INTERACTIONS BETWEEN RIPARIAN LEAVES AND ALGAL MICROBIAL ACTIVITY IN STREAMS/

The effects of leaf leachates derived from six forest trees on algal b iomass development was examined in a 3-week experiment in a New Zealan d spring. The trees all occur in riparian zones and were Fagus sylvati ca and Alnus glutinosa from Europe, Eucalyptus globulus from Australia , Pinus radiata from western North America, and two New Zealand specie s, Fuchsia excorticata and Nothofagus solandri. Leachates from five sp ecies inhibited algal growth relative to controls, whereas leachate fr om a sixth species (F. excorticata) was stimulatory. In contrast, cell ulose breakdown was unaffected by five leachates and inhibited by the other (F. sylvatica). In a second experiment, colonization of leaves a nd inert substrata (polythene strips) by algae was examined with SEM a fter 16 days. Algal abundance was greatest on polythene strips and lea ves of F. sylvatica, and substantially lower on the other species. Our results indicate that both leaf texture and chemical composition can affect algal colonization and growth, and that chemicals derived from leaves have the potential to both inhibit and stimulate ecosystem proc esses in streams.