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Globally, excessive grazing is identified as one of the key disturbances leading to grassland degradation and soil carbon (C) loss. Grazing exclusion has been proposed as an effective practice to restore degraded grasslands and to promote C sequestration. However, there is still little knowledge about how soil C changes with grazing exclusion in high-altitude alpine ecosystems with very cold climates. We synthesized data from 63 sites in the literature and 15 sites in a field sampling and investigated the dynamics of soil C stocks following grazing exclusion in alpine grasslands of the Tibetan Plateau. The results showed that the soil C stock increased with grazing exclusion at most sites, with average C sequestration rates of 0.84, 0.58, and 0.49 Mg ha−1 yr−1 in the soil layers of 0–10, 10–20, and 20–30 cm, respectively. Based on these results, if 60 million ha of the grasslands on Tibetan Plateau were excluded from grazing livestock by 2020 according to the national plan, then approximately 0.11 Pg C yr−1 would be sequestered in the soil which equates to about 4.4% of fossil fuel and cement CO 2 emissions in China in 2013. Generally, the rates of soil C increase exhibited a declining pattern with increasing years of grazing exclusion, with a significant decrease occurring after ten years of grazing exclusion. Of the factors examined, the rates of absolute and relative soil C change were both positively related to mean annual precipitation but negatively related to the year of grazing exclusion and initial soil C stock, respectively. The rates of soil C changes increased linearly with those of N change, and no matter how soil C changed (whether it increased or decreased), soil C:N ratios remained stable over the years of grazing exclusion. Our results implied that grazing exclusion is beneficial for soil C sequestration in degraded alpine grassland, especially in humid areas. Moreover, the intrinsic increase in N could keep up with the pace of soil C changes and would sustain soil C sequestration during the recovery process. • Grazing exclusion increased soil carbon in alpine grasslands of the Tibetan Plateau. • Grazing exclusion can sequester 1.91 Mg C ha−1 yr−1 at soil depth of 0–30 cm. • Carbon sequestration rate declined significantly after ten years of grazing exclusion. • Grazing exclusion is more beneficial for soil carbon sequestration in humid regions. • Nitrogen increase could keep up with the pace of soil carbon changes. [ABSTRACT FROM AUTHOR]

Abstract Nitrogen (N) and phosphorus (P) availabilities can affect soil C cycling by altering both plants and microbial activity. It remains unclear how the changes in plant and microbial processes could regulate C dynamics of different soil fractions, thereby affecting soil C sequestration. Based on a field fertilization experiment in a subalpine spruce plantation, we examined the effects of N, P and combined N and P addition (NP) treatments on plant C inputs, soil C contents and enzyme activities of bulk soil and different aggregate fractions. We aimed to explore the mechanisms by which N and P addition affected soil C sequestration. After 4-year fertilization, the N treatment increased soil C content by 21%, accompanied by suppressed polyphenol oxidase activity (−43%). However, the P and NP treatments decreased soil C content by 14% and 7%, respectively, accompanied by reduction in fine root biomass (−51% and −50%, respectively). Fertilization also affected soil aggregate C pools, with decreased C content in the macroaggregates (5000–250 μm; MaA) under the P and NP treatments, and increased C content in the silt and clay fraction (<53 μm; S&C) under all fertilization treatments. The step-AIC analysis showed that the effects of fertilization on bulk soil C content were best explained by changes in soil polyphenol oxidase activity and fine root biomass. Overall, our results indicate that N-induced soil C accrual, mainly accumulating in the S&C, could be largely driven by the suppressed oxidase activity, and that decreases in soil C content under the P and NP treatments, mostly occurring in the MaA, was likely associated with the reduced C inputs by fine roots. Highlights • N and P addition showed opposing effects on soil C sequestration. • N-induced soil C accumulation was associated with the reduced oxidase activity. • N-induced soil C accrual mainly accumulated in silt and clay fractions. • P-induced reduction in soil C was associated with the reduced fine root biomass. • P-induced decreases in soil C mostly occurred in macroaggregate fractions. [ABSTRACT FROM AUTHOR]

• Dwarf bamboo overabundance simplified vegetation structure and caused giant panda habitat degradation. • Soil organic carbon, N and P stocks decreased with increasing degradation intensity. • Dwarf bamboo overabundance initiated a decrease in soil organic carbon, N and P stocks by influencing the litter quality. Although forest degradation caused by dwarf bamboo overabundance has a significant effect on the survival of wild giant pandas, the degradation process and its impact on soil C, N and P stocks remain unclear. By investigating the vegetation structure and physicochemical analysis of litter and soil, we explored the changes in soil organic carbon (SOC), total nitrogen (TN), available nitrogen (AN), total phosphorus (TP) and available phosphorus (AP) stocks and the driving forces at three degradation levels triggered by dwarf bamboo overabundance in an important giant panda habitat—the subalpine coniferous forest. Dwarf bamboo overabundance following forest logging prevented tree regeneration, resulting in simplified a vegetation structure; even after 23 years of natural recovery, the clear-cut forestlands remained in the shrub stage, and the tree density and basal area were only 1.6% and 38%, respectively, of those in primary subalpine coniferous forest. With increasing degradation intensity, the litter stock and litter quality showed a decreasing trend, as did the SOC, N and P stocks in the litter layer and topsoil. The vegetation structure and litter quality together explained more than 90% of the variance in the C, N and P stocks (SOC: 97.3%, TN soil : 93.5%, AN soil : 96.2%, TP soil : 97.2% and AP soil : 97.0%), and litter quality had greater explanatory power than the vegetation structure. The SEM analysis results showed that the increase in dwarf bamboo density caused by the reduction in tree basal area affected the litter C/N and C/P ratios, and ultimately reduced the SOC, N soil and P soil stocks. This study highlights that dwarf bamboo overabundance not only causes forest degradation but also reduces the carbon sequestration function of giant panda habitat, leading to the loss of soil N and P. We suggest that reducing bamboo abundance can promote the recovery of the soil carbon, nitrogen and phosphorus stocks in degraded giant panda habitats. [ABSTRACT FROM AUTHOR]

