The negative effects of soil microorganisms on plant growth only extend to the first weeks

土壤微生物对植物生长的负面影响只延续到最初几周 土壤微生物群落可以显著影响植物的生长表现。在本文中,我们提出一个问题：土壤微生物群落对植物生长的影响可以持续多久。我们监测了早期、中期和晚期3个阶段的植物生长速率,在无菌土壤或活土壤中对一种菊科植物疆千里光(Jacobaea vulgaris)进行了两次分别为49天和63天的生长实验。在第3个实验中,我们用4种不同的时间处理方法研究了种植前土壤接种时间对该植物相对生长速率的影响。研究结果表明,3个实验中,在无菌土壤和活土壤中生长的植物的生物量差异都增加了。此外,在前2–3周,灭菌土壤中植物的相对生长速率仅显著高于活土壤中植物的相对生长速率。在第3个实验中,植物生物量随着接种和种植之间时间的增加而减少。总体而言,这些结果表明,疆千里光在无菌土壤中的生长优于在活土壤中。土壤接种对植物生物量的负面影响似乎可以延伸到整个生长期,但源于最初几周发生的对相对生长速率的负面影响。     

Plant–soil feedbacks of forest understorey plants transplanted in nonlocal soils along a latitudinal gradient

• Climate change is driving movements of many plants beyond, as well as within, their current distributional ranges. Even migrant plants moving within their current range may experience different plant–soil feedbacks (PSF) because of divergent nonlocal biotic soil conditions. Yet, our understanding to what extent soil biotic conditions can affect the performance of within‐range migrant plants is still very limited.
• We assessed the emergence and growth of migrant forest herbs (Milium effusum and Stachys sylvatica) using soils and seeds collected along a 1,700 km latitudinal gradient across Europe. Soil biota were manipulated through four soil treatments, i.e. unsterilized control soil (PSF_US), sterilized soil (PSF_S), sterilized soil inoculated with unsterilized home soil (PSF_S+HI) and sterilized soil inoculated with unsterilized foreign soil (PSF_S+FI, expected to occur when both plants and soil biota track climate change).
• Compared to PSF_S, PSF_US had negative effects on the growth but not emergence of both species, while PSF_S+FI only affected S. sylvatica across all seed provenances. When considering seed origin, seedling emergence and growth responses to nonlocal soils depended on soil biotic conditions. Specifically, the home–away distance effect on seedling emergence differed between the four treatments, and significant responses to chemistry either disappeared (M. effusum) or changed (S. sylvatica) from PSF_US to PSF_S.
• Soil biota emerge as an important driver of the estimated plant migration success. Our results of the effects of soil microorganisms on plant establishment provide relevant information for predictions of the distribution and dynamics of plant species in a changing climate.

     

Mycorrhizal status of the endangered species Astragalus applegatei Peck as determined from a soil bioassay

 The mycorrhizal status of Astragalus applegatei Peck is reported for the first time on plants from a greenhouse soil bioassay. Seedlings were grown in a potting mix inoculated with soil collected near A. applegatei plants in nature. Plants were also grown in non-inoculated potting mix. Only plants from the native soil inoculation survived. Abundant colonization of VAM fungi was found in all 15 plants analyzed from the native soil treatment, and chlamydospores produced by Glomus spp. were observed. Mycorrhizal colonization was estimated to be 23% of total fine root length after 6 weeks and 53% after 14 weeks. Our results provide ecologically important information for conservation and restoration efforts underway to recover populations of this endangered species. Accepted: 22 June 1998     

Contrasting response of seedlings of two tropical species Clusia minor and Clusia multiflora to mycorrhizal inoculation in two soils with different pH

