Effects of Tillage Depth on Nutrients and Microbial Communities in Tobacco-Planting Soil

The implementation of appropriate tillage practices is of great significance for agricultural production. However, the effects of different tillage depths on soil nutrients content and microbial communities in tobacco-planting soils are still lacking systematic research. In this study, three different tillage depths of 15 cm (T1), 20 cm (T2), and 30 cm (T3) were set up for field experiments in Liupanshui, Guizhou Province, to explore the effects of tillage depth on tobacco-planting soil nutrients and bacterial and fungal communities based on 16S rRNA and ITS sequencing and figure out the key factors affecting soil microbial communities. The results showed that T2 and T3 increased the contents of organic matter, total nitrogen, total phosphorus, available phosphorus, and available potassium in tobacco-planting soil, and increased the diversity of bacterial communities compared with T1. There was no significant difference in the structure of bacterial and fungal communities in different tillage depth treatments, but some dominant genera were significantly enriched in T2 and T3. Desulfobacter, Setophoma, Humicola, and Acremonium were significantly enriched in T2. Chthonomonas and Fusarium were significantly enriched in T3. These genera favor the decomposition of organic matter and the cycling of nutrients, and control soil pests and diseases. Redundancy analysis indicated that TP and AK were the key factors influencing the dominant genera of bacteria and fungi. This study provides a scientific basis for the selection of soil tillage depth for tobacco production in this region.

Effects of flue gas desulfurization gypsum and clover planting on qualities of soil and winter jujube in coastal saline-alkali orchard of north China

Flue gas desulfurization gypsum and clover planting alleviated the soil salinization stress.Soil pH and total phosphorus affected the bacterial communi-ties.Total phosphorus affected the fungal communities.Flue gas desulfurization gypsum and clover planting improved jujube quality.The coastal area of Shandong Province,characterized by coastal saline tidal soil,is one of the main production areas of winter jujube in China.However,the low soil fertility and poor soil structure in jujube orchard restricted the development of the jujube industry.The objectives of this study were to 1)evaluate the effect of application of flue gas desulfurization(FGD)gypsum and clover planting on soil quality improvement and soil microbial community structure of jujube orchard;2)investigate the effects of two measures on the nutrition and quality of winter jujube.The results showed that FGD gypsum reduced the soil total salt content by 65.6%,and clover planting increased the soil organic matter content by 30.7%,which effectively alleviated the soil salinization stress and improved the soil structure.Soil pH and total phosphorus(TP)were the main determinants influencing bacterial community composition,and TP was the dominant factor of the fungal community composition in the saline-alkali soils.Meanwhile,FGD gypsum addition and clover planting significantly increased the sugar degree and Vc content of winter jujube,thus improved jujube quality,and further contributed to the ecological sustainable development of winter jujube industry.

Drying-rewetting cycles reduce bacterial diversity and carbon loss in soil on the Loess Plateau of China

With global climate change, soil drying-rewetting(DRW) events have intensified and occurred frequently on the Loess Plateau of China. However, the extent to which the DRW cycles with different wetting intensities and cycle numbers alter microbial community and respiration is barely understood. Here,indoor DRW one and four cycles treatments were implemented on soil samples obtained from the Loess Plateau, involving increase of soil moisture from10% water-holding capacity(WHC) to 60% and 90% WHC(i.e., 10%–60% and 10%–90% WHC, respectively). Constant soil moistures of 10%, 60%,and 90% WHC were used as the controls. The results showed that bacterial diversity and richness decreased and those of fungi remained unchanged under DRW treatments compared to the controls. Under all moisture levels, Actinobacteriota and Ascomycota were the most dominant bacterial and fungal phyla,respectively. The bacterial network was more complex than that of fungi, indicating that bacteria had a greater potential for interaction and niche sharing under DRW treatments. The pulse of respiration rate declined as the DRW cycle increased under 10%–60% WHC, but remained similar for different cycles under 10%–90% WHC. Moreover, the DRW treatments reduced the overall carbon loss, and the direct carbon release under 10%–60% WHC was larger than that under 10%–90% WHC. The cumulative CO_(2) emissions after four DRW cycles were significantly positively correlated with microbial biomass carbon and negatively correlated with fungal richness(Chao 1).

