The impact of bird's nest ferns on stemflow nutrient concentration in a primary rain forest, Sabah, Malaysia.

摘要

A study was conducted in the lowland evergreen dipterocarp forest at Danum Valley Field Centre, Sabah, Malaysia, to determine the effect of bird's nest ferns (Asplenium nidus complex) on the total ion conductivity, and nitrate and potassium concentrations in stemflow during natural rainstorm events. Data were collected between April and May 2004. Twenty ferns were randomly selected from which to make water collections, and at each of these sites, water collection gauges were placed on the trunk of the supporting tree, above and directly below the fern to collect stemflow and at the ground level, 1 m from the base of the tree to collect throughfall. Water collected from each sites were measured for ion conductivity, nitrate and potassium. Canopy openness, DBH, maximum diameter of the fern and percentage epiphyte cover on the trunk above the fern were also recorded for each site. The pattern of nutrient release (continuous or in pulse) from the ferns was also analysed by selecting 12 ferns, which were poured with distilled water after at least a period of 5 days without rain. Water was then collected at the base of the fern, and were measured for total ion conductivity, and nitrate and potassium concentration.Total ion conductivity was significantly higher in stemflow samples below the fern than in throughfall samples. Samples from below the fern showed higher total ion conductivity compared with above-fern samples. Nitrate concentration was significantly higher in the stemflow samples below the fern than in samples above the fern and in throughfall. Potassium concentration was significantly higher in samples collected below the fern than in throughfall samples. Results show that bird's nest ferns clearly affect nitrate concentrations in stemflow. Nitrate s not easily leached from plant material but is predominantly released through litter decomposition. Decomposition of the leaf litter stored in bird's nest ferns is therefore likely to be responsible for the enrichment in stemflow. No variables were significant in determining the potassium concentration in the stemflow samples below the fern, although DBH showed a significant positive relationship to the potassium concentration in the stemflow above the fern. A more open canopy will result in more rainwater falling straight through and therefore will not be enriched by contact with plant surfaces. Open areas will also be lighter and therefore probably have larger ferns growing in them. Water samples collected from distilled water that had percolated through the ferns showed a clear pulsed release of nutrients, which is likely due to an initial lag when the fern material is dry and the water simply washes over the material. As the volume of water collected below ferns was not lower than the volume of water collected above ferns, bird's nest ferns increasing the nutrient concentration of stemflow will increase the amount of nutrients available to other epiphytes, algae and fungi on the trunk.