桂西北喀斯特地区退化群落灌草不同器官N、P生态化学计量内稳性特征

Nitrogen and phosphorus stoichiometric homoeostasis in different organs of shrubs and herbs in degraded vegetation communities in the karst area of northwestern Guangxi

植物的生态化学计量内稳性特征是长期适应环境的结果,与其生态适应性策略有关。探明喀斯特退化群落灌草不同器官N、P元素的化学计量特征及其内稳性特征,为喀斯特地区植被群落退化过程中植物的适应策略研究提供依据,基于桂西北喀斯特地区5种退化程度植被群落的调查取样,测定不同退化群落灌木(叶、茎和根)和草本(地上部分和地下部分)N、P含量,分析其化学计量特征、不同器官间的相互关系及其与土壤理化性质的相关性以及内稳性特征。结果表明:(1)灌木不同器官P含量表现为叶>茎>根,N含量和N∶P表现为叶>根>茎,草本P、N含量及N∶P均为地上部分>地下部分;随退化程度加剧,灌木各器官和草本地下部分的N、P含量及灌木根N∶P均呈降低变化趋势,草本地上部分的N、P含量在前四个退化阶段为降低趋势,在Ⅴ阶段有所升高,草本地下部分N∶P则呈现先升高后降低趋势,其他N∶P无显著性变化;灌草叶片N∶P均小于14;(2)N和P含量在各器官中均呈显著正相关关系;灌草的不同器官之间的同一营养元素及元素比,以及灌木和草本之间的各器官的同一营养元素及元素比均呈正相关关系;(3)灌草各器官N、P含量、N∶P与土壤TN、TP、N∶P存在显著的正相关关系,灌草各器官P含量与土壤C∶P显著负相关;(4)灌木各器官H_(N)、Hp和H_(N∶P)均表现为叶>茎>根,草本地上部分的H_(N)大于地下部分,Hp和H_(N∶P)则反之;灌草同种器官不同元素之间则表现为N>P>N∶P。喀斯特地区退化群落中灌木较草本具有更高的内稳性,灌草生长主要受N限制,且N元素表现较高的内稳性;灌草各器官在植被群落退化过程中对N、P含量变化的响应具有一致性和协同性。

Characteristics of plant ecological stoichiometry homeostasis are the result of long-term adaptation to the environment and are related to their ecological adaptation strategies.Nitrogen(N)and phosphorus(P)stoichiometric homoeostasis in different organs of shrubs and grasses in the degraded vegetation communities were studied to provide scientific basis for adaptation strategies of plants in the process of vegetation community degradation in the karst area of northwestern Guangxi.Based on the investigation and sampling of five degraded vegetation communities in the karst area of northwestern Guangxi,the N and P contents of shrubs(leaves,stems,and roots)and herbs(aboveground and underground parts)in different degraded communities were determined.The stoichiometric characteristics,interrelationships between different organs,correlations with soil physicochemical properties,and homoeostasis characteristics were analyzed.The P contents in different organs of shrubs showed a trend:leaf>stem>root,while the N content and N:P showed a trend:leaf>root>stem.The P,N content and N:P of herbs all showed a trend:aboveground>underground parts.With the intensified degradation of the vegetation community,the N and P contents of various organs of shrubs and underground parts of herbs,the N:P content of shrub roots showed a decreasing trend;the N and P contents in aboveground parts of herbs showed a decreasing trend in the first four degradation stages,and increased in the fifth stage;the N:P content of underground parts of herbs showed a trend of increase firstly and then significantly increased.While there was no significant change in N∶P in other organs.N∶P of plant leaves was less than 14 in shrubs and herbs.N and P showed significantly positive correlation in all organs;There were positive correlation between the same nutrient element and element ratio among different organs,as well as between shrubs and herbs.N,P and N:P in different organs of shrubs and herbs were significantly positively correlated with soil N,P and N:P.P content in various organs of shrubs and herbs were significantly negatively correlated with soil C:P.The H_(N)、Hp and H_(N∶P) of various organs in shrubs showed a trend:leaf>stem>root.The H_(N) of aboveground parts of herbs was greater than that of the underground part,while the Hp and H_(N∶P) were opposite.The homoeostasis of different elements in the same organ of shrubs and herbs showed H_(N)>Hp>H_(N∶P).The growth of shrubs and herbs in karst area was mainly limited by N,and N element had the highest homeostasis.The responses of different organs of shrubs and herbs to changes in N and P content during vegetation community degradation were homogeneity and cooperativity.