Ecosystem carbon exchange in two terrestrial ecosystem mesocosms under changing atmospheric CO 2 concentrations

Abstract

The ecosystem-level carbon uptake and respiration were measured under different CO concentrations in the tropical rainforest and the coastal desert of Biosphere 2, a large enclosed facility. When the mesocosms were sealed and subjected to step-wise changes in atmospheric CO between daily means of 450 and 900 μmol mol, net ecosystem exchange (NEE) of CO was derived using the diurnal changes in atmospheric CO concentrations. The step-wise CO treatment was effectively replicated as indicated by the high repeatability of NEE measurements under similar CO concentrations over a 12-week period. In the rainforest mesocosm, daily NEE was increased significantly by the high CO treatments because of much higher enhancement of canopy CO assimilation relative to the increase in the nighttime ecosystem respiration under high CO. Furthermore, the response of daytime NEE to increasing atmospheric CO in this mesocosm was not linear, with a saturation concentration of 750 μmol mol. In the desert mesocosm, a combination of a reduction in ecosystem respiration and a small increase in canopy CO assimilation in the high CO treatments also enhanced daily NEE. Although soil respiration was not affected by the short-term change in atmospheric CO in either mesocosm, plant dark respiration was increased significantly by the high CO treatments in the rainforest mesocosm while the opposite was found in the desert mesocosm. The high CO treatments increased the ecosystem light compensation points in both mesocosms. High CO significantly increased ecosystem radiation use efficiency in the rainforest mesocosm, but had a much smaller effect in the desert mesocosm. The desert mesocosm showed much lower absolute response in NEE to atmospheric CO than the rainforest mesocosm, probably because of the presence of C plants. This study illustrates the importance of large-scale experimental research in the study of complex global change issues.

Drought effect on isoprene production and consumption in Biosphere 2 tropical rainforest

“…Although soil bulk density, soil organic matter content and major nutrient concentrations in B2L tropical rainforest were very similar to those of several Puerto Rican rainforests (Silver & Fall, 1991), they were more alkaline (pH ca. 7.5 compared with pH of 5.1 found in Puerto Rican rainforests by Silver and Fall, 1991) and contain slightly higher P, K and other nutritional elements (Leigh et al , 1999; Lin et al , 1999). The soil fauna is, however, very limited (ants, cockroaches).…”

The effect of elevated atmospheric CO2 and drought on sources and sinks of isoprene in a temperate and tropical rainforest mesocosm

“…Ringed by a shade belt of bananas and ginger, after 12 years, the upper canopy mesocosm exceeds 15 m, filling about 50% of the upper enclosure, with secondary canopy and understory plants well established. Although the TRF was exposed to a series of short‐term elevated CO 2 treatments (Lin et al , 1999) and drought treatments since 1998, seasonal net ecosystem CO 2 exchanges (net assimilation and respiration) have remained closely comparable with those of field sites in Amazonia (Andreae et al , 2002; Osmond et al , 2004) with little evidence of marked memory effects. The constructed soil in the TRF has a subsoil layer (up to 5 m deep) and a topsoil layer (0.3 and 3.2 m in depth) (Leigh et al , 1999).…”

Plant growth in elevated CO2alters mitochondrial number and chloroplast fine structure

“…Each chamber had three P. radiata trees. (28,29). In 1996, during the 6 months preceding the first leaf sampling, the average CO 2 concentration was 83 Ϯ 5.2 Pa, and during the previous 5 years, concentrations were well above 36 Pa.…”