title: Tolerance or avoidance: drought frequency determines the response of an N2-fixing tree.
abstract: Climate change is increasing drought frequency, which may affect symbiotic N2fixation (SNF), a process that facilitates ecosystem recovery from disturbance. Here, we assessed the effect of drought frequency on the ecophysiology and SNF rate of a common N2-fixing tree in eastern US forests. We grew Robinia pseudoacacia seedlings under the same mean soil moisture, but with different drought frequency caused by wet-dry cycles of varying periodicity. We found no effect of drought frequency on final biomass or mean SNF rate. However, seedlings responded differently to wet and dry phases depending on drought frequency. Under low-frequency droughts, plants fixed carbon (C) and nitrogen (N) at similar rates during wet and dry phases. Conversely, under high-frequency droughts, plants fixed C and N at low rates during dry phases and at high rates during wet phases. Our findings suggest that R. pseudoacacia growth is resistant to increased drought frequency because it employs two strategies - drought tolerance or drought avoidance, followed by compensation. SNF may play a role in both by supplying N to leaf tissues for acclimation and by facilitating compensatory growth following drought. Our findings point to SNF as a mechanism for plants and ecosystems to cope with drought.
authors.affiliation: Odum School of Ecology, University of Georgia, 140 E. Green St, Athens, GA, 30602, USA.
authors.forename: Jeffrey M
authors.identifier: http://orcid.org/0000-0001-5571-2599
authors.initials: JM
authors.lastname: Minucci
authors.affiliation: Coweeta Hydrologic Lab, USDA Forest Service, Southern Research Station, 3160 Coweeta Lab Rd, Otto, NC, 28763, USA.
authors.forename: Chelcy Ford
authors.initials: CF
authors.lastname: Miniat
authors.affiliation: Warnell School of Forestry and Natural Resources, University of Georgia, 180 E. Green St, Athens, GA, 30602, USA.
authors.forename: Robert O
authors.initials: RO
authors.lastname: Teskey
authors.affiliation: Odum School of Ecology, University of Georgia, 140 E. Green St, Athens, GA, 30602, USA.
authors.forename: Nina
authors.initials: N
authors.lastname: Wurzburger
mesh_terms: D055864:Droughts / Q000706:statistics & numerical data*; D009584:Nitrogen / Q000378:metabolism; D009586:Nitrogen Fixation; D018515:Plant Leaves / Q000378:metabolism; D031301:Robinia / Q000254:growth & development* / Q000502:physiology; D014197:Trees / Q000502:physiology*
chemical_list: D009584:Nitrogen
keywords: Robinia pseudoacacia (black locust); acclimation; climate change; compensatory growth; ecosystem; lag times; symbiotic nitrogen fixation; temporal variability