Predictions of where minimal damage to jarrah roots could result in tree death

Abstract

SUMMARYField observations of Eucalyptus marginata Donn ex Smith (jarrah) trees on sites infested with Phytophthora cinnamomi Rands showed tbat sudden and sustained stem shrinkage at 1-3 m preceded crown death. This was interpreted as indicating severe water deficiency in the stem base before the foliage died. Reduced root conduction might bt an important factor leading to tree death. Measurements of conduit length in stems and roots showed that c. 15 % were 1 m long and the remainder 40-50 cm long. Quahtative measurements of sapwood conduction were made in 20 cm-long segments of large horizontal jarrah roots using gas flow at positive pressure. Conduction, expressed as cm'' gas fiow mm' ^ min"' increased with increasing distance from tbe tree bole. This increase was associated witb an increase in vessel cross-sectional area, not with increasing vessel number or a decrease in the proportion of tylosed vessels. Observations on roots from trees from two sites, part of each site being infested with P. cinnamomi, indicated tbat maximum conduction mm'^ along a root was associated with site, not whether or not tbe site was infested with P. cinnamomi. Our caicuiations show that conduction in large horizontal roots is not constant, but decreases close to tbe base of a jarrah tree, so that damage close to the bole will have the greatest effect on water movement to the foliage.

Effects of variable root damage caused by Phytophthora cinnamomi on water relations of chestnut saplings

“…Is the damage induced on the plant only related to the reduction in water absorption or is the parasite inducing a generalized dysfunction in water relations? During field experiments, death was found to occur in jarrah when trees had lost an important part of the root system or when they had been girdled at the collar [6,7,8], supporting the first hypothesis. However, in inoculated E. sieberi seedlings, a 91% reduction in hydraulic conductivity of the root system was followed by a decrease in stomatal conductance, transpiration, leaf water potential and water stress in shoots, despite less than one sixth of the root system being infected [10].…”

Response of Mycorrhizal Diversity to Current Climatic Changes

“…Davison [393] investigated the interaction between waterlogging alone and in combination with infection by P. cinnamomi. She articulated that there were indeed a complex of disorders: deaths of mid-and understorey species caused by P. cinnamomi, deaths of groups of Eucalyptus marginata (jarrah) caused by waterlogging, a background mortality of isolated jarrah deaths, and a crown decline of jarrah-on some sites all problems occurred simultaneously (see also [394]). Thus through either a predisposition and/or a multiple stress hypothesis, decline of keystone species in forest ecosystems will impact on the viability and ultimately the diversity of mycorrhizas.…”

Resolving confusions about jarrah dieback - don’t forget the plants

“…Two of these deaths are shown in Fig. 1 (Davison and Tay 1995a). The trees showed sudden and sustained stem shrinkage at 1.3 m for several weeks or months before the crown died, with the foliage changing in colour from green to brown within a 4 week period.…”

“…If gas is blown gently through the sapwood, bubbles of gas will emerge at the other end which can be collected and measured. Most of the xylem vessels in jarrah roots are 40 to 50 cm long, with the remainder about 1 m in length (Davison and Tay 1995a), so that in root segments that are only 20 cm long most of the vessels will be open at both ends. Fig.…”

“…1; Shea et al 1982;Crombie and Tippett 1990;Davison and Tay 1995a). So if this symptom is caused by P. cinnamomi this pathogen must be able to extensively invade the sapwood and reduce conductivity.…”