Mimicking natural deterrent strategies in plants using adhesive spheres.

With a continuous increase in world population and food production, chemical pesticide use is growing accordingly, yet unsustainably. As chemical pesticides are harmful to the environment and developmental resistance in pests is increasing, a sustainable and effective pesticide alternative is needed. Inspired by nature, we mimic one defense strategy of plants, glandular trichomes, to shift away from using chemical pesticides by moving toward a physical immobilization strategy via adhesive particles. Through controlled oxidation of a biobased starting material, triglyceride oils, an adhesive material is created while monitoring the reactive intermediates. After being milled into particles, nanoindentation shows these particles to be adhesive even at low contact forces. A suspension of particles is then sprayed and found to be effective at immobilizing a target pest, thrips, Frankliniella occidentalis. Small arthropod pests, like thrips, can cause crop damage through virus transfer, which is prevented by their immobilization. We show that through a scalable fabrication process, biosourced materials can be used to create an effective, sustainable physical pesticide.

Leafminer attack accelerates the development of soil-dwelling conspecific pupae via plant-mediated changes in belowground volatiles.

Herbivore population dynamics are strongly influenced by the interactions established through their shared host. Such plant-mediated interactions can occur between different herbivore species and different life developmental stages of the same herbivore. However, whether these interactions occur between leaf-feeding herbivores and their soil-dwelling pupae is unknown. We studied whether tomato (Solanum lycopersicum) leaf herbivory by the American serpentine leafminer Liriomyza trifolii affects the performance of conspecific pupae exposed to the soil headspace of the plant. To gain mechanistic insights, we performed insect bioassays with the jasmonate-deficient tomato mutant def-1 and its wild-type, along with phytohormones, gene expression and root volatiles analyses. Belowground volatiles accelerated leafminer metamorphosis when wild-type plants were attacked aboveground by conspecifics. The opposite pattern was observed for def-1 plants, in which aboveground herbivory slowed metamorphosis. Leafminer attack induced jasmonate and abscisic acid accumulation and modulated volatile production in tomato roots in a def-1-dependent manner. Our results demonstrate that aboveground herbivory triggers changes in root defence signalling and expression, which can directly or indirectly via changes in soil or microbial volatiles, alter pupal development time. This finding expands the repertoire of plant-herbivore interactions to herbivory-induced modulation of metamorphosis, with potential consequences for plant and herbivore community dynamics.

Latex Metabolome of Euphorbia Species: Geographical and Inter-Species Variation and its Proposed Role in Plant Defense against Herbivores and Pathogens.

Based on the hypothesis that the variation of the metabolomes of latex is a response to selective pressure and should thus be affected differently from other organs, their variation could provide an insight into the defensive chemical selection of plants. Metabolic profiling was used to compare tissues of three Euphorbia species collected in diverse regions. The metabolic variation of latexes was much more limited than that of other organs. In all the species, the levels of polyisoprenes and terpenes were found to be much higher in latexes than in leaves and roots of the corresponding plants. Polyisoprenes were observed to physically delay the contact of pathogens with plant tissues and their growth. A secondary barrier composed of terpenes in latex and in particular, 24-methylenecycloartanol, exhibited antifungal activity. These results added to the well-known role of enzymes also present in latexes, show that these are part of a cooperative defense system comprising biochemical and physical elements.

Chemical Differentiation of Plant Latexes and Their Anti-herbivory Activity against Thrips Frankliniella occidentalis.

