Effects of digestate-encapsulated biochar on plant growth, soil microbiome and nitrogen leaching.

The increasing amount of food waste and the excessive use of mineral fertilizers have caused detrimental impacts on soil, water, and air quality. Though digestate derived from food waste has been reported to partially replace fertilizer, its efficiency requires further improvement. In this study, the effects of digestate-encapsulated biochar were comprehensively investigated based on growth of an ornamental plant, soil characteristics, nutrient leaching and soil microbiome. Results showed that except for biochar, the tested fertilizers and soil additives, i.e., digestate, compost, commercial fertilizer, digestate-encapsulated biochar had positive effects on plants. Especially, the digestate-encapsulated biochar had the best effectiveness as evidenced by 9-25% increase in chlorophyll content index, fresh weight, leaf area and blossom frequency. For the effects of fertilizers or soil additives on soil characteristics and nutrient retention, the digestate-encapsulated biochar leached least N-nutrients (<8%), while the compost, digestate and mineral fertilizer leached up to 25% N-nutrients. All the treatments had minimal effects on the soil properties of pH and electrical conductivity. According to the microbial analysis, the digestate-encapsulated biochar has the comparable role with compost in improving the soil immune system against pathogen infection. The metagenomics coupling with qPCR analysis suggested that digestate-encapsulated biochar boosted the nitrification process and inhibited the denitrification process. This study provides an extensive understanding into the impacts of the digestate-encapsulated biochar on an ornamental plant and offers practical implications for the choice of sustainable fertilizers or soil additives and food-waste digestate management.

Comparison of vegetable production, resource-use efficiency and environmental performance of high-technology and conventional farming systems for urban agriculture in the tropical city of Singapore.

Urban farming can improve cities' food security and resilience, but the performance of different farming systems with respect to land and investment constraints has not been systematically investigated. Here, we compared conventional soil-based farming, vertical farming with natural lighting (Vnat), and indoor vertical farming. This study aimed to compare (1) the dynamic production of leafy vegetables over time given the same amount of investment and land constraints, (2) the associated water and energy use, and (3) the global warming potential (GWP) of the urban farming sector if each of the three farming systems was solely used in the tropical city-state of Singapore. A system dynamics (SD) model was constructed to map the potential quantity of leafy vegetables produced, together with the water and energy use of each farming system. The land and monetary investment constraints were set at an additional 0.3% of the total land area of Singapore and an annual investment of SGD 10-20 million (0.001-0.005% of Singapore's annual GDP). Vnat farming was predicted to have the highest production level (110,000 t) and self-sufficiency (76.9% of total demand) by 2050 based on the SD model. This would be >3 times the self-sufficiency level achieved by indoor and soil-based farming systems given the same investment and land constraints. Indoor farming was simulated to use <14% the land area of Vnat while soil-based farming exhausted the additional 0.3% of the land allocated. Indoor farming was also the most energy intensive system, requiring 100 times more than Vnat farming. Comparison of the GHG emission rates showed that indoor farming had the greatest GWP-at 2.51 kg CO2-eq per kg of lettuce produced. Our results suggest that Vnat farming may be the best form of urban farming system to provide large amounts of food in Singapore, considering the production level, the amount of resources used, and the environmental impacts.

Food-waste anaerobic digestate as a fertilizer: The agronomic properties of untreated digestate and biochar-filtered digestate residue.

Anaerobic digestion produces large quantities of digestate as a by-product, which can potentially be applied as an organic fertilizer, but untreated anaerobic digestate (AD) may contain phytotoxins and the large volume of AD makes transportation and storage difficult. This study explored two relatively inexpensive processing methods to improve the agronomic performance of AD as a fertilizer via vegetable cultivation experiments. We first investigated the effect of dilution on AD's performance using four leafy vegetables (Chinese spinach, water spinach, Chinese cabbage and lettuce). The optimal concentrations of the AD were 20-40% (v/v in 250 mL applications per single-plant pot) for all four vegetables based on shoot fresh weight and comparable to the control treatment using commercial fertilizer. AD application also introduced Synergistetes bacteria into the growing medium, but the overall bacterial diversity and composition were similar to those of the control treatment. Considering the nutrient separation in the liquid and solid fractions of AD and the need to reduce the volume, we then experimented with the recovery of nutrients from both the liquid and solid fractions by filtering AD using two types of wood-based biochar (100 g biochar: 1 L AD) before applying the AD-biochar residues as side dressing at 1% (w/w). Both types of biochar achieved yields comparable to the treatment using a commercial fertilizer for the three vegetables tested (kale, lettuce and rocket salad). Our results show that dilution and biochar filtration can improve the agronomic performance of AD, making it a sustainable substitute for commercial fertilizer.

