Effects Of Nitrogen And Phosphorus On The Growth Physiological Characteristics And Soil Chemical Properties Of Sapindus Mukorossi Seedlings

Sapindus mukorossi is a multi-functional economic tree species which integrates medicine,chemical industry and biomass energy.Its economic development value has been widely concerned and afforestation area has been increasing.It is also widely planted in Chongqing.However,due to the lack of intensive planting technology,the seedling raising measures of Sapindus mukorossi can not keep up,which greatly limits the development of local Sapindus mukorossi planting industry.Fertilization is an important measure to build high-yielding forests.Rational formula fertilization can promote the rapid growth and development of young forest,maintain soil fertility,reduce the negative effect of fertilizer,and promote the development of local industry.In this paper,potted seedlings of 2-year-old Sapindus mukorossi were used as materials,and the"3414"incomplete fertilization scheme was adopted.A total of 9 different nitrogen and phosphorus ratio fertilization treatments were set up.By studying the effects of fertilization with different N and P ratios on the growth index,photosynthetic parameters,plant nutrient content and soil chemical properties of the seedlings,the suitable N and P ratios for the growth of local seedlings were explored.It can provide scientific reference for rapid seedling cultivation and standardized cultivation management.The main results are as follows:?1?Among the 9 different N and P fertilization treatments,the plant height?163.44 cm?,ground diameter?2.14 cm?and total biomass?373.05 g?of the seedlings treated with T8?N₂P₁?were the highest,and the root-shoot ratio was 1.11,which increased 33.25%,57.64%,53.58%and 2.78%respectively compared with the four growth indicators of the seedlings treated with T1?N₀P₀?.?2?Among the parameters of light response curve,the maximum net photosynthetic rate(P_max)of seedlings treated with T8?N₂P₁?was the highest,reaching 17.02?mol·m^-2·s^-1,which was 172.32%higher than that of T1?N₀P₀?.The apparent quantum efficiency?AQY?of the leaf was also the largest in T8 treatment,and its value was 0.077 mol·mol^-1,which was 70.77%higher than that of T1 treatment.The maximum dark respiration rate?R_d?of leaves was T9?N₂P₃?,the R_d value was 1.96?mol·m^-2·s^-1,and the rest of treatments R_d ranged from 1.50 to1.67?mol·m^-2·s^-1 with little difference.The leaf light saturation point?LSP?and light compensation point?LCP?were the highest in T8 fertilization treatment,which were 1616.66?mol·m^-2·s^-1 and 140.02?mol·m^-2·s^-1,respectively.They had strong light utilization ability and low light conversion ability.?3?The maximum diurnal average net photosynthesis rate?P_n?of leaves in April,July and October was T8?N₂P₁?.The order of P_n was:P_n in July(6.70?mol·m^-2·s^-1)>P_n in April(4.98?mol·m^-2·s^-1)>P_n in October(3.86?mol·m^-2·s^-1).Compared with T1?N₀P₀?in the same period,the diurnal average P_n in April,July and October increased by 7.57%,65.02%and 1.58%,respectively.It was clear that the T8 treatment significantly increased diurnal average P_n of Sapindus mukorossi in summer.Compared with different N-gradient treatments and P-gradient treatments,the seedlings diurnal average P_n of Sapindus mukorossi increased first and then decreased with the increase of the amount of applied N or P.Comparing the diurnal average transpiration rate?T_r?of seedlings with different treatments in different periods,it was found that the maximum diurnal average T_r of leaves in April was T7?N₂P₀?,and the value was 2.82mmol·m?2·s?1,and the minimum diurnal average T_r appeared in T3?N₀P₂?fertilization treatment,and the value was 0.97 mmol·m?2·s?1.In July and October,the maximum diurnal T_r was T1?N₀P₀?without fertilization treatment,and the diurnal average T_r in each fertilization treatment was significantly less than that in T1 treatment.The diurnal average water use efficiency?WUE?of 3 months seedling leaves was different from that of the minimum and maximum.Among them,the leaves diurnal average WUE of T5?N₂P₂?fertilization treatment in April was the largest and the diurnal average WUE(3.85?mol·mmol^-1)of T8 was the smallest.the diurnal average WUE(10.61?mol·mmol^-1)of T3?N₀P₂?in July was the largest and the diurnal average WUE(4.35?mol·mmol^-1)of T9?N₃P₂?was the smallest.The diurnal