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opencc-zeroNov 2020View details →

Data for degrees earned by faculty teaching in soil science preparatory programs at universities in the USA

In the early 2000s some were concerned that few soil science graduate students were receiving their bachelor's degrees in soil science. However, no studies were conducted to investigate this or how it may have changed over time. Information available on university webpages for faculty in the USA was used to determine the faculty's bachelor's, master's, and doctoral degree disciplines. Faculty rank was used to determine if a change had occurred in the percent of faculty who received their bachelor's degrees in soil science over time. Only 16% of faculty teaching in programs that prepare graduates to work as soil scientists received their bachelor's degrees in soil science. This percentage increased to 56% and 67% who received their master's and doctoral degrees, respectively, in soil science, but about 26% of faculty who teach in soil science preparatory programs did not have any degrees that could be identified as a "soil science" degree. The degrees that faculty received their training in also differed by their current soil science specialty area. About 13% of assistant professors and 20% of full professors received their bachelor's degrees in soil science, so the percentage of students entering soil science graduate programs with a bachelor's degree in soil science appears to have declined with time. However, a majority of soil science graduate students having bachelor's degrees from other fields also appears to have been common going back at least several decades.

opencc-zeroDec 2020View details →

Data from: Contrasting responses of nitrogen: phosphorus stoichiometry in plants and soils under grazing: a global meta-analysis

1. Grazing by ungulate herbivores can greatly alter nitrogen ([N]) and phosphorus ([P]) concentrations in plants and soils. It is not clear, however, how grazing might affect N:P co-limitation in grasslands depending on soil N and P availability. 2. Here we selected 173 peer-reviewed studies, which measured 12 key variables associated with changes in [N], [P] and N:P ratios (i.e. N:P stoichiometry) in soils and plants in the presence or absence of herbivore grazing. Subsequently, we addressed the magnitude and direction of grazing effects on these variables using a meta-analysis approach. 3. Grazing increased leaf [N] and [P] but decreased total and available soil [N] and [P]. Grazing also increased leaf N:P ratios while decreasing root and total soil N:P ratios. 4. The response ratio (RR) of leaf N:P was negatively correlated with RR of plant-available soil [P] and positively correlated with RR of available soil N:P ratio (rather than with RR of total soil N:P). 5. Intensive grazing (e.g., heavy grazing or long-term grazing) had in general more positive effects on plant N:P stoichiometry and negative effects on soil N:P stoichiometry than light grazing. Responses of plant-soil N:P stoichiometry to grazing greatly varied depending on plant functional group identity, plant organizational level (i.e. species and community) and grassland type. 6. Synthesis and applications. Our study suggests that understanding changes in available soil N:P stoichiometry (rather than total soil N:P) in response to grazing is crucial to predict nutrient co-limitation in grassland biomes. Our findings show that P is more important for plant growth than generally thought due to greater reduction of plant-available soil [P] under grazing. A better mechanistic understanding of the relationships between plant and available soil N:P stoichiometry under grazing will greatly help improve the sustainability of natural and semi-natural grassland ecosystems.

opencc-zeroDec 2020View details →

Data from: Sorption and desorption of bicyclopyrone on soils

Bicyclopyrone is a herbicide that is targeted for the control of herbicide-resistant weeds. However, there is a lack of extensive data on its sorption and factors that control its sorption in the soil system. In this study, we evaluated a series of 25 different soils, with a variety of soil properties to assess if an empirical relationship could be developed to predict the sorption coefficient for bicyclopyrone. Overall, there were no statistically significant relationships observed with organic carbon, cation exchange capacity, or clay content. There solely was a moderate negative correlation with soil pH (R=-0.65). Additionally, Freundlich isotherm analysis suggests that the KD could be adequate to characterize the sorption behavior for the range of soils evaluated here.

opencc-zeroDec 2010View details →

Data from: Is diversification history of maize influencing selection of soil bacteria by roots?

