Variation in P. angustifolia functional traits and soil conditioning along gradients of latitude and elevation: Implications for feedbacks and range-shifts

Background/Question/Methods

Anthropogenic changes to the global climate are affecting broad taxonomic groups in diverse biomes. Predictions indicate that plants will experience climate-induced redistributions to their geographic ranges, moving to higher elevations and latitudes. Previous work highlights the importance of geographic boundaries, illustrating that the capacity for species range shifts lies in dynamics at leading and trailing edges of a distribution. While climate, soils, and species interactions can be responsible for structuring distributions, plants exert local influence on their environment by conditioning soil environments through functional traits, affecting their distribution and creating feedbacks when conditioned soils influence plant growth or fitness. Utilizing a ~1770 km gradient of latitude and ~1500 m in elevation we surveyed Populus angustifolia across its distribution, identifying seventeen watersheds with naturally occurring stands. We aimed to understand the level of variation in plant traits and soils existing across the landscape to inform predictions about potential range shifts in latitude and elevation. We hypothesized:1) a range of plant functional traits vary across gradients of latitude and elevation and; 2) this variation affects conditioning of associated soil environments, both of which may influence a species ability to migrate based on the strength and direction of feedback.

Results/Conclusions

Plant traits varied with latitude and elevation. High latitude sites exhibited lower mean leaf area and mass than low latitudes. Similarly, higher elevation sites exhibited lower mean leaf area and mass than low elevations. Significant effects of tree conditioning (e.g. differences between tree and interspace soils) indicate differential soil conditioning by P. angustifolia, related to plant functional traits. Soils associated with trees had higher pH than paired interspace soil at low latitudes, and higher conductivity across all latitudes. Interestingly, effects of elevation on conductivity were not consistent across latitudes - mid latitudes showed a negative relationship with elevation, while low latitudes showed a positive relationship. Strongest soil conditioning was observed at the range margins (low latitude, low elevation sites, and high latitude, high elevation sites). With watershed as a cofactor, SLA explained 24%, 43%, 40%, and 12% in soil pH, conductivity, total carbon and nitrogen, respectively. Overall, this study provides evidence that P. angustifolia functional traits vary, that conditioning of its soil environment occurs via plant traits, and that both characteristics vary with latitude and elevation. We also highlight the greater strength of conditioning at the trailing and leading edge having potentially large ramifications for feedbacks and range shifts.