| This study was based on the Qinghai-Tibet Plateau, analyzed the dynamics of soil resolved organic nitrogen and inorganic nitrogen content in alpine grasslands quantify the uptake characteristics of different plants to soil inorganic N and resolved organic nitrogen, and reveal the nitrogen nutrition characteristics of alpine grasses. This study was carried at Qinghai Tongde county forage seed breeding farms, Da Wu of Maqin county and Haibei alpine meadow ecosystem station of CAS.1.The soil average nitrogen content is that: the soil NO3--N accounted for 50.87%(0~10 cm) and 56.14%(10~20 cm) of dissolved total nitrogen(DTN) in artificial grassland of Tongde. The resolved organic nitrogen(DON) accounted for 34.84%(0~10 cm) and 23.35%(10~20 cm) of DTN. NH4+-N is minimum only 14.28%(0~10 cm) and 20.27%(10~20 cm) of DTN. The content of soil NH4+-N increased, NO3--N decreased, that of DTN and DON content decreased firstly, then increased with the growing season.2.The average nitrogen content of soil in artificial grassland established in degraded grassland of Guoluo is that: the soil NO3--N accounted for 63.63%(0-10 cm) and 52.11%(10-20 cm) of DTN. The DON accounted for 29.06%(0-10 cm) and 38.20%(10-20 cm) of DTN. NH4+-N was minimum only 7.44%(0-10 cm) and 9.69%(10-20 cm) of DTN. The content of soil NH4+-N increased, NO3--N content decreased. DTN and DON content increased firstly, then decreased with the growing season.3.After three years, the soil NO3--N content decreased by 5 times in Tongde artificial grasslands, and it decreased higher in 0-10 cm than 10-20 cm, soil NH4+-N DTN and DON content decreased about 2.6, 3 and 1.8 times respectively. After three years in Guoluo, the NO3--N content decreased by 2 times, and there was no significant difference about the content of soil NH4+-N, and total nitrogen decreased by 1.5 times(0-10 cm) and 2.5 times(10-20 cm), DON content in 0-10 cm depths have no obvious change, but decreased by 10 times at depth of 10 to 20 cm.4. The plant above ground tissues δ15N natural abundance of alpine artificial grassland was about 2.02‰~8.45‰ in Tongde, its variation range was 6.43‰; Roots δ15N natural abundance was 1.69‰ ~ 3.77‰, this variation range was 2.08‰. Nitrogen concentration of the plant above ground tissues were 31.08~47.42 g·kg-1, and that of the roots were 10.69~12.20 g·kg-1. The soil δ15N natural abundance was 4.19‰~5.01‰, the variation range was 0.82‰. Soil nitrogen concentration were 2.37~2.73 g·kg-1. The alpine plants at two year’s artificial grasslands like Poa pratensis, Festuca ryloviana, Festuca sinensis, Poa crymophila and Elymus sibiricus had the strongest ability of absorbing inorganic nitrogen, and their amount of absorbing inorganic nitrogen accounted for 42.2% ~ 54.54% of total nitrogen absorption, the alpine plants at four year’s artificial grasslands like Poa pratensis, Festuca sinensis and Elymus sibiricus like to absorb Ammonium nitrogen, and ammonium nitrogen accounted for 35.32%~51.34% of total nitrogen absorption. Poa pratensis, Poa crymophila, Festuca sinensis,Festuca ryloviana and Elymus sibiricus can absorb glycine, but their absorptive capacity is lower, and their absorption amount of glycine accounted for 24.65%, 23.80%, 16.67%, 22.59% and 23.62% of total nitrogen absorption respectively.5. The total recovery rate of 15N-GLY was 104.06%, 15N-NH4 Cl was 75.63% and 15N-KNO3 was 79.54% in the alpine plants and soil at two year’s artificial grasslands; The total recovery rate of 15N-GLY was 71.55%, 15N-NH4 Cl was 60.66% and 15N-KNO3 was 66.20% in the alpine plants and soil at four year’s artificial grasslands; Most of 15 N compounds distributed in soil in the short term experiment labeled 15 N, and the recovery rate of 15N-GLY accounted the total recovery rate for 82.47%, 