【作者】 王波；

【导师】 沈其荣；

【作者基本信息】 南京农业大学 ， 植物营养学， 2007， 博士

【摘要】 过去的研究表明，将营养液中部分硝态氮用铵态氮来取代不仅能显著提高旱地作物的生物量，而且也能显著降低旱地作物体内的硝酸盐含量，这对提高因硝酸盐含量过高而对市民健康构成严重威胁的叶菜类蔬菜的品质来说具有很重要的作用。因此，在生产上可以通过在蔬菜地上施用铵态氮肥和硝化抑制剂来实现降低蔬菜中硝酸盐含量的目标，进而实现农民增收，农业增效。同时还可以降低因为大量施用硝态氮肥而引发的硝态氮流失所带来的环境风险。然而，有关不同生菜品种对不同铵硝比反应差异及其机理的影响仍然知之不多。本论文以生菜为研究对象，采用水培条件，从植物营养和植物生理的角度来探讨不同生菜品种对不同铵硝比反应差异及其机理的影响规律，并筛选出对不同铵硝配比敏感及钝感的生菜品种，然后利用所筛选出的典型品种生菜研究不同形态氮素营养对生菜的光合特性、根系生长发育特性、NO₃^-的吸收动力学特性、内源激素及液泡中NO₃^-调动特性的影响。研究结果表明：1不同铵硝配比对不同品种生菜的生物量（地上部、地下部）有显著的影响，供试5个品种（奶油生菜、中选1号、软尾生菜、耐抽苔生菜和耐热耐抽苔）的生物量（地上部、地下部）均随着营养液中NH₄⁺-N比例的增加而增加，并在营养液中铵硝配比为25：75时达最高。然后，随着NH₄⁺-N比例的进一步增加，5个生菜的生物量（地上部、地下部）反而迅速下降，当营养液中铵硝配比为50：50时，其生物量反而低于全硝处理。说明通过改变营养液中铵硝配比可以改变生菜的生长发育，但营养液中过高或过低的NH₄⁺-N比例均要影响生菜的生物量，只有适宜的铵硝配比对生菜生长发育才具有较好地促进作用。本研究认为适合生莱生长的最佳铵硝配比为25：75。不同铵硝配比对生菜根系的根冠比有影响，随着营养液中NH₄⁺-N比例的增加，生菜的根冠比先上升，然后下降。2不同铵硝配比对生菜地上部硝酸盐含量有显著影响，5个品种生菜地上部的硝酸盐含量均是随着营养液中NH₄⁺-N比例的上升而下降。3不同品种生菜对不同铵硝配比的反应不一样。从不同铵硝配比与生菜生物量（地上部、地下部）及生菜地上部硝酸盐含量的响应情况来看，在供试的5个生菜品种中，申选1号（SX 1）和耐热耐抽苔（Nrnct）属于典型生菜品种，其中申选1号对不同铵硝配比最为敏感，是敏感型生菜品种，而耐热耐抽苔对不同铵硝配比敏感程度最低，是钝感型生菜品种。4不同铵硝配比对2个典型品种生菜的光合特性有显著的影响。随着营养液中NH₄⁺-N比例的增加，生菜叶片叶绿素含量、净光合速率及气孔导度均随着增加，并在营养液中NH₄⁺-N比例为25％时达最高。然后，随着NH₄⁺-N比例的进一步增加到50％，上述特性反而迅速下降。叶片的胞间二氧化碳浓度随着营养液中NH₄⁺-N比例的增加而下降，并在营养液中NH₄⁺-N比例为25％时达最低。然后，随着NH₄⁺-N比例的进一步增加到50％，叶片的胞间二氧化碳浓度反而有所增加。通过对影响生菜光合作用的影响因子进行分析发现叶肉导度是影响不同形态氮素营养对生莱光合作用的主要限制因子。5从不同铵硝配比对不同品种生菜光合特性影响的角度来看，与热耐抽苔生菜相比，申选1号对环境中不同铵硝配比的变化更为敏感，热耐抽苔对环境中不同形态氮素营养及不同铵硝配比的变化钝感。6不同铵硝配比对生菜的根系特征参数有显著的影响。随着营养液中NH₄⁺-N比例从0％增加到10％及25％，生菜根系表面积、体积、总根长及侧根数量均随之增加，并在营养液中NH₄⁺-N比例为25％时达最高，且在0％处理与25％处理的差异均达到显著或极显著水平。随着营养液中NH₄⁺-N比例的进一步增加到50％，根系表面积、体积、总根长及侧根数量参数反而迅速下降。同时试验还发现，不同形态氮素营养对不同直径根系长度的影响主要是表现在对直径为0-0.15mm根系上。7从不同铵硝配比对不同品种生菜根系特征参数影响的角度来看，与热耐抽苔生菜相比，申选1号对环境中不同形态氮素营养的变化更为敏感。8不同铵硝配比对生菜根系和叶片中的内源激素含量有显著的影响。随着营养液中NH₄⁺-N比例的增加，生菜根系和叶片的IAA含量及iPAs含量均随着增加，并在营养液中NH₄⁺-N比例为25％时达最高。然后，随着NH₄⁺-N比例的进一步增加到50％，生菜根系和叶片的IAA含量及iPAs含量反而下降。生菜根系和叶片的ABA含量随着营养液中NH₄⁺-N比例的增加而下降，并在营养液中NH₄⁺-N比例为25％时达最低。然后，随着NH₄⁺-N比例的进一步增加到50％，生菜根系和叶片的ABA含量反而增加。随着试验进程从4叶期推进到6叶期、8叶期，供试生菜根系和叶片中的内源激素水平随之下降。9从不同铵硝配比对不同品种生菜内源激素水平影响的角度来看，申选1号根系和叶片中的IAA和iPAs含量均高于耐热耐抽苔，且2个品种的差异均达到显著水平，申选1号根系和叶片中的ABA含量均低于耐热耐抽苔，分别为耐热耐抽苔根系和叶片中的ABA含量的93.0％和96.9％，2个品种的差异均没有达到显著水平。10通过对申选1号和耐热耐抽苔吸收NO₃^-的动力学研究发现，在全NO₃^-N营养液中，随着营养液中NO₃^-浓度的增加，2个品种生菜吸收NO₃^-的速率也随着增加，但增加的幅度随着营养液中NO₃^-浓度的增加而减少。环境中NH₄⁺-N的存在对生菜吸收NO₃^-的速率有明显影响。将全NO₃^--N营养液中的10％NO-3^--N用NH₄⁺-N取代和在全NO₃^--N营养液中直接添加10％NH₄⁺-N后，生菜吸收NO₃^-的速率与在全NO₃^--N营养液中相比有明显下降。与全NO₃^--N营养液中生菜吸收NO₃^-的动力学参数比较后发现，环境中NH₄⁺-N的存在影响生菜吸收NO₃^--N的动力学参数。将全NO₃^--N营养液中的10％NO₃^--N用NH₄⁺-N取代和在全NO₃^--N营养液中直接添加10％NH₄⁺-N后对生菜吸收NO₃^-的动力学参数有明显影响。有NH₄⁺-N存在时，生菜吸收NO₃^-的Vmax与在全NO₃^--N营养液中相比有显著下降。有NH₄⁺-N存在时，生菜吸收NO₃^-的Km与在全NO₃^--N营养液中相比有少量增加，但差异不显著。