Differences In Root Penetration Ability Of Different Maize Varieties And Their Effects On Water And Nitrogen Uptake And Utilization

The root system is a vital organ that supports crop growth,absorbing and utilizing water and nitrogen.Root penetration ability plays a crucial role in a crop ’ s response to the mechanical impedance of the root growth environment,ensuring sustained growth.The mechanical impedance,soil water content,and nitrogen nutrient concentration exhibit heterogeneity and spatiotemporal variations,which influence the root system’s penetration ability,crop growth,and aboveground components.Roots enhance their penetration ability by modifying endogenous hormones,cell structure,morphology and configuration,responding to abiotic stress such as mechanical resistance,water availibility,and nitrogen levels during their growth.Consequently,differences in root and aboveground growth,as well as root penetration ability,exist among different varieties of the same crop.This study integrates soil column and field experiments to elucidate the "external influence-internal response" relationship between the root system,root penetration ability,aboveground growth,and factors like mechanical impedance,water and nitrogen availability.In greenhouse soil column experiments,we controlled mechanical impedance intensity(uniform mechanical impedance: low mechanical impedance-agar concentration 0.3%,high mechanical impedance-agar concentration 0.6%,sudden mechanical impedance: soil bulk density 1.0g/cm3 mechanical impedance intensity 6.79 g,wax layer concentration 80%mechanical impedance intensity 36.65g),water content(drought WS and watering WW),and nitrogen application(no nitrogen N0 and normal nitrogen NC)to study and analyze the variations in root penetration ability among different maize varieties.We compared the changes in root endogenous hormone concentration,cell anatomy at the root tip,root morphology and architecture,and aboveground components,as well as their effect on water and nitrogen absorption and utilization.In a rain-fed field experiment,we controlled soil mechanical impedance treatments(natural condition T1,deep tillage T2,plow bottom compaction T3,complete compacted T4),and nitrogen application(no nitrogen N0,low nitrogen N1,normal nitrogen N2).We examined the effects of tillage and nitrogen application on soil mechanical resistance,root system,penetration ability,aboveground nitrogen accumulation,yield,and water and nitrogen uptake and utilization at three growth stages: six-leaf stage(V6),tasseling stage(VT),and maturity stage(R6).It is clear that maize varieties with robust root penetration ability hold significant potential for breeding,soil enhancement,weight reduction,and yield improvement in future low-input and sustainable agricultural practices.This research provides theoretical basis and practical guidance for optimizing tillage methods,timing of watering,and precise fertilization in future maize cultivation.The main research findings are as follows:(1)Different maize varieties exhibit varying levels of root penetration ability,which in turn influence root plasticity and architecture,resulting in a wide range of root penetration capabilities.A screening experiment was conducted to assess the root penetration ability of154 distinct maize varieties.Low bulk density soil with high-strength wax flakes was used as the soil column screening methods,and the number of penetrating roots as well as the distribution of roots across different soil layers were used as screening criteria.From the pool of 154 maize varieties,three were identified as possessing strong root penetration abilities,while 73 exhibited weaker root penetration abilities.Among these,four conventional regional planting varieties were included: SD2001(3 penetrating roots,13-18 upper roots,6-10 lower roots),SD22(2 penetrating roots,13-18 upper roots,6-10 lower roots),LC825(1 penetrating roots,13-18 upper roots,6-10 lower roots),JD60(7 penetrating roots,upper roots 18-23,lower root 14-18).Therefore,JD60 with strong root penetration ability and LC825 with weak root penetration ability were finally determined.