Study On Seed Production Techniquues Of Tibetan Wild Elymus Nutans In Lhasa Valley

Nematodes are widely found in soils and are an important component of ecosystems.Soil nematodes are often used as indicator organisms to describe soil health^[1]and also to reflect the state of soil food webs due to the rich endogenous information of soil nematode communities^[2].In this experiment,we investigated the changes of soil nematode community structure and subsurface food web in barley farmland due to different varieties of barley,using soil nematodes as indicator organisms and starting from the nematode system,in order to investigate the effects of different varieties of barley on soil nematode diversity and soil food web structure and function in farmland at high altitude.At present,there are few studies on the food web of barley farmland,and only sporadic studies on soil nematode communities in Tibetan barley fields in China have been reported in Mirei Township,Linzhi City and Linzhou County^[3].The sample site set up in this experiment was located in the student practice base farm of Tibet Agricultural and Animal Husbandry College in Bayi District,Linzhi City,Tibet,and nine barley species were used as the research objects.Soil samples were collected during the growth period of winter barley,and after sampling,nematodes in the soil of different barley species were identified,the physical and chemical properties of the soil were tested,and the effects of different barley species on soil nematode biodiversity and the structure and function of the subsurface food web were analyzed.The experimental results were as follows.（1）From barley fields of nine varieties,a total of 1804 soil nematodes were caught,at a density between 278 and 634k D100g-1,and a mean of 436nematode-100g-1 in dry soil,belonging to 41 genera belonging to 2 classes,6orders and 25 families in the phylum Nematoda.（2）Because of the close geographical position,the same tillage and fertilization methods,and the small difference in average annual temperature and annual precipitation between different types of barley,the Heterodera and Merlini are the dominant genera in the field of barley.（3）The soil nematode communities of different varieties varied from species to species,and the more abundant the species,the higher the evenness and diversity of soil nematodes were,and the most diversity was in Holly 19.（4）Soil nematodes of different varieties of barley were mainly phytophagous,and cp2 was the dominant one among them,and the strategy was dominated by r-measures.（5）The soil health of Holly 19 and Holly 16 was the best,while that of Holly 18 was the worst.（6）Holly 8 has been subjected to more outside disturbance and higher stability.（7）The results indicated that Holly 18（CK）and Holly 1 were superior in soil nutrition,N concentration,C/N ratio,high disturbance of food web structure,dominant bacteria degradation,and instability of food web.The other barley varieties have good soil nutrition,rich N,low C/N ratio,low to moderate disturbance of soil,balanced growth of bacteria and fungi,and stable food web.This suggests that planting different barley varieties contributes to stable maturation of the food web.（8）The composition of PWN in barley field was mainly affected by the rapid action of P,TN and PH.Changes in the physical and chemical properties of Changesin can directly or indirectly affect the growth of the barleygrowth and the activity of PWN through changing the composition of soil nematode.