Measurement and partitioning of in situ CO[subscript]2 fluxes in turfgrasses using a pressurized chamber



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Field measurements of photosynthesis in turfgrass often are conducted with handheld chambers that are temporarily placed over the canopy and soil. Because gas exchange measurements include soil respiration (R [subscript]s), results do not represent net canopy photosynthesis (P [subscript c,net]) but rather net ecosystem exchange of CO2 (NEE), or gross canopy photosynthesis (P [subscript g]) less the sum of canopy respiration (R [subscript]c]) and R [subscript]s. Chambers attached to steady-state, portable photosynthesis systems normally are partially pressurized which may partially suppress R [subscript]s (depending on pressure magnitude and soil moisture and type) and may overestimate NEE. Objectives of this research were to: 1) develop a chamber in which pressure could be manipulated; 2) measure CO2 fluxes at neutral pressure (chamber pressure equals atmospheric) to estimate NEE; 3) measure P [subscript]c,net by applying increasing pressure until R [subscript s] is prevented from entering the chamber; and 4) partition CO2 fluxes among P [subscript]g, R [subscript]c, and R [subscript] s. Pressure fluctuations of [plus or minus]1.0 Pa were uncontrollable which caused large differences in CO[subscript]2 exchanges near neutral pressure and prevented measurements of NEE. Chamber pressurization from 50 to 200 Pa suppressed most but not all R [subscript]s which disallowed measurement of P [subscript]cnet using a single pressurized reading. A new procedure provided estimates of P [subscript]c,net, R [subscript]c, and P [subscript]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 [subscript]s that could not be suppressed with pressure. This was subtracted from pressurized readings over sunlit and shaded unclipped canopies to estimate P [subscript]c,net and R [subscript]c, respectively.



Photosynthesis, Surface chamber, Turfgrass carbon balance, Chamber pressure effects