Organic Nutrients Research Articles

Enhancing Garlic (Allium sativum L.) Productivity by Maximizing the Efficacy of Applied Nutrients with Alligator Weed Compost

ABSTRACT Researchers have extensively studied the significant biomass production of weeds, which competes with the main crops. The utilization of weeds, particularly aquatic ones like alligator weed, as organic nutrient sources, as compost and an organic mineral source could be beneficial in cropping systems. The hypothesis of this study suggests that by using alligator weed compost as a natural source of nutrients, garlic production can become less dependent on synthetic fertilizers, improve yield quality, and facilitate optimization of inorganic nutrients. The experiment included various combinations of alligator weed compost and nitrogen (N), phosphorous (P), and potassium (K) fertilizers, including the recommended NPK, 250 kg ha−1 and 500 kg ha−1 compost, and these compost amounts were combined at 75%, 50%, and 25% of the recommended NPK dose. Nitrogen and potassium were applied in three splits, a full dose of phosphorus was applied at sowing while compost was applied before sowing. The combination of 500 kg ha−1 compost application and 50% recommended NPK showed the most promising results. Garlic bulb yield and quality significantly increased in all compost and NPK combinations, particularly with this specific mix. Bulb yield was increased by 41% over the recommended NPK usage during both study years. Additionally, the ascorbic acid and pyruvic acid contents in the bulbs increased by 99% and 6%, respectively, compared to the recommended NPK. Likewise, in plant phenology, the same compost and NPK combination increased the plant height at maturity and leaf length at maturity by 18% and 10%, respectively, over the recommended NPK. In summary, the use of alligator weed organic fertilizers presents a viable alternative to NPK fertilizers due to its ability to retain applied nutrients and supply essential nutrients. As we look ahead to changing climates, utilizing alligator weed compost could be a sustainable approach in cropping systems.

Assessing the influence of land use change on soil quality across different ecosystems in Kolli hills, Eastern Ghats

Soil quality indices (SQIs) assess an ecosystem’s susceptibility to land-use change (LUC), highlighting the impacts on soil parameters. This study developed an SQI for six ecosystems in the Kolli Hills (KH), Eastern Ghats (EG), India: evergreen forest (EF), deciduous forest (DF), thorn forest (TF), agricultural system (AS), horticulture system (HS), and plantation system (PS). Soil samples were collected at two depths, surface (15 cm) and subsurface (30 cm), from 240 sites (40 samples per depth per ecosystem) and analyzed. LUC altered the soil physical and chemical properties. AS and HS had higher sand content (54.63%), bulk density (1.47 Mg m−3), and particle density (2.48 Mg m−3), whereas EF and DF had higher clay content (63.91%), porosity (52.03%), and available soil moisture (18.33%), all of which decreased with depth. The organic carbon and nutrient levels were greater in EF, DF, TF, and PS, with EF having the highest values (soil organic carbon: 60.70 g kg−1; nitrogen: 322.21 kg ha−1; phosphorus: 80.54 kg ha−1; potassium: 617.06 kg ha−1, iron—83.16 mg kg−1, manganese—60.16 mg kg−1, zinc—5.16 mg kg−1 and copper—5.35 mg kg−1) at 15 cm and decreasing with depth. In conclusion, the SQI for surface soil was the maximum in EF (2.50), followed by DF, TF, PS, HS, and AS, with a similar pattern in subsurface samples, suggesting an urgent need for land management strategies to improve soil quality in these ecosystems of the Eastern Ghats.

