Anne Cochrane

ABSTRACT Given the predicted changes in rainfall patterns for many Mediterranean climate regions, identifying seed tolerance to moisture stress in the earliest phase of plant development is an important consideration for species conservation, management and restoration. Here, we used polyethylene glycol (PEG 8000) to induce plant water deficit similar to drought stress in a field situation. Seeds of four Western Australia Banksia R.Br. (Proteaceae) species were incubated at seven levels of moisture potential (0 to 1.5 MPa) and three constant temperatures (10 C, 15 C and 20 C). In the absence of moisture stress, germination was uniformly high, but increasing drought stress led to reduced and delayed germination in all species. Overall, the threshold moisture potential value for a significant decline, and delay, in germination was –0.25 MPa. Results suggested that one species (B. coccinea) is likely to be most vulnerable to germination failure under predicted changes in rainfall patterns, whereas another (B. media) is likely to be less vulnerable. There was significant variation in population response to drought stress. However, this variation could not be explained by rainfall across species distributions. We discuss the PEG approach for assessing seed sensitivity to moisture stress, particularly in the context of shifting rainfall under climate change.

ABSTRACT Temperature is a significant factor influencing seed germination and for many species temperature-mediated germination cues are vital for plant persistence. Rising temperatures forecast as a result of anthropogenic climate change may have a substantial influence on the population and range dynamics of plant species. Here, we report on the thermal constraints on seed germination in natural populations of four congeneric Banksia species collected from a longitudinal climate gradient in Western Australia. We investigated whether germination niche: (1) varied between species; (2) varied among populations of each species; and (3) varied in a consistent manner reflecting the climatic gradients of seed origin. We hypothesized that species would differ and that populations from warmer sites would have a broader temperature window for germination than populations from cooler sites. Species differed in the breadth of their germination niche, but temperatures that stimulated the most rapid and complete germination were similar across all species. A sharp reduction in germination percentage occurred above the optimum temperature, which coincided with significant delays in germination relative to the optimum. The temperatures causing these declines varied among populations. Across the species, there was a significant correlation between optimum germination temperature and mean annual temperature at seed source; however, there was no relationship at the population level for individual species. These data provide insight into the vulnerability of Banksia species to climate change, with those populations that require lower temperatures for germination, or have narrower optimal ranges for germination, likely to be most vulnerable to a warming climate.

ABSTRACT Temperature and moisture impact strongly on the early stages of a plant's life cycle. Global climate change is altering the environmental cues that seeds receive resulting in compromised seedling emergence and changes to seedling performance. Here, we investigate how temperature and moisture affect these early stages of plant development in four Banksia species collected from a longitudinal climate gradient in South West Western Australia. A common garden was used to examine the between-species and among-population variation in seedling emergence, growth and leaf traits under two soil temperature regimes and three levels of precipitation. We predicted that reduced moisture and increased temperature would delay and reduce total seedling emergence and negatively affect seedling performance. Furthermore, we expected that within species there would be geographically structured variation in response to the treatments. Species differed significantly in all measured traits. Soil warming resulted in strong impacts on regenerative traits, significantly slowing seedling emergence in two species and reducing total seedling emergence in three species. In addition, warming altered seedling performance with significant reductions to the above-ground leaf biomass ratio of three species. In contrast, response to soil moisture manipulation was minimal across all species but possibly due to issues regarding implementation of an effective moisture treatment. The species that showed the greatest decline in emergence under warmed conditions (B. quercifolia) also showed the smallest vegetative shift; the species with the smallest decline in emergence (B. coccinea) showed a relatively large vegetative shift. Among-population differences were significant for many traits, however, trait differentiation was inconsistent across species and, contrary to our hypothesis, the variation we observed was not clearly associated with the climate gradient. As these among-population differences in traits are not easy to predict, we caution the use of simple rules for choosing seed populations for conservation and restoration.

Disease progress curves were evaluated for the assessment of the susceptibility of the flora of the South-West Botanical Province of Western Australia threatened by Phytophthora cinnamomi infection. Disease progress was analysed with the logistic model because this model describes numerous observed disease progress curves. In addition, the three logistic model parameters, upper asymptote (Kmax), lag time (t1/2K) and intrinsic rate of increase (r), have rational physical interpretations. Because the logistic model parameters for percentage of plants with collar lesions were significantly related to parameters for percentage mortality, only the logistic model parameters for percentage mortality were used in subsequent analysis. Susceptible hosts had the greatest Kmax, shortest t1/2K and fastest r. These parameters change to lowest Kmax, longest t1/2K and slowest r for resistant plant taxa. There was a greater change of Kmax with t1/2K than with r. The Kmax and r parameters did not differ significantly between isolates of the pathogen. Variation in mortality curve parameters between years was greater for Banksia grandis than for the more susceptible B. brownii. There was no significant linear relationship between mortality curve parameters for B. brownii and temperature variables. For B. grandis there were four significant linear relationships between a mortality curve parameter and a temperature variable. Potting mix soil favoured greatest disease progress with the shortest t1/2K and fastest r. Susceptibility to P. cinnamomi determined in a shadehouse environment following soil inoculation was significantly positively correlated with susceptibility recorded in disease centres in natural environments.