Respiration, photosynthesis, and carbon partitioning among four tree species of tropical wet forest

Background/Question/Methods

Individual tree species differ in morphology, phenology, tissue chemistry, and resource use, and these differences can affect ecosystem carbon cycling.  To what extent do tree species differ in respiration, photosynthesis, and carbon partitioning at the ecosystem level? We examined this question using experimental plantations of four native tree species in wet tropical forest of Costa Rica.  Aboveground respiration was estimated by scaling chamber measurements to the stand using species-specific empirical relationships observed for foliage and wood and extrapolated through time using a temperature function.  Photosynthesis and carbon partitioning were estimated by combining aboveground respiration to published data on plant growth and belowground respiration.

Results/Conclusions

Foliar respiration averaged 0.7 - 0.8 μmol m^-2 s^-1 and wood CO₂ efflux averaged 0.8 - 1.3 μmol m^-2 s^-1 with only slight differences among species.  Species difference in foliar respiration was related to leaf mass per area, and wood CO₂ efflux to wood diameter.  Foliar respiration rates were also related to leaf nitrogen and photosynthetic capacity and but was best extrapolated using leaf mass. Wood CO₂ efflux rates were best extrapolated to the ecosystem with surface area. Temperature response of foliar respiration was similar among tree species except for one species, but daily and annual temperature fluctuations produced only 3% difference on annual flux.  Aboveground respiration was similar among species and averaged 9 - 12 Mg C ha^-1 yr^-1 and was proportional to biomass and annual growth.  The ratio of respiration to productivity aboveground was similar among species at one.  Annual carbon gain (photosynthesis) averaged 31 - 41 Mg C ha^-1 yr^-1 with most of the differences among species in belowground components.  Our results suggest strong abiotic control of aboveground respiration, and that species differ in partitioning to belowground.