Impact of Polystyrene Microplastics on Soil Properties, Microbial Diversity and Solanum lycopersicum L. Growth in Meadow Soils

The pervasive presence of microplastics (MPs) in agroecosystems poses a significant threat to soil health and plant growth. This study investigates the effects of varying concentrations and sizes of polystyrene microplastics (PS-MPs) on the Solanum lycopersicum L.’s height, dry weight, antioxidant enzyme activities, soil physicochemical properties, and rhizosphere microbial communities. The results showed that the PS0510 treatment significantly increased plant height (93.70 cm, +40.83%) and dry weight (2.98 g, +100%). Additionally, antioxidant enzyme activities improved across treatments for S. lycopersicum L. roots. Physicochemical analyses revealed enhanced soil organic matter and nutrient levels, including ammonium nitrogen, phosphorus, and effective potassium. Using 16S rRNA sequencing and molecular ecological network techniques, we found that PS-MPs altered the structure and function of the rhizosphere microbial community associated with S. lycopersicum L. The PS1005 treatment notably increased microbial diversity and displayed the most complex ecological network, while PS1010 led to reduced network complexity and more negative interactions. Linear discriminant analysis effect size (LEfSe) analysis identified biomarkers at various taxonomic levels, reflecting the impact of PS-MPs on microbial community structure. Mantel tests indicated positive correlations between microbial diversity and soil antioxidant enzyme activity, as well as relationships between soil physicochemical properties and enzyme activity. Predictions of gene function revealed that PS-MP treatments modified carbon and nitrogen cycling pathways, with PS1005 enhancing methanogenesis genes (mcrABG) and PS1010 negatively affecting denitrification genes (nirK, nirS). This study provides evidence of the complex effects of PS-MPs on soil health and agroecosystem functioning, highlighting their potential to alter soil properties and microbial communities, thereby affecting plant growth.

Enhancement of Fertilizer Efficiency Through Chinese Milk Vetch and Rice Straw Incorporation

The incorporation of rice straw (RS) and Chinese milk vetch (CMV) with reduced chemical fertilizers (CFs) is a viable solution to reduce the dependency on CF. However, limited research has been conducted to investigate the impact of CMV and RS with reduced CF on rice production. A field trial was conducted from 2018 to 2021 with six treatments: CK (no fertilizer), F100 (100% NPK fertilizer (CF)), MSF100 (100% CF+CMV and RS incorporation), MSF80 (80% CF+CMV+RS), MSF60 (60% CF+CMV+RS), and MSF40 (40% CF+CMV+RS). The results revealed that compared with the F100, the MSF80 treatment maintained a significantly higher mean grain yield over the four years, with an increase of 5.8~24.5%. MSF80 treatment also improved nitrogen (N), phosphorus (P), and potassium (K) use efficiencies, sustainable yield index, and partial factor productivity. Soil organic matter (SOM), total nitrogen (TN), ammonium N (NH4+-N), nitrate N (NO3−-N), available phosphorus (AP), and available potassium (AK) contents were significantly enhanced under MSF80 across different growth stages in both 2020 and 2021 seasons over F100. Pearson correlation analysis revealed a strong positive correlation among SOM, TN, NH4+-N, AP, AK, and rice yield. Additionally, Partial Least Squares Path Modeling (PLS-PM) demonstrated significant relationships between organic amendments, soil nutrients, nutrient uptake, and yield. The above findings suggest that combining RS returning with CMV incorporation is a long-term sustainable strategy for maintaining soil health, and it could reduce fertilizer addition by 20% without prejudicing rice grain yield under a rice-green manure rotation system.

Ecuadorian Cacao Mucilage as a Novel Culture Medium Ingredient: Unveiling Its Potential for Microbial Growth and Biotechnological Applications

