Biology of Fungi on Plants in the Sub-Antarctic

Abstract

A study of microfungi growing on three major plant species on the island of South Georgia was made during the Antarctic summer of 1979 - 1980. Commonly isolated species included Botrytis cinerea, Chaetophoma sp., Chrysosportum pannorum, Cladosporium sphaerospermum, Penicillium spp. and Mucor hiemalis, plus a large number of sterile mycelia. As leaves aged, their water contents decreased and levels of soluble carbohydrates were reduced. On falling to the litter layer, leaf carbohydrate levels declined further, but water contents were increased. The litter mycoflora was markedly different from that of standing dead leaves. All of the most commonly isolated phylloplane species were capable of cellulose oxidation and all showed protease activity. Pectinase activity was exhibited by all of the phylloplane species tested. Only Botrytis cinerea appeared to be capable of lignin degradation. Significant cellulase activity continued at 1°C, with an optimum around 20°C. Studies on the effects of temperature and relative humidity on germination and growth have shown relative humidity to be an important factor in determining the germination percentage. Substrate water activities below 0.90 caused a cessation of growth in all of the species tested except for Cladosporium sphaerospermum. All species tested had temperature optima for growth at around 20°C, but were capable of growth at-1°C. Germination of Chaetophoma sp. was restricted to temperatures above 10°C, but all other species tested showed germination at 50°C. When placed in water, moribund and dead leaves showed leakage of up to 90% of total available reducing sugars in a few hours. No effect could be detected of freeze-thaw cycles upon leakage. Linear extension of Botrytis cinerea was inhibited by volatile factors released from other colonies, and hyphae of ‘this’ fungus were often observed to grow helically around hyphae of Chaetophoma and Cladosporium sphaerospermum.