Conversion of pure Chinese fir plantation to multi-layered mixed plantation enhances the soil aggregate stability by regulating microbial communities in subtropical China

Background:Soil aggregates are the basic units of soil structure,and their stability is a key indicator of soil quality and capacity to support ecosystem functions.The impacts of various environmental factors on soil aggregates have been widely studied.However,there remains elusive knowledge on the synergistic effects of changing forest stand structure on soil aggregate stability(SAS),particularly in subtropical China where soil erosion remains a critical issue.Methods:We investigated variations in the components of soil humus(HS),including humic acids(HAs),fulvic acids(FAs),and humins(HMs),under pure Chinese fir(Cunninghamia lanceolata)plantation(PP)and multilayered mixed plantation(MP)comprising C.lanceolata,Castanopsis hystrix,and Michelia hedyosperma.The state of soil aggregate stability,was determined by three separate methods,i.e.,dry-sieving,wet-sieving,and the Le Bissonnais.High-throughput sequencing was used to determine the diversity and composition of microbial communities under PP and MP.We then built partial least squares path models(PLS-PM)for assessing the responses of SAS to the variations in soil microorganisms and HS components.Results:The MP stands had significantly greater SAS(P<0.05),higher content of HAs and more rapid organic matter humification within aggregates,than the PP stands.High-throughput sequencing confirmed that the Pielou andα-diversity index values(Chao1 and Shannon)for fungi were all significantly higher under MP than under PP,while no marked difference was found in bacterialα-diversity between the two plantation types.Moreover,there were markedly greater abundance of three bacterial phyla(Verrucomicrobia,Chloroflexi,and Gemmatimonadetes)and three fungal phyla(Ascomycota,Kickxellomycota,and Glomeromycota),and significantly less abundance of two bacterial phyla(Planctomycetes and Firmicutes)and four fungal phyla(Basidiomycota,Mortierellomycota,Mucoromycota,and Rozellomycota)under MP than under PP.The Chloroflexi and Ascomycota phyla appeared to be the primary drivers of soil aggregate distribution.Our findings revealed that the promotion of SAS under MP was mainly driven by increased soil organic matter(SOM)content,which altered bacterial communities and enhanced fungal diversity,thereby increasing HAs content and the rate of organic matter humification.Conclusions:Considering the combined effects of enhanced soil quality,productivity,and relevant economic costs,introducing broadleaved tree species into Chinese fir plantations can be an effective strategy for stabilizing soil structure against erosion in subtropical China.Our study elucidated the controls on variations of SAS in Chinese fir-dominated plantations and demonstrated the benefit of converting pure Chinese fir plantation to multi-layered mixed plantations in increasing soil structural stability and improving site quality.

Asymmetric Variation in Soil Carbon Emission in Sub-Tropics

Carbon dioxide emission from soil, known as soil respiration, is one of the major sources of the atmospheric carbon. Understanding the relationship between emission rate and the factors associated with the emission process is important in global carbon emission management. The present study investigated soil respiration at three ecologically diverse locations in northern India. CO2 emission was measured in-situ by modified alkali absorption method at three different depths, top-soil (0 cm - 2 cm depth), mid-soil (20 cm depth) and deep-soil (40 cm depth) at each location. Rate of carbon emission from soil varied with location and time. The rate was higher at Riverine Zone (RZ) which had high soil moisture content and profuse ground vegetation compared to Hilly Zone (HZ) containing dry soil and scarce vegetation. The emission rate was also greater in grassland than the plantation area. Rate of carbon emission from soil was heterogeneous along different depths below the ground. Diel variation in emission rate was greater at HZ compared to RZ. Higher microbial population in soil was detected in RZ than HZ. However, the bacterial count out-numbered the fungal count in soils at most places. The study indicates a positive relationship between soil respiration rate and microbial abundance. The fungal population was strongly correlated with CO2 emission rate.