Carbonates constitute a significant proportion of the soil mass in many semi-arid soils. Due to their solubility, they can be affected by changes in the soil water regime. This needs to be taken into account when assessing the environmental and agronomical impacts of the adoption of irrigation. To gain knowledge on the importance of the effect of irrigation on carbonates dynamics in the tilled layer (0–20 cm) of agricultural soils, we conducted a two-step study embracing field observations and numerical simulation. First, carbonates storage and their size distribution were quantified for two different situations (irrigation and non-irrigation) in three irrigation districts with different time under irrigation (Valtierra (19 years), Miranda (5 years) and Funes (12 years)) in Navarre (Spain). Soil sampling was designed to ensure homogeneous comparisons in the most characteristic soil types at each site ( Xeric Haplocalcid , Typic Calcixerept and Xeric Haplocalcid , respectively). Carbonates concentration was systematically lower with irrigation in the finest (< 50 μm) soil fraction: 22.2 ± 1.4 g carbonates 100 g − 1 fraction without irrigation for 16.1 ± 0.9 with irrigation in Valtierra, 26.7 ± 1.1 for 19.1 ± 3.8 in Miranda and 27.8 ± 2.9 for 22.7 ± 1.5 at Funes1. However, the net annual balance of total carbonates-C between irrigated and non-irrigated condition was neutral at the three sites. This can be explained by agricultural management affecting carbonates in the sand-size fraction, including the addition of carbonates with fertilizers, and coarse carbonate particles brought to the surface by tillage. In a second step, a simplified model was developed for use with easily available data in most irrigation districts, and numerical simulations of the geochemical interactions between the soil, the soil solution and irrigation water were run using actual soil and soil solution data from the tilled layer of another pair of plots in Funes (Funes2). Sensitive analysis was also conducted to investigate the potential impact of water quality and crop types as sources of variability on the model outputs. The modelling results showed annual values of carbonates-C loss in the range between 13.52 and 12.06 g m − 2 year − 1 in the studied depth under irrigation, depending on the quality of irrigation water, for 0.46 g m − 2 without irrigation. These data were within the range of carbonates budgets found in the literature but one order of magnitude lower than the observed results in the fine fraction in the field. Overall, our results showed that irrigation can significantly alter carbonates dynamics in semi-arid Mediterranean land, which implies that human use can significantly alter the mineral phase of these soils in a relatively short time lapse. Simple geochemical models can be a useful approach to evaluate changes in the carbonates balance at the local and regional scale when irrigation is applied, although they have to be improved to account for other factors related to agricultural management and local geochemical conditions. [ABSTRACT FROM AUTHOR]

Evaluating the response of soil organic matter decomposition to warming and changes in rainfall is critical to assess the likelihood of proposed positive feedbacks from the terrestrial to the atmospheric system. The response of soil respiration and extracellular activities (EEAs) to long-term warming and recurrent summer drought was studied in a wet shrubland ecosystem in Wales (UK), after 13 years of climate change simulation in a whole-ecosystem experiment. Over a year soil respiration, temperature and moisture was monitored in the field. During the summer season, coinciding with maximum soil respiration rates, soil inorganic N and P, microbial biomass and the extracellular activities (EEAs) of a selection of enzymes involved in C, N and P cycling were analysed. Based on previous field measurements of C and N mineralization, we expected a stronger response of C-cycling EEAs, in comparison to N-cycling EEAs, to drought and warming, and a greater sensitivity of C-cycling EEAs to drought than to warming. Drought had a clear impact on soil respiration during the summer season. However, the availability of inorganic N or P was not significantly affected by the treatments. Microbial biomass and C:N ratio also remained unchanged. In contrast to one of our hypothesis, C-cycling EEAs measured under non-optimal conditions that simulated soil environment in the field (pH of 4.1 and with a temperature incubation of 10 °C) showed no significant differences due to long-term warming and recurring drought treatments. Possibly, this assay approach may have obscured treatment effects on the soil enzyme pool. Our results highlight the need for developing methods for the in-situ analysis of EEAs to determine rates of reactions. [ABSTRACT FROM AUTHOR]

