Changes in water, nitrogen and carbon cycling in loblolly pine (Pinus taeda L.) during a mortality event
Abstract
Depending on the type of disturbance, the mortality process of an individual tree may occur over an extended period leading to changes in tree and ecosystem functioning throughout this time period and before ultimate tree death is evident. Therefore, the goals of this research were to quantify physiological changes occurring in loblolly pine (Pinus taeda L.) during an extended mortality event. In July 2015, ten trees were girdled to simulate a Southern pine beetle disturbance and trees were monitored until their eventual mortality which occurred from Aug. to Dec. of 2016. Sapflow rates and litterfall were monitored throughout the mortality process and photosynthetic rates and leaf nitrogen concentrations were measured at the height of the 2016 growing season. Girdled pines had significantly higher sapflow compared with control pines in the first month following girdling, then sapflow did not differ significantly for the remainder of the 2015 growing season. From Dec. 2015 to Dec. 2016, control trees had about 25% higher sapflow compared with girdled pines, but both groups maintained a similar relationship between sapflow and soil moisture. Extensive litterfall occurred throughout the 2016 growing season and litter had 50% higher N concentration than the prior growing season. N concentration of fresh leaves collected in 2016 did not differ in girdled vs. control pines but control pines had 64% higher maximum Rubisco-limited carboxylation rates (Vcmax) and 68% higher electron transport-limited carboxylation rates (Jmax) compared to girdled pines. Control pines also had 66% higher foliage densities and 44% larger growth ring widths than girdled pines at the end of the 2016 growing season. Taken together, these results highlight the physiological changes that occur in pines undergoing mortality before needles completely discolor and drop. Compared with control pines, girdled pines exhibited greater changes in carbon and nitrogen compared with water use suggesting that sapflow per unit leaf area was increased to compensate for the losses in total leaf area. These data highlight the importance of physiological measurements taken throughout a mortality event to more accurately quantify the changes in ecosystem-scale water, nitrogen and carbon balance occurring during disturbance episodes.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2017
- Bibcode:
- 2017AGUFM.B51E1851R
- Keywords:
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- 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCES;
- 0439 Ecosystems;
- structure and dynamics;
- BIOGEOSCIENCES;
- 0498 General or miscellaneous;
- BIOGEOSCIENCES;
- 1813 Eco-hydrology;
- HYDROLOGY