Rootstock Influence on Gas Exchange among Cornus

Grafting is a common propagation technique for woody ornamental plants.  However, there is a dearth of knowledge on the effects of rootstock on the physiology and water use of woody ornamental plants.  Cornus florida and Cornus kousa, two common nursery crops, were self- and reciprocally grafted and subjected to increasingly drier substrate moisture conditions to evaluate the effect of rootstock.  Transpirational moisture loss over the range of container moisture levels from 90 to 60% of container capacity was linear. There was a small difference in transpiration rate observed for C. florida ‘Cherokee Princess’ and C. kousa ‘National’ when budded on to C. florida vs. C. kousa seedling rootstocks. Transpiration was 13 and 5% greater when C. kousa was used as the rootstock for C. florida ‘Cherokee Princess’ and C. kousa ‘National’, respectively. This suggests that C. kousa root systems had a greater capacity for water absorption and movement compared to C. florida root systems. Photosynthesis and stomatal conductance followed a sigmoidal relationship as substrate moisture content was reduced.  For both clonal scions, there was a trend for photosynthetic rate to be higher on seedling C. florida compared to C. kousa rootstocks as container moisture content was reduced. Photosynthetic rate differences due to rootstock were 4, 11, 14, and 100% for C. florida ‘Cherokee Princess’ and 15, 14, 8, and 91% for C. kousa ‘National’ as the moisture content was reduced from 90, 80, 70, and 65% of container capacity, respectively. There was no consistent trend for a rootstock effect on stomatal conductance. For C. florida ‘Cherokee Princess’ stomatal conductance was reduced on the C. kousa rootstock at moisture contents lower than 70% of container capacity, but C. kousa ‘National’ scion on C. kousa rootstock only showed a difference at 70% of container capacity, whereas scions on the C. florida rootstock showed reduced stomatal conductance. However, at 65% of container capacity, both photosynthesis and stomatal conductance were reduced to zero for scions on the C. kousa rootstocks, while scions were still active at that moisture content on C. florida rootstocks. These data demonstrate that rootstock effects on transpiration and gas exchange must be considered when these attributes are considered important for physiological studies or irrigation modeling studies.