Soil respiration (Rs) is the second largest carbon flux in terrestrial ecosystems and therefore plays a crucial role in global carbon (C) cycling. This biogeochemical process is closely related to ecosystem productivity and soil fertility and is considered as a key indicator of soil health and quality reflecting the level of microbial activity. Wildfires can have a significant effect on Rs rates and the magnitude of the impacts will depend on environmental factors such as climate and vegetation, fire severity and meteorological conditions post-fire. In this research, we aimed to assess the impacts of a wildfire on the soil CO 2 fluxes and soil respiration in a semi-arid ecosystem of Western Australia, and to understand the main edaphic and environmental drivers controlling these fluxes for different vegetation types. Our results demonstrated increased rates of Rs in the burnt areas compared to the unburnt control sites, although these differences were highly dependent on the type of vegetation cover and time since fire. The sensitivity of Rs to temperature ( Q 10) was also larger in the burnt site compared to the control. Both Rs and soil organic C were consistently higher under Eucalyptus trees, followed by Acacia shrubs. Triodia grasses had the lowest Rs rates and C contents, which were similar to those found under bare soil patches. Regardless of the site condition (unburnt or burnt), Rs was triggered during periods of higher temperatures and water availability and environmental factors (temperature and moisture) could explain a large fraction of Rs variability, improving the relationship of moisture or temperature as single factors with Rs. This study demonstrates the importance of assessing CO 2 fluxes considering both abiotic factors and vegetation types after disturbances such as fire which is particularly important in heterogeneous semi-arid areas with patchy vegetation distribution where CO 2 fluxes can be largely underestimated. [ABSTRACT FROM AUTHOR]

We assessed the impact of a single application of wood biochar on soil chemical and physical properties and aerobic rice grain yield on an irrigated kaolinitic clay Ferralsol in a tropical Savannah. We used linear mixed models to analyse the response of soil and plant variables to application rates of biochar (0, 8, 16 and 32 t ha − 1 ) and mineral N fertilization (0, 30, 60 and 90 kg N ha − 1 ), and their interaction. The response was analysed within three aerobic rice-growing seasons (S), equivalent to 1.5, 2.5 and 3.5 years after biochar application (S1.5, S2.5 and S3.5). The fraction of oxidisable C in soil increased with biochar application rate, irrespective of N fertilization, at S2.5 and S3.5, whereas the rice stress-free available water (soil water retention between − 6 and − 100 kPa) decreased with biochar application rate at S1.5 and S2.5. Rice grain yield and yield components varied with the seasons according to the changes in soil properties and weather conditions. A single application rate up to 32 t ha − 1 of the wood biochar type used in this study had no impact on aerobic rice yield increase on a kaolinitic clay Ferralsol under the climatic conditions of the Brazilian Savannah prone to dry spells. Most likely, the beneficial effects of wood biochar on soil chemical properties on rice production were offset by a decrease in soil water retention capacity and N uptake by the crop. [ABSTRACT FROM AUTHOR]

Decisions to use crop residues as soil cover for conservation agriculture create trade-offs for farmers who own cattle in crop-livestock systems. Trade-offs among soil C, crop and animal and crop productivity were analysed using the NUANCES-FARMSIM (FArm-scale Resource Management SIMulator) dynamic model. Retention on the soil surface of 0, 25, 50, 75 and 100% of the maize stover yield produced per farm, and the use of the remainder as animal feed was quantified over a 12 year period for four farm types in Murehwa, Zimbabwe. Retaining 100% maize residues in the field led to an annual loss of on average 68 and 93 kg body weight per animal for cattle on farms of the relatively wealthiest farmers (Resource Group, RG1) who had most land and cattle and RG2 respectively), and is therefore unsustainable for livestock production. There was an increase in grain yield of 1.6 t farm −1 and 0.7 t farm −1 for RG1 and RG2 respectively. Farmers without cattle (RG3 and RG4) may have a greater incentive for retaining their crop residues but they have to invest labour to keep the residues during the dry season. However, improved crop productivity for these farmers is limited by lack of access to fertiliser. The current practice of allocating all crop residues to animals results in average gross margin of US$7429 and US$4037 for RG1 and RG2 farmers respectively. Our results showed that from an economic perspective, it is logical that farmers prioritise the sustenance of cattle with crop residues over soil fertility management. We conclude that at current productivity levels, farmers who own cattle have limited scope to allocate crop residues for soil cover as it leads to significant loss in animal production and economic value. [ABSTRACT FROM AUTHOR]

