Hydraulic architecture of deciduous and evergreen dry rainforest tree species from north-eastern Australia

Abstract

Hydraulic conductivity and xylem anatomy were examined in stems of two evergreen species, Alphitonia excelsa (Fenzal) Benth. and Austromyrtus bidwillii (Benth.) Burret., and two drought-deciduous species, Brachychiton australis (Schott and Endl.) A. Terracc. and Cochlospermum gillivraei Benth., from a seasonally dry rainforest in north Queensland, Australia. The deciduous species possessed hydraulic architecture typical of drought-sensitive plants, i.e. low wood density, wider xylem vessels, higher maximal rates of sapwood specific hydraulic conductivity (K s ) and high vulnerability to drought-induced embolism. In contrast, the evergreen species had lower rates of K h and leaf specific conductivity (K L ) but were less susceptible to embolism. The evergreen species experienced leaf water potentials <−4.0 MPa during the dry season, while the deciduous species shed their leaves before leaf water potentials declined below −2.0 MPa. Thus, the hydraulic architecture of the evergreens allows them to withstand the greater xylem pressure gradients required to maintain water transport to the canopy during the dry season. Our results are consistent with observations made in neotropical dry forests and demonstrate that drought-deciduous species with low wood density and high water storage capacity are

Diversity of deciduousness and phenological traits of key Indian dry tropical forest trees

“…More than 4-month-deciduous waterstoring tree species, showing low wood density and low LMA, initiate leaf fall just after the cessation of rains (during early dry season) and complete it within a short period, reflecting an adaptive strategy to restrict the loss of large amount of water stored in their light wood stems. Other deciduous species (< 2-month-deciduous and 2-4-month deciduous), with relatively higher wood density and LMA, maintain their leaves further into the dry season possibly due to greater ability of these species to tolerate negative tree water potentials (Choat et al, 2005). Replacement of old leaves with new in the mid dry season in leaf-exchanging species may be a water conservation strategy to face the seasonal drought condition.…”

Global convergence in the vulnerability of forests to drought

“…There are many examples in the literature of species with low embolism resistance growing in areas of low rainfall or seasonal drought. This includes riparian and ground-water-dependent vegetation 10 , and drought-deciduous trees in tropical dry forests 27 . These species avoid very negative Y x by some combination of predictable access to ground water (deep roots), internal water storage and reduced leaf area or other shifts in biomass allocation 10,23,28 .…”

Deciduousness in a seasonal tropical forest in western Thailand: interannual and intraspecific variation in timing, duration and environmental cues

“…Several recent studies have investigated aspects of the physiological controls and constraints on foliar phenology. For example, studies of trees in seasonal dry tropical forest have investigated water relations and gas exchange (Choat et al 2006), hydraulic architecture (Choat et al 2005), and relationships between hydraulics and photosynthesis (Brodribb et al 2002) across seasons and in species with differing foliar phenologies. An extensive field survey such as ours can provide the necessary context for species selection to target specific phenological comparisons or contrasts that may be informative and help bridge the gap between correlative and physiological analyses.…”