Changes In Nutrient Concentrations Research Articles

Impact of water depth and flow velocity on organic matter removal and nitrogen cycling in floating constructed wetlands

The configuration of water depth (WD) and flow velocity (FV) in floating constructed wetlands (FCWs) reflects the complex interactions between hydraulic conditions and wastewater treatment performance. Properly configuring hydraulic conditions can optimize performance. This study explored the removal and degradation of organic matter and nitrogen (N) in FCWs with three different WDs (50 cm (SD), 70 cm (MD), and 95 cm (DD)) under four FV conditions (0, 0.3, 1.0, and 1.5 m/d). It also analyzed the regulatory effects of hydraulic conditions on microbial community structure to provide new insights for configuring hydraulic conditions in FCWs. The results indicate that variations in WD and FV do not significantly affect COD removal (p > 0.05), with removal efficiency (RE) consistently reaching 90 % across all conditions. However, hydraulic conditions do influence the degradation rate (k) of COD, with increased FV enhancing the k in MD and DD. In contrast, WD significantly impacts the removal of NH4+−N (p < 0.05), with RE in SD exceeding 80 % across all four FVs. The primary reason is that increased WD reduced the abundance of nitrifying bacteria (Nitrosomonas and Nitrospira) and functional genes (hao and pmoABC-amoABC). Meanwhile, increased WD and FV significantly enriched the denitrifying bacteria genera (such as Massilia, Bacillus, Ensifer, and Rhodobacter) and certain functional genes (nap and nir), favoring the denitrification process and enhancing the dissimilatory nitrate reduction to ammonium (DNRA) process. Furthermore, microbial community diversity, richness, and the number of operational taxonomic units (OTUs) were highest in SD, but decreased with increased WD. This is mainly related to changes in oxygen (O2) transmission and nutrient concentration. These findings help us understand the mechanisms by which hydraulic regulation affects the removal of organic matter and N in FCWs. They also propose potential solutions from a hydraulics perspective to enhance N removal.

Soil fertility status under mixed pastures in irrigated Tsitsikamma dairy farms: case studies

Animal manures are increasingly receiving renewed interest as an alternative to synthetic fertilizers. While they may improve ecosystem functions, there is limited information on short-term effects of organic amendments on soil reaction and nutrient dynamics in irrigated mixed dairy pastures, especially in the context of the Tsitsikamma region, South Africa. This study examined the soil fertility status of minimum tilled 6-year-old pasture-mixed dairy farms (F1, F2, F3, F4 and F5) in the Upper (UT) and Lower (LT) Tsitsikamma regions treated with different rates of NPK (nitrogen, phosphorus, potassium) fertilizer alone or in combination with poultry manure (PM) and/or dairy effluent (DE). Soil samples were collected at 0–15, 15–30, 30–45 and 45–60 cm depth intervals and analysed for soil pH, P, K, Ca and Mg. Results of this study revealed variable trends on soil pH and nutrient changes between farms, suggesting an influence of some inherent soil properties in addition to the 6-year applied management practices. When averaged over sampled farms, surface placement of soil amendments and limited soil disturbance resulted in surface stratification of soil pH, P, K, Ca and Mg. On the other hand, integration of organic and inorganic fertilizers induced significant changes in nutrient contents and stocks to a depth of 60 cm, especially in the LT region. A combination of NPK fertilizer, PM and/or DE applied in pasture mixtures generally showed potential to improve soil fertility in both regions. As such, adoption of this combination by farmers could cut down reliance on expensive synthetic fertilizers and costs of dairy production. However, studies are still necessary in this region to validate the observed results.

