Effects of temperature on leaf hydraulic architecture of tobacco plants

Modifications in leaf anatomy of tobacco plants induced greater leaf water transport capacity, meeting greater transpirational demands and acclimating to warmer temperatures with a higher vapor pressure deficit. Temperature is one of the most important environmental factors affecting photosynthesis and growth of plants. However, it is not clear how it may alter leaf hydraulic architecture. We grew plants of tobacco (Nicotiana tabacum) 'k326' in separate glasshouse rooms set to different day/night temperature conditions: low (LT 24/18 °C), medium (MT 28/22 °C), or high (HT 32/26 °C). After 40 days of such treatment, their leaf anatomies, leaf hydraulics, photosynthetic rates, and instantaneous water-use efficiency (WUEi) were measured. Compared with those under LT, plants exposed to HT or MT conditions had significantly higher values for minor vein density (MVD), stomatal density (SD), leaf area, leaf hydraulic conductance (K leaf), and light-saturated photosynthetic rate (A sat), but lower values for leaf water potential (ψ l) and WUEi. However, those parameters did not differ significantly between HT and MT conditions. Correlation analyses demonstrated that SD and K leaf increased in parallel with MVD. Moreover, greater SD and K leaf were partially associated with accelerated stomatal conductance. And then stomatal conductance was positively correlated with A sat. Therefore, under well-watered, fertilized conditions, when relative humidity was optimal, changes in leaf anatomy seemed to facilitate the hydraulic acclimation to higher temperatures, meeting greater transpirational demands and contributing to the maintenance of great photosynthetic rates. Because transpiration rate increased more with temperature than photosynthetic rate, WUEi reduced under warmer temperatures. Our results indicate that the modifications of leaf hydraulic architecture are important anatomical and physiological strategies for tobacco plants acclimating to warmer temperatures under a higher vapor pressure deficit.