Menge Duncan N L, Batterman Sarah A, Liao Wenying, Taylor Benton N, Lichstein Jeremy W, Ángeles-Pérez Gregorio
Department of Ecology, Evolution, and Environmental Biology, Columbia University, New York, NY, 10027, USA.
Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ, 08544, USA.
Ecol Lett. 2017 Jul;20(7):842-851. doi: 10.1111/ele.12778. Epub 2017 May 16.
The rarity of nitrogen (N)-fixing trees in frequently N-limited higher-latitude (here, > 35°) forests is a central biogeochemical paradox. One hypothesis for their rarity is that evolutionary constraints limit N-fixing tree diversity, preventing N-fixing species from filling available niches in higher-latitude forests. Here, we test this hypothesis using data from the USA and Mexico. N-fixing trees comprise only a slightly smaller fraction of taxa at higher vs. lower latitudes (8% vs. 11% of genera), despite 11-fold lower abundance (1.2% vs. 12.7% of basal area). Furthermore, N-fixing trees are abundant but belong to few species on tropical islands, suggesting that low absolute diversity does not limit their abundance. Rhizobial taxa dominate N-fixing tree richness at lower latitudes, whereas actinorhizal species do at higher latitudes. Our results suggest that low diversity does not explain N-fixing trees' rarity in higher-latitude forests. Therefore, N limitation in higher-latitude forests likely results from ecological constraints on N fixation.
在通常受氮限制的高纬度（此处指纬度> 35°）森林中，固氮树木的稀缺是一个核心的生物地球化学悖论。关于它们稀缺的一种假说是，进化限制限制了固氮树木的多样性，阻止固氮物种填补高纬度森林中现有的生态位。在此，我们利用来自美国和墨西哥的数据对这一假说进行检验。尽管高纬度地区固氮树木的丰度比低纬度地区低11倍（分别占基部面积的1.2%和12.7%），但固氮树木在高纬度地区的分类单元中所占比例仅略低于低纬度地区（分别占属的8%和11%）。此外，固氮树木在热带岛屿上数量丰富但种类较少，这表明绝对多样性低并不限制它们的丰度。在低纬度地区，根瘤菌类群主导着固氮树木的丰富度，而在高纬度地区则是放线菌根物种占主导。我们的结果表明，多样性低并不能解释固氮树木在高纬度森林中的稀缺现象。因此，高纬度森林中的氮限制可能是由于固氮过程受到生态限制所致。