说明NH₄⁺-N存在对生莱吸收NO₃^-的动力学参数的影响主要表现在对Vmax的影响，对Km影响较小。同时还发现环境有NH₄⁺-N存在时，生菜吸收NO₃^-的Cmin增加。11不同品种生菜吸收NO₃^-的速率不同。不管有无NH₄⁺-N的存在，申选1号在有NO₃^--N的营养液中吸收NO₃^-的速率均大于耐热耐抽苔，且随着营养液中NO₃^-浓度的增加，两者的差距逐渐加大。与全NO₃^--N营养液中生菜吸收NO₃^-的动力学参数比较后发现，环境中NH₄⁺-N的存在，耐热耐抽苔Vmax下降的程度大于申选1号，耐热耐抽苔Km增加的程度小于申选1号。12通过对申选1号和耐热耐抽苔液泡中硝酸根离子的再调动和再利用的研究发现：在正常供应硝酸盐时，液泡中硝酸盐活度远远高于细胞质中硝酸盐活度。在氮亏缺的时候，生菜的地上部、地下部生物量的增长均较缓慢，地下部生长速率相对较快，根冠比逐渐增加。液泡中的硝酸盐迅速下降，但下降到一定程度后就不再下降，而细胞质中的硝酸盐活度在整个氮亏缺培养时期均能够维持在一个较低的浓度(4.0 mmol1^-1)，并保持基本稳定。在恢复供应硝酸根离子后，细胞质中的硝酸盐继续保持稳定(4.0mmol 1_-1)，液泡中的硝酸盐活度迅速增加，但地上部、地下部生物量的增长有一个滞后的效应，地上部生长速率相对较快，根冠比逐渐下降。不同生菜基因型在氮亏缺及恢复供应硝酸根时表现不一样。与耐热耐抽苔相比，在氮素亏缺时，申选1号液泡中硝酸盐活度下降的较快，且能维持一个更低的水平。在恢复氮素供应时，申选1号液泡中硝酸盐活度上升较耐热耐抽苔更迅速。综上所述，不同铵硝配比通过影响生菜根系特性、光合特性及生菜内源激素含量来影响生菜地上部、地下部生物量；铵硝配比对不同生菜品种的影响存在明显差异，这种差异除了在根系特性、光合特性及生菜内源激素含量上有表现外，还表现在不同生菜品种吸收NO₃^-的速率及吸收动力学参数存在明显的差异，以及在氮亏缺和恢复供氮后液泡中硝酸盐调动速率有明显不同；生菜液泡中的硝酸盐在氮亏缺时能被调动出来，以维持细胞质中硝酸盐浓度稳定，从而保证细胞的正常功能的发挥。更多还原

【Abstract】 Previous studies showed that partial replacement of nitrate （NO₃） by ammonium（NH₄⁺） in nutrient solution could significantly increase the biomass and decrease the NO₃concentration of aerobically growing crops. NO₃ accumulation, especially in leafyvegetables, was paid much attention because of its hazardous effects on human and animalhealth. The consumption of foods including high NO₃ content has a potential hazardousrisk on health when NO3- is reduced to nitrite （NO₂） form. Thus, enhancing the percentageof NH₄⁺-N in fertilizer application and addition of nitrification inhibitor in vegetableproduction is a potential nitrogen management. However, the mechanism of the effect ofdifferent nitrogen （N） forms on growth of leafy vegetables is still unknown. Thisdissertation is aimed to clarify the mechanism of NH₄⁺ enhancement on lettuce growth fromthe aspects of physiology and biochemistry. Hydroponic experiments were carried out tostudy the effect of different forms of N on photosynthetic characteristics, root growth anddevelopment, NO₃ uptake kinetics, NO₃ release and remobilization in root vacuoles,translation of plant endogenous hormones, as well as the yield and quality of lettuce.The results obtained are listed as follows.1. Five cultivars of lettuce, very popularly cultivated in south-east China, such as Ny,Sx1, Rw, Net and Nrnct, responded in a significantly different way to different ratios ofNH₄⁺-N : NO₃-N. Biomasses of roots and shoots of these cultivars increased with theincreasing of NH4^-N:NO₃-N ratio, and obtained the greatest value at 25:75 ofNH₄⁺-N:NO₃-N. Therefore, different ratios of NH4^oN:NO₃-N in nutrient solution couldinfluence the biomass of lettuce, and the best