Ecosystem Sciences

Aquaponics is a recognised food system for its circular nutrient management potentiality, as it redirects aquaculture waste into plant production. However, current practices still fall short of closing nutrient loops, with substantial losses occurring through dissolved effluents and solid waste. This review examines strategies to reduce losses, recover nutrients, internally recycle dissolved streams, and valorise solid side streams in aquaponics, with particular attention to nitrogen and phosphorus due to their dual role as essential, and often limiting, inputs in aquaculture and plant production as well as key pollutants with major eutrophication potential. First, we identify the fate of dissolved and solid nutrients from both aquaculture and hydroponic subsystems. Second, we evaluate strategies to recover these nutrients, exploring opportunities to recycle dissolved nutrients and water, reuse solid waste, and reduce system-wide impacts. Third, we discuss the importance of integrating these processes at a system level and reflect on how current innovations can be better aligned with circular bioeconomy principles. Our synthesis concluded that while the integration of these strategies into optimally efficient, circular aquaponic systems is an ongoing challenge, several key nutrient recovery technologies are themselves well-established and have been successfully implemented. Addressing the gap in knowledge and industry practice will require systems thinking, deeper cross-disciplinary collaboration, and applied research that goes beyond isolated interventions.

As an essential trace element, selenium (Se) has important biological functions, and Se-containing polysaccharides (Se-PS) have therefore received increasing attention for their unique structural features and bioactivities. In this study, Se tea polysaccharides (SeTPSs) were isolated from a Se-rich black tea and purified to obtain fractions with Se contents ranging from 146 to 572ppb. Se content was determined by ICP-QQQ-MS, and the SeTPSs fractions were further characterized for molecular weight (MW) distribution, monosaccharide composition, structural features, conformation, thermal stability, and antioxidant activity. Results showed that the SeTPSs are heteropolysaccharides, with Se found in the polysaccharide material and showing Se-associated structural features, and the SeTPSs exhibited varying Se content, molecular structure, and antioxidant activity. Notably, SeTPSs demonstrated enhanced antioxidant activity and thermal stability compared to regular tea polysaccharides. These findings expand the comparative dataset for Se-rich polysaccharides and provide a foundation for future studies on organoselenium-containing macromolecules and their potential health effects.

The capacity of nutrient-limited forests to enhance carbon (C) sequestration under elevated CO2 (eCO2) remains a critical uncertainty in C cycle modeling. While existing evidence suggests that low phosphorus (P) bioavailability may constrain CO2 fertilization effects on plant growth, the extent to which this limitation modulates ecosystem responses to eCO2 in forests adapted to P-deficient soils remains poorly understood. Here, using eight P-enabled models, we simulated the magnitudes and mechanisms through which P bioavailability interacts with eCO2, emulating an ecosystem-scale P enrichment experiment at a P-limited Eucalyptus forest undergoing long-term Free-Air CO2 Enrichment. While models predicted pronounced P effects on tree growth, P enrichment unexpectedly did not increase the CO2 effects on tree growth and ecosystem C sequestration. Models prioritized either CO2-driven or P-driven growth, but rarely both. This tradeoff emerged due to model-specific assumptions on 1) partitioning of the extra P in soil labile versus nonlabile pools; 2) plant photosynthetic acclimation to P deficiency; 3) C and nutrient use strategies regulating plant size and allocation; and 4) microbial-driven soil decomposition processes. By generating divergent yet biologically plausible outcomes, these predictions establish critical testable hypotheses for empirical research and highlight multiple P-related pathways that may influence the future land C sink.