Biochar utilisation in the anaerobic digestion of food waste for the creation of a circular economy via biogas upgrading and digestate treatment.

A wood waste-derived biochar was applied to food-waste anaerobic digestion to evaluate the feasibility of its utilisation to create a circular economy. This biochar was first purposed for the upgrading of the biogas from the said anaerobic digestion, before treating and recovering the nutrients in the solid fraction of the digestate, which was finally employed as a biofertilizer for the organic cultivation of three green leafy vegetables: kale, lettuce and rocket salad. Whilst the amount of CO2 the biochar could absorb from the biogas was low (11.17 mg g-1), it could potentially be increased by modifying through physical and chemical methods. Virgin as well as CO2-laden biochar were able to remove around 31% of chemical oxygen demand, 8% of the ammonia and almost 90% of the total suspended solids from the digestate wastewater, which was better than a dewatering process via centrifugation but worse than the industry standard of a polytetrafluoroethylene membrane bioreactor. Nutrients were recovered in the solid fraction of the digestate residue filtered by the biochar, and utilised as a biofertilizer that performed similarly to a commercial complete fertilizer in terms of aerial fresh weight growth for all three vegetables cultivated. Contingent on the optimal upgrading of biogas, the concept of a circular economy based on biochar and anaerobic digestion appears to be feasible.

Gasification biochar from horticultural waste: An exemplar of the circular economy in Singapore.

Organic waste, the predominant component of global solid waste, has never been higher, resulting in increased landfilling, incineration, and open dumping that releases greenhouse gases and toxins that contribute to global warming and environmental pollution. The need to create and adopt sustainable closed-loop systems for waste reduction and valorization is critical. Using organic waste as a feedstock, gasification and pyrolysis systems can produce biooil, syngas, and thermal energy, while reducing waste mass by as much as 85-95% through conversion into biochar, a valuable byproduct with myriad uses from soil conditioning to bioremediation and carbon sequestration. Here, we present a novel case study detailing the circular economy of gasification biochar in Singapore's Gardens by the Bay. Biochar produced from horticultural waste within the Gardens was tested as a partial peat moss substitute in growing lettuce, pak choi, and pansy, and found to be a viable substitute for peat moss. At low percentages of 20-30% gasification biochar, fresh weight yields for lettuce and pak choi were comparable to or exceeded those of plants grown in pure peat moss. The biochar was also analyzed as a potential additive to concrete, with a 2% biochar mortar compound found to be of suitable strength for non-structural functions, such as sidewalks, ditches, and other civil applications. These results demonstrate the global potential of circular economies based on local biochar creation and on-site use through the valorization of horticultural waste via gasification, generating clean, renewable heat or electricity, and producing a carbon-neutral to -negative byproduct in the form of biochar. They also indicate the potential of scaled-up pyrolysis or gasification systems for a circular economy in waste management.

Biochar industry to circular economy.

Biochar, produced as a by-product of pyrolysis/gasification of waste biomass, shows great potential to reduce the environment impact, address the climate change issue, and establish a circular economy model. Despite the promising outlook, the research on the benefits of biochar remains highly debated. This has been attributed to the heterogeneity of biochar itself, with its inherent physical, chemical and biological properties highly influenced by production variables such as feedstock types and treating conditions. Hence, to enable meaningful comparison of results, establishment of an agreed international standard to govern the production of biochar for specific uses is necessary. In this study, we analyzed four key uses of biochar: 1) in agriculture and horticulture, 2) as construction material, 3) as activated carbon, and 4) in anaerobic digestion. Then the guidelines for the properties of biochar, especially for the concentrations of toxic heavy metals, for its environmental friendly application were proposed in the context of Singapore. The international status of the biochar industry code of practice, feedback from Singapore local industry and government agencies, as well as future perspectives for the biochar industry were explained.

Biochar for urban agriculture: Impacts on soil chemical characteristics and on Brassica rapa growth, nutrient content and metabolism over multiple growth cycles.

