Leaf Functional Traits And Stoichiomeyry Of Typical Plant Communities In Karst Areas,southern Yunnan Province

In southwestern China,the primary forest vegetation was strongly disturbed and degenerated into secondary shrub communities due to geological characteristics,climatic conditions and long-term human disturbance.In those karst areas,the soil layers are shallow,arid and barren,maintaining arid-based dis-climax community.In order to recover forest vegetation,promote the ecological function of plant communities,and increase economic income,massive plantations have been established in the last three decades.On the regional scale,plantation stands distributed in the mosaic patterns with the natural secondary shrub communities.Moreover,compared with the secondary shrub community,the plant compositions of communities,the physical and chemical properties of soils,and plant stoichiometry were also altered in plantations.As a part of National R&D Project(2016YFC0502501),we chose the natural secondary shrub community and three typical plantations(Pinus yunnanensis,Alnus japonica and Platycladus orientalis)as study object.In July 2017,sample plots were set up to conduct tree growth survey and collect the samples of soils and plants.Leaf functional traits(LL,LW,LLW,LA,and SLA),the concentrations of 13 elements(C,N,S,P,K,Ca,Mg,Na,Fe,Al,Cu,Zn,and Mn)in soils and plant leaves were investigated.We also measured the concentrations of soil available nutrients(NO3--N,NH4+-N,available P,Ca,Mg,Na,Fe,Cu,Zn and Mn concentrations).The stoichiometric traits were analyzed.The main results are as follows:Firstly,compared with shrub community,speices compositions of ground-vegetation in the plantation stands were substantly changed.For instant,among 20 plant species in the shrub communities,only 3,6 and 3 occurred in Yunnan pine,alder and cypress stands,respectively.Most of plant species under the canopy of plantation stands were shade tolerant with strong adaptability.Secondly,compared with the secondary shrub community,plantations slightly changed the soil chemical properties.Moreover,there were also significant differences among three plantations:1)Four communities belong to the neutral soil.The pH of the soil in cypress forest increased,and the soil in alder forest is slightly acidic.2)According to CDA,the total content and available nutrients of soil significantly distinguished the four communities.Among them,the total Fe,P,K and Mn,exchangeable Ca,Mg and NH4+-N concentrations in soil contributed the most to the difference.3)Soil stoichiometric straits varied across three plantation stands.For instant,soil fertility was significantly lower(total C,N,S,Na,and exchangeable Ca and NO3--N)in cypress stands,and C/N ratio was also significantly higher in this stand type.Higher available Na,Fe,Zn concentrations,C/K ratio and lower available Mg concentration were observed in Yunnan pine stands.Relative to other communities,soil NH4+-N was significantly higher,and the exchangeable Mg concentration and C/K ratio were significantly lower in alder stands.4)pH was correlated to the content and ratio of various elements,and the element conscentrations of soils showed more correlations in plantations compared with the shrub communities.Thirdly,there were significant differences in plant stoichiometric traits between shrub community and plantations.In particular,leaf N,P,S,K,Cu concentrations of undergrowth plants in plantation stands significantly higher compared with those in shrub communities,and leaf P and S concentrations of undergrowth plants were ranked as alder,cypress,Yunnan pine and shrub communities.Moreover,shrub plants showed P-limiting phenomenon.Finally,compared with shrub communities,leaf functional traits of undergrowth plants in plantation stands were significantly altered.For instance,undergrowth plants in plantation stands were significantly bigger leaf area,leaf length and specific area index.In addition,elemental concentrations of leaves,in particular,P were significantly correlated with leaf functional traits in these communities.Our results implied that when secondary shrub community were artificially modified in karst region,we should take the demand purpose,effect on soil biochemical properties,biodiversity conservation and vegetation landscape requirements,the climax into consideration.Furthermore,it is nessecery to choose suitable tree species and put forward the silvicultural management scheme as to get the optimal social,landscape and ecological benefits.