Photosynthetic, hydraulic and biomechanical responses of Juglans californica shoots to wildfire

Abstract

Leaf gas exchange and stem xylem hydraulic and mechanical properties were studied for unburned adults and resprouting burned Juglans californica (southern California black walnut) trees 1 year after a fire to explore possible trade-offs between mechanical and hydraulic properties of plants. The CO(2) uptake rates and stomatal conductance were 2-3 times greater for resprouting trees than for unburned adults. Both predawn and midday water potentials were more negative for unburned adult trees, indicating that the stems were experiencing greater water stress than the stems of resprouting trees. In addition, the xylem specific conductivity was similar in the two growth forms, even though the stems of resprouting trees were less vulnerable to water-stress-induced embolism than similar diameter, but older, stems of adult trees. The reduced vulnerability may have been due to less cavitation fatigue in stems of resprouts. The modulus of elasticity, modulus of rupture and xylem density were all greater for resprouts, indicating that resprouts have greater mechanical strength than do adult trees. The data suggest that there is no trade-off between stem mechanical strength and shoot hydraulic and photosynthetic efficiency in resprouts, which may have implications for the success of this species in the fire-prone plant communities of southern California.

Structural determinants of increased susceptibility to dehydration‐induced cavitation in post‐fire resprouting chaparral shrubs

“…Interestingly, Utsumi et al . () also found this pattern, that is, significantly altered P 50 post‐fire relative to unburned plants, but no change in K s for a different southern California shrub species, Juglans californica . Differences between unburned and resprouting plants in structure and function may persist beyond the year immediately after fire (Kaneakua ; Pausas et al .…”

“…We also examined the plant biomechanical traits of xylem density and modulus of rupture (MOR) because these had been reported previously to have varied between unburned and resprouting plants of a different chaparral species (Utsumi et al . ) and are correlated with chaparral plant hydraulic traits (Jacobsen et al . , , ).…”

“…These changes complicate predictions of stand resilience with future changes in climate or with changes in disturbance or recruitment regimes. Some previous studies suggest that hydraulic traits may vary with the transition from seedling or juvenile to adult plants (Sperry & Saliendra 1994;Rice et al 2004) or during post-disturbance resprouting (Utsumi et al 2010;Ramirez et al 2012;Pratt et al 2014;Pausas et al 2016;Schwilk et al 2016). However, these studies have examined relatively few species, and patterns of trait change have varied by species and study (for instance, see Linton et al 1998;Matzner et al 2001;Rice et al 2004).…”

Transpiration in recovering mixed loblolly pine and oak stands following wildfire in the Lost Pines region of Texas

“…The switch to younger vegetation, both resprouts and nonsprouting saplings, serves as the first visual indication of change to postfire stand structure. Age shifts have been shown to result in greater gas exchange and water use per unit leaf area than mature trees remaining in less severely burned areas (Castell, Terradas, & Tenhunen, ; Utsumi, Bobich, & Ewers, ). Greater water use in young individuals and resprouts may be associated with greater sapwood to leaf area ratios and stomatal conductance per unit leaf area than older individuals (Delzon & Loustau, ; Ewers, Gower, Bond‐Lamberty, & Wang, ).…”

“…Greater water use in young individuals and resprouts may be associated with greater sapwood to leaf area ratios and stomatal conductance per unit leaf area than older individuals (Delzon & Loustau, ; Ewers, Gower, Bond‐Lamberty, & Wang, ). Additionally, resprouts have greater root : shoot ratios than mature trees, which help increase hydraulic efficiency and lower leaf areas, which means individual leaves can receive more water per root area (Schafer, Breslow, Hollingsworth, Hohmann, & Hoffmann, ; Utsumi et al, ). Age difference is not the only factor affecting the hydrologic cycle of a stand.…”