(2)The root system and its penetration ability exhibit distinct differences in uniform and altered mechanical impedance environments.In the context of uniform mechanical impedance and consistent nitrogen concentration,tvarying levels of mechanical impedance strength arriving from different AGAR concentrations have a noticeable impact on the root system.These effects manifest as changes in the root crown angle,insertion depth,and penetration angle.In this scenario,the root system assumes a spiral structure,imparting elasticity and adaptability to its penetration ability.Conversely.in an environment characterized by abrupt mechanical impedance,the root system encountered sudden changes in mechanical impedance at different soil depths.These change significantly affect the root system’s behavior in both upper and lower soil layers.The effects on root length,total root count(TTC),and nitrogen accumulation can be summarized as follows: water availability >nitrogen application,upper soil layers(water and nitrogen)> lower soil layers(water and nitrogen).Furthermore,the influences on aboveground biomass,plant height,nitrogen accumulation,water use efficiency,and nitrogen absorption efficiency can be ranked as follows: mechanical resistance depth > nitrogen application > water availability.(3)The internal factors contributing to differences and alterations in the root penetration ability of various maize varieties were elucidated.Under uniform mechanical impedance conditions,along with consistent water and nitrogen levels,the concentration of the endogenous hormone Abscisic Acid(ABA)remained unchanged.However,significant changes in ABA concentration were observed under mutated mechanical impedance.Conversely,Gibberellin(GA3)and Cytokinin(IP)concentrations showed no significant variations.The concentrations of Ethylene(ACC),Auxin(IAA),Jasmonate(JA),Salicylic Acid(SA)and trans-Zeatin-riboside(t ZR)were influenced by different water and nitrogen conditions in both uniform and mutated mechanical impedance environments,with distinct alterations occurring.Various concentrations of stress hormones synergically regulated changes in root cell structure,resulted in divergent modifications in root morphology and structure,thereby impacting root penetration ability.(4)To assess the external influences on changes in the root penetration ability of different maize varieties,various soil mechanical impedance treatments directly impacted the mechanical impedance strength,soil profile water content,and nitrate nitrogen content across different soil layers in the field.The alterations in soil mechanical impedance were observed as follows: T4 > T3 > T1 > T2,and 2020 > 2021.The findings revealed that the root penetration ability of maize reduced soil compaction,albeit to a lesser extent than that achieved through soil mechanical impedance treatments.As the increase of mechanical impedance strength increased with soil depth,soil water content rose while soil nitrate nitrogen content decreased,gradually declined.The effects of soil mechanical impedance on root length density,root surface area density,specific root length,and root diameter of various maize varieties were most pronounced in the 0-20 cm soil layer compared to the30-40 cm soil layer.Furthermore,as soil depth and mechanical impedance strength increased,root length density,root surface area density,root diameter,and root activity exhibited a gradual decrease,while specific root length increased.Mechanical impedance played a pivotal role in altering root morphology,architecture,and ultimately,root penetration ability.(5)The field study aimed to determine the external impact of varying root penetration abilities among different maize varieties.The relationship between nitrogen application and maize root morphology and architecture was found to be influenced by the strength of mechanical impedance.This effect was notably significant in 2021 when soil mechanical impedance strength of soil decreased.Conversely,there was no discernible effect when the soil mechanical impedance strength remained high in 2020.When the mechanical impedance strength decreased in 2021,the influence of nitrogen application on root length density and root surface area density followed this order: LC825 > JD60.These findings suggested that the impact of soil mechanical impedance treatments on root morphology and architecture across diverse maize cultivars exceeded that of nitrogen application.However,it’s worth noting that the effects of nitrogen application varied significantly among maize cultivars.In other words,the effect of soil mechanical impedance treatment on root penetration ability was more substantial than that of nitrogen application,and nitrogen application contributed to increasing the divergence in root penetration ability among different maize varieties.Furthermore,throughout the entire maize growth period,changes in root morphology and growth costs exhibited an initial increase followed by a subsequent decrease.This trend was observed when evaluating root length density and specific root length were as follows: V6 and R6 < VT.Similarly,root penetration ability displayed an initial increase followed by a decrease.