Temperature as a control over ecosystem CO2 fluxes in a high-elevation, subalpine forest

Area of Science:

• Forest Ecology
• Ecosystem Science
• Climate Change Research

Background:

• Subalpine coniferous forests play a role in carbon sequestration.
• Previous studies suggested cool temperatures limit CO(2) uptake in these ecosystems.
• Understanding temperature effects on forest carbon exchange is crucial for climate modeling.

Purpose of the Study:

• To test the hypothesis that cool growing season temperatures limit CO(2) uptake in a subalpine coniferous forest.
• To quantify the impact of temperature on net ecosystem CO(2) exchange (NEE) and ecosystem respiration (R(e)).
• To differentiate the effects of temperature on photosynthesis versus respiration.

Main Methods:

• Utilized the eddy covariance approach to measure NEE over two growing seasons.
• Analyzed light-saturated NEE (NEE(sat)) and ecosystem respiration (R(e)) in relation to temperature.
• Employed path analysis to isolate the seasonal effects of temperature on ecosystem fluxes.

Main Results:

• NEE(sat) showed a temperature optimum between 7-12°C.
• Increasing temperatures from 7°C to 18°C reduced net CO(2) uptake capacity by 15% due to increased R(e).
• Both ecosystem quantum yield and PPFD compensation point decreased at higher temperatures.

Conclusions:

• Contrary to previous hypotheses, cool temperatures do not limit CO(2) uptake in this forest.
• Warm mid-summer temperatures increase ecosystem respiration, significantly reducing carbon sequestration potential.
• Temperature's dynamic role influences seasonal carbon fluxes, with respiration being a key limiting factor at warmer temperatures.