KARAKTERISASI KOMPOSISI KIMIA DAN POTENSI PEMANFAATAN CAMPURAN TANAH GAMBUT KALIMANTAN TIMUR DENGAN FLY ASH DAN BOTTOM ASH UNTUK PERTANIAN

The utilization of coal combustion waste, specifically fly ash and bottom ash, as a soil amendment offers an opportunity to enhance the fertility of peat soils in East Kalimantan, which typically have low levels of essential nutrients such as nitrogen (N), phosphorus (P), and potassium (K). This study aims to evaluate the impact of adding coal ash on peat soil's chemical composition and quality as a growing medium. The chemical composition analyzed includes alumina (Al₂O₃), silica (SiO₂), phosphorous anhydride (P₂O₅), iron(III) oxide (Fe₂O₃), and calcium oxide (CaO). X-ray Fluorescence (XRF) was used to determine changes in nutrient content. The results indicate that adding coal ash increases the levels of potassium (K) and silica (SiO₂), but decreases the levels of nitrogen (N) and phosphorus (P₂O₅). Additionally, adding coal ash affects soil pH, which impacts nutrient availability. These findings indicate that while coal ash can enhance soil enrichment with potassium and silica, its impact on nitrogen, and phosphorus must be carefully managed to optimize fertilization and promote healthy plant growth.

Change in leaf C:N:P stoichiometry and its correlations with soil available nutrients and dry matter yield in common vetch/oat intercropping under N fertilization

AbstractC, N, and P concentrations and stoichiometric ratios of the leaf are important for adaptive plant growth and nutrient utilization. However, our knowledge of how these traits change with N fertilization in intercropping systems remains limited. Hence, a 2‐year experiment was conducted with four cropping patterns, including two‐row common vetch (Vicia sativa L.) intercropping with one‐row oat (Avena sativa L.), one‐row common vetch intercropping with two‐row oat as well as sole oat and common vetch cropping with 0, 50, and 100 kg N/ha fertilization. Leaf total nitrogen (LTN) and phosphorus (LTP) concentrations and C:N:P stoichiometric ratios were measured and their linkages with soil nutrient availability were analysed. N fertilization significantly increased LTN, N:P, and C:P, while significantly decreasing LTP and C:N. Intercropping affected leaf nutrient concentrations and stoichiometric ratios, which were affected by N fertilization, basic soil fertility, and crop species. Intercropping and N fertilization affected soil nitrate nitrogen (SNN), available phosphorus (SAP) content, and dry matter (DM) yield. There were strong correlations between the leaf nutritional traits of oats and SNN, SAP, and DM, but few correlations were observed with common vetch. In conclusion, intercropping led to contrasting changes in leaf nutrient concentrations and stoichiometric ratios, which varied with N fertilization and crop species. We failed to reveal solid and direct effects of intercropping ratio on leaf nutritional traits. These findings contribute to a better understanding of crop nutritional traits and the link between leaves and soil in response to intercropping and N fertilization.

Disentangling the contributions of anthropogenic nutrient input and physical forcing to long-term deoxygenation off the Pearl River Estuary, China

Deoxygenation in estuarine and coastal waters worldwide has been largely attributed to the increasing anthropogenic nutrient input, whereas the contribution by long-term (decadal) changes in physical forcing is less investigated. This study aims to disentangle the impacts of three-decade changes in summer river nutrient concentration and physical forcing on the deoxygenation off a large eutrophic estuary, the Pearl River Estuary (PRE) in China. Using a coupled physical-biogeochemical model, we reproduce the observed summer oxygen conditions under the historical (the 1990s) and present (the 2020s) status of river nutrient concentration, freshwater discharge, and wind forcing. We show that the bottom hypoxic (dissolved oxygen < 2 mg/L) area off the PRE in the 2020s has increased by 73 % relative to the 1990s. The expansion is a result of the increased bottom water oxygen consumption outweighing the enhanced vertical oxygen supply, with the former driven by the sharp increase in inorganic nitrogen and phosphorus concentrations (160 %) and the latter caused by the decadal decline in both freshwater discharge (38 %) and wind speed (12.5 %) in summer. Model experiments suggest that if the observed changes in physical forcing had not occurred, the dramatic increase in anthropogenic nutrient concentrations from the 1990s to 2020s could have led to a much greater expansion of hypoxic area (249 %). On the contrary, the decadal decrease in summer freshwater discharge alone (while keeping the nutrient loading the same as in the 1990s) almost eliminates hypoxia off the PRE by weakening water column stratification and limiting the offshore spread of nutrients and organic matter, whereas the declined wind speed increases the hypoxic area by 247 % mainly through enhancing water column stability. Our results reveal that long-term changes in physical forcing are confounding the effects of anthropogenic nutrient input on deoxygenation, underlining the need to consider regional forcing changes in nutrient management to meet water quality goals.

