不同生境下报春苣苔的光合作用日变化特性

国家一级濒危植物报春苣苔Primulina tabacum Hance是苦苣苔科多年生草本植物。研究不同生境下报春苣苔在干湿季的光合作用日变化动态及其对环境因子响应,结果表明：旷地午间时段,光合有效辐射（PAR）增加伴随着空气湿度（RH）的显著下降,此时报春苣苔的净光合速率（Pn）因受光抑制和气孔限制的影响而下降。岩洞生境下报春苣苔的Pn没有受到抑制,但其Pn和光合碳水化合物（CH2O）生成速率较低,洞内光照缺乏是限制其光合碳同化的原因之一。3个样地检测的Pn、CH2O产生速率、气孔导度（Gs）、蒸腾速率（Tr）以及Rubisco的Vo/Vc比率等在湿季均优于干季。主成分分析表明叶片Narea与Chl含量、比叶重（LMA）以及气孔密度对光合作用具有显著影响。Pearson相关分析表明不同生境下影响报春苣苔Pn的关键生态因子有所不同,旷地强光环境下过高的叶片水蒸气压亏缺（VPD）和气温（ta）直接限制净光合速率的水平,而在岩洞弱光高湿环境中,PAR则成为Pn的限制因子。同一环境因子在不同生境下对报春苣苔Pn的影响也有所不同：在旷地强光生境下,空气湿度（RH）的适度增加有利于降低过高的VPD,促进气孔开放而提高Pn。而在岩洞低光条件下,过高RH则会使降低VPD而不利于叶片的气体交换,使光合作用受影响。这个结果启示,在进行报春苣苔野外回归栽培时,应该注意PAR和RH等环境因子的控制。

Diurnal photosynthetic performances of Primulina tabacum Hance grown in different Karst habitats

Primulina tabacum Hance is a critically endangered perennial herb belonging to the family Gesneriaceae.It has a very restricted distribution in limestone area from shaded caves to open area in Karst habitat in south China.This study investigated the relationships between the net photosynthesis rates（Pn） of this species and environmental factors.In open area（OA） site,excess radiation energy was accompanied with low air relative temperature（RH）,thus water and CO2 deficit in leaves were the major factor to cause midday depression of photosynthesis in this field.By providing a shade and humid shield,cave is a suitable habitat to protect P.tabacum against photoinhibition.In twilight zone（TZ） of cave,the lack of sunlight significantly decreased plant carbon assimilation（Pn and CH2O production rate） by affecting the diurnal pattern of gas exchange in both dry and wet seasons.The tested parameters of Pn、CH2O production rate,stomatal conductance（Gs）,transpiration rate（Tr） and oxidation/carboxylation（Vo/Vc） ratio of Rubisco in three sites all showed better performances in wet season as compared with that in dry season.Principle analysis suggested that Pn was significantly affected by the leaf mass per unit area（LMA）,N content on a leaf area basis（Narea）,total Chl（a＋b） content and stomatal density.Correlation analysis between Pn and environmental factors revealed that the primary influencing factors for Pn in OA were vapor pressure deficit（VPD,p0.01） and air temperature（ta,p0.01）,whereas in EZ and TZ,PAR is the most primary influencing factor for Pn.Moreover,our study revealed that same environmental factor can,in fact,had contrary effect on PN in different habitats.In OA site,the higher RH in the morning can maintain lower level of VPD,thus benefit the performance of photosynthesis of leaf,and while in cave habitats,the increase in RH caused a decrease of Pn with a significant low VPD.Our results indicated that the PAR and RH should be carefully considered in the reintroduction of P.tabacum in Karst region.