[Ecosystem carbon uptake was co-limited by nitrogen and phosphorus in alpine meadow on the Qinghai-Tibet Plateau].

Alpine grassland is threatened by the import of chemicals, fertilizers and other external resources with increasing human activities on the Qinghai-Tibet Plateau. It is unclear how carbon cycle of alpine grasslands is affected by the inputs of external resources such as nitrogen, phosphorus, and potassium (N, P, K) and their interactions. We conducted a 3 year experiment on the interactive addition of N, P and K with alpine grassland as the research object to clarify ecosystem carbon exchange process in response to resource addition by measuring community coverage and ecosystem carbon exchange. The results showed the alpine meadow was represented by carbon sequestration during the growing season. The mean value of net ecosystem CO2 exchange (NEE) was -13.0 μmol·m-2·s-1 under the control treatment. NEE, ecosystem respiration (ER), and gross ecosystem productivity (GEP) showed no significant responses when N, P and K were added separately. NEE was significantly increased by 95.3% and 63.9%, GEP was significantly increased by 45.5% and 33.0% under the combined addition of NP and NPK, but ER remained stable. The combined addition of NP or NPK mainly increased NEE and GEP by increasing the coverage of plant communities and affecting ecosystem water use efficiency. Plant community coverage was increased by 18.1% and 21.4%, respectively. The addition of NP increased productivity and autotrophic respiration in alpine meadow. It might cause soil acidification to inhibit heterotrophic respiration, thereby did not change ER due to the two aspects canceling each other out. The addition of N, P, K alone and NK and PK did not change ecosystem carbon exchange, while the combined addition of NP increased NEE and GEP on the nutrient-deficient alpine meadows, indicating that ecosystem carbon uptake was co-limited by N and P in alpine meadow.随着人类活动加剧,青藏高原高寒草地面临外来资源输入的威胁,而外源资源输入如氮、磷、钾(N、P、K)及其交互作用如何影响高寒草地生态系统碳循环尚不明确。本研究在藏北高寒草甸进行了连续3年N、P、K元素交互的添加试验,测定群落盖度和生态系统碳交换等数据,旨在阐明资源添加对高寒草甸生态系统碳交换过程的影响。结果表明: 在植物生长季,高寒草甸生态系统总体表现为碳汇,对照下NEE均值为-13.0 μmol·m-2·s-1。单独添加N、P、K对生态系统净CO2交换(NEE)、生态系统呼吸(ER)和总生态系统生产力(GEP)等碳通量组分均无显著影响;在NP、NPK组合添加下NEE显著增加了95.3%和63.9%,GEP显著增加了45.5%和33.0%,而ER没有显著改变。NP、NPK组合添加主要通过提高植物群落盖度和影响生态系统水分利用效率提高NEE和GEP,其中植物群落盖度分别提高了18.1%和21.4%。NP资源添加提高了高寒草甸生产力和自养呼吸,但同时可能导致土壤酸化,抑制异养呼吸,二者相互抵消,从而没有改变ER。对于养分匮乏的高寒草甸,单独添加N、P、K和NK、PK组合添加没有改变生态系统碳交换,而NP组合添加提高了NEE和GEP,表明高寒草甸生态系统碳吸收过程可能受到N、P等多种养分资源的共同限制。.