Cavitation and water storage capacity in bole xylem segments of mature and young Douglas-fir trees

Abstract

Hydraulic specific conductivity, vulnerability to cavitation and water storage capacity of Douglasfir sapwood was determined for samples from six young (1.0-1.5 m tall) and six mature trees (41-45 m tall). Measurements on samples from young trees showedthere were no effects of two contrasting sample types (entire stem segments vs sectors chiseled out of entire stems) on any of the calculated hydraulic parameters, for vulnerability to cavitation and water storage capacity. Measurements on mature trees were made on wood from four heights on the bole and from two sapwood depths. Outer and inner sapwood at the base of the tree had higher water storage capacities and were more vulnerable to cavitation than was sapwood from the tree top. At every height, old trees were more vulnerable to cavitation than at 1.0 m from the ground in young trees. The water storage capacities showed three distinct phases at the base of the trunk. Young trees had similar water storage capacity (per unit volume of sapwood) to the topof the mature trees, which was lower than the water storage capacity throughout the rest of the bole xylem. The way in which capacitance was calculated (on a volumetric basis vs a relative water content basis) affected the conclusion one would draw at the low water potentials (<-3 MPa). Within a tree, we found an apparent trade-off between having both hydraulic specific conductivity and stem water storage, and vulnerability to cavitation.

Maximum height in a conifer is associated with conflicting requirements for xylem design

“…For branches at 56 and 34 m, this threshold was Ϫ3.2 and , respectively (Fig. 5), and consistent with the embolism threshold observed for Douglas-fir seedlings in an earlier study (27). Thus, the height-related trend in the air-seeding pressure of branches was markedly steeper than that of the embolism threshold.…”

“…The trunk is the superhighway through which the water moves, but the branches make up the distribution network and typically show more pronounced transpirationinduced fluctuations in xylem tension (5). Transient release of stored water into the transpiration stream resulting from hydraulic capacitance of sapwood is likely to exert a greater damping effect on fluctuations in xylem tension in massive trunks than in more slender branches (27)(28)(29). In addition, lower xylem specific conductivity in branches than trunks (9,15) contributes to steeper axial tension gradients in branches.…”

“…The air-seeding pressure is widely used as an index of xylem vulnerability to embolism (27,32). Air-seeding pressure for branches at 56 and 34 m was Ϫ4.9 and Ϫ4.5 MPa, respectively (Fig.…”

Acoustic Emissions to Measure Drought-Induced Cavitation in Plants

“…A plant's vulnerability to cavitation is often used as a key feature of its drought resistance [29], and has been defined by plotting the percentage loss of hydraulic conductivity (PLC, %) against decreasing xylem water potential (ψ, MPa), which results in a vulnerability curve (VC) (Figure 1) [30]. The xylem water potential at 50% PLC (P50) is the most common parameter to describe a species "drought resistance".…”

Diurnal and seasonal variation in root xylem embolism in neotropical savanna woody species: impact on stomatal control of plant water status

“…The volumetric RWC-based capacitance (in RWC MPa -1 ), defined as ning 1980) was computed over the natural range of Y root encountered by each species. Because wood density varies between species, it was more accurate to express the capacitance as the ratio of change in RWC, which represents the proportion of non-cell wall space that is occupied by water, to change in Y root (Domec & Gartner 2001). However, for comparative reasons, capacitance (in g cm -3 MPa -1 ) was also expressed as the change in water mass relative to the sample volume per unit change in Y root .…”