Cacao mucilage is typically disposed of during processing, yet its abundant content of organic compounds, polysaccharides, and nutrients renders it valuable for various applications. This scientific study investigates the suitability of cacao mucilage as an alternative culture medium for Lactiplantibacillus plantarum, Saccharomyces cerevisiae, and Aspergillus niger, aiming to provide a viable alternative to traditional media. Through a mixed-design approach, the powdered mucilage, peptone, and yeast extract ingredients were optimized using the recovery rates of each micro-organism as the response variable. The optimal formulation of the medium, consisting of 49.6% mucilage, 30% yeast extract, and 20.9% peptone, resulted in remarkable microbial recovery rates. L. plantarum achieved an outstanding recovery rate of 98.18%, while S. cerevisiae and A. niger exhibited recovery rates of 90.57% and 89.90%, respectively. Notably, these recovery rates surpassed those obtained using conventional culture mediums. Thus, cacao mucilage emerges as an effective component for formulating a natural culture medium that facilitates the growth of yeasts, lactic acid bacteria, and fungi. The yeast extract peptone mucilage (YPM) medium demonstrated enhanced growth, particularly for yeasts and lactic acid bacteria, with recovery rates exceeding 90%. Conversely, A. niger displayed a relatively lower recovery rate. These findings emphasize the potential of cacao mucilage as a valuable resource for preparing natural culture media that promotes the growth of yeasts, lactic acid bacteria, and fungi, offering promising prospects for various applications in microbiology and biotechnology.

Organic Fertilization Leads to N Limitation Rather than P Limitation in Both Vegetable Soils

Organic amendments are widely used to enhance soil fertility and nutrient cycling in greenhouse cultivation, but their effectiveness can vary depending on their origin and composition. This study investigated the impact of four organic materials (rice husk, coconut coir, biochar, and sheep manure) on nutrient cycling and enzyme activities in two of greenhouse tomato soils. The distribution of soil nutrients and enzyme activities was analyzed under controlled conditions during a pot experiment. The addition of organic amendments, regardless of their source, significantly altered the microbial resource allocation, reducing the carbon limitation while increasing the nitrogen demand. The effect on soil nutrient pools was largely determined by the chemical composition of the amendments. In clayey soils, biochar and rice husk additions most effectively promoted enzyme activities related to carbon, nitrogen, and phosphorus acquisition. Under sandy soil conditions, sheep manure increased carbon and phosphorus acquisition enzymes, while biochar most effectively enhanced nitrogen acquisition enzymes. Biochar emerged as a particularly effective amendment, enhancing organic carbon sequestration across different soil types. The chemical composition of the amendments, specifically, the content of carboxyl C, aromatic C, and O-alkyl C, played a crucial role in influencing soil nutrient limitations. In clayey soils, the mean C:N:P ratios for CK, T1, T2, T3, and T4 treatments were 1:1.375:0.625, 1:1.244:0.662, 1:0.839:0.610, 1:1.161:0.689, and 1:1.038:0.549, respectively. In sandy soils, the ratios were 1:1.117:0.698, 1:1.18:0.75, 1:1.096:0.731, 1:1.217:0.689, and 1:1.06:0.669, respectively. These findings suggest that the addition of organic amendments can improve nutrient retention and enzyme activities, but their effects on soil nutrient pools are influenced by both the composition of the amendments and the soil texture. This research enhances our understanding of organic amendments and soil nutrient transformations, and aids in optimizing the application of organic materials for improved soil management in greenhouse cultivation.

Determining the Effect of Different Organic Nutrient Sources on the Growth and Yield of Radish (Raphanus sativus L.)

Indiscriminate use of chemical fertilizers is a common practice which is hazardous both for soil health and environment. Chemical fertilizers have been widely used due to their immediate availability of nutrients; however, their long-term effects on soil and crop sustainability necessitate alternatives such as organic fertilizers. It has been more than three decades that global agriculture has been depicted towards organic agriculture owing to sustainability and reduced environmental effects. A field experiment was conducted at Institute of Agriculture and Animal Science (IAAS), Lamjung Campus from December 2022 to February 2023, with the objective to study the effect of various sources of organic manure on the growth and yield of radish. The experiment was conducted in Randomized Complete Design using 7 treatments (Control, Farm Yard Manure(FYM), Poultry Manure(PM), Goat Manure, FYM + Poultry Manure, FYM + Goat Manure, Poultry Manure + Goat Manure) with 3 replications of each. Tokinashi variety of radish was used in the experiment. Radish is an important root vegetable known for its nutritional value and quick growth cycle, making it a key crop for studying the impacts of organic manure. Experiment was done in field with the plot size of (2 x 1) m² and spacings of 30 cm x 20 cm with the total land area of 90 m². The growth and yield of radish were significantly affected by the different treatments. The highest total root yield (204.33) and biological yield (263.67) was found in Poultry manure. The study suggested that the application of poultry manure was more beneficial and resulted in significantly better growth and yield performance of radish.