• The farmland soil in Jiangxi Province is facing a serious threat of acidification. • parental materials and soil group greatly affect soil C, N and P stoichiometry. • The MAT and MAP is significantly related to soil C, N and P stoichiometry. • The cropping system has essential effect on soil C, N and P stoichiometry. • Straw return could clearly increase the soil N:P ratio. Soil carbon (C), nitrogen (N), and phosphorus (P) contents and its stoichiometry are important indicators of the elemental balance in ecological interactions and processes. Farmland usually is featured by extensive anthropogenic actions which profoundly alters the soil C, N, P contents and its stoichiometry. However, it remains largely unknown how the soil C, N and P stoichiometry in farmlands is comprehensively affected by natural factors including parental material, soil types, annual mean temperature, annual precipitation, and soil management measures such as crop rotation and straw return at large spatial scale. The main aim of this study is to analyze the summary statistics, spatial variability, as well as main controls of soil C, N and P stoichiometry in farmland of the whole Jiangxi Province, which is one of the most important food production base. Our results found that the average concentration of soil organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP) is 17.91, 1.58 and 0.52 g kg−1 in farmland soil of Jiangxi Province, respectively. The averaged value of the soil C:N, the soil C:P ratio, and the soil N:P ratio is 11.73, 38.31 and 3.38, correspondingly. Great differences were detected for C, N and P stoichiometry in farmland soil derived from different parental materials or different soil groups. The mean annual temperature (MAT) is significantly and negatively related to soil C:N ratio, soil C:P ratio as well as soil N:P ratio while the annual precipitation (MAP) is significantly and positively related to soil C:P ratio, soil N:P ratio but significantly and negatively related to soil C:N ratio. The structural equation model analysis showed that soil properties and soil management have greater influences on soil C, N and P stoichiometry than climate and lithology. Our results could provide important implications for soil management and agricultural production. [ABSTRACT FROM AUTHOR]

Conservative site management practices such as harvest residue retention can potentially convey long term benefits for site sustainability, but they are only practiced to a limited extent in many Eucalyptus plantations in the tropical regions. Burning and/or removal of harvest residues can remove substantial quantities of nutrients, but it is still common practice in many parts of India. We explored the effect of harvest residue retention or removal on soil properties at 4 multi-rotation Eucalyptus plantations in Kerala, India. Soil carbon, N and P content were little influenced by differing harvest residue treatments. Interestingly, soil N mineralization rates were affected only minimally by harvest residue retention at individual sites, however, laboratory incubations demonstrated a significant increase in soil N-mineralization potential with increasing harvest residue additions. Soil microbial biomass was influenced to a lesser extent by harvest residue retention. We conclude that harvest residue retention can help to sustain the soil fertility in subsequent rotations and minimize the loss of nutrients from the sites, but fertilizers are still likely to be an important part of the nutrient management regime for productive plantations. [ABSTRACT FROM AUTHOR]

Highlights: [•] We compared above-ground biomass accumulation (ABA) in tropical forest restoration. [•] ABA rates were plantations>island tree plantings>control treatments. [•] Duration of prior pasture use best explained differences in planted tree ABA rate. [•] Tree height after two years was a strong predictor of planted tree ABA rate. [•] Soil nutrient concentrations explained minimal differences in ABA rate. [Copyright &y& Elsevier]

Highlights: [•] We examined soil C and N content in loblolly pine and sweetgum experiments. [•] Irrigation increased total soil C in sweetgum. [•] Soil C and N was sequentially fractionated in solutions of increasing density. [•] Silviculture treatments generally did not affect soil C and N fractionation. [ABSTRACT FROM AUTHOR]

Abstract: There is considerable controversy concerning detection in soils of the protein, glomalin, which is produced by arbuscular mycorrhizal fungi. Glomalin was originally defined as a substance that cross reacts with a monoclonal antibody formed against a substance in the cell walls of an arbuscular mycorrhizal fungus. Thus, one can use an immunological approach to detect glomalin. However, it was recently shown that other proteins cross react with the antibody. The other, more common, approach involves assay of soil protein using the Bradford reaction. This approach assumes that the Bradford assay is specific to protein, and that the assayed protein is largely glomalin, either because other proteins are in low concentration, or because the extraction process eliminates the possibility of their detection. These assumptions, however, have been called into question recently. One way to test whether the Bradford assay can be useful in quantifying glomalin is to determine whether the concentrations of Bradford-reactive substances are consistent with predictions for glomalin. For example, if recently produced glomalin is more labile than older glomalin, the concentrations of the two fractions should not be highly correlated. Moreover, when a contrast is established between mycorrhizal and nonmycorrhizal vegetation, recently produced glomalin should soon occur in higher concentration in soils supporting mycorrhizal vegetation. Older glomalin should not be found in higher concentrations in the soils of mycorrhizal vegetation until some time later. We tested these predictions by employing the Bradford assay during the course of a three-year field experiment in which canola (nonmycorrhizal) and soy (mycorrhizal) were grown in separate plots in year 1, both of which were followed by maize (mycorrhizal) in years 2 and 3. The correlation between the concentrations of fraction 1 Bradford-reactive substances (also known as easily extractable glomalin and frequently assumed to be recently produced) and fraction 2 (the more difficult-to-extract fraction and frequently assumed to be older glomalin), was very poor. In year 1, the concentration of fraction 1 was significantly greater in soy plots than in canola plots. Finally, fraction 2 was only significantly higher in the former soy plots than in former canola plots in years 2 and 3. These data support the hypothesis that the Bradford assay was useful in detecting glomalin in this case. [Copyright &y& Elsevier]

