Environmental characteristics, and growth traits and leaf chemistry of tundra plants in a warming experiment at Alexandra Fiord

Understanding plant trait responses to elevated temperatures in the Arctic is critical in light of recent and continuing climate change, especially because these traits act as key mechanisms in climate-vegetation feedbacks. Since 1992, we have artificially warmed three plant communities at Alexandra Fiord, Nunavut, Canada (79°N). In each of the communities, we used open-top chambers (OTCs) to passively warm vegetation by 1-2 °C. In the summer of 2008, we investigated the intraspecific trait responses of five key species to 16 years of continuous warming. We examined eight traits that quantify different aspects of plant performance: leaf size, specific leaf area (SLA), leaf dry matter content (LDMC), plant height, leaf carbon concentration, leaf nitrogen concentration, leaf carbon isotope discrimination (LCID), and leaf d15N. Long-term artificial warming affected five traits, including at least one trait in every species studied. The evergreen shrub Cassiope tetragona responded most frequently (increased leaf size and plant height/decreased SLA, leaf carbon concentration, and LCID), followed by the deciduous shrub Salix arctica (increased leaf size and plant height/decreased SLA) and the evergreen shrub Dryas integrifolia (increased leaf size and plant height/decreased LCID), the forb Oxyria digyna (increased leaf size and plant height), and the sedge Eriophorum angustifolium spp. triste (decreased leaf carbon concentration). Warming did not affect d15N, leaf nitrogen concentration, or LDMC. Overall, growth traits were more sensitive to warming than leaf chemistry traits. Notably, we found that responses to warming were sustained, even after many years of treatment. Our work suggests that tundra plants in the High Arctic will show a multifaceted response to warming, often including taller shoots with larger leaves.鉴于当前及仍在持续的气候变化，理解北极地区植物功能性状对升温的响应至关重要，尤其是这些性状作为气候-植被反馈过程的关键调控机制时。自1992年起，我们在加拿大努纳武特地区亚历山德拉峡湾（79°N）对三个植物群落开展人工增温实验。每个群落均采用开顶箱（open-top chambers, OTCs）对植被进行被动增温，增温幅度为1~2℃。2008年夏季，我们针对5种关键植物，探究了其经过16年持续增温后的种内功能性状响应。本研究考察了可量化植物功能表现多维度特征的8项功能性状：叶面积、比叶面积（specific leaf area, SLA）、叶片干物质含量（leaf dry matter content, LDMC）、株高、叶片碳浓度、叶片氮浓度、叶片碳同位素判别（leaf carbon isotope discrimination, LCID）以及叶片δ¹⁵N。长期人工增温对其中5项性状产生了显著影响，且所有研究物种均至少有1项性状发生响应。常绿灌木松毛翠（Cassiope tetragona）的响应频次最高：叶面积与株高增加，比叶面积、叶片碳浓度及LCID降低；其次为落叶灌木北极柳（Salix arctica）：叶面积与株高增加，比叶面积降低；常绿灌木全缘叶仙女木（Dryas integrifolia）：叶面积与株高增加，LCID降低；非禾本草本植物山蓼（Oxyria digyna）：叶面积与株高增加；以及莎草科细秆羊胡子草（Eriophorum angustifolium spp. triste）：叶片碳浓度降低。增温对叶片δ¹⁵N、叶片氮浓度及LDMC无显著影响。总体而言，生长性状对增温的敏感性高于叶片化学性状。值得注意的是，本研究发现即使经过多年增温处理，植物对升温的响应仍持续存在。本研究结果表明，高北极地区的苔原植物将对升温呈现多维度响应，通常表现为植株更高、叶片更大。