Effect of Different Nitrogen Levels on Growth, Yield, and Nitrogen Use Efficiency (NUE) of Hardinath Hybrid Dhan-1 in Madhesh Province, Nepal

Determining the optimum dose of nitrogen fertilizer application for hybrid rice is vital for boosting production and productivity of rice. Therefore, this study examines the effect of different nitrogen levels on the growth, yield, and nitrogen use efficiency (NUE) of Hardinath Hybrid Dhan-1 in Madhesh Province, Nepal. A field experiment conducted in 2020 at the National Rice Research Program, Hardinath, Dhanusha tested six nitrogen levels (0, 75, 100, 125, 150, and 175 kg ha-1) with four replications under Randomized Complete Block Design during rainy season (June-September). The results showed that nitrogen application significantly improved plant growth and yield, with the highest grain yield (4.99 t ha-1) achieved at 150 kg N ha-1. Increasing nitrogen beyond this level did not further boost yield, indicating that excessive nitrogen does not improve productivity. Nitrogen use and agronomic efficiency were also highest at 150 kg N ha-1, marking it as the ideal rate for optimal rice performance. Soil health, in terms of organic matter and nutrient availability, improved with higher nitrogen levels, while the highest nitrogen uptake occurred at 175 kg N ha-1. In conclusion, 150 kg N ha-1 is recommended as the optimal nitrogen level to enhance hybrid rice yield and NUE, promoting sustainable rice production in the region. These findings highlight the need for optimal nitrogen management to improve crop yield and soil properties while minimizing environmental impact.

Effect of Hydrolysate Derived from Subcritical Seawater Treatment of Buckwheat Waste on the Growth of Lettuce (Lactuca sativa L.)

This study explores the effects of a subcritical seawater treatment (SST) on buckwheat waste (BW), and the use of the hydrolysate as a liquid fertilizer to improve the growth of lettuce (Lactuca sativa L.). Three temperature treatments (110 °C, 170 °C, 230 °C) were used for the SST, and the ionic composition in the seawater achieved the depolymerization and degradation of BW. The X-ray diffraction of the residual solids showed that the structure of BW was destroyed. Compared with seawater, the hydrolysate contained higher amounts of elements beneficial to plant growth, such as N, P, K, and organic compounds such as phenolics and sugars, as a result of the degradation of BW caused by the SST. The hydrolysate was tested as a liquid fertilizer (treatments H110°C, H170°C, H230°C) to irrigate lettuce. The content of proteins, phenolics, and chlorophyll, as well as the weight of the lettuce in the H110°C and H170°C treatments, were significantly higher than those in the seawater and the H230°C irrigation treatments (p < 0.05). The hydrolysate from the SST of BW, being rich in various organic and inorganic nutrients, can act as a liquid fertilizer that promotes the growth of lettuce, whereas hydrolysate from higher SST temperatures might inhibit the growth of lettuce, because of the excessive total nitrogen and organic acid.