Soil Solution Properties of Tropical Soils and Brachiaria Growth as Affected by Humic Acid Concentration

The soil solution is the compartment where plants uptake nutrients and this phase is in equilibrium with the soil solid phase. Changes in nutrient content and availability in the soil solution can vary among soil types in response to humic acid concentrations, thereby affecting Brachiaria growth. However, there are no studies demonstrating these effects of humic acid application on different soil types and how they affect Brachiaria growth. Thus, the aim of this study was to evaluate the effects of humic acid concentrations (0, 5, 10, 25, and 60 mg kg−1 carbon-humic acid) on Brachiaria brizantha growth and soil solution properties of contrasting tropical soils. Plants were grown for 35 days in greenhouse conditions in pots containing Sandy Entisol, Clayey (Red Oxisol), and Medium Texture (Red-Yellow Oxisol). Soil solution was assessed for pH, electrical conductivity (EC), carbon, and nutrient content. Shoot and root dry matter, as well as macro and micronutrients accumulation in the shoot, were determined. In a soil type-dependent effect, pH, EC, and concentrations of nutrients in solutions changed in response to carbon-humic acid concentration. In the less-buffered soils, Sandy Entisol and Red-Yellow Oxisol, the addition of 30–40 mg kg−1 carbon-humic acid increased root proliferation by 76–89%, while Brachiaria biomass produced in all soils increased by approximately 30%. Levels of carbon in solution were high (&gt;580 mg L−1) and varied depending on the investigated soil type. Though solution carbon contents did not appear to be a driving factor controlling the positive effects of humic acid concentrations on Brachiaria dry matter, there was a direct relationship between other properties and nutrient content in the soil solution, and Brachiaria dry matter production.

Quantifying the biogenic silica production of picoplankton in the oligotrophic ocean: A case study in the South China Sea

Silicon (Si) utilization is not limited to eukaryotes. Recent research has suggested that the pattern of a large contribution of picocyanobacteria to biogenic silica (bSi) stocks might be widespread in the oligotrophic open ocean. We are the first to measure the size-fractionated bSi standing stocks and production rates in the oligotrophic South China Sea (SCS), which has obvious characteristics of oligotrophic waters. The 150 m integrated bSi standing stocks in the pico-sized fractions averaged 23 % of the total; the contribution of picoplankton to the total bSi production rate was 44 %. Interestingly, our estimated contributions of Synechococcus alone to the <2 μm bSi standing stock and < 2 μm bSi production rates averaged 14 % and 66 %, respectively, indicating that the significant and persistent contribution of bSi was strongly associated with marine picocyanobacteria. Furthermore, the dynamic changes in nutrient concentrations, especially in DIN and DIP, also potentially affected the variability in picoplankton bSi stocks and production rates, while the effects of temperature and salinity were not obvious. In this study, we have provided new information on measurable bSi in the picoplankton size fraction and its production rate in the SCS. We have demonstrated that picoplankton contributes a measurable, and at times significant, proportion to both the total bSi standing stock and its production rate in the SCS. A high silicon content within picocyanobacteria has important implications for understanding both their ecology and their contribution to biogeochemistry.

Transport processes of dissolved and particulate nitrogen and phosphorus over urban road surface during rainfall runoff

