Ozone uptake characteristics in different dominance hierarchies of poplar plantation

The ozone uptake characteristics of poplar under natural conditions in different dominance hierarchies were studied based on sap flow methods. The results showed that: the diurnal variation of ozone concentration was of single peak type, with the value ranging between 25.5 and 175.0μg/m3; the tendency of its variation was consistent with that of temperature; the diurnal variations of the ozone uptake rate (F_o_3) and canopy ozone conductance (G_o_3) in different tree shape levels were of unimodal type; the change of F_o_3 followed an order of depressed tree (43.24nmol/(m2·s)) > middle tree (29.77nmol/(m2·s)) > dominant tree (24.56nmol/(m2·s)), while the value of G_o_3 ranked as the dominant tree (101.59mmol/(m2·s)) > depressed tree (92.92mmol/(m2·s)) > middle tree (81.60mmol/(m2·s)). The mean value of F_o_3 was (32.52±7.87) nmol/(m2·s), while that of G_o_3 was (92.04±8.18) mmol/(m2·s) in different tree shape levels. The effects of Rs, VPD and t on G_o_3 and F_o_3 were in an order of dominant tree > depressed tree > middle tree. Peak concentrations of ozone lagged behind the peak value of sap flow density, and over-high ozone concentration would inhibit transpiration. There was a good consistency between the changes of atmospheric ozone concentration and sap flow density, and sap flow technique is suitable for the calculation of ozone uptake of plants.