Study On Seed Dispersal Characteristics Of The Poisonous Weed Of Achnatherum Inebrians In Grassland

Seed dispersal affects the population structure of the mother plant and its offspring by affecting the seed density and the distance between the seed and the mother plant on the spatial scale.It determines the regeneration and development of a population or community.Achnatherum inebrians is one of the main poisonous plants in the natural grassland of northern China.At present,it is expanding in desert,grassland and meadow grassland.Once invaded,it can quickly occupy an absolute advantage in the community.In order to provide theoretical and technical support for the expansion mechanism and prevention and control of A.inebrians seeds,the response of A.inebrians seeds to three different diffusion pathways of wind,water and animals was studied.The main results are as follows:（1）The results showed that the settling velocity of the awned seeds was significantly lower than that of the no-awned seeds under the wind dispersal pathway（p<0.05）;the horizontal moving distance of the seeds increased with the increase of wind speed,and awned had no effect on the horizontal moving distance.Under the action of natural wind,the dispersal distance of high,middle and short plants was 0-220cm;the secondary dispersal distance of seeds was 0-18cm.Among the three plants,the fitting effect of seed drop rate and distance was the best,and the model is:y _middle=0.00288+0.0065x-0.00004246x²+0.000000062284x³.Therefore,the attachment awned and high wind speed all enhanced the wind dispersal of A.inebrians seeds,and A.inebrians seeds belong to short-range dispersal in wind dispersal.（2）Under the water medium dispersal pathway,the water absorption rate of the seeds showed two stages of rapid and slow water absorption,rapid water absorption in the first two hours and saturation in the 32h.The germination rate of seeds soaked in water for 1 day and 2 days was the highest,reaching more than 70%,while the germination rate decreased significantly after soaking for 4 days and 8 days（p<0.05）.The germination rate of awned seeds soaked in water for 8 days was significantly higher than that of no-awned seeds（p<0.05）.The floating rate of seeds kept above 70%after floating for 168h at low speed of 0 and25r/min,and decreased to 10%after floating for 2h at high speed of 50 and 100 r/min.the floating rate of seeds continued to decrease when floating in the river,and reached 13%after 168h.The floating rate of no-awned seeds was significantly higher than that of awned seeds in low speed and river（p<0.05）.Under the effect of natural rainfall,the first dispersal distance and the number of seeds dropped increased with the increase of plant height.The dispersal distance of high and middle plants was 0-220cm,and the second dispersal distance of seeds was 0-12cm.Among the three kinds of plants,the fitting effect of seed drop rate and distance of high plant is the best,and the model is y _high=0.0116+0.0056x-0.00002353x².Therefore,the rapid water absorption can increase the weight of seeds and the degree of adhesion to the soil,thus reducing the secondary dispersal.The slow water loss of seeds can keep the vigor of seeds;but the long-time soaking can reduce the vigor of seeds;the attachment awned inhibits the water dispersal distance of seeds.Under the action of river,seeds spread in a long distance,but under natural rainfall,seeds spread in a short distance.（3）Under the path of animal dispersal,the number of attached seeds of horse,cattle and sheep fur reached 71.59,240.48 and 386.29 respectively after walking 3km in the community,and the attachment rate of seeds was sheep>cattle>horse（p<0.05）,while the seed drop rate was sheep<cattle<horse（p<0.05）after walking 05 h.with the delay of walking days,the attachment rate of seeds on horse,cattle and sheep fur showed a downward trend,and the 10th day after walking,the attachment rate of seeds on horse,cattle and sheep fur decreased,compared with the highest adhesion rate,the adhesion rate of the composite decreased by 72.03%,81.26%and 76.11%respectively.The results show that the back of a horse is the easiest to attach seeds,and the back and side parts of cattle and sheep are easy to attach seeds;After attaching seeds,there is no significant difference in the seed drop rate of the side and abdomen of livestock;The side part of the seed is most easily attached to the fur,and the seed attached to the top of the seed is the least easy to fall.Within 24 hours,the spread range of rodents and ants to seeds was 0-15cm and 0-40cm respectively.Therefore,livestock play a long-distance dispersal role on the seeds of A.inebrians,and sheep are easier to increase the dispersal intensity of seeds than horses and cattle.Ants and rats conduct short-distance dispersal on the seeds of A.inebrians.