Nutrient pollutants serve as indicative pollutants in urban stormwater runoff, and usually coexist and transport in particulate and dissolved phase in runoff, which is complex and crucial for effective pollution control. In this study, nitrogen and phosphorus runoff samples were collected during various natural rainfall events to explore its transport process over urban road surface during rainfall runoff. The results showed that nitrogen mainly exists in the dissolved phase (mean proportion: 62.04 %), while phosphorus mainly exists in the particulate phase (mean proportion: 65.58 %). More nitrogen and phosphorus are present and transported in dissolved phase in initial rainfall runoff over urban roads. Nutrient concentration changes during rainfall events were influenced by factors such as rainfall intensity and surface runoff, resulting in multiple peaks. Transport rate peak and concentration peak did not coincide. The proportion of dissolved total nitrogen in the runoff process ranged mainly between 40 % and 80 %, and the proportion of dissolved ammonia was distributed between 60 % and 100 %. The proportion of dissolved phosphorus was more evenly distributed across each proportion interval. Influenced by the differences in phase proportions, first flush processes of nitrogen and phosphorus are not the same. Urban stormwater management measures should prioritize both the initial concentration peaks and the peaks in nutrient transport rates during rainfall. This approach is essential for enhancing the efficiency of stormwater pollutant collection and treatment.

Once in Three-Year Deep-Banding and Annual Shallow-Banding of P, K and Cu Fertilizer Effects on Crops and Soil Nutrients

Deep-banding of the immobile nutrients (P, K, and Cu) is considered one technique that may improve crop production under temperate dryland systems, where moister soil conditions prevail at seeding followed by relatively drier soil during the growing period. The objectives were to compare growth and yield of canola (Brassica napus L.), field pea&amp;rsquo;s (Pisum sativum L.) and wheat (Triticum aestivum L.); and nutrient concentrations in crops and soil from once in three-year deep-banding (12.5-15 cm) and annual shallow-banding (3.75 to 5 cm diagonally deeper than seeding depth) of P, K and Cu under direct seeding systems. Small plot trials were conducted at the three sites; representing Brown (Dark Brown Chernozem), Black (Black Chernozem), and Grey (Dark Grey Luvisol) soil zones in Alberta, Canada; which represent crop growing conditions for most areas of western Canada. The nine treatments were annual shallow-banding and once in three year deep-banding of P, K, Cu and PKCU nutrients plus a control (no P, K, or Cu fertilizer). Applied thrice the recommended rate for deep-banding (in 2018) treatments and the recommended rate for the annual shallow-banding treatments in 2018, 2019 and 2020. All three phases of pea&amp;rsquo;s-wheat-canola rotation were grown at each site to generate nine years of data for each crop. The density, height, NDVI (normalized difference vegetation index) and biomass of plants, yield for crops and nutrient concentrations in seed and biomass of crops and soil showed significantly positive responses to P, K, and PKCu additions in some cases; generally not linked to the deep or shallow placement of tested nutrients. Changes in nutrient concentrations in seed and biomass of crops in response to nutrient additions were not consistent. Treatments with P showed response more often than with the K and Cu. The soil P and Cu concentrations increased in response to their additions in some cases, but no change was observed from the K addition. Once in three-year deep-banding or annual shallow-banding methods were equally effective. The findings provide another option (once in three year deep-banding) for applying the P, K and Cu fertilizers.

The Impact of Three White-Rot Fungi on Nutrient Availability, Greenhouse Gas Emissions, and Volatile Fatty Acid Production in Myceliated Sorghum.

Our study employed Pleurotus ostreatus, P. djamor, and Trametes versicolor (white rot fungi = WRF) in the process of solid-state fermentation (SSF) to convert sorghum grains into myceliated sorghum (MS). The MS was then used for in vitro studies to assess changes in nutrient content compared to untreated sorghum (control). The results demonstrated a significant (p < 0.001) increase in dry matter (DM), crude protein (CP), ash, neutral detergent fiber (NDF), and acid detergent fiber (ADF) contents of MS. Specifically, CP and ash values saw a remarkable increase from 68 to 330% and 40 to 190% in MS, respectively. Additionally, NDF and ADF degradability values increased significantly (p < 0.001) by 81.5% and 56.2% in P. djamor-treated MS at 24 h post-incubation. The treatment × time interaction was also significant (p < 0.001) for greenhouse gas (GHG) emissions. T. versicolor MS exhibited the highest total volatile fatty acid (TVFA) and propionate production. The use of WRF in the SSF process led to a significant improvement in the nutritional value of sorghum. Despite the varying effects of different WRF on the nutritional parameters in MS, they show potential for enhancing the feed value of sorghum in animal feed.