A wide range of plant lines has been propagated by farmers during crop selection and dissemination, but consequences of this crop diversification on plant-microbe interactions have been neglected. Our hypothesis was that crop evolutionary history shaped the way the resulting lines interact with soil bacteria in their rhizospheres. Here, the significance of maize diversification as a factor influencing selection of soil bacteria by seedling roots was assessed by comparing rhizobacterial community composition of inbred lines representing the five main genetic groups of maize, cultivated in a same European soil. Rhizobacterial community composition of 21-day-old seedlings was analyzed using a 16S rRNA taxonomic microarray targeting 19 bacterial phyla. Rhizobacterial community composition of inbred lines depended on the maize genetic group. Differences were largely due to the prevalence of certain Betaproteobacteria and especially Burkholderia, as confirmed by quantitative PCR and cloning/sequencing. However, these differences in bacterial root colonization did not correlate with plant microsatellite genetic distances between maize genetic groups or individual lines. Therefore, the genetic structure of maize that arose during crop diversification (resulting in five main groups), but not the extent of maize diversification itself (as determined by maize genetic distances), was a significant factor shaping rhizobacterial community composition of seedlings.

Data from: Complementarity and selection effects in early and mid-successional plant communities are differentially affected by plant-soil feedback

1. Many studies that provided evidence for a positive relationship between plant diversity and productivity have proposed that this effect may be explained by complementarity among species in resources utilization, or selection of particularly productive species in high-diversity plant communities. Recent studies have related the higher productivity in diverse plant communities to suppression of pathogenic soil biota. If soil biota plays a role in diversity–productivity relationships, the question remains about how they may influence complementarity and selection effects. 2. Here we examine how complementarity and selection effects may depend on soil biota using a plant–soil feedback approach. We used monocultures and mixtures of early successional plant species, which are known to have mostly negative plant–soil feedback effects, and mid-successional plant species, which generally have neutral plant–soil feedback. 3. We found that plant–soil feedback effects differed between monocultures and mixed plant communities, as well as between early and mid-successional plants. This resulted in a significant interaction effect between diversity and successional stage. In monocultures, plant–soil feedback tended to be negative for early and positive for mid-successional plant species. Interestingly, the community feedback responses of the mixed communities were opposite, being positive for early and negative for mid-successional community. 4. Plant–soil feedback differentially affected complementarity and selection effects of early and mid-successional plant communities: it enhanced complementarity effects of early and decreased selection effects of mid-successional species. 5. Synthesis. Soil biota that drive plant–soil feedback effects can influence the diversity–productivity relationship not only through decreased biomass production in monocultures compared to mixtures, but also through influencing complementarity and selection effects among species in mixed plant communities. Our results reveal that biodiversity–productivity relationships depend on plant–soil feedback interactions, which depend on the successional position of the plant. We propose that including successional position and trait-based analyses of plant–soil feedback in diversity-functioning studies will enhance understanding consequences of biodiversity loss for productivity and other ecosystem processes.

Data from: Use of elastic stability analysis to explain the stress-dependent nature of soil strength

The peak and critical state strengths of sands are linearly related to the stress level, just as the frictional resistance to sliding along an interface is related to the normal force. The analogy with frictional sliding has led to the use of a 'friction angle' to describe the relationship between strength and stress for soils. The term 'friction angle' implies that the underlying mechanism is frictional resistance at the particle contacts. However, experiments and discrete element simulations indicate that the material friction angle is not simply related to the friction angle at the particle contacts. Experiments and particle-scale simulations of model sands have also revealed the presence of strong force chains, aligned with the major principal stress. Buckling of these strong force chains has been proposed as an alternative to the frictional-sliding failure mechanism. Here, using an idealized abstraction of a strong force chain, the resistance is shown to be linearly proportional to the magnitude of the lateral forces supporting the force chain. Considering a triaxial stress state, and drawing an analogy between the lateral forces and the confining pressure in a triaxial test, a linear relationship between stress level and strength is seen to emerge from the failure-by-buckling hypothesis.

opencc-zeroDec 2012View details →

Data from: Molecular field analysis of trophic relationships in soil-dwelling invertebrates to identify mercury, lead and cadmium transmission through forest ecosystems

