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Forest soil acidification caused by acid deposition is a serious threat to the forest ecosystem. To investigate the liming effects of biomass ash (BA) and alkaline slag (AS) on the acidic topsoil and subsoil, a three-year field experiment under artificial Masson pine was conducted at Langxi, Anhui province in Southern China. The surface application of BA and AS significantly increased the soil pH, and thus decreased exchangeable acidity and active Al in the topsoil. Soil exchangeable Ca2+ and Mg2+ in topsoil were significantly increased by the surface application of BA and AS, while an increase in soil exchangeable K+ was only observed in BA treatments. The soil acidity and active Al in subsoil were decreased by the surface application of AS. Compared with the control, soluble monomeric and exchangeable Al in the subsoil was decreased by 38.0% and 29.4% after 3 years of AS surface application. There was a minimal effect on soluble monomeric and exchangeable Al after the application of BA. The soil exchangeable Ca2+ and Mg2+ in the subsoil increased respectively by 54% and 141% after surface application of 10 t ha-1 AS. The decrease of soil active Al and increase of base cations in subsoil were mainly attributed to the high migration capacity of base cations in AS. In conclusion, the effect of surface application of AS was superior to BA in ameliorating soil acidity and alleviating soil Al toxicity in the subsoil of this Ultisol.

Featured paper: See Editorial p553

ABSTRACTConcern over increasing water scarcity has led to the introduction of the concept of agricultural water productivity and an emphasis on interventions to achieve ‘more crop per drop’. Yet, a...

Water use efficiency (WUE) plays important role in understanding the interaction between carbon and water cycles in the plant-soil-atmosphere system. However, little is known regarding the impact of altered precipitation on plant WUE in arid and semi-arid regions. The study examined the effects of altered precipitation [i.e., ambient precipitation (100% of natural precipitation), decreased precipitation (DP, −50%) and increased precipitation (IP, +50%)] on the WUE of grass species (Stipa grandis and Stipa bungeana) and forb species (Artemisia gmelinii) in a temperate grassland. The results found that WUE was significantly affected by growth stages, precipitation and plant species. DP increased the WUE of S. grandis and S. bungeana generally, but IP decreased WUE especially in A. gmelinii. And the grasses had the higher WUE than forbs. For different growth stages, the WUE in the initial growth stage was lower than that in the middle and late growth stages. Soil temperature, available nutrients (i.e., NO3–, NH4+, and AP) and microorganisms under the altered precipitations were the main factors affecting plant WUE. These findings highlighted that the grasses have higher WUE than forbs, which can be given priority to vegetation restoration in arid and semi-arid areas.

Tropical and subtropical mangrove swamps, under normal conditions, can sequester large amounts of carbon in their soils but as coastal wetlands, they are prone to hurricane disturbances. This study adds to the understanding of carbon storage capabilities of mangrove wetlands and explores how these capacities might change within the scope of a changing storm climate. In September 2017, Naples Bay, FL, USA (28°5′ N, 81°47′ W) encountered a direct hit from hurricane Irma, a Saffir–Simpson category 3 storm. By comparing carbon storage, forest community structure, and aboveground productivity collected in 2013 and in 2019, we estimated the effects of hurricane Irma on mangrove functions. Aboveground biomass increased during the study period at a rate of approximately 0.72 kg m−2 yr−1, significantly less than the average found in undisturbed mangrove forests. Soil carbon storage decreased at all study sites. On average, 2.7 kg-C m−2 was lost in the top 20 cm between sample collections. Carbon loss in belowground pools could point to a feedback of mangrove swamps on climate change as they lose their ability to store carbon and increase net atmospheric carbon. Nevertheless, mangrove swamps remain resilient to tropical storms in the long term and can recover their carbon storage capacity in the years following a storm.

Medium-chain fatty acids (MCFA) such as caproic, heptanoic, and caprylic acids are monocarboxylic acids, which can be used as precursor molecules to synthesize biodiesel, bioplastics, antimicrobials, and corrosion inhibitors.

The natural hydrology of streams and rivers is being extensively modified by human activities. Water diversion, dam construction, and climate change have the potential to increase the frequency and intensity of low-flow events. Flow is a dominant force structuring stream aquatic insect communities, but the impacts of water diversion are poorly understood. Here we report results of an experimental stream flow diversion designed to test how aquatic insect communities respond to a low-flow disturbance. We diverted 40% to 80% of the water in three replicate streams for three summers, leading to summer flow exceedance probabilities of up to 99.9%. Shifts in habitat availability appeared to be a major driver of aquatic insect community responses. Responses also varied by habitat type: total insect density decreased in riffle habitats, but there was no change in pool habitats. Overall, the total biomass of aquatic insects decreased sharply with lowered flow. Collector-filterers, collector-gatherers, and scrapers were especially susceptible, while predatory insects were more resistant. Despite extremely low flow levels, there was no shift in aquatic insect family richness. The experimental water withdrawal did not increase water temperature or decrease water quality, and some wetted habitat was always maintained, which likely prevented more severe impacts on aquatic insect communities.

Contaminants such as petroleum hydrocarbons, heavy metals and pesticides can cause direct toxic effects when released into aquatic environments. Sensitive species may be impaired by sublethal effects or decimated by lethality, and this ecological alteration may initiate a trophic cascade or a release from competition that secondarily leads to responses in tolerant species. Contaminants may exert direct effects on keystone facilitator and foundation species, and contaminant-induced changes in nutrient and oxygen dynamics may alter ecosystem function. Thus, populations and communities in nature may be directly and/or indirectly affected by exposure to pollutants. While the direct effects of toxicants usually reduce organism abundance, indirect effects may lead to increased or decreased abundance. Here we review 150 papers that reference indirect toxicant effects in aquatic environments. Studies of accidental contaminant release, chronic contamination and experimental manipulations have identified indirect contaminant effects in pelagic and benthic communities caused by many types of pollutants. Contaminant-induced changes in behavior, competition and predation/grazing rate can alter species abundances or community composition, and enhance, mask or spuriously indicate direct contaminant effects. Trophic cascades were found in 60% of the manipulative studies and, most commonly, primary producers increased in abundance when grazers were selectively eliminated by contaminants. Competitive release may also be common, but is difficult to distinguish from trophic cascades because few experiments are designed to isolate the mechanism(s) causing indirect effects. Indirect contaminant effects may have profound implications in environments with strong trophic cascades such as the freshwater pelagic. In spite of their undesirable environmental influence, contaminants can be useful manipulative tools for the study of trophic and competitive interactions in natural communities.