桧叶白发藓对不同氮源胁迫的形态和生理响应

Growth and physiological responses of Leucobryum juniperoideum to different nitrogen stresses

桧叶白发藓(Leucobryum juniperoideum)在我国东南部常见,被认为是一种理想的、适用于庭院栽培的苔藓植物,而氮是植物必需的矿质元素,但过量摄人会对其造成伤害,近年来氮沉降水平的提高对苔藓植物的多样性造成了严重影响。该研究为揭示氮沉降加剧对桧叶白发藓的影响,以经6个月断茎培养的桧叶白发藓配子体为材料,用(Ca(NO_3)_2、NH_4HCO_3和NH_4NO_3代表三种氮源,设置2、4、8、16 gN·m^(-2)4个水平,以喷洒去离子水为对照,进行不同氮源的胁迫试验。结果表明:氮处理浓度的增加引起组织氮含量的显著提高,增加幅度分别为69.1%、25.7%和43.1%;同时引起植株坏死率显著上升,增加幅度分别为16.5%、12.5%和13.9%。三种氮源处理对株高和净重的影响有显著差异,低浓度的铵态氮(4 gN·m^(-2))引起株高和净重的显著增加,而硝态氮和混合态氮处理差异不显著;加氮浓度的进一步提高,引起株高和净重的减低,硝态氮处理的减低幅度最大,铵态氮的降低幅度最小。三种氮源处理均引起叶绿素含量先上升后下降,但同一水平铵态氮处理的叶绿素含量要高于其它两种氮处理,而且引起叶绿素含量下降的处理浓度要高于其它两种氮源;三种氮源均引起SOD活性显著增加、可溶性蛋白和脯氨酸含量先升后降,但不同氮源间生理指标的变化不同步。这说明桧叶白发藓对硝态氮胁迫的响应比铵态氮敏感,硝态氮的增加对桧叶白发藓造成严重危害,而少量的铵态氮(4 gN·m^(-2))则能促进桧叶白发藓的生长。研究结果可作为桧叶白发藓繁殖与生产的氮源。

Leucobryurn juniperoideurn is a common bryophyte in the southeast china,which is considered to be an ideal ornamental plant used in garden. Nitrogen （N） is a kind of necessary element to plant growth, but ex- cess N can be capable of causing serious injury to the most plants. According to recent studies, the diversity of bryophytes was severely decreased by the more and more increasing N deposition. In order to reveal the growth and physiological responses of L. juniperoideurn to the intensification of N deposition, three forms of nitrogen, i.e. lime nitrate （Ca（NO3）2） representing the nitrate N, ammonium bicarbonate （NH4 HCO3） re- presenting the ammonium N and ammonium nitrate （NH4NO3） representing the mixed N, were used in the treatments of simulating N deposition. The gametophyte material used in this experiment was propagated by shattered fragments and cultured in the greenhouse six months ahead of the first fertilization. The gradient of N concentration was 0, 2, 4, 8, 16 gN· m^-2 prepared using a solution of lime nitrate, ammonium nitrate and ammonium nitrate respectively. The results showed that the tissue N contents of L. juniperoideum were raised as the increasing of the three kinds of nitrogen concentration and the increasing tissue N contents of Ca（NO3）2, NH4 HCO3 and NH4 NO3 were 69. 1%, 25.7% and 43.1% respectively. The dead plant rate of L. juniperoideum gametophyte also increased as the three kinds of nitrogen fertilization concentration rising, but there are remarkable differences among the three kinds of nitrogen treatments, and the dead plant rate of Ca（NO3）2, NH4HCO3 and NH4NO3 were 16.5%, 12.5% and 13.9% respectively. As well as the net weight of the L. juniperoideum, the plant height came out different as the three kinds of nitrogen concentration ris- ing. The net weight and the plant height all added by the treatments of low concentration NH4 HCO3 （4 gN · m^-2） ,but not by nitrate N and mixed N treatments, and three kinds of nitrogen treatments all cause the re- duction of the net weight and the plant height as the N concentration rising. The changes of the Chlorophyll （a, b） contents by three N treatments all occurred from increase to decrease, but the Chlorophyll （a,b） con- tents of NH4 HCO3 treatments were higher than other N forms at the same concentration, and the NH4 HCO3 concentration of decreasing Chlorophyll （a, b） content was higher than Ca （NO3）2 and N H4NO3. There exis- ted an obviously similar variation tendency of the superoxide dismutase （SOD） among the three kinds of nitro- gen treatments ,which increased as the N concentration rising, while the soluble protein content and the pra- line content increased at lower N concentration and reduced at higher N concentration. These physiological in- dexes were not synchronous among the three N treatments. It was demonstrated in the experiments that L. juniperoideum was more sensitive to nitrate N than ammonium N, and small ammonium N additions （4 gN · m^-2） tended to increased its growth,while nitrate N additions decreased its growth. Therefore, ammoni- um N could be used as the N source of L. juniperoideum and the low concentration of nitrogen additions was critical to the fertilization of L. juniperoideum.