Helophytes adapt to water and N-enrichment stresses by adjusting and coordinating stoichiometry characteristics in main organs.

Exploring the adaptation strategies of plants under stressful environments from an ecological stoichiometry perspective is a critical but underexplored research topic, and multi-organ collaborative research for multi-species can provide a comprehensive understanding. In this study, helophytes were selected as the subjects, and water depth and water N-enrichment were set as the stressors. A simulation experiment including three water depths (drought stress, control and flooding stress) and four water N-enrichment levels (control, low, medium and high N-enrichment stresses) for six helophyte species was carried out. Overall, C concentrations in all plant organs remained stable under water (drought-flooding stress) and N-enrichment stress. N concentrations increased under both flooding and drought stresses, while P concentrations and the N:P ratio showed an increase and decrease under only flooding stress, respectively. N concentration and N:P ratio increased with water N-enrichment level. The interaction only promoted the accumulation of N concentrations in aboveground organs. Especially, several species also changed organ C concentrations to adapt to water stress and adjusted root N concentrations for the combined stresses of flooding or drought and high N. Leaf and stem were strongly synergistic in N element, and leaf and root were mainly synergistic in P element. Water N-enrichment determined organ element concentrations more than water depth, and species identity dictated organ C:N:P ratios. Our results reveal that the allocation and synergy of nutrients among organs are important adaptive strategies for plants in stressful environments. Meanwhile, increasing water N-enrichment can be an unignored stressor, and species identity should be paid attention as a countermeasure.

Anthropocene microplastic stratigraphy of Xiamen Bay, China: A history of plastic production and waste management.

Microplastics (MPs) are considered one of the significant stratigraphic markers of the onset of the Anthropocene Epoch; however, the interconnections between historic plastic production, waste management as well as social-economic and timing of MP accumulation are not well understood. Here, stratigraphic data of MPs from a sediment core from Xiamen Bay, China, was used to reconstruct the history of plastic pollution. Generalized Additive Modeling indicates a complex temporal evolution of MP accumulation. The oldest MPs deposited in 1952 was 30,332 ± 31,457 items/kg•dw, coincide with the infancy of the plastic industry and onset of the Anthropocene. The Cultural Revolution (1966-1976) curtailed these initial increases. Subsequent rapid growth in MPs during the late 1970s was peaked at 189,241 ± 29,495 items/kg•dw in 1988 and was followed by a drastic decline in the late 1980s to a low value in 1996 (16,626 ± 26,371 items/kg•dw), coinciding with proliferation of MP sources, coupled with evolution of plastic production, consumption, and regulation. Increasing MPs over the past decades implies that previous mitigation measures have been compromised by the escalated influx of MPs from increasing plastics production, legacy MPs remaining in circulation and insufficient waste management for a growing population. The present methodology and results represent a conceptual advance in understanding how changes in policy and economics over time correlate to changes in MP records in Anthropocene strata, which may help make decisions on plastic pollution mitigation strategies worldwide.

Microplastic abundance, characteristics, and removal in wastewater treatment plants in a coastal city of China.

Studying the abundance, characteristics, and removal of microplastics (MPs) in wastewater treatment plants (WWTPs) in coastal cities is of great significance for understanding the impacts of human activities on the marine environment, but currently, little information on this topic is available in China. Therefore, the abundance, characteristics, and removal of MPs in seven WWTPs of Xiamen, a typical coastal city in China, are studied. Sixty samples were collected using an improved sampling method involving an electromagnetic flowmeter and a fast digital camera. The influent MPs concentration is 1.57-13.69 items/L, and it is reduced to 0.20-1.73 items/L in the effluent, indicating that 79.3-97.8% MPs is removed. Based on the daily effluent discharge and MPs removal rate, it is estimated that ∼6.5 × 108 MPs are released from the seven WWTPs into the Xiamen Bay each day. The light microscopic and micro-Raman spectroscopic analysis indicates that ∼62.68% of particles are plastic polymers, including polypropylene (31.6%), polyethylene (21.9%), polystyrene (10.1%), propylene/ethylene copolymer (9.2%), and polyethylene terephthalate (7.5%). The color of MPs is mainly composed of white (27.3%) and clears (25.8%). Our results show that granules (41.1%) are the dominant shape of MPs, followed by fragments (31.3%), fibers (23.7%), and pellet (3.9%). The characteristics of MPs such as sizes, shapes, and types affect the MPs removal in WWTPs. Our findings show that MPs concentration in the influent is positively correlated with the suspended solids (SS), however, in the effluent, it is associated with the WWTPs operating load, as reflected by obviously higher MP abundance in overloaded ones.