Effects of light and nutrient limitations on thermal respiratory acclimation and nocturnal dynamics of leaf dark respiration

Background/Question/Methods

Tissue dark respiration provides energy and metabolites for many biosynthetic, maintenance and transport processes in plants, but results in losses of assimilated C typically exceeding 50% of gross photosynthesis. This research addressed two important issues concerning leaf dark respiration. First, we assessed the effects of growth temperature, light and fertilization on the temperature response of respiration.  Thermal acclimation of leaf respiration depends largely on two important respiratory parameters: base respiration (cool respiration) and the temperature response of respiration (E_O).  Second, we assessed the temporal temperature response of respiration throughout the dark period.  It is unknown whether these variables change throughout the dark period of a 24 hour span.  A principal goal of this research was to understand the fundamental mechanistic underpinnings of the temporal dynamic in leaf dark respiration through manipulations of leaf carbohydrate pools and leaf nitrogen status of plants growing at contrasting growth temperatures. Using soybean as a model species, 36 plants were randomly assigned and grown in four greenhouses [Two high temperature (HT; 30°C, 23°C) houses and two low temperatures (LT; 20°C day, 13°C night)] houses.  Within each house plants were subjected to high light, low light, fertilized and unfertilized treatments using a full factorial arrangement. 

Results/Conclusions

When respiratory parameters (cool respiration R₁₃, warm respiration R₂₅ and the temperature response of respiration E_o) were assessed at three times throughout the night (6pm, 11pm, 4am), we observed no differences among our measurement period in any respiratory parameters nor did we observe a decline in leaf starch throughout the night.  As such, times were pooled to assess thermal acclimation of respiration under the assigned treatments.  We observed acclimation in HT (high temperature) plants but only under optimal growing conditions (high light, high fertilization).  As limitations were imposed (shade or no fertilization) acclimation occurred less frequently; and when plants were grown under low light with no fertilization, no acclimation was observed.  Significant differences were evident mainly in E_o and R₂₅, not R₁₃ indicative of Type1 acclimation as described by Atkin and Tjoelker (2003).  Significant correlations between leaf starch were evident in HT plants but not low temperature (LT) plants and significant correlations were evident between R₁₃ and Leaf N in LT plants, but not HT plants further emphasizing separate limitations acting on warm and cool respiration.  These findings have large implications for natural ecosystems and may play a role in assessing an ecosystems resiliency to climate change (present and future).