Differences in mycotrophic growth and response to phosphorus (P) fertilization were studied in seedlings of two woody native species: Clusia minor L. and Clusia multiflora H.B.K. from a cloud montane forest of tropical America. Greenhouse investigation was undertaken to determine the relationships between mycorrhizal dependency of host species associated with P utilization and growth in two different soils contrasting in pH (acidic and neutral) and nutrient content. Four treatments were performed: sterilized soil; sterilized soil plus 375 mg/kg of triple superphosphate (TSP); sterilized soil inoculated with Scutellospora fulgida (20 g/pot); and sterilized soil plus S. fulgida and TSP, with 10 replications per treatment for the two species. Results showed that both Clusia species presented high growth response to increasing P availability, which indicates that the root morphology (magnolioid roots) of these species is not a limiting factor for the incorporation of P from soils. Plants inoculated with arbuscular mycorrhizal fungi (AMF) in acidic soil had significantly increased shoot and root biomass, leaf area and height, in comparison to the biomass of P-fertilized plants and nonmycorrhizal plants. In neutral soil, seedlings of C. minor and C. multiflora were negatively affected by inoculation with AMF. In contrast, a significant decrease in growth was observed when inoculated plants were compared with noninoculated plants on neutral soil. Results indicate that an increase in the availability of a limiting nutrient (P) can turn a balanced mutualistic relationship into a less balanced nonmutualistic one.     

Seed germination and seedling emergence of Euryodendron excelsum H. T. Chang: implications for species conservation and restoration

Euryodendron excelsum H. T. Chang is a critically endangered plant from the family Theaceae that is endemic to China. It is now present in only one remnant population in a very narrow range and with a highly isolated and fragmented distribution pattern. The species is distributed close to the local villages and faces extinction because of the high level of anthropogenic disturbance. Thus, conservation and restoration of this species is urgent. The species reproduces by seed, but its germination requirements and seedling emergence are rarely understood. In this study, the germination requirements, desiccation tolerance and seedling emergence of the species were studied under controlled laboratory conditions. The results indicated that seeds of E. excelsum were non‐dormant. Optimal temperatures for germination were 15°C to 25°C; the germination percentage decreased and the mean germination time increased at high temperature. Seed germination was inhibited in the dark, suggesting that the seeds were positive photoblastic. Water stress also significantly inhibited germination percentage; no seeds germinated at 15% polyethylene glycol 6000. The fresh seeds had moderate moisture content of 28.6% and showed strong tolerance of dehydration. Thus, the seeds of E. excelsum tended to be orthodox. Seeds on the soil surface had the highest emergence percentage, which declined with depth of burial. Soil types significantly affected seedling emergence; seeds had higher emergence percentage in sandy soil than in mixed soil and clayed soil. Our study demonstrated that ex situ conservation and reintroduction of E. excelsum using seedling propagation from seeds is feasible.     

Bioremediation of Soils Contaminated with Nigerian Petroleum Products Using Composted Municipal Wastes

The efficiency of ready-to-use, source-separated, composted municipal organic wastes of Nigerian origin on degradation of soil total petroleum hydrocarbons (TPHs) in soils polluted with petroleum products (crude oil, diesel, and spent engine oil) was assessed in screen house experiments. The effect of compost:soil ratios and combined effect of compost-phytoremediation technique were also studied. TPH was determined spectrophotometrically, after extraction with 1:1 acetone-dichloromethane mixture at 425 nm. Soil pH, electrical conductivity, and phytotoxicity to seed germination and growth of maize (Zea mays L.) served as risk assessments on soil quality and evidence of recovery for the oil-impacted soil. Results showed that the treatments increased soil pH and electrical conductivity but reduced TPH. Reductions in TPH by compost technology ranged from 40% to 75.87%. Toxicity to seed germination reduced from 100% to 16.12%. Positive correlations were obtained for plant agronomical parameters and growth period, for all treatments, with coefficients in the range of .905 to .996, p < .05. This study revealed that ready-to-use composted waste has the potential for bioremediation of soils polluted with petroleum and petroleum products. This study is a contribution to the data bank of relatively simple bioremediation methods, suitable for workers in the developing countries, where there is no easy access to high-technology facilities. However, further development of this technique to achieve zero residual TPH is recommended.     

