Department of Ecology, Evolution, & Environmental Biology, 1200 Amsterdam Avenue, Columbia University, New York, New York 10027, USA.
Am J Bot. 2012 Oct;99(10):1702-14. doi: 10.3732/ajb.1200251. Epub 2012 Sep 14.
Consequences of global climate change are detectable in the historically nitrogen- and phosphorus-limited Arctic tundra landscape and have implications for the terrestrial carbon cycle. Warmer temperatures and elevated soil nutrient availability associated with increased microbial activity may influence rates of photosynthesis and respiration. •
This study examined leaf-level gas exchange, cellular ultrastructure, and related leaf traits in two dominant tundra species, Betula nana, a woody shrub, and Eriophorum vaginatum, a tussock sedge, under a 3-yr-old treatment gradient of nitrogen (N) and phosphorus (P) fertilization in the North Slope of Alaska. •
Respiration increased with N and P addition-the highest rates corresponding to the highest concentrations of leaf N in both species. The inhibition of respiration by light ("Kok effect") significantly reduced respiration rates in both species (P < 0.001), ranged from 12-63% (mean 34%), and generally decreased with fertilization for both species. However, in both species, observed rates of photosynthesis did not increase, and photosynthetic nitrogen use efficiency generally decreased under increasing fertilization. Chloroplast and mitochondrial size and density were highly sensitive to N and P fertilization (P < 0.001), though species interactions indicated divergent cellular organizational strategies. •
Results from this study demonstrate a species-specific decoupling of respiration and photosynthesis under N and P fertilization, implying an alteration of the carbon balance of the tundra ecosystem under future conditions.
全球气候变化的后果在历史上氮和磷有限的北极苔原景观中是可检测的，并对陆地碳循环有影响。与微生物活性增加相关的变暖温度和提高的土壤养分可用性可能会影响光合作用和呼吸作用的速率。
本研究在阿拉斯加北坡进行了为期 3 年的氮 (N) 和磷 (P) 施肥处理梯度下，对两种主要的苔原生态物种（木质灌木柳属和丛生莎草属）的叶片水平气体交换、细胞超微结构和相关叶片特性进行了研究。
呼吸作用随着 N 和 P 的添加而增加——在两个物种中，最高的速率对应于叶片 N 浓度最高的地方。光照下呼吸作用的抑制（“Kok 效应”）显著降低了两个物种的呼吸作用速率（P < 0.001），范围从 12-63%（平均值为 34%），并且通常随着两种物种的施肥而降低。然而，在这两个物种中，观察到的光合作用速率并没有增加，并且光合作用氮利用效率通常随着施肥的增加而降低。叶绿体和线粒体的大小和密度对 N 和 P 的施肥高度敏感（P < 0.001），尽管物种间的相互作用表明细胞组织策略存在分歧。
本研究的结果表明，在 N 和 P 施肥下，呼吸作用和光合作用出现了特定物种的解耦，这意味着在未来条件下，苔原生态系统的碳平衡将会发生改变。
