天然草地植物叶角质层蜡质的化学组成及其对自由放牧的响应

Chemical profiles of cuticular waxes in arid steppe plant species and their response to continuous grazing

植物角质层蜡质在保护植物免受极端环境危害方面发挥着重要作用。在内蒙古草甸草原和典型草原,分别选取围栏封育样地和自由放牧退化样地,在植物生长季采集3种植物(羊草、克氏针茅和糙隐子草)的叶片,采用色质谱技术分析了植物叶角质层蜡质总量、组分及碳链分布特点,比较了几种植物叶角质层蜡质特征对过度放牧的响应机制,旨在为合理利用和管理草原提供理论依据。结果表明,几种植物叶角质层蜡质总量存在显著种间差异,整体表现为羊草>克氏针茅>糙隐子草。羊草中,鉴定出7类化合物,分别是脂肪酸、烷烃、次级醇、初级醇、β-谷甾醇、β-二酮和烷基间苯二酚;在克氏针茅中,鉴定出5类化合物,分别是脂肪酸、烷烃、初级醇、α-香树脂醇以及β-谷甾醇;在糙隐子草叶中鉴定出6类化合物,分别是脂肪酸、烷烃、醛类、初级醇、烷基酯和β-香树脂醇。羊草次级醇相对含量最高,糙隐子草初级醇含量最高,而克氏针茅烷烃含量最高。草地类型显著影响了糙隐子草蜡质总量及其烷基酯的相对含量、克氏针茅烷烃相对含量及羊草次级醇和β-二酮相对含量。而草地利用方式显著影响了糙隐子草脂肪酸相对含量、克氏针茅蜡质总量、α-香树脂醇和β-谷甾醇相对含量及羊草蜡质总量和次级醇相对含量。在典型草原,糙隐子草和克氏针茅叶角质层蜡质总量均表现为自由放牧草地>围封草地(P<0.05);而羊草与之相反。在草甸草原,糙隐子草叶角质层蜡质总量样地间差异不显著;克氏针茅表现为放牧草地>围封草地(P<0.05);羊草叶角质层蜡质总量表现为围封草地>放牧草地(P<0.05)。不同植物角质层蜡质表现出的差异性响应模式,说明不同植物在长期进化过程中形成了各自特有的适应机制。综合分析认为,草地植物可以通过调整自身蜡质合成,改变蜡质组分和含量以适应外界环境引起的胁迫。

Cuticular wax plays an important role in protecting plants from harsh environments.Understanding the responses of cuticular wax to grazing may provide information that can be used to improve grassland management regimes.Leaves fromStipa krylovii,Leymus chinensis and Cleistogenes squarrosa were taken from ungrazed and continuously grazed typical and meadow steppes in Inner Mongolia,China.We analyzed the characteristics of cuticular waxes among plant species and steppe types.The results indicated that the total wax coverage differed greatly among plant species,with the highest in L.chinensis,followed by S.krylovii with the lowest in C.squarrosa.Seven wax compounds were identified in L.chinensis,including fatty acids,alkanes,secondary alcohols,primary alcohols,β-sitsterols,β-diketones and alkylresorcinols.Five wax compounds were identified in S.kryloviiincluding fatty acids,alkanes,primary alcohols,α-amyrin andβ-sitsterols and six in C.squarrosaincluding fatty acids,alkanes,aldehydes,primary alcohols,alkyl esters andβ-amyrin.The relative content of secondary alcohols was the highest in L.chinensis while primary alcohols were highest in C.squarrosa,whereas alkanes were highest in S.krylovii.Steppe types significantly influenced total wax coverage and the relative abundance of alkyl esters in C.squarrosa,total wax coverage in S.krylovii,and the relative abundance of secondary alcohols andβ-diketones in L.chinensis.Grazing significantly influenced the relative abundance of fatty acids in C.squarrosa,total wax coverage and the relative abundance ofα-amyrin andβ-sitsterols in S.krylovii,and total wax coverage and the relative abundance of secondary alcohols in L.chinensis.The distribution of different chain length alkanes were relative stable,whereas those of primary alcohols,fatty acids and aldehydes varied greatly between steppe types and grazing management.It is suggested that different steppe plant species developed their own specific cuticular wax adaptive mechanisms during their evolution.Steppe plants may be able to adapt to changing environments through altering wax biosynthesis and deposition.