Department of Earth and Environmental Science, Columbia University, New York City, NY, USA.
Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY, USA.
Commun Biol. 2024 Aug 6;7(1):950. doi: 10.1038/s42003-024-06600-z.
A significant warming effect on arctic tundra is greening. Although this increase in predominantly woody vegetation has been linked to increases in gross primary productivity, increasing temperatures also stimulate ecosystem respiration. We present a novel analysis from small-scale plot measurements showing that the shape of the temperature- and light-dependent sink-to-source threshold (where net ecosystem exchange (NEE) equals zero) differs between two tussock tundra ecosystems differing in leaf area index (LAI). At the higher LAI site, the threshold is exceeded (i.e the ecosystem becomes a source) at relatively higher temperatures under low light but at lower temperatures under high light. At the lower LAI site, the threshold is exceeded at relatively lower temperatures under low light but at higher temperatures under high light. We confirmed this response at a single site where LAI was experimentally increased. This suggests the carbon balance of the tundra may be sensitive to small increases in temperature under low light, but that this effect may be significantly offset by increases in LAI. Importantly, we found that this LAI effect is reversed under high light, and so in a warming tundra, greater vegetation cover could have a progressively negative effect on net carbon uptake.
北极苔原的显著变暖效应是绿化。尽管这种以木质为主的植被增加与总初级生产力的增加有关，但气温升高也会刺激生态系统呼吸。我们提出了一项新的分析，来自小规模试验测量，表明在叶面积指数（LAI）不同的两种丛生苔原生态系统中，温度和光照依赖性汇源阈值（净生态系统交换（NEE）等于零的地方）的形状不同。在较高 LAI 地点，在低光照下相对较高的温度下超过阈值（即生态系统成为源），但在高光下温度较低。在低 LAI 地点，在低光照下相对较低的温度下超过阈值，但在高光下温度较高。我们在一个 LAI 被实验性增加的单一地点证实了这一反应。这表明苔原的碳平衡可能对低光照下的温度小幅度升高敏感，但这种影响可能会被 LAI 的增加显著抵消。重要的是，我们发现这种 LAI 效应在高光下是相反的，因此在变暖的苔原中，更大的植被覆盖可能对净碳吸收产生逐渐负面的影响。
