Reproductive phenological shifts and other phylogenetic trait changes in the Arbutoideae (Ericaceae) in the context of drought, seed predation, and fire.

Phenology is an ecologically critical attribute that commonly is coordinated with other plant traits. Phenological shifts may be the result of evolutionary adjustments to persistently new conditions, or transitory, varying with annual flux in abiotic conditions. In summer-dry, fire-prone Mediterranean-climates, for example, many plant lineages have historically migrated from forests to more arid shrublands resulting in adaptive trait changes. These shifts in habitat abiotic conditions and biotic interactions influence morphology of flowers and fruits and will interact with phenological timing. The Arbutoideae (Ericaceae) is one lineage that illustrates such modifications, with fruit characters evolving among genera from fleshy to dry fruit, thin to stony endocarps, and bird to rodent dispersal, among other changes. We scored herbarium collections and used ancestral trait analysis to determine phenological shifts among the five Arbutoid genera found in semi-arid climates. Our objective was to determine if phenology shifts with the phylogenetic transition to different reproductive characters. Our results indicate that phenological shifts began with some traits, like the development of a stony endocarp or dry fruits, but not with all significant trait changes. We conclude that early phenological shifts correlating with some reproductive traits were permissive for the transition to other later character changes.

Prominent role of sulfate reduction in robust sulfur retention in subtropical soil

Sulfur budgets in catchments indicated that about 80% of the deposited sulfur was retained in the subtropical soil, it alleviates the historical acidification caused by elevated deposition. The strong sulfur retention was attributed to the reversible sulfate adsorption in previous studies. Here we report that sulfate reduction is a prominent yet thus far overlooked mechanism for sulfur retention, based upon the comprehensive evidence of soil sulfur storage and multi-isotope within entire soil profile along a hydrological continuum in a typical subtropical catchment of China. Using a dual isotopic mass balance model, we determined that annual flux of reduction accounted for approximately 38% of sulfur retention, which was close to the proportion of reduced species in soil. Consequently, the release of sulfur legacy would be less serious with the decreasing sulfur deposition in China, compared to the projections only considering adsorption.

Methane Emission from Palsa Mires in Northeastern European Russia

Measurement data on methane fluxes in the palsa mire ecosystem at the border of tundra and taiga zones in northeastern European Russia are presented. It was found for the first time that an intense methane flux from the surface of the permafrost mound (palsa) is determined by the spring thawing of the seasonally thawed horizon in the layer of 14–25 cm. During this period, the emission was 4–20 times higher than the summer values. In lichen communities of peat mounds, the CH4 sink prevailed during the summer-autumn period. The total methane flux in different parts of the mire in June–September varied from 0.18 to 16.5 kg CH4/ha. In general, the palsa mire emitted 81 kg CH4/ha per year to the atmosphere. The methane emission from the surface of peat mounds and hollows made up 20% and 80% of the annual flux, respectively.

Microplastic transport, deposition and burial in seafloor sediments by turbidity currents

<p>Plastic pollution of the world’s oceans represents a threat to marine eco-systems and human health and has come under increasing scrutiny from the general public. Today the global input of plastic waste into the oceans is in the order of 10 million tons per year and predicted to rise by an order of magnitude by 2025; much of this plastic ends up on the seafloor. Plastics, and microplastics, are known to be concentrated in submarine canyons due to their proximity to terrestrial plastic sources, i.e. rivers. Plastics are transported in canyons by turbidity currents, mixtures of sediment and water which flow down-canyon due to their density; these flows can also ‘flush’ canyons, eroding and entraining the sediment lining the canyon walls and bottom. A single turbidity current can last for weeks and transport more sediment than the annual flux of all terrestrial rivers combined. Although it is known that these flows play a critical role in delivering terrestrial sediment and organic carbon to the seafloor, their ability to transport and bury plastics is poorly-understood. Using flume experiments we investigate turbidity currents as agents for the transport and burial of microplastic fragments and fibers. Microplastic fragments are focused at the flow base, whereas fibers are more homogeneously distributed throughout the flow. Surprisingly though, the resultant deposits show the opposite trend with fibers having a higher concentration that fragments. We explain this observation with a depositional mechanism whereby fibers are dragged out of suspension by settling sand grains, are trapped in the aggrading sediment bed and are buried in the deposits. Conversely, fragments may remain suspended in the flow and are less likely to be trapped on the bed. Our results suggest that turbidity currents can transport microplastics over long distances across the ocean floor, and that turbidity currents potentially distribute and bury large quantities of microplastics in seafloor sediments.</p>

A Method for Estimating Annual Cumulative Soil/Ecosystem Respiration and CH4 Flux from Sporadic Data Collected Using the Chamber Method

Measurements of greenhouse gas fluxes over many ecosystems have been made as part of the attempt to quantify global carbon and nitrogen cycles. In particular, annual flux observations are of great value for regional flux assessments, as well as model development and optimization. The chamber method is a popular approach for soil/ecosystem respiration and CH4 flux observations of terrestrial ecosystems. However, in situ flux chamber measurements are usually made with non-continuous sampling. To date, efficient methods for the application of such sporadic data to upscale temporally and obtain annual cumulative fluxes have not yet been determined. To address this issue, we tested the adequacy of non-continuous sampling using multi-source data aggregation. We collected 330 site-years monthly soil/ecosystem respiration and 154 site-years monthly CH4 flux data in China, all obtained using the chamber method. The data were randomly divided into a training group and verification group. Fluxes of all possible sampling months of a year, i.e., 4094 different month combinations were used to obtain the annual cumulative flux. The results showed a good linear relationship between the monthly flux and the annual cumulative flux. The flux obtained during the warm season from May to October generally played a more important role in annual flux estimations, as compared to other months. An independent verification analysis showed that the monthly flux of 1 to 4 months explained up to 67%, 89%, 94%, and 97% of the variability of the annual cumulative soil/ecosystem respiration and 92%, 99%, 99%, and 99% of the variability of the annual cumulative CH4 flux. This study supports the use of chamber-observed sporadic flux data, which remains the most commonly-used method for annual flux estimating. The flux estimation method used in this study can be used as a guide for designing sampling programs with the intention of estimating the annual cumulative flux.

A biological source of marine sedimentary iron oxides

The biogeochemical cycle of iron is intricately linked to numerous element cycles. Although reductive biological processes that bridge the iron cycle to other element cycles are established, little is known about microbial oxidative processes on iron cycling in sedimentary environments—resulting in the formation of iron oxides. Here, we show that a major source of sedimentary iron oxides originates from the metabolic activity of iron-oxidizing bacteria from the class Zetaproteobacteria, stimulated by burrowing animals in coastal sediments. Zetaproteobacteria were estimated to be a global total of 1026 cells in coastal, bioturbated sediments and would equate to an annual production of approximately 7.9 x 1015 grams of sedimentary iron oxides—twenty-five times larger than the annual flux of iron oxides by rivers. These data suggest that iron-oxidizing Zetaproteobacteria are keystone organisms in marine sedimentary environments given their low numerical abundance; yet exert a profound impact via the production of iron oxides.