Effect Of Application Of Different Fertilizers On Plant Growth And Root Morphological Characteristics Of Strawberry And Its Physiological Mechanism

Application of commercial organic fertilizers is very important for theproduction of green foods and organic foods. Strawberry and different fertilizercombinations were used in this experiment. Treatments included organic fertilizer A（OFA）, organic fertilizer B （OFB）, organic-inorganic compound fertilizer （OIF）,chemical fertilizers only （UN） and no amending （CK）. The aim of this research was tocompare the influences of different fertilizer applications on 1) Dynamics of soilNO₃^--N, NH₄⁺-N and microbial biomass N; 2) Strawberry root and shoot biomassaccumulation; 3) Root growth and development; 4) Nitrogen （N） uptake anddistribution in strawberry; 5) Changes of plant endogenous hormones and the relatedroot morphology; 6) Yield and quality of strawberry fruit.The results obtained are listed as follows.1. Fertilizer applications inhibited root growth of strawberry during very seedlingstage. Furthermore, UN and OIF application inhibited shoot growth until early fruitstage whereas application of organic N fertilizers （OFA and OFB） had a continuousincrease effect on shoot biomass after they decreased root growth for a very short timeduring the seedling stage. Root dry biomasses in OFA and OFB treatments were85.9% and 35.2% higher than that in CK, while they were decreased by 12.1% and1.2% in OIF and UN treatments 60 days after strawberry seedlings were transplanted,respectively.2. Highest accumulation of root and shoot biomass were found during 134～175days after transplanting. Fertilizer application affected root biomass, shoot biomassand their accumulation rate in a different way and thus, the ratio of root and shootbiomass to total biomass and root/shoot were changed. Root/shoot ratio increased atseeding stage, and then decreased after early flowering stage. The "high-low-high"variation tendency of root/shoot ratios during the whole growth period wasbenefitablc to strawberry biomass accumulation in middle-late growth stages, and toroot physiological activities during lateral fruit mature period. This variation tendencycould be obtained by application of organic fertilizers（OFA and OFB）.3. Fertilizer application improved N uptake by plants, thus increasing N accumulation in plants and N distribution in fruits. Average accumulation of N perday was 10.8 mg/plant in N fertilizationtreatment, and 5.1mg/plant in CK. N distribution in different organs of alltreatments at the end of fruiting season was in the order of fruit＞stem and petiole＞root. The N accumulated in fruit with organic fertilizers treatments （OFA and OFB）accounted for half of the total N taken up by strawberry plants, namely 53.5% and51.7%, while those with inorganic fertilizer （UN） or Organic-inorganic fertilizertreatments （OIF） were only 46.1% and 39.8% of the total N absorbed, respectively.4. In terms of equal N application, the yields of strawberry was increased byOFA and OFB, but decreased by UN and OIF. This was mainly caused by too muchinorganic N present in the soils not suitable for strawberry growth. Fertilizerapplication could improve strawberry quality. Sugar/acid ratio of the strawberry, forexample, was increased by 23.7-28.7% in organic fertilizer application treatmentwhile it was increased only 14.2% in inorganic fertilizer treatment.5. There was significantly positively linear dependence between SPAD values ofstrawberry leaves on specific node in different stages and the total N in plant with thesame stage. The correlation coefficient values varied from 0.8107 to 0.8531.Therefore, non-destructive testing of N nutrient situation would be facilitated by thelinear dependence.6. Root growth was inhibited after fertilizer application in the initial stage ofstrawberry transplanting and it was more strongly affected by inorganic N fertilizerapplication. N fertilizer application also decreased the specific root length （SRL） ofseedling stage but the effects disappeared soon with strawberry growth. There was anegative relationship between root diameter and SRL, which resulted in a big value offine roots in UN and OIF treatments.7. In the initial stage after transplanting, lateral root number and lateral rootdensity of strawberry plants were evidently affected by fertilization. Sixty days aftertransplanting, the lateral root number of strawberry in OFA and OFB treatment wereincreased by 8.9% and 20.5% compared with CK, respectively, whist those of UN andOIF treatments were still less than CK. Lateral root density of strawberry in OFA andOFB treatment were 17.9% to 57.3% higher