| The stability of artificial sand-fixing vegetation in desert areas is of great importance in consolidating the effectiveness of desertification control and ensuring regional ecological security.To further investigate the ecological mechanisms that limit the stability of artificial sand-fixing vegetation,this study systematically examined the seed ecological process of C.korshinskii in the sand-fixing forest belt at the southeast edge of Tengger Desert.This included studying key factors that restrict the natural regeneration of the population,such as seed production(seed rain),diffusion,feeding,and sand burial(germination)Field research was conducted in Shapotou National Nature Reserve from May to November 2022.Seeds were collected from isolated trees of C.korshinskii,covering 75-100%(N1),50-75%(N2),30-50%(N3),and 0-30%(N4)of crust and bare sand(Bs).Field simulation experiments were conducted to study the processes of seed production(seed rain),diffusion,feeding,and sand burial(germination).The results indicate that:(1)The seed rain dispersal of C.korshinskii population in the southeast edge of Tengger Desert mainly includes seed maturity stage and seed falling stage.The seed rain exhibited a single peak curve,with June 15th as the double peak of seed rain quantity and seed vitality,accounting for approximately 67.79%of the total seed count,with a vitality value of about 60%.A total of 4578 seeds were collected from all sample plots,with plump seeds accounted for 73.41%of the total,incomplete seeds accounted for only 2.23%,and rotten and damaged seeds accounted for 1/4 of the total.The average density of seed rain at different stages is as follows:at the early stage of seed drop>at the middle stage of seed drop>at the late stage of seed drop>at the mature stage of seed.Similarly,the morphological indicators(seed length,seed width,and thousand seed weight)were highest at the early stage of seed drop.(2)After simulating through field wind tunnel experiments,the proportion of seeds remaining in situ accounted for 51.72%of the total,while the seeds spread in close range accounted for 39.16%,seeds spread in long distance accounted for 5.64%,and seeds buried in sand accounted for 3.48%.As crust coverage increased,the distance of seed dispersal gradually increased,and the likelihood of seeds being buried gradually decreased.When the crust coverage was between 75%and 100%,the probability of long-distance seed dispersal was the highest at 45.56%,with lowest probability of seed resistance to long-distance dispersal,and no probability of seed burial.When the crust coverage was between 50%and 75%,the highest probability of non long-distance dispersal was 73.33%.When the crust coverage was between 30%and 50%,the highest probability of seed resistance to long-distance dispersal was 62.22%.The probability of seeds being buried increased when the crust coverage was between 0 and 30%.The minimum probability of long-distance dispersal in bare sand was 5%.(3)As the wind speed increased,the horizontal dispersal distance of seeds increased,and smaller seeds tended to disperse farther,making secondary wind dispersal more likely to occur.When the wind speed was higher than 13.6 ms-1,sand cover was generated on the low crust coverage sample land,and buried seeds were transported again.After fitting the seed dispersal rate with distance,the best fitting effect was observed between the medium seed dispersal rate and distance,described by a model of-1.660x+0.182x2-0.002x3+4.084.(4)Through camera observation experiments,it was found that 64.87%of surface seeds were eaten by rodents on site,with rats accounting for 97.02%and rabbits only accounting for 2.98%.The remaining 34.53%of seeds were dispersed by wind,while only 0.6%remained on the surface due to the high coverage of litter in the sample plots.The final feeding rates in various plots were as follows:N1:66.33%,N2:51.33%,N3:86.00%,N4:97.67%,and Bs:23.00%.The number of seeds eaten in low coverage plots was greater than that in high coverage plots.In bare sand plots,the majority of seeds were dispersed or buried by wind,with the highest diffusion rate reaching 78%.The peak time period for seeds to be eaten was from 01:00 to 02:00.(5)According to the sand burial test,the optimal sand burial depth for C.korshinskii seed germination was 5-10 cm,while the optimal sand burial depth for seedling growth was 0-2cm.The highest rates of seed decay and retention were observed at a soil depth of 2-5cm.In high coverage plots,the germination rate,decay rate,and retention rate of C.korshinskii were higher compared to those in low coverage plots,whereas the seedling and loss rates were higher in low coverage plots compared to high coverage plots.In summary,there were usually three types of mechanisms for population renewal obstacles:source limitation,diffusion limitation,and habitat limitation.Research on the complete seed ecological process of C.korshinskii,from seed production to successful seedling establishment,showed that there was no source limitation in its natural regeneration,and it was mainly controlled by diffusion and habitat limitation.The key factors that limited the natural regeneration of C.korshinskii included insufficient long-distance diffusion ability,high animal feeding rate,concentrated and high loss rate of seed rain,and underlying surface conditions(crust coverage).In other words,the artificial C.korshinskii population in the sand-fixing forest belt in the southeast of Tengger Desert faced significant obstacles to natural regeneration. |