From the rhizosphere to plant fitness: Implications of microplastics soil pollution

Microplastics (MPs) are a widespread contaminant in the terrestrial environment, with potential impacts on the soil-plant system not yet well understood. This study explores the effects of oxidised low-density polyethylene-MPs (LDPE-MPs) on the rhizosphere ecology and plant fitness of Fragaria x ananassa (Duchesne ex Weston) Duchesne ex Rozier. The rhizospheric microbial community was investigated under the influence of 0,5 % LDPE-MPs by internal transcribed spacer (ITS) and 16 S rRNA metagenomic analysis; photosynthetic parameters, antioxidant enzyme activities, and nutrient accumulation were assessed to evaluate plant physiological and biochemical status. Genes related to jasmonic acid (JA), ethylene biosynthesis, and nitrate signalling pathways were analysed to define the plant molecular response. Our results showed a shift in the rhizosphere microbial community. We identified MPs molecular biomarkers in the contaminated rhizosphere (Fusarium, Thanatephorus and Pseudallescheria) with potential pathogenic functions and two novel molecular biomarkers (Ohtaekwangia and Ascobolus). MPs pollution negatively impacts plant fitness, which showed decreased chlorophyll a and b (40 and 48 %, respectively), a change in nutrient content (fluctuations between 14,42 and 26,7 %) at the leaf level and increased activity of antioxidant enzymes. Gene expression related to JA, ethylene biosynthesis, and nitrogen signalling pathways is enhanced in plants grown in contaminated soil, as well as the root endophytic and epiphytic microorganism interactions. Our results demonstrate that MPs pollution influences the rhizosphere microbial community and functions, and consequently, negatively impacts plant health.

Nutrient Accumulation in Silver Birch (Betula pendula Roth) Biomass in a Lignite Mining Area

The influence of lignite mining on vegetation constitutes a key issue due to the role of plants in restoring and maintaining the ecological balance of ecosystems. In this context, the identification of its impact on the functioning of silver birch (Betula pendula Roth) as a species often colonizing disturbed habitats takes on particular importance. Therefore, we aimed to determine the changes in nutrient content in silver birch overgrowing a spoil heap and in the vicinity of a fly ash settling pond and power plant. For this purpose, plant tissues (fine and coarse roots, stemwood, bark, coarse and fine branches, leaves) and soil samples (0–10, 10–20, 20–40, 20–40 cm deep) were examined. The basic soil characteristics were determined, along with the N, P, K, Ca, Mg, S, Fe, Mn, Cu, and Zn contents of the soil and plant samples. The soils varied in terms of soil pH and were poor in total organic carbon and other elements. The plant nutrient content varied strongly across the analyzed tissues, with the leaves usually containing the most and the stemwood the least nutrients. Statistical analysis indicated significant differences between the control vs spoil heap (particularly in Mn, S, and Mg) and the stand close to the settling pond (particularly in Ca, Mn, P, K, and S). We found that the chemical properties of the spoil heap and fly ash originating from the lignite mining operations are likely factors influencing nutrient accumulation in silver birch trees.

Effects of catchment land use on temperate mangrove forests

Human land use changes are threatening the integrity and health of coastal ecosystems worldwide. Intensified land use for anthropogenic purposes increases sedimentation rates, pollutants, and nutrient concentrations into adjacent coastal areas, often with detrimental effects on marine life and ecosystem functioning. However, how these factors interact to influence ecosystem health in mangrove forests is poorly understood. This study investigates the effects of catchment human land use on mangrove forest architecture and sedimentary attributes at a landscape-scale. Thirty sites were selected along a gradient of human land use within a narrow latitudinal range, to minimise the effects of varying climatic conditions. Land use was quantified using spatial analysis tools with existing land use databases (LCDB5). Twenty-six forest architectural and sedimentary variables were collected from each site. The results revealed a significant effect of human land use on ten out of 26 environmental variables.Eutrophication, characterised by changes in redox potential, pH, and sediment nutrient concentrations, was strongly associated with increasing human land use. The δ15N values of sediments and leaves also indicated increased anthropogenic nitrogen input. Furthermore, the study identified a positive correlation between human land use and tree density, indicating that increased nutrient delivery from catchments contributes to enhanced mangrove growth. Propagule and seedling densities were also positively correlated with human land use, suggesting potential recruitment success mechanisms. This research underpins the complex interactions between human land use and mangrove ecosystems, revealing changes in carbon dynamics, potential alterations in ecosystem services, and a need for holistic management approaches that consider the interconnectedness of species and their environment. These findings provide essential insights for regional ecosystem models, coastal management, and restoration strategies to address the impacts of human pressures on temperate mangrove forests, even in estuaries that may be relatively healthy.

