Leaf Functional Traits And Ecological Stoichiometry Characteristics Of Rhododendron Spccies Along An Eelevation Gradient

The basic traits and functional characteristics of plant individuals reflected their adaptation strategies to the environment during its long evolutionary process.Leaf was the most sensitive vegetative organs of plants to environmental change during evolution.The elevation gradient contained a variety of environmental factors such as temperature,humidity,light intensity and so on in a small range,which provided an unique and idear opportunities to study plant response and adapt to environmental changes.Studies on the variation of leaf traits and their interrelationships at local scales across an elevation gradient could help us to further understand the adaptation mechanism of plants in responsing to environmental changes.Thus,we investigated 8 leaf functional traits and 6 stoichiometric characteristics of 6 Rhododendron species(such as Rhododendron rex subsp.rex,Rhododendron lacteum,Rhododendron rubiginosum,Rhododendron pubicostatum,Rhododendron sikangense var.exquisitum,Rhododendron sphaeroblastum var.wumengense)along an altitudinal gradient in Jiaozi Mountain,Yunnan Province.In adition,the relationship between leaf traits and soil nutrients,and the economic spectrum of Rhododendron species were also determined.The present study will provide scientific basis for exploring the adaptation strategy of Rhododendron to elevation gradients and climate change.The main findings and results were showed as follow:They are no significant correlationship between leaf functional traits and elevations of 6 Rhododendron species in Jiaozi Mountain,Yunnan province.However,it was significantly correlated with each leaf functional trait at the species level(p<0.01).The variance analysis showed that there were significant differences among the studied 8 leaf functional traits in each speceis.Specially,Rhododendron rex had larger LDMC,LMA and lesser SLA,and the content of leaf LTN,LTP were lower than that in others.Rhododendron rubiginosum had lesser LA,LDMC,LMA and larger SLA,and the content of leaf LTN,LTP were higher than that in others.In addition,there was a significant negative correlation between Lth and SLA,and positive correlated with LMA(p<0.05)regardless of at the elevation or species levels.Leaf SLA was negatively correlated with LDMC and LMA(p<0.05);Leaf LDMC was significant positively correlated with LMA(p<0.05).The contents of LOC,LTN and LTP of 6 Rhododendron species had no significant difference at different elevations in Jiaozi Mountain of Yunnan Province.There wes a extrelemy significant positive correlation between LTN and LTP(p<0.01),and a extrelemy significant negative correlation between LTP and N:P(p<0.01)of 6 Rhododendron species.The mean values of leaf LTN was 13.78g/kg,which was lower than the global and national average content of LTN in plant leaves.The mean values of leaf LTP was 1.27g/kg,which was also lower than that in the whole world,but slightly higher than that in the whole country.The average ratio of leaf of N:P was 11.08,which was less than 14,observably.It indicated that the growth of Rhododendron in Jiaozi Mountain was mainly restricted by N element.The STN and STP contents in soil of 6 Rhododendron species first increased and then decreased with elevation increasing.The mean values of STN(1.19g/kg)and STP(0.17g/kg)in soil were significantly lower than that of 0?10 cm soil in China.The average value of soil N:P was 7,which was remarkably higher than that of it in China.Base on the above analysis,we may conclude that the major soil factors affecting leaf traits were pH,SOM,STP and STN.In summary,our present study comfired that the leaf characteristics of 6 Rhododendron species were distributed with a spectrum of leaf functional traits.Among them,the position of Rhododendron rex subsp.rex in the leaf economic spectrum was closed to the end of slow investment-return,with the leaf was thicker,greater,larger LMA and lower in leaf LTN and LTP contents.However,the position of Rhododendron rubiginosum in the leaf economic spectrum was closed to the end of quick investment-return,with the leaf was thinner,smaller,littler LMA and higher in leaf LTN and LTP contents.