Facilitation of seedling establishment: Reduction in irradiance enhances winter growth of Eucalyptus pauciflora

We determined whether plants benefit from a reduction in irradiance when gr owth is limited by low temperatures. Growth of snow gum (Eucalyptus paucifl ora Sieb, ex Spreng,) seedlings was studied in response to two irradiance r egimes (100% and 50% sunlight) under field conditions during autumn and win ter. Seedlings were planted on north (exposed) and south (sheltered) sides of vertical screens transmitting 50% incident sunlight. This planting arran gement allowed assessment of affects of excess irradiance on growth of seed lings subject to common temperature minima, Over winter, sheltered seedling s were less photoinhibited, had higher photosynthetic CO, assimilation rate s, lost less leaf area, and maintained a higher leaf-area ratio than expose d seedlings. These differences were consistent with greater growth of shelt ered than exposed seedlings by the end of winter. These results show that s hading may contribute to facilitation of regeneration by nurse plants in fr ost-prone environments.