ratio of NH₄⁺-N:NO₃-N for lettuce growthand development is 25 : 75. Different ratio of NH₄⁺-N:NO₃-N in nutrient solution couldaffect the ratio of root and shoot, which was increased with the increased application ofNH₄⁺-N, and then decreased with the further increasing of applied NH₄⁺-N.2. Different ratios of NH₄⁺-N:NO₃-N in nutrient solution significantly affected thecontents of NO₃ in shoots of five cultivars. NO₃ contents of five cultivars decreased withthe increasing of the percentage of NH₄⁺-N in total N applied. 3. Different cultivar of lettuce responded differently to different NH₄⁺-N:NO₃^--N ratios innutrient solution. Sx1 was a mostly sensitive eultivar and Nrnct was a mostly insensitivecultivar to different ratios of NH₄⁺-N:NO₃^--N in terms of biomass production and NO3₃^-content among the cultivars tested in this experiment.4. The photosynthetic characteristics of cultivars, Sx1 and Nrnct, responded in asignificantly different way to different ratios of NH₄⁺-N:NO₃^--N. The SPAD readings, netphotosynthesis rate （Pn） and stomatol conductance （Cond） of Sx1 and Nrnct cultivarsincreased with the increasing of NH₄⁺-N:NO₃^--N ratio from 0:100 to 25:75, and they werefound to be the highest in 25:75 for NH₄⁺-N:NO₃^--N. However, they decreased with theincreasing of NH₄⁺-N:NO₃^--N ratio further. In contrast to the responses of SPAD readings,Pn and Cond of these cultivars to different ratios of NH₄⁺-N:NO₃^--N, the intercellular CO₂concentration （Ci） of these eultivars decreased with the increasing of, NH₄⁺ percentage andthe minimum Ci was found in the treatment of 25:75 for NH₄⁺-N:NO₃^--N. This indicatedthat NH₄⁺ addition could promote the photosynthesis of lettuce. The enhanced effect ofNH₄⁺ addition on photosynthesis characteristics should be attributed to Ci mainly.5. Results from the photosynthesis experiments showed that the cultivar named as Sx1was a more sensitive genotype to different ratios of NH₄⁺-N:NO₃^--N than the cultivarnamed as Nrnct in this experiment. Therefore, Sx1 was a sensitive genotype and Nrnct wasa insensitive genotype to different ratios of NH₄⁺-N:NO₃^--N.6. Different ratios of NH₄⁺-N:NO₃^--N in nutrient solution could greatly affect the rootgrowth of Sxl and Nrnct. Total root surface area, root volume, total root length and rootnumber increased with increased application of NH₄⁺-N, percentage from 0％to 25％, Theywere found to be the highest in 25:75 of NH₄⁺-N:NO₃^--N, and then decreased quickly withthe further increase NH₄⁺ amount. This result indicated that moderate NH₄⁺ addition couldimprove the development of root growth of lettuce. The effects of