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Latebreaking Poster

Session: Communities (Latebreaking)

LB 9-77 - Contrasting global biogeographic patterns of nitrogen-fixing trees, shrubs, and herbs

Thursday, August 10, 2023
5:00 PM – 6:30 PM PDT
Location: ESA Exhibit Hall
Symbiotic nitrogen-fixing plants provide natural bioavailable nitrogen (N) inputs, which can relieve terrestrial ecosystems of N limitation. Substantial work has focused on the latitudinal distribution of N fixers, but these studies have focused solely on the distribution of N-fixing trees. These analyses have established the paradox that N-fixing trees are abundant in N-rich lower-latitude forests (where N fixers should not have a strong competitive advantage) and rare in N-limited higher-latitude forests (where N fixers should have the strongest competitive advantage). Many shrubs and herbaceous plants also have the capacity to form symbiotic relationships with N-fixing bacteria, yet the distribution patterns of shrub and herbaceous N-fixers remain poorly understood. In this study, we leveraged global plant community data from sPlot, global climate data from WorldClim (version 2.1), and global soils data from SoilGRIDS to assess the biogeographic distribution of N-fixing trees, shrubs, and herbs, how the distribution of different N-fixing growth forms relate to each other, and how these patterns relate to key environmental conditions. In contrast to the global latitudinal patterns of N-fixing trees, the relative abundance of N-fixing herbaceous plants increases with latitude. N-fixing shrubs do not exhibit any strong global biogeographic patterns. This results in a tradeoff where latitudes with low N-fixing tree abundances often have high abundances of other N-fixing growth forms. Contrary to that of N-fixing trees, the relative abundance of N-fixing herbaceous plants globally decreases with increasing mean annual temperature, mean annual precipitation, and N limitation. These data highlight that the potential for substantial N fixation exists at high latitudes despite the paucity of N-fixing trees due to the abundances of N-fixing herbs and shrubs in high latitude ecosystems. The fact that environmental conditions do not impact N-fixer abundances equally across growth forms raises fundamental questions about why the success of the N fixation strategy responds differently to the environment between herbs, shrubs, and trees.