(6)Differences in root penetration ability among various maize varieties lead to significant variations in aboveground biomass,plant height,nitrogen accumulation,and yield.In soil column test conditions,with moisture levels controlled,the aboveground biomass of different maize varieties gradually decreases as the increase of the depth of abrupt mechanical impedance increases.Plant height and aboveground nitrogen accumulation exhibit an increase under drought conditions,while under watering conditions,they initially rise and then decline.When controlling nitrogen application conditions are controlled,as the depth of mutated mechanical impedance increases,the aboveground plant height,nitrogen accumulation,and nitrogen absorption efficiency of different maize varieties gradually increase,while the aboveground biomass gradually decreases.Nitrogen application contributes to increased aboveground nitrogen accumulation and reduces the impact of mechanical impedance on grain nitrogen content.The grain yield of JD60 in 2021 was decreased by 6% under N0 conditions,increased by 31% under natural conditions,59%under deep tillage,and 73% under plow bottom compaction compared to 2020.Under N1 conditions,it increased by 57% under natural conditions,37% under deep tillage,41% under plow bottom compaction,and 75% under full compaction.In 2021,the grain yield of LC825 increased by 19% under N0 conditions and 57% under natural conditions,36% under deep tillage,and 80% under plow bottom compaction compared to 2020.Under N1 conditions,it increased by 55% under natural conditions,51% under deep tillage,50% under plow bottom compaction,and 91% under full compaction compared to 2020.Therefore,the increase in mechanical resistance due to soil mechanical impedance treatments leads to decreased grain yield decreased,and the root system enhances crop yield by improving soil compaction,resulting in a highly significant effect.Additionally,water and nitrogen fertilization have positive effects on corn grain yield.(7)The variations in root penetration ability among different maize varieties impact their water and nitrogen absorption and utilization in varying mechanical impedance conditions.In soil column experiments,aswith the increase of the depth of abrupt mechanical impedance,the water use efficiency of different maize varieties exhibited a decreasing trend when controlling moisture conditions.However,nitrogen fertilizer utilization efficiency differed for JD60 and LC825,with JD60 initially increasing and then decreasing,while LC825 displayed the opposite trend.In a field rain-fed experiment cinducted in 2020,during abundant rainfall and under N0 conditions,the water use efficiency of JD60 in T1,T2,T3,and T4 decreased by 57%,increased by 50%,decreased by 13%,and increased by 23%,respectively,compared to LC825.Under N1 conditions,JD60’s water use efficiency in T1,T2,T3,and T4 increased by 51%,16%,32%and 51%compared to LC825.JD60 also exhibited higherpartial productivity of nitrogen fertilizer in T1,T2,T3 and T4,with increases of 12%,16%,13%and 61%,respectively,compared to LC825.These results indicated superior water utilization by JD60.In 2021,with reduced rainfall and narrower gaps,JD60’s water use efficiency in T1,T2,T3,and T4 was decreased by 28%,decreased by27%,increased by 23%,and decreased by 27%,under N0 conditions compared to LC825.Under N1 conditions water use efficiency of JD60 in T1,T2,T3,and T4 decreased by 20%,increased by 24%,increased by 22%,and decreased by 27%,respectively,compared to LC825.The partial productivity of nitrogen fertilizer for JD60 in T1,T2,T3,and T4increased by 17%,decreased by 8%,decreased by 2%,and decreased by 12%,respectively.Under N2 conditions,water use efficiency of JD60 in T1,T2,T3,and T4 increased by 17%and increased by 11%,respectively,compared to LC825.The partial productivity of nitrogen fertilizer for JD60 in T1,T2,T3,and T4 increased by 5%,decreased by 26%,increased by 15%,and decreased by 5%,respectively.These results underscored significant differences in root penetration ability among various maize varieties.The study identified specific internal causes and external factors influencing these differences and changes in root penetration ability,highlighting the "external influence-internal response" relationship between root penetration ability and factors such as mechanical impedance,water,and nitrogen.Furthermore,the study demonstrated how varying root penetration abilities affect the differences in aboveground growth and its yield.