濒危种四合木与其近缘种霸王水分关系参数和光合特性的比较

运用压力室-容积技术(P-V技术)对西鄂尔多斯地区特有的濒危植物四合木(Tetraena mongolica Maxim.)和生长于同一生境的近缘种霸王(Zygophyllum xanthoxylon (Bunge) Maxim.)的7个水分关系参数饱和含水量时最大渗透势(Ψ_s^sat) 、初始质壁分离时的渗透势(Ψ_s^tlp) 、初始质壁分离时渗透水相对含量(ROWC^tlp) 、初始质壁分离时的相对含水量(RWC^tlp) 、质外体水的相对含量(AWC) 、束缚水与自由水的比值(V_a / V₀),以及细胞最大弹性模量(ε^max)进行了测定,同时利用Li-6400光合作用测定系统测定了二者叶片气体交换参数的日变化,从生理生态学角度探讨了二者生存力、适应力的差异。结果表明:1)四合木的ε^max、ROWC^tlp值和RWC^tlp值均显著低于霸王,而Ψ_s^sat值Ψ_s^tlp值、AWC和V_a / V₀高于霸王。二者保持膨压的能力和方式不同,四合木表现为较小的细胞体积和较强的持水能力,主要以高的组织弹性来保持膨压,而霸王主要以增加细胞质浓度的渗透调节来维持膨压,弹性调节较弱。且四合木保持最大膨压的能力和维持最低膨压的极限渗透势低于霸王,耐旱性弱于霸王。2)自然条件下,四合木和霸王叶片的光合速率(Pn)、蒸腾速率(Tr)日进程均呈"双峰"曲线,主峰出现在11:00时,次峰出现在15:00时左右,光合作用的午间降低是由气孔导度(Gs)降低造成的。二者相比,四合木光合速率和水分利用效率(WUE)低于霸王,光合能力和对干旱环境适应能力弱于霸王。研究表明四合木在生理生态学方面的生存力、适应力弱于霸王。

Comparative analysis of water related parameters and photosynthetic characteristics in the endangered plant Tetraena mongolica Maxim. and the closely related Zygophyllum xanthoxylon (Bunge) Maxim.

Tetraena mongolica Maxim.belongs to a monotypic genus in the Zygophyllaceae and is a super xerophyte and a relic subshrub of the Tethys.This species is endemic to a very limited area of West Erods region in the western part of the Ordos Plateau in China.The limited distribution of this subshrub makes it an important conservation target.It is ranked as a second-class national endangered plant species as defined by China′s Red Book(endangered species list) and has been considered unique from both a plant taxonomical and regional systematics points of view.Also,from a practical standpoint,it plays an important role as a windbreaker and stabilizer of sand and contributes to soil conservation and the regulation of hydrological regimes.Populations of T.mongolica serve as an important element in ecosystem functioning and buffer local ecosystems against desertification.Deterioration of the environment and human activities in recent years have resulted in a high degree of landscape fragmentation and habitat loss in the area.As a result,population size and density of T.mongolica have been decreasing dramatically and populations are gradually being replaced by the closely related Zygophyllum xanthoxylon(Bunge) Maxim..T.mongolica has become severely endangered.So research on the conservation biology of this species has attracted attention.A comparative analysis in T.mongolica and its relative Z.xanthoxylon are ecologically important and will help document the threats to T.mongolica and offer a scientific basis for establishing protective measures for this species.One way to show the differentiation of adaptability in different plants is to study the characteristics of photosynthesis and water metabolism in these species.In this paper,seven water relation parameters were measured: osmotic potential at saturated point(Ψsats),osmotic potential at turgor loss point(Ψstlp),relative osmotic water content at turgor loss point(ROWCtlp),relative water content at turgor loss point(RWCtlp),relative content of apoplastic water(AWC),bound water/ free water(Va/V0),and maximum bulk modulus of elasticity(εmax).The press-volume technique was used and photosynthetic characteristics were measured with a Li-6400 portable photosynthesis system.The goal was to compare the endangered plant T.mongolica to its relative Z.xanthoxylon to investigate differences in their viability and adaptability.The results show,first,T.mongolica had a higher Ψsats,Ψtlps,AWC,Va /V0 and lower εmax,ROWCtlp,RWCtlp than Z.xanthoxylon.The two plants maintained their turgor pressure in different ways.T.mongolica maintains turgor pressure by elastic adjustment with small changes in cell volume and a strong ability to retain water.Z.xanthoxylon uses osmotic adjustment,which had a weak adjustment ability.T.mongolica is less able to maintain turgor pressure and has a lower water potential,which gives it a lower level of drought resistance than Z.xanthoxylon.Second,the curves of the diurnal change in the net photosynthetic rates(Pn) and transpiration rates(Tr) of these two plants had double peaks.The first peak appeared at 11:00 and the second at 15:00 with declines in Pn and Tr observed at midday in these two plants.When compared with Z.xanthoxylon,T.mongolica had lower a Pn and water use efficiency,which demonstrates its weaker photosynthetic capability and lower adaptability to a drought prone environment.The results revealed the physio-ecological viability and drought adaptability of T.mongolica were weaker than Z.xanthoxylon.