Checking billy barr’s snow log…
Understanding how plant form and function respond to climate change is critical for mitigating the ecosystem-wide impacts. Plants possess chemical, physiological and structural characteristics, commonly referred to as traits, that enable them to acclimate to changes in the environment. However, some populations are unable to persist under novel conditions because of genetic or developmental constraints. Plant populations unable to adapt to novel environmental conditions may become extinct in their current environment, with implications for local communities and ecosystem functioning. In situ empirical studies provide scientists with the opportunity to observe plant responses to climate change in real time and are important for filling this gap in knowledge. Plant responses to climate change are influenced by a myriad of climatic effects and indirectly by species interactions. Throughout my dissertation, I used Populus tremuloides and perennial herbaceous plants in subalpine meadows to improve our understanding of plant responses to climate change. Since the beginning of their evolutionary timescale, plants have faced a myriad of environmental challenges and have developed a myriad of traits to adapt to current conditions. The first land plants originated around 500 million years ago from ancestral freshwater algae. On terrestrial lands, plants encountered various environmental challenges such as harsh ultraviolet radiation, mechanical damages, pathogen infections and desiccation. In spite of these challenges, land plants are found in almost every terrestrial habitat today. To overcome these challenges, it is theorized that land plants acquired the capacity to synthesize a hydrophobic skin, or cuticle, to cover the aerial surfaces and protect plant tissue against dessication, ultraviolet radiation and other environmental stressors. The stomata were another plant adaptation that revolutionized plant dominance on terrestrial land. Stomata are holes on the epidermis of the adaxial and abaxial side of the leaf. Plants open stomata during optimal conditions to obtain CO2 from the atmosphere for metabolic processes, and water and oxygen are lost as a by-product. Guard cells, which regulate water loss, become turgid when there is an increase in solute concentration during optimal conditions. However, during non-optimal conditions, such as water-limited environments, the guard cells become flaccid, resulting in stomatal closure. In these conditions, plants are unable to obtain CO2 for metabolic processes and it is commonly assumed water loss is completely avoided. However, the cuticle is not completely impermeable to water and water loss also occurs through the cuticle, in parallel to water loss via stomatal conductance. This source of water loss becomes a problem in water-limited environments where water loss persists although CO2 can not enter the leaves, resulting in water loss without the benefit of carbon gain. This source of water loss has the potential to disrupt the plant water balance. Excess water loss can lead to plant death. Unlike stomatal water loss, which plants can regulate, plants are unable to regulate the water loss via the cuticle. Several studies have tried to understand the sources of variation, but findings lack a mechanistic framework. To address this gap in knowledge, I investigated cuticular conductance in plants around the Rocky Mountain Biological Laboratory, a subalpine research facility in Western Colorado. I measured the minimum leaf conductance (gmin, a proxy for cuticular conductance) of trees and perennial herbaceous plants, two dominant plant types in this system, to improve our understanding of the drivers of minimum leaf conductance in this sensitive system, with insights from this research applicable to other subalpine/alpine communities or other terrestrial systems all over the world. First, I studied the scaling relationship between minimum leaf conductance and leaf size across scales. Trait-trait relationships may not be consistent across scales, so I conducted a meta-analysis to understand if the relationship between gmin is allometric or isometric on a global scale. I then compared the relationship using data along an elevational gradient to understand if the relationship persists across a global and local scale. Second, I studied how ploidy level differences may influence gmin between co-occurring Populus tremuloides trees. Then, I used an established reciprocal whole community turf transplant experiment in the Colorado Rocky Mountains to assess how functional traits respond to cooling and warming temperatures. I also used this experimental design to understand if trait plasticity differs between cooling and warming transplanted communities. In the final chapter, I used the reciprocal turf transplant experiment to identify gmin as a key component of the Leaf Economic Spectrum.
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