Effects Of Ridge-furrow Plastic Film Mulch On Root Growth And Root-associated Microbiota Of Dryland Maize

Ridge-furrow plastic film mulch(RFPM)is with great significance to crop production in rainfed agricultural areas.Microorganism is an important component in agroecosystem,and root-associated microbes,known as the plant’s second genome,are closely related to crop roots.However,it is still unknown how RFPM affects the microbes in the compartments along soil-root continuum,and the impact of its functions on maize growth and root region carbon sequestration needs to be examined.This study investigated the effects of RFPM on maize root traits,root-associated microbes and their interrelationships:firstly,the meta-analysis was used to summarize the overall effect of plastic film mulch on crop root phenotypes and soil microorganisms.Notably,the effect of RFPM therein is prominent.Subsequently,based on a long-term in-situ experiment,with the soil-crop-microbe relationships as the central theme,it was made clear how maize root traits were specific under RFPM and how root-associated microbes were regulated.Meanwhile,the microbiological mechanism of how RFPM affect maize yield formation was explored,and the mechanism of microbial metabolic affect root region carbon sequestration affected by RFPM was studied.The main findings are as follows:(1)The meta-analysis showed that,overall,plastic film mulch significantly promoted the crop root growth and soil microbial activities in general,root dry weight density,root diameter,root length density increased significantly(P<0.05),with the average effect sizes of 0.313,0.218,and 0.387 respectively;the microbial richness,abundance and eco-functionality increased significantly(P<0.05),with the average effect sizes of 0.037,0.104,and 0.129respectively.The effect of RFPM is particularly prominent,and the effect sizes of these indicators are further increased.For maize,plastic film mulch had the best root growth promotion effect in its bell-mouth stage.The effect sizes of soil microbial biomass carbon,carbon acquisition enzyme activity,nitrogen acquisition enzyme activity,and oxidase activity were significantly positively correlated with that of crop yield(P<0.05).These results provide an important basis for study the effects of RFPM on maize root traits,microbes,and their interactions at the field in situ scale.(2)Field study showed that RFPM changed the maize root architecture,with a larger root top angle(66.4±6.11°).The maize root system is deeply rooted downwards to absorb water under control,while the soil moisture is sufficient under RFPM,and the root system grows horizontally to obtain nutrients.Moreover,RFPM also promoted maize root growth and biomass accumulation,increasing yield by 70.93%and root length density by 13.16%compared to control.The effect of RFPM on the maize root phenotype indicated that the relationship between soil-crop-microbe in the root region has also changed,provided bases for the following research on the effect of RFPM on maize growth and root region carbon sequestration from a microbial perspective.(3)The root-associated microbial co-occurrence networks were dominated by bacteria.Compared to the control,the average path length of RFPM was significantly lower(P<0.05,3.742),and the average clustering coefficient was significantly higher(P<0.05,0.498),indicating a more stable network was formed under RFPM.The interactions between maize root phenotypic variables and root-associated microorganisms were also boosted by RFPM,and the proportion of positive correlations to all correlations rose from 46.25%in the control to 54.63%.The maize rhizoplane microbial assembly process changed from being dominated by stochastic processes to deterministic processes affected by RFPM.This resulted in a significant(P<0.05)enrichment of plant growth-promoting microbiota via the soil-root continuum.The partial least squares path model showed the indirect impact on microbes by RFPM is mediated by soil hydrothermal status and root phenotypes,which thereby played an important role in maize growth(PLS-PM,R~2=98.2%).The results of this chapter show that RFPM regulates maize root phenotypes by affecting the soil hydrothermal status,thereby causing a response of the soil-root continuum microbes to promote crop growth.The rhizoplane therein is the compartment that most strongly affected by RFPM.The microbial co-occurrence network shows that bacteria play a more important ecological role than fungi.