| Stable isotope technology, mathematical models and remote sensing technology are considered to be the three modern technologies in the study of global changes. As a new technology, stable isotope application in ecology has experienced fast development in recent decades. However, there is no report found applying stable isotope technology to alpine meadow degradation related research. Based on the fact that there are different views on whether alpine meadow is degraded or not, the carbon and nitrogen composition, stable isotope natural abundance and density of alpine meadow plant and soil were analyzed with Isoprime100. The objectives were to: 1) compare the differences of carbon and nitrogen stable isotope composition of plants and soils in different alpine meadow communities; 2) find evidences which reflect vegetation change and lay a foundation for studying alpine meadow degradation, protection and sustainable utilization.Plant and soil samples were taken from alpine meadows in Maqin and Dari county at the headwater region of the Yellow River. A total of 58 plant species samples, 32 composite quadrat samples and 180 soil samples were collected at different alpine communities, i.e. the non-degraded meadow, light degraded meadow, heavily degraded meadow and mix-seeded pasture. The carbon and nitrogen contents, isotopic composition of plant and soil sample were analyzed. The carbon and nitrogen density and the relationships between carbon and nitrogen contents, isotopic composition of soil were also explored. The main results and conclusions are as followings:1) The plant carbon content of 58 species varies between 28.64% and 51.55% and nitrogen content is from 0.89% to 4.04%. The δ13C abundance varies between-29.50‰ and-24.69‰ and the δ15N value is from-4.57‰ to 8.32‰. All species analyzed are C3 plants and no C4 and CAM plants were found. The low annual mean temperature may be the main factor restraining the distribution of C4 plants.2) The plant carbon content of different communities is in the order of mix-seeded pasture(45.54 ± 1.49%) > non-degraded meadow(43.18 ± 0.89%) > light degraded meadow(42.18 ± 1.25%) > heavily degraded meadow(39.68 ± 2.63%). The average nitrogen content of the four alpine meadow communities is 2.28%, 2.30%, 2.13% and 2.10%, respectively. Alpine degradation may result in decreased plant carbon content.3) The plant δ13C abundance of different alpine meadow communities varies mainly between-27.00‰ and-26.00‰ and the δ15N abundance varies is mainly from-1.00‰ to 1.00‰. Alpine degradation can result in decreased plant δ13C abundance, but not the δ15N abundance. Changes in plant composition of communities are the main factors that resulting decreasedδ13C.4) The SOC concentration of different alpine meadow communities varies between 1.28% and 4.08% and the TN concentration from 0.16 % to 1.0%. The minimum of C:N is 7.89 and the maximum is 9.97, and the average ratio is 8.71. The SOC and TN concentration decrease with soil depth, which is coincide with roots and litter fall entering soil are mainly distributed in upper soil layer. The changes in soil C:N reflects the difference soil mineralization.5) The soil organic carbon density(0 ~ 30cm) in non-degraded meadow, lightly degraded meadow, severely degraded meadow and mix-seeded pasture is 8.17, 7.14, 6.67 and 6.46 kg · m-2,and total nitrogen density is 0.94, 0.83, 0.77, 0.75 kg · m-2, respectively. Alpine meadow degradation and establishing mix-seeded pasture may cause significant reduction of soil carbon and nitrogen density, and the change mainly occurs in 0 ~ 20 cm soil layer.6) The soil δ13C abundance varies from-25.42 ‰ and-24.20 ‰, which is more than 2 permillage points higher that in plants. The soil δ15N abundance is from 3.37 ‰ and 4.69 ‰, and significantly higher than in atmosphere. Both soil δ13C and δ15N abundance have significant differences among different alpine communities(P<0.05), showing increasing trend with soil depth. The plant absorption and growth facilitate the output of 12 C and 14 N,leaving heavier 15 C and 15 N in soil.7) The soil δ13C abundance in mix-seeded pasture soil is significantly lower than that of in heavily and lightly degraded meadow(P<0.05), while soil δ15N is significantly higher than that of in heavily and lightly degraded meadow(P <0.05). The δ13C differences between non-degraded, lightly degraded and heavily degraded meadows are in 0 ~ 10 cm soil layer, and no significant deference was detected(P>0.05). Plowing degraded alpine meadow caused soil organic carbon lose and resulted in decreased 13 C relative abundance. Vigorous growing and higher above ground biomass of mix-seeded pasture utilized more soil 14 N, leaving elevated soil δ15N. |
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