Effects Of N Deposition On Growth Of Schima Superba And Provenances Differences In Phosphorus-barren Soil

Schima superba is a representative and widely distributed and dominant evergreenbroadleaf tree species in the subtropical forests in southern China. The timber of this species istough, dense and glossy, which can be used for both architecture and furniture. S.superba isalso an important biological fire-resisting and ecological protection species. Nowadays, lowsoil P content in southern China is serious and the forest soil fertility recession has seriouslyaffected the productivity of plantation and management. So forest phosphorus efficiency hasbeen studied more. More recently, the rate of deposition of nitrogen (N) is high in subtropicalforests in southern China. The soil N increased and much more environment factors changedand improved the plant growth. However, the changes of plant growth, root growth, leafphotosynthetic and phosphrous efficiency of S.superba under different N-deposition andP-limitation conditions have not been documented. The factorial design of the experimentincluded S.superba seedlings of eight provenances of different producting areas and and levelsof N addition using NH4NO3(0,50,100, and200kg N ha-1year-1). The results may reveal themechanisms of plant growth, biomass, root growth, phosphrouse absorpt and photosyntheticunder N deposition. It may reflect the difference in response to N and P among differentprovenances. The objectives of this study were to provide insight for selecting and breeding offavorite genotypes with higher P efficiency. The main results obtained from experiments are asfollows:1. Effects of simulated N deposition on the soil pH, N and P availabilityThe N dposition could cause the soil acidification. The effect of soil acidification wasmore significant on low P soil than in high P soil. The soil pH decreased and the soilacidification increased as the increasing of the N dposition content and treatment time. In theinitial stage of N dposition, the available P decreased as the strengtherning of plant absorptionand the chelation of iron and aluminum ion with available phosphorus. Then the available phosphorus reduced slowly with N addition, which is related to the transformation of the fixedP as the aggravating of the soil acidfication and the plant growth restriction. The content ofhydrolyzable nitrogen in soil increased with increasing of N concentration and treatment time.The accumulation effect of the N deposition on soil N may in crease the forest productivity, buton the other hand, it may increase the potential of the loss of soil available N.2. Effects of simulated N deposition on plant root morphological characteristic and rootexudation in S.superbaThe effects of elevated N deposition on root morphological characteristic, organic acidcontent and Apase activity in root exudation were studied by carrying out a pot experimentwith conditions of P deficiency and normal P suplly. The results showed that root growth,density, biomass and spatial distribution of S. superba were increased with N addition, but highconcentrations of N deposition would do harm on root. In the early time, the root apicalmeristem formation is inhibited, the root become thicken under P deficiency. It was discoveredthat N addition also significantly improved root hair development and elogation. The organicacid and Apase content were higher in P deficienvy than in normal P. Meanwhile, the Ndeposition had a promoting role on secretion of organic acids. Among the organic acid, theamount of acetic acid accounted for more than50%, and followed by malic acid. The oganicacid content was increased under50N deposition, but inhibited under100or200treatment.The acetic acid and malic acid were sharp increased with the treatment time and seedlings age,and there were another two new compositions, which was tartaric acid and malonic acid,involved in the activation of fixed soil P. Oxalic acid as a constant and a large number ofsecondary metabolites acid presented in the root exudates, and played a role to improve theeffectiveness of the rhizosphere P.3. Effects of simulated N deposition on photosynthetic character, leaf solube protein andApase activity in S.superbaThe synthesis and activity of plant chlorophyⅡ, soluble protein and photosyntheticenzymes are directly effected by N, so N addition have an impact on plant photosynthesis. Inthis study, the photosynthetic light response curve, leaf pigments and soluble protein contents were determined and further reveal the mechanism of N deposition impact on plant growth,root morphology and nutrient absorption. The results showed that N addition increased the leafphotosynthesis and maximum net photosynthetic rate (Pmax), but reduced the material andenergy consumption, so the products were easier accumulated and the plant was easy to growthin the barren