Abstract: There is currently only limited understanding of the influence of conifer plantation management on soil carbon (C) and nitrogen (N) storage in maritime Europe. The study reported herein examined the effect of clear felling on belowground C and N stocks, and CO2 effluxes at paired clear-felled, and standing plantation sites in North Wales. Clear-felled conifer stands were compared in three different time lapses (3, 5 and 8years after harvesting). The O horizon (and associated C) was completely absent on the year 3 and year 8 clear-felled stands. There was no significant influence of clear-felling on mineral soil C and N at 0–10cm depth between clear felled and unharvested sites, however, differences were observed in subsoil depths (10–20cm and 20–50cm). Clear-felled sites exhibited an initial gain in surface soil C and N through year 5 (likely due to incorporation of the O horizon into the mineral soil) after which the C stock decreased by year 8. Approximately 50Mg C and 3MgN ha−1 yr−1appear to have been lost from mineral soils 7years after clear felling. Clear felling significantly (p <0.05) increased soil CO2 efflux and soil surface temperature. Total CO2 emission from soils at clear felled sites was 148% higher than that of uncut plantations. Alternative harvest strategies should be considered that reduce C losses from plantations in North Wales. [Copyright &y& Elsevier]

Abstract: To increase food production while mitigating climate change, cropping systems in the future will need to reduce greenhouse gas emission per unit of production. We conducted an analysis of 95 arable farms in Norway to calculate farm scale emissions of greenhouse gases, expressed both as CO2 eq per unit area, and CO2 eq per kg DM produced and to describe relationships between the farms’ GHG intensities and their economic efficiencies (gross margin). The study included: (1) design of a farm scale model for net GHG emission from crop production systems; (2) establishing a consistent farm scale data set for the farms with required soil, weather, and farm operation data; (3) a stochastic simulation of the variation in the sources of GHG emission intensities, and sensitivity analysis of selected parameters and equations on GHG emission intensities; and (4) describing relationships between GHG emission intensities and gross margins on farms. Among small seed and grain crops the variation in GHG emissions per kg DM was highest in oilseed (emission intensity at the 75th percentile level was 1.9 times higher than at the 25th percentile). For barley, oats, spring wheat, and winter wheat, emissions per kg DM at the 75th percentile levels were between 1.4 and 1.6 times higher than those at the 25th percentiles. Similar trends were observed for emissions per unit land area. Invariably soil N2O emission was the largest source of GHG emissions, accounting for almost half of the emissions. The second largest source was the off farm manufacturing of inputs (∼25%). Except for the oilseed crop, in which soil carbon (C) change contributed least, the on farm emissions due to fuel use contributed least to the total GHG intensities (∼10%). The soil C change contributed most to the variability in GHG emission intensities among farms in all crops, and among the sensitivity elasticities the highest one was related to environmental impacts on soil C change. The high variation in GHG intensities evident in our study implies the potential for significant mitigation of GHG emissions. The GHG emissions per kg DM (intensity) decreased with increasing gross margin in grain and oilseed crops, suggesting that crop producers have economic incentives to reduce GHG emissions. [Copyright &y& Elsevier]

Abstract: Between 1996 and 2001 an experimental set up in a chaparral community near San Diego, CA, examined various plant and ecosystem responses to CO2 concentrations ranging from 250 to 750 μl l−1. These experiments indicated a significant increase in soil C sequestration as CO2 rose above the ambient levels. In 2003, two years after the cessation of the CO2 treatments, we returned to this site to examine soil C dynamics with a particular emphasis on stability of specific pools of C. We found that in as little as two years, C content in the surface soils (0–15 cm) of previously CO2 enriched plots had dropped to levels below those of the ambient and pretreatment soils. In contrast, C retained in response to CO2 enrichment was more durable in the deeper soil layers (>25 cm deep) where both organic and inorganic C were on average 26% and 55% greater, respectively, than C content of ambient plots. Using stable isotope tracers, we found that treatment C represented 25% of total soil C and contributed to 55% of soil CO2 efflux, suggesting that most of treatment C is readily accessible to decomposers. We also found that, C present before CO2 fumigation was decomposed at a faster rate in the plots that were exposed to elevated CO2 than in those exposed to ambient CO2 levels. To our knowledge, this is the first report that allows for a detail accounting of soil C after ceasing CO2 treatments. Our study provides a unique insight to how stable the accrued soil C is as CO2 increases in the atmosphere. [Copyright &y& Elsevier]

Abstract: The present paper deals with C and N storage in soil and vegetation, litter fall and CO2 efflux from the soil 32–33 years after early thinning in a Norway spruce (Picea abies (L.) Karst.) stand in order to evaluate the effect of thinning regime on C sequestration. At 22 years old, the stand was reduced from 3190 to 2070, 1100 and 820 trees per hectare in four replicates. The N2070 treatment represents the recommended start density in practical forestry, while the other represent a moderate to large reduction in tree number at the present stand age. Aboveground biomass was estimated from single tree measurements of diameter and height based on allometric functions. Litter fall was collected during one and a half years and soil respiration was measured on five occasions during one summer. Ground vegetation was mapped and sampled for biomass, C and N determination. A significant decrease in aboveground tree (including stump-root system) C storage of 27% and 22% due to thinning was found in the N820 and N1100 treatments, respectively, compared to the N2070 treatment. Ground vegetation C storage was little affected by treatment, while litter fall C showed a non-significant decrease in the N820 and N1100 treatments compared to the N2070 treatment. Soil respiration was significantly lower in parts of the summer in the N2070 treatment compared to the N820 treatment. The reason for this is still unexplained since no differences in soil temperature, soil moisture or litter fall chemistry was found between the treatments. No significant treatment effects on humus and mineral soil C storage could be detected. With the present soil variability, the time period of 32 years is probably too short to detect soil C differences due to thinning. The N storage followed the same pattern as for C. [Copyright &y& Elsevier]