average WUE(6.71?mol·mmol^-1)of T7 treatment in October was the largest and T2?N₁P₁?diurnal average WUE(4.02?mol·mmol^-1)was the smallest.There was no obvious regularity in the diurnal average WUE size in each period.The diurnal average G_S of seedling leaves of Sapindus mukorossi varied greatly in different seasons.The diurnal average G_S of leaves of Sapindus mukorossi in July was significantly higher than that in April and October.With the increase of nitrogen application,the diuranl average G_S of leaves increased first and then decreased.Under nitrogen and phosphorus combined treatment,the diurnal average G_S value of T3 treatment?N₀P₂?was the highest(0.079 mol·m^-2·s^-1),and the T7 treatment?N₂P₀?was the smallest(0.034 mol·m^-2·s^-1).The diurnal average G_S of T7 treatment?N₂P₀?was maximum(0.122 mol·m^-2·s^-1),T3 was smallest(0.041 mol·m^-2·s^-1).The diurnal average G_S of T0 treatment was maximum(0.087mol·m^-2·s^-1)in October,T6 is the smallest(0.048 mol·m^-2·s^-1).?4?Among the 9 fertilization treatments,the total N content of the seedlings ranged from28.28 to 45.59 g/kg.The total N content of T5?N₂P₂?fertilization treatment was the highest,while that of T1?N₀P₀?fertilization treatment was the lowest.The total nitrogen content of plants treated with T2-T9 increased 32.25%,22.87%,52.96%,61.23%,55.80%,5.32%,29.45%and 23.04%respectively compared with T1.The total P content of seedlings in all treatments ranged from 3.62 g/kg to 5.35 g/kg.The maximum value appeared in T4?N₁P₂?fertilization treatment,and the minimum value remained in T1 treatment.The total P content of plants treated with T2-T9 increased by 1.43%,25.72%,47.62%,21.85%,4.66%,8.92%,21.22%and 36.61%respectively compared with T1.The total K content of seedlings in each group ranged from 18.44 g/kg to 26.89 g/kg.The maximum value was in T6?N₃P₂?fertilization treatment,and the minimum value was in T1 treatment.The total K content of plants treated with T2-T9 increased by 23.93%,1.26%,6.23%,22.09%,44.03%,0.44%,16.13%and42.75%respectively compared with T1.?5?Comparing the total nutrient distribution of seedlings with different nitrogen application levels,it was found that the seedlings total N content of N2 application level was the highest,the seedlings total P content of N1 application level was the highest,and the seedlings total K content of N3 application level was the highest.At different P gradient levels,the total N content of plants at P1 level was the highest,the total P content of plants at P2 level was the highest,and the total K content of plants at P3 level was the highest.In this experiment,the content of total N and P increased first and then decreased with the increase of N or P application level,while the content of total K increased with the increase of N or P application level.?6?The soil pH value of each treatment ranged from 7.11 to 7.67 in July and from 7.37 to7.69 in October,with little change.Soil organic matter content ranged from 11.71 to 13.08 g/kg in July and from 10.32 to 12.82 g/kg in October.The minimum value appeared in T1?N₀P₀?fertilization treatment.In July and October,T6?N₃P₂?fertilization treatment had higher total nitrogen content than other fertilization treatments.The lowest total nitrogen content was T1?N₁P₁?treatment,and there was no significant difference in total nitrogen content between other N and P ratios Comparison of different treatments of soil available nutrients found in all treatments,soil alkali hydrolyzable nitrogen fertilization in July were higher than T1?N₀P₀?,different fertilization treatments and soil nitrogen content were increased,The nitrogen content of T5?N₂P₂?treatment is the highest,increased 86.62%in October.In July,T1,T7 and T8treatments decreased soil available phosphorus content,while other treatments increased soil available phosphorus content,among which T3 fertilizer treatment increased the most?256.89%?.The effective phosphorus content of each treatment in October was still at the maximum of T3,and was 25.32 mg/kg.?7?The whole plant biomass and reasonable biomass allocation was taked as the goal,the fertilizer effect equation was established,and the best ratio of nitrogen and phosphorus was obtained by simulation optimization.The ratio of nitrogen to phosphorus is N:P₂O₅=3.78:1.It is recommended to apply 10.05 g N and 2.66 g P₂O₅ per plant every year.It is more suitable for the growth of seedlings.