Foliar flavonoids across an elevation gradient: Plasticity in response to UV, and links with floral pigmentation patterning

Metabolites produced in the flavonoid biosynthetic pathway (FBP) mitigate abiotic stress caused by factors such as ultraviolet (UV) light. Testing whether constitutive flavonoid production or flavonoid plasticity differ between populations spanning ecological gradients can reveal whether geographic patterns are consistent with local adaptation. Abiotic induction of flavonoids can occur in leaves as well as flowers where flavonoids influence UV color patterns perceived by pollinators. Assessing how foliar flavonoids are associated with floral color phenotypes can shed light on how pleiotropy affects biochemical phenotypes across tissues. We exposed Argentina anserina (Rosaceae) plants from alpine and lower elevation populations to low and high levels of UV and measured foliar and petal flavonoid production using UHPLC coupled mass spectrometry. We associated foliar flavonoid abundance with petal flavonoid abundance, and the size of the UV absorbing petal area (‘UV bullseye’). We found that total foliar flavonoids increased in response to UV due to flavonol upregulation, but only one class of flavonols, fisetin, exhibited stronger plasticity in alpine populations. Alpine populations tended to increase the quercetin-kaempferol ratio more than low elevation populations when exposed to higher UV, a signature of photoprotection and radical scavenging. Relationships between foliar flavonoids and the floral UV bullseye differed between alpine and low elevation populations. Previous work showed kaempferol glycosides contributed to variation in UV bullseye size at high elevation, while non-kaempferols spanning multiple FBP branches were associated with bullseye size at low elevation. Here, we found that alpine plants with less foliar kaempferol and greater kaempferol allocation to petals than leaves had larger floral UV-bullseyes, suggesting that floral UV patterning may be shaped by a biochemical tradeoff between tissues. Overall, nuanced elevational differences in flavonoid plasticity revealed by detailed metabolite classification provided support for local adaptation. Additionally, our study highlights that flavonoid production in leaves could influence the evolution of flavonoid-based floral phenotypes.