THE INFLUENCE OF HUMIDITY UPON TRANSPIRATION AND GROWTH IN PSILOCYBE CUBENSIS

The influence of humidity upon individual basidiocarps of of Psilocybe cubensis was studied using an environmentally controlled wind tunnel and a computer program which helped to model growth and development. Regression models were developed which were able to explain 77% of the variation in the transpiration rate and 68% of the variation in growth rate. Transpiration and growth of this mushroom were significantly correlated with the humidity ofthe air. The fastest growth and the lowest transpiration occurred at the highest humidities. No inhibition of growth was detected at 0 pascals VPD (100% RH). Misting accelerated growth and transpiration while light had no effect. Although humidity was a very important factor influencing transpiration and growth, the size and shape of the mushroom were also important in water relations. The final water content of basidiocarps with thin stipes or those with larger surface area-to-volume ratios was significantly lower that of thickstiped mushrooms or those with small surface area-to-volume ratios even when grown under equal humidity. Growth rates under conditions which promoted the highest levels of hydration of the basidiocarp were rapid (up to estimated 4% increase in dry weight per h). Few precise studies of the influence of humidity on mushroom growth have been conducted. The appearance of fleshy mushrooms in nature is frequently associated with the presence of moisture. Indeed, the fact that most fleshy mush? rooms come up after rains and grow in, or very near, moist substrates suggests that they may be adapted to humid habitats. Most research on the influence of humidity on mushroom growth has been conducted with commercially important species. For the growth of Agaricus bi? sporus (J. Lange) Pilat, Edwards (1978) recommends 90% RH for wind flows of 50-100 mm/sec and 80% RH for air flows of 25 mm/sec in the temperature range 15-16 C. For Pleurotus sp., Kurtzman and Zadrazil (1982) report that humidities lower than 60% RH would be expected to cause rapid drying of the substrate while localized condensation would be expected to occur with humidities of 95%. Kurtzman and Chang-Ho (1982) recommend between 78 and 92% RH for Volvariella volvacea (Bull. ex Fr.) Sing., depending upon the ventilation. Badham (1983) found that high relative humidities (> 90% RH) and low wind speeds (< 100 mm/sec) favored the growth of Psilocybe cubensis (Earle) Sing. in the laboratory and natural environment. Many authors emphasize the importance of minimizing a build-up of carbon dioxide despite the maintenance of high humidity. Transpiration in several species of mushrooms was studied by Zoberi (1981). He found that evaporative water loss decreased with an increase in atmospheric humidity. Within the range of his experiments, the water content ofthe substrate did not have a great influence on the transpiration rate. A precise laboratory study that considered the influence of humidity on growth and transpiration of basid? iocarps was that of Plunkett (1956). He showed that the woody mushroom Po? lyporus brumalis Pers. ex Fr. grew poorly at high humidities while the growth of the fleshy mushroom Collybia velutipes [Flammulina velutipes (Fr.) Karst.] was