Assessing frost damage in a set of historic wheat varieties using a passive heating system

Low temperatures during the flowering period of cereals can lead to floret sterility, yield reduction, and economic losses in Australian crops. In this study we investigated the physiological bases of yield determination in a historic set of wheat varieties grown under frost-prone field conditions in Southern Australia. We tested the hypothesis that selection for yield inadvertently improved frost tolerance. We measured yield and yield components, including the distribution of grains within the spike, in a factorial experiment combining twelve wheat varieties (released from 1973 to 2015), two sowing dates (19th April and 22nd May 2017), and two thermal regimes, ambient control and frost-protected. To protect crops from frost we used moveable, lightweight passive heating systems before each frost event (≤ 0°C). Phenotypic plasticity of yield, grain number and grain weight were analysed. We found a positive relationship between phenotypic plasticity of grain yield and phenotypic plasticity of grain number, but no correlation between yield and year of release. Across varieties, the average numbers of grains per spike was 35.1 ± 0.3 in frostprotected crops compared to 16.1±0.1 in frosted controls in the first sowing, and 29.7 ± 0.3 and 22.9 ± 0.2 respectively in the second sowing. Preventing frost improved spike fertility by increasing the proportion of grains in distal positions within spikelets in relation to controls.Ariel Ferrante, Cesar M. Cossani, Jason A. Able, Victor O. Sadra

Yield and spike fertility in a historic set of wheat cultivars in response to frost

Ariel Ferrante, Cesar M. Cossani, Jason A. Able, Victor O. Sadra

Reducing methylmercury accumulation in the food webs of San Francisco Bay and its local watersheds

San Francisco Bay (California, USA) and its local watersheds present an interesting case study in estuarine mercury (Hg) contamination. This review focuses on the most promising avenues for attempting to reduce methylmercury (MeHg) contamination in Bay Area aquatic food webs and identifying the scientific information that is most urgently needed to support these efforts. Concern for human exposure to MeHg in the region has led to advisories for consumption of sport fish. Striped bass from the Bay have the highest average Hg concentration measured for this species in USA estuaries, and this degree of contamination has been constant for the past 40 years. Similarly, largemouth bass in some Bay Area reservoirs have some of the highest Hg concentrations observed in the entire US. Bay Area wildlife, particularly birds, face potential impacts to reproduction based on Hg concentrations in the tissues of several Bay species. Source control of Hg is one of the primary possible approaches for reducing MeHg accumulation in Bay Area aquatic food webs. Recent findings (particularly Hg isotope measurements) indicate that the decades-long residence time of particle-associated Hg in the Bay is sufficient to allow significant conversion of even the insoluble forms of Hg into MeHg. Past inputs have been thoroughly mixed throughout this shallow and dynamic estuary. The large pool of Hg already present in the ecosystem dominates the fraction converted to MeHg and accumulating in the food web. Consequently, decreasing external Hg inputs can be expected to reduce MeHg in the food web, but it will likely take many decades to centuries before those reductions are achieved. Extensive efforts to reduce loads from the largest Hg mining source (the historic New Almaden mining district) are underway. Hg is spread widely across the urban landscape, but there are a number of key sources, source areas, and pathways that provide opportunities to capture larger quantities of Hg and reduce loads from urban runoff. Atmospheric deposition is a lower priority for source control in the Bay Area due to a combination of a lack of major local sources and Hg isotope data indicating it is a secondary contributor to food web MeHg. Internal net production of MeHg is the dominant source of MeHg that enters the food web. Controlling internal net production is the second primary management approach, and has the potential to reduce food web MeHg more effectively and within a much shorter time-frame. MeHg cycling and control opportunities vary by habitat. Controlling net MeHg production and accumulation in the food web of upstream reservoirs and ponds is very promising due to the many features of these ecosystems that can be manipulated. The most feasible control options in tidal marshes relate to the design of flow patterns and subhabitats in restoration projects. Options for controlling MeHg production in open Bay habitat are limited due primarily to the highly dispersed distribution of Hg throughout the ecosystem. Other changes in these habitats may also have a large influence on food web MeHg, including temperature changes due to global warming, sea level rise, food web alterations due to introduced species and other causes, and changes in sediment supply. Other options for reducing or mitigating exposure and risk include controlling bioaccumulation, cleanup of contaminated sites, and reducing other factors (e.g., habitat availability) that limit at risk wildlife populations