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Nitrogen fixation strategies can explain the latitudinal shift in nitrogen‐fixing tree abundance
Author(s) -
Menge Duncan N. L.,
Lichstein Jeremy W.,
Ángeles-Pérez Gregorio
Publication year - 2014
Publication title -
ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.144
H-Index - 294
eISSN - 1939-9170
pISSN - 0012-9658
DOI - 10.1890/13-2124.1
Subject(s) - obligate , actinorhizal plant , facultative , nitrogen fixation , abundance (ecology) , ecology , latitude , biology , fixation (population genetics) , temperate climate , frankia , geography , root nodule , paleontology , biochemistry , geodesy , bacteria , gene
The rarity of symbiotic nitrogen‐fixing trees in higher‐latitude compared to lower‐latitude forests is paradoxical because higher‐latitude soils are relatively N poor. Using national‐scale forest inventories from the United States and Mexico, we show that the latitudinal abundance distribution of N‐fixing trees (more than 10 times less abundant poleward of 35° N) coincides with a latitudinal transition in symbiotic N‐fixation type: rhizobial N‐fixing trees (which are typically facultative, regulating fixation to meet nutritional demand) dominate equatorward of 35° N, whereas actinorhizal N‐fixing trees (typically obligate, maintaining fixation regardless of soil nutrition) dominate to the north. We then use theoretical and statistical models to show that a latitudinal shift in N‐fixation strategy (facultative vs. obligate) near 35° N can explain the observed change in N‐fixing tree abundance, even if N availability is lower at higher latitudes, because facultative fixation leads to much higher landscape‐scale N‐fixing tree abundance than obligate fixation.