend mixture cover crops on soil C fractions at the 0–150mm depth from 2001 to 2003. Active fractions of soil C included potential C mineralization (PCM) and microbial biomass C (MBC) and slow fraction as soil organic C (SOC). Experiments were conducted in Dothan sandy loam (fine-loamy, kaolinitic, thermic, Plinthic Kandiudults) under dryland cotton (Gossypium hirsutum L.) in central Georgia and in Tifton loamy sand (fine-loamy, siliceous, thermic, Plinthic Kandiudults) under irrigated cotton in southern Georgia, USA. Both dryland and irrigated cotton were planted in strip tillage system where planting rows were tilled, thereby leaving the areas between rows untilled. Total aboveground cover crop and cotton C in dryland and irrigated conditions were 0.72–2.90MgCha−1 greater in rye+blend than in other cover crops in 2001 but was 1.15–2.24MgCha−1 greater in rye than in blend and rye+blend in 2002. In dryland cotton, PCM at 50–150mm was greater in June 2001 and 2002 than in January 2003 but MBC at 0–150mm was greater in January 2003 than in June 2001. In irrigated cotton, SOC at 0–150mm was greater with rye+blend than with crimson clover and at 0–50mm was greater in March than in December 2002. The PCM at 0–50 and 0–150mm was greater with blend and crimson clover than with rye in April 2001 and was greater with crimson clover than with rye and rye+blend in March 2002. The MBC at 0–50mm was greater with rye than with blend and crimson clover in April 2001 and was greater with rye, blend, and rye+blend than with crimson clover in March 2002. As a result, PCM decreased by 21–24g CO2–Cha−1 d−1 but MBC increased by 90–224g CO2–Cha−1 d−1 from June 2001 to January 2003 in dryland cotton. In irrigated cotton, SOC decreased by 0.1–1.1kgCha−1 d−1, and PCM decreased by 10g CO2–Cha−1 d−1 with rye to 79g CO2–Cha−1 d−1 with blend, but MBC increased by 13g CO2–Cha−1 d−1 with blend to 120g CO2–Cha−1 d−1 with crimson clover from April 2001 to December 2002. Soil active C fractions varied between seasons due to differences in temperature, water content, and substrate availability in dryland cotton, regardless of cover crops. In irrigated cotton, increase in crop C input with legume+nonlegume treatment increased soil C storage and microbial biomass but lower C/N ratio of legume cover crops increased C mineralization and microbial activities in the spring. [Copyright &y& Elsevier]

• Global climate change is generally expected to increase net primary production, resulting in increased soil carbon (C) inputs. To gain an understanding of how such increased soil C inputs would affect C cycling in the vast grasslands of northern China, we conducted a field experiment in which the responses of plant and microbial biomass and respiration were studied. • Our experiment included the below-ground addition of particulate organic matter (POM) at rates equivalent to 0, 60, 120 and 240 g C m−2, under either natural precipitation or under enhanced precipitation during the summer period (as predicted for that region in recent simulations using general circulation models). • We observed that addition of POM had a large effect on soil microbial biomass and activity and that a major part of the added C was rapidly lost from the system. This suggests that microbial activity in the vast temperate grassland ecosystems of northern China is energy-limited. Moreover, POM addition (and the associated nutrient release) affected plant growth much more than the additional water input. • Although we performed no direct fertilization experiments, the response of plant productivity to POM addition (and associated release of nutrients) leads us to believe that plant productivity in the semiarid grassland ecosystems of northern China is primarily limited by nutrients and not by water. [ABSTRACT FROM AUTHOR]

