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Denitrifying woodchip bioreactors offer an opportunity to intercept and reduce nitrogen loads between agricultural fields and downstream aquatic ecosystems. Here we assessed the performance of three in-drain bioreactor beds installed in open drains receiving runoff and shallow ground water from rain-fed sugarcane production in the Wet Tropics of Australia. Drain nitrate-N concentrations were generally low, with a mean of 0.2 mg L−1 and maximum of 3.3 mg L−1, which may have been partially due to denitrification in the contributing soils. Bioreactors reduced the concentration of nitrate-N in intercepted waters (average 41% reduction). However, removal rates were often limited by nitrate-N availability. Load reduction over the 2018/19 season was just 0.11 kg N ha−1 yr−1. This limited performance was in large part due to the dynamic nature of nitrogen loads in this system. Specifically, a high proportion of the annual nitrogen load occurring during 'first-flush' events immediately after fertilization (i.e. 72% during a 10-day period in 2018/19) resulting in considerable bypass flow (i.e. low interception). Our study is the first in the Australian Wet Tropics to assess the annualized performance and total load reductions of in-drain denitrifying bioreactor beds. Although showing their potential, our results highlight the fact that denitrifying bioreactor performance is determined by the hydraulic context of the catchment, and the proportion of the annual nitrate load that can be successfully intercepted. [ABSTRACT FROM AUTHOR]

Tropospheric ozone (O 3 ) is a major air pollutant and greenhouse gas, affecting carbon dynamics, ecological interactions, and agricultural productivity across continents and biomes. Elevated [O 3 ] has been documented in tropical evergreen forests, the epicenters of terrestrial primary productivity and plant-consumer interactions. However, the effects of O 3 on vegetation have not previously been studied in these forests. In this study, we quantified ambient O 3 in a region shared by forests and urban/commercial zones in Panama and found levels two to three times greater than in remote tropical sites. We examined the effects of these ambient O 3 levels on the growth and chemistry of seedlings of Ficus insipida , a regionally widespread tree with high stomatal conductance, using open-top chambers supplied with ozone-free or ambient air. We evaluated the differences across treatments in biomass and, using UPLC-MS-MS, leaf secondary metabolites and membrane lipids. Mean [O 3 ] in ambient air was below the levels that induce chronic stress in temperate broadleaved trees, and biomass did not differ across treatments. However, leaf secondary metabolites – including phenolics and a terpenoid – were significantly downregulated in the ambient air treatment. Membrane lipids were present at lower concentrations in older leaves grown in ambient air, suggesting accelerated senescence. Thus, in a tree species with high O 3 uptake via high stomatal conductance, current ambient [O 3 ] in Panamanian forests are sufficient to induce chronic effects on leaf chemistry. [ABSTRACT FROM AUTHOR]

Abstract: Global warming and associated increases in the frequency and amplitude of extreme weather events, such as heat waves, may adversely affect tropical rainforest plants via significantly increased tissue temperatures. In this study, the response to two temperature regimes was assessed in seedlings of the neotropical pioneer tree species, Ficus insipida. Plants were cultivated in growth chambers at strongly elevated daytime temperature (39°C), combined with either close to natural (22°C) or elevated (32°C) nighttime temperatures. Under both growth regimes, the critical temperature for irreversible leaf damage, determined by changes in chlorophyll a fluorescence, was approximately 51°C. This is comparable to values found in F. insipida growing under natural ambient conditions and indicates a limited potential for heat tolerance acclimation of this tropical forest tree species. Yet, under high nighttime temperature, growth was strongly enhanced, accompanied by increased rates of net photosynthetic CO2 uptake and diminished temperature dependence of leaf-level dark respiration, consistent with thermal acclimation of these key physiological parameters. [Copyright &y& Elsevier]

Tropospheric ozone (O 3) is a secondary pollutant and a greenhouse gas with a positive radiative forcing. Many studies have documented its negative impacts on plant growth and human health. Historically, studies have focused on determining levels of exposure in mid- and high-latitude regions. In the tropics, high O 3 concentrations are expected due to large concurrent and future precursor emissions. In Africa, seasonal biomass burning (from both natural and anthropogenic fires) during the dry season plays a crucial role in O 3 precursor production. However, O 3 observational studies in tropical Africa are currently missing. To fill this major knowledge gap, we established in November 2019 a continuous monitoring of near-surface O 3 in the Congo Basin at the Yangambi research centre in the Democratic Republic of the Congo. Using this unique dataset in the heart of the second-largest tropical forest in the world, we assessed the ability of current remote sensing products to capture the magnitude and temporal dynamics of in situ tropospheric O 3 concentrations, especially O 3 concentration variation between dry and wet seasons until March of 2022. We compared near-surface atmospheric O 3 measurements collected in Yangambi and four different reanalysis products: European Centre for Medium-Range Weather Forecasts Reanalysis (ECMWF) v5 (ERA5), Copernicus Atmospheric Monitoring Service reanalysis (CAMSRA), Modern-Era Retrospective Analysis for Research and Applications version 2 (MERRA-2) and Japanese Reanalysis (JRA-55). The results show that reanalysis products overestimated the magnitude of near-surface O 3 across the region with a mean bias of 27.3 ppbv, 19.9 ppbv, 10.8 ppbv and 1.0 ppbv for ERA5, CAMSRA, MERRA-2 and JRA-55, respectively. ERA5 and CAMSRA reanalysis were the only products able to capture, to some extent, the observed annual variation, showing higher O 3 concentrations during dry season months, despite the inability to reproduce the daily cycle of near-surface O 3. • The first-ever dataset of near-surface ozone was collected in the core of the African tropical forests. • It fills a critical gap in a relevant area as ozone has been thought to reach large concentrations in central Africa. • Access the ability of state-of-the-art reanalysis products to capture the magnitude and temporal dynamics of in situ O3. • The reanalysis products fail to reproduce the seasonality and the daily cycles of tropospheric ozone. [ABSTRACT FROM AUTHOR]

• Cassava is a staple crop for many countries but is cyanogenic and can be lethal if consumed without adequate processing. • Potential climate effects on cassava's edible tissues and toxic compounds may have major implications on human health. • Here, the interactive effects of elevated temperature and [CO 2 ] on cassava growth, storage and defence were evaluated. • Cyanide decreased under elevated temperature, but plant biomass and tuber number increased with additional elevated [CO 2 ]. • Our findings highlight how future predicted climatic changes may impact cassava production and quality. Rising atmospheric CO 2 concentrations and global warming can alter how plants partition their resources. This is important for food crops through changes in resource allocation to edible tissues and toxic defence compounds. While research suggests elevated temperature and [CO 2 ] independently drive changes in plant metabolism and stress levels, and photosynthetic rates, respectively, it is less clear how these environmental changes impact plants when combined. Cassava is an important dietary staple for many developing nations. However, the safety of cassava depends on cyanogenic glucoside concentrations. In a climate-controlled greenhouse, the effects of elevated temperature in the presence and absence of elevated [CO 2 ] on the growth, physiology and chemical defence of cassava at two growth stages were examined. Growth in cassava was initially increased by elevated temperature. However, across time, simultaneous elevated [CO 2 ] led to an increasing biomass advantage over plants grown at ambient [CO 2 ] and temperature. Elevated temperature and [CO 2 ] also significantly increased tuber initiation and early tuber expansion. Tuber and leaf cyanide concentrations were significantly reduced under elevated temperature, while elevated temperature and [CO 2 ] produced tuber cyanide concentrations similar to the higher levels found in plants grown at ambient conditions. The findings highlight how future climate change may impact both cassava production and quality. [ABSTRACT FROM AUTHOR]