Soil-plant co-stimulation during forest vegetation restoration in a subtropical area of southern China

Background: Soil and vegetation have a direct impact on the process and direction of plant community succession, and determine the structure, function, and productivity of ecosystems. However, little is known about the synergistic influence of soil physicochemical properties and vegetation features on vegetation restoration. The aim of this study was to investigate the co-evolution of soil physicochemical properties and vegetation features in the process of vegetation restoration, and to distinguish the primary and secondary relationships between soil and vegetation in their collaborative effects on promoting vegetation restoration in a subtropical area of China.Methods: Soil samples were collected to 40 cm in four distinct plant communities along a restoration gradient from herb(4–5 years), to shrub(11–12 years), to Pinus massoniana coniferous and broadleaved mixed forest(45–46 years), and to evergreen broadleaved forest(old growth forest). Measurements were taken of the soil physicochemical properties and Shannon–Wiener index(SD), diameter at breast height(DBH), height(H), and biomass. Principal component analysis, linear function analysis, and variation partitioning analysis were then performed to prioritize the relative importance of the leading factors affecting vegetation restoration.Results: Soil physicochemical properties and vegetation features showed a significant trend of improvement across the vegetation restoration gradient, reflected mainly in the high response rates of soil organic carbon(SOC)(140.76%), total nitrogen(TN)(222.48%), total phosphorus(TP)(59.54%), alkaline hydrolysis nitrogen(AN)(544.65%),available phosphorus(AP)(53.28%), species diversity(86.3%), biomass(2906.52%), DBH(128.11%), and H(596.97%).The soil properties(pH, SOC, TN, AN, and TP) and vegetation features(biomass, DBH, and H) had a clear coevolutionary relationship over the course of restoration. The synergistic interaction between soil properties and vegetation features had the greatest effect on biomass(55.55%–72.37%), and the soil properties contributed secondarily(3.30%–31.44%). The main impact factors of biomass varied with the restoration periods.Conclusions: In the process of vegetation restoration, soil and vegetation promoted each other. Vegetation restoration was the cumulative result of changes in soil fertility and vegetation features.

General and specialized metabolites in peanut roots regulate arbuscular mycorrhizal symbiosis

Arbuscular mycorrhizae(AM)fungi form symbiotic associations with plant roots,providing nutritional benefits and promoting plant growth and defenses against various stresses.Metabolic changes in the roots during AM fungal colonization are key to understanding the development and maintenance of these symbioses.Here,we investigated metabolic changes in the roots of peanut(Arachis hypogaea L.)plants during the colonization and development of AM symbiosis,and compared them to uncolonized roots.The primary changes during the initial stage of AM colonization were in the contents and compositions of phenylpropanoid and flavonoid compounds.These compounds function in signaling pathways that regulate recognition,interactions,and pre-colonization between roots and AM fungi.Flavonoid compounds decreased by 25%when the symbiosis was fully established compared to the initial colonization stage.After AM symbiosis was established,general metabolism strongly shifted toward the formation of lipids,amino acids,carboxylic acids,and carbohydrates.Lipid compounds increased by 8.5%from the pre-symbiotic stage to well-established symbiosis.Lyso-phosphatidylcholines,which are signaling compounds,were only present in AM roots,and decreased in content after the symbiosis was established.In the initial stage of AM establishment,the content of salicylic acid increased two-fold,whereas jasmonic acid and abscisic acid decreased compared to uncolonized roots.The jasmonic acid content decreased in roots after the symbiosis was well established.AM symbiosis was associated with high levels of calcium,magnesium,and D-(+)-mannose,which stimulated seedling growth.Overall,specific metabolites that favor the establishment of AM symbiosis were common in the roots,primarily during early colonization,whereas general metabolism was strongly altered when AM symbiosis was well-established.In conclusion,specialized metabolites function as signaling compounds to establish AM symbiosis.These compounds are no longer produced after the symbiosis between the roots and AM becomes fully established.

Responses of Soil Enzyme Activities and Microbial Community Composition to Moisture Regimes in Paddy Soils Under Long-Term Fertilization Practices