Despite the extensive studies on latex, some fundamental questions on their chemical specialization and the factors influencing this specialization have yet to be investigated. To address this issue, latexes and their bearing tissues from diverse species were profiled by 1HNMR and GC-MS. Additionally, the antiherbivory activity of these materials was tested against thrips (Frankliniella occidentalis Pergande, 1895). The multivariate data analysis showed a clear separation between latexes and leaves from the same species. Conversely, the chemical profiles of latexes from different species were highly similar, that is, they displayed much less metabolic species-specificity. These shared chemical profiles of latexes were reflected in their overall higher mortality index (80.4% ± 7.5) against thrips compared with their bearing tissues (55.5% ± 14.9). The metabolites correlated to the antiherbivory activity of latexes were triterpenoids and steroids. However, the activity could not be attributed to any single terpenoid. This discrepancy and the reduction of the latex activity after fractionation suggested a complementary effect of the compounds when in a mixture as represented by the latex. Additionally, aqueous fractions of several latexes were found to possess simple spectra, even with only 1 metabolite. These metabolites were determined to be organic acids that might be involved in the modulation of the rate of latex coagulation, potentially increasing the sealing and trapping effects of the latex.

Diversity and evolution of cytochrome P450s of Jacobaea vulgaris and Jacobaea aquatica.

BACKGROUND: Collectively, plants produce a huge variety of secondary metabolites (SMs) which are involved in the adaptation of plants to biotic and abiotic stresses. The most characteristic feature of SMs is their striking inter- and intraspecific chemical diversity. Cytochrome P450 monooxygenases (CYPs) often play an important role in the biosynthesis of SMs and thus in the evolution of chemical diversity. Here we studied the diversity and evolution of CYPs of two Jacobaea species which contain a characteristic group of SMs namely the pyrrolizidine alkaloids (PAs). RESULTS: We retrieved CYPs from RNA-seq data of J. vulgaris and J. aquatica, resulting in 221 and 157 full-length CYP genes, respectively. The analyses of conserved motifs confirmed that Jacobaea CYP proteins share conserved motifs including the heme-binding signature, the PERF motif, the K-helix and the I-helix. KEGG annotation revealed that the CYPs assigned as being SM metabolic pathway genes were all from the CYP71 clan but no CYPs were assigned as being involved in alkaloid pathways. Phylogenetic analyses of full-length CYPs were conducted for the six largest CYP families of Jacobaea (CYP71, CYP76, CYP706, CYP82, CYP93 and CYP72) and were compared with CYPs of two other members of the Asteraceae, Helianthus annuus and Lactuca sativa, and with Arabidopsis thaliana. The phylogenetic trees showed strong lineage specific diversification of CYPs, implying that the evolution of CYPs has been very fast even within the Asteraceae family. Only in the closely related species J. vulgaris and J. aquatica, CYPs were found often in pairs, confirming a close relationship in the evolutionary history. CONCLUSIONS: This study discovered 378 full-length CYPs in Jacobaea species, which can be used for future exploration of their functions, including possible involvement in PA biosynthesis and PA diversity.

Constitutive and Inducible Resistance to Thrips Do Not Correlate With Differences in Trichome Density or Enzymatic-Related Defenses in Chrysanthemum.

Western flower thrips (WFT), Frankliniella occidentalis, is a serious insect pest of Chrysanthemum [Chrysanthemum × morifolium Ramat. (Asteraceae)]. Here we have investigated whether genotypic variation in constitutive and inducible resistance to WFT correlates with phenotypic differences in leaf trichome density and the activity of the defense-related enzyme polyphenol oxidase (PPO) in chrysanthemum. Non-glandular and glandular leaf trichome densities significantly varied among ninety-five chrysanthemum cultivars. Additional analyses in a subset of these cultivars, differing in leaf trichome density, revealed significant variation in PPO activities and resistance to WFT as well. Constitutive levels of trichome densities and PPO activity, however, did not correlate with chrysanthemum resistance to WFT. Further tests showed that exogenous application of the phytohormone jasmonic acid (JA) increased non-glandular trichome densities, PPO activity and chrysanthemum resistance to WFT, and that these effects were cultivar dependent. In addition, no tradeoff between constitutive and inducible resistance to WFT was observed. JA-mediated induction of WFT resistance, however, did not correlate with changes in leaf trichome densities nor PPO activity levels. Taken together, our results suggest that chrysanthemum can display both high levels of constitutive and inducible resistance to WFT, and that leaf trichome density and PPO activity may not play a relevant role in chrysanthemum defenses against WFT.

