Developing tree ring genomics to understand the genetic basis of and predict forest response to climate change

Introduction

Economically important and ecologically dominant conifers are succumbing to drought, disease, early-budding, and other challenges globally because mature trees are no longer adapted to their current environment under climate change. If we can understand how individual trees respond to different environments, we can match seed sources to an appropriate environment.

Limitations of Existing Approaches

Existing approaches for understanding adaptive responses to variable environments are effective, but agronomic approaches are limited by:

1. Long generation times.
2. The genetic diversity they can evaluate.
3. Significant variants discovered in environmental GWAS in natural populations, which are often associated both with adaptation and demographic structure, confounding inference.

Proposed System

We propose a system for quickly estimating adaptive responses for any forest tree. Focusing on annual growth measurements, measured from increment core samples, provides replication of a given genotype across hundreds of experienced year-environments.

This allows us to partition growth variation into generalizable environmental responses for years with historical weather or biotic information, using quantitative genomic and ecological approaches to control for correlated responses.

Focus on Norway Spruce

We focus on the economically and ecologically important conifer Norway spruce (Picea abies) to:

1. Develop models and infrastructure to understand the fraction of annual growth that can be attributed to genotype, environment, and genotype-by-environment interactions (GxE).
2. Map the genetic basis of adaptive response using estimates for GxE as a response in genome-wide association studies (GWAS).
3. Predict genetic responses to novel environments.

Conclusion

This approach will enable estimation of the genetic basis of adaptive responses in any population, providing the means to evaluate a tree’s performance in any modeled environment. As environments shift under climate change, this will provide a powerful tool to select parents for healthy, resilient forests.