Contamination pathways in complex food chains in soil ecosystems can be difficult to elucidate. Molecular analysis of predator gut content can, however, rapidly reveal previously unidentified trophic interactions between invertebrates and thereby uncover pathways of pollutant spread. Here we measured concentrations of the toxic metals lead, cadmium and mercury in carabid beetle predators and their prey. Invertebrates were sampled at one control and four heavy metal polluted sites in order to reveal the impact of diet composition and seasonal variation in prey availability on metal burden in carabids and metal transfer pathways through forest ecosystems. This is the first report, to our knowledge, of carabid diet composition based on PCR analysis of gut contents at the forest community level, rather than in cultivated fields. Extensive screening using group- and species-specific primers revealed that carabids ate primarily earthworms and slugs, as well as smaller numbers of woodlice and springtails. Metal concentrations in carabids correlated with seasonal changes in diet. Mercury accumulated in beetle predators more than in their slug prey. Since earthworms, slugs and carabid beetles are the major prey of many birds and mammals, prey-predator transfer and associated toxicity are major risks at mercury-contaminated sites. Carabids may be useful bioindicators for assessing the impact of pollutants on soil ecosystems, as long as species and seasonal factors are taken into account.

opencc-zeroMay 2020View details →

Data from: Effects of aridity on soil microbial communities and functions across soil depths on the Mongolian Plateau

1. Arid and semi-arid grassland ecosystems cover about 15% of the global land surface and provide vital soil carbon (C) and nitrogen (N) sequestration. Although half of the soil C and N is stored in deep soils (below 30 cm), no regional-scale study of microbial properties and their functions through the soil profile has been conducted in these drylands. 2. To explore the distribution and determinants of microbial properties and C and N mineralization rates through soil profile along aridity gradient at a regional scale, we investigated these variables for four soil layers (0-20, 20-40, 40-60, and 60-100 cm) in 132 plots on the Mongolia Plateau. 3. Soil microbial properties (biomass and bacteria:fungi ratio) and C and N mineralization rates decreased with increasing soil depth and aridity at the regional scale. Aridity-induced declines in soil microbial properties mainly resulted from the negative effects of aridity on ANPP/root biomass and soil organic C (SOC) in the surface soil layers (0-20 and 20-40 cm) but from the direct and indirect (via SOC and soil C/N) negative effects of aridity in the deep soil layers (40-60 and 60-100 cm). 4. Aridity-induced declines in soil C mineralization rates mainly resulted from the negative indirect effect of aridity on SOC and microbial properties in each soil layer, with weaker effects of SOC and stronger effects of soil microbes in the deep soil layers. Aridity-induced declines in soil N mineralization rates mainly resulted from the negative indirect effect of aridity on SOC in the three soil layers above 60 cm and mainly resulted from the negative direct effect of aridity in the 60-100 cm soil layer. 5. Aridity via direct or indirect effects strongly determined the patterns of soil microbial properties and C and N mineralization throughout soil profiles on the Mongolian Plateau. These findings suggest that the increases in aridity are likely to induce changes in soil microorganisms and their associated functions across soil depths of semi-arid grasslands, and future models should consider the dynamic interactions between substrates and microbial properties across soil depths in global drylands.

opencc-zeroDec 2012View details →

Data from: Interactions between C:N:P stoichiometry and soil macrofauna control dung decomposition of savanna herbivores

1. Although dung of mammalian herbivores is an important pathway for nutrient return in savanna ecosystems, differences in dung decomposition rates among species have been little studied. 2. We measured rates of dung deposition and decomposition for various herbivores in a moist Tanzanian savanna, and related differences among species to nutrient concentrations and the activities of soil macrofauna (e.g., different mesh sizes of decomposition bags, or presence and absence of dung beetles). 3. Dung C:N:P stoichiometry varied widely among species, which could in part be explained by differences in feeding strategy (browsers vs. grazers) and digestive physiology (ruminants vs. non-ruminants). Rates of both decomposition and nutrient release were influenced by the C:N:P stoichiometry of dung, with lower relative losses of the least abundant nutrient. Surprisingly, soil macrofauna increased relative losses of the least abundant nutrient, thereby stabilizing the ratio of N loss to P loss. Dung beetles increased rates of N and P release from wildebeest dung significantly and also increased N availability in the soil. 4. We conclude that rates of nutrient return in dung depend not only on where herbivores deposit their dung, but also on its C:N:P stoichiometry, the activity of soil macrofauna, and interactions between these factors. These factors may therefore influence the relative availabilities of N and P in the soil and hence the functioning of savanna ecosystems.

opencc-zeroDec 2018View details →

Data from: Plant host identity and soil macronutrients explain little variation in sapling endophyte community composition: is disturbance an alternative explanation?

