14C Allocation in tree-soil systems.

Area of Science:

• Plant Physiology
• Forest Ecology
• Carbon Cycling

Background:

• Understanding whole-tree carbon (C) allocation is crucial for forest ecosystem dynamics.
• Seasonal patterns of C distribution between aboveground and belowground biomass influence tree growth and carbon sequestration.
• Quantifying root respiration and its contribution to total soil respiration is essential for accurate carbon budget estimations.

Purpose of the Study:

• To investigate seasonal patterns of whole-tree carbon allocation in hybrid poplar.
• To quantify carbon allocation to roots and root respiration.
• To determine the primary source of carbon for root growth and maintenance.

Main Methods:

• Two-year-old hybrid poplar trees were labeled with (14)CO(2) in a field chamber during July and September.
• Climate and CO(2) concentrations were controlled to mimic ambient conditions.
• Recovery and distribution of (14)C were analyzed to track carbon allocation and respiration.

Main Results:

• Canopy CO(2) assimilation rates varied between July and September.
• Root respiration constituted approximately 20% of total soil respiration.
• In July, 80% of labeled carbon was allocated aboveground; by September, 51% was allocated to the root system, mirroring biomass distribution.

Conclusions:

• Current photosynthate is the primary source for root growth and maintenance during the growing season.
• Carbon allocation patterns in hybrid poplar shift seasonally, with increased root allocation later in the season.
• The (14)CO(2) labeling method effectively tracks seasonal carbon translocation pathways in trees.