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Rice straw increasingly remains on the fields for nutrient supply to the next generation of crop plants. It can be applied either fresh or after burning to black carbon or ash. A central concern during rice cultivation is accumulation of carcinogenic arsenic and the question arises how much rice straw application contributes to nutrient versus arsenic supply in paddy fields. Laboratory incubation experiments were performed to assess the effect of rice straw, black carbon and ash on element mobilization. Our experiments showed initially higher silicon and phosphorus release from black carbon compared to fresh straw amendments. However, more re-sorption to soil lead to finally slightly lower pore water concentrations for black carbon versus fresh straw amendments. Highest arsenic, iron, manganese and dissolved organic carbon concentrations were observed after fresh rice straw application. Black carbon and ash application lead to only minor increases of arsenic compared to controls without amendments. Overall, for silicon and phosphorus the soil acts as sink while for iron and arsenic it was the main source. In summary, burning of rice straw to black carbon prior to application seems to yield a high increase in desired nutrient and a decrease in undesired arsenic mobilization in paddy soils.

Temperate grasslands exhibit strong spatial and temporal variation in water regimes. Thus, grassland plants experience potentially stressful water regimes, which may influence their tissue silicon (Si) and nitrogen (N) concentrations. Plant Si and N concentrations play important ecological roles in temperate grasslands, for example, by influencing plant performance and herbivory, yet comparisons of species' responses to a broad range of water regimes, including drought, waterlogging and flooding, are lacking.We conducted a mesocosm experiment with 10 temperate grassland species of two life‐forms (grasses and forbs) exposed to four different soil water regimes (drought, a benign control, waterlogged and flooded conditions), and analysed their Si and N concentrations.Grasses showed lower Si concentrations under drought and flooding compared to the benign control and the highest concentrations emerged under waterlogging. Overall, plant Si responses of grasses were more uniform, while in forbs, responses varied both in direction and magnitude across species. For N concentrations, all species and life‐forms showed the highest concentrations under drought compared to the benign control, while half of the species exhibited decreasing concentrations under waterlogging and/or flooding. The water regimes, especially waterlogging and flooding, induced changes in species rankings of plant Si and N concentrations, with stronger shifts in forbs than in grasses.Our results indicate that spatial and temporal variation of water regimes may influence plant Si and N concentrations in temperate grassland species. Plant Si responses to water regimes might be highly species‐specific in forbs but more similar in grasses, whereas plant N responses are likely to be relatively uniform across species and life‐forms.The strong plasticity in plant Si and N concentrations we observed might have pervasive consequences for ecological processes, such as herbivory. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Species composition of grasslands and pastures is an important control on biomass production and ecological functioning, with a significant role of grasses and legumes. A change in composition of legumes/grasses abundance and biomass ratio results in altered nutrient cycling and composition of higher trophic-level communities (e.g., grazers). However, in addition to pasturing and fire effects, other parameters may also potentially affect grassland composition. Grasses are known as silicon (Si) accumulators and legumes as calcium (Ca) accumulators. We propose a new testable hypothesis, and a conceptual model, on the role of Si/Ca availability in controlling legume/grass dominance/competition in grassland systems. Based on available literature, we argue that Si/Ca availability is an important trigger for shifts in abundance of both plant families. The differential uptake of Si and Ca by legumes and grasses affects grassland biogeochemistry and microbial (fungal) biomass. In addition, altered litter stoichiometry, through impact of Ca and Si uptake on N, C, and P turnover, affects the decomposition processes. [ABSTRACT FROM AUTHOR]

