Changing oxygen concentration around the rootstock alters spear elongation and sprouting of white asparagus

Abstract We investigated the effects of manipulating the atmospheric oxygen (O 2 ) concentration around white asparagus rootstocks planted in pots to evaluate the applicability of this technique for growth regulation in white asparagus production. The O 2 concentrations around the pots were adjusted to 5%, 10%, 20%, 40%, 60%, and 80%, and plants were exposed to these conditions over a 38-d period. We found that the time of both initial sprouting (i.e., when the length of the first emerging spears reached >30 mm) and harvesting were delayed when the O 2 concentration around the pots was 5%; moreover, decreases in the soluble solids contents (SSCs) of the storage roots were inhibited at 5% O 2 relative to the control (20% O 2 ). These delays were likely due to a hypoxic effect, which inhibits the metabolism of some respiratory substrates such as sugars and/or organic acids. Under the 5% O 2 treatment, the O 2 concentration during the gaseous phase of the soil in the pot was estimated to be 12.4–14.4%; therefore, sprouting should be delayed when the O 2 concentration around the roots is 2 concentration around the spears was within the range of 60–80%. Considering that the 40% O 2 concentration did not affect the rate of spear elongation, it appears that the threshold for this phenomenon is an O 2 concentration of 40–60%. When the rootstocks grown under each O 2 treatment were replanted and cultured under normal atmospheric conditions for 25 d, no significant differences were found in growth and yield ability, such as the time of initial harvesting, number of harvested spears, yield, and spear weight. Therefore, the effects of different atmospheric O 2 concentrations did not continue after cessation of the experimental treatments. Our results suggest that controlling the O 2 concentration around rootstocks may be a new method for the growth regulation of white asparagus. We also expect that the new method can be applied in a closed cultivation system as well as in a plant factory.