Effects of manipulation of water and nitrogen regime on the water relations of the desert shrub Larrea tridentata

Abstract

Water and nitrogen regimes of Larrea tridentata shrubs growing in the field were manipulated during an annual cycle. Patterns of leaf water status, leaf water relations characteristics, and stomatal behavior were followed concurrently. Large variations in leaf water status in both irrigated and nonirrigated individuals were observed. Predawn and midday leaf water potentials of nonirrigated shrubs were lowest except when measurements had been preceded by significant rainfall. Despite the large seasonal variation in leaf water status, reasonably constant, high levels of turgor were maintained. Pressure-volume curve analysis suggested that changes in the bulk leaf osmotic potential at full turgor were small and that nearly all of the turgor adjustment was due to tissue elastic adjustment. The increase in tissue elasticity with increasing water deficit manifested itself as a decrease in the relative water content at zero turgor and as a decrease in the tissue bulk elastic modulus. Because of large hydration-induced displacement in the osmotic potential and relative water content at zero turgor, it was necessary to use shoots in their natural state of hydration for pressure-volume curve determinations. Large diurnal and seasonal differences in maximum stomatal conductance were observed, but could not easily be attributed to variations in leaf water potential or leaf water relations characteristics such as the turgor loss point. The single factor which seemed to account for most of the diurnal and seasonal differences in maximum stomatal conductance between individual shrubs was an index of soil/root/ shoot hydraulic resistance. Daily maximum stomatal conductance was found to decrease with increasing soil/root/ shoot hydraulic resistance. This pattern was most consistent if the hydraulic resistance calculation was based on an estimate of total canopy transpiration rather than the more commonly used transpiration per unit leaf area. The reasons for this are discussed. It is suggested that while stomatal aperture necessarily represents a major physical resistance controlling transpiration, plant hydraulic resistance may represent the functional resistance through its effects on stomatal aperture.

Plant water status and hydraulic conductance during flowering in the southern California coastal sage shrub Salvia mellifera (Lamiaceae)

“…However, in response to water addition, we observed that K H and Ψ shoot increased with only moderate changes in leaf and fl oral gas exchange. Large increases in Ψ shoot and K H have been observed with experimental irrigation in southern California desert shrubs ( Meinzer et al, 1988 ), consistent with our measured responses of Ψ shoot and K H . Therefore, although transpiration rates were similar between control and irrigated plants, increased whole-plant hydraulic conductance is the major response to irrigation during fl owering in S. mellifera .…”

Reversible decreases in the bulk elastic modulus of mature leaves of deciduousQuercusspecies subjected to two drought treatments

“…On the other hand, decreases in e under water stress have been observed in mature leaves in apple ( Malus domestica , Davies & Lakso 1979), evergreen xerophytic shrub ( Larrea tridentata , Meinzer et al . 1988), three sugarcane cultivars ( Saccharum spp., Saliendra & Meinzer 1991), and Eucalyptus platypus (White, Turner & Galbraith 2000).…”

Leaf Water Relations and Maintenance of Gas Exchange in Coffee Cultivars Grown in Drying Soil

“…Bulk leaf turgor responses to drought can be quantitatively partitioned between osmotic and elastic adjustment components using the pressure-volume technique (8). Some species exhibit only one ofthese modes ofadjustment, whereas others exhibit a combination of the two (4,8,13, 17,18,19) On d 14, 22, 25, and 29, similar samples, each containing a pair of opposite leaves, were excised at dawn for determination of leaf water relations characteristics by the P-V method (27). Since hydration of cut shoots has been shown to cause changes in tissue elasticity and other biophysical characteristics in leaves of some species (5, 13), the leaf samples were sealed in plastic bags immediately after excision and were not subjected to any hydration treatment.…”

“…4,6,8,13,15,17,19). Both solute accumulation and increased tissue elasticity lower the water potential at which turgor loss occurs as *L' declines during drought.…”

“…Bulk leaf turgor responses to drought can be quantitatively partitioned between osmotic and elastic adjustment components using the pressure-volume technique (8). Some species exhibit only one ofthese modes ofadjustment, whereas others exhibit a combination of the two (4,8,13,17,18,19), though to date relatively few species have been evaluated. ' Published as Paper No.…”