增温对青藏高原高寒草甸3种植物氮磷化学计量与重吸收的影响

Effects of warming conditions on plant nitrogen-phosphorus stoichiometry and resorption of three plant species in alpine meadows on the Tibetan Plateau

全球气候变化将对生态系统造成重要影响,尤其是那些对气候变化极为敏感的高寒草甸生态系统。然而,全球变暖对高寒草甸植物氮磷化学计量特征和重吸收作用的影响仍不清楚。为了研究青藏高原高寒草甸植物的氮磷化学计量特征和重吸收作用,本研究采用开顶箱(OTCs)进行了3年的人工增温实验。选择3种优势物种和4种不同高度的OTC(0.4、0.6、0.8、1 m),设置4种增温处理(全年增温、冬季增温、夏秋冬季增温和春夏秋季增温)。结果表明,在不同增温方法下,土壤温度随OTC高度的增加而显著升高。随着温度的上升,高山嵩草(Kobresia pygmaea)的氮限制增加,矮生嵩草(K.humilis)的磷限制增加,而钉柱委陵菜(Potentilla saundersiana)的氮磷限制对温度的增加不敏感。在温度升高的情况下,氮磷重吸收效率比(NRE:PRE)与氮磷比(N:P)都表现出相同的变化趋势。3种物种的化学计量特征对温度升高的响应存在差异,显示出氮、磷限制对温度变化的反应是多方面的,而且草地生态系统可能具备一定程度的自我调节能力。上述结果表明,全球气候变暖情景下,仅依赖单一优势物种的化学计量指标来代表整个生态系统的氮、磷限制并不准确,使用N:P比值来反映营养限制可能会产生误导。

Global climate change is expected to have a signifcant impact on ecosystems worldwide,especially for alpine meadows which are considered as one of the most vulnerable components.However,the effects of global warming on the plant nitrogen–phosphorus stoichiometry and resorption in alpine meadows remain unclear.Therefore,to investigate the plant nitrogen–phosphorus stoichiometry and resorption in alpine meadows on the Qinghai-Tibet Plateau,we conducted an artifcial warming study using open-top chambers(OTCs)over the 3 years of warming period.We selected three dominant species,four height types of OTCs(0.4,0.6,0.8 and 1 m)and four warming methods(year-round warming,winter warming,summer–autumn–winter warming and spring–summer–autumn warming in the experiment)in this experiment.In our study,soil temperature signifcantly increased with increasing the height of OCTs under the different warming methods.Kobresia pygmaea presented an increase in nitrogen(N)limitation and Kobresia humilis presented an increase in phosphorus(P)limitation with increasing temperature,while Potentilla saundersiana was insensitive to temperature changes in terms of nitrogen and phosphorus limitations.Both nitrogen resorption effciency:phosphorus resorption effciency and N:P trends in response to rising temperatures were in the same direction.The differential responses of the chemical stoichiometry of the three species to warming were observed,refecting that the responses of nitrogen and phosphorus limitations to warming are multifaceted,and the grassland ecosystems may exhibit a certain degree of self-regulatory capability.Our results show that using chemical dosage indicators of a single dominant species to represent the nitrogen and phosphorus limitations of the entire ecosystem is inaccurate,and using N:P to refect the nutritional limitations might have been somewhat misjudged in the context of global warming.