Study On The Effects Of Different Environmental Factors On Morphology And Physiology Of Acer Catalpifolium,an Endangered Species In The Rainy Zone Of West China

Acer catalpifolium Rehd.,belongs to Sapindaceae family and Acer genus,is a perennial deciduous broad-leaved tree species,mainly distributed in the Rainy Zone of West China(RZWC)located in the northwest edge of Chengdu plain,Sichuan province.It has been listed in the second class protection plant of China,after reevaluation,National Forestry and Grassland administration has recognized it as a“critically endangered wild plants with extremely small population”(WPESP)due to the narrow natural distribution and a small population in the wild.The special climatic and geographical conditions of the natural distribution area of A.catalpifolium and the impact of global climate change,drived the frequent occurrence of acid rain and accompanied by a high level of nitrogen deposition in this region,at the same time,the composition of subforest environmental factors(such as light and water)have became complex in this region due to human activities.The impact of severe environmental and climate changes on the growth of A.catalpifolium remains unclear.In view of this,this study was firstly conducted an investigation of the population structure and community characteristics of A.catalpifolium,analyzed potential impact factors to A.catalpifolium population,and then,a seirs of controlled experiments were established to simulate environmental changes(different soil moisture and light conditions,acid rain and nitrogen deposition)and observe the morphological and physiological changes of A.catalpifolium(an endangered plant in the RZWC).After integrated the field investigation and simulation experiments,an wild reintroduction study was conducted to determined suitable light environment and fertilization procedures based on the morphology and physiological of A.catalpifolium.At the end,the plant nitrogen and phosphorus stoichiometric measure was adopted to analyze nutrients limitation of natural distributed A.catalpifolium and responses of foliar N and P concentration to different environemtal factors and habitat conditions changes.The main results of this paper are as follows:Investigation of the original habitat community of A.catalpifolium.A.catalpifolium mainly distributed in evergreen broad-leaved and deciduous broad-leaved mixed forest,the tree layer,shrub layer and herb layer of different communities accompanied with 52,74 and 52 plant species respectively.As for abundance distribution proportion of A.catalpifolium,Boresi(BRS)site(For.Acer catalpifolium-Camellia szechuanensis)had largest distribution,followed by Fuhusi(FHS)(For.Phoebe zhennan-Eurya nitida),Zhangshancun(ZSC)(For.Cryptomeria fortunei-Oreocnide frutescens),Baoguosi(BGS)(For.Cupressus funebris-Phoebe zhennan)and Caishenmiao(CSM)site(For.Cunninghamia lanceolata-Machilus pingii).For the aspect of communities characteristics,the species diversity indices in FHS,BRS,BGS and CSM sites were greater than that of ZSC site.The investigation of population age structure of A.catalpifolium revealed the gap in the distribution of seedling and young trees level.In the original habitat community of A.catalpifolium,the dominant species in different communities occupy more environmental resources,such as the dominant species in the plot of CSM is Cunninghamia lanceolata and Bothrocaryum controversum,in the plot of ZSC is Cryptomeria fortune and Pterocarya stenoptera.It was found that there were few seedlings and young trees,the population structure is an inverted pyramid and it is difficult to regenerate in the natural state.The investigation of the original habitat community of A.catalpifolium provides some basic data for the simulation experiment and the selection of field habitat.Simulation experiments:The experimental results of water light interaction showed that drought and shade had significant negative effects on plant growth,biomass accumulation,and physiological functions.Lowering specific leaf areas(SLA),increasing root biomass allocation,and pigment content were the main strategies for enhancing water and light capturing abilities to acclimate to the limited ambient resources.75%soil water holding capacity and moderate shade had benefits for the growth of two species.The results of simulating acid rain precipitation(different addition modes(soil addition and foliar spraying,forms(H₂SO₄:HNO₃ ratio of 7.5:1(SDAR)or 5:4.1(NBAR)and different acidity levels(p H2.5,p H3.5 and p H4.5))showed that,acid rain promoted the growth of A.catalpifolium under soil addition mode,and plant height and biomass increased with the decrease of acid rain p H,NBAR had greater enhancement compared to SDAR,acid rain also improved foliar gas exchange abilities,maximum Pn(in light and CO₂ saturated condition),potential photochemical