than those of UN and OIF treatments. Inaddition, root surface area and volume of strawberry 60 days after transplanting weresignificantly increased by the application of OFA and OFB. These results showed thatthe development of lateral root was effectively induced by organic N fertilizer and thus, root surface area for nutrients uptake of strawberry were elevated.8. Fertilizer application significantly increased soil NO₃^--N and NH₄⁺-N and themicrobial biomass N mainly depended on the C/N of organic matters applied in soil.The soil available N of OFA, OFB and OIF treated soil were decreased by 49.2%,79.9% and 28.7%, respectively but the average microbial biomass N were increasedby 91.2%, 83.0% and 68.2%, respectively, compared with CK in the whole growthperiod of strawberry plants. The study indicated that the content of mineral N inorganic fertilizer （OFA and OFB） and organic-inorganic fertilizer （OIF） treatmentswas less than that of urea N （UN） but application of organic fertilizers could facilitateimmobilization of soil N by soil microbes and increase soil N supply bufferingcapacity, which was very useful to the gowth of strawberry plant.9. Contents of endogenous IAA and ABA in leaves and roots in fertilization sitesduring the initial stages （20 days after transplanting） were significantly higher thanthose in CK. However, at 60 days after transplanting, the contents of IAA and ABA inleaves and roots in OFA and OFB treatments were lower than those in UN and OIFtreatments. Fertilization significantly increased the content of iPAs in leaves and rootsof strawberry seedlings and UN and OIF application had higher iPAs content than OFtreatments. In addition, the ratio of endogenous IAA/iPAs was significantly decreasedby fertilizer applications and UN and OIF had a more effect than OF.10. There were significant correlations between the contents of soil available Nand root morphological characteristics （root biomass, root diameter, root tips, lateralroot number, total root length, length of adventitious root, specific root length （SRL）and lateral root density）. Among them, positive correlation was only found betweensoil available N and root diameter. The correlation between the average content of soilavailable N and root diameter, lateral root number and lateral root density withdifferent treatments could be quantified finely by quadratic regression equation.11. Better linear correlation was found between root morphologicalcharacteristics and the contents of endogenous IAA and iPAs in strawberry. Therewere significant correlations between the contents of endogenous IAA and otherindexes of roots except degree of branching with the correlation coefficient rangedfrom 0.6941 to 0.9253. The content of endogenous iPAs was not as good as thecontent of endogenous IAA correlating to root morphological characteristics, and thesignificantly negative correlations were only found between the content ofendogenous iPAs and root biomass, root diameter, total root length, length of adventitious root and specific root length （P＜0.01）. No correlation was found amongthe content of endogenous ABA and root morphological characteristics.12. The changes of soil N nutrient and the differences in endogenous hormone inplants all greatly affected root formation during strawberry seedling stage. Theremight be two mechanisms for N to modulate strawberry root formation: the inducedmechanism by endogenous hormones and the induced mechanism by N supply （generegulation by nitrate-N supply）. According to the correlations between rootmorphological characteristics and the contents of endogenous hormone in strawberryand soil nitrate-N, it could be deduced that endogenous hormone is the dominatingfactor to induce the root formation.In conclusion, strawberry plants grow slowly at seedling stage, so a soil with lowmineral N content could supply enough N for their growth. Too much mineral Nsupply could restrict root growth. However, application of pure organic fertilizerscould help the increase of root biomass, root tips, lateral root number, total root length,length of adventitious root, specific root length and lateral root density at lateralseedling stages. The changes of endogenous hormones and nitrate-N played importantroles in the modulation of root formation for strawberry plants. The application of Nfertilizers significantly affected the status of soil available N and plant growth; theroot to shoot ratio was optimized in the course of plant growth with the application ofOFA and OFB by increasing the ratio of nitrate-N to arnmonium-N in soil, which wasfavorable to improvement of yield and quality of strawberry fruit.