With possible food crises looming in the near future, urban farming, including small-scale community and home gardens for home consumption, presents a promising option to improve food security in cities. These small-scale farms and gardens often use planter boxes and raised beds filled with lightweight soil or potting mixes. While previous studies on biochar focused on its application on large-scale contiguous farmlands, this study aimed to evaluate the suitability of biochar as a partial soil substitute to produce a durable and lightweight soil-biochar mix for small-scale urban farms. The effects of biochar on the chemical properties of the soil-biochar mix, crop yield and, particularly, crop nutrients and metabolic content were assessed. A germination test using pak choi seeds (Brassica rapa L. cultivar group Pak choi, Green-Petioled Form) showed that the biochar contained phytostimulants. Through a nursery pot experiment over four growth cycles, biochar treatments performed better than pure soil at retaining water-soluble NO3- and K+ ions, but were worse at retaining PO43- ions. Nonetheless, despite its positive effect on soil NO3- retention, biochar application did not improve crop yield significantly when the application rate varied from 0% to 60% (v/v). Untargeted metabolomic analyses showed that biochar application may increase the production of carbohydrates and certain flavonoids and glucosinolates. The results of this study showed that biochar can potentially be used to improve pak choi nutritional values and applied in large quantity to obtain a lightweight soil mix for urban farming.

Closing the food waste loop: Food waste anaerobic digestate as fertilizer for the cultivation of the leafy vegetable, xiao bai cai (Brassica rapa).

The increasing world population necessitates the production of larger amounts of food in a safe and environmentally sustainable manner, while concomitantly managing an increasing amount of food waste similarly. These needs can theoretically be met by the recycling of the nutrients in food waste via anaerobic digestion, which also produces renewable energy. This hypothesis is proven by the growing of a commonly consumed leafy vegetable, xiao bai cai (Brassica rapa), by the addition of food waste anaerobic digestate in place of commercial fertilizer. Different concentrations of the digestate were tested, as well as different heat treatments to simulate hygienization, and the results for most part (aerial fresh weight, dry weight, chlorophyll content) are not significantly different from growth utilizing commercial inorganic 15:15:15 NPK fertilizer. Microbial analysis of the growth media was also carried out to explicate digestate effects and to show that some common foodborne disease pathogens were not detected.

The crab spider-pitcher plant relationship is a nutritional mutualism that is dependent on prey-resource quality.

Nutritional mutualisms are one of the three major categories of mutualisms and involve the provision of limiting nutrients (resources) to one species by another. It was recently shown in laboratory experiments that two species of pitcher-dwelling crab spiders (Thomisidae), Thomisus nepenthiphilus and Misumenops nepenthicola, increased capture rates of flesh flies (Sarcophagidae) for their host, Nepenthes gracilis. The spiders ambushed pitcher-visiting flesh flies and dropped their carcasses into pitchers after consuming them. The consumption of shared prey-resources by crab spiders and pitcher plants presents the possibility of parasitism between them. However, ecologically generalizable mechanisms that predict the context-dependent outcomes of such mutualisms are not known. The effectiveness framework (mutualism effectiveness = quality × quantity) is useful for examining the total effect of mutualisms, but its quality component can be difficult to define. We identify the crab spider-pitcher plant interaction as a type of resource conversion mutualism and propose that the quality component in such interactions is the amount of the underlying resource contained in each unit of resource processed. We then used the crab spider-pitcher plant interaction to test the hypothesis that resource conversion mutualisms are more beneficial to the nutrient recipient when operating through high-quality resources (i.e., large prey, in this interaction). We sampled the prey and inquilines of 107 N. gracilis upper pitches in situ and analysed the differences between pitchers that were inhabited or uninhabited by crab spiders, and the differences between nutritional contents of prey that were consumed by crab spiders or not. Pitchers inhabited by T. nepenthiphilus contained higher numbers of several prey taxa, many of which were flying insects. Consumption by T. nepenthiphilus reduced the nutrient contents in all prey examined. Overall, T. nepenthiphilus-assisted prey capture is likely to result in a net nutrient gain for N. gracilis that is proportional to the size of prey consumed by T. nepenthiphilus. Our results suggest that resource conversion mutualisms are more likely to operate through high-quality resources, since the nutrient-processing species necessarily reduces the quality of the resource it processes while increasing its availability to the nutrient recipient species.

Asterid Ray Floret Traits Predict the Likelihood of Florivory by the Polyphagous Katydid, Phaneroptera brevis (Orthoptera: Phaneropterinae).

Insect-flower visitation is crucial for many angiosperms because insects can facilitate pollination. Floral traits can attract pollinators so studying how they correlate with insect-flower visitation can elucidate how insects and plants interact and coevolve. However, there are few studies on how floral traits correlate with florivory. Not all floral traits that predict attractiveness of flowers to pollinators are applicable for florivory because they may not necessarily reflect the palatability of the flower parts. Leaf functional traits have been studied extensively to predict herbivory, but we are not aware of studies that adopt such leaf traits in florivory. We addressed these limitations by investigating the research questions: 1) How do floral traits differ among different species? 2) How do the floral traits predict the likelihood of florivory? We measured 10 floral traits, including adopting common leaf traits associated with herbivory (e.g., specific leaf area and leaf dry matter content), among three Asteraceae species: Bidens pilosa L., Sphagneticola trilobata (L.) Pruski, and Tridax procumbens L. We then performed the cafeteria assay using a polyphagous floriphilic katydid, Phaneroptera brevis (Serville 1838). We found that ray floret dry matter content correlates negatively with the likelihood of florivory of the asterid ray floret, whereas the total biomass of the ray floret correlates positively with the likelihood of florivory of the entire capitulum. The specific ray floret area also correlates nonlinearly with the likelihood of florivory of the asterid ray florets. We believe that these florivory traits can be applied to the flowers of other species.