Soil Inoculation Alters Leaf Metabolic Profiles in Genetically Identical Plants.

Abiotic and biotic properties of soil can influence growth and chemical composition of plants. Although it is well-known that soil microbial composition can vary greatly spatially, how this variation affects plant chemical composition is poorly understood. We grew genetically identical Jacobaea vulgaris in sterilized soil inoculated with live soil collected from four natural grasslands and in 100% sterilized soil. Within each grassland we sampled eight plots, totalling 32 different inocula. Two samples per plot were collected, leading to three levels of spatial variation: within plot, between and within grasslands. The leaf metabolome was analysed with 1H Nuclear magnetic resonance spectroscopy (NMR) to investigate if inoculation altered the metabolome of plants and how this varied between and within grasslands. Inoculation led to changes in metabolomics profiles of J. vulgaris in two out of four sites. Plants grown in sterilized and inoculated soils differed in concentrations of malic acid, tyrosine, trehalose and two pyrrolizidine alkaloids (PA). Metabolomes of plants grown in inoculated soils from different sites varied in glucose, malic acid, trehalose, tyrosine and in one PA. The metabolome of plants grown in soils with inocula from the same site was more similar than with inocula from distant sites. We show that soil influences leaf metabolomes. Performance of aboveground insects often depends on chemical composition of plants. Hence our results imply that soil microbial communities, via affecting aboveground plant metabolomes, can impact aboveground plant-insect food chains but that it is difficult to make general predictions due to spatial variation in soil microbiomes.

Foraging efficiency and size matching in a plant-pollinator community: the importance of sugar content and tongue length.

A long-standing question in ecology is how species interactions are structured within communities. Although evolutionary theory predicts close size matching between floral nectar tube depth and pollinator proboscis length of interacting species, such size matching has seldom been shown and explained in multispecies assemblages. Here, we investigated the degree of size matching among Asteraceae and their pollinators and its relationship with foraging efficiency. The majority of pollinators, especially Hymenoptera, choose plant species on which they had high foraging efficiencies. When proboscides were shorter than nectar tubes, foraging efficiency rapidly decreased because of increased handling time. When proboscides were longer than nectar tubes, a decreased nectar reward rather than an increased handling time made shallow flowers more inefficient to visit. Altogether, this led to close size matching. Overall, our results show the importance of nectar reward and handling time as drivers of plant-pollinator network structure.

Trichome Independent Resistance against Western Flower Thrips in Tomato.

Western flower thrips (WFT) are a major pest on many crops, including tomato. Thrips cause yield losses, not only through feeding damage, but also by the transmission of viruses of which the Tomato Spotted Wilt Virus is the most important one. In cultivated tomato, genetic diversity is extremely low, and all commercial lines are susceptible to WFT. Several wild relatives are WFT resistant and these resistances are based on glandular trichome-derived traits. Introgression of these traits in cultivated lines did not lead to WFT resistant commercial varieties so far. In this study, we investigated WFT resistance in cultivated tomato using a F2 population derived from a cross between a WFT susceptible and a WFT resistant cultivated tomato line. We discovered that this WFT resistance is independent of glandular trichome density or trichome-derived volatile profiles and is associated with three QTLs on chromosomes 4, 5 and 10. Foliar metabolic profiles of F3 families with low and high WFT feeding damage were clearly different. We identified α-tomatine and a phenolic compound as potential defensive compounds. Their causality and interaction need further investigation. Because this study is based on cultivated tomato lines, our findings can directly be used in nowadays breeding programs.

Ultraviolet radiation exposure time and intensity modulate tomato resistance to herbivory through activation of jasmonic acid signaling.