Reproductive allocation,seed dispersal and germination of <Emphasis Type="Italic">Myricaria laxiflora</Emphasis>, an endangered species in the Three Gorges Reservoir area

Myricaria laxiflora is an endangered plant that grows in the flood zone along the Yangtze River in the Three Gorges area from 70 m to 155 m above sea level. To understand the spatial distribution patterns of the species and to provide information for developing conservation strategies, we used field surveys to study its seed reproduction and dispersion, and used growth chambers to study seed germination. Results showed that M. laxiflora produced many flowering branches, inflorescences and seeds. Seeds were very small and output was high although biomass allocation to reproduction was low (∼4%). Reproductive allocation was strongly correlated with the biomass of stems and leaves. Seeds were dispersed either by the wind or the river current. Wind-dispersed seeds usually settled within 25 m from parent plants leading to a clumped distribution of individuals in populations. Water-dispersed seeds often landed and established on strands of firth where the fine sediment and gentle sloping were available. Seedlings that emerged from water-dispersed seeds were distributed along the water flood line. The life-span of M. laxiflora seeds was about 7 days. Seeds could germinate within 24 h when they absorbed adequate amounts of water. Soil water content was a key factor limiting the establishment ability of M. laxiflora. Experiments showed that the minimum soil water content for germination to occur was 10% on sand or 17% on sandy soil substrates, and the optimal conditions were on saturated soils. The water content of sandy soils on the riverbank was lower than 10% in autumn, the dry season, and seeds were able to germinate only on sandy beaches that were intermittently inundated by the fluctuating river current. These characteristics of seed dispersal and germination limit the ability for M. laxiflora to expand its distribution. These results provide information essential for the conservation and reintroduction of this endangered species.     

西宁南山4种灌木根际和非根际土壤微生物、酶活性和养分特征

西宁南山区植被退化情况严重,人工造林植被恢复被看作是最有效的恢复手段,其中选择合适造林树种尤为关键。选择人工种植的唐古特白刺Nitraria tangutorum、柠条Caragana korshinskii、西北小蘗Berberis vernae和短叶锦鸡儿Caragana brevifolia共4种灌木树种造林试验区为研究对象,通过测定根际和非根际土壤微生物数量、酶活性及养分含量,综合比较种植4种灌木树种根际和非根际土壤肥力差异,科学评价其对土壤的改善效果。研究表明:(1)土壤微生物数量和酶活性总体呈现出根际高于非根际的规律,仅放线菌数量和脲酶活性出现了根际低于非根际现象。(2)土壤养分方面,4种灌木根际土壤和非根际土壤p H值、全N、全P、全K含量差异不显著,有机质、有效P、速效K含量均呈现出根际非根际,而碱解N则是根际非根际。(3)土壤酶活性与土壤微生物数量相关性不显著,土壤有机质含量与土壤细菌、真菌数量呈极显著正相关,有效P含量与土壤细菌、真菌和放线菌数量呈极显著正相关,速效K含量与过氧化氢酶、酸性磷酸酶活性呈显著正相关,全N、碱解N含量均与脲酶活性呈显著正相关。(4)从土壤肥力综合水平来看,根际非根际,其中根际土壤中西北小蘗柠条短叶锦鸡儿唐古特白刺,研究结果表明西北小蘗和柠条能大幅提高土壤肥力,改良土壤效果较好。     

Effects of Revegetation on Soil Microbial Biomass,Enzyme Activities,and Nutrient Cycling on the Loess Plateau in China

