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Title: The exchange of carbon dioxide in tropical forest
Author: Meir, Patrick William
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1996
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This study investigated the structure of, and carbon dioxide fluxes at, a 'primary' rain forest (PRF) in SW Amazonia, Brazil, and a distributed secondary rain forest (SRF) in SW Cameroon. The total above-ground biomass and leaf area index (LAI) at PRF were respectively 220 (±95% c.l. 48) Mg ha-1 and 4.0 (±95% c.l. 0.7) m2 m-2, and at SRF 90 (±95% c.l. 9.4) Mg ha-1 and 4.4 (±95% c.l. 0.9) m2 m-2. A novel method was devised to quantify the vertical profile in LAI: SRF was distinguished from PRF by a higher concentration of leaf area near the ground. Three methods were used to determine the flux of CO2 from soil and gave overall agreement (static and dynamic chambers, and eddy covariance). The mean soil efflux in PRF and SRF was respectively 5.5 μmol m-2 s-1 (±95% c.l. 0.2; n = 42) and 4.5 μmol m-2 s-1 (±95% c.l. 0.2; n = 178) at 20 - 24 °C. The temperature response was higher in PRF than SRF (Q10 = 2.3 vs 1.9). Soil efflux rates were also obtained from cerrado vegetation in central Brazil, where the efflux was 3.2 μmol m-2 s-1 (±95% c.l. 0.2; n = 10) the Q10 1.6, at 16 - 23 °C. Heterogeneity in emission was higher in SRF than in PRF and could be described by a non-linear model incorporating the variables: soil temperature, organic carbon and total nitrogen (r2 = 0.82). Carbon was the most important variable determining respiration in SRF; soil moisture was not limiting. There was no observable effect of season on efflux rates in either rain forest, but a decline occurred in cerrado during the dry season. Effluxes of CO2 were measured from stems and branches of diameter 0.002 m - 1.6 m in 24 species in PRF and 17 species in SRF; emission rates were 0.1 - 3.3 μmol m-2 s -1 with a Q10 of 1.8 in PRF, and 0.2 - 5.2 μmol m-2 s -1 with a Q10 of 1.6 in SRF. Maintenance respiration was 80% and construction respiration 20% of total woody tissue respiration (Rt) in SRF. A functional model described the relationship between Rt and diameter in SRF better than a purely empirical one (r2 = 0.66). A novel method was devised in estimate sap CO2 concentrations which in SRF were 1.2 - 11.0 nmol 1-1 for Distemonanthus benthamianus and Musanga cecropioides. Sap CO2 levels were highly sensitive to sap pH, and represented 1 - 30% of cuvette-measured leaf photosynthesis. Maintenance leaf respiration (Rm) was measured through the vertical profile during the night in PRF and SRF. Rm increased with height at both sites: ˜0.2 in PRF vs ˜0.3 in SRF at 1.5 m and ˜0.5 in PRF vs ˜0.9 in SRF at 26 m (values normalised to 22 °C, units: μmol m-2 s-1). Leaf nitrogen and potassium concentrations (Nleaf and Pleaf) declined with height in the canopy. Pleaf concentrations were higher in SRF than PRF where Pleaf appeared to limit respiration. Rm was not significantly related.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available