Stimulation of weed seed germination by 1–(3-chlorophthalirnido) cyclohexanecarboxamide (AC 94377)

The N-substituted phthalimide, AC 94377, promoted the germination of dry-stored seeds of 17 out of 24 weed species in Petri-dish tests maintained at 22°C. In a further test it was able to substitute for light and/or alternating temperatures in promoting the germination of some species. AC 94377 was more active than GA, in stimulating Solanum nigrum seed to germinate. When mixed with soil in the laboratory, AC 94377 again promoted germination of S. nigrum but the level and persistence of activity differed between soils. In the glasshouse, with soil containing a natural weed seed population, more seedlings emerged from treated than from untreated soil but this number represented fewer than half of the apparently viable seeds present. Field applications of AC 94377 promoted the germination of hand-sown seeds of certain weed species but did not increase the number of seedlings emerging from the natural weed seed bank.     

Limiting nutrients for periphyton growth in sub-alpine, forest, agricultural and urban streams

1. Nutrient-diffusing artificial substrata were used in summer and autumn to assess limiting nutrients for periphytic algal growth in streams draining sub-alpine, forested, agricultural and urban catchments in eastern Victoria, Australia. 2. Chlorophyll a density was primarily limited by nitrogen in most cases; often phosphorus was secondarily limiting. One sub-alpine, one forest and one agricultural stream were primarily phosphorus limited in at least one season. Added trace elements and vitamins did not increase chlorophyll density. 3. The dominant filamentous algal genera did not differ greatly between various nutrient enrichments. However, the relative abundance of Stigeodanium spp. was sometimes increased on substrata containing the limiting nutrient. 4. The results suggest that nutrient limitation is a widespread phenomenon in Victorian streams, and that limiting nutrients can be inferred from stream-water nitrogen to phosphorus ratios in many instances.