INTERACTION BETWEEN ALGAE AND SEED-GERMINATION IN TROPICAL DUNE SLACKSPECIES - A FACILITATION PROCESS

The importance of algae dune slack stabilisation has been extensively analysed, but little has been done regarding their potentially favoura ble role in germination and establishment of phanerogams. Dune slack i s a seasonal freshwater habitat that depends on water table level fluc tuation. Our hypothesis is that in these highly unpredictable systems, algae maintain a certain degree of humidity in the soil and, thus, pe rmit phanerogam germination and establishment. The objective of this s tudy was to compare the germination of four species characteristic of tropical dune systems: Cyperus articulatus L., Fimbristylis cymosa R. Br., Fuirena simplex Vahl and Rhynchospora colorata (L.) Pfeiffer, in different substrates and degrees of humidity. For germination trials, seeds of the four species were placed each on three substrates: in san d (control), filamentous algae on sand and cotton on sand. Two irrigat ion protocols were followed: continual watering (wet treatment) and we ekly watering (dry treatment). Each week during a 21-week period, the number of germinated seeds from each species was recorded. The highest percentage of germination for the four species was observed during we t treatment. C. articulatus had the highest germination rate of the fo ur species in algae (70%), and cotton (51%) on sand. Highest germinati on for F. simplex, F. cymosa and R. colorata took place in algae, alth ough the percentages were very low. Differences in germination between the three substrates for these species were statistically significant (P < 0.05). During dry treatment, C. articulatus was the only species that exhibited a significant germination, principally in algae and co tton. The results suggest that algae maintain substrate humidity and f avour germination of the four species. This could be important in sand dune slacks where marked fluctuations in temperature and humidity occ ur. (C) 1998 Published by Elsevier Science B.V.