The Effect of Wildfire on Soil Mercury Concentrations in Southern California Watersheds

Mercury (Hg) stored in vegetation and soils is known to be released to the atmosphere during wildfires, increasing atmospheric stores and altering terrestrial budgets. Increased erosion and transport of sediments is well-documented in burned watersheds, both immediately post-fire and as the watershed recovers; however, understanding post-fire mobilization of soil Hg within burned watersheds remains elusive. The goal of the current study is to better understand the impact of wildfire on soil-bound Hg during the immediate post-fire period as well as during recovery, in order to assess the potential for sediment-driven transport to and within surface waters in burned watersheds. Soils were collected from three southern California watersheds of similar vegetation and soil characteristics that experienced wildfire. Sampling in one of these watersheds was extended for several seasons (1.5 years) in order to investigate temporal changes in soil Hg concentrations. Laboratory analysis included bulk soil total Hg concentrations and total organic carbon of burned and unburned samples. Soils were also fractionated into a subset of grain sizes with analysis of Hg on each fraction. Low Hg concentrations were observed in surface soils immediately post-fire. Accumulation of Hg coincident with moderate vegetative recovery was observed in the burned surface soils 1 year following the fire, and mobilization was also noted during the second winter (rainy) season. Hg concentrations were highest in the fine-grained fraction of unburned soils; however, in the burned soils, the distribution of soil-bound Hg was less influenced by grain size. The accelerated accumulation of Hg observed in the burned soils, along with the elevated risk of erosion, could result in increased delivery of organic- or particulate-bound Hg to surface waters in post-fire systems.     

Predictive modeling of spatial patterns of soil nutrients related to fertility islands

In arid shrublands, soil resources are patchily distributed around shrub canopies, forming well-studied “islands of fertility.” While soil nutrient patterns have previously been characterized quantitatively, we develop a predictive model that explicitly considers the distance from shrubs of varying canopy sizes. In 1-ha macroplots in both the Sonoran and Mojave Deserts, we used Plant Root Simulator? probes to measure nutrient availability along transects extending north and south from creosote bushes (Larrea tridentata). We modeled the decline of nutrients with distance from focal shrubs using hierarchical mixed models that included the effects of transect direction and shrub canopy size. Of the nutrients considered, nitrogen and potassium had the strongest response to distance from focal shrubs. In the Sonora, both depended on canopy size and had different patterns to the north versus the south. In the Mojave, potassium depended on size and direction, but nitrogen only on canopy size. We used the fitted model equations and the location and canopy size of all Larrea shrubs within the macroplots to estimate nutrient concentrations at a 20 cm resolution. This produced maps showing nutrient “hotspots” centered on Larrea. Our models predicted up to 60 % of the variation in nutrient availability the following growing season. Our models efficiently used a moderate number of sample locations to predict nutrient concentrations over a large area, given easily measured values of shrub size and location. Our method can be applied to many systems with patchily distributed resources focused around major structural landscape features.     

CASE REPORT: Unilateral eyelid lesion and ophthalmologic findings in an aardvark (Orycteropus afer): case report and literature review

Objective To summarize the medical knowledge surrounding aardvarks to date, to describe the ophthalmic examination of a specimen with a chronic history of an upper eyelid lesion, of an assumed blind left eye, and to detail the anesthesia procedure performed. Procedure A 23‐year‐old aardvark was examined under general anesthesia and multiple ocular abnormalities were detected in the left eye (globe deviation, corneal opacities, iridodonesis, and aphakia). A thickening of the palpebral conjunctiva affecting the medial upper eyelid with erosion of the normal eyelid margin anatomy was identified. The adnexal lesion was resected by a wedge resection and histopathology was performed. Suture breakdown 3 days postoperatively required a second surgery, where buried sutures were used. The surgical techniques and postoperative care are discussed. Results The histopathology revealed mucosal hyperplasia and moderate neutrophilic and lymphoplasmacytic blepharitis. No causal organisms were identified. Following initial wound dehiscence and a modified surgical technique, the upper eyelid healed without complication and retained complete function. Conclusions The eyelid lesion involved a benign inflammatory and hyperplastic pathology of unknown etiology. Adjusting routine ophthalmic surgical techniques to wildlife and zoo animals can be challenging and complicated. It is important to understand the nature of the animals being managed, their circadian cycle, and habitat, to adjust and individualize the surgical approach, instrumentation, suture material, and perioperative treatment.     

MAIZE HYBRIDS DIFFER IN THEIR 24-H PATTERNS OF PHYTOSIDEROPHORE RELEASE

Iron (Fe) chlorosis tolerant gramineous species respond to Fe-deficiency stress by releasing phytosiderophores. The objective of this study was to characterize the diurnal pattern of phytosiderophore release from Fe-chlorosis tolerant and susceptible maize (Zea mays L.) hybrids. Phytosiderophore was collected from individual, Fe-deficient maize plants in 10 mg L^?1 Micropur solution during 4-h collection periods. The diurnal pattern of phytosiderophore release differed among maize hybrids. Similar levels of phytosiderophore were released during light and dark conditions for three hybrids. Greater phytosiderophore release was measured from a fourth hybrid when the collection procedure began 2-h after the initiation of light compared to 2-h before the initiation of dark. When a single plant was used for six consecutive collection periods, phytosiderophore release declined during the final 8- to 12-h of collection. The decline in phytosiderophore release was attributed to dissolution of apoplastic Fe and deactivation of the Fe-stress response mechanism.     

Colonization and survival capacities underlying the multifaceted life of Rhodococcus sp. PBTS1 and PBTS2

Little is known about the epidemiology of the newly emerged disease on pistachio rootstock designated pistachio bushy top syndrome (PBTS). Here, we analysed the survival and colonization capacities of the two causative agents, Rhodococcus corynebacterioides-like PBTS1 and R. fascians PBTS2, in the different habitats they occupy. Additionally, we examined their chromosomal sequences for genes that would support their ecology and provide experimental evidence for some of their predicted functions. We demonstrate that the soil competence of PBTS2 is better than that of PBTS1 and that both bacteria behave chemotactically, allowing them to translocate from soil to the rhizoplane. Once on the rhizoplane and the phylloplane, the PBTS bacteria form extensive epiphytic biofilms, probably aided by exopolysaccharide production. From these biofilms, the bacteria colonize the plant's interior tissues through the formation of ingression sites, likely created by the localized activity of cell wall-degrading enzymes. The observed systemic spreading of the PBTS strains throughout the plant tissues is probably mediated by surface motility and agrees with the occurrence of symptoms in both the aerial and root parts of the plant host. Based on all available information, we provide a working model on this pathosystem to be used as a conceptual framework for future research.