1. Bacterial endophytes may be fairly host specific; nonetheless, an important subset of taxa may be shared among numerous host species forming a community-wide core microbiome. Moreover, other key factors, particularly the supply of limiting macronutrients and disturbances, may supersede the importance of host identity. 2. We tested the following four non-mutually exclusive hypotheses: 1. The Host Identity Hypothesis: endophytes vary substantially among different host plant species. 2. The Core Microbiome Hypothesis: a subset of microbial taxa will be shared among all host plant species. 3. The Soil Resource Supply Hypothesis: endophytes vary substantially among habitats with experimentally elevated levels of macronutrients. 4. The Disturbance-Disruption Hypothesis: disturbances created by the periodic application of antibiotics structure bacterial endophyte communities. 3. We tested these hypotheses by characterizing endophytes using high-throughput sequencing among seedlings of five phylogenetically diverse tree species nested within a long-term, full factorial nitrogen, phosphorus, and potassium soil fertilization experiment. We artificially disturbed one of our focal species by applying antibiotics every 10-14 days for 29 months within the soil (N,P,K) fertilization experiment. 4. While we detected a significant effect of host identity and soil nutrient additions, together they explained little variation in endophyte community composition (< 10%). We found unequivocal evidence for a core microbiome shared by all species. Specifically, we found nine OTUs were present among 95% or more of all control saplings, representing a third of the total reads. These bacterial taxa belonged to the Actinobacteria. 5. In contrast, disturbance (antibiotics) explained more endophyte variation than all nutrient addition combinations combined and twice the variation explained by host identity for all five tree species. Synthesis: Our results challenge the idea that host identity is a primary filter shaping bacterial endophyte communities; this suggests that many of the same bacterial taxa occur inside plant hosts even if those host plants are phylogenetically diverse. Moreover, we documented a distinct core microbiome shared among our five focal tree species. Finally, we found that disturbance was an important driver of microbial community composition, which parallels the importance of disturbance in other areas of community ecology.

Data from: Seasonality of soil moisture mediates responses of ecosystem phenology to elevated CO2 and warming in a semi-arid grassland

Vegetation greenness, detected using digital photography, is useful for monitoring phenology of plant growth, carbon uptake, and water loss at the ecosystem level. Assessing ecosystem phenology by greenness is especially useful in spatially extensive, water-limited ecosystems such as the grasslands of the western United States, where productivity is moisture dependent and may become increasingly vulnerable to future climate change. We used repeat photography and a novel means of quantifying greenness in digital photographs to assess how the individual and combined effects of warming and elevated CO2 impact ecosystem phenology (greenness and plant cover) in a semi-arid grassland over an 8-year period. Climate variability within and among years was the proximate driver of ecosystem phenology. Individual and combined effects of warming and elevated CO2 were significant at times, but mediated by variation in both intra- and inter-annual precipitation. Specifically, warming generally enhanced plant cover and greenness early in the growing season but often had a negative effect during the middle of the summer, offsetting the early season positive effects. The individual effects of elevated CO2 on plant cover and greenness were generally neutral. Opposing seasonal variations in the effects of warming and less so elevated CO2 cancelled each other out over an entire growing season, leading to no net effect of treatments on annual accumulation of greenness. The main effect of elevated CO2 dampened quickly, but warming continued to affect plant cover and plot greenness throughout the experiment. The combination of warming and elevated CO2 had a generally positive effect on greenness, especially early in the growing season and in later years of the experiment, enhanced annual greenness accumulation. However, interannual precipitation variation had larger effect on greenness, with 2-3 times greater greenness in wet years than in dry years. Synthesis. Seasonal variation in timing and amount of precipitation governs grassland phenology, greenness, and the potential for carbon uptake. Our results indicate that concurrent changes in precipitation regimes mediate vegetation responses to warming and elevated atmospheric CO2 in semi-arid grasslands. Even small changes in vegetation phenology and greenness in response to warming and rising atmospheric CO2 concentrations, such as those we report here, can have large consequences for the future of grasslands.

