【作者】 韦莉莉；

【导师】 严重玲；

【作者基本信息】 厦门大学 ， 生态学， 2007， 博士

【摘要】 红树植物作为一类典型的盐土植物,一直是生理生态学以及污染生态学领域研究植物适应机制、尤其是应对极端生态环境的模式植物。红树植物在盐生条件下生理生态的特性得到广泛地研究。植物的稳定碳同位素组成(以δ¹³C表示)是植物长期生理生态的综合响应指标,然而,关于红树植物δ¹³C与红树林特殊生境之间相关关系的研究却很少。过去的研究者通常认为盐土植物δ¹³C对盐度的响应模式与非盐土植物相同。然而,通过对红树植物光合作用的研究结果的分析可知,大部分红树植物在盐生条件下的光合作用（Pn）和气孔导度（Gs）大于非盐生条件下的值。由于植物的Pn和Gs是决定植物δ¹³C的主要参数,较高的Gs将引起δ¹³C的增大。据此推测,红树植物的δ¹³C与盐度的关系与非盐土植物不同。本文以福建省分布的主要红树树种桐花树、秋茄和白骨壤为例,研究盐分条件下三种红树植物稳定碳同位素组成特征,为红树林研究的进一步开展提供基础数据。在此基础上,进一步探讨红树植物的δ¹³C是否可以作为不同种红树问耐盐性的指示指标。同时,结合其他分析手段和技术,分析盐分条件下红树植物δ¹³C变化的原因,并试图探讨盐生环境下红树植物光合代谢途径是否发生转换。实验包括一个野外试验和三个盆栽模拟试验,得到如下主要结论:（1）生长于系列盐度下的桐花树和秋茄幼苗,叶片的δ¹³C分别在15‰和20‰盐度下最低。在0～15‰盐度范围内,桐花树叶片的δ¹³C随盐度的增加而减小;在高于15‰的盐度下,桐花树叶片的δ¹³C随盐度的增加而增大。这种变化趋势随处理时间的延长而加剧,但是叶片δ¹³C在各盐度之间的差异不显著。其中,在高盐度（30‰）下生长长达130天的桐花树幼苗,叶片的δ¹³C则明显降低,与同一盐度下生长60天的叶片相比,δ¹³C降低了1.20‰。与桐花树幼苗的变化趋势相类似,在0～20‰盐度范围内,秋茄叶片的δ¹³C随盐度的增加而减小;在高于20‰的盐度下,桐花树叶片的δ¹³C随盐度的增加而增大。同样,随处理时间的延长,盐度对叶片δ¹³C的影响加剧,而且盐度之间的差异达到显著水平。综上所述,两种红树植物幼苗在最适盐度条件下,叶片的δ¹³C最低;且这种变化趋势随着处理时间的延长而加剧。（2）秋茄幼苗叶片的净光合速率和气孔导度随盐度的变化与叶片δ¹³C的变化趋势正好相反。在0～20‰的盐度下,Pn和Gs随着盐度的增加而增大。表明在适宜盐度下气孔开度大于非盐分处理的叶片,更多的CO₂进入叶片,同时气孔对C-13歧视加强,使吸收的CO₂含C-13的比例减小,从而导致叶片δ¹³C的降低。当盐度大于20‰,随着盐度的增加,Pn和Gs减小。气孔对碳同位素的选择降低,即对C-13的分馏效应降低,因而叶片的δ¹³C逐渐增大。由此可见,在一定盐度范围内,叶片δ¹³C的变化主要是气孔调节的结果。（3）桐花树和秋茄幼苗有机酸含量或pH的昼夜差异均不显著,表明两种红树幼苗在盐分条件下,没有诱导发生CAM代谢。从两种红树的δ¹³C变化范围来看,桐花树的δ¹³C在-30.36～-26.55‰之间,秋茄的δ¹³C在-31.96～-28.13‰之间,属于典型的C₃植物。可见,盐分条件下桐花树和秋茄幼苗没有发生光合代谢途径的转换。（4）在0～30‰盐度下,白骨壤幼苗的δ¹³C随盐度的变化没有表现出显著的峰值,各盐度之间的差异未达显著水平。从气体交换系统测定的结果来看,Pn随盐度增加而降低,Gs却随盐度的增加而增大。这与其他红树植物不同,但是引起白骨壤Gs增大的原因不是气孔开度的增加而与气孔密度的增加有关。可见,气孔调节不是白骨壤δ¹³C变化的主要原因。从光合参数的分析可知,羧化效率随盐度的增加而显著降低,这可能是白骨壤叶片光合降低的原因之一。另外,白骨壤叶片的光呼吸速率和CO₂补偿点随盐度的增加显著降低,这些现象表明C₄代谢有所增强。这可能是引起白骨壤δ¹³C变化的另一个重要原因。白骨壤叶片pH的昼夜差异不显著,表明没有CAM代谢的发生。（5）桐花树幼苗叶和根的δ¹³C随盐度的变化趋势一致,而盐分似乎对茎的δ¹³C没有产生影响。叶和茎的δ¹³C差异很小,并显著低于根的δ¹³C。白骨壤幼苗五个部分（叶、茎的上部、茎的下部、根的上部和根的下部）的δ¹³C依自然生长位置由叶向根依次增大,且对盐度的响应模式基本一致。同一器官不同部分之间的差异显著,而生长位置相邻的不同器官之间的差异不显著。这些现象表明,器官之间δ¹³C的差异与物质的运输过程有关。（6）在系列盐度下生长的桐花树幼苗,叶片的δ¹³C在15‰盐度下最低。秋茄幼苗的叶片δ¹³C在20‰盐度下最低。表明15‰和20‰的盐度分别是桐花树和秋茄幼苗的最适生长盐度,显然桐花树的最适生长盐度低于秋茄。可见,红树植物叶片的δ¹³C可以用来比较不同种红树之间的耐盐性。这为不同种盐土植物之间耐盐性的比较提供了一种可行的方法。更多还原

