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.

鉴于近期且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尤为关键——此类性状正是气候-植被反馈循环的核心调控途径。自1992年起，我们在加拿大努纳武特地区亚历山德里亚峡湾（79°N）的3个植物群落开展了人工增温实验。针对每个群落，我们采用开顶式增温箱（open-top chambers, OTCs）对植被进行被动增温，增温幅度为1~2℃。2008年夏季，我们针对经历16年连续增温的群落，探究了5个关键物种的种内功能性状响应模式。本研究共测定8项功能性状以量化植物性能的不同维度：叶面积、比叶面积（specific leaf area, SLA）、叶干物质含量（leaf dry matter content, LDMC）、株高、叶碳浓度、叶氮浓度、叶碳同位素判别值（leaf carbon isotope discrimination, LCID）以及叶δ¹⁵N。长期人工增温对5项功能性状产生了显著影响，且所有研究物种均至少有1项性状出现响应。常绿灌木松毛翠（Cassiope tetragona）的性状响应频次最高，表现为叶面积与株高增加，同时比叶面积、叶碳浓度及叶碳同位素判别值均显著降低；其次为落叶灌木北极柳（Salix arctica），其叶面积与株高增加、比叶面积降低；常绿灌木全缘叶仙女木（Dryas integrifolia）则表现为叶面积与株高增加、叶碳同位素判别值降低；非禾本科草本肾叶山蓼（Oxyria digyna）的响应为叶面积与株高增加；莎草科窄叶羊胡子草（Eriophorum angustifolium spp. triste）仅出现叶碳浓度降低的响应。增温处理对叶δ¹⁵N、叶氮浓度及叶干物质含量无显著影响。整体而言，生长类功能性状对增温的响应敏感性显著高于叶片化学性状。值得注意的是，本研究发现即便经过多年增温处理，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对升温将呈现多维度的响应模式，通常表现为株高更高、叶片更大的特征。