(4)For the assembly of abundant bacteria,RFPM enhanced the proportion of deterministic processes,while it increased the proportion of stochastic processes for rare bacteria.Abundant bacteria members played a role in stabilizing root-related bacterial co-occurrence network at the individual level,occupying a core position in the network and indirectly supporting maize growth and yield formation;their centrality in the network was significantly(P<0.05)higher than that of the control.The impact of rare bacteria on maize yield was reflected in the overall community level,and its correlation with maize biomass and yield was significant(r=0.76,P<0.05);the correlation between those of abundant bacteria was not significant(P>0.05),and the correlation coefficient is only-0.19.The results of this chapter show that there are important connections of abundant and rare bacteria with maize root phenotypes and growth,and these relationships can be further deepened through RFPM.(5)RFPM enhanced maize root growth,modified root exudation,and altered the assembly,structure,and function of rhizoplane microbes.Root exudation metabolism was significantly(P<0.05)linked with microbial assembly,structure,and function;it also increased the proportion of deterministic assembly of rhizoplane microbes to 46.32%under RFPM,with 40.93%-41.34%under the control.RFPM significantly(P<0.05)enhanced the abundance of phenolic acids secreted by maize roots,leading to a significant(P<0.05)increase in the abundance of microbial type II secretion system and lipopolysaccharide biosynthesis genes.The maize rhizoplane soil amino sugars contents were 14.33%-31.63%lower than that of the control under RFPM,which also intensified the use of microbial-derived substrates by live microorganisms.The structural equation model showed RFPM affect the relationships among root region environment,root phenotype,root exudation,rhizoplane microbes,and ultimately promote maize growth by regulating rhizoplane microbial functions(SEM,R~2=84.1%).The results of this chapter show that the effect of RFPM on root exudation is the most important factor to regulate the rhizoplane microbes,and then affect maize growth;the increase in the abundance of phenolic acids secreted by maize roots results in the promotion of microbial functions related to the turnover and utilization of amino sugar microbial residues.(6)The in vivo anabolic pathway changes were inversely linked with changes in soil organic carbon(SEM,normalized total impact=0.398),while decoupled from ex vivo catabolic pathway.Maize rhizoplane soil organic carbon content was significantly(P<0.05)decreased by 10.18%–15.32%under RFPM compared to the control,but bulk soil organic carbon in the maize field was unaffected(P>0.05).On the rhizoplane,RFPM downregulated the in vivo anabolic pathway and upregulated the ex vivo catabolic pathway.The relative abundance of the Sphingomonadaceae-dominated core module M1 was significantly positively(r=0.83,P<0.05)linked with the in vivo pathway in both bulk soil and rhizoplane;the relative abundance under control was higher than that of RFPM.On the rhizoplane,the relative abundance of module M2 dominated by Chitinophagaceae was significantly negatively(r=-0.72,P<0.05)correlated with the ex vivo pathway,and its relative abundance under control was lower than that of RFPM.The results of this chapter show that RFPM decreased the in vivo pathway of maize rhizoplane microbes,resulting in the reduction of microbial necromass carbon accumulation,and then the maize rhizoplane carbon sequestration declined.In summary,combined analyses about soil science,crop science,and bioinformatics,this study shows that compared with traditional cultivation mode,RFPM improves the soil hydrothermal environment and promotes maize root growth,leading to changes in the assembly,structure,and function of maize root-associated microbial communities,thereby promoting maize growth and yield.It reveals the mechanism by which maize root microbial communities respond to RFPM and feedback to maize growth dynamics.On the other hand,RFPM increases the abundance of maize phenolic acid secretion,accelerates the turnover and utilization of microbial necromass by microorganisms,and reduces maize root region carbon sequestration.This elucidates the mechanism by which maize root microbial communities respond to RFPM and feedback to the root region fertility pattern.These results deepened our understanding of soil-crop-microbe relationships in agroecosystems from a microecological perspective.In addition to providing a framework for future evaluation of the impact of RFPM in crop production and farmland eco-environment protection in drylands,it established the basis for precision soil,crop,and microbe control to achieve sustainable agricultural development.