Shy herbivores forage more efficiently than bold ones regardless of information-processing overload.

The neural constraint hypothesis is central to understanding decision-making by foraging herbivorous insects which make decisions less efficiently when they face multiple choices for numerous resource types and/or at high densities instead of a fewer choices. Previous studies have also shown the relationship between personality type and decision-making style. How personality types correlate with foraging efficiency among herbivores is however, largely untested. To answer this question, we used a widespread, polyphagous, floriphilic katydid, Phaneroptera brevis (Orthoptera: Tettigoniidae) and two naturalised, Asteraceae, food plants, Bidens pilosa and Sphagneticola trilobata, as model systems. After we determined each katydid's exploration and boldness levels, we examined its foraging efficiency across different combinations of floral resource choice and density. We showed: (1) For the first time within the Tettigonioidea lineage that this katydid exhibits different personality types in exploration and boldness. (2) Contrary to our prediction, we did not find any support for the neural constraint hypothesis because more floral resource choice at a high density did not reduce foraging efficiency. (3) Surprisingly, bold katydids tend to be less efficient foragers than shy ones. Our findings have enhanced understanding of herbivore behavioural ecology and knowledge to better deal with potential pest herbivores.

Pollination of Ficus elastica: India rubber re-establishes sexual reproduction in Singapore.

Ficus elastica, otherwise known as India Rubber (although its geographical origins are unclear), was an important source of latex in the early 19th century and was widely cultivated in tropical Asia. Like all figs, F. elastica is dependent on tiny, highly specific wasps for pollination, and detailed studies based out of Singapore in the 1930s suggested that through the loss of its pollinator F. elastica was extinct in the wild. However, around 2005 wild seedlings of F. elastica began appearing in Singapore. We identified the pollinator as Platyscapa clavigera, which was originally described from F. elastica in Bogor in 1885. A visit to Bogor Botanical Gardens revealed that not only was F. elastica being pollinated by P. clavigera in the gardens, but there was clear evidence it had been reproducing naturally there over many decades. Although Singapore has a native fig flora of over 50 species, F. elastica went unpollinated for at least 70 years and probably from the time it was introduced during the 19th century. These observations illustrate the extraordinary specificity of this interaction and, through the fig's ability to wait for its pollinators, demonstrates one way in which such highly specific interactions can be evolutionarily stable.

Four New Xanthones from Cratoxylum cochinchinense and Their In Vitro Antiproliferative Effects.

The study of the chemical constituents of branches and twigs of Cratoxylum cochinchinense collected in Singapore led to the isolation and structural elucidation of four new xanthones, named cratoxanthone A (1), B (2), C (3), and D (4), together with six known xanthones (5-10) and one known dihydroanthracenone (11). Eight xanthones (including 1 and 2) and 11 were tested for their antiproliferative activity in three human carcinoma cell lines (lung adenocarcinoma A549, colorectal carcinoma Colo205, and epidermoid carcinoma KB) and a human acute lymphoblastic leukemia B cell line (NALM-6), and the mitochondrial membrane potential was determined in KB cells. New xanthones 1 and 2 attenuated NALM-6 cell proliferation with IC50 values of 17.78 and 8.27 µM, respectively. Furthermore, KB cells treated with these compounds had significantly decreased mitochondrial membrane potentials. Notably, the proliferation of A549 cells was specifically inhibited by 11, but not the xanthones.

Whitefly predation and extensive mesonotum color polymorphism in an Acletoxenus population from Singapore (Diptera, Drosophilidae).