Impact of inoculum on domestic wastewater treatment in high-rate ponds in pilot-scale: Assessment of organic matter and nutrients removal, biomass growth, and content

Impact of inoculum on domestic wastewater treatment in high-rate ponds in pilot-scale: Assessment of organic matter and nutrients removal, biomass growth, and content

EFEITO DAS DOSES DE DEJETO LÍQUIDO DE SUÍNOS NOS ATRIBUTOS FÍSICOS, QUÍMICOS E ELETROQUÍMICOS EM UM LATOSSOLO DO CERRADO

EFFECT OF LIQUID SWINE WASTEWATER DOSES ON PHYSICAL, CHEMICAL AND ELECTROCHEMICAL ATTRIBUTES IN A CERRADO OXISOL. The addition of organic residues enhances soil and plant organic matter and nutrient content. To gauge the impact of varying liquid swine waste (LSW) levels on soil, we studied changes in a clayey Oxisol’s physical, chemical, and electrochemical traits from the Cerrado. LSW doses (0, 50, 150, 450, 600 m3 ha-1) were applied to the 0-0.20 m layer in a randomized design with three replicates. Post a 30-day incubation at 60% field capacity, the soil underwent mineralogical, physical (clay dispersed in water - CDW), chemical (sodium adsorption ratio - SAR, cation exchange capacity - CEC, base saturation - V%), and electrochemical (pH in H2O and KCl, ∆pH, point of zero charge - PZC, point of zero salt effect - PZSE, surface electric potential - ψo, and electrical conductivity - EC) analyses. The levels of exchangeable Ca, K, Mg, Na, and available P increased with increasing LSW doses. Increasing LSW doses in the soil led to an increase in EC, but soil salinization was not observed at the highest dose. With the application of LSW doses, there was a decrease in pH, ∆pH, PZSE, and an increase in CEC, PZC and ψo. Despite the increase in ψo, low clay dispersibility was observed.

Discerning Natural and Anthropogenic Factors Driving the Variation of Estuarine CH 4 and N 2 O

Estuaries are commonly recognized as a major source of greenhouse gases due to the massive anthropogenic input of organic matter and nutrients, which is associated with highly active microbial assemblages. However, the combined effects of natural and anthropogenic factors and their relative contributions to estuarine greenhouse gas emissions are not well understood, particularly at the confluence of fresh water and seawater. In this study, biweekly sampling was conducted from November 2021 to January 2024 at the main outlet of the Pearl River in south China, which is characterized by a subtropical climate, a eutrophic environment, and heavy anthropogenic activity. Measurements were obtained of the dissolved methane (CH 4 ), nitrous oxide (N 2 O), and associated seasonally varying physical and chemical parameters at a high temporal resolution. Analysis of the measurement data revealed that the dissolved CH 4 and N 2 O concentrations were decreased by increases in the river discharge, which enhanced the dilution effect, and reductions in anthropogenic activities, such as the enforcement of measures to prevent COVID-19. The different dynamic processes of the nitrogen and carbon cycles may have contributed to the differences in the variations of the CH 4 and N 2 O concentrations (e.g., N 2 O varied within a narrower range than CH 4 ). By presenting and analyzing the 2-year time series of estuarine CH 4 and N 2 O with a high temporal resolution under complex natural and anthropogenic forcing, this study underscores the importance of human influence on greenhouse gas inventories and emissions.

Effect of different liquid organic nutrient sources on nutrient uptake by different high yielding scented and fortified rice varieties under organic production system

Effect of different liquid organic nutrient sources on nutrient uptake by different high yielding scented and fortified rice varieties under organic production system

ANALYSE DES EFFETS DU COMPOST SUR LES PARAMETRES DE CROISSANCE ET LES RENDEMENTS DE BIOMASSE DE BRACHIARIARUZIZIENSIS ET PANICUM MAXIMUM EN REPUBLIQUE DE GUINEE

This study assessed the impact of different compost doses (0, 20 and 30 t/ha) on growth parameters and biomass yields of two forage species (Brachiariaruziziensis and Panicum maximum) in sandy-clay-silty soil in tropical climates. Climate data showed favorable conditions in 2022 compared to 2021, with an increase in rainfall, relative humidity and average temperatures. Soil physico-chemical analyzes showed a decrease in organic matter and nutrients in the control plots, confirming the importance of compost input to maintain soil fertility. The results indicate that the dose of 20 t/ha optimized growth parameters (stem diameter, plant height, number of stems) and biomass yields, but did not result in nutrient saturation or excessive leaching. This dose is therefore an appropriate solution to improve forage productivity in tropical soils while promoting sustainable resource management.

