Agaricus bisporus mushrooms are supplied with water through both apoplastic as well as symplastic routes from distinct substrate layers

Agaricus bisporus is grown commercially on compost topped with a peat-based casing layer. Water is translocated from compost and casing to enable formation of mushrooms. Here, water translocation from casing and different parts of the compost into mushrooms was studied and linked to their water potential and contributing factors thereof: i.e. osmotic- and matric potentials. Water in the mushrooms mainly originated from the casing and to a lesser extent from the top and middle layers of the compost. Based on these results, alternative casing regimes were tested to increase mushroom production. This resulted in a total yield increase of up to 1.4-fold when the old casing was topped with a fresh layer of casing or when the casing was replaced after harvesting the second flush. Data indicate that the difference in water potential can drive passive water translocation from the casing to the first flush, without expending cellular energy. However during the second flush, no such water potential gradient is established between casing and the mushrooms, yet mushrooms still develop. The water potential in the compost indicates that water cannot be translocated to the mushrooms at all. Therefore, other components of the water potential should drive this water flow. We have indications that this component is the turgor of the mycelium. Moreover, we found a novel route of water translocation from casing to mushrooms via the apoplast.