Data from: Subordinate plants sustain the complexity and stability of soil micro-food webs in natural bamboo forest ecosystems

Subordinate plants have a significant impact on soil organisms in primary successional floodplains and grassland ecosystems, but their role in subtropical forest ecosystems remains unclear. An experiment was conducted in a subtropical forest to test the hypothesis that removal of shrubs or subordinate arbour tree species would reduce the complexity and stability of the soil micro-food web. Principal response curves (PRCs) were performed to assess the responses of soil microbial and nematode communities to plant removal compared with a control through time. The effect of plant removal on complexity and stability in the soil micro-food web was assessed using a suite of indices including ratio of omnivorous-predatory to herbivorous nematode abundance (OP : H ratio), nematode diversity, resistance and resilience. Furthermore, increments of bamboo productivity among treatments were estimated. Soil microbial community structure changed in response to plant removal in 2009, but recovered in 2010, and the only change observed was increased soil fungal biomass. In contrast, plant removal had greater impact on soil nematode community composition in 2010 than 2009. Subordinate arbour tree species removal (with or without shrubs) decreased the values of nematode richness, evenness, diversity, ratio of microbial-feeding to herbivorous nematode abundance (M : H ratios), OP : H ratios and resistance indices in 2010, but only decreased OP : H ratios in 2009 and increased the values of nematode dominance in 2010. Although increments in bamboo productivity were statistically similar among treatments, there was a trend decreasing progressively from control to shrub removal + selective-cutting of subordinate arbour tree species, shrub removal, and selective-cutting of subordinate arbour tree species treatments. Synthesis and applications. Subordinate plants help sustain the complexity and stability of soil micro-food webs in subtropical bamboo forest ecosystems. Therefore, protection of subordinate plants and maintaining high plant diversity are important parts of a responsible management strategy in subtropical bamboo forests.

Data from: Spatial-temporal variability and related factors of soil organic carbon in Henan province

Spatial variability and influence factors are important to evaluate soil organic carbon(SOC) and the carbon pool in large areas. In the present study, sampling was conducted from May to November 2011 in Henan province, a typical agricultural region of central China, to study the effects of soil properties and anthropogenic factors on SOC variability in cropland. Physicochemical properties of soil samples were analyzed, which were collected at 280 sites from the surface layer (at a depth of 0–20 cm), and related data about the sampling sites were also collected from the Second State Soil Survey of China (SSSSC), conducted in 1981. The main results were as follows: 1) Increasing trends in soil organic carbon density (SOCD) and soil organic carbon pool (SOCP) were obvious from 1981 to 2011, and we conclude that cropland presents great carbon sequestration potential for the future. Carbon pool ability varied with soil properties: the order of fixed carbon amount in different soil types was found to be Inceptisols > Luvisols > Semi-hydromorphic soil > Anthrosols, and the average SOCP increased significantly from 1981 to 2011. 2) Soil bulk density, pH and returning straw are the key influence factors for SOCD in the past 30 years. 3) Although random factors (returning straw) only explain 29.1% of SOCD variability, the factor should be paid more attention, because application of returning strawwas the most dominant anthropogenic factors, which can be used to improve cropland productivity and carbon sink capacity within a short period if they are properly managed in the future.

Data from: Effects of biochar on fate and toxicity of herbicide fenoxaprop-ethyl in soil

The biochar as soil amendment in agriculture has attracted considerable attention. In the study, the fate and toxicity of the herbicide fenoxaprop-ethyl were evaluated in soils with and without 5% rice husk biochar amendment. Fenoxaprop-ethyl and metabolite fenoxaprop degraded followed first-order kinetics in the two soils. Fenoxaprop-ethyl decreased fast with half-lives less than 2 days. Large amounts of fenoxaprop formed and remained in control soil. However, fenoxaprop was much lower in biochar-amended soil with reduction over 85% at the 35th day. The estimated half-lives of fenoxaprop were 56.9 and 1.5 days in control and biochar-amended soils, respectively. Biochar restrained the formation and promoted the dissipation of fenoxaprop. Biological indicator earthworms (Eisenia fetida) were used in a 14-day acute toxicity test. Fenoxaprop-ethyl shown low toxic to earthworms with LC50 value of 322.9 μg/g. Biochar amendment was nontoxic to earthworms and effectively reduced the toxicity. The results suggested that the application of biochar may reduce the risks of fenoxaprop-ethyl in the soil environment.

opencc-zeroDec 2010View details →

Data from: Soil sampling and isolation of extracellular DNA from large amount of starting material suitable for metabarcoding studies