Effect of Liquid Fertilizer Based on Local Microorganisms on Soil Fertility and Maize Production

The use of liquid fertilizers based on local microorganisms offers a sustainable solution for enhancing soil fertility and maize production. This study provides a comprehensive literature review of 11 Scopus-indexed articles to examine the effects of these fertilizers on soil health and crop yield. The findings reveal significant improvements in soil organic matter, microbial diversity, and nutrient availability, alongside enhanced maize growth parameters such as germination, biomass accumulation, and grain yield. Despite the variability in results due to environmental factors and application methods, these fertilizers demonstrate the potential to reduce dependency on synthetic inputs and align with sustainable agricultural practices. Challenges related to scalability, economic feasibility, and long-term impacts necessitate further research to optimize their implementation in diverse agricultural settings.

Assessment of long-term Site-Specific Nutrient Management (SSNM) on soil organic carbon dynamics and sequestration in a rice-rice cropping system

This study examined the long-term effects of the Site-Specific Nutrient Management Integrated Plant Nutrient System (SSNM-IPNS) on carbon sequestration, stock, loss and mineralization in soil within a 26-year-old ricerice cropping system at wetland of Tamil Nadu Agricultural University, Coimbatore. The research focused on the impact of integrated organic and inorganic nutrient application on carbon fractions compared to conventional fertilization methods under wetland ecosystems. Results indicated that the SSNM-IPNS approach significantly enhances soil total organic carbon (TOC), with levels reaching 1.56% compared to just 0.78% in control treatments. Furthermore, labile carbon fractions such as permanganate-oxidizable carbon (POx-C), microbial biomass carbon (MBC), water-soluble carbon (WSC), and particulate organic carbon (POC) were found to be greater in the SSNM-IPNS management. Increased rates of carbon mineralization and basal respiration also reflected a more active and efficient microbial community in these soils. Soil microbial indices, including the microbial quotient (qMic) and the metabolic quotient (qCO2), further emphasized the benefits of the SSNM-IPNS approach in enhancing soil health. Overall, the findings demonstrate that SSNM -IPNS significantly improves carbon sequestration, nutrient cycling, and soil fertility, promoting sustainable agricultural practices vital for long-term productivity in intensive cropping systems. This research underscores the importance of adopting innovative nutrient management practices for sustainable agriculture.

Synergy of Golden Snail Local Microorganism (LMO) and Seed Age in Optimizing Rice Seed Germination

This research aims to synergize local microorganisms (LMO) of golden snails (Pomacea canaliculata) and seed age in optimizing rice seed germination (Oryza sativa L.). Golden snail LMO, which is rich in organic nutrients and beneficial microorganisms, has the potential to improve seed quality and viability. The study used a factorial randomized block design (RBD) with two factors: golden snail LMO concentration (Control, 20 ml/L water, 40 ml/L water) and seedling age (7 days, 11 days, and 15 days after sowing). The variables observed included seed germination, simultaneity grows and growth speed. The results showed that the golden snail LMO concentration of 20 ml/L and seed age of 11 days after sowing gave the highest results for the observed variables, namely seed germination and growth speed while the interaction between golden snail LMO concentration mas 40 ml/L and seed age of 15 days after sowing gave the highest results for the variable observing growth synchrony. The combination of the two factors showed a positive interaction that supported the germination process effectively. This study concludes that the use of golden snail LMO and selecting the right seed age can be an ecological and efficient approach to increasing rice seed productivity, supporting sustainable agriculture.