【Abstract】 Mangrove plant,as a typical halophytic species,their ecological response to salinity has been widely studied.But little is know of the correlations between stable carbon isotope composition(presented by convention asδ¹³C) and salinity,even though plantδ¹³C have been thought to be an index of reflection of the integrated response of physiological characteristic to environmental factors.δ¹³C in plant tissues is correlated with their intrinsic salt tolerances,leading to varied patterns ofδ¹³C in different plants species or different parts of a certain plant.Previous studies showed that halophytic species had a similar pattem ofδ¹³C variation as compared with nonhalophytic species.From the model of Farquhar et al.（1982） expression for discrimination in leaves of C₃ plants,variation in plantδ¹³C is mainly associated with stomatal and photosynthetic effects.However,the pattems of CO₂ exchange properties have been shown to be different between halophytic and nonhalophytic species as affected by salinity.Therefore,I hypothesized that the correlation betweenδ¹³C and salinity for mangrove plants differ from nonhalophytic species.To test the hypothesis,δ¹³C variation of three dominant mangrove species in Fujian province under salinity were studied.Based on the primary results,I discussed whetherδ¹³C could be used to compare the salt tolerance between mangrove plants belonging of different species.In addition,I tried to explore the mechanism ofδ¹³C changes of mangrove plants induced by salinity,and to determine the photosynthetic pathway of mangrove species under salinity using the stable isotope technique combined with gas exchange measurements and other relative technique.Following are the major conclusion:ⅰ) Leafδ¹³C exhibited special patterns in A.corniculatum and K.candel as response to salinity.In A.comiculatum,an increase in salinity from 0 to 15‰induced reduction in leafδ¹³C;while as salinity above 15‰,leafδ¹³C increased.The similar pattern was also found in K.candel,but the maximum values of leafδ¹³C occurred at 20‰.These changes became more pronounced for long time treated with salinity,although the differences between salt treatments were non-significant for A. corniculatum.These results indicate that the patterns of leafδ¹³C in A.corniculatum and K.candel differ from those in nonhalophyte,these two species showed the lowestδ¹³ at the optimum salinity.In A.corniculatum,a great lower leafδ¹³C were observed in 130-d samples relative to 60-d samples at high salinity（30‰）.ⅱ) The patterns of photosynthetic parameters including net photosynthetic rate（Pn）, stomatal conductance（Gs）,transpiration rate（Tr）,and intercellular CO₂ concentration（Ci） were opposite to leafδ¹³C.As salinity increased from 0 to 20‰,Pn,Gs and Tr increased, revealing that the decrease in leafδ¹³C was caused by stomatal opening;while as salinity higher than 20‰,these parameters decreased,which resulted in an increase in leafδ¹³C.Therefore,it could be concluded that changes in leafδ¹³C of these two mangrove species mainly resulted by stomatal adjustment as affected by salinity.ⅲ) There was no significant differences in malic acid content of A.corniculatum or pH value of K.candel between day and night,revealing that theses two species have not been induced into crassulacean acid metabolism by salinity.The values ofδ¹³C in A.corniculatum and K.candel were-30.36～-26.55‰and -31.96～-28.13‰respectively,which were within the range of C₃ plants.Therefore,it could be concluded that these two mangrove species are typical C₃ plants.ⅳ) Unlike in the case of A.corniculatum and K.candel,the changes in leafδ¹³C of A.marina always increased as salinity increased from 0 to 35‰,but the differences between salinity were not significant.Pn decreased with increasing salinity,while Gs increased.An increase in Gs paralleled the increase of stomatal density,indicating that the increase of Gs was the result of increasing stomatal density but not of the stomatal opening.The reduction in carboxylation efficiency（CE） was also detected and which maybe one reason for Pn prohibition.In addition,the decrease of photorespiration（Rp） and CO₂ compensation point（Γ） indicated that C₄ photosynthetic metabolism increased to some extent.The differences in pH between day and night were not significant,indicating no CAM occurred.Summary,δ¹³C variation is correlated with depression of Pn and CE,and the enhanced C₄ photosynthesis which maybe also an important factor in contribution to the tolerance of the species to high salinity. ⅴ) In A.corniculatum,root and leaf exhibited quite similar response patterns inδ¹³C to salinity,butδ¹³C in stem showed less variation.δ¹³C in both stem and leaf were significant lower than in root.δ¹³C in seedling parts in A.marina increased followed the order of leaf＜above-stem＜below-stem＜above-root＜below-root.The similar variation patterns inδ¹³C were observed in various seedling parts.It is interesting noted that different parts of one seedling organ showed significant difference inδ¹³C; while,δ¹³C in different organs linked together showed non-significant differences.It is suggested that the differences between plant parts are correlated with the discrimination to C-13 during transport processes.ⅵ) The difference in optimum salinity of A.corniculatum and K.candel inferred by leafδ¹³C provides a feasible method for comparing salt tolerance between plants of different species,and it is useful for mangrove restoration.更多还原