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Aim The aim of this study was to determine how spatial variation in vegetation type and landscape connectivity influence fire intervals in a semi-arid landscape with low relief and complex mosaics of woodland and shrubland vegetation. Location Our study focused on a 15,500-km 2 area of relatively undisturbed and unmanaged land in south-western Australia, referred to as the Lake Johnston region. Methods We modelled fire-interval data from a 67-year (1940–2006) digital fire history database using a two-parameter Weibull function, and tested for the effects of vegetation type and landscape connectivity on estimates of the length of fire intervals (Weibull parameter b) and the dependence of fire intervals on fuel age (Weibull parameter c). Results Vegetation type and landscape connectivity significantly influenced fire interval probability distributions. Fire intervals in shrublands (dense low shrub assemblage) were typically shorter (b = 46 years) and more dependent on fuel age (c = 2.33) than most other vegetation types, while fire intervals in open eucalypt woodlands were much longer (b = 405 years) and were less dependent on fuel age (c = 1.36) than in shrub-dominated vegetation types. Areas adjacent to or surrounded by salt lakes burnt less frequently ( b= 319 years) and fire intervals were less dependent on fuel age (c = 1.48) compared with more exposed areas (e.g. b 1.68). Fire intervals in thickets (dense tall shrub assemblage) were longer (b = 101 years) than would be expected from fuel loads, most likely because they were protected from fire by surrounding fuellimited woodlands. Main conclusions Fire intervals in south-western Australia are strongly influenced by spatial variation in vegetation (fuel structure) and landscape connectivity. The importance of fuel structure as a control of fire intervals in south-western Australia contrasts with other landscapes, where topographical gradients or climatic influences may override the effects of underlying vegetation. We found that, regardless of low relief, topographical features such as large salt lake systems limited the connectivity and spread of fire among landscape units in an analogous manner to lakes or mountainous features elsewhere.

Dry sclerophyll forest dominated by Jarrah (Eucalyptus marginata Donn ex Sm.) covers about 1.6 Mha of south-western Australia and is, relative to other eucalypt forests, low in many nutrients, especially N and P. If fire is excluded from these forests, Banksia grandis Willd. (Proteaceae) often grows in dense thickets as the dominant understorey. Jarrah has an extensive surface (0-20 cm) system of fine lateral roots with ectomycorrhizal associations, while B. grandis produces a mat of cluster (proteoid) roots (0-20 cm) in the late winter and early spring. We measured seasonal changes in acid phosphatase activity and concentrations of ergosterol, microbial P and other P fractions (NaOH-extractable inorganic and organic P, Bray inorganic P) in soil from a forest where B. grandis was either present (Jarrah + Banksia) or absent (Jarrah). Acid phosphatase activity was between 30 and 40 μmol p-NP g -1 h -1 in the moist winter and spring, but declined to less than 10 μmol p-NP g -1 h -1 during the dry summer. Microbial P varied from less than 10 μg g -1 in the late summer to more than 50 μg g -1 during the wetter times of the year. Ergosterol also increased about four-fold as soil moisture content increased (P ≤ 0.05). Acid phosphatase was significantly and positively related to both ergosterol and microbial P in both Jarrah + Banksia and Jarrah soils, but the intercepts and slopes of the regressions varied seasonally and were not significantly different (P ≤ 0.05) between species composition. About 50% of the variation in phosphatase activity in Jarrah soils was explained by variation in fungal biomass (ergosterol), regardless of season, while in Jarrah + Banksia soils, 74% was explained by fungal biomass when soils were dry, decreasing to less than 10% as soil moisture increased. Linear regression models showed that ergosterol and microbial P are good predictors of acid phosphatase activity in soil, but their relative importance is dependent on plant species composition and season. We propose that the relative importance of fungal biomass as a determinant of phosphatase activity in the soil decreases as the seasonal flush of cluster roots dominate in the Jarrah + Banksia soils, while in Jarrah soils the phosphatase flush is primarily due to increased activity of the fungal biomass. Seasonal and spatial heterogeneity in microbial P, ergosterol and in the source of acid phosphatase in the soil are therefore a consequence of plant species composition and root type and will influence nutrient availability at the ecosystem scale.

Mycorrhiza formation represents a significant carbon (C) acquisition alternative for orchid species, particularly those that remain achlorophyllous through all life stages. As it is known that orchid mycorrhizas facilitate nutrient transfer (most notably of C), it has not been resolved if C transfer occurs only after lysis of mycorrhizal structures (fungal pelotons) or also across the mycorrhizal interface of pre-lysed pelotons. We used high-resolution secondary ion mass spectrometry (nanoSIMS) and labelling with enriched (13) CO2 to trace C transfers, at subcellular scale, across mycorrhizal interfaces formed by Rhizanthella gardneri, an achlorphyllous orchid. Carbon was successfully traced in to the fungal portion of orchid mycorrhizas. However, we did not detect C movement across intact mycorrhizal interfaces up to 216 h post (13) CO2 labelling. Our findings provide support for the hypothesis that C transfer from the mycorrhizal fungus to orchid, at least for R. gardneri, likely occurs after lysis of the fungal peloton.

A system is described for the direct potentiometric flow injection analysis of phosphates using a cobalt wire electrode. It is proposed that the electrode response to phosphate is a result of Co 3 (PO) 2 precipitate formation at the electrode surface. The electrode response to phosphate was found to be depend on the phthalate concentration, carrier pH, flow rate and injected volume. A linear response with a slope of −41±0.5 mV/decade was obtained in the concentration range of 1.0×10 −5 – 5.0×10 −3 M with a detection limit of 1×10 −6 M, using a carrier solution containing 25 mM potassium hydrogen phthalate at pH 4.0. The proposed method was used for the determination of soil extracts with a fast analysis, low cost, high sensitivity and selectivity.

Variation in the frequency, extent and intensity of wildfires can drive changes in the composition, structure, diversity and functioning of ecosystems in fire-prone regions worldwide. However, relationships between climatic variation and wildfire occurrence remain poorly understood in many fire- prone regions. We investigated fire occurrence and extent across 15,500 km 2 of semi-arid southwest Australia in relation to inter-annual and/or seasonal variation in regional climate and broad-scale circulation patterns. Superposed epoch analysis (SEA) was used to determine whether wildfire occurrence was related to anomalously high or low regional rainfall or temperature. In particular, we tested if years of minor fire extent (i.e., ,250 km 2 burnt) and major fire extent (i.e., .1,000 km 2 burnt) occurred under different climatic conditions. We also used SEA to determine if wildfires occurred during or following periods of extremes of drivers of regional climate, including the El Nio southern oscillation (ENSO), the Indian Ocean dipole, atmospheric blocking in the adjacent Southern Ocean, and the southern annular mode (SAM). Fire occurrence was linked to dry and hot conditions typically associated with the El Ni˜ no phase of ENSO, with few or no fires in years with cool and wet summers. However, major fire years tended to occur during drought conditions that followed wet and cool conditions in spring and summer of the preceding year. These wet and cool periods were typically associated with the presence of blocking highs in the Southern Ocean to the south of Western Australia. We hypothesise that high rainfall in spring and summer favours the growth of ephemeral plants while subsequent drought conditions promote fuel drying, resulting in more continuous and highly flammable fuel beds capable of sustaining larger fires. Regional climatic patterns are likely driven by interactions among the SAM, atmospheric blocking, and decaying tropical cyclones. As climatic extremes are expected to increase in intensity and frequency in the future, it is likely that the occurrence of extensive wildfires in semi-arid southwest Australia will also increase, potentially driving changes in the distribution and composition of fire-sensitive plant communities.