Revegetation is a traditional practice widely used for soil and water conservation on the Loess Plateau in China. However, there has been a lack of reports on soil microbial–biochemical indices required for a comprehensive evaluation of the success of revegetation systems. In this study, we examined the effects of revegetation on major soil nutrients and microbial–biochemical properties in an artificial alfalfa grassland, an enclosed natural grassland, and an artificial shrubland (Caragana korshinskii), with an abandoned cropland as control. Results showed that at 0–5, 5–20, and 20–40 cm depths, soil organic carbon, alkaline extractable nitrogen and available potassium were higher in natural grassland and artificial shrubland compared with artificial grassland and abandoned cropland. Soil microbial biomass C (Cmic) and phosphorous (Pmic) substantially decreased with depth at all sites, and in abandoned cropland was significantly lower than those of natural grassland, artificial grassland, and artificial shrubland at the depth of 0–5 cm. Soil microbial biomass N (Nmic) was higher in artificial shrubland and abandoned cropland compared with that in natural and artificial grasslands. Both Cmic and Pmic were significantly different between the 23‐year‐old and the 13‐year‐old artificial shrublands at the 0–5 cm depth. The activities of soil invertase, urease, and alkaline phosphatase in natural grassland and artificial shrubland were higher than those in artificial grassland and abandoned cropland. This study demonstrated that the regeneration of both natural grassland and artificial shrubland effectively preserved and enhanced soil microbial biomass and major nutrient cycling, thus is an ecologically beneficial practice for recovery of degraded soils on the Loess Plateau.     

Frankia inoculation,soil biota,and host tissue amendment influence Casuarina nodulation capacity of a tropical soil

The effects of soil biota, Frankia inoculation and tissue amendment on nodulation capacity of a soil was investigated in a factorial study using bulked soil from beneath a Casuarina cunninghamiana tree and bioassays with C. cunninghamiana seedlings as capture plants. Nodulation capacities were determined from soils incubated in sterile jars at 21 °C for 1, 7, and 28 days, after receiving all combinations of the following treatments: ± steam pasteurization, ± inoculation with Frankia isolate CjI82001, and ± amendment with different concentrations of Casuarina cladode extracts. Soil respiration within sealed containers was determined periodically during the incubation period as a measure of overall microbial activity. Soil respiration, and thus overall microbial activity, was positively correlated with increasing concentrations of Casuarina cladode extracts. The nodulation capacity of soils inoculated with Frankia strain Cj82001 decreased over time, while those of unpasteurized soils without inoculation either increased or remained unaffected. The mean nodulation capacity of unpasteurized soil inoculated with Frankia CjI82001 was two to three times greater than the sum of values for unpasteurized and inoculated pasteurized soils. Our results suggest a positive synergism between soil biota as a whole and Frankia inoculum with respect to host infection.     

Soil microbial parameters and stability of soil aggregate fractions under different grassland communities on the Loess Plateau,China

Over-grazing and large-scale monocultures on the Loess plateau in China have caused serious soil erosion by water and wind. Grassland revegetation has been reported as one of the most effective counter measures. Therefore, we investigated soil aggregation, aggregate stability and soil microbial activities as key parameters for soil remediation through grassland revegetation. The results showed that soil microbial biomass carbon (Cmic) and microbial biomass nitrogen (Nmic) increased under revegetated grass communities compared to cropland and overgrazed pastures and were higher in surface layers (0–10 cm) than in the subsurface (10–20 cm). Although there are variations between the four investigated grassland communities, their values were 10 to 50 times higher in comparison to the cropland and overgrazed pastures, similar to the increase in soil enzyme activities, such as β-glucosidase and β-glucosaminidase. Soil aggregate stability (SAS) showed clear differences between the different land uses with two main soil aggregate fractions measured by ultra sound: < 63 μm and 100–250 μm, with approximately 70% and 10% of the total soil volume respectively. We also found positive correlations between SAS and soil microbial parameters, such as Cmic, Nmic, and soil enzyme activities. From this, we concluded that revegetation of eroded soils by grasses accelerates soil rehabilitation.     

