ELEVATED CO2 ENHANCES GROWTH IN THE RAIN-FOREST UNDERSTORY PLANT, PIPER CORDULATUM, AT EXTREMELY LOW-LIGHT INTENSITIES

Seedlings of the rain forest understory shrub Piper cordulatum were gr own for several months at ambient and elevated concentrations of atmos pheric CO2. Photon flux density (PFD) during 12-h photoperiods was mai ntained at extremely low levels (< 10 mu mol m(-2) s(-1)). Despite the se low PFDs, dry matter accumulation and leaf area production were inc reased in air containing elevated (approximately twice-ambient) CO2 co ncentrations compared to ambient air. In leaves that had developed in deep shade and at ambient CO2, rates of net CO2 uptake, measured at 6 mu mol photons m(-2)s(-1), were 30% higher at elevated than at ambient CO2. Rates of net CO2 loss in the dark were 10% lower at elevated tha n at ambient CO2.