CO₂ exchange of a tropical rainforest at Pasoh in Peninsular Malaysia

• Published in: Agricultural and forest meteorology Vol. 148; no. 3; pp. 439 - 452
• Main Authors: Kosugi, Yoshiko, Takanashi, Satoru, Ohkubo, Shinjiro, Matsuo, Naoko, Tani, Makoto, Mitani, Tomonori, Tsutsumi, Daizo, Nik, Abdul Rahim
• Format: Journal Article
• Language: English
• Published: Amsterdam [Oxford]: Elsevier Science Ltd 13.03.2008; Oxford Elsevier; New York, NY
• Subjects: Agricultural and forest climatology and meteorology. Irrigation. Drainage; Agronomy. Soil science and plant productions; air temperature; Biochemistry and biology; Biological and medical sciences; canopy; carbon dioxide; Chemical, physicochemical, biochemical and biological properties; diurnal variation; dry season; ecosystem respiration; eddy covariance method; Fundamental and applied biological sciences. Psychology; gas exchange; General agronomy. Plant production; leaf conductance; net ecosystem exchange; photosynthesis; Physics, chemistry, biochemistry and biology of agricultural and forest soils; seasonal variation; soil respiration; Soil science; soil water content; solar radiation; tropical rain forests; vapor pressure; vapor pressure deficit; water vapor; wet season; Malaysia; Asia; South east Asia; Biometeorology; Rain forest; Tropical zone; Carbon dioxide; Property of soil; Tropical rain forest; Tropical forest; Soil respiration; CO2 exchange; Biological activity; Statistical method; Southeast Asia; Eddy covariance; Covariance; Applied mathematics; Eddy correlation method; Soil science; Gas exchange; Tropical rainforest
• ISSN: 0168-1923; 1873-2240
• DOI: 10.1016/j.agrformet.2007.10.007

The eddy covariance method was used to observe carbon dioxide flux (F c) for 3 years over an old-growth tropical rainforest at Pasoh in Peninsular Malaysia. The average nighttime F c and NEE were 3.6 and 4.7μmolm⁻² s⁻¹, respectively, when friction velocity (u * )>=0.2, while the average soil respiration rate measured occasionally with the chamber method was estimated to be 4.1μmolm⁻² s⁻¹ if we used the relationship between volumetric soil water content, or 3.8μmolm⁻² s⁻¹ if we used the pure average of nine observations. The comparison of F c, NEE and soil respiration strongly suggests that nighttime CO₂ efflux was underestimated even when the CO₂ storage term is considered. The correction of F c data for low u * did not correct this underestimate, and it was strongly suggested that this forest was not a strong carbon sink, as raw F c data, even with the u * filtering, implied. Monthly average daytime diurnal changes in CO₂ exchange over the canopy were fairly constant from 2003 to 2005 despite fluctuations in soil moisture, solar radiation, air temperature and vapor pressure deficit between dry and wet periods. An obvious inhibition of canopy CO₂ exchange in the afternoon coupling with increases in VPD and air temperature was observed year-round. In the case of nighttime NEE, a slight increase in wet period was observed. Diurnal pattern of CO₂ exchange revealed that obvious restriction of canopy photosynthesis in the afternoon was occurred in this forest irrespective of soil moisture. Seasonal and annual patterns of CO₂ exchange reveal that one of the main causes which induce the difference in NEE pattern between Amazonian and Southeast Asian rainforests was not the difference in daytime photosynthesis but the difference in ecosystem respiration related with dry and rainy seasons. The decrease of CO₂ uptake (increase of NEE) at wet period was also observed at this site, but did not form an obvious seasonality such as in Amazonian forests.