| Grassland is one of the most important renewable natural resources,providing a variety of ecosystem services for human survival and development.The quality of grassland management is not only related to the sustainable development of animal husbandry,but also related to the function of regional ecological environment.Grazing and mowing have a very important impact on grassland.Leymus chinensis,a dominant species of temperate arid and semi-arid regions,is the main source of food for animal grazing and animal barn feeding,and has important effect to the development of animal husbandry.Therefore,the study of the effect of grazing or mowing on growth of L.chinensis,has important significance for scientific management and utilization of grassland resources.The experiment set up a treatment group that reserved growing point of L.chinensis,and another treatment group that removed growing point of L.chinensis,and analyzed the yiled,quality,biomass allocation,nutrient allocation,and sustainability.The results are as follows:(1)When the growing point height of L.chinensis was 0 cm,2 cm,6 cm,10 cm and 14 cm,the height of L.chinensis was 18.3 cm,24.4 cm,31.0 cm,34.9 cm and 39.1cm,respectively.When the growing point height of L.chinensis was 0 cm,2 cm,6 cm,10 cm and 14 cm,the grazing stubble height was 4 cm,6 cm,10 cm,13.5 cm and 17cm,respectively.With the increase of growing point height and the prolongation of mowing year,the recovery times of L.chinensis decreased and the recovery period increased,but the regeneration performance of L.chinensis with the growing point reserved was better than that of L.chinensis with the growing point removed.When the growing point height of L.chinensis was 2 cm,the treatments with both growing point reserved and growing point removed recovered 4 times in 2020,but decreased to 2times and 3 times in 2021,respectively.In 2020 and 2021,when the growing point height of L.chinensis was 14 cm,the treatment with growing point removed only recovered one time each year,while the treatment with growing point reserved recovered 3 times and 2 times,respectively.(2)The accumulated yield of L.chinensis increased with the increase of the growing point height in both the treatments with growing point reserved and growing point removed.In treatment group with growing point removed in 2020,the accumulated yield of L.chinensis was RM/CK:258.0 g/m~2,RM/2:198.7 g/m~2,RM/6:189.3 g/m~2,RM/10:212.6 g/m~2,RM/14:256.2 g/m~2.In the treatment group with growth point reserved in 2020,the accumulated yield of L.chinensis was RS/CK:259.2g/m~2,RS/2:211.3 g/m~2,RS/6:224.4 g/m~2,RS/10:226.2 g/m~2,RS/14:247.4 g/m~2.Of all treatment in 2020,only the accumulated yield of RM/14 and RS/14 were not significant compared to CK.In 2021,the accumulated yiled of L.chinensis in both the treatment group with growing point reserved and growing point removed decreased to different degrees compared with that in 2020,and only the accumulated yield of RS/14showed no significant difference with CK.The CP content of L.chinensis in all treatments was large beween inter-annuals.CP content in 2020 in both treatment group with growing point reserved and treatment group with growing point removed increased with the increase of growth point height.Howerer,the variation was not obvious in 2021.Of all the treatments,the CP content of L.chinensis in growing point of 2 cm and 6 cm declined obviously between interannuals,the CP content of RM/2and RM/6 decreased by 30%and 25.6%,respectively,and that of RS/2 and RS/6decreased by 28.4%and 30.3%,respectively.In terms of CP yield,the CP yield of the treatments with the growing point of 2 cm and 6 cm decreased obviously within two years,while the CP yield of the treatments with the growing point of 14 cm remained stable from year to year.The NDF and ADF contents of L.chinensis in all treatments were significantly lower than the CK,and the NDF and ADF yields in all treatments were significantly lower than the CK except for RM/14 in both years.(3)There was a significant positive linear correlation between accumulated yield of L.chinensis and individual leaf biomass,and a significant negative linear correlation between accumulated yiled of L.chinensis and leaf N content and P content.With the increase of the height of the growing point,the individual leaf biomass of the treatment group with growing point reserved and treatment group with growing point removed increased.Leaf biomass of the treatment group with growing point reserved was higher than that of the treatment group with growth point removed.Compared with the CK,the leaf biomass of all treatments was significantly lower,but the leaf to individual tiller biomass ratio of L.chinensis was significantly higher than the CK.The N content and P content of leaves of the treatment group with growing point reserved and the treatment group with growing point removed showed the same trend of interannual change,and both of them decreased with the increase of the growing point height.(4)There were significant differences in stoichiometric ratio of individual leaves between the treatment group with growing point reserved and the treatment group with growing point removed,indicating different growth strategies of L.chinensis.N:P in the leaves of the treatment group with growing point reseved and the treatment group with growing point removed showed a decreasing trend in the first year with the increase of the height of growth point,but the change was not obvious among treatments in the second year,and all treatments significantly decreased in the inter-year.The changes of C:N and C:P in the leaves of the treatment group with growing point reserved and the treatment group with growing point removed were not obvious in the first year with the increase of height of growing point,but increased in the second year with all treatments,and increased obviously in all treatments in the inter-year.The above results showed that the lower the growing point of L.chinensis,the higher the N:P of individual leaves of L.chinensis,representing a higher growth rate,but it was not sustainable in the interannual period.On the contrary,the higher the growing point of L.chinensis,the higher the C:N and C:P of individual leaves of L.chinensis,representing a higher nutrient use efficiency,and showed an increasing trend in the interannual period.When the growing point was 14 cm,the treatment with growing point reserved showed the best performance.(5)With the decrease of the height of growing point,the root indexes of the treatment group with growing point reserved and the treatment group with growing point removed showed a tendency of deterioration,and the root indexes of the treatment group with growing point reserved were obviously better than that of the treatment group with growth point removed.For the treatment group with growing point removed,the root biomass,root C accumulation,root N accumulation,root soluble sugar accumulation,root starch accumulation and root traits of L.chinensis were significantly lower in all treatments compared to the CK.Of the treatment group with growing point reserved,the performance of growing point of 2 cm and 6 cm was worst,as almost all the root indexes were lower than the CK.The performance of growing point of 10 cm was good,as the root biomass,root C accumulation,root N accumulation,root P accumulation,root soluble sugar accumulation and root starch accumulation were not significant to CK,but the total root length,the total root surface area and total root volume decreased significantly compared to the CK.The treatment with the growing point of 14 cm had the best performance,and there was no significant difference with CK in all indexes except the total root volume. |
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