Warming induced shade tolerance to become a key trait in invasion success of free-floating plant Pistia stratiotes over the native Hydrocharis morsus-ranae

Changes in nutrient concentration, temperature and light intensity due to climate change can alter the species composition of aquatic ecosystems, since global climate change can intensify the process of eutrophication. Eutrophication can enhance the biological invasion and the distribution of alien aquatic plants. Here we investigated the competition ability of alien Pistia stratiotes and native Hydrocharis morsus-ranae and the effect of different light intensities, temperatures and nutrient concentrations on the functional traits of the two species. In short term (8 days) monoculture experiment, we applied low (0.5 mg L-1 N; 0.05 mg L-1 P) and high nutrient concentrations (2 mg L-1 N; 0.2 mg L-1 P), four different light intensities (25–295 μmol m−2 s−1) as well as cold and warm (21.5; 27.5 ± 0.5°C) water treatments in full factorial design. In mixed cultures we cultivated the plants for 28 days with various biomass ratio, in shaded and well illuminated conditions, at a high nutrient concentration (4 mg L-1 N 1 mg L-1 P). In monocultures, the relative growth rate of P. stratiotes in warm water was significantly higher than that of H. morsus-ranae, however, this difference was not significant in colder water. In the co-culture experiment, P. stratiotes had significantly higher growth rate compared to H. morsus-ranae regardless of initial plant biomass ratio. Under shaded (65 ± 5 μmol m−2 s−1) conditions, P. stratiotes outcompeted H. morsus-ranae, resulting in its decay. Experimental results imply that with elevated temperature, the spread of alien P. stratiotes can be expected. Furthermore, under shaded conditions, P. stratiotes has a higher chance of occupying the water surface over the native plant H. morsus-ranae.

Energy, nutrient and overall healthiness of processed packaged foods in Fiji, a comparison between 2018 and 2020

In Fiji, packaged foods are becoming increasingly available. However, it is unknown if nutrition composition of these foods has changed. This study aims to assess changes in energy, nutrient content and healthiness of packaged foods by comparing data from five major supermarkets in Fiji in 2018 and 2020. Foods were categorised into 14 groups; nutrient composition information was extracted and healthiness assessed using Health Star Rating (HSR). Descriptive statistics and a separate matched products analysis was conducted summarising differences in nutrient content and HSR. There was limited evidence of change in the nutrient content of included products however, there was a small reduction in mean saturated fat in the snack food category (-1.0 g/100 g, 95% CI -1.6 to -0.4 g/100 g). The proportion of products considered healthy based on HSR, increased in the convenience foods category (28.4%, 95% CI 8.3 to 48.5) and decreased in non-alcoholic beverages (-35.2%, 95% CI -43.6 to -26.9). The mean HSR score increased in the fruit and vegetables category (0.1 (95% CI 0.1, 0.2)) and decreased for non-alcoholic beverages (-1.1 (-1.3, -0.9)) and the sauces, dressings, spreads, and dips category (-0.3 (-0.3, -0.2)). Strengthened monitoring of the food supply is needed to improve the healthiness of foods available.