Efficacy of Biostimulants on Growth, Flowering and Yield of Dendrobium var. Sonia White

The experiment was conducted during March, 2022–February, 2023 at Greenhouse Complex, Department of Floriculture and Landscape Architecture, ASPEE College of Horticulture, Navsari Agricultural University, Navsari, Gujarat, India to assess the effects of various biostimulants on the performance of Dendrobium var. Sonia White under naturally ventilated polyhouse conditions. Nine treatments were carried out at monthly intervals over a year in a Completely Randomized Design (CRD) with three repetitions, using a foliar spray of different biostimulants viz. Chitosan viz. 75, 100, 125 ppm; Brassinosteroid viz. 0.25, 0.50, 0.75 ppm; Novel Organic Liquid Nutrients at 2%; Gliricidia Nutrient Extract at 2%. The result indicated that among all treatments, the application of 0.75 ppm Brassinosteroid (T6) at monthly intervals resulted in maximum plant height (43.94 cm), leaf area (45.82 cm2) and chlorophyll content (0.478 mg g-1) after 12 months. In terms of flowering parameters, it also resulted in the highest number of spikes plant-1 (4.87), longest spike length (49.42 cm), highest number of florets spike-1 (12.01), longest floret length (7.59 cm), longest spike longevity (52.44 days), longest vase life (31.96 days) along with Highest Net realization (`Rs. 7457160 per ha-1) and BCR (2.03) in Dendrobium var. Sonia White.

Impact of Crop Residue Management on Soil Health under Rice- Wheat Cropping System in Southern Bihar, India

The study investigates the effects of paddy straw bale management on soil health and the productivity of a rice-wheat cropping system in Southern Bihar. Conducted from 2021 to 2023, the experiment involved four treatments: control (FP), tillage + recommended dose of fertilizer (RDF), zero tillage (ZT) + mulching, and burning + ZT (RDF). Soil samples and crop yields were analyzed to evaluate physico-chemical properties, microbial activities, and economic viability. Results revealed that ZT + mulching significantly enhanced soil properties, including organic carbon, nutrient availability (NPK), and microbial activity, compared to other treatments. Grain and straw yields were highest under ZT + mulching for both rice (80.01 and 84.25 q ha-1) and wheat (53.4 and 57.35 q/ha), with improved plant height, panicle density, and grain quality. Economic analysis indicated the highest benefit-cost ratio under ZT + mulching (3.18 for rice and 2.92 for wheat). This sustainable practice demonstrated its potential to mitigate residue burning's negative impacts, enhance soil health, and boost productivity, offering a viable strategy for long-term agricultural sustainability in the region.

Predictable shifts from nutrient to energy limitation determine the responses of planktonic autotrophs, bacteria and mixoplankton to browning

Abstract Within aquatic ecosystems, heterotrophic, mixotrophic and autotrophic plankton are entangled in a complex network of competitive, predatory and mutualistic interactions. “Browning,” the increase of colored dissolved organic matter (CDOM) from terrestrial catchments, can affect this network of interactions by simultaneously decreasing light availability and increasing organic carbon and nutrients supplies. Here, we introduce a conceptual, process-based numerical model to investigate the effects of browning on a microbial food web consisting of heterotrophic bacterioplankton, bacterivorous phago-mixoplankton, autotrophic phytoplankton and the resources light, inorganic phosphorus and DOM. Additionally, we explore how the investment in autotrophic vs. phagotrophic resource acquisition influences mixoplankton performance. Several model predictions are in broad agreement with empirical observations under increasing CDOM supply, including increased bacterial biomass and inorganic phosphorous, decreased light penetration, the potential for a unimodal phytoplankton biomass response and a local minimum in mixoplankton biomass. Our results also suggest that mixoplankton with a high investment in phototrophy perform best in many conditions but that phosphorous acquisition via prey is crucial under high light-low nutrient conditions. Overall, our model analyses suggest that responses to altered CDOM supply are largely determined by systematic changes in the relative importance of nutrient vs. energy limitation of each plankton group.