PARENT SESSION
Oral Session 10: Physiology I: Temperature, Light, and Growth.
Presiding: C Knight
Monday, August 2, 8:00 AM to 11:30 AM, Meeting Room C 123.

Evergreen tree seedlings acclimate to increased night temperatures under field conditions.

EGERTON, JOHN¹, BRUHN, DAN¹, BALL, MARILYN¹, ¹ Cooperative Research Centre for Greenhouse Accounting, Canberra, ACT, Australia

ABSTRACT- Global warming is causing more rapid increase in night than day temperatures. This asymmetry invites the question: how will increase in night-time temperature affect growth of temperate evergreens? To answer this question, seedling snow gums (Eucalyptus pauciflora) were grown under field conditions subject to natural variation in the weather. Nocturnal heating was provided by a Free Air Temperature Increase (FATI) system of infra-red lamps. Four treatments were imposed: control (no heating), and warming to raise night temperatures 1, 2 or 3 ^oC above ambient. Climatic conditions during the study were mild compared to long-term records. Gas exchange characteristics were surveyed at intervals of 6 weeks. Rates of photosynthesis and night-time respiration varied seasonally, with values being minimal in winter. Within a survey, nocturnal heating treatments had no significant effects on either light saturated rates of CO₂ assimilation or rates of respiration at night (R_n) when measured at growth temperatures. Further measurements showed that R_n was highly responsive to immediate changes in temperature, and thus similar values of R_n achieved at different growth temperatures were caused by acclimation. Bud break and stem elongation in spring differed little between treatments. At the end of the experiment there were no significant differences in either biomass or allocation with different levels of nocturnal warming. These data show that, because of acclimation, small scale variation in night temperature may have less effect on carbon balances than expected.

Key words: Acclimation, Growth, Respiration, Temperature