Effects of Casuarina equisetifolia L. Litter on germination of Helianthus annuus L

Casuarina equisetifolia L. (Australian pine) affects ecosystems through multiple

mechanisms, including litter accumulation and chemical interactions. We evaluated how

litter concentration and soil mixture aging affected germination of Helianthus annuus L.

(common sunflower). Casuarina branchlets were incorporated into soil at 30, 150, and 300

g/kg and incubated for 0, 7, 14, or 21 days prior to sowing. Germination declined with

increasing litter concentration, with the highest concentration producing > 80 % probability

of zero germination across all aging periods. Soil incubated for 7 days showed higher

germination than non-incubated soil, whereas 14 and 21 days did not differ. Controls soil

without litter had complete germination, while branchlet-only controls had zero. These

results indicated a potential concentration-dependent reduction in germination under

controlled conditions, consistent with previously reported phytotoxic or allelopathic

patterns. Short-term soil incubation caused partial inhibition, although the mechanisms were

not evaluated.