Figure 2.

Moisture constraints on R_s and R_eco. (a) The relationship between soil water potential and soil respiration (R_s, μmol m⁻² s⁻¹; R²=0.43, p<0.001); data are from a soil drought experiment at an eastern Amazon rainforest, Caxiuana (Sotta et al. 2007). (b) Net ecosystem exchange (NEE) in a transitional forest, Sinop, Mato Grosso (Vourlitis et al. 2005). During the four-month dry season (May–August), R_eco is more sensitive to moisture stress than is maximum photosynthesis, A_max (a decline of 28% in R_eco versus 5% in A_max; Vourlitis et al. 2005). Data show changes in diel and daily NEE of CO₂. Positive values indicate CO₂ release (mean NEE (±s.d.) of 30-min data (filled circle) and average daily NEE by month (open circles); horizontal solid line is diel NEE=0 and horizontal dashed line is daily NEE=0).