Patterns of tree dieback in Queensland, Australia: The importance of drought stress and the role of resistance to cavitation

Department of Agronomy and Range Science and Center for Population Biology, University of California, Davis, CA 95616, USA.
Oecologia (Impact Factor: 3.09). 05/2004; 139(2):190-8. DOI: 10.1007/s00442-004-1503-9
Source: PubMed


During the extreme 1992-1997 El Niño drought event, widespread stem mortality, or tree "dieback", of both mature and juvenile eucalypts occurred within the tropical savannas of northeast Australia. Most of the dieback occurred in individuals of the ironbark species complex ( Eucalyptus crebra- E. xanthoclada) while individuals of the bloodwood species Corymbia erythrophloia, exhibited significantly less stem mortality. Indicative of greater water stress, predawn and midday xylem water potentials of ironbark adults and saplings were significantly more negative than predawn values of bloodwoods. The very negative xylem water potentials in ironbarks suggest that stem mortality in both adult and juvenile ironbarks results from drought-induced embolism and that ironbarks perhaps have a shallower and less extensive root system than bloodwoods. Although predawn and midday water potentials for ironbark adults and saplings were similar, a census of mature and juvenile ironbark trees indicated that mortality was higher in adult trees. Cavitation vulnerability curves indicated that ironbark saplings may be better buffered against cavitation than adult trees. If they possess smaller root systems, saplings are more likely than adults to experience low xylem water potentials, even in non-drought years. Xylem conduits produced in adult trees during periods of normal rainfall, although perhaps more efficient in water conduction, may be more vulnerable to cavitation during infrequent severe droughts.

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    • "Reports of dieback are increasingly common in native and invasive plant species globally (La Porta et al. 2008). Microorganisms are often implicated (e.g., M u e l l e r -D o m b o i s 1 9 8 7 ; Kowalski and Holdenrieder 2009; Herrero et al. 2011; Ismail et al. 2012; Mehl et al. 2013), and dieback in some tree and shrub species has been found to result from single pathogens, sometimes in the presence of stressors (Rice et al. 2004; La Porta et al. 2008; Pautasso et al. 2013; Scarlett et al. 2013; Aghighi et al. 2014). More often, causal explanations remain elusive (Houston 1992; Slippers and Wingfield 2007; Sakalidis et al. 2011; Jami et al. 2013). "
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    ABSTRACT: Background and aims Dieback is pervasive in many populations of invasive woody weeds globally. Previous studies on dieback have focused on specific potential causative biotic agents, but most cases remain unexplained. The potential role of endophytic microbial communities in dieback, including the relative importance of endophytes with pathogenic or protective capabilities, remains poorly studied. We tested whether changes in archaeal, bacterial and fungal endophyte community structure is associated with dieback occurrence in the invasive, leguminous tree, Parkinsonia aculeata L. (parkinsonia). Methods We sampled roots, stems and stem tips from healthy and dieback-affected parkinsonia and conducted terminal restriction fragment length polymorphism (T-RFLP) analysis on DNA extracted from these samples using domain-specific primers for archaea, bacteria and higher fungi. Results Microbial community composition strongly differed with parkinsonia disease status (archaea, bacteria and fungi) and plant part (archaea and fungi). Plant part and disease status effects were strongest in archaea. We also found evidence implicating both pathogenic and potentially protective endophytes in the onset of dieback. Conclusions This is the first study that has shown significant associations between changes in endophyte community composition and dieback presence. Our results highlight the complexity of those changes and provide support for the hypothesis that diverse pathogenic and protective endophytes may be implicated in dieback.
    Full-text · Article · Jun 2015 · Plant and Soil
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    • "Drought and anthropogenically modified hydrological conditions may result in a range of stress induced responses in trees (e.g. Rice et al., 2004), including adaptive canopy thinning and branch sacrifice (dieback) to reduce transpiration demand and conserve hydraulic status (Tyree and Sperry, 1988; Rood et al., 2000). Extreme moisture deficit may also result in embolism, cavitation and failure in transporting xylem tissue, ultimately causing death (Tyree and Ewers, 1991; McDowell et al., 2008). "
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    ABSTRACT: Groundwater decline is widespread, yet its implications for natural systems are poorly understood. Previous research has revealed links between groundwater depth and tree condition; however, critical thresholds which might indicate ecological ‘tipping points’ associated with rapid and potentially irreversible change have been difficult to quantify. This study collated data for two dominant floodplain species, Eucalyptus camaldulensis (river red gum) and E. populnea (poplar box) from 118 sites in eastern Australia where significant groundwater decline has occurred. Boosted regression trees, quantile regression and Threshold Indicator Taxa Analysis were used to investigate the relationship between tree condition and groundwater depth. Distinct non-linear responses were found, with groundwater depth thresholds identified in the range from 12.1 m to 22.6 m for E. camaldulensis and 12.6 m to 26.6 m for E. populnea beyond which canopy condition declined abruptly. Non-linear threshold responses in canopy condition in these species may be linked to rooting depth, with chronic groundwater decline decoupling trees from deep soil moisture resources. The quantification of groundwater depth thresholds is likely to be critical for management aimed at conserving groundwater dependent biodiversity. Identifying thresholds will be important in regions where water extraction and drying climates may contribute to further groundwater decline.
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    • "Species able to tolerate low leaf water contents and leaf water potentials survive longest in dry conditions (Poorter and Markesteijn 2008). The physiological traits of leaf water potential and stomatal conductance have been widely used as measures of plant water stress (e.g., Attiwill and Clayton-Greene 1984; Myers and Neales 1984; Filella and Penuelas 2003; Rice et al. 2004). Such traits have been identified as being indicative of drought tolerance (e.g., King 1997; Smith et al. 1997; Curran et al. 2009). "
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    ABSTRACT: Ecophysiological vulnerability can be understood as the degree of susceptibility or inability of an organism to adapt their physiological functions to ecological and environmental changes. Changes in water availability and water stress are critical for species, which may respond differentially to different precipitation events. We analyzed the response of leaf water potential and stomatal conductance to water stress to assess the ecophysiological vulnerability and evaluated the drought tolerance of four tree species from the central mountain region of Veracruz, Mexico: Alnus acuminata, Quercus xalapensis, Liquidambar styraciflua, and Pinus ayacahuite. Drought stress was imposed for 15 days (except for Q. xalapensis) and then watered for 25 days in order to evaluate the species recovery under three watering treatments: 16.67, 33.33, and 50 % field capacity. Individuals were screened throughout the experiment. Leaf water potential and stomatal conductance were measured daily showing significant decrement and differential recovery for each species. L. styraciflua and P. ayacahuite needed more water and more days to recover, whereas Q. xalapensis needed less water and resisted more days without water. We found A. acuminata as a drought-tolerant/ avoider species. After analyzing the precipitation and temperature trends for the region, we found negative precipitation trends with an increase in consecutive dry days, and we found positive temperature trends. We also developed potential distribution maps for all the species in the region, and after analyzing the precipitation and temperature changes, the potential distribution maps, the resistance to water stress, the number of days before leaf drop, the W and stomatal responses, and the water amount and number of days required to recover, we found L. styraciflua as the most vulnerable species and Q. xalapensis as the least vulnerable.
    Full-text · Article · May 2014 · Regional Environmental Change
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