2017 ESA Annual Meeting (August 6 -- 11)

COS 151-6 - Could changes in N-form availability and plant N-form preferences influence species composition at the temperate-boreal forest ecotone?

Thursday, August 10, 2017: 3:20 PM
D129-130, Oregon Convention Center
Rachel A. King, Department of Ecology, Evolution, and Behavior, University of Minnesota, Peter B. Reich, Department of Forest Resources, University of Minnesota, St. Paul, MN and Sarah E. Hobbie, Department of Ecology, Evolution, and Behavior, University of Minnesota, Saint Paul, MN
Background/Question/Methods

Changing climate is expected to alter the future range of many species. While studies commonly focus on the direct impacts of climate, fewer evaluate how climate-mediated changes in N availability may contribute to shifts in plant species distributions. Understanding these impacts is particularly important in systems which may see changes in available N-forms, such as the temperate-boreal forest ecotone. Changes in N-form availability could impact species differently, as certain N-forms may not provide equivalent nutrition for all species. However, predicting which species may be affected by changes in N-forms remains challenging. This research examines whether traits associated with organic or inorganic nutrient economies influence plant responses to different N-forms. We hypothesized that species’ N-preferences will vary according to the type of mycorrhizal association, latitudinal range, and plant N demand. To test this hypothesis, we grew seedlings of 11 temperate and boreal tree species in pots with different N-forms (amino acids, ammonium, nitrate, or an equal mixture of all N-forms). After one growing season, we measured total biomass, total N, mycorrhizal colonization, and height. We defined the N-preferences of each species by comparing N-uptake and plant growth on each N-form to the N-uptake or growth on the mixture of all N-forms.

Results/Conclusions

The form of N supplied significantly affected plant growth across species, though not necessarily in relation to the traits examined. Tree seedlings did not exhibit different preferences for different N forms. Rather, NO3- was the N source preferred by all species regardless of latitudinal range or plant N demand (here represented by leaf Nmass). Mycorrhizal type influenced the degree of preference for NO3-, as ectomycorrhizal species showed greater increases in growth on NO3than arbuscular mycorrhizal species. However, all species still had the greatest growth on NO3-. Overall, these results suggest that species varying across the traits examined do not differ substantially in their preferences for distinct N forms. Therefore, changes in the relative availability of different N forms, coupled with preference for specific N-forms, are not expected to drive changes in species growth or N uptake at the temperate-boreal forest ecotone. However, competition for the same preferred form of N could play a role in determining the future composition of forests in the boreal region. These results help inform our understanding and guide future research on the impacts of changes in N cycling on species composition.