Climate and Bedrock

How does bedrock impact our forests at different scales? 

Nutrient availability and plants:

Plants need small to moderate amount of chemical compounds in the soil - macronutrients (essential to plant survival) and micronutrients (needed in small concentrations) - to survive. Different macro/micronutrients impact homeostasis in various ways such as regulation of photosynthesis, cold stress tolerance, cell wall construction and maintenance, and intra-cellular communication. 

• Calcium: Building block of cell walls, important in cold/stress tolerance, cellular signalling

• Magnesium: Component of chlorophyll molecules, binds RUBISCO (involved with photosynthesis)

• Potassium: Regulation of stomatal opening (gas exchange - loss of water and uptake of CO2 for photosynthesis), orientation of plant in response to light/gravity

• Aluminum/Manganese: Toxic in high concentrations - compete with other macronutrients to bind receptors

Nutrient availability and bedrock:

Macro/micronutrients in forests can be found in several pools including: leaf litter (intact fallen leaves), organic horizon (decomposing leaf litter and other biological matter), and mineral soil horizons, as well as in living plant tissues (such as leaves and roots). Bedrock, the layer of rock underlying soil in a forest, impacts what types of nutrients will be available in the mineral soil and at what concentration. Two main types of bedrocks exist in Pennsylvania: 

• Shale: Produces fine textured soils that typically have higher concentrations of calcium, magnesium and potassium. These soils also have high water retention 

• Sandstone: Produces coarse textured soils that typically have high concentrations of aluminum and manganese. These soils have lower water retention than the shale sites. 

Trees that grow up at different sites also impact the nutrient concentration by dropping their leaves, which then decompose into the organic layer of soil. Nutrients are also taken up by the trees and stored in leaves/roots, impacting nutrient levels in the soil matrix. 

Gene expression and bedrock:

Plants have the same DNA for their entire life - this DNA serves as a set of "instructions" for the plant to produce the proteins it needs to perform day to day function.  Within DNA are genes, contained sections that code for certain functions (ie: growth, cold tolerance, pest resistance, ion-binding). The number of copies produced (called gene expression) can vary based on environment. For instance, a plant might produce more copies of a "Calcium-binding" gene in an environment with lower calcium availability in order to meet its nutrient needs under limited availability. Genes can be upregulated (more copies produced) or downregulated (fewer copies produced). Differences in gene expression happen for one of two main reasons:

• Adaptation: Having more (or less) of this gene helps a plant in its conditions (example - plant produces more copies of a calcium-binding gene to pick up calcium in a low-nutrient environment). 

• Maladaptation: A plant that can’t adapt expresses these genes more (or less) in response (A plant that can't pick up enough calcium might break down cell walls it can't maintain without calcium). 

We predict that some of our study species will experience physiological stress at the sandstone sites because of lower availability of key micronutrients, and have changes in gene expression, while other species that have lower nutrient requirements will have unaffected gene expression as their nutrient-load needs are still being met.