青藏高原多年冻土区不同水分条件的高寒草甸根系功能性状对增温的响应

Responses of root functional traits to experimental warming in the alpine meadow with different soil moisture in the permafrost region of the Qinghai-Tibet Plateau

在青藏高原多年冻土广泛分布的风火山地区,选择小嵩草(Kobresia pygmea)草甸和藏嵩草(Kobresia tibetica)沼泽化草甸为研究对象,采用开顶增温室(Open top chambers, OTCs)模拟气候变暖,探讨模拟增温对土壤水分差异的两种草甸地下生物量及根系功能性状的影响。结果显示:(1)增温显著增加小嵩草草甸0-20 cm根系生物量,主要是由于表层(0-10 cm)根系生物量显著增加,而对藏嵩草沼泽化草甸根系生物量无影响。(2)增温显著增加了小嵩草草甸根组织密度,同时提高了藏嵩草沼泽化草甸10-20 cm的比根长和比根面积(3)增温降低了小嵩草草甸的根系碳含量及10-20 cm根系氮含量,增加了藏嵩草沼泽化草甸的碳含量及10-20 cm根系氮含量,显著提高了小嵩草草甸和藏嵩草沼泽化草甸深层(10-20 cm)根系碳氮比。这些结果预示着增温使得土壤水分较低的小嵩草草甸朝着资源保守的慢速生长型发展,以适应暖干化的环境;土壤水分较高的藏嵩草沼泽化草甸朝着资源获取的快速生长型发展,加速利用土壤中的养分满足植物生长需要。可见,土壤水分可以调节高寒草甸对气候变暖的演变趋势,强调了水分的重要性。

Predicted warming is considered to intensively affect plant community structure and function in Qinghai-Tibet Plateau, and available soil moisture could mediate the responses of alpine plant community to climate warming. However, many studies have focused on the effects of climate warming alone on single alpine ecosystem, less was known what effects of climate warming will have on community with different soil moisture. Plasticity of root functional traits plays an important role in plant growth and survival under changing climate, reflects the utilization strategy of soil resources. Thus, we used open top chambers(OTCs) to artificially warm two different plant communities in Qinghai-Tibet Plateau from 2012 to 2016. We harvested root biomass, measured root length, diameter, area, and root carbon, nitrogen concentrations in both alpine meadows with different soil moisture. The results showed that(1) warming significantly increased root biomass at the depth of 0-10 cm and 0-20 cm in the alpine meadow, but didn′t change root biomass in the swamp meadow.(2) Warming significantly increased root tissue density at the depth of 0-10 cm and 10-20 cm in the alpine meadow, but significantly increased specific root length and specific root area at the depth of 10-20 cm in the swamp meadow.(3) Warming remarkably decreased root nitrogen concentration at depth of 10-20 cm and root carbon concentration at the depth of 0-10 cm and 10-20 cm in the alpine meadow, but increased root carbon at the depth of 0-10 cm and 10-20 cm as well as nitrogen concentrations at the depth of 10-20 cm in the swamp meadow. Moreover, warming significantly increased root carbon:nitrogen ratio at the depth of 10-20 cm in both alpine meadows. The present results indicated that warming may promote the Kobresia pygmea meadow with lower soil water content to develop conservative strategy so as to adapt the warmer and drier environment, as well as promote the Kobresia tibetica swamp meadow with ample soil water to develop acquisitive strategy to promptly utilize soil nutrients for plant growth in future. Generally, our results suggested that soil water could mediate effects of climate warming on alpine meadows, emphasizing the importance of soil water under future warming in the study region.