Comparative Study on the Determination of Chlorophyll-a in Lake Phytoplankton by a YSI Multi-Parameter Water Quality Meter and Laboratory Spectrophotometric Method

Algal blooms caused by eutrophication are a major global problem, and the monitoring and prediction of algal densities in lakes are important indicators of eutrophication management. However, the reliability of the commonly used chlorophyll-a (Chl-a) to characterize phytoplankton density in lake environments needs to be further investigated. In this paper, we sampled and analyzed 365 samples from nine plateau lakes in Yunnan Province during the dry and rainy seasons. The Chl-a data measured by the laboratory spectrophotometric method and the portable YSI multi-parameter water quality meter (YSI) directly used in the field were compared, and regression analysis and correlation analysis with phytoplankton density were performed. Most of the Chl-a values measured by the laboratory instrument were greater than those measured by the YSI, and the correlation between the two methods was weak (0.492, p &lt; 0.001). The correlation between Chl-a and phytoplankton density measured by the YSI reached 0.67 (p &lt; 0.001) in the dry season, while the laboratory methods used to measure Chl-a to characterize phytoplankton density may have led to an overestimation of phytoplankton density due to nonspecific sources of Chl-a. However, both methods are relatively inaccurate for characterizing phytoplankton density. For different trophic states of lakes, nutrient concentration changes affect the Chl-a concentration of phytoplankton. During different seasons, changes in the fluorescence intensity of phytoplankton in response to environmental conditions prevent the YSI results from reflecting the authentic phytoplankton density. Furthermore, high species diversity can lead to inconsistent changes in Chl-a and phytoplankton because the content of Chl-a in individual cells of different phytoplankton is different. The relationship between Chl-a and phytoplankton density was species specific. Therefore, when applying Chl-a to characterize phytoplankton density in lakes, it is necessary to consider environmental conditions, phytoplankton community structure and other practical conditions. In addition, laboratory analytical methods and instrumental techniques and instruments need to be improved.

Elevated CO2 exacerbates the risk of methylmercury exposure in consuming aquatic products: Evidence from a complex paddy wetland ecosystem

Elevated CO2 levels and methylmercury (MeHg) pollution are important environmental issues faced across the globe. However, the impact of elevated CO2 on MeHg production and its biological utilization remains to be fully understood, particularly in realistic complex systems with biotic interactions. Here, a complete paddy wetland microcosm, namely, the rice-fish-snail co-culture system, was constructed to investigate the impacts of elevated CO2 (600 ppm) on MeHg formation, bioaccumulation, and possible health risks, in multiple environmental and biological media. The results revealed that elevated CO2 significantly increased MeHg concentrations in the overlying water, periphyton, snails and fish, by 135.5%, 66.9%, 45.5%, and 52.1%, respectively. A high MeHg concentration in periphyton, the main diet of snails and fish, was the key factor influencing the enhanced MeHg in aquatic products. Furthermore, elevated CO2 alleviated the carbon limitation in the overlying water and proliferated green algae, with subsequent changes in physico-chemical properties and nutrient concentrations in the overlying water. More algal-derived organic matter promoted an enriched abundance of Archaea-hgcA and Deltaproteobacteria-hgcA genes. This consequently increased the MeHg in the overlying water and food chain. However, MeHg concentrations in rice and soil did not increase under elevated CO2, nor did hgcA gene abundance in soil. The results reveal that elevated CO2 exacerbated the risk of MeHg intake from aquatic products in paddy wetland, indicating an intensified MeHg threat under future elevated CO2 levels.

Facilitation drives tree seedling survival at alpine treelines

Abstract Alpine treelines are considered ecological monitors recording the impacts of climate change on trees and forests. To date, most treeline research has focused on how climate change drives treeline dynamics. However, little is known about how biotic interactions mediate treeline shifts, particularly in the case of tree recruitment, a bottleneck of treeline dynamics. We hypothesized that inter- and intraspecific facilitation determined the establishment and survival of tree seedlings at alpine treelines. To test this hypothesis, 630 Abies georgei var. smithii seedlings with different ages (4–6, 7–9 and 10–15 years old) were transplanted into three growth habitats (canopy-in, canopy-out and meadow) across the alpine treeline ecotone (4300–4500 m) in the Sygera Mountains, on the southeastern Qinghai-Tibetan Plateau. Microclimate, height growth, mortality rates and leaf functional traits of transplanted seedlings were measured over 3 years. We found that the variations in leaf functional traits were driven by microclimate. After the transplantation, the leaf concentrations of soluble sugars and starch and C:P ratio increased, whereas leaf size decreased. The resource use of seedlings gradually shifted to a more conservative strategy as indicated by changes in non-structural carbohydrates and nutrient concentrations. Radiation, temperature and moisture conditions, mediated by plant interactions, influenced seedling mortality and annual growth by affecting leaf morphological traits. Our findings illustrate how facilitation plays a crucial role in altering solar radiation and leaf trait functioning, determining seedling survival and growth at alpine treelines. We provide new insights into the underlying mechanisms for tree establishment and alpine treeline shifts in response to climate change.

