The Science

Springtime budbreak and branch development induces substantial carbon (C) costs in trees. New branch growth in evergreen trees relies on both old and new C from stored sugars and spring photosynthesis, respectively. Drought stress during branch development can hinder translocation of stored sugars and reduce new C uptake.

The Impact

Evergreen trees invest in long-lived leaves that provide C uptake over multiple years. As climate changes, there may be more extended or frequent drought events. If drought occurs during spring budbreak, it can restrict branch expansion and physiological capacity, which in turn may impact net annual C uptake over multiple years. These findings could be useful for informing Earth system models that simulate spring canopy development and ecosystem carbon exchange.

Summary

The researchers studied effects of drought and re-hydration on early season branch development, carbon uptake, and internal carbon cycling in 10-year-old Picea mariana (black spruce) trees. During a six-week drought treatment, researchers measured dynamics of key morphological and physiological processes. Development of the photosynthetic apparatus was delayed in droughted trees by two weeks in comparison with that of well-watered trees. Drought stress reduced springtime carbon availability for growth, and the drought-stressed trees prioritized use of new C uptake for respiration over structural branch and leaf components. Drought during branch expansion ultimately resulted in longer branches, but the display of leaves was more compact, with reduced branch volume. Since evergreen species such as black spruce retain active leaves for multiple years, impacts of early season drought on plant vigor could be carried forward into subsequent years.

Principal Investigator

Jeffrey Warren
Oak Ridge National Laboratory
warrenjm@ornl.gov

Program Manager

Daniel Stover
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
daniel.stover@science.doe.gov

Funding

U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research. Oak Ridge National Laboratory is managed by UT-Battelle, LLC, for the DOE under contract DE-AC05-1008 00OR22725.

References