Distribution and floristics of moss- and lichen-dominated soil crusts in a patterned Callitris glaucophylla woodland in eastern Australia

Factors that alter the relative importance of abiotic and biotic drivers on the fertile island in a desert-oasis ecotone

Dryland vegetation forms a "fertile island effect" due to water and nutrient retention. However, there has been little research on the mechanism underlying C-, N-, P-accumulation and overall fertile island at the community level. We therefore presented the systematic investigation on this issue through the survey in desert-oasis ecotone. The survey covering the vegetation composition, plant height, crown area and vegetation cover. The main parameters measured included soil moisture, soil pH, soil salinity and nine soil indicators related to C, N and P cycling. The results revealed that the effect of fertile island was directly relevant to either soil moisture or pH. This effect was more obvious with the increase of soil moisture and the decrease of pH value. In addition, the plant diversity was believed to be the main biotic driven factor for fertile island. Furthermore, the results also indicated that both the soil moisture and plant diversity would accelerate the accumulation of P and N, while the pH played the negative effect. The other main observation obtained was that the vegetation cover had positive effect on accumulation of C. As a result, the mechanisms related to drought and salinization could drive the difference of C-, N- and P-accumulation. The main findings also provided an effective reference to better understand the mechanism of fertile island and its desertification procedure in desert-oasis ecotone.

The influence of climatic legacies on the distribution of dryland biocrust communities

Predicting the distribution of biocrust species, mosses, lichens and liverworts associated with surface soils is difficult, but climatic legacies (changes in climate over the last 20 k years) can improve our prediction of the distribution of biocrust species. To provide empirical support for this hypothesis, we used a combination of network analyses and structural equation modelling to identify the role of climatic legacies in predicting the distribution of ecological clusters formed by species of mosses, lichens and liverworts using data from 282 large sites distributed across 0.6 million km² of eastern Australia. Two ecological clusters contained 87% of the 120 moss, lichen and liverwort species. Both clusters contained lichen, moss and liverwort species, but were dominated by different families. Sites where the air temperature increased the most over 20k years (positive temperature legacies) were associated with reductions in the relative abundance of species from the lichen (Peltulaceae and Teloschistaceae) and moss (Bryaceae) families (Cluster A species), greater groundstorey plant cover and lower soil pH. Sites where precipitation has increased over the past 20k years (positive precipitation legacy) were associated with increases in the relative abundance of lichen (Cladoniaceae, Lecideaceae and Thelotremataceae) and moss (Pottiaceae) families (Cluster B species) and lower levels of soil pH. Sites where temperatures have increased the most in the past 20k years suppressed the negative effects of plant cover on Cluster B by reducing plant cover. Increased intensity of grazing suppressed the negative effect of soil pH and the positive effect of soil carbon, on the relative abundance of Cluster B taxa. Finally, increasing temperature and precipitation legacies reduced the negative effect of soil pH on Cluster B. Understanding of the importance of climatic legacies improves our ability to predict how biocrust assemblies might respond to ongoing global environmental change associated with increasing land use intensification, increasing temperature and reduced rainfall.

Small-scale vertical distribution of algae and structure of lichen soil crusts

Although many studies have been conducted on the ecological functions and ecophysiological characteristics of lichen soil crusts (LSCs), no explanation of these results has been provided based on crust structures. Using algae soil crusts (ASCs) as comparison, this work studied the small-scale vertical distribution of algal biomass and stratification in two types of LSCs, by combining the binocular stereomicroscope observations, microscope observations, plate cultures, chlorophyll analysis, and polysaccharides analysis. The results showed an obvious difference in the proportion but not the composition of the algae species between the ASCs and the two LSCs. Approximately 60% and 80% of the total algal biomass were concentrated in the top 1 mm of the soil profile and thalli in the ASCs and LSCs, respectively. This implies that symbiotic algae are the dominant species and primary organic carbon producers in LSCs, and the algal biomass decreased with the depth in both the ASCs and LSCs. The small-scale vertical distributions of the crustal algal biomass and polysaccharides were characterized by obvious successional stage, whereas these were unrelated to the crust type within the successional stage. Additionally, a large amount of fungi, which were always piercing the entire crusts, were observed in the LSCs, but only occasionally in the ASCs. These special structures are purported to cause the LSCs to achieve specific ecological functions, such as higher carbon fixation and greater compressive strength. High biomass, large living space, and advantageous resource utilization privilege suggest that the lichen association is mutualistic and the direction from ASCs to LSCs is developmental.

Frequent fire promotes diversity and cover of biological soil crusts in a derived temperate grassland

The intermediate disturbance hypothesis (IDH) predicts that species diversity is maximized at moderate disturbance levels. This model is often applied to grassy ecosystems, where disturbance can be important for maintaining vascular plant composition and diversity. However, effects of disturbance type and frequency on cover and diversity of non-vascular plants comprising biological soil crusts are poorly known, despite their potentially important role in ecosystem function. We established replicated disturbance regimes of different type (fire vs. mowing) and frequency (2, 4, 8 yearly and unburnt) in a high-quality, representative Themeda australis-Poa sieberiana derived grassland in south-eastern Australia. Effects on soil crust bryophytes and lichens (hereafter cryptogams) were measured after 12 years. Consistent with expectations under IDH, cryptogam richness and abundance declined under no disturbance, likely due to competitive exclusion by vascular plants as well as high soil turnover by soil invertebrates beneath thick grass. Disturbance type was also significant, with burning enhancing richness and abundance more than mowing. Contrary to expectations, however, cryptogam richness increased most dramatically under our most frequent and recent (2 year) burning regime, even when changes in abundance were accounted for by rarefaction analysis. Thus, from the perspective of cryptogams, 2-year burning was not an adequately severe disturbance regime to reduce diversity, highlighting the difficulty associated with expression of disturbance gradients in the application of IDH. Indeed, significant correlations with grassland structure suggest that cryptogam abundance and diversity in this relatively mesic (600 mm annual rainfall) grassland is maximised by frequent fires that reduce vegetation and litter cover, providing light, open areas and stable soil surfaces for colonisation. This contrasts with detrimental effects of 2-year burning on native perennial grasses, indicating that this proliferation of cryptogams has potentially high functional significance for situations where vegetation cover is depleted, particularly for reducing soil erosion.

Managing arid zone natural resources in Australia for spatial and temporal variability - an approach from first principles

Outback Australia is characterised by variability in its resource drivers, particularly and most fundamentally, rainfall. Its biota has adapted to cope with this variability. The key strategies taken by desert organisms (and their weaknesses) help to identify the likely impacts of natural resource management by pastoralists and others, and potential remedies for these impacts. The key strategies can be summarised as five individual species’ responses (ephemerals, in-situ persistents, refuging persistents, nomads and exploiters), plus four key emergent modes of organisation involving multiple species that contribute to species diversity (facilitation, self-organising communities, asynchronous and micro-allopatric co-existence). A key feature of the difference between the strategies is the form of a reserve, whether roots and social networks for Persistents, or propagules or movement networks for Ephemerals and Nomads. With temporally and spatially varying drivers of soil moisture inputs, many of these strategies and their variants can co-exist. While these basic strategies are well known, a systematic analysis from first principles helps to generalise our understanding of likely impacts of management, if this changes the pattern of variability or interrupts the process of allocation to reserves. Nine resulting ‘weak points’ are identified in the system, and the implications of these are discussed for natural resource management and policy aimed at production or conservation locally, or the regional integration of the two.