Seasonal patterns of tissue water relations in three Mediterranean shrubs co‐occurring at a natural CO₂ spring

Abstract

Seasonal changes in tissue water relations of Erica arborea L., Myrtus communis L. and Juniperus communis L., grown in a Mediterranean environment, were analysed under field conditions over a 12 month period by comparing plants grown in the proximity of a natural CO 2 spring (about 700 mmol mol -1 atmospheric CO 2 concentration, [CO 2 ]) with plants in ambient conditions. Tissue water relations varied in response to changes in water availability, but the seasonal course of tissue water relations parameters was also related to ontogeny. Tissue water relations of these co-occurring shrubs were not alike. Osmotic potentials and saturated mass/dry mass ratio were lowest during peak drought stress periods. Diurnal changes in osmotic potential at the point of turgor loss were least early in the season, maximal in mid-season, and decreased again in autumn. Turgor potentials decreased as drought progressed and were highest in late fall and mid-winter. Symplastic water fraction was highest in mid-spring for E. arborea and M. communis and decreased during the summer, while the opposite was observed for J. communis. Common to all species, under elevated [CO 2 ], was an increase of turgor pressure, particularly during the summer months. Other parameters showed species-specific responses to long-term elevated [CO 2 ]. In particular, exposure to elevated [CO 2 ] increased osmotic potentials in E. arborea under drought, while the opposite was the case for J. communis. Site differences in predawn to midday shifts were not strong in any of the species. Differences in tissue water relations suggest that the coexistence of these shrubs in the same environment with similar water availability are partially based on differential water relations strategies and water use patterns. Regardless of the mechanisms, growth of these shrubs in elevated [CO 2 ] may be either less, similarly or more affected by drought stress than plants in ambient [CO 2 ] depending on the species and season.

Effects of Elevated [CO2] and Low Soil Moisture on the Physiological Responses of Mountain Maple (Acer spicatum L.) Seedlings to Light

“…In this study, the elevated [CO 2 ] increased biomass allocation to root, and the magnitude of increase was greater under the low than the high soil moisture (Danyagri and Dang unpublished ). These results are in agreement with the findings of other studies that found increased biomass allocation to root as a drought tolerant mechanism under low soil moisture and elevated [CO 2 ] [61].…”

Tissue-water relations of two co-occurring evergreen Mediterranean species in response to seasonal and experimental drought conditions

“…In previous studies, AWF (Wenkert et al 1978) and TW/ DW (Davis and Mooney 1986;Tognetti et al 2000) have been reported to vary ontogenically. Nevertheless, adjustments through changes in cell volume in response to drought are not uncommon and have been reported in evergreen sclerophylls (Calkin and Pearcy 1984) as well as in species that do not exhibit osmotic adjustment, such as carob (Nunes et al 1989).…”

Long-term effects of elevated atmospheric CO2 on species composition and productivity of a southern African C4 dominated grassland in the vicinity of a CO2 exhalation

“…Natural CO 2 springs have been used with great success to test long-term effects of elevated CO 2 on leaf traits (Ko¨rner and Miglietta 1994), photosynthesis, biochemistry and growth of grasses (Cook et al 1998), carboxylation and light utilization of trees (Stylinski et al 2000), tree growth (Ha¨ttenschwiler et al 1997), decomposition and nutrient dynamics (Cotrufo et al 1999), plant water relations (Tognetti et al 2000) and soil nitrogen and carbon cycling and storage (Tate and Ross 1997;Ross et al 2000). These 'natural' experiments have provided valuable insights into how to scale up predictions derived from short-term laboratory, microcosm or FACE experiments.…”