Photosynthetic activity and water relations of sprouts of Pasania edulis

Abstract

In order to investigate the factors causing fast growth of sprouts of Pasania edulis, photosynthetic activity and water relation characteristics of lower (mature) leaves and upper (expanding) leaves of the sprouts were compared with those of seedlings and adult trees of P. edulis. Apparent quantum yield was generally low.Maximum photosynthetic rate was highest in the lower leaves of sprouts. Stomatal frequency was higher in sprout leaves than in seedling leaves. Osmotic potential at the water saturation point and water potential at the turgor loss point, in leaves, were higher in sprouts than in seedlings and adult trees. Symplasmic water content per unit leaf area was higher in sprouts than in seedlings. These water relation parameters in leaves indicated that sprout leaves are superior in maintaining cell turgor against water loss, but are not tolerant to water stress. In field measurements, sprout leaves showed higher stomatal conductance and transpiration rates. These results indicated that sprout leaves fully realized their high potential productivity even under field conditions. The leaf specific conductance, from the soil to the leaf, was higher in sprouts than in seedlings. Large and deep root systems of the original stumps of the sprouts may be attributed to the high leaf specific conductance.Key words: leaf specific conductance; leaf water relations; potential productivity; stump root system; water stress. INTRODUCTIONIt has been established that sprouts grow faster than seedlings. The fast growth of sprouts may play an important role in the regeneration and recovery of disturbed vegetation, and has been applied in the practical management of fuel wood forests over a long period (Blake 1983). The ecological significance of sprouts in natural forest regeneration processes has also been reported for several hardwood species (Auclair 1975; Tryon & Powell 1984;Ohkubo et al. 1988;Peters & Ohkubo 1990).Recently, several researchers have reported the physiological and morphological differences between seedling and coppice shoot leaves in relation to the high productivity of sprouts (Blake 1980; Accepted 15 December 1992. Tschaplinski & Blake 1989a,b; Ito & Suzaki, 1990). Most of these studies dealt with the characteristics and changes in gas exchange activity of coppiced seedlings, which do not have large stump root systems. However, the fast growth of sprouts observed in young coppice forests may be due to the pre-existing stump root system which is a source of a large amount of storage and is the water and mineral absorbing organ (Ito et al. 1989). Thus, in this study, the characteristics of photosynthesis and water relations of stump sprouts (developed after clear-cutting of large trees) were examined in comparison with seedlings in order to understand the fast growth of sprouts. In particular, the differences in the potential productivity of leaves and their actual behavior under field conditions were examined with regard to water relations. The role of the stump root system as the water absorbing or...

Basal reiteration improves the hydraulic functional status of mature Cinnamomum camphora trees

“…This is similar to stump sprouts, which have higher hydraulic conductance than seedlings because of their well developed root systems (Ito and Gyokusen 1993;Kauppi et al 1990). In addition, the hydraulic conductivity of the shoot axis is higher for sprouts than for seedlings (Ito et al 1995a;Saha et al 2005).…”