Acletoxenus is a small genus of Drosophilidae with only four described species that are closely associated with whiteflies (adults and larvae). Here, the first video recordings of larvae feeding on whiteflies (Aleurotrachelus trachoides) are presented. Typical morphological adaptations for predation by schizophoran larvae are also described: the larval pseudocephalon lacks a facial mask and the cephaloskeleton is devoid of cibarial ridges that could be used for saprophagy via filtration. Despite being a predator, Acletoxenus is unlikely to be a good candidate for biological control of whiteflies because the life cycle is fairly long (24 days), lab cultures could not be established, and the puparia have high parasitization rates by a pteromalid wasp (Pachyneuron leucopiscida). Unfortunately, a confident identification of the Singapore Acletoxenus population to species was not possible because species identification and description in the genus overemphasize coloration characters of the mesonotum which are shown to be unsuitable because the Singapore population has flies with coloration patterns matching three of the four described species. Based on morphology and DNA sequences, the population from Singapore is tentatively assigned to Acletoxenus indicus or a closely related species.

Potential application of gasification to recycle food waste and rehabilitate acidic soil from secondary forests on degraded land in Southeast Asia.

Gasification is recognized as a green technology as it can harness energy from biomass in the form of syngas without causing severe environmental impacts, yet producing valuable solid residues that can be utilized in other applications. In this study, the feasibility of co-gasification of woody biomass and food waste in different proportions was investigated using a fixed-bed downdraft gasifier. Subsequently, the capability of biochar derived from gasification of woody biomass in the rehabilitation of soil from tropical secondary forests on degraded land (adinandra belukar) was also explored through a water spinach cultivation study using soil-biochar mixtures of different ratios. Gasification of a 60:40 wood waste-food waste mixture (w/w) produced syngas with the highest lower heating value (LHV) 5.29 MJ/m(3)-approximately 0.4-4.0% higher than gasification of 70:30 or 80:20 mixtures, or pure wood waste. Meanwhile, water spinach cultivated in a 2:1 soil-biochar mixture exhibited the best growth performance in terms of height (a 4-fold increment), weight (a 10-fold increment) and leaf surface area (a 5-fold increment) after 8 weeks of cultivation, owing to the high porosity, surface area, nutrient content and alkalinity of biochar. It is concluded that gasification may be an alternative technology to food waste disposal through co-gasification with woody biomass, and that gasification derived biochar is suitable for use as an amendment for the nutrient-poor, acidic soil of adinandra belukar.

Economic and environmental impacts of harmful non-indigenous species in southeast Asia.

Harmful non-indigenous species (NIS) impose great economic and environmental impacts globally, but little is known about their impacts in Southeast Asia. Lack of knowledge of the magnitude of the problem hinders the allocation of appropriate resources for NIS prevention and management. We used benefit-cost analysis embedded in a Monte-Carlo simulation model and analysed economic and environmental impacts of NIS in the region to estimate the total burden of NIS in Southeast Asia. The total annual loss caused by NIS to agriculture, human health and the environment in Southeast Asia is estimated to be US$33.5 billion (5(th) and 95(th) percentile US$25.8-39.8 billion). Losses and costs to the agricultural sector are estimated to be nearly 90% of the total (US$23.4-33.9 billion), while the annual costs associated with human health and the environment are US$1.85 billion (US$1.4-2.5 billion) and US$2.1 billion (US$0.9-3.3 billion), respectively, although these estimates are based on conservative assumptions. We demonstrate that the economic and environmental impacts of NIS in low and middle-income regions can be considerable and that further measures, such as the adoption of regional risk assessment protocols to inform decisions on prevention and control of NIS in Southeast Asia, could be beneficial.

Rotenoid derivatives from Derris trifoliata with nitric oxide production inhibitory activity.

Study of the chemical constituents of the stems of Derris trifoliata Lour. (Leguminosae) collected in Singapore led to the isolation and identification of three known and two new rotenoid derivatives. The new derivatives, named derrisfolin A (1) and B (2), inhibited nitric oxide production in murine macrophage-like RAW 264.7 cells stimulated with interferon-gamma and lipopolysaccharide.

Cancer chemopreventive activity of rotenoids from Derris trifoliata.

A study of the chemical constituents of the stems of Derris trifoliata Lour. (Leguminosae) led to the isolation and identification of one new rotenoid, 6aalpha,12aalpha-12a-hydroxyelliptone ( 3), together with five other known rotenoids. In a search for novel cancer chemopreventive agents (anti-tumor promoters), we carried out a primary screening of five of the rotenoids isolated from the plant for their inhibitory effects on Epstein-Barr virus early antigen (EBV-EA) activation induced by 12- O-tetradecanoylphorbol 13-acetate (TPA) in Raji cells. The inhibitory activity of 3 was found to be equivalent to that of beta-carotene without any cytotoxicity. Deguelin ( 4) and alpha-toxicarol ( 5) exhibited a marked inhibitory effect on mouse skin tumor promotion in an in vivo two-stage carcinogenesis test. This investigation indicated that rotenoids might be valuable anti-tumor promoters.