H2O and CO2 fluxes at the floor of a boreal pine forest

We measured H₂O and CO₂ fluxes at a boreal forest floor using eddy covariance (EC) and chamber methods. Maximum evapotranspiration measured with EC ranged from 1.5 to 2.0 mmol m^-2 s^-1 while chamber estimates depended substantially on the location and the vegetation inside the chamber. The daytime net CO₂ exchange measured with EC (0–2 μmol m^-2 s^-1) was of the same order as measured with the chambers. The nocturnal net CO₂ exchange measured with the chambers ranged from 4 to 7 μmol m^-2 s^-1 and with EC from ∼4 to ∼5 μmol m^-2 s^-1 when turbulent mixing below the canopy was sufficient and the measurements were reliable.

We studied gross photosynthesis by measuring the light response curves of the most common forest floor species and found the saturated rates of photosynthesis (P_max) to range from 0.008 (mosses) to 0.184 μmol g^-1 s^-1 (blueberry). The estimated gross photosynthesis at the study site based on average leaf masses and the light response curves of individual plant species was 2–3 μmol m^-2 s^-1. At the same time, we measured a whole community with another chamber and found maximum gross photosynthesis rates from 4 to 7 μmol m^-2 s^-1.