different N forms anddifferent ratios of NH₄⁺-N:NO₃^--N on total root length of these cultivars were exhibitedmainly on the root length of diameter of 0-0.15mm.7. In terms of the effects of different ratios of NH₄⁺-N:NO3₃^--N on root architectures of Sx1 and Nrnct cultivars, Sx1 had greater response and be more sensitive than that of Nrnct under moderate ratio of NH₄⁺-N:NO₃^--N.8. The Contents of endogenous hormone in Sx1 and Nrnct were significantly affected. The contents of IAA and iPAs of roots and shoots increased with the increasing of NH₄⁺-N:NO₃^--N ratio, and they were found to be the highest in 25:75 of NH₄⁺-N:NO₃^--N. However, they decreased with the further increase of NH-4⁺-N:NO₃^--N ratio from 25:75 to50:50. In contrast to the responses of IAA and iPAs contents to different ratios ofNH₄⁺-N:NO₃^--N, the contents of ABA in roots and shoots decreased as the percent of NH₄⁺increased, and the minimum ABA contents in roots and shoots were found in the treatmentof 25:75 for NH₄⁺-N:NO₃^--N. Then, they increased with the increasing NH₄⁺-N:NO₃^--Nratio from 25:75 to 50:50. With the development of growth from 4-leaves to 6-leaves and8-leaves, the contents of ABA, IAA and iPAs in Sx1 and Nrnct decreased in roots andshoots.9. The contents of IAA and iPAs in roots and shoots of Sx1 were higher than those ofNrnct, and there were significant difference between that in Sx1 and Nrnct. The contents ofABA in roots and shoots of Sx1 were 93.0％and 96.9％of that in Nrnct, respectively.10. Results from the NO₃^- uptake kinetics by Sx1 and Nrnct showed that, with theincreasing of NO₃^- content, the NO3₃^- uptake rate by Sx1 and Nrnct increased 100％NO₃^- -Nnutrient solution, while the increment of NO₃^- uptake decreased. After replaced 10％NO₃^--N by 10％NH₄-N and enhanced 10％NH₄-N in nutrient solution, the rates of NO₃^-uptake by Sx1 and Nmct decreased significantly, compared with that in the solution withoutNH₃⁺-N. Vmax of NO₃^- uptake in 0％NH₄⁺-N nutrient solution was higher significantlythan that in nutrient solution with 10％NO₃^--N replacement by 10％NH₄^--N. The Km ofNO₃^-uptake in 0％NH₄⁺-N nutrient solution was lower than that in nutrient solution with10％NO₃^-N replacement by 10％NH₄⁺-N, but there was no significant difference. Thisindicated that the inhibition of NO₃^- uptake by NH₄⁺-N was mainly due to the higher Vmax.NH₄⁺-N enhancement also inhibited NO₃^- uptake by increased the Cmin.11. Different cultivar has different NO₃^-uptake rate. The NO₃^-uptake rates of Sx1 werehigher than those of Nrnct in solution with NH₄⁺-N and without NH₄⁺-N. With the NO₃^-content increasing, the difference