The relationship between observed discrimination (Δ_obs) and net photosynthetic rate (A), stomatal conductance to H₂O (g_sw), and the ratio of partial pressure of CO₂ in intercellular spaces and the atmosphere around the leaf (p_i/p_a). When pooled across months these parameters exhibited significant linear relationships with Δ_obs, including A (P <0.0001, r²=0.13) and p_i/p_a (P <0.0001, r²=0.29), but not g_sw (P=0.24, r²=0.0006).