Water relations and gas exchange in poplar and willow under water stress and elevated atmospheric CO₂

Abstract

Predictions of shifts in rainfall patterns as atmospheric [CO2] increases could impact the growth of fast growing trees such as Populus spp. and Salix spp. and the interaction between elevated CO2 and water stress in these species is unknown. The objectives of this study were to characterize the responses to elevated CO2 and water stress in these two species, and to determine if elevated CO2 mitigated drought stress effects. Gas exchange, water potential components, whole plant transpiration and growth response to soil drying and recovery were assessed in hybrid poplar (clone 53-246) and willow (Salix sagitta) rooted cuttings growing in either ambient (350 &mgr;mol mol-1) or elevated (700 &mgr;mol mol-1) atmospheric CO2 concentration ([CO2]). Predawn water potential decreased with increasing water stress while midday water potentials remained unchanged (isohydric response). Turgor potentials at both predawn and midday increased in elevated [CO2], indicative of osmotic adjustment. Gas exchange was reduced by water stress while elevated [CO2] increased photosynthetic rates, reduced leaf conductance and nearly doubled instantaneous transpiration efficiency in both species. Dark respiration decreased in elevated [CO2] and water stress reduced Rd in the trees growing in ambient [CO2]. Willow had 56% lower whole plant hydraulic conductivity than poplar, and showed a 14% increase in elevated [CO2] while poplar was unresponsive. The physiological responses exhibited by poplar and willow to elevated [CO2] and water stress, singly, suggest that these species respond like other tree species. The interaction of [CO2] and water stress suggests that elevated [CO2] did mitigate the effects of water stress in willow, but not in poplar.

Water relations in Norway spruce trees growing at ambient and elevated CO₂ concentrations

“…Understanding how these processes are affected by an increase in CO 2 concentration is therefore fundamental to any sound prediction of future response of both natural and agricultural communities to atmospheric change (Long 1999). Changes in these basic processes are responsible for shifts in both resource allocation and resource using efficiency in plants growing under elevated CO 2 concentration (Saxe et al 1998, Johnson et al 2002, Tognetti and Peñuelas 2003.…”

Different responses of two contrasting Populus davidiana populations to exogenous abscisic acid application

“…Although much is known about physiological and morphological responses to water deficits in woody plant studies, particularly in poplar (Tschaplinski et al, 1998;Brignolas et al, 2000;Johnson et al, 2002;Amlin and Rood, 2003;Siemens and Zwiazek, 2003), few studies have focused on the relationship among drought tolerance, water-use efficiency and plant hormones.…”

Physiological Reaction of Salix Viminalis to Stress of Anthropogenic Origin

“…Soil bed salinity again appeared to be the factor most reducing the assimilation and transpiration intensity caused by limited access to water in the soil resulting from reduced chemical potential of water. Furthermore, increased resistance of diffusive stomata is worth noticing in soil bed salinity conditions, which is caused by extensive accumulation of Na and Cl ions in leaves (Johnson et al, 2002;Sperry et al, 2002). Petroleum derivative compounds also strongly reduced both assimilation and transpiration.…”