Growth And Physiological Response Of Quercus Variabilis Seedlings To The Coupling Effects Of Water And Fertilizers

Quercus variabilis is one of the precious native tree species in China.Its material is excellent and has a great effect on China’s economic development and protection of ecological balance.However,in the large-scale cultivation of Q.variabilis,the lack and immaturity of technologies such as irrigation and fertilization will lead to low survival rate of nursery seedlings and slow growth of seedlings,which cannot meet the actual production and afforestation needs.Therefore,improving the water and fertilizer system of Q.variabilis in the process of raising seedlings has great significance for the development of valuable and high-quality timber forests of Q.variabilis.In this experiment,the sowing seedlings of Q.variabilis were used as materials,and the four-factor（soil water（W）,nitrogen application（N）,phosphorus application（P）and potassium application（K））five-level quadratic regression universal rotation combination design were uesd.Determination of growth indexes,biomass indexes,leaf photosynthesis and fluorescence parameters,nutrient accumulation and distribution indexes of Q.variabilis seedlings by various treatments.A relevant model was established to analyze the coupling effect of water and fertilizer on Q.variabilis.The influence of seedling growth on the optimal combination of water and fertilizer for the growth of Q.variabilis.At the same time,the physiological responses of seedlings under the coupling of water and fertilizer were analyzed to provide a theoretical basis for the cultivation and afforestation of Q.variabilis seedlings.The results are as follows:（1）The seedling height and ground diameter of Q.variabilis seedlings grew best from June to July.Analysis the variance of each growth index showed that the growth of seedling under different treatments was significant（p<0.05）,among which T8,T16 and T18 with sufficient water and fertilizer supply is better growth.Soil water and nitrogen fertilizer had significant positive effects on growth indicators and biomass.Phosphorus fertilizer had no significant effect on ground diameter.Potassium fertilizer had no significant effect on each indicator,and the main effect size was W>N>P>K.The coupling effect shows that,except for ground diameter,W×N had significant positive coupling effects on all other growth indicators.Except for leaf area,W×P had significant positive coupling effects on other indicators.W×K had significant positive coupling effects on biomass.N×P had significant positive coupling effects on leaf area,root dry weight,and biomass.N×K had significant negative coupling effects on ground diameter,and the coupling effect between water and fertilizer is greater than the coupling effect between fertilizers.The multi-objective decision analysis the indicators resulted in the best combination of water and fertilizer:79.81%of the field’s maximum water holding capacity（FC）,220.78 mg·plant^-1 of nitrogen,43.30 mg·plant^-1 of phosphorus,and 19.96 mg·plant^-1 of potassium fertilizer.（2）Soil water,nitrogen,and phosphorus are positively affecting soluble sugar,soluble starch,and soluble protein of Q.variabilis seedlings,and the effect is W>N>P,K had no significant effect on these indicators.Soil water and nitrogen fertilizer were the main limiting factors for photosynthesis of Q.variabilis and the interaction of water and nitrogen had a significant positive effect on photosynthesis.With the simultaneous increase of soil water and nitrogen fertilizer,the Pn,Gs and SPAD value of seedling leaves increased to different degrees.In addition,appropriate phosphate and potassium fertilizers can promote photosynthetic physiology of seedling leaves.Chlorophyll fluorescence parameters are similar to photosynthesis.Soil water,nitrogen fertilizer,and phosphorus fertilizer had significant effects on the fluorescence indicators including Fv/Fo,Fv/Fm,NPQ,q P andΦPSII of Q.variabilis seedlings,and the effect size is W>N>P.K is no significant effect on each index,and the interaction effects of each index are different.（3）From the perspective of plant nutrient accumulation and distribution,the concentration of N element was leaf>root>stem,the concentration of K element was leaf>root>stem and the concentration of P element was similar to that of leaf and root.The treatments with lower soil water and lower fertilization levels also resulted in lower nutrient concentrations in various organs of the seedlings.Regression analysis of leaf nutrient concentration found that W×N had significant positive coupling effects on leaf N concentration.W×P and N×K had negtive effects on leaf P concentration,and W×K had significant negative coupling effects on leaf K concentration.Studies on leaf carbon and nitrogen isotopes found thatδ¹³C of seedling leaves treated with low soil water and high nitrogen fertilizer was relatively high,whileδ¹⁵N of seedling leaves treated with high soil water and high nitrogen fertilizer was relatively high.Soil water had a significant negative effect onδ¹³C,nitrogen and phosphorus fertilizers have a significant positive effect,and potassium fertilizer has no significant effect.Soil water and nitrogen fertilizer had a significant positive effect onδ¹⁵N,while potassium fertilizer had a significant negative effect.W×N and W×P had significant negative coupling effects onδ¹³C.The interaction effect of fertilizer onδ¹⁵N is greater than the interaction effect of water and fertilizer.Soil water is the most important factor affectingδ¹³C andδ¹⁵N.（4）The results of correlation analysis showed that there was a very significant correlation between the growth of seedlings and biomass.Seedling growth,biomass,and non-structural carbohydrates,soluble proteins,photosynthetic parameters,chlorophyll fluorescence parameters,and leaf N concentration were significantly correlated.Among them,chlorophyll content is the most important factor affecting seedling growth.Leafδ¹³C had no significant correlation with leaf nutrient concentration,significantly correlated with Pn and Gs,and significantly correlated with seedling height.δ¹⁵N was significantly positively correlated with leaf N concentration,and significantly correlated with growth,biomass,and photosynthetic indicators.It shows that the seedlings have higher utilization efficiency of N element,which promotes the growth of seedlings.In general,in the early growth stage of Quercus variabilis,it can grow well only under good soil water and fertilizer environment.When soil water and nitrogen fertilizers are scarce,applying excessive amounts of phosphorus and potassium fertilizers will obviously inhibit seedlings.In actual production,seedlings should also be given sufficient irrigation and nitrogen fertilizers.