三峡库区消落带土壤水分变化对落羽杉（Taxodium distichum）幼苗根部次生代谢物质含量及根生物量的影响

模拟三峡库区消落带土壤淹水变化特征设置了常规生长水分条件(CK组,土壤含水量为田间持水量的60%～63%)、轻度干旱水分胁迫(T1组,土壤含水量为田间持水量的47%～50%)、土壤水饱和(T2组,土壤表面一直处于潮湿状态)以及水淹(T3组,苗木根部淹水超过土壤表面1cm)4个不同处理组,研究落羽杉当年实生幼苗根部次生代谢物质含量与生物量的变化(均以干重计)。研究表明,不同水分处理对落羽杉幼苗主根、侧根和根部苹果酸、莽草酸含量以及生物量的影响程度有所差异,其中以T3组受到的影响最为明显。主根苹果酸、莽草酸含量在整个试验期的总体平均值,T3组显著低于CK组,分别达28.0%和16.4%;相反侧根苹果酸、莽草酸总体平均含量T3组则极其显著地高于CK组分别达105.7%和152.6%,根部平均值T3组显著地高于CK组分别达32.7%和26.2%。与之形成鲜明对比,主根、侧根和根部苹果酸、莽草酸含量在整个试验期的总体平均值,T1、T2与CK组相互之间分别均无显著差异。各处理组之间主根生物量没有显著差异;与CK和T1组相比,T3组侧根生物量分别降低38.3%和40.8%,根部生物量分别降低31.9%和31.1%,但与T2组相比均未达到显著差异。主根苹果酸含量与根系各部分莽草酸含量和生物量之间均无显著相关性,相反侧根、根部的苹果酸与莽草酸含量以及二者与生物量相互间均表现出显著或极显著相关性。在三峡库区消落带土壤含水量变化条件下,落羽杉幼苗将充分利用侧根增强代谢适应调节能力,通过产生大量苹果酸和莽草酸、减少根部生物量积累适应根部水淹环境,通过维持与CK组同样水平的代谢和生长而适应轻度干旱与饱和水环境。

Influences of mimic soil water change on the contents of malic acid and shikimic acid and root-biomasses of Taxodium distichum seedlings in the hydro-fluctuation belt of the Three Gorges reservoir region

Four different kinds of water treatment were applied to examine the change of contents of malic acid and shikimic acid as well as its relationship with biomass,in the roots of Taxodium distichum seedlings(all data being calculated in dry weight) under mimic soil water change in the hydro-fluctuation belt of the Three Gorges Reservoir Region.The main purpose was to find the mechanism of the plant's metabolic adaptation to water level changes.The water treatments were 1) normal growth water condition(i.e.,CK with soil water content being 60%-63% of soil water field capacity),2) light drought water stress condition(i.e.,T1 with soil water content being 47%-50% of soil water field capacity),3) soil water saturation condition(i.e.,T2 with soil water content being saturated) and 4) soil submersion condition(i.e.,T3 with soil being submerged 1 cm).Different water treatments had different effects on the biomass as well as on the contents of malic acid and shikimic acid in the taproot,lateral root and the whole root of T.distichum seedlings,among which T3 had the most significant influence.The contents of malic acid and shikimic acid in the taproot of T3 during the entire experimental period were significantly decreased,by 28.0% and 16.4% respectively compared to CK.In contrast,being compared to CK,the contents of malic acid and shikimic acid in the lateral root of T3 were significantly increased,by 105.7% and 152.6%,respectively,which directly led to their significant increase by 32.7% and 26.2%,respectively,in the whole root of T3.However,the contents of either malic acid or shikimic acid did not significantly differ among T1,T2 and CK,respectively in the taproot,lateral root and the whole root.Throughout the overall experimentation,the biomass of taproot showed no significant difference between the four treatments,but the biomass of lateral root in T3 was significantly decreased by 38.3% and 40.8% as compared to that in CK and T1 respectively.Thus,a significant reduction of 31.9% and 31.1% was exhibited in the biomass of the whole root in T3 compared to CK and T1 respectively,whereas,there was no significant difference to that of T2.The content of malic acid in taproot was not significantly correlated with either the content of shikimic acid or the biomass of taproot,lateral root and the whole root.However,a significant correlation was found between contents of malic acid and shikimic acid in the lateral root and the whole root respectively,and that significant relationship was also displayed between the contents of malic acid and shikimic acid and biomass in the lateral root and the whole root respectively.Under circumstances of soil dynamic submergence in the hydro-fluctuation belt,T.distichum seedlings will take full advantage of the lateral root to develop abilities of metabolic adaptation,with a significant increase of contents of malic acid and shikimic acid as well as a reduction of root biomass to respond to the environment of submergence,in contrast to such responses of maintaining metabolism and growth at the same level of CK to the environment of light drought and water saturation.