Investigating shade tolerance and phenotypic plasticity of Virginia spiraea (Spiraea virginiana Britton),, a federally threatened shrub

Rosie Dickson

Biology

Jonathan Horton

Virginia spiraea (Spiraea virginiana Britton, Rosaceae), is a shade-intolerant, disturbance-adapted, riparian shrub species native to the southern Appalachian Mountains. This species was listed as threatened in 1990, and a recovery plan was developed in 1992. Current reassessment of the recovery plan includes proposals for propagation and outplanting to supplement and restore wild populations. Without flooding disturbance, competing vegetation needs to be actively managed to reduce shade for spiraea to thrive. Genotypes with greater shade acclimation would likely have higher survival in natural populations, would require less frequent shade-reduction management, and could be integrated into populations that need restoration. In summer 2022, we examined photosynthetic characteristics (maximum light-saturated photosynthetic, dark respiration rates, quantum yield, light compensation point, and pigment concentrations), and the ability to respond to sunflecks (photosynthetic induction and loss), of cloned propagules from five different source populations along an artificial light gradient (100),,, 75%, 50%, and 20% of full sun), in a common garden. Data were compared among light treatments and source populations using ANOVA or non-parametric tests. Light treatment had significant effects of maximum photosynthesis, dark respiration, specific leaf mass, and light compensation, but not quantum yield, pigment concentrations, or sunfleck utilization. Source population did not have a significant effect on any parameter. The five source populations were all from the same river drainage (New River, Ashe County, NC),, and studies have shown little genetic difference among individuals within the same drainage. Higher genetic variability has been shown between drainages. Future studies should examine photosynthetic characteristics of individuals from genetically contrasting source populations. More work needs to be done to understand the species’ plasticity and acclimation potential under a wider range of environmental conditions to help develop a plan for successful recovery of Virginia spiraea in wild populations.

Jan-9-2024