Stomatal control of photosynthesis in detached leaves of woody and herbaceous plants

Abstract

Photosynthesis and transpiration were assayed in leaves and needles of some woody species (Pinus sibirica Du Tour, P. sylvestris L., Larix sibirica Ledeb., Betula pendula Roth., Quercus robur L.), annual herbaceous plants (Amaranthus cruentus L. cv. Tampala, Celosia argentea L. f. cristata (L.), Gomphrena dispersa Standl., Solanum tuberosum L., Helianthus annuus L., H. tuberosus L.), and perennial herbs (Inula helenium L., Poligonum weyrichii F. Schmidt, Polymnia sonchifolia Poepp. & Endl.). A high-precision portable gas-analyzing system GFS-3000 with a climate-controlled chamber was used for measurements on leaves both before and after leaf detachment from the shoot under conditions optimal for photosynthesis: photosynthetically active radiation of 2000 μE/(m2 s), 22–25°C, and a relative humidity of 65–70%. The steady-state gas exchange in illuminated leaves of all plant species examined was characterized by a directly proportional relationship between photosynthesis and transpiration (R 2 = 0.87). This means that the temporal course of H2O and CO2 gas exchange in detached leaves suffices to characterize the status of stomatal control of photosynthesis. The general trend in the effect of leaf detachment, observed in herbaceous and woody plants, is that the stomatal control of photosynthesis was retained within first 3–5 min after leaf excision. By contrast, the increase in transpiration after leaf detachment was species-specific. Because of this circumstance, the measurements of transpiration by rapid weighing method may result in overestimation of transpiration rates by 10–15% for some plant species, compared to steady-state rates of gas exchange in undetached leaves.