Are two strategies better than one? Manipulation of seed density and soil community in an experimental prairie restoration

Restoration practitioners have a variety of practices to choose from when designing a restoration, and different strategies may address different goals. Knowledge of how to best use multiple strategies could improve restoration outcomes. Here, we examine two commonly suggested strategies in a single tallgrass prairie restoration experiment: increased forb sowing density and prairie soil inoculation. We designed a study with two different forb seeding densities. Within these densities, we transplanted seedlings into 1‐m² plots that had been grown in either a whole prairie soil inoculum or sterilized prairie soil. After 4 years, we found positive effects of both high forb sowing density and inoculation treatments on the ratio of seeded to nonseeded plant cover in these plots, and negative effects of both treatments on nonseeded plant diversity. No effects of either treatment were seen on seeded plant diversity. Each strategy also affected the plant community in different ways: high forb sowing density increased seeded forb richness and decreased native nonseeded plant cover, while inoculation decreased non‐native cover, and tended to increase average successional stage of the community. These effects on restoration outcome were typically independent of each other, with the result that plots with both manipulations had the most positive effects on restoration outcomes. We thus advocate the combined use of these restoration strategies, and further studies which focus on both seeding and soil community manipulation in restoration.     

Effect of applying an arsenic-resistant and plant growth-promoting rhizobacterium to enhance soil arsenic phytoremediation by Populus deltoides LH05-17

Aims: Bioremediation of highly arsenic (As)‐contaminated soil is difficult because As is very toxic for plants and micro‐organisms. The aim of this study was to investigate soil arsenic removal effects using poplar in combination with the inoculation of a plant growth–promoting rhizobacterium (PGPR). Methods and Results: A rhizobacterium D14 was isolated and identified within Agrobacterium radiobacter. This strain was highly resistant to arsenic and produced indole acetic acid and siderophore. Greenhouse pot bioremediation experiments were performed for 5 months using poplar (Populus deltoides LH05‐17) grown on As‐amended soils, inoculated with strain D14. The results showed that P. deltoides was an efficient arsenic accumulator; however, high As concentrations (150 and 300 mg kg^?1) inhibited its growth. With the bacterial inoculation, in the 300 mg kg^?1 As‐amended soils, 54% As in the soil was removed, which was higher than the uninoculated treatments (43%), and As concentrations in roots, stems and leaves were significantly increased by 229, 113 and 291%, respectively. In addition, the As translocation ratio [(stems + leaves)/roots = 0·8] was significantly higher than the uninoculated treatments (0·5). About 45% As was translocated from roots to the above‐ground tissues. The plant height and dry weight of roots, stems and leaves were all enhanced; the contents of chlorophyll and soluble sugar, and the activities of superoxide dismutase and catalase were all increased; and the content of a toxic compound malondialdehyde was decreased. Conclusions: The results indicated that the inoculation of strain D14 could contribute to the increase in the As tolerance of P. deltoides, promotion of the growth, increase in the uptake efficiency and enhancement of As translocation. Significance and Impact of the Study: The use of P. deltoides in combination with the inoculation of strain D14 provides a potential application for efficient soil arsenic bioremediation.     

Developing manufactured soils from industrial by‐products for use as growth substrates in mine reclamation

Suitable soils for reclamation can be acquired through excavation and translocation of local soils, increasing the industrial footprint on previously undisturbed lands and causing negative environmental impacts. Manufactured soils (Technosols) could be a viable soil source when the availability of suitable natural soils is limited. The purpose of this study was to manufacture a Technosol from an admixture of woody residuals, primary paper sludge, and two subtypes of nonacid generating crushed mine rock, to function as a growth substrate for revegetation of mined land. Technosols manufactured with 0, 25, 50, and 75% organic materials (v/v) were assessed in a 10‐week growth study using annual ryegrass biomass production and allocation as a performance indicator. Technosols containing no organic materials had significantly lower plant nutrient concentrations than Technosols containing an organic constituent and, after 5 weeks of growth, ryegrass grown on nonorganic Technosols had greater root:shoot ratios than ryegrass grown on organic Technosols. Organics increase the water holding capacity and nutrient concentrations of Technosols and should be included in manufacturing Technosols for revegetation. Technosols manufactured with primary paper sludge produced lower shoot biomass than Technosols manufactured with woody residuals, which could be in part due to the higher pH of the paper sludge. Technosols can be manufactured for revegetation purposes and individual components should be assessed before and after mixing. Further development of Technosols should include field testing and amendment or fertilizer use to improve soil nutrient content.     

