Direct and acclimatory responses of dark respiration and translocation to temperature

Abstract

Background and aims: Accounting for the acclimation of respiration of plants to temperature remains a major problem in analysis of carbon balances of plants and ecosystems. Translocation of carbohydrates out of leaves in the dark requires energy from respiration. In this study relationships between the responses of leaf respiration and translocation to temperature are examined.

Methods: Direct and acclimatory responses to temperature of respiration and translocation in the dark were investigated in mature leaves of soybean and amaranth. In some cases translocation from leaves was prevented by heat-girdling the phloem in the leaf petiole, or photosynthesis during the previous day was altered.

Key results: In both species short-term increases in temperature early in the dark period led to exponential increases in rates of respiration. However, respiration rates decreased toward the end of the dark period at higher temperatures. Stopping translocation largely prevented this decrease in respiration, suggesting that the decrease in respiration was due to low availability of substrates. In soybean, translocation also increased with temperature, and both respiration and translocation fully acclimated to temperature. In amaranth, translocation in the dark was independent of temperature, and respiration did not acclimate to temperature. Respiration and translocation rates both decreased with lower photosynthesis during the previous day in the two species.

Conclusions: Substrate supply limited total night-time respiration in both species at high temperatures and following days with low photosynthesis. This resulted in an apparent acclimation of respiration to high temperatures within one night in both species. However, after long-term exposure to different temperatures there was no evidence that lack of substrates limited respiration in either species. In amaranth, respiration did not limit translocation rates over the temperature range of 20-35 degrees C.

Fig. 1.

Responses of respiration to temperature of leaves of (A) Glycine max and (B) Amaranthus hypochondriacus. Responses are given for short-term changes in temperature applied to the whole plant or just the measured leaf within 2 h of the beginning of the dark period, for the mean rate over the whole dark period, and mean values for the whole night for leaves in which the phloem was disrupted by heat girdling. Error bars are s.e. for n = 3 or 4. For clarity, error bars are not provided for the short-term responses for the leaf.

Fig. 2.

(A) Responses of translocation rate over the whole dark period to temperature, and (B) relationships between translocation rate and mean respiration rate for the same temperature treatments, for leaves of Glycine max and Amaranthus hypochondriacus. In G. max, the linear regression of translocation rate on temperature had the equation: translocation = −17·3 + 0·92 × temperature, with r² = 0·96, and the regression of translocation rate on respiration rate had the equation: translocation = −9·6 + 8·3 × respiration, with r² = 0·99. Regressions for A. hypochondriacus were not significant. Error bars are s.e. for n = 3 or 4.

Fig. 3.

Relationships between mean respiration rate over the whole dark period and mean photosynthetic assimilation rate of the previous day, and relationships between translocation rate and mean respiration rate for the same changes in assimilation rate, for leaves of Glycine max and Amaranthus hypochondriacus. In A. hypochondriacus, the linear regression of respiration on assimilation had the equation: respiration = 0·16 + 0·058 × assimilation, with r² = 0·99. In G. max, the linear regression of translocation on respiration had the equation: translocation = 0·62 + 3·39 × respiration, with r² = 0·97. Other lines are provided for clarity only. Error bars are s.e. for n = 3 or 4.