title: Global climate change will increase the abundance of symbiotic nitrogen-fixing trees in much of North America.
abstract: Symbiotic nitrogen (N)-fixing trees can drive N and carbon cycling and thus are critical components of future climate projections. Despite detailed understanding of how climate influences N-fixation enzyme activity and physiology, comparatively little is known about how climate influences N-fixing tree abundance. Here, we used forest inventory data from the USA and Mexico (>125,000 plots) along with climate data to address two questions: (1) How does the abundance distribution of N-fixing trees (rhizobial, actinorhizal, and both types together) vary with mean annual temperature (MAT) and precipitation (MAP)? (2) How will changing climate shift the abundance distribution of N-fixing trees? We found that rhizobial N-fixing trees were nearly absent below 15°C MAT, but above 15°C MAT, they increased in abundance as temperature rose. We found no evidence for a hump-shaped response to temperature throughout the range of our data. Rhizobial trees were more abundant in dry than in wet ecosystems. By contrast, actinorhizal trees peaked in abundance at 5-10°C MAT and were least abundant in areas with intermediate precipitation. Next, we used a climate-envelope approach to project how N-fixing tree relative abundance might change in the future. The climate-envelope projection showed that rhizobial N-fixing trees will likely become more abundant in many areas by 2080, particularly in the southern USA and western Mexico, due primarily to rising temperatures. Projections for actinorhizal N-fixing trees were more nuanced due to their nonmonotonic dependence on temperature and precipitation. Overall, the dominant trend is that warming will increase N-fixing tree abundance in much of the USA and Mexico, with large increases up to 40° North latitude. The quantitative link we provide between climate and N-fixing tree abundance can help improve the representation of symbiotic N fixation in Earth System Models.
authors.affiliation: Department of Ecology, Evolution and Environmental Biology, Columbia University, New York, NY, USA.|Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ, USA.
authors.forename: Wenying
authors.identifier: 0000-0001-8777-1817
authors.initials: W
authors.lastname: Liao
authors.affiliation: Department of Ecology, Evolution and Environmental Biology, Columbia University, New York, NY, USA.
authors.forename: Duncan N L
authors.initials: DNL
authors.lastname: Menge
authors.affiliation: Department of Biology, University of Florida, Gainesville, FL, USA.
authors.forename: Jeremy W
authors.initials: JW
authors.lastname: Lichstein
authors.affiliation: Colegio de Postgraduados, Texcoco, Mexico.
authors.forename: Gregorio
authors.initials: G
authors.lastname: Ángeles-Pérez
mesh_terms: D057231:Climate Change; D065928:Forests; D008800:Mexico; D009586:Nitrogen Fixation; D011157:Population Dynamics; D011891:Rain; D013559:Symbiosis; D013696:Temperature; D014197:Trees / Q000502:physiology*; D014481:United States
keywords: actinorhizal; climate; precipitation; rhizobial; symbiotic nitrogen fixation; temperature