Effects of Ruta graveolens leaves on soil characteristics and on seed germination and early seedling growth of four crop species

Effects of rue (Ruta graveolens) leaves on soil characteristics and on germination and seedling growth of four crop species (radish, zucchini, cauliflower and tomato) were investigated. Soil not previously associated with rue was mulched and amended with its fresh leaves. The objectives of the present study were to determine: (i) the changes in soil chemical characteristics after addition of rue leaves, (ii) the growth responses in soils treated with R. graveolens leaves, and (iii) whether the soil chemistry changes affect plant growth. Results indicate that soil incorporated with rue leaves had higher values of water‐soluble phenolics, electrical conductivity and nitrate, and lower pH values compared to untreated soil. Seed germination of radish and tomato was suppressed in covered and amended soils compared to control soil. Seedling development for all the species was suppressed in incorporated and amended soil, compared to the rue‐free soil. Correlations between soil chemical characteristics, germination and seedling growth of plants are also discussed.     

不同pH值土壤及其浸提液对羊草种子萌发和幼苗生长的影响

研究了不同pH值土壤以及重度盐碱土和非盐碱土浸提液对羊草(Leymus chinensis)种子萌发及幼苗生长的影响。不同pH值土壤由配土和调酸两种方式取得,前者由重度盐碱土(pH=10．24)与非盐碱土(pH=7．49)按不同比例配制,后者是由重度苏打盐碱土经硫酸调酸处理得到。配土发芽的实验结果表明,当pH值在7．49-9．14时,种子的发芽率均在50％以上,且幼苗能够正常生长;pH=9．53时,羊草种子的发芽率低于50％,仅部分幼苗个体能够成活;当pH>9．86时,幼苗在萌发后50天左右全部枯死。说明羊草种子个体萌发期最大耐受pH值在9．14-9．53之间。重度苏打盐碱土调酸发芽实验结果表明,当调酸后的土壤pH值降至7．0-10．0时,均能显著促进羊草种子的萌发,且幼苗生长正常。确定了羊草种子萌发的最适pH值为8．0-8．5。土／水比为1:1的非盐碱土浸提液能够显著提高羊草种子发芽率,而重度苏打盐碱土浸提液对羊草种子萌发没有产生显著抑制。     

Inoculation with native soil improves seedling survival and reduces non-native reinvasion in a grassland restoration

Losses of grasslands have been largely attributed to widespread land-use changes, such as conversion to row-crop agriculture. The remaining tallgrass prairie faces further losses due to biological invasions by non-native plant species, often with resultant ecosystem degradation. Of critical concern for conservation, restoration of native grasslands has been met with little success following eradication of non-native plants. In addition to the direct and indirect effects of non-native invasive plants on beneficial soil microbes, management practices targeting invasive species may also negatively affect subsequent restoration efforts. To assess mechanisms limiting germination and survival of native species and to improve native species establishment, we established six replicate plots of each of the following four treatments: (1) inoculated with freshly collected prairie soil with native seeds; (2) inoculated with steam-pasteurized soil with native seeds; (3) noninoculated with native seeds; or (4) noninoculated/nonseeded control. Inoculation with whole soil did not improve seed germination; however, addition of whole soil significantly improved native species survival, compared to pasteurized soil or noninoculated treatments. Inoculation with whole soil significantly decreased reestablishment of non-native invasive Bothriochloa bladhii (Caucasian bluestem); at the end of the growing season, plots receiving whole soil consisted of approximately 30% B. bladhii cover, compared to approximately 80% in plots receiving no soil inoculum. Our results suggest invasion and eradication efforts negatively affect arbuscular mycorrhizal hyphal and spore abundances and soil aggregate stability, and inoculation with locally adapted soil microbial communities can improve metrics of restoration success, including plant species richness and diversity, while decreasing reinvasion by non-native species.     