The effects of fertilization on activity and composition of soil microbial community depend on nutrient and water availability;however,the combination of these factors on the response of microorganisms was seldom studied.This study investigated the responses of soil microbial community and enzyme activities to changes in moisture along a gradient of soil fertility formed within a long-term(24 years)field experiment.Soils(0–20 cm)were sampled from the plots under four fertilizer treatments:i)unfertilized control(CK),ii)organic manure(M),iii)nitrogen,phosphorus,and potassium fertilizers(NPK),and iv)NPK plus M(NPK+M).The soils were incubated at three moisture levels:constant submergence,five submerging-draining cycles(S-D cycles),and constant moisture content at 40%water-holding capacity(low moisture).Compared with CK,fertilization increased soil organic carbon(SOC) by 30.1%–36.3%,total N by 27.3%–38.4%,available N by 35.9%–56.4%,available P by 61.4%–440.9%,and total P by 28.6%–102.9%.Soil fertility buffered the negative effects of moisture on enzyme activities and microbial community composition.Enzyme activities decreased in response to submergence and S-D cycles versus low moisture.Compared with low moisture,S-D cycles increased total phospholipid fatty acids(PLFAs)and actinomycete,fungal,and bacterial PLFAs.The increased level of PLFAs in the unfertilized soil after five S-D cycles was greater than that in the fertilized soil.Variations in soil microbial properties responding to moisture separated CK from the long-term fertilization treatments.The coefficients of variation of microbial properties were negatively correlated with SOC,total P,and available N.Soils with higher fertility maintained the original microbial properties more stable in response to changes in moisture compared to low-fertility soil.

New approaches for evaluation of soil health, sensitivity and resistance to degradation

Assessment of soil health requires complexevaluation of properties and functions responsible for abroad range of ecosystem services. Numerous soil qualityindices (SQI) have been suggested for the evaluation ofspecific groups of soil functions, but comparison of variousSQI is impossible because they are based on a combinationof specific soil properties. To avoid this problem, wesuggest an SQI-area approach based on the comparison ofthe areas on a radar diagram of a combination of chemical,biological and physical properties. The new approach isindependent of the SQI principle and allows rapid andsimple comparison of parameter groups and soils. Anotherapproach analyzing the resistance and sensitivity ofproperties to degradation is suggested for a detailedevaluation of soil health. The resistance and sensitivityof soil properties are determined through comparison withthe decrease of soil organic carbon (SOC) as a universalparameter responsible for many functions. The SQI-areaand resistance/sensitivity approaches were tested based on quences after the ab and on ment of agricultural soils. Both the SQI-area and the resistance/sensitivity approaches areuseful for basic and applied research, and for decisionmakersto evaluate land-use practices and measure thedegree of soil degradation.

Compositional variations of active autotrophic bacteria in paddy soils with elevated CO_(2) and temperature

Global warming is an increasingly serious ecological problem,we examined how the active autotrophic microbes in paddy soils respond to the elevated CO_(2) and temperature.Here we employed stable isotope probing(SIP)to label the active bacteria using the soil samples from a fully factorial Simulated Climate Change(SCC)field experiment where soils were exposed to ambient CO_(2) and temperature,elevated temperature,elevated CO_(2),and both elevated CO_(2) and temperature.Around 28.9% of active OTUs belonged to ammonia-oxidizing bacteria(AOB)and nitrite-oxidizing bacteria(NOB).Nitrosospira taxa was dominant in all soils and 80.4% of carbon-fixing bacteria under elevated temperature were classified as Nitrosomonas nitrosa.While no labeled NOBs were detected when temperature or CO_(2) were elevated independently,diverse NOBs were detected in the ambient conditions.We found that elevated CO_(2) and temperature had contrasting effects on microbial community composition,while relatively small changes were observed when CO_(2) and temperature were elevated simultaneously.Summarily these results suggest that carbon-fixing bacteria can respond positively to elevated CO_(2) concentrations,but when it’s accompanied with increase in the temperature this positive response could be weakened.Multiple abiotic factors thus need to be considered when predicting how microbial communities will respond to multiple climatic factors.

Human and climatic drivers of land and water use from 1997 to 2019 in Tarim River basin,China

Climate and human activities change spatial and temporal distribution of water and land use.The Tarim River,the largest inland river in China,faced a long-term exploitation of land and water over a rapid economic development.We analyzed land and water use from 1997 to 2019 in Tarim River Basin by Landsat images,and data on hydrology,climate,population,economy and PM_(2.5)(air particulate matter≤2.5μm).Agricultural land expanded the fastest(4-11%),followed by natural vegetation(15-16%)and water area(4-5%)with population and economic increase.Air quality(PM_(2.5)μg m^(−3))improved in upper(62-27)and middle(48-17)reaches.The water area in lower increase 5%because of ecological water delivery since 2000.Land use in the lower reach was dominated by agriculture,where the downstream runoff consumption increased by 6.8 times.The average annual air temperature and precipitation gradually increased by 0.5℃and 51 mm in source and 0.9℃and 30 mm in main reaches.The average annual water consumption in upper and middle reaches was 4×10^(9)m^(3),accounting for 87%of input runoff in the main reach.Water consumption in middle reach increased by 33 times in 2009-2017.The industry structure was changing from primary to secondary and tertiary industry.To sum up,implementation of water saving strategies and ecological water delivery restored local ecology.Sustainable strategies should be applied facing industrialization.Furthermore,changing the industry structure and restoring the degraded farmlands to grasslands or forests would keep sustainability of Tarim River Basin.

