Oral Session # 77: Plant Ecology VI: Temperature and Water Stress.
Presiding: C Ford
Thursday, August 7. 1:30 PM to 5:00 PM, SITCC Meeting Room 102.

Nocturnal warming of Eucalyptus pauciflora.

Loveys, Beth1, Williams, William*,2, Edwards, Everard1, Egerton, Jack1, Pippen, Wayne1, Loveys, Brian3, Ball, Marilyn1, 1 Research School of Biological Sciences, Canberra, ACT, Australia2 St. Mary's College of Maryland, Saint Marys City, MD3 CSIRO Plant Industry, Adelaide, SA, Australia

ABSTRACT- Virtually all climate-change scenarios include increased night temperature, but there has been little research on how warmer nights might affect plant growth. Increased minimum temperatures could result in a longer growing season thus increasing carbon gain, but they could also lead to increased respiration rates thus reducing carbon gain. We investigated the effect of increased night temperature on the carbon gain of field-grown Eucalyptus pauciflora (snow gum) by gently heating them at night with infrared heaters while otherwise leaving them exposed to natural weather conditions. We measured growth and gas exchange during a 5-month period under four treatments: control (no heating), 2°C above ambient shoot only, +2°C shoot and root, and +4°C shoot and root. Warming by 4° accelerated stem elongation and bud break compared to the 2° treatment and the control, but the 4° plants suffered considerable damage from a late-spring frost just before the completion of the experiment. At the conclusion of the experiment the +4°C treated plants were largest and the control plants were the smallest. All warming treatments had significantly higher assimilation rates under saturating light (Asat) than the controls, and there was no difference in Asat among different degrees of warming. Warmed plants consistently exhibited higher rates of electron transport and Rubisco activity than controls. A one-night respiration measurement of all plants just before harvest showed that control plants had significantly lower respiration than warmed plants at their treatment temperatures, but respiration measured at a common temperature was not different among treatments. Thus, there was no evidence for temperature acclimation. Elevated night temperatures seem to accelerate growth and photosynthesis, but they also increase respiration and may increase susceptibility to frost damage.

Key words: Eucalyptus pauciflora, fati, climate change, respiration