The impact of atmospheric N deposition on the dynamics of various carbon fractions was investigated in two Scots pine forest soils (cambisol, podzol) of Northern Germany in microcosm experiments. Total organic carbon (TOC), CO2 emission, microbial carbon (Cmic) as well as organic hot- and coldwater extractable carbon fractions (Chwe, Ccwe) were analyzed before, during, and after soil incubation in microcosms, run in three treatments: 0, +45, and +90 kg N ha−1a−1. On both sites, the N treatment showed no response to total organic carbon (TOC) contents in most of the investigated soil layers. Microbial carbon (Cmic) was significantly increased in the organic layer of both soil types by the N application. Subsequent to the N application, the CO2 emission increased in all mineral soil layers of the cambisol but remained almost unaffected in the podzol. After the N application, a remarkable increase of hotwater extractable C (Chwe) was detected for the organic layer of the cambisol but not for the podzol, whereas coldwater extractable C (Ccwe) concentrations decreased at both sites. The N application did not have a significant impact on the leachate concentrations of total organic carbon (TOC), dissolved organic carbon (DOC), and particulate organic carbon (POC) in the podzol, whereas the concentrations of these C fractions were decreased in the organic layer and the 35–70~cm mineral soil layer of the cambisol. The N treatment changed the contents of most of the investigated C fractions in both soil types and resulted in a considerable C~mobilization. But the processes of the C~mobilization between the cambisol and the podzol were completely different. According to the presented data, the cambisol obtaining moderate atmospheric N loads is much more sensitive to additional N inputs than the podzol that already received high amounts of atmospheric N. [ABSTRACT FROM AUTHOR]

The application of organic fertilizer to soils may affect the rate of native soil organic matter mineralisation, inducing a positive priming effect (PE), with an increase of evolution of CO 2 and a release of nutrient that may be in excess of crop demand. The objective of this study was to evaluate the effect of different Meliaceae derivatives, characterised by different C:N ratios, on the total soil CO 2 -C evolution, CO 2 -C fractions from the derivatives, PE magnitude, and to understand the mechanism that regulates PE. In a laboratory incubation experiment, the effects of three Meliaceae derivatives, named neem 5, neem 6, and melia leaves, were evaluated using the natural 13C abundance method, employing a naturally C 4 -plant labelled soil. Total CO 2 -C losses were proportional to the plant-derived C inputs. Soil CO 2 -C produced by the addition of the derivatives ranged between 22% (neem 6) and 40% (neem 5 and melia leaves) of the total C incorporated into the soil. All the derivatives studied induced a positive PE that increased with the amount of C added, but was not related to their chemical structure. Priming effect was also unaffected by soil mineral nitrogen, showing a response with little or no correlation with the ability of microbial biomass to locate nutrients in the soil (N mining). At the end of the experiment, the proportion of C primed corresponded to approximately 24%–28% of the added C, with no difference among the derivatives, and contributed to total CO 2 -C loss by approximately 31%, 30%, and 27% for neem 5, melia leaves, and neem 6, respectively. • Neem cake and leaves of Melia azedarach derived C inputs induced a positive PE. • PE involved approximately one fourth of the C added into the soil. • PE accounted for about 30% of the total CO2-C released from the soil. • PE was directly related to the rate of C input, it was not related to soil mineral N. [ABSTRACT FROM AUTHOR]

Application of ammonium nitrate (NH4NO3) to cores of Sphagnum magellanicum in situ at 2-week intervals for 20 weeks from mid-June at a raised mire in north-east Scotland stimulated growth at only 1 g N m−2 year−1, whereas greater additions, equivalent to 3 and 10g N m−2, had no significant effect. The N concentration of the moss tissues increased linearly with increasing levels of NH4NO3 up to 10g N m−2 year−1. In cores receiving an additional of 10g N m−2 year−1, there was a significant increase in the concentration of organic N extracted from the moss in the surface 5 cm with 0.5 M K2SO4. The concentration of organic N correlated linearly with the quantity of N applied. NH4NO3 significantly reduced the rate of CO2 evolved from samples from a depth of 5–10 cm, and increased microbial C as measured by the substrate-induced respiration (SIR) method. Overall, inorganic N additions at 1 g N m−2 year−1 reduced the specific rate of respiration and activity of the microbial biomass at this depth. The mean total N:P ratios for the profile ranged from 24 to 28, suggesting that the site was P-deficient, which probably limited the growth response of S. magellanicum. [ABSTRACT FROM AUTHOR]