Abstract: Depending upon how soil is managed, it can serve as a source or sink for atmospheric carbon dioxide (CO2). As the atmospheric CO2 concentration continues to increase, more attention is being focused on the soil as a possible sink for atmospheric CO2. This study was conducted to examine the short-term effects of crop rotation and N fertilization on soil CO2 emissions in Central Iowa. Soil CO2 emissions were measured during the growing seasons of 2003 and 2004 from plots fertilized with three N rates (0, 135, and 270kgNha−1) in continuous corn and a corn–soybean rotation in a split-plot design. Soil samples were collected in the spring of 2004 from the 0–15cm soil depth to determine soil organic C content. Crop residue input was estimated using a harvest index based on the measured crop yield. The results show that increasing N fertilization generally decreased soil CO2 emissions and the continuous corn cropping system had higher soil CO2 emissions than the corn–soybean rotation. Soil CO2 emission rate at the peak time during the growing season and cumulative CO2 under continuous corn increased by 24 and 18%, respectively compared to that from corn–soybean rotation. During this period, the soil fertilized with 270kgNha−1 emitted, on average, 23% less CO2 than the soil fertilized with the other two N rates. The greatest difference in CO2 emission rate was observed in 2004; where plots that received 0N rate had 31% greater CO2 emission rate than plots fertilized with 270kgNha−1. The findings of this research indicate that changes in cropping systems can have immediate impact on both rate and cumulative soil CO2 emissions, where continuous corn caused greater soil CO2 emissions than corn soybean rotation. [Copyright &y& Elsevier]

Abstract: The purpose of this research was to test the hypothesis that variability in 11 soil properties, related to soil texture and soil C and N, would increase from small (1m) to large (1km) spatial scales in a temperate, mixed-hardwood forest ecosystem in east Tennessee, USA. The results were somewhat surprising and indicated that a fundamental assumption in geospatial analysis, namely that variability increases with increasing spatial scale, did not apply for at least five of the 11 soil properties measured over a 0.5-km2 area. Composite mineral soil samples (15cm deep) were collected at 1, 5, 10, 50, 250, and 500m distances from a center point along transects in a north, south, east, and westerly direction. A null hypothesis of equal variance at different spatial scales was rejected (P⩽0.05) for mineral soil C concentration, silt content, and the C-to-N ratios in particulate organic matter (POM), mineral-associated organic matter (MOM), and whole surface soil. Results from different tests of spatial variation, based on coefficients of variation or a Mantel test, led to similar conclusions about measurement variability and geographic distance for eight of the 11 variables examined. Measurements of mineral soil C and N concentrations, C concentrations in MOM, extractable soil NH4-N, and clay contents were just as variable at smaller scales (1–10m) as they were at larger scales (50–500m). On the other hand, measurement variation in mineral soil C-to-N ratios, MOM C-to-N ratios, and the fraction of soil C in POM clearly increased from smaller to larger spatial scales. With the exception of extractable soil NH4-N, measured soil properties in the forest ecosystem could be estimated (with 95% confidence) to within 15% of their true mean with a relatively modest number of sampling points (n⩽25). For some variables, scaling up variation from smaller to larger spatial domains within the ecosystem could be relatively easy because small-scale variation may be indicative of variation at larger scales. [Copyright &y& Elsevier]

Abstract: Green manuring practices can influence soil microbial community composition and function and there is a need to investigate the influence compared with other types of organic amendment. This study reports long-term effects of green manure amendments on soil microbial properties, based on a field experiment started in 1956. In the experiment, various organic amendments, including green manure, have been applied at a rate of 4tCha−1 every second year. Phospholipid fatty acid analysis (PLFA) indicated that the biomass of bacteria, fungi and total microbial biomass, but not arbuscular mycorrhizal (AM) fungi, generally increased due to green manuring compared with soils receiving no organic amendments. Some differences in abundance of different microbial groups were also found compared with other organic amendments (farmyard manure and sawdust) such as a higher fungal biomass and consequently a higher fungal/bacterial ratio compared with amendment with farmyard manure. The microbial community composition (PLFA profile) in the green manure treatment differed from the other treatments, but there was no effect on microbial substrate-utilization potential, determined using the Biolog EcoPlate. Protease and arylsulphatase activities in the green manure treatment were comparable to a mineral fertilized treatment receiving no additional C, whereas acid phosphatase activity increased. It can be concluded that green manuring had a beneficial impact on soil microbial properties, but differed in some aspects to other organic amendments which might be attributed to differences in quality of the amendments. [Copyright &y& Elsevier]