environment. However, when the N concentration was higher and the treatmenttime was longer, the leaf photosynthesis was reduced and material and energy consumptionwere increased, and the adaptability to low light conditions was reduced. N depositionincreased in leaf pigments contents and capacity of leaves light-harvesting, so it was beneficialto photosynthesis. But the carotenoid and solube protein content were reduced, the activity ofApase was decreased and MDA content reduced ether. N deposition had a certain effect onoxidative damage, but high concentrations of N deposition inhibited the plant chlorophyⅡcontent. The leaf solube protein content and activity of Apase were reduced significantly underlonger N deposition, and so as to the totle chlorophy content and chlorophy a/b. whencompaired with the comparison in longer time treatment, the totle chlorophy content andchlorophy a/b were increased, that means S.superba could increas the chlorophy a/b ratio tocompensate the photosynthesis decreased, thereby imroving the resistance.4. Effects of simulated N deposition on the plant growth and nutrients content inS.superbaThe effects of NH4NO3evevated from0to200kg N ha-1year-1on plant growth, biomassand N or P content in different organ were studied by carrying out a pot experiment withconditions of P deficiency (5.49mg·kg-1) and normal P suplly (60mg·kg-1). The resultsshowed that N addition had a positive effect on the growth of shoot and root of seedlings of S.superba no matter P was deficient or not. Early on, plant height, SBD, shoot biomass and totlebiomass were the highest among specimens subjected to N50treatment, but a decreasing trendwas observed when N treatment was increased to N200levels. The shoot growth was found tobe more sensitive to added N than root growth was under P deficiency. Roots showed a delayedresponse to N addition, and their growth and PUE increased at higher levels of added N. The N and C content and NAE were increased with N addition, while P content and PAE had nochange. The PAE and NAE were positively correlated with plant growth, dry matteraccumulation, and effective elements absorbtion could increase plant growth and biomass andfurther increasing of C reserves. The PUE was increased with N addition, but no increasingunder higher N concentration. However, NUE was decreased with N addition and treatment oftime. In the early time, RAR of S.superba was decreased under P deficiency; however, it wasincreased with the treatment time and seedlings age. The PAE, leaf P content and PUE of rootwere increased also, which means aged seedlings enhanced ability to adapt to the evilenvironment and increased the anti-barren capacity.5. Effects of simulated N deposition on growth and development of different provenancesof S.superbaUnder N deposition, the growth of different provenances was showed as:ZJLQ>FJJO>FJGT>HNGY>JXXF and ZJHZ. The ZJHZ provenance in the northern edge ofthe producing areas had stronger photosysthetic capacity. The shoot growth was increasedunder low concentration of N deposition and the leaf pigment and solube protein contentincreased. But the assimilation was not easy to accumulate and the root growth was slow. Thephotosynthesis of ZJHZ provenance was reduced under higher N concentration. The respirationcontinued increasing and shoot growth was reduced, whereas root was rapid developed. TheZJLQ and FJJO provenances in the central and southern central areas had strongerphotosynthetic ability and lower respiratory consumption, so the assimilation was easier toaccumulate and more adaptive to N deposition. Under low concentration N deposition,the>0.5mm diameter root growth was growth fast and root had stronger development. Thephotosynthetic ability was increased with N addition. The aboveground grown strongly andhad largest productivity under100N deposition, while the respiration was largest, so thebiomass could not accumulated and the production was lowest under200N deposition. Theaboveground growth of FJGT, JXXF and HNGY from southern sub-centers producing areashad similar performance as ZJHZ, such as lower photosynthetic capacity, moderate respirationand lower biomass accumulation. The root growth of these provenances was slow and even inhibited under N deposition. In addition, the provenances in the high altitudes had a developedroot system but a poor shoot growth because of the barren site and low temperatures in thatareas. N addition promoted root growth of these provenances and changed the root intothinning. The provenances in the low-altitude had better site environment, which has amplewater and fertilizer and suitable temperature. The suitable environment resulted in lessdeveloped root system and vigorous shoot growth. The root turn to be thicker and strongerunder N deposition and N and P absoption efficiency increased, so there was more dry matteraccumulated.