15N-NH4 Cl accounted for 68.85% and 15N-KNO3 accounted for 58.07% in soil at two year’s artificial grasslands; And the recovery rate of 15N-GLY accounted the total recovery rate for 88.68%, 15N-NH4 Cl accounted for 77.94% and 15N-KNO3 accounted for 81.15% in soil at four year’s artificial grasslands. The recovery rate of nitrogen in the plants at two year’s and four year’s artificial grasslands higher than in the roots.6. The absorption about 15N-NH4+ and 15N-NO3- of Kobresia humilis alpine meadow 12 species plants at the condition of N, P and water addition in soil were studied by 15 N Isotope tracing method at Haibei alpine meadow ecosystem station of CAS. The results showed: the δ15N natural abundance of 12 alpine meadow plants were-3.52‰~0.94‰, its variation range was 4.46‰, the nitrogen content in plants were 1.31%~3.36%, and the Leguminosae had the highest nitrogen concentration. Under the different condition, the Leguminosae like Gueldenstaedtia diversiffolia and Oxytropis ochrocephala, the Gentianaceae like Gentiana straminea and Gentiuna aristata, they had a lowest absorption about nitrate nitrogen and ammonium nitrogen. And under different treatments they had no significant difference(P>0.05).7.Under the N treatment, the nitrate nitrogen absorption value of Elymus nutans and Potentilla nivea increased significantly, and the ammonium nitrogen absorption value of Potentilla nivea also increased significantly, while the nitrate ammonium nitrogen absorption value of Poa annua significantly decreased in the alpine meadow; Under the P treatment, the nitrate nitrogen absorption value of Elymus nutans decreased significantly, and the nitrate nitrogen absorption value of Carex tristachya, Kobresia humilis and Potentilla nivea increased significantly in the alpine meadow; And the nitrogen absorption value of another plants were no changes significantly under the N or P treatment.8. Under natural conditions the total recovery rate of 15N-KNO3 was 50.30% and 15N-NH4 Cl was 59.62%, under the N treatment the total recovery rate of 15N-KNO3 was 92.61%~108.66% and 15N-NH4 Cl was 48.09%~51.80%, under the P treatment the total recovery rate of 15N-KNO3 was 50.20%~57.46% and 15N-NH4 Cl was 57.55%~73.31% in the plants and soil at the alpine meadow. Most of 15N-KNO3 and 15N-NH4 Cl distributed in soil in the short term experiment labeled 15 N, and they accounted the total recovery rate for 60.36%~84.29% and 71.24%~76.77%, the plants 15N-KNO3 and 15N-NH4 Cl recovery rate accounted for 6.78%~18.75% and 6.78% ~ 11.48%, the roots recovery rate accounted for 8.94% ~ 28.83% and 14.23%~21.27%, obviously, the plants nitrogen recovery rate was lower than roots. Under the N treatment, the recovery rate of 15N-KNO3 difference was significant, and the recovery rate of 15N-NH4 Cl difference was not significant, under the P treatment, the recovery rate of 15N-NH4 Cl and 15N-KNO3 difference was not significant.9. The grass AM mycorrhizal infection rate and the effect of absorption phosphorus by AM mycorrhiza about the alpine plants were studied. The forms of mycorrhiza had vesicle, intraradical hyphae,extraradical phyphae and arbuscule. The AM infection rate of Poa crymophila was the highest in three-year-old artificial grassland, and was 69.78%, infection rate of Festuca ryloviana was the lowest,and it was 36.44%;in five-year-old Artificial grassland the infection rate of Bromus inermis and Elymus nutans are the highest, and they are 68.45% and 68.22%; AM infection rate of Ptenuiflora was the lowest, it was 48.42%. The variance analysis results showed that: there was no significant difference between AM mycorrhizal infection rate of Alpine pasture and phosphorus content of Alpine pasture.(p>0.05). |
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