Short-Term Effects of Experimental Warming and Precipitation Manipulation on Soil Microbial Biomass C and N, Community Substrate Utilization Patterns and Community Composition

Soil microorganisms are major drivers of soil carbon(C) cycling;however,the response of these microorganisms to climate change remains unclear.In the present study,we investigated how 18 months of multifactor climate treatments(warmed air temperature by 3℃ and decreased or increased precipitation manipulation by 30%) affected soil microbial biomass C and nitrogen(N),community substrate utilization patterns,and community composition.Decreased and increased precipitation significantly reduced microbial biomass C by 13.5% and 24.9% and microbial biomass N by 22.9% and 17.6% in unwarmed plots,respectively(P<0.01).Warming enhanced community substrate utilization by 89.8%,20.4%,and 141.4% in the natural,decreased,and increased precipitation plots,respectively.Particularly,warming significantly enhanced the utilization of amine and carboxylic acid substrates among all precipitation manipulation plots.Compared with the natural air temperature with natural precipitation treatment,other treatments affected fungal community richness by -0.9% to 33.6% and reduced the relative abundance of the dominant bacterial and fungal groups by 0.5% to 6.8% and 4.3% to 10.7%,respectively.The warming and/or precipitation manipulation treatments significantly altered Zygomycota abundance(P<0.05).Our results indicate that climate change drivers and their interactions may cause changes in soil microbial biomass C and N,community substrate utilization patterns,and community composition,particularly for the fungal community,and shifts in the microorganism community may further shape the ecosystems function.

Decreased soil pH weakens the positive rhizosphere effect on denitrification capacity

The stimulating effect of rhizosphere on denitrification is considered to be an unavoidable loss of soil nitrogen(N)and detrimental to crop N use efficiency,which is regulated by crop growth and soil properties.Soil acidification,occurring rapidly in many intensive farming lands,affects both crop growth and soil properties,thereby altering rhizosphere effect on denitrification.However,the mechanism by which soil acidification regulates rhizosphere denitrification still remains unclear.Here,we determined the denitrification capacity(DC)and associated community compositions of nirK-and nirS-type denitrifiers in maize rhizosphere and bulk soils at four acidity gradients(pH=6.8,6.1,5.2,and 4.2).Results showed that the stimulating effect of rhizosphere on DC strongly depended on soil pH.Compared to bulk soil,rhizosphere soil had significantly higher DC at pH 5.2,but not at pH of 4.2.With increasing soil acidity,the stimulation of rhizosphere on DC(calculated as the difference in DC between rhizosphere and bulk soils)decreased from 8.01 to 0.01 mg N kg-1d-1.Moreover,soil acidification significantly reduced the differences in dissolved organic carbon(DOC)and abundance of key nirK-type denitrifier taxa between rhizosphere and bulk soils,both of which were positively related to the stimulation of rhizosphere on DC.These findings demonstrated that soil acidification could weaken the positive rhizosphere effect on denitrification via regulated C availability and associated nirK-type denitrifier community,potentially reducing N loss risk in rhizosphere soil.The independent role of soil p H should be fully considered when modelling N behaviour in plant-soil systems.

稻鳝生态种养不同施肥处理对土壤理化及微生物性状的影响

【目的】基于稻鳝生态种养长期定位试验,探讨稻鳝生态种养模式下不同施肥处理对稻田土壤(0~20 cm和20~40 cm)理化性状和微生物群落数量的影响。【方法】采用大田小区试验,共设置6个处理:无稻鳝种养+施肥处理(RT),稻鳝种养+无肥空白(CK),稻鳝种养+施肥处理(IRT),稻鳝种养+70%施肥(IT70%),稻鳝种养+70%施肥+秸秆还田(ITS70%),稻鳝种养+70%施肥+30%有机肥(ITO70%)。【结果】与RT相比,ITS70%处理使0~20 cm和20~40 cm土层的土壤容重显著降低,0~20 cm和20~40 cm土层的土壤R0.25、MWD、GWD显著提升,分别提高了32.15%、75.47%、103.20%和41.04%、100%、118%,使0~20 cm和20~40 cm土层的土壤有机质含量显著提升,分别提高了31.03%和39.23%,使0~20 cm和20~40 cm土层的土壤细菌拷贝数显著提升了27.28%和29.28%,使20~40 cm土层的土壤真菌拷贝数显著提升了21.43%;ITO70%处理使0~20 cm土层的土壤容重显著降低了29.63%;IRT处理则使0~20 cm和20~40 cm土层的土壤全钾含量显著提高了31.65%和23.63%,使0~20 cm和20~40 cm土层的土壤速效钾含量显著提升了31.88%和45.68%。【结论】综上所述,与常规稻田施肥相比,稻鳝生态种养不同施肥类型均使稻田土壤理化性状和微生物群落数量得到有效改善,其中70%施肥并配合秸秆还田改善效果最佳。