Biomass partitioning in a future dry and CO2 enriched climate: shading aggravates drought effects in Scots pine but not European black pine seedlings

1. Climate change alters both water and CO2 availability for plants, but it is largely unknown how they interact with light to affect tree seedling establishment and early growth. Light availability is often regulated by forest management, thus understanding how these resources co-limit the regeneration success of tree species and populations with contrasting drought tolerances is essential for adaptive forest management and particularly for assisted migration. 2.We studied biomass partitioning of 3-year-old Scots pine (Pinus sylvestris) and European black pine (Pinus nigra) seedlings in response to combined effects of light (22% and 40% shade), soil water availability (moist and dry conditions) and CO2 (ambient and elevated), and examined the responses of seedlings from Central Alpine and Mediterranean origin. Seedlings of nine populations with varying drought tolerances were grown in a common garden in the European Central Alps. Shoot height, vertical root length, shoot and root bioma...