The effects of sod cutting and additional liming on potential net nitrification in heathland soils

The effects of sod cutting, a common restoration measure to remove excess nutrients from grass-dominated heathlands, on nitrification were studied in dry and wet Dutch heathlands and in incubation experiments. In the field, soil ammonium and nitrate concentrations were measured after treatment by sod cutting, with or without additional liming. Potential net nitrification was measured by incubating soil samples of all treatments with extra ammonium in a climate chamber at pH 6. Potential net nitrification of heaths dominated by Molinia caerulea was significantly higher than that of dwarf-shrub dominated heaths. Sod cutting of the former areas significantly decreased potential net nitrification, whereas in the latter areas no differences were found. Liming of sod-cut soils greatly increased potential net nitrification and the accumulation of ammonium in the soil up to toxic concentrations could be prevented. Our results show that the combination of sod cutting and liming would create suitable soil conditions for the germination and establishment of endangered plant species of dry and wet heathlands. The success of restoration projects of these areas can thus be increased.     

Biotic and Abiotic Soil Properties Influence Survival of Listeria monocytogenes in Soil

Listeria monocytogenes is a food-borne pathogen responsible for the potentially fatal disease listeriosis and terrestrial ecosystems have been hypothesized to be its natural reservoir. Therefore, identifying the key edaphic factors that influence its survival in soil is critical. We measured the survival of L. monocytogenes in a set of 100 soil samples belonging to the French Soil Quality Monitoring Network. This soil collection is meant to be representative of the pedology and land use of the whole French territory. The population of L. monocytogenes in inoculated microcosms was enumerated by plate count after 7, 14 and 84 days of incubation. Analysis of survival profiles showed that L. monocytogenes was able to survive up to 84 days in 71% of the soils tested, in the other soils (29%) only a short-term survival (up to 7 to 14 days) was observed. Using variance partitioning techniques, we showed that about 65% of the short-term survival ratio of L. monocytogenes in soils was explained by the soil chemical properties, amongst which the basic cation saturation ratio seems to be the main driver. On the other hand, while explaining a lower amount of survival ratio variance (11%), soil texture and especially clay content was the main driver of long-term survival of L. monocytogenes in soils. In order to assess the effect of the endogenous soils microbiota on L. monocytogenes survival, sterilized versus non-sterilized soils microcosms were compared in a subset of 9 soils. We found that the endogenous soil microbiota could limit L. monocytogenes survival especially when soil pH was greater than 7, whereas in acidic soils, survival ratios in sterilized and unsterilized microcosms were not statistically different. These results point out the critical role played by both the endogenous microbiota and the soil physic-chemical properties in determining the survival of L. monocytogenes in soils.     

Microbial community responses reduce soil carbon loss in Tibetan alpine grasslands under short‐term warming

Changes in labile carbon (LC) pools and microbial communities are the primary factors controlling soil heterotrophic respiration (R_h) in warming experiments. Warming is expected to initially increase R_h but studies show this increase may not be continuous or sustained. Specifically, LC and soil microbiome have been shown to contribute to the effect of extended warming on R_h. However, their relative contribution is unclear and this gap in knowledge causes considerable uncertainty in the prediction of carbon cycle feedbacks to climate change. In this study, we used a two‐step incubation approach to reveal the relative contribution of LC limitation and soil microbial community responses in attenuating the effect that extended warming has on R_h. Soil samples from three Tibetan ecosystems—an alpine meadow (AM), alpine steppe (AS), and desert steppe (DS)—were exposed to a temperature gradient of 5–25°C. After an initial incubation period, soils were processed in one of two methods: (a) soils were sterilized then inoculated with parent soil microbes to assess the LC limitation effects, while controlling for microbial community responses; or (b) soil microbes from the incubations were used to inoculate sterilized parent soils to assess the microbial community effects, while controlling for LC limitation. We found both LC limitation and microbial community responses led to significant declines in R_h by 37% and 30%, respectively, but their relative contributions were ecosystem specific. LC limitation alone caused a greater R_h decrease for DS soils than AMs or ASs. Our study demonstrates that soil carbon loss due to R_h in Tibetan alpine soils—especially in copiotrophic soils—will be weakened by microbial community responses under short‐term warming.