Responses of floral traits to water limitation across soil types and along climatic gradients

Abstract

Understanding how environmental changes affect plant-pollinator interactions is of increasing importance given that new environmental extremes continue to be reached. Drought may be a particularly destabilizing force for plant-pollinator interactions because moisture availability can affect floral trait expression. Past work has found variability in how some floral traits respond to moisture limitation, motivating work on the potential drivers of the variability in responses. Here we asked how flower size and nectar provisioning to pollinators change with moisture limitation, and if seed provenance mediates trait responses. Specifically, we conducted a greenhouse common garden using seeds of the serpentine-tolerant annual Antirrhinum vexillocalyculatum collected from pairs of populations on and off drought-prone serpentine soil and along moisture and temperature gradients. We experimentally quantified responses to two moisture treatments, and we found no evidence that seeds from different soil types vary in drought responses. However, plants from seeds from different temperature regimes varied in the way that water limitation affected nectar volume, and those from different precipitation regimes varied in the way that water limitation affected flower size. Water limitation reduced floral display and reward for plants from some populations but increased trait means in other populations. This suggests that drought will reduce floral resources for pollinators overall, but plants from some environments may continue to invest in pollination mutualisms under moisture limitation.