青藏高原东南缘不同坡向对陇蜀杜鹃花性状的影响

Variations in floral traits of Rhododendron przewalskii with slope aspect in the southeastern Tibetan Plateau

植物的花表型多样性是长期自然选择的结果,是植物对异质性环境的适应性响应.以青藏高原东缘的高山灌丛陇蜀杜鹃(Rhododendron przewalskii)为研究对象,分析花性状在不同坡向的变化特征及其相关关系,力求理解高寒异质生境下的植物适合度,加深对传粉生物学中生殖器官可塑性的认识.结果显示:(1)东坡的土壤温度及pH值均显著大于东北坡(P=0.02,P=0.001),其土壤容重显著小于东北坡(P<0.001),而其他土壤养分特征在坡向间无显著性差异.(2)陇蜀杜鹃的花大小在不同坡向具有显著性差异,即东坡(花管直径:22.74±0.15 mm;花管长度:19.86±0.56 mm)>东北坡(21.00±0.12 mm;18.31±0.34 mm);雌蕊长度在东坡显著大于其东北坡,但出管距离(柱头探出花管的距离)结果则相反;此外,柱头大小及形状在坡向间并无显著差异.花性状在个体间和坡向间变异均较大,其中柱头大小和出管距离变异系数在东坡和东北坡分别为最大,分别为29.13%、28.03%.(3)花管直径与花管长度、雌蕊长与花梗长、花柱长与雌蕊长和花梗长、子房与雌蕊长在两个坡向均为极显著正相关(东坡:P<0.001,P<0.001,P<0.01,P<0.001,P<0.001;东北坡:P<0.001,P<0.001,P<0.01,P<0.001,P<0.001);柱头大小与花柱长、雌蕊长、花梗长在东坡为极显著正相关(P<0.01,P<0.001,P<0.01);柱头大小与子房长在东北坡显著正相关(P=0.01),与柱头形状显著负相关(P=0.02).(4)花管直径与花管长度在东坡为异速生长关系,东北坡为等速生长关系;两个坡向上出管距离增加的速率均大于花管长度增加速率.传粉生物学功能性状间的权衡分析表明,东坡偏好增加花管直径,而东北坡偏好增加出管距离以增加繁殖成效.可见,不同坡向的陇蜀杜鹃种内花部性状的高变异性,有利于其在高寒生境中展示出较高的繁衍机会,性状权衡对坡向差异偏好响应有利于陇蜀杜鹃适应高山异质环境.

The diverse phenotypes of floral traits are evolutionary outcomes of natural selection and adaptive responses to heterogeneous environments.This study aimed to understand plant fitness in alpine heterogeneous habitats and reproductive organ plasticity in terms of pollination biology.Rhododendron przewalskii is a typical alpine shrub on the south-eastern edge of the Tibetan Plateau.A comparative and correlational analysis of the floral traits of R.przewalskii growing on different aspects was performed.Our results showed that 1)the soil temperature and pH values at the eastern aspect were significantly greater(P=0.02,P=0.001),whereas the soil bulk density was significantly lower(P<0.001),than those of the north-eastern aspect.Other soil factors showed no significant differences between the two slope aspects.2)The flower size of R.przewalskii was significantly different in the two aspects.The flower size was greater at the east aspect(floral opening diameter:22.74±0.15 mm;corolla tube length:19.86±0.56 mm)than those at the northeast aspect(21.00±0.12 mm and 21.00±0.12 mm,respectively).The pistil length was also significantly larger in the eastern aspect than in the northeast.However,stigma exsertion presented a contradictory result.In addition,there was no significant difference in the size and shape of the stigma between the two aspects.Floral traits exhibited large variation between individuals and aspects.The coefficient of variation(CV)of stigma size was greater(29.13%)in the east,whereas the CV of stigma exsertion was larger(28.03%)in the northeast aspect.3)Floral opening diameter and corolla tube length,pistil length and pedicel length,style length and pistil and pedicel lengths,and ovary length and pistil length were significantly positively correlated at both aspects(east:P<0.001,P<0.001,P<0.01,P<0.001,P<0.001,respectively;northeast:P<0.001,P<0.001,P<0.01,P<0.001,P<0.001,respectively).In addition,stigma size,style length,and pistil length had significant positive correlations with the pedicel length at the east aspect(P<0.01,P<0.001,P<0.01,respectively),and at the northeast aspect,the stigma size was significantly positively correlated with the ovary length(P=0.01),whereas it was significantly negatively correlated with the stigma shape(P=0.02).4)The floral opening diameter and the corolla tube length had an allometric growth relationship at the eastern aspect but an isometric growth relationship at the northeast aspect.Moreover,floral opening diameter tended to increase in the eastern aspect in terms of trade-offs between functional traits of pollination biology,whereas the flower preferred to regulate stigma exsertion at the northeast aspect for better reproduction efficiency.The study revealed that floral traits of R.przewalskii vary with changes in aspect,which enables them to avail higher reproductive opportunities in a heterogeneous alpine habitat.The tradeoff between floral traits and their preferences in different aspects is a crucial evolutionary adaptation that ensures the survival of R.przewalskii in a heterogeneous alpine environment.