of NO₃^- uptake rates between Sx1 and Nrnct increased.Added NH₄⁺-N, the decreasing percentage of Vmax for Nmct was higher than that for Sx1,and the increasing percentage of Km for Nrnct was lower than that for Sx1.12. The activities of NO₃^- in vacuoles were higher than that in cytoplasms during the firstperiod of being planted in Yamazaki solution. After NO₃^- was removed from culturesolution, the biomasses of shoots and roots increased, and also the ratios of root and shootincreased. After the deprivation of NO₃^-, the activities of NO₃^- in vacuoles decreased greatlyfrom the 1st day to 3rd day, and decreased slowly from 4^th day to 7^th day, while the NO₃^-activities in cytoplasms were 4.0 mmol L^-1 and did not changed. This suggested that vacuolar NO₃^- could be released into cytosol to maintain a steady NO₃^- concentration forensure normal plant growth. From the second day re-supply NO₃^- again, NO₃^-concentrations in vacuoles increased quickly, and the biomasses boomed since the forth day.As the relative growth rate of shoots were higher than that of roots, the ratios of root andshoot decreased. The NO₃^- activities in cytoplasms were hardly changed in either NO₃^-supplied or deprived conditions. NO₃^- in vacuole of Sx1 had more mobilization than that ofNrnct. In the fifth day after deprivation of N, the NO₃^- concentrations in vacuoles of Sx1and Nrnct were 12.97 mg L^-1 and 27.67 mg L^-1, respectively. And the increment of NO₃^-concentration in vacuole of Sx1 was higher than that of Nrnct in re-supply NO₃^- condition.This showed that Sx1 was a high N use efficiency cultivar comparing with Nrnct in term ofthe characteristics of NO₃^- release and remobilization in root vacuoles.In conclusion, different ratios of NH₄⁺-N:NO₃^--N in solution could significantly affectroot architecture, photosynthetic characteristics and endogenous hormones, which, in turn,affected the root and shoot biomasses of lettuce cultivars. Different species of lettuce had adifferent ways to respond to different ratios of NH₄⁺-N:NO₃^--N in solutions. This respondeddifferences were found not only in the changes of root architecture, photosyntheticcharacteristics and endogenous hormone contents, but in NO₃^- uptake characteristics as well.Different cultivars of lettuce had also a different ability to remobilize the NO₃^- in vacuolesafter deprivation and re-supply of N in the solution. The NO₃^- in vacuoles of lettuce plantscould be rcmobilized after deprivation of N in the solution, which could sustain a relativelystable NO₃^- concentration in cytoplasm and thus ensure a normal function of cells.更多还原