Assessment of Green Manure Crops and their Impacts on Mineralizable Nitrogen and Changes of Nutrient Contents in the Soil

To evaluate the green manure crops those can promote soil properties and the ability of nitrogen (N) mineralization in paddy soil, a pot experiment was conducted at the Department of Agronomy, Yezin Agricultural University, Naypyidaw, Myanmar from April to August 2022. The experimental design was a randomized complete block design with three replications. Ten green manure crops were sown as treatments: soybean (Glycine max (L.) Merr), green gram (Vigna radiata L. Wildzek.), black gram (Vigna mungo L. Hepper.), cowpea (Vigna catjang), cowpea white (Vigna unguiculata (L.) Walp.), lab lab bean (Lablab purpureus (L.) Sweet.), mayflower bean (Phaseolus vulgaris L.), rice bean (Vigna umbellata), sunn hemp (Crotalaria juncea L.), and dhaincha (Sesbania bispinosa (Jacq.)). At the flowering stage, various green manures were incorporated into the soil, and their growth characters were measured along with the mineralizable N, total N, phosphorus (P2O5), and potassium (K2O) contents of the soil. The results indicated that rice bean, sunn hemp, and dhaincha had higher shoot and root length, shoot and root fresh weight, and dry weight compared to other varieties. In addition, they contain a higher percentage of total N content and total P2O5, and consequently, its C:N ratio was lower. After incorporating green manures into the soil, the mineralizable N increased gradually from 0 weeks to 10 weeks and then, the nutrient values decreased. Among green manures, sunn hemp, dhaincha, and rice bean were found to have higher mineralizable N (%) and applicable mineralized N than others. In conclusion, the incorporation of green manures into the soil improves the N, P2O5, and K2O contents of the soil, along with the mineralizable N content. Among green manure crops, dhaincha, rice bean, and sunn hemp were superior to other varieties due to higher biomass yield, mineralizable N (%), and chemical compositions, especially total N content.

Changes in Nutrient Content and Physicochemical Properties of Cavendish Bananas var. Pei Chiao during Ripening

Banana is a typical tropical fruit that is widely cultivated in tropical and subtropical regions, and consumed daily because of its superior nutritional profile. This study aimed to investigate the changes in bananas’ physicochemical properties and nutritional composition from ripening stages 1 to 9. The analysis included color (peel and flesh), texture, total starch content, resistant starch content, free sugar content, minerals (calcium, magnesium, potassium, sodium, iron, phosphorus), and vitamin content. At the same time, the browning enzyme activities of polyphenol oxidase (PPO), peroxidase, oxalic acid, and tannin were also measured. In this study, the banana peel gradually changed from dark green to light green to yellow during the ripening process, eventually appearing with many black spots, while the pulp color changed from white to light yellow and decreased in brightness. The pulp became softer with a prolonged ripening period, which was inconsistent with the time point of peel color change (ripening period 4–5). However, total starch content decreased from 74% to 31%, resistant starch originally at 32% gradually decreased to 5%, and free sugar content gradually increased with increasing ripening period. Vitamin C content and PPO activity decreased significantly during the ripening period, while other vitamins and minerals did not change significantly. In contrast, oxalic acid, tannin content, and peroxidase activity were negatively correlated with the ripening period. Therefore, this study reveals the changes in the nutrient content of bananas at different ripening stages, which may provide helpful information for researchers and producers to identify suitable raw materials for producing stable and high-nutrition-value banana-related foods during the peak raw material abundance seasons while reducing business risk.