DNA metabarcoding corresponds to the DNA-based identification of multiple species from a single complex and degraded environmental sample. We developed new sampling and extraction protocols suitable for DNA metabarcoding analyses, targeting soil extracellular DNA. The proposed sampling protocol has been designed to reduce as much as possible the influence of the local heterogeneity by processing large amount of soil, resulting from the mixing of many different cores. The DNA extraction is based on the use of saturated phosphate buffer. The sampling and extraction protocols were validated first by analyzing plant DNA from a set of 12 plots corresponding to four plant communities in alpine meadows, and second by conducting pilot experiments on fungi and earthworms. The results of the validation experiments clearly demonstrated that sound biological information can be retrieved when following these sampling and extraction procedures. Such a protocol can be implemented at any time of the year without any preliminary knowledge of specific types of organisms during the sampling. It offers the opportunity to analyze all groups of organisms using a single sampling/extraction procedure and opens the possibility to fully standardize biodiversity surveys.

opencc-zeroDec 2011View details →

Data from: Evolution of root plasticity responses to variation in soil nutrient distribution and concentration

Root plasticity, a trait that can respond to selective pressure, may help plants forage for nutrients in heterogeneous soils. Agricultural breeding programs have artificially selected for increased yield under comparatively homogeneous soil conditions, potentially decreasing the capacity for plasticity in crop plants like barley (Hordeum vulgare). However, the effects of domestication on the evolution of root plasticity are essentially unknown. Using a split container approach, we examined differences in root plasticity among three domestication levels of barley germplasm (wild, landrace, and cultivar) grown under different concentrations and distribution patterns of soil nutrients. Domestication level, nutrient concentration, and nutrient distribution interactively affected average root diameter; differential root allocation (within-plant plasticity) was greatest in wild barley (H. spontaneum), especially under low nutrient levels. Correlations of within-plant root plasticity and plant size were most pronounced in modern cultivars under low nutrient conditions. Barley plants invested more resources to root systems when grown in low nutrient soils and allocated more roots to higher nutrient locations. Root plasticity in barley is scale dependent and varies with domestication level. Although wild barley harbors a greater capacity for within-plant root plasticity than domesticated barley, cultivars exhibited the greatest capacity to translate within-plant plasticity into increased plant size.

Data from: Dryland soils in northern China sequester carbon during the early-2000s warming hiatus period

1. Drylands, covering ~45% of the Earth's terrestrial surface and supporting ~38% of the global population, play a dominant role in the trend and inter-annual variability of global land carbon (C) sink. Given that a large proportion of organic C is stored in soils, our knowledge on soil C dynamics in drylands is crucial to evaluate terrestrial C-climate feedback. However, credible understanding on this issue is still greatly limited by the lack of direct observations. 2. Here, based on a regional resampling of historical sites collected during 2002-2004, we explored the soil organic C changes in various layers over the past decade across the arid/semi-arid grasslands on the Inner Mongolian Plateau. 3. Our results revealed that the soil organic C density (SOCD) in this typical dryland increased significantly over the monitoring period, with a mean increase of 50.6 g C m-2 yr-1 or 0.8% yr-1 in the top 50 cm depth. Moreover, soil C dynamics exhibited contrasting spatial patterns between different layers: the rate of C accumulation in surface soils (0-10 cm) decreased, whereas that in deep soils (30-50 cm) exhibited an increasing trend along the aridity gradient. 4. Collectively, these findings demonstrate that dryland soils function as an important C sink, with the drier region tending to sequester C in deeper soils due to the greater root biomass allocation.

Data from: Grazer effects on soil carbon storage vary by herbivore assemblage in a semi-arid grassland

1. Accounting for 10-30% of global soil organic carbon, grassland soils potentially present a large reservoir for storing atmospheric CO2. Livestock grazing management can substantially affect grassland soil carbon (C) storage, but few controlled experiments have explored how herbivore assemblages (different herbivore species and combinations) affect soil C storage. 2. We examined effects of moderate grazing by different herbivore assemblages (no grazing; sheep grazing; cattle grazing; mixed grazing by sheep and cattle) on soil organic carbon storage in two types of grassland communities (high forbs/high diversity and low forbs/low diversity), within a semi-arid grassland with a five-year grazing history. 3. We found that herbivore assemblage generated varying effects on soil C storage and the effects were subject to grassland community types. In the low diversity community, none of three herbivore assemblages studied had obvious effects on soil C storage. In the high diversity community, however, sheep grazing significantly decreased soil C storage due to high selectivity for high quality forbs, and cattle grazing had no effects on soil C storage, while mixed grazing by sheep and cattle significantly increased soil C storage. Overall, soil C storage was highest in mixed-grazed grassland sites with high diversity. 4. Synthesis and applications. Our study suggests that explicitly incorporating grazer species and the combination of grazing livestock into grassland grazing management may help mitigate greenhouse gas emissions. Caution should be exercised when using grazer species with high food selectivity when grazing management is also aimed at climate mitigation, especially in grasslands with abundant high quality forbs and high plant diversity, as sheep grazing may reduce soil carbon (C) storage. Moreover, mixed grazing, including multiple herbivore species, may contribute to a reduction in foraging selectivity for a plant community by means of complementary foraging. It could therefore be considered as an optimal grazing management strategy to maintain and improve soil C storage.