Phenological Stage, Plant Biomass, and Drought Stress Affect Microbial Biomass and Enzyme Activities in the Rhizosphere of Enteropogon macrostachyus

Indigenous grasses have been effectively used to rehabilitate degraded African drylands. Despite their success, studies examining their effects on soil bioindicators such as microbial biomass carbon(C) and enzyme activities are scarce. This study elucidates the effects of drought stress and phenological stages of a typical indigenous African grass, Enteropogon macrostachyus, on microbial biomass and enzyme activities(β-glucosidase, cellobiohydrolase, and chitinase) in the rhizosphere soil. Enteropogon macrostachyus was grown under controlled conditions. Drought stress(partial watering) was simulated during the last 10 d of plant growth, and data were compared with those from optimum moisture conditions. The rhizosphere soil was sampled after 40 d(seedling stage), 70 d(elongation stage), and 80 d(simulated drought stress). A high root:shoot ratio at seedling stage compared with elongation and reproduction stages demonstrated that E. macrostachyus invested more on root biomass in early development, to maximise the uptake of nutrients and water. Microbial biomass and enzyme activities increased with root biomass during plant growth. Ten-day drought at reproduction stage increased the microbial biomass and enzyme activities, accompanying a decrease in binding affinity and catalytic efficiency. In conclusion, drought stress controls soil organic matter decomposition and nutrient mobilization, as well as the competition between plant and microorganisms for nutrient uptake.

Root exudate chemistry affects soil carbon mobilization via microbial community reassembly

Plant roots are one of the major mediators that allocate carbon captured from the atmosphere to soils as rhizodeposits,including root exudates.Although rhizodeposition regulates both microbial activity and the biogeochemical cycling of nutrients,the effects of particular exudate species on soil carbon fluxes and key rhizosphere microorganisms remain unclear.By combining high-throughput sequencing,q-PCR,and NanoSIMS analyses,we characterized the bacterial community structure,quantified total bacteria depending on root exudate chemistry,and analyzed the consequences on the mobility of mineral-protected carbon.Using well-controlled incubation experiments,we showed that the three most abundant groups of root exudates(amino acids,carboxylic acids,and sugars)have contrasting effects on the release of dissolved organic carbon(DOC)and bioavailable Fe in an Ultisol through the disruption of organo-mineral associations and the alteration of bacterial communities,thus priming organic matter decomposition in the rhizosphere.High resolution(down to 50 nm)NanoSIMS images of mineral particles indicated that iron and silicon colocalized significantly more organic carbon following amino acid inputs than treatments without exudates or with carboxylic acids.The application of sugar strongly reduced microbial diversity without impacting soil carbon mobilization.Carboxylic acids increased the prevalence of Actinobacteria and facilitated carbon mobilization,whereas amino acid addition increased the abundances of Proteobacteria that prevented DOC release.In summary,root exudate functions are defined by their chemical composition that regulates bacterial community composition and,consequently,the biogeochemical cycling of carbon in the rhizosphere.

Benefits and limitations of biochar for climate-smart agriculture:a review and case study from China

Biochar has gained significant attention in agricultural and environmental research over the last two decades.This comprehensive review evaluates the effects of biochar on soil organic carbon(SOC),emission of non-CO_(2) greenhouse gases,and crop yield,including related mechanisms and major influencing factors.The impacts of biochar on SOC,methane and nitrous oxide emissions,and crop yield are controlled by biochar and soil properties and management practices.High-temperature biochar produced from lignin-rich feedstocks may decrease methane and nitrous oxide emissions in acidic soils and strengthen long-term carbon sequestration due to its stable aromatic structure.In contrast,low-temperature biochar from manure may increase crop yield in low-fertility soils.Applying biochar to farmlands in China can increase SOC content by 1.9 Pg C and reduce methane and nitrous oxide emissions by 25 and 20 Mt CO_(2)-eq year^(−1),respectively,while increasing crop yields by 19%.Despite the increasing evidence of the positive effects of biochar,future research needs to explore the potential factors that could weaken or hinder its capacity to address climate change and secure crop production.We conclude that biochar is not a universal solution for global cropland;however,targeted applications in fields,landscapes,or regional scales,especially in low fertility and sandy soils,could realize the benefits of biochar as a climate-smart measure.

