Influence of photosynthetic parameters on leaf longevity
Botanic Garden, Ural Branch
of Russian Academy of Sciences
620144 Yekaterinburg, 8 Marta, 202a
e-mail: serge.vasfilov@mail.ru
Higher plants show a wide range of leaf lifespan (LL) variability. LL is calculated as a sum of functional LLf (corresponding to the time of active photosynthesis and CO2 accumulation in the leaf) and nonfunctional LLn (the time of photosynthetic activity absence). For evergreen species of boreal zones, LLn corresponds to the period of winter rest. Photosynthetic potential of leaf (PPL), interpreted as the maximum possible amount of CO2 that can be fixed during its life, can be estimated on the basis of maximum photosynthesis rate (Pa ) dynamics during LLf ; the maximum (Pa max ) being achieved in mature leaf. Photosynthetic potential depends on LLf more strongly than on Pa max. The PPL/LLf , ratio is indicative of the rate of PPL realization over leaf lifespan. As LLf shows strong positive correlation with LL, the latter parameter can also characterize the rate of PPL realization. Long LLf in evergreen species provides higher PPL, which is advantageous by comparison with deciduous ones. In evergreen species, the PPL itself is realized slower than in deciduous ones. The increase in LL, and LL is accompanied by the increase in leaf constructional cost (LCCa) as well as the decrease in photosynthesis rate. At that, photosynthesis rate per unit of dry weight (Pm) decreases much faster than that per unit of leaf area (Pa ). Apparently, when considering dry leaf weight, the apoplast share seems to be much higher in long-living leaves of evergreen species than in short-living leaves of deciduous species. The leaf payback (LP) may be stabilized by unidirectional shifts in PPL and LCCa . Species with short/long LL, and high/low PPL realization rate are typical for early/late succession stages and for habitats with the environmental conditions favorable/ adverse for photosynthesis and growth. If the conditions for photosynthesis and growth are favorable, high PPL realization rate provides advantage in competition. The PPL realization rate is coupled with the rate of leaf senescence.
