Stomatal Size in Populus Is Related to Climate and Exhibits Plasticity Across Growing Environments

Abstract

Climate change is an ongoing problem that is predicted to continue impacting ecosystems around the world. It is important to understand how plants will respond to novel climatic conditions, either by migration (moving to more favorable regions), phenotypic plasticity (adjustment of traits within a generation in response to the environment), or adaptation (evolution across generations). Many plant traits have been linked to environmental conditions, including stomatal properties and associated gas exchange rates, which are crucial for regulating water loss and conducting photosynthesis. Stomatal traits such as size, length, and density have been predicted to vary with climatic factors such as rainfall, humidity, and temperature. Poplar trees (Populus) are model organisms that grow from cuttings, enabling the replicated study of wild-collected genetic clones grown in multiple environments or geographic locations. This replication allows for comparisons both within and between growing environments, resulting in estimates of both plasticity and adaptation. Additionally, poplar species are often geographically widespread and therefore may have adapted to local environments across North America. Our study aims to evaluate the effects of rainfall and humidity on stomatal length between common gardens in the Midwest region of the United States containing replicated genotypes of poplars collected from across climatic gradients. We predicted that: 1) Stomatal length would display phenotypic plasticity, with larger stomata in the wetter/more humid common garden, and 2) Stomatal length of poplars in the common gardens would be positively related to both rainfall and humidity of their source locations.