opencc-zeroDec 2016View details →

Data from: Soil gross N ammonification and nitrification from tropical to temperate forests in eastern China

1. Nitrogen (N) ammonification and nitrification are two primary microbial processes controlling the availability of soil ammonium (NH4+), a key nutrient for vegetative growth. The large-scale patterns of gross ammonification (GA) and gross nitrification (GN) rates represent soil microbial adaptations to different vegetative and environmental conditions. In this study, we investigated GA and GN rates in nine forest soils along a 3500-km north-south transect in eastern China (NSTEC). 2. We used 15N-labeling techniques, along with field experiments and laboratory incubations, to as-sess in situ and potential rates of the GA and GN. The mean in situ GA rate was 4.9 ± 0.5 mg N kg–1 day–1, whereas the mean potential rate of GA was 32.0 ± 8.6 mg N kg–1 day–1. The mean in situ GN rate was 1.7 ± 0.3 mg N kg–1 day–1 (potential GN rate: 3.2 ± 0.6 mg N kg–1 day–1). GA was sig-nificantly higher than GN along the transect and there were high variations in GA and GN among different forests. Significant relationships were identified between meteorological factors (tempera-ture and precipitation) and the GA and GN rates during the sampling month (August 2013). How-ever, the mean GA rate in primary forest was significantly lower in the Huzhong (HZ), Dongling (DL), Taiyue (TY), and Dinghu (DH) sites compared with other sites, whereas with the exception of the Liangshui (LS) sampling site, the mean GN rate in primary and secondary forests showed the same trends. Significant differences in GA rates were found between primary and secondary forests at the LS and Chang Bai (CB) sites, and differences were detected in GN rate at the HZ, LS, and Jiulian (JL) sites. 3. Structural equation modeling analysis suggested that soil N contents, microbial biomass N pool sizes, and bacterial abundance are the primary determinants of the in situ rates of GA and GN. The strong control of edaphic factors on GA and GN indicates a need to improve soil N models with more explicit representation of edaphic factors and their control on soil N transformations.

Data from: Insecticide applications to soil contribute to development of Burkholderia mediating insecticide resistance in stinkbugs

Some soil Burkholderia strains are capable of degrading the organophosphorus insecticide, fenitrothion, and establish symbiosis with stinkbugs, making the host insects fenitrothion-resistant. However, the ecology of the symbiotic degrading Burkholderia adapting to fenitrothion in the free-living environment is unknown. We hypothesized that fenitrothion applications affect the dynamics of fenitrothion-degrading Burkholderia, thereby controlling the transmission of symbiotic degrading Burkholderia from the soil to stinkbugs. We investigated changes in the density and diversity of culturable Burkholderia (i.e. symbiotic and nonsymbiotic fenitrothion degraders and nondegraders) in fenitrothion-treated soil using microcosms. During the incubation with five applications of pesticide, the density of the degraders increased from less than the detection limit to around 106/g of soil. The number of dominant species among the degraders declined with the increasing density of degraders; eventually, one species predominated. This process can be explained according to the competitive exclusion principle using Vmax and Km values for fenitrothion metabolism by the degraders. We performed a phylogenetic analysis of representative strains isolated from the microcosms and evaluated their ability to establish symbiosis with the stinkbug Riptortus pedestris. The strains that established symbiosis with R. pedestris were assigned to a cluster including symbionts commonly isolated from stinkbugs. The strains outside the cluster could not necessarily associate with the host. The degraders in the cluster predominated during the initial phase of degrader dynamics in the soil. Therefore, only a few applications of fenitrothion could allow symbiotic degraders to associate with their hosts and may cause the emergence of symbiont-mediated insecticide resistance.