Partitioning in Trees and Soil (PiTS) Part 2 - Shading in Dogwood
Members of the PiTS research team prepare the dogwoods trees for data gathering.
A second PiTS experiment has been initiated at the UT arboretum (Dogwood PiTS - shading in dogwood). The site was chosen after an extensive survey of the Oak Ridge Reservation and surrounding area. The important criteria were proximity to electrical power, relatively small trees (< 7 m) that were well spaced, capability to isolate trees by trenching, and site security. The Dogwood PiTS site is located on the University of Tennessee Forest Resources Research and Education Center (FRREC) in Oak Ridge, TN.
Research was initiated in January 2012 at the FRREC in a dogwood stand planted in 1996. This stand has previously supported various genetics and cultivation studies by the University of Tennessee and trees are mature (~ 5 m) and well-spaced (3.7 x 3.7 m). This study improves upon the first labeling project in loblolly pine, by physically isolating the belowground system by trenching, and spatially isolating treatments by distance. In this study, we are particularly interested in the belowground system, C turnover rates, storage, roots and mycorrhizae. As such, we have again heavily instrumented the site, with minirhizotron tubes, automated soil respiration chambers, soil moisture sensors and sap flow sensors. In addition, cylindrical mesh chambers (20 cm d x 40 cm h) that exclude symbiotic fungal hyphae or roots, and controls (with aperture of 0, 61 or 2460 ?m, respectively) were installed near each tree to separate new C partitioning among various belowground components.
GPP is being manipulated seasonally (Spring, Summer, Fall) by shading and the team is monitoring changes in C flux through the system using 13C labeling events. Plant carbon uptake, water use, growth and respiration will be tracked both above and belowground. Fate of new C as new biomass, litter, mycorrhizal transfer or respiratory release will be assessed. Results will be used in a modeling framework.
The first of three dogwood labeling events was successfully conducted in May 2012. Multiple plastic covered PVC chambers were placed over individual dogwood trees and a 13CO2 label was applied and circulated through the chambers using fans. Air conditioners were used to slow the solar heating of the chamber (and trees) to lengthen the foliar CO2 uptake period. After several hours, plastic was removed and subsequent gross primary production (GPP) of the trees was manipulated by either shade or full sun (control) treatments. To assess impact of GPP manipulation on C partitioning, the 13C label in tree foliage, phloem, roots, soil and soil efflux were sampled over the next 21 days. In addition, sampling of 13CO2 soil efflux from root and mycorrizal free exclusion chambers, root only exclusion chambers and control chambers surrounding each tree allowed for assessment of C flow into mycorrizal fungi - which is an especially understudied phenomenon. Dogwood PiTS will continue through the growing season, with several additional labeling events planned.
Members of the research team include:
ORNL Climate Change Science Institute and Environmental Sciences Division
Jeffrey Warren, Task leader, physiology, water relations
Colleen M. Iversen, Plant-soil interaction
Richard J. Norby, Soil respiration, tree growth response
Joanne Childs, Minirhizotron measurements
Deanne Brice,Stable isotope labeling
Jiafu Mao, Dan Ricciuto, Peter Thornton, Ecosystem model
University of Tennessee Institute Of Agriculture
Kevin Hoyt, Director, Forest Resources AgResearch and Education Center (FRREC)
Jennifer Franklin, Associate Professor, Department of Forestry, Wildlife and Fisheries
Jessica Bryant, Graduate Student, Department of Ecology & Evolutionary Biology
Empirical results from the initial FRREC PITS experiment in loblolly pine were published in: Warren JM, Iversen CM, Garten CT, Norby RJ, Childs J, Brice DJ, Evans RM, Gu L, Thornton PE, Weston DJ (2012). Timing and magnitude of carbon partitioning through a young loblolly pine (Pinus taeda L.) stand using 13C labeling and shade treatments. Tree Physiology, 32:799-813.