Soil Nitrogen Content In Alpine Grasslands And Uptake Of Alpine Plants For Nitrogen In Water Culture Environment

This research is carried on the alpine ecosystem in Qinghai-Tibet Plateau. Based on plant nutrition theory and stable isotope labeling technique, we analyze spatial and temporal change dynamics of soil organic nitrogen and inorganic nitrogen content. Quantify the uptake characteristics of different forages to soil inorganic N and dissolved organic nitrogen(DON), and reveal the organic nutrition characteristics of alpine grasses. This research is conducted on Qinghai Tongde county, Maqin county and Haibei alpine meadow ecosystem station of CAS. The results shows:1.The most dominant free amino acids individuals in alpine meadow are phenylalanine and aspartic acid, followed by leucine, arginine, proline, histidine, glutamic acid, lysine and glycine, which make up 80-90% of total free amino acid content. The soil soluble organic nitrogen(DON) content of Kobresic tibetica meadow has two peak figures, 17.11 and 25.94 mg kg-1, respectively in early April and September, reaching the minimum, only 7.63 mg kg-1, at the end of June. The DON content of Kobresia humilis meadow has two peaks value, 23.6mg kg-1 and 20.36 mg kg-1, respectively by the end of April and in early October, at the end of June reaching the minimum, only 11.00 mg kg-1, The DON content of degraded Kobresia humilis meadow soil seasonal dynamic is as similar as Kobresia humilis meadow, the highest value is 15.82 mg kg-1 that appears in the end of April, and the lowest value in the end of June is only 5.57 mg kg-1.2. The soil soluble organic nitrogen of Kobresia Humilis Meadows accounted for 50.01% of soil total soluble nitrogen, soil NH4-N accounted for 49.99% of soil total soluble nitrogen. Soil soluble amino acids accounted for 21.80% of soil total nitrogen soluble, soil soluble amino acids accounted for 43.60% of soluble organic nitrogen in the soil. Research results show that: Compared with soil inorganic nitrogen, soil soluble organic nitrogen pool and soluble amino acids nitrogen pool occupies an important share in the alpine meadow soil nitrogen, it is an important component of plant research on soil nitrogen absorption components indispensable.3. In the first year of artificial grasslands, soil NO3--N is the main part which account for 54%-59%, DON is the second part which account for 22%-29%, NH4+-N is minimum only 17%. Follow with seasonal dynamic of soil nitrogen in the first year of artificial grassland, the content of NH4+-N is increasing with growing season, highest in September. NO3--N is highest in June, decreasing with growing season, Soil dissolve total nitrogen and dissolve organic nitrogen are higher in June and September, lower in growing season(July and August).4.The artificial grasslands in Guoluo, it’s seasonal dynamic of soil nitrogen as same as Tongde. NO3--N and DON has a advantage, each account for 49% and 43%, only NH4+-N has 8%. The NH4+-N in One year artificial grassland is increasing with grow season, highest in September. The soil NO3--N and DON are the highest in July, and decrease significantly with growth season. So soil DON is a important part in alpine meadow, the content only follow with NO3--N but higher than NH4+-N.5.Compare with one year’s and three year’s artificial grasslands in Tongde, the soil nitrogen content decrease rapidly in three year’s artificial grasslands, such as soil NO3--N decreased about 5 times, 3 times of NH4+-N, DTN declined 2.5times, only DON has a unconspicuous decline, with increase of planting year. Thus the reason why artificial grassland has a discontinuity productivity is that artificial grassland has lower available nutrient with increase of planting year.6.The results about the uptake of 10 alpine forage to three type nitrogen form in 100 u M N content water culture environment show: Elymus sibircus L.cv. Qingmu No.1absorbed 15 N is 8.108 umol 15N g-1 DW in total. Poa crymophila absorbed 15 N is 7.973 umol 15 N g-1 DW in total. Alopecurus aequalis absorbed 15 N is 7.629 umol 15 N g-1 DW in total. H. Violaceum,Fustuca sinensis keng. Cv.,Puccinellia tenuiflora, Puccinellia tenuiflora and Elymus nutans absorbed 15 N is 5.208-6.528 umol 15 N g-1 DW in total. However, the leguminosae forage Onobrychis viciaefolia Scop and grass pastures Festuca ryloviana absorbed dose 15 N is the lowest, only 3.964 umol 15N g-1 DW and 2.555 umol 15N g-1 DW. For ten alpine forages, the highest absorption is NH4+-N, next in importance is amino acid, and the lowest absorption is NO3--N.7.Under the salt stress(50 mmol L-1and 250 mmol L-1 Na Cl), the result of isotope labeling that two plant species absorbed different nitrogen show: salt stress can drop grass to absorb nitrogen, Under the salt stress Puccinellia tenuiflora absorb the nitrogen higher than Elymus nutans. It can be inferred that Puccinellia tenuiflora is suited to plant in The Qinghai-Tibet plateau saline soils than Elymus nutans.