供氮水平和稳定性对苹果矮化砧M9T337幼苗生长及15N吸收、利用的影响

摘要

[Objectives] Studying the effects of the stability and levels of nitrogen supply on the growth and nitrogen absorption characteristics of apple seedlings will help further understanding the physiological mechanism of apple seedlings,which will provide theoretical basis for nitrogen fertilization in apple orchards.[Methods] Hydroponic culture method was used with M9T337 dwarf rootstocks seedlings as tested materials.NO3--N concentrations of deficiency,appropriate and excess (NO3--N 0.5,5 and 25 mmol/L in turn) were setup in the cultural solution.The seedlings were cultured in the three solutions for 10 days,then the treatments were transferred as the following five ones:NO3--N concentration varied from deficit to excess treatment (N1),from excess to deficit treatment (N2),keeping appropriate (N3),keeping deficiency (N4) and keeping excess (N5).The 10 days seedlings were continually cultured for another 10 days in above treatments.The plant dry matter,root morphology and root NO3 uptake flux,contents of NO3-and nitrate reductase enzyme activity in the roots and leaves,and the plant total N content and 15N absorption were measured.[Results] The highest plant dry matter was obtained in the N3 treatment and the least in the N4 treatment.The biggest increase of shoot dry matter was found in the N1 treatment at the 20th day after the treatment.The most significant effect on root length,root surface area and quantity of tips of seedlings was in the N3 treatment,followed by the N4 treatment,and least in the N5 treatment.The biggest increase appeared in the N2 treatment,with the root length and root surface increment of 31.5％ and 34.9％ respectively between the two sampling intervals.One day after the change in NO3--N concentration,the highest NO3 uptake flux was found in the N1 treatment,which was 46.37 pmol/(cm2·s),and no significant difference with that in N3 treatment.On the 10th day after NO3--N concentration change,the root NO3 uptake flux in the N3 treatment was significantly higher than in the others.A clear trend of NO3 outflow was found in the N5 treatment,and the root NO3-uptake flux in the N1 treatment was decreased by 62.0％,in the first day of NO3--N concentration change.The Ndff values in different organs,the total N content and 15N absorption were the biggest in the N3 treatment,the smallest in the N4 treatment,and the biggest increases appeared in the N1 treatment.At the 1 lth day after the treatment,the contents of NO3-in the roots and leaves reached the highest in the N5 treatment,and there was no significant difference between the N5 and N3 treatments.While the NO3-content in leaves under the N3 treatment was significantly decreased byl 3.4％ compared with the N5 treatment in 20th day.The leaf nitrate reductase activity in the N5 treatment was significantly lower than that in the N3 treatment at the 12th day after the treatment,and it displayed an order of N3 ＞ N1 ＞ N5 ＞ N2 ＞ N4 at the 20th day after the treatment.[Conclusions] Low NO3-supply will lead to insufficient absorption of NO3 in plants,excess supply will restrain the assimilation of NO3-N and root growth.Appropriate and steady supply of nitrogen could maintain high root NO3-uptake flux and Ndff value,thus enhancing the leaf nitrate reductase activity gradually,and then increasing the absorption and utilization of nitrogen by seedlings,which is the preferred form to the growth of apple seedlings.%[目的]研究氮素供应水平及稳定性对苹果幼苗生长及氮素吸收特性的影响,可以深化理解苹果对氮素供应的响应生理机制,为果树生产科学供氮提供理论依据.[方法]以M9T337矮化自根砧苹果幼苗为供试材料进行水培试验.设置营养液中NO3--N浓度不足、适宜、过量三个水平(NO3--浓度为依次为0.5、5、25mmol/L).苹果幼苗先在三个浓度的培养液中培养10d,在此基础上,增设培养液NO3--N浓度从不足变过量处理(N1)、从过量变不足处理(N2)、持续适宜供氮处理(N3)、持续不足处理(N4)及持续过量处理(N5),苹果幼苗继续生长10天,总培养时间为20天.测定了苹果幼苗生物量、根系形态和NO3-流量大小,根系和叶片硝酸还原酶活性和硝态氮含量,以及15N吸收利用.[结果]供试苹果幼苗处理20 d后,以稳定适量供氮处理N3的生物量最大,持续不足供氮处理N4最小,N1处理地上部干重增幅最高;N3处理根系总长、总表面积最大,根尖数最多,N4处理次之,N5处理最小.N2处理两次取样间隔内增幅最大,其根系总长及总表面积分别增加了31.5％和34.9％;NO3--N浓度变换ld后,N1处理根系NO3-吸收流量最大,为46.37 pmol/(cm2·s),和N3处理间无显著差异.NO3--N浓度变换10d后,N3处理根系NO3-吸收流量显著高于其他处理,N5处理变为外排,N1处理较NO3--N浓度变换ld时降低了62.0％;各器官Ndff值、植株总氮量及15N吸收量均以N3处理最高,N4处理最低,N1处理增幅最大;处理第l1d,N5处理根系和叶片硝态氮含量最大,和N3处理间无显著差异.处理第20 d,N3处理叶片硝态氮含量比N5处理低13.42％,差异达显著水平;N5处理叶片硝酸还原酶活性在处理12d后显著低于N3处理,处理20 d时,叶片硝酸还原酶活性大小为N3＞N1 ＞N5＞N2＞N4.[结论]供氮不足限制幼苗氮素吸收,供氮过量导致氮素同化及根系生长受抑,均不利于苹果幼苗生长.适宜且稳定的供氮可以保持较高的NO3吸收速率和Ndff值,逐渐提高叶片NR活性,促进体内硝态氮同化,达到对氮素的高效吸收利用,实现苹果幼苗最适生长.