Fire can have large effects on ecosystems, with phosphorus being highly important in this regard, especially when considering productivity in burned or adjacent ecosystems after fire. Unfortunately, existing data pose contradictions and methodological challenges to assessing P availability. Here, the impact of fire on topsoil available P was estimated using three different types of organic soil layers (raw humus from spruce, humus from beech, and peat) and two fire regimes (obtaining black carbon and ash). Our findings suggest a strong fire impact on P availability, by enhancing available P during burning to black carbon (~10-fold), and to ash (~2- to 7.5-fold) dependent on calcite content. Fire impact on P availability is on a similar order of magnitude as mineral weathering and annual P cycling/ uptake in/by ecosystems. Furthermore, the proportion of available P in relation to total P depends on the origin of the organic soil layers. When related to the remaining mass after burning, as is commonly done, P availability can be overestimated by up to 1400%. Results from this study provide a realistic magnitude of shifts in P release and P availability by fire events of different intensity for widely abundant ecosystem conditions. Taking the importance of P for ecosystem processes into account, these results are highly relevant, because fires for fuel reduction are a common application, and for temperate and boreal ecosystems even moderate climate change scenarios predict an increasing appearance of fires in these regions. [ABSTRACT FROM AUTHOR]

The increasing cultivation of genetically modified corn plants ( Zea mays ) during the last decades is suggested as a potential risk to the environment. One of these genetically modified variety expressed the insecticidal Cry1Ab protein originating from Bacillus thuringiensis (Bt), resulting in resistance against Ostrinia nubilalis, the European corn borer . Transgenic litter material is extensively studied regarding the decomposition in soils. However, only a few field studies analyzed the fate of the Cry1Ab protein and the impact of green and senescent leaf litter from corn on the decomposition rate and related ecosystem functions in aquatic environments. Consequently, a microbial litter decomposition experiment was conducted under controlled semi-natural conditions in batch culture using two maize varieties: one variety with Cry1Ab and another one with the appertaining Iso-line as control treatment. The results showed no significant differences between the treatment with Cry1Ab and the Iso-line regarding loss of total mass in dry weight of 43% for Iso-line and 45% for Bt-corn litter, lignin content increased to 137.5% (Iso-line) and 115.7% (Bt-corn), and phenol loss decreased by 53.6% (Iso-line), 62.2% (Bt-corn) during three weeks of the experiment. At the end of the experiment Cry1Ab protein was still detected with 6% of the initial concentration. A slightly but significant lower cellulose content was found for the Cry1Ab treatment compared to the Iso-line litter at the end of the experiment. The significant higher total protein (25%) and nitrogen (25%) content in Bt corn, most likely due to the additionally expression of the transgenic protein, may increase the microbial cellulose degradation and decrease microbial lignin degradation. In conclusion a relevant year by year input of protein and therefore nitrogen rich Bt corn litter into aquatic environments may affect the balanced nutrient turnover in aquatic ecosystems. [ABSTRACT FROM AUTHOR]

Highlights: [•] Chironomus plumosus has a main impact on elemental mobilization from sediments. [•] DOC, N, Mg, Ca, Sr, Mo and U were highly influenced by bioturbation/bioirrigation. [•] Al, Fe, Co, Cu, Zn and Ce were affected only at start (larvae dig into sediments). [•] Mn, Ni, As, Cd and Cs mobilization were affected at start and slightly afterwards. [•] Invertebrate bioturbation/bioirrigation is a main process in element cycling. [Copyright &y& Elsevier]

• Heat effects form fire potentially plays an important role in global Si cycling. • Heat increased Si availability up to ~700% in different mineral soils. • Heat increased amorphous Si up to 1.9 × 104% in these soils. Altered fire regimes as a response to climate change are significantly affecting terrestrial ecosystems and biogeochemical cycles. In this context, not only natural fires but also anthropogenic fires like rice straw burning have to be considered. While heat effects of fire on some nutrient cycles (e.g., carbon, nitrogen, phosphorus) have been well-studied, little is known about consequences of heat for the silicon (Si) cycle. There is some information that heat increases the release of Si from soil organic matter. However, nothing is known about the effect of heat on Si availability in mineral soils to the best of our knowledge. We analyzed the effect of heat on Si availability in six different mineral soils. Our data show that heat is increasing Si availability (Mehlich-3 extractable) of all tested soils. The same pattern was found for amorphous Si (alkaline extraction) for most of these soils. Consequently, heated soils might represent a strong and immediate source for plant available Si. Ecosystem characteristics (e.g., vegetation, soil type) that affect uptake-leaching balances determine the further fate of the released Si. In summary, heat might affect Si cycling not only by strongly increasing Si availability in soil organic matter but also in mineral soils. [ABSTRACT FROM AUTHOR]