Articles
DO ROOTS OF ROSE CUTTINGS SUFFER FROM OXYGEN DEFICIENCY DURING PROPAGATION IN ROCKWOOL? (REFEREED)
We questioned whether this was the optimal rooting medium, particularly with regards to oxygen availability.
In a number of experiments it was shown that number of roots, root length and shoot growth of c.v. ‘Frisco’ were increased when a pressure head of -6.5 cm was applied.
Compared to aerated water culture (8.5 mg O2l-1), alcohol dehydrogenase (ADH) activity and porosity were increased in roots grown in rockwool blocks without pressure head (0 cm treatment). Similar effects were found in roots grown in a stagnant water culture.
These effects in rockwool and stagnant water culture indicated oxygen stress, since similar (but more severe) effects were found by limiting the oxygen supply, resulting in a concentration of 1.3 mg O2l-1 in water culture.
When different pressure heads (+2, 0, -3.3, -6.5, -10 cm) were applied in rockwool, optimal rooting and shoot growth was achieved at -6.5 cm.
The volume fractions of water and air in the whole blocks and in the lower 2.75 cm part of rockwool blocks (where the actual root initiation and root growth takes place) were determined and calculated at the different pressure heads.
From these results, the data on root ADH activity and on root/shoot growth, it was concluded that oxygen stress is minimal and rooting is optimal at a volumetric air content between 20 and 25 % in the lower 2.75 cm of the rockwool; this corresponds to a volumetric air content between 37 and 42% in the whole block.