Positive effect of carbohydrate-metabolizing bacteria determines increasing soil organic carbon during long-term fertilization and straw returning in the black soil region of China

In the context of global efforts to reduce carbon(C)emissions,several studies have examined the effects of agricultural practices such as straw returning and fertilization on C sequestration by microorganisms.However,our understanding of the specific microbial groups and their roles in long-term C increase remains limited.In this study,a 36-year(1984-2020)farmland experiment was conducted to investigate the impact of bacterial C metabolism on the augmentation of organic C in a Typic Hapludoll(Mollisol)in the black soil region of Jilin Province,Northeast China.Our results demonstrated a noteworthy increase in the diversity of microorganisms in the farmland as a result of long-term straw returning and application of mixed chemical fertilizers.However,by examining the functions of microorganisms involved in C metabolism,it was observed that the effects of fertilization on C metabolism were relatively consistent.This consistency was attributed to a deterministic competitive exclusion process,which minimized the differences between treatment groups.On the other hand,the influence of straw addition on C metabolism appeared to follow a more random pattern.These changes in microbial activity were closely linked to the downregulation of core metabolic pathways related to C metabolism.Notably,long-term fertilization had a negative impact on soil organic C levels,while long-term straw returning plus fertilization resulted in a positive increase in soil organic C.These findings have important implications for enhancing soil organic C and grain yield in the regions with typical black soil.

Integrative multi-omics approaches reveal that Asian cultivated rice domestication influences its symbiotic relationship with arbuscular mycorrhizal fungi

Potential changes in the symbiotic relationship between rice(Oryza sativa)and microorganisms have occurred during the domestication of Asian cultivated rice(O.sativa)from common wild rice(Oryza rufipogon)and in response to global climate change,along with evolving adaptations to the environment.The potential genes may express differently or dominate the symbiotic relationships between arbuscular mycorrhizal fungi(AMF)and plants,which may be beneficial to rice breeding.To date,research on this important topic has been limited.In this study,we aimed to examine the symbiotic relationships of Asian common wild and cultivated rice species with AMF.By conducting a comparative metagenomic analysis of the rhizospheres of wild and cultivated rice species,we identified differences in Rhizophagus intraradices-related genes associated with wild and cultivated rice,as well as functional genes of AMF.Furthermore,we obtained root-related genes associated with AMF from transcriptome data of rice roots.Our results collectively suggest that R.intraradices-related genes in the rhizosphere of wild rice may be more conducive to its colonization.Additionally,bacteria from the Nitrosomonadaceae and Nitrospiraceae families identified in the rhizosphere of wild rice exhibited positive correlations with R.intraradices-related genes with protein identifiers 1480749 and1871253,which may indicate that nitrobacteria can enhance the functions of R.intraradices in association with wild rice.Next,in a case study using comparative transcriptome analysis of root samples obtained from R.intraradices-inoculated wild and cultivated rice plants,we found significantly higher expression levels of the strigolactone pathway-related genes DWARF3(D3)and DWARF14(D14)in R.intraradices-inoculated common wild rice than in R.intraradices-inoculated cultivated rice.This study provides a theoretical basis for identifying the effects of domestication on mycorrhizal symbiosis-related genes,which could be promoted in wild rice in the future.

Long-term fertilization and residue return affect soil stoichiometry characteristics and labile soil organic matter fractions

Ecological stoichiometry provides the possibility for linking microbial dynamics with soil carbon(C),nitrogen(N),and phosphorus(P)metabolisms in response to agricultural nutrient management.To determine the roles of fertilization and residue return with respect to ecological stoichiometry,we collected soil samples from a 30-year field experiment on residue return(maize straw)at rates of 0,2.5,and 5.0 Mg ha^-1 in combination with 8 fertilization treatments:no fertilizer(F0),N fertilizer,P fertilizer,potassium(K)fertilizer,N and P(NP)fertilizers,N and K(NK)fertilizers,P and K(PK)fertilizers,and N,P,and K(NPK)fertilizers.We measured soil organic C(SOC),total N and P,microbial biomass C,N,and P,water-soluble organic C and N,KMnO4-oxidizabIe C(KMnO4-C),and carbon management index(CMI).Compared with the control(F0 treatment without residue return),fertilization and residue return significantly increased the KMn〇4-C content and CMI.Furthermore,compared with the control,residue return significantly increased the SOC content.Moreover,the NPK treatment with residue return at 5.0 Mg ha^-1 significantly enhanced the C:N,C:P,and N:P ratios in the soil,whereas it significantly decreased the C:N and C:P ratios in soil microbial biomass.Therefore,NPK fertilizer application combined with residue return at 5.0 Mg ha^-1 could enhance the SOC content through the stoichiometric plasticity of microorganisms.Residue return and fertilization increased the soil C pools by directly modifying the microbial stoichiometry of the biomass that was C limited.

Simulation and experiment on prediction of total rice seeds mass in vibrating tray for vacuum plate seeder

To improve the seeds pick-up precision of a vacuum plate seeder,it is important to accurately control the relative distance between suction plate and seeds layer in vibrating tray.Under the excitation of reciprocating vibration with a time varying interference in direction angle,the seeds motion is simulated using the discrete element method(DEM).By analyzing the seeds distribution characteristics,it was found that the seeds-mass-per-unit-area(SMA)was approximately plane distributed in the tray.Then,four square areas on the bottom of rectangular tray were divided symmetrically near the four vertices to measure the corresponding SMA respectively,and a monitoring plane model was established to predict the average SMA and total seeds mass in the tray.The prediction results of DEM simulation showed that the maximum and the mean relative errors were 6.75%and 2.85%.The influences of the normal vector of monitoring plane model and the standard deviation of SMA in four monitoring areas on the prediction errors were analyzed.A method for improving prediction accuracy by using linear regression correction was proposed,and the maximum and the mean relative errors could be reduced to 5.01%and 2.07%.When the tray was vibrated with the frequency of 11 Hz and the amplitude of 4 mm,experiments were carried out on the vacuum plate seeder test-rig.A Kalman filter was adopted to suppress the SMA measurement noise in four monitoring areas.Prediction results indicated that the maximum and the mean relative errors were 10.2%and 3.46%with the average SMA in range of 0.9-1.5 g/cm2,respectively.The paper can provide a basis for further study on the automatic control of suction plate motion according to the variation of seeds mass in the tray.