Ultraviolet (UV) radiation can modulate plant defenses against herbivorous arthropods. We investigated how different UV exposure times and irradiance intensities affected tomato (Solanum lycopersicum) resistance to thrips (Frankliniella occidentalis) by assessing UV effects on thrips-associated damage and host-selection, selected metabolite and phytohormone contents, expression of defense-related genes, and trichome density and chemistry, the latter having dual roles in defense and UV protection. Short UV daily exposure times increased thrips resistance in the cultivar 'Moneymaker' but this could not be explained by changes in the contents of selected leaf polyphenols or terpenes, nor by trichome-associated defenses. UV irradiance intensity also affected resistance to thrips. Further analyses using the tomato mutants def-1, impaired in jasmonic acid (JA) biosynthesis, od-2, defective in the production of functional type-VI trichomes, and their wild-type, 'Castlemart', showed that UV enhanced thrips resistance in Moneymaker and od-2, but not in def-1 and Castlemart. UV increased salicylic acid (SA) and JA-isoleucine concentrations, and increased expression of SA- and JA-associated genes in Moneymaker, while inducing expression of JA-defensive genes in od-2. Our results demonstrate that UV-mediated enhancement of tomato resistance to thrips is probably associated with the activation of JA-associated signaling, but not with plant secondary metabolism or trichome-related traits.

Identification and characterization of metabolite quantitative trait loci in tomato leaves and comparison with those reported for fruits and seeds.

INTRODUCTION: To date, most studies of natural variation and metabolite quantitative trait loci (mQTL) in tomato have focused on fruit metabolism, leaving aside the identification of genomic regions involved in the regulation of leaf metabolism. OBJECTIVE: This study was conducted to identify leaf mQTL in tomato and to assess the association of leaf metabolites and physiological traits with the metabolite levels from other tissues. METHODS: The analysis of components of leaf metabolism was performed by phenotypying 76 tomato ILs with chromosome segments of the wild species Solanum pennellii in the genetic background of a cultivated tomato (S. lycopersicum) variety M82. The plants were cultivated in two different environments in independent years and samples were harvested from mature leaves of non-flowering plants at the middle of the light period. The non-targeted metabolite profiling was obtained by gas chromatography time-of-flight mass spectrometry (GC-TOF-MS). With the data set obtained in this study and already published metabolomics data from seed and fruit, we performed QTL mapping, heritability and correlation analyses. RESULTS: Changes in metabolite contents were evident in the ILs that are potentially important with respect to stress responses and plant physiology. By analyzing the obtained data, we identified 42 positive and 76 negative mQTL involved in carbon and nitrogen metabolism. CONCLUSIONS: Overall, these findings allowed the identification of S. lycopersicum genome regions involved in the regulation of leaf primary carbon and nitrogen metabolism, as well as the association of leaf metabolites with metabolites from seeds and fruits.

Phytochemical Background Mediates Effects of Pyrrolizidine Alkaloids on Western Flower Thrips.

Plants produce an extremely diverse array of metabolites that mediate many aspects of plant-environment interactions. In the context of plant-herbivore interactions, it is as yet poorly understood how natural backgrounds shape the bioactivity of individual metabolites. We tested the effects of a methanol extract of Jacobaea plants and five fractions derived from this extract, on survival of western flower thrips (WFT). When added to an artificial diet, the five fractions all resulted in a higher WFT survival rate than the methanol extract. In addition, their expected combined effect on survival, assuming no interaction between them, was lower than that of the methanol extract. The bioactivity was restored when the fractions were combined again in their original proportion. These results strongly suggest synergistic interactions among the fractions on WFT survival rates. We then tested the effects of two pyrrolizidine alkaloids (PAs), free base retrorsine and retrorsine N-oxide, alone and in combination with the five shoot fractions on WFT survival. The magnitude of the effects of the two PAs depended on the fraction to which they were added. In general, free base retrorsine was more potent than retrorsine N-oxide, but this was contingent on the fraction to which these compounds were added. Our results support the commonly held, though seldom tested, notion that the efficacy of plant metabolites with respect to plant defence is dependent on their phytochemical background. It also shows that the assessment of bioactivity cannot be decoupled from the natural chemical background in which these metabolites occur.

Methyl Jasmonate Changes the Composition and Distribution Rather than the Concentration of Defence Compounds: a Study on Pyrrolizidine Alkaloids.