Abstract: The purpose of this research was to measure forest soil C stocks and estimate turnover times along a 1.3 km rise in elevation in the southern Appalachian Mountains. Turnover times were calculated based on estimated soil C inputs and near steady state soil C stocks in the O-horizon and the mineral soil to a 30-cm soil depth. Monte Carlo methods were used in the calculations to accommodate uncertainties in model parameterization. Measured mean stocks and calculated median turnover times of soil C ranged from 4.4 to 12.2 kg C m−2 and 11 to 31 years, respectively. The predicted turnover times reflect a high proportion of labile soil C over the selected sampling depth. Both forest soil C stocks and the predicted turnover time of soil C increased with altitude. There were no consistent trends for stand basal area and forest soil C inputs along the elevation gradient suggesting that altitudinal changes in soil C stocks and turnover times could be attributed to different rates of soil organic matter decomposition. Soil respiration flux did not vary significantly with altitude, but soil respiration normalized for existing soil C stocks indicated decreasing rates of soil organic matter decomposition with increasing elevation. Measured soil N stocks and differences in O-horizon litter chemistry indicated increasing N availability from low-elevation to high-elevation forests. Soil C storage and turnover time increased from warmer, drier, less N-rich forests to colder, wetter, more N-rich forests. Considered together, these data support assumptions of a declining rate of soil organic matter decomposition with increasing elevation in the southern Appalachian Mountains. Representative characterization of long-term litter C inputs is one of the most challenging aspects of the present analysis. [Copyright &y& Elsevier]

Abstract: Tillage affects the ability of coarse-textured soils of the southeastern USA to sequester C. Our objectives were to compare tillage methods for soil CO2 flux, and determine if chemical or physical properties after 25 years of conventional or conservation tillage correlated with flux rates. Data were collected for several weeks during June and July in 2003, October and November in 2003, and April to July in 2004 from a tillage study established in 1978 on a Norfolk loamy sand (fine-loamy, kaolinitic, thermic Typic Kandiudults). Conventional tillage consisted of disking to a depth of approximately 15cm followed by smoothing with an S-tined harrow equipped with rolling baskets. Conservation tillage consisted of direct seeding into surface residues. Flux rates in conservation tillage averaged 0.84g CO2 m−2 h−1 in Summer 2003, 0.36g CO2 m−2 h−1 in Fall 2003, 0.46g CO2 m−2 h−1 in Spring 2004, and 0.86g CO2 m−2 h−1 in Summer 2004. Flux rates from conventional tillage were greater for most measurement times. Conversely, water content of the surface soil layer (6.5cm) was almost always higher with conservation tillage. Soil CO2 flux was highly correlated with soil water content only in conventional tillage. In conservation tillage, no significant correlations occurred between soil CO2 flux and soil N, C, C:N ratio, pH, bulk density, sand fraction, or clay fraction of the surface 7.5cm. In conventional tillage, sand fraction was positively correlated, while bulk density and clay fraction were negatively correlated with soil CO2 flux rate, but only when the soil was moist. Long-term conservation tillage management resulted in more uniform within- and across-season soil CO2 flux rates that were less affected by precipitation events. [Copyright &y& Elsevier]

Abstract: Intensive management of southern pine plantations has yielded multifold increases in productivity over the last half century. The process of harvesting merchantable material and preparing a site for planting can lead to a considerable loss of organic matter. Intensively managed stands may experience more frequent disturbance as rotations decrease in length, exposing the stands to conditions that favor decomposition. To better understand the effects of organic matter removal on forest floor CO2 efflux (S ff), we measured S ff quarterly in 2001 in a 10-year-old loblolly pine (Pinus taeda L.) plantation in eastern North Carolina that received different harvest and site preparation treatments. The treatments examined were removal of merchantable bole (OM0) and whole-tree and forest floor removal (OM2). The organic matter removal treatments did not affect soil moisture or soil temperature, the major variables that control seasonal fluctuations in S ff. Mean S ff ranged from 2.23 to 6.63μmolm−2 s−1 and there were no significant differences between the treatments, despite higher lateral root mass in OM0 (1552±427gm−2) versus OM2 (701±86gm−2). In both treatments, S ff did not correlate to root mass directly beneath each measurement chamber. In OM0, S ff had a negative relationship with distance from the nearest tree, while OM2 showed no effect of tree proximity. Whole-tree and forest floor removal during harvest and site preparation did not result in differences in S ff or soil C, 10 years after establishment. Both treatments resulted in a greater quantity of soil C, indicating that the disturbance associated with harvesting enhanced soil C, at least over the short term. We attribute this increase in soil C to rapid decomposition of previous stands root system. [Copyright &y& Elsevier]

Abstract: Scotch broom (Cytisus scoparius) is a leguminous shrub, native to Europe that has invaded significant areas of the Pacific Northwest and rigorously competes with native vegetation. Mineral soils under scotch broom colonies and adjacent coastal prairie on the Mendocino Coast of Northern California were sampled to determine how soil properties and microbial processes have been affected. Soils under scotch broom were significantly more acidic and had greater organic matter content than prairie soils. The activities of two soil enzymes responsible for processing major detrital carbon and phosphorus pools were significantly higher under scotch broom. Organic matter accumulation with no change in C:N, a greater increase in phosphatase activity (123%) than in β-glucosidase (84%) under scotch broom, and a significant difference between soil C:P under scotch broom (619) and prairie vegetation (470) all suggest that the coupling of nutrient cycles has changed. [Copyright &y& Elsevier]

