The stratigraphic expression of a large negative carbon isotope excursion from the Ediacaran Johnnie Formation, Death Valley

The Rainstorm Member of the Ediacaran Johnnie Formation of the southern Basin and Range, US, records a large negative excursion in carbon isotope ratios of carbonate strata (δ^(13)C_VPDB > −6‰). The character of the excursion raises fundamental questions about whether this isotopic pattern is accurately capturing the time-series behavior of marine dissolved inorganic carbon (DIC) or is a product of diagenesis. To explore this issue, we examined the expression of this isotopic excursion within the Johnnie oolite, a ~2 m thick marker bed, which records the highest rate of change in δ^(13)C. Sedimentologically, the oolite unit is thought to be time-transgressive; if the isotopic excursion reflects time-series behavior of the carbon cycle, its expression in the oolite across the basin should systematically align the sections according to their slight diachroneity. Detailed carbon and oxygen isotopic stratigraphy of the oolite at seven different locations indicates the magnitude of the excursion at the base of the oolite is spatially variable such that after a palinspastic reconstruction the sections align along a systematic north to south gradient in the isotopic data. The oolite preserved in the Old Dad Mountains, the most southerly section measured, is an outlier to this trend (and the most difficult to ordinate accurately in the reconstruction), showing the largest isotopic range between the onset of carbonate deposition and top of the oolite. Several hypotheses are congruent with these data, but the sum of observations is best explained by a scenario wherein the oolite is time-transgressive and deposited in a north to south manner throughout the onset of the isotopic excursion. If correct, this implies that the stratigraphic δ^(13)C pattern reflects time series behavior of marine DIC

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

The name jarrah dieback has been used for two different disorders, leading to considerable confusion. It was coined in the 1940s to describe the sudden death of groups of jarrah (Eucalyptus marginata) trees in south western Western Australia, which occurred on poorly drained sites, following exceptionally heavy rainfall. In the 1960s these sites were shown to be infested by Phytophthora cinnamomi and jarrah deaths were attributed to it, even though it was only isolated from 5 % of sampled trees. Also the definition of jarrah dieback was expanded to include deaths of many other plants on infested sites, from which P. cinnamomi was more readily isolated. Jarrah trees die from severe water deficiency, indicating problems with water conduction through roots. Xylem vessel diameters vary along roots, being narrow at the root collar, while distally they are larger, providing water storage. Jarrah transpires vigorously during summer, accessing water at depth on sites with deep soil, but being more dependent on internally stored water when root systems are shallower. Following waterlogging, sapwood vessels become blocked with tyloses, reducing both conductivity and potential water storage; such trees may have insufficient water reserves for summer survival. In jarrah P. cinnamomi is unlikely to cause water deficiency because sapwood invasion is rapidly contained in healthy roots. Recent investigations into P. cinnamomi invasion and host responses in other plants show that it can potentially cause a vascular wilt in Banksia spp. and chronic, symptomless infections in herbaceous plants. Susceptibility to waterlogging damage, and/or mortality resulting from infection by P. cinnamomi can only be clarified by detailed knowledge of the hosts and their vulnerabilities. This is essential for making diagnoses, devising management strategies, and avoiding the confusions of the past

Avocado diseases in the Americas.

23 p.Relativamente poco se ha conocido en relación con las enfermedades que afectan el árbol de aguacate (Persea americana) hasta los últimos quince o veinte años. Un árbol nativo de varias secciones de América Latina, el aguacate es un recién llegado al cultivo a gran escala. En el cultivo de este cultivo en los Estados Unidos y en América Latina, una serie de enfermedades se reconoce ahora