Ecological Characteristics Of Seed Germination And Seedling Emergence Of Ten Desert Plant Species

China is one of the most serious countries which are damaged by desertification.Desertification has a great negatively impacts on ecological environment,but also has impeded economic development.Therefore,it is very necessary to restore degraded ecosystems in many desertification areas.The key step of the success of vegetation regeneration is whether the seeds can germinate and the seedlings can merge and establish.Many factors such as temperature,moisture and seed burail depth often affect process of vegetation regeneration.In this paper,the ten dominant species Ammopiptanthus mongolicus,Artemisia sphaerocephala,Astragalus adsurgens,Caragana intermedia,Caragana korshinskii,Cleistogenes songorica,Haloxylon ammodendron,Hedysarum fruticosum,Hedysarum scoparium and Sarcozygium xanthoxylon in the desert areas as experimental materials to study the effects of temperature,water level on seed germination in the laboratory.At the same time,we also conducted an irrigation times and seed burial depth experiment in sand to test the interactive effects of irrigation times and seed burial depth on seedling emergence and seedling establishments.Our aims are going to understand well the ecological characteristics of seed germination and emergence of different desert plants and provide scientific basis for the successful establishment of these species in desertification areas.The main research results are as follows:1.The thresholds of different species germination were different,according to the thermal time model proposed by Garcia-Huidobrod(1982).The optimum temperature(To)was 33.7 ? for C.songorica,and 28.3 ? for A.mongolicus and other species from 17.4 to 24.9 ?.The basic temperature is 0.3 ?for A.adsurgens,followed by H.ammodendron 1.9 ?,the other species between 6.7 and 15 ?.Maximum germination temperature of H.ammodendron was 45.3 ?,followed by C.songorica was 43.9?,and the other species was from 25.0 to 43.3 ?.The germination temperature range was 1.9~45.3 ? for H.ammodendron and 15~30.0 ? for S.xanthoxylon.2.According to the method of Cheng and Bradford(1990),studied germination time course of the response of ten species of desert to different temperatures at suboptimal temperature ranges.The seed germination reached the 100%,the order of the temperature time value of germination was: A.mongolicus(79 ?·d),H.ammodendron(94 ?·d),A.sphaerocephala(114 ?·d),H.fruticosum(127 ?·d),S.xanthoxylon(132 ?·d),H.scoparium(177 ?·d),A.adsurgens(18 ?·d),C.intermedia(217 ?·d),C.korshinskii(302 ?·d),C.songorica(334 ?·d).3.The responses of different species to drought stress were specific-species.The threshold of germination water potential in all species was-2.19 MPa for H.ammodendron and C.korshinskii,-1.55 MPa for C.intermedia and A.mongolicus-1.05 Mpa.The water potential threshold for germination of other species ranged from-1.77 to-1.54 MPa.The germination of A.mongolicus and A.sphaerocephala at-0.4 MPa increased by 13% and 5% compared with CK,respectively.There was a significant positive correlation between germination and osmotic potential(according to the water potential model proposed by Bradford(1990)).4.The irrigation times and sand burial depth had significant interaction effects on the emergence.The emergence of all species was the highest at 1 cm,but the number of suitable irrigation times varied from different species.Among them,the emergence of H.ammodendron,H.scoparium and C.songorica were more drought-resistant,and the emergence was the highest when irrigation was taken two times.A.mongolicus,A.sphaerocephala and A.adsurgens were the highest in irrigation 3 times,S.xanthoxylon and H.fruticosum were the highest in 4 times,C.korshinskii and C.intermedia had the highest water requirement,and the highest of emergence was 5 times.5.The suitable conditions for the establishment of A.mongolicus and C.intermedia were similar with the emergence.The other species were not completely consistent.A.sphaerocephala and C.songorica the seeding establishment were the highest when no irrigation,0 cm buried depth.H.ammodendron was highest at 1 time,sand burial 1 cm.C.korshinskii 3 times of irrigation,4 cm of sand burial depth.A.adsurgens,H.scoparium and S.xanthoxylon were the highest in irrigation 3 times and 1 cm in sand,while H.fruticosum was the highest in irrigation and 5 times sand burial 1 cm.