This study tested the possible root biomass improvements in crop rotations after the conversion of grasslands, and crop samples from maize, winter wheat, and winter barley were collected during 2011–2013 from a long-term experimental site in Lusignan, France (http://www.soere-acbb). Root biomass C quantification was performed using δ13C isotopic signatures to determine the presence of both C3 and C4 plants. We also calculated the recovery rate of maize root biomass C. The results showed that after crop rotations, 0–60 cm root biomass C values were 44.1, 34.2, and 18.7 g C m−2 for maize, winter wheat, and winter barley respectively. The Root biomass C of crops after conversion to grassland was approximately 2–3 times those observed after crop rotations. However, incorporating ley grassland duration into crop rotations showed limited improvements in shoot biomass C and grain yield of the crops, regardless of the decreased rate of N fertilizer for maize. Moreover, root biomass C had a significant relationship with N supply from residues (P <.05). Nevertheless, shoot biomass C of only maize showed significance in its relationships with N supply and root biomass C. In addition, in each 30 cm soil layer (0–30 cm, 30–60 cm, and 60–90 cm), the recovery rate of maize roots decreased to approximately 15% when root biomass C increased to 10 g C m−2. However, further increases in root biomass C had little impact on the recovery rate. In conclusion, compared with continuous cropland, incorporating ley grassland duration into crop rotations increases root biomass C of crops, but this change may not be a significant increase of the shoot biomass C or grain yield. This finding simply indicates the improved C input from crops and the potential to increase soil organic C, as well as providing a model for the sustainability of crop rotations. Unlabelled Image • Incorporating ley grassland into crop rotation increased residual N supply for crops. • Incorporating ley grassland into crop rotation increased root biomass C of crops. • Incorporating ley grassland in crop rotation may not improve shoot biomass C of crops. • Variations of shoot biomass C may not reflect the variations of root biomass C. • If root biomass C are large enough, their recovery rates are close to a constant. [ABSTRACT FROM AUTHOR]

Along the Patagonian coast, there are processing factories of marine products in land that produce fish-processing effluents. The aim of the present study was to assess the physicochemical properties and the prokaryotic community composition of soils receiving fish-processing effluent discharges (effluent site-ES), and to compare them with those of unaltered soils (control site-CS) in the arid Patagonian steppe. We analyzed soil prokaryotic communities (using amplicon-based sequencing of 16S rRNA genes), soil physicochemical properties and fish-processing effluent characteristics. Soil moisture, electrical conductivity (EC), total and inorganic C were significantly higher in ES than in CS (p <.05). Effluent discharges induced a decrease in the total number of operational taxonomic units (OTUs) and in the Shannon diversity index (p =.0009 and.01, respectively) of soil prokaryotic community. Proteobacteria, Actinobacteria and Acidobacteria were the dominant phyla in CS, while ES soil showed a more heterogeneous composition of phyla. Linear discriminant analysis (LDA) effect size (LEfSe) analysis showed that fish-processing effluent discharges promoted an enrichment of Firmicutes and Bacteroidetes, which are active contributors to organic matter mineralization, along with a decrease of oligotrophic phyla such as Acidobacteria, Chloroflexi, Armatimonadetes and Nitrospirae, commonly found in nutrient-poor arid soils. The concentrations of inorganic C and ammonium, the EC and the soil moisture explained 73% of the total variation within the community composition. Due to its salinity and nutrients, fish-processing effluents have potential mainly for native salt-tolerant plant irrigation, however the impacts of soil prokaryotic community shifts over plant growth remain to be determined. Unlabelled Image • Fish-processing effluent discharges increased soil salinity, total and inorganic C. • Effluent discharges decreased soil microbial diversity and total OTUs. • Effluent discharges promoted an enrichment of Firmicutes and Bacteroidetes in soil. • Effluent discharges induced a decrease of oligotrophic phyla in soil. • Inorganic C, ammonium, EC and soil moisture explained 73% of community variation. [ABSTRACT FROM AUTHOR]

This study investigates microbial communities in soil from sites under different land use in Kenya. We sampled natural forest, forest plantations, agricultural fields of agroforestry farms, agricultural fields with traditional farming and eroded soil on the slopes of Mount Elgon, Kenya. We hypothesised that microbial decomposition capacity, biomass and diversity (1) decreases with intensified cultivation; and (2) can be restored by soil and land management in agroforestry. Functional capacity of soil microbial communities was estimated by degradation of 31 substrates on Biolog EcoPlates™. Microbial community composition and biomass were characterised by phospholipid fatty acid (PLFA) and microbial C and N analyses. All 31 substrates were metabolised in all studied soil types, i.e. functional diversity did not differ. However, both the substrate utilisation rates and the microbial biomass decreased with intensification of land use, and the biomass was positively correlated with organic matter content. Multivariate analysis of PLFA and Biolog EcoPlate™ data showed clear differences between land uses, also indicated by different relative abundance of PLFA markers for certain microorganism groups. In conclusion, our results show that vegetation and land use control the substrate utilisation capacity and microbial community composition and that functional capacity of depleted soils can be restored by active soil management, e.g. forest plantation. However, although 20-30 years of agroforestry farming practises did result in improved soil microbiological and chemical conditions of agricultural soil as compared to traditional agricultural fields, the change was not statistically significant. [ABSTRACT FROM AUTHOR]