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Notes and Unique Phenomena

MEASUREMENT AND PARTITIONING OF IN SITU CARBON DIOXIDE FLUXES IN TURFGRASSES USING A PRESSURIZED CHAMBER

^a Dep. of Hortic., Forestry and Recreation Resour., 2021 Throckmorton Hall, Kansas State Univ., Manhattan, KS 66506
^b Dep. of Agron., 2004 Throckmorton Hall, Kansas State Univ., Manhattan, KS 66506

^* Corresponding author (bremer{at}ksu.edu)

Received for publication March 3, 2004. Field measurements of photosynthesis in turfgrass often are conducted with hand-held chambers that are temporarily placed over the canopy and soil. Because gas exchange measurements include soil respiration (R_s), results do not represent net canopy photosynthesis (P_c,net) but rather net ecosystem exchange of CO₂ (NEE) or gross canopy photosynthesis (P_g) less the sum of canopy respiration (R_c) and R_s. Chambers attached to steady-state, portable photosynthesis systems normally are partially pressurized, which may partially suppress R_s (depending on pressure magnitude and soil moisture and type) and may overestimate NEE. Objectives of this research were to: (i) develop a chamber in which pressure could be manipulated, (ii) measure CO₂ fluxes at neutral pressure (chamber pressure equals atmospheric) to estimate NEE; (iii) measure P_c,net by applying increasing pressure until R_s is prevented from entering the chamber, and (iv) partition CO₂ fluxes among P_g, R_c, and R_s. Pressure fluctuations of ±1.0 Pa were uncontrollable, which caused large differences in CO₂ exchanges near neutral pressure and prevented measurements of NEE. Chamber pressurization from 50 to 200 Pa suppressed most but not all R_s, which disallowed measurement of P_c,net using a single pressurized reading. A new procedure provided estimates of P_c,net, R_c, and P_g from pressurized measurements of turf under sunlit and shaded conditions and from turf clipped at ground level. Flux from clipped plots under pressurization provided estimates of R_s that could not be suppressed with pressure. This was subtracted from pressurized readings over sunlit and shaded unclipped canopies to estimate P_c,net and R_c, respectively.

Abbreviations: LAI, leaf area index • NEE, net ecosystem exchange of CO₂ • P_c,net, net canopy photosynthesis • P_g, gross photosynthesis • R_c, canopy respiration • R_s, soil respiration • R^'_s, residual soil respiration at high chamber pressures