Microplastics affect activity and spatial distribution of C,N, and P hydrolases in rice rhizosphere

Microplastics provide a new ecological niche for microorganisms,and the accumulation levels of microplastics(MPs)in terrestrial ecosystems are higher than those in marine ecosystems.Here,we applied the zymography to investigate how MPs–polyethylene[PE],and polyvinyl chloride[PVC])at two levels(0.01%and 1%soil weight)impacted the spatial distribution of soil hydrolases,nutrient availability,and rice growth in paddy soil.MPs increased the above-ground biomass by 13.0%–15.5%and decreased the below-ground biomass by 8.0%–15.1%.Addition of 0.01%and 1%MPs reduced soil NH4+content by 18.3%–63.2%and 52.2%–80.2%,respectively.The average activities of N-and P-hydrolases increased by 0.8%–4.8%and 1.9%–6.3%with addition of MPs,respectively.The nutrient uptake by rice plants and the enzyme activities in hotspots increased with MP content in soil.The accumulation of MPs in paddy soil could provide an ecological niche that facilitates microbial survival,alters the spatial distribution of soil hydrolases,and decreases nutrient availability.

Call for joint international actions to improve scientific understanding and address soil erosion and riverine sediment issues in mountainous regions

During the International Workshop on Soil Erosion and Riverine Sediment in Mountainous Regions held in November 2022,scientists from many countries shared their state-of-the-art knowledge and brainstormed to improve scientific understanding for coping with climate change and anthropogenic impacts.Information summarized in this discussion includes proposed key scientific questions and suggested joint actions to reduce soil erosion and riverine sediment problems in mountainous regions.

DMPP mitigates N_(2)O and NO productions by inhibiting ammonia-oxidizing bacteria in an intensified vegetable field under different temperature and moisture regimes

Vegetable soils with high nitrogen input are major sources of nitrous oxide(N_(2)O)and nitric oxide(NO),and incorporation of the nitrification inhibitor 3,4-dimethylpyrazole phosphate(DMPP)into soils has been documented to effectively reduce emissions.However,the efficiency of DMPP in terms of soil N_(2)O and NO mitigations varies greatly depending on soil temperature and moisture levels.Thus,further evaluations of DMPP efficiency in diverse environments are required to encourage widespread application.A laboratory incubation study(28 d)was established to investigate the interactive effects of DMPP,temperature(15,25,and 35?C),and soil moisture(55% and 80% of water-holding capacity(WHC))on net nitrification rate,N_(2)O and NO productions,and gene abundances of nitrifiers and denitrifiers in an intensive vegetable soil.Results showed that incubating soil with 1%DMPP led to partial inhibition of the net nitrification rate and N_(2)O and NO productions,and the reduction percentage of N_(2)O production was higher than that of NO production(69.3%vs.38.2%)regardless of temperature and soil moisture conditions.The increased temperatures promoted the net nitrification rate but decreased soil N_(2)O and NO productions.Soil moisture influenced NO production more than N_(2)O production,decreasing with the increased moisture level(80%).The inhibitory effect of DMPP on cumulative N_(2)O and NO productions decreased with increased temperatures at 55%WHC.Conversely,the inhibitory effect of DMPP on cumulative N_(2)O production increased with increased temperatures at 80%WHC.Based on the correlation analyses and automatic linear modeling,the mitigation of both N_(2)O and NO productions from the soil induced by DMPP was attributed to the decreases in ammonia-oxidizing bacteria(AOB)amoA gene abundance and NO_(2)^(-)-N concentration.Overall,our study indicated that DMPP reduced both N_(2)O and NO productions by regulating the associated AOB amoA gene abundance and NO_(2)^(-)-N concentration.These findings improve our insights regarding the implications of DMPP for N_(2)O and NO mitigations in vegetable soils under various climate scenarios.

根际激发效应的发生机制及其生态重要性

土壤激发效应是指由各种有机物质添加等处理所引起的土壤有机质周转强烈的短期改变。根际是激发效应最主要也是最重要的发生部位。根际激发效应能够反映生态系统土壤碳氮周转的速度,并影响植物、土壤微生物等对养分的获取和竞争,维持生态系统各组分间的养分平衡。虽然对根际激发效应的产生机制已取得一定程度的认知,但是对根际激发效应在土壤碳氮转化过程中的作用机理及其生态重要性依然缺乏足够的理解。该文在论述激发效应的研究历史和主要发生部位的基础上对最新研究进展进行了综合分析,提出了一个具体的根际激发效应的发生机制,深入剖析了影响根际激发效应的生物与非生物因素,并阐释了根际激发效应的生态重要性,对未来根际激发效应的研究方向进行了展望。