Nitrogen losses following fertilizer application not only cause nutrient loss to the crops, but also have negative environmental impacts, including ammonia (NH3) and greenhouse gas emissions (GHG) (e.g., nitrous oxide, N2O). Numerous studies have been carried out to investigate the efficiency of fertilizer use, aiming to increase crop yield and reduce environmental impacts including GHG and other gaseous emissions. There are different measurement approaches of quantifying gaseous nitrogen (N) losses, and static chamber methods are the most commonly used approach for directly measuring emissions from soils. However, chambers interfere with the soil environment, the small measurement footprint of chambers is unable to represent the large source area and are poorly suited for long-term measurements. Here, we demonstrated the use of slant-path Fourier transform infrared spectroscopic (FTIR) technique to continually measure NH3 and N2O emission rates from wheat crops for 4 weeks following fertilizer application. The study was conducted in a wheat farm in Victoria, Australia in winter season in August 2025. Urea with (treatment) and without (control) a urease inhibitor was applied to the wheat crop at a rate of 98 kg N/ha. Line-averaged concentrations of NH3 and N2O from each plot were continually measured with vertically separated measurement paths using an OP-FTIR and wind information was recorded by a 3-D sonic anemometer. Fifteen-min average NH3 and N2O emission rates were calculated based on the measured concentrations and wind information. The results showed that NH3 emission rates increased immediately after urea was applied, with greater increase than the untreated urea. Ammonia emission rates from the urease inhibitor treatment increased in the third week following fertilization, while ammonia emission rates from the control site started decreasing. Preliminary results show that the accumulative NH3 and N2O emissions from the urea plot were ~3 and 1.6 times higher than that from the urease inhibitor treated plot, respectively. The higher NH3 and N2O emissions following non-treatment urea application highlighted the benefits of a urease inhibitor for reducing N loss under high ambient temperature and lack of rainfall for 2 weeks following fertilization. Further benefits could be achieved in N use efficiency by reducing the N application rate when using the urease inhibitor.

Humans and nature have an entangled past, present and future, which has become obscured in an era of biodiversity loss and increasingly urbanised human populations. The recent focus on biodiversity-positive design, as one of many related approaches to re-engage with these entanglements, signals a re-emerging global recognition of the fundamental connections between humans and nature.Within the growing body of guidance documents for Biodiversity-Positive Design, there is a common recognition that biodiversity is a multi-dimensional concept and can mean many different things to many different people. Indeed, the profusion of language and frameworks related to biodiversity offer enormous flexibility in how a goal or vision for biodiversity can be framed within a project, and ultimately influence the realised biodiversity gain at the end of the project. The importance of considering the site-specific voices and opportunities places novel ecosystems and pollination services on equal footing with efforts to expand populations of rare plants or create habitat for under-represented fauna.This presentation does not seek to challenge this flexibility in expressing the situated biodiversity associated with place. Instead, it takes a closer look at those projects that explicitly seek to bend the biodiversity extinction curve and counter the potential for the biotic homogenisation of cities. By drawing upon three frameworks (Nature Futures, Kowarik's 4 Natures and the frames of "wild", "stray" and "care") and global datasets of biodiversity in cities, the presentation will seek to provide a more nuanced understanding of how the socio-cultural and eco-evolutionary histories of cities reposition the relative contributions that different frames of nature offer for suppporting the unique biodiversity in cities in multiple continents. This knowledge is critical for bringing a more nuanced approach to Biodiversity-Positive Design, where the objective is to support the dimensions of biodiversity related to vulnerability, endemism and foregrounding outcomes that are unique to a place.

1. Questionable research practices (QRPs) bias the published literature towards apparently strong and conclusive results, resulting in low rates of replicability. Recent metaresearch reveals that ecology is not immune to the ‘reproducibility crisis’ seen in other disciplines, due to similar rates of QRPs and a lack of transparency in published research. However, metaresearch to date focuses on hypothesis-testing research and treats data-dependent analytic decisions as inherently questionable. This is not a good fit for ecology and related fields that conduct exploratory or predictive research using complex models, where data-dependent decisions are often necessary and legitimate aspects of the modelling process. 2. To aid in understanding why and how frequently QRPs occur, and how severe the consequences might be, we develop a conceptual framework describing QRPs in ecological modelling, distinguishing questionable from legitimate data-dependent decisions. we present a typology of QRPs organised by decision-making mechanism and target, reframing QRPs in modelling as practices that inflate perceived model credibility, rather than as producing false-positive statistical results. 3. We identified six QRP classes that may occur at various points in the modelling process: selective reporting, S-hacking (manipulating performance metrics), model fishing, sample curation, HARKing and overhyping. These practices threaten the reliability and reproducibility of model-based research by artificially inflating the apparent credibility of models. 4. We aim to raise awareness among modellers about different types of QRPs and how they might emerge in ecological modelling. We offer strategies to mitigate QRP risks, while preserving legitimate adaptive decision-making characteristic of ecological modelling.

The online version contains supplementary material available at 10.1007/s42995-026-00360-x.