efficiency of photosystem II(Fv/F0),electron transport rates(ETR);the performance of growth and physiological functions under foliar spraying mode showed opposite trends.The results of adding different amounts of ammonium nitrate(NH₄NO₃)to the soil to simulate different scenarios of nitrogen deposition,for instance the original habitat and the possible nitrogen deposition in the future(N3:30 kg N ha^-1 yr^-1?N6:60 kg N ha^-1 yr^-1?N10:100 kg N ha^-1 yr^-1?N15:150 kg N ha^-1 yr^-1 and N20:200 kg N ha^-1 yr^-1),results showed that,the plant height,ground diameter,leaf area and SLA of A.catalpifolium was enhanced after recieving a proper amounts of nitrogen deposition,however,higher N deposition show little improvement or even inhibition of plant growth,root to shoot ratio and apparent N revovery rate was decreased with increasing of N addition,the N saturated threshold for biomass is around 95.13 to 96.56kg N ha^-1.In the physiologically speaking,appropriate nitrogen deposition significantly increase the net photosynthetic rate,maximum Pn,photochemical efficiency of photosystem II,photosynthetic pigment and polyphenolic index of A.catalpifolium.Field habitat selection of A.catalpifolium:Under four of light environment,no shading,forest edge,forest gap and understory of the forest(canopy density from low to high),with increase of canopy density the base diameter,crown width and number of new branches were increased at first and the dereased;The maximum single leaf area and single leaf mass were found in the forest margin habitat,and the specific leaf area increased with the increase of canopy density;With the increasing of canopy density,intercellular CO₂ concentration,transpiration rate and stomatal conductance of A.catalpifolium showed a trend of first decrease and then increase,flavonoid index showed oppsite trend,and chlorophyll content showed an upward trend with incrase of shade.Different soil fertilization measures(including chemical fertilizer and organic substances application)have benefits to improve plant height,base diameter leaf length and width;CK has longest petiole and phosphorus fertilizer and peat soil treatments observed greatest single leaf weight.In terms of physiological characteristics,soil fertilization measures can promote the photosynthesis of A.catalpifolium(net photosynthetic rate,chlorophyll fluorescence parameters,etc),content of photosynthetic pigment and the increase of flavonoids parameters,but it has no significant effect on anthocyanin parameters.Stoichiometric characteristics of A.catalpifolium:The wild population of Acer catalpifolium showed leaf nitrogen concentration(LNC)of 14.49?25.44 mg g^-1,leaf phosphorus concentration(LPC)of 1.29?3.81 mg g^-1,leaf N/P(L-N:P)of 4.87?13.93 which indicate general nitrogen limitation,and the L-N/P was mainly affected by soil available N and P;LNC and LPC of A.catalpifolium were both higher under L1 light condition,L-N/P is higher under L3W3 treatment;LNC and LPC of Acer catalpifolium were the highest under nitrogen deposition level of N10,and L-N/P was higher under N20;There was no significant difference in LNC between foliar applied acid treatments and CK,and LPC under soil applied high acidity(NS2.5 and SS2.5)treatments were significantly higher than that those in foliar application and CK;Under different canopy density,higher LNC and lower LPC were observed in the understory habitat,L-N/P was higher in gap and understory of forest;LNC of Acer catalpifolium increased significantly in nitrogen fertilizer treatment,while substrate and fertilizer treatments had less effect on LPC of A.catalpifolium,and L-N/P was lower in phosphate fertilizer treatment compared to others.To sum up,the current situation of A.catalpifolium in the field is mainly characterized by the scarcity of seedling and young tree age populations.According to the characteristics of simulated experiments(according to the environmental features of RZWC),moderate shading and water supply are beneficial to the growth of A.catalpifolium seedling.Leaf spraying with acid rain inhibited its growth,nitric acid balanced acid rain was more harmful to A.catalpifolium than sulfuric acid dominant acid rain,and soil treatment showed the opposite trend.Under a certain nitrogen deposition level,the growth and nitrogen addition of A.catalpifolium showed a linear response,exceeding the threshold,and the synergizing effect of N addition stopped or even appeared inhibition of growth.In the process of habitat selection,the growth of young trees was significantly promoted by the application of phosphorus fertilizer,nitrogen and phosphorus fertilizer and earthworm manure.In this study,the suitable conditions of wild habitats of A.catalpifolium were identified,which provided theoretical and practical basis for the protection and population rejuvenation of endemic endangered species in the region.