In this study we investigated the effect of methyl jasmonate (MeJA) application on pyrrolizidine alkaloid (PA) concentration and composition of two closely related Jacobaea species. In addition, we examined whether MeJA application affected herbivory of the polyphagous leaf feeding herbivore Spodoptera exigua. A range of concentrations of MeJA was added to the medium of Jacobaea vulgaris and J. aquatica tissue culture plants grown under axenic conditions. PA concentrations were measured in roots and shoots using LC-MS/MS. In neither species MeJA application did affect the total PA concentration at the whole plant level. In J. vulgaris the total PA concentration decreased in roots but increased in shoots. In J. aquatica a similar non-significant trend was observed. In both Jacobaea species MeJA application induced a strong shift from senecionine- to erucifoline-like PAs, while the jacobine- and otosenine-like PAs remained largely unaffected. The results show that MeJA application does not necessarily elicits de novo synthesis, but rather leads to PA conversion combined with reallocation of certain PAs from roots to shoots. S. exigua preferred feeding on control leaves of J. aquatica over MeJA treated leaves, while for J. vulgaris both the control and MeJA treated leaves were hardly eaten. This suggests that the MeJA-induced increase of erucifoline-like PAs can play a role in resistance of J. aquatica to S. exigua. In J. vulgaris resistance to S. exigua may already be high due to the presence of jacobine-like PAs or other resistance factors.

Plant Latex, from Ecological Interests to Bioactive Chemical Resources.

Historically, latex-bearing plants have been regarded as important medicinal resources in many countries due to their characteristic latex ingredients. They have also often been endowed with a social or cultural significance in religious or cult rituals or for hunting. Initial chemical studies focused on the protein or peptide content but recently the interest extended to smaller molecules. Latex has been found to contain a broad range of specialized metabolites such as terpenoids, cardenolides, alkaloids, and phenolics, which are partly responsible for their antibacterial, antifungal, anthelmintic, cytotoxic, and insect-repellent activities. The diversity in biology and chemistry of latexes is supposedly associated to their ecological roles in interactions with exogenous factors. Latexes contain unique compounds that are different to those found in their bearing plants. Exploring the feasibility of plant latex as a new type of bioactive chemical resource, this review paper covers the chemical characterization of plant latexes, extending this to various other plant exudates. Also, the factors influencing this chemical differentiation and the production, transportation, and chemistry of the latex exudates are described, based on ecological and biochemical mechanisms. We also proposed a latex coagulation model involving 4 general conserved steps. Therefore, the inherent defensive origin of latexes is recognized as their most valuable character and encourages one to pay attention to these materials as alternative sources to discover metabolites with insecticidal or antimicrobial activity.

Light Intensity-Mediated Induction of Trichome-Associated Allelochemicals Increases Resistance Against Thrips in Tomato.

In cultivated tomato (Solanum lycopersicum), increases in photosynthetically active radiation (PAR) induce type VI leaf glandular trichomes, which are important defensive structures against arthropod herbivores. Yet, how PAR affects the type VI trichome-associated leaf chemistry and its biological significance with respect to other photomorphogenic responses in this agronomically important plant species is unknown. We used the type VI trichome-deficient tomato mutant odorless-2 (od-2) and its wild type to investigate the influence of PAR on trichome-associated chemical defenses against thrips (Frankliniella occidentalis). High PAR increased thrips resistance in wild-type plants, but not in od-2. Furthermore, under high PAR, thrips preferred od-2 over the wild type. Both genotypes increased type VI trichome densities under high PAR. Wild-type plants, however, produced more trichome-associated allelochemicals, i.e. terpenes and phenolics, these being undetectable or barely altered in od-2. High PAR increased leaf number and thickness, and induced profound but similar metabolomic changes in wild-type and od-2 leaves. Enhanced PAR also increased levels of ABA in wild-type and od-2 plants, and of auxin in od-2, while the salicylic acid and jasmonate concentrations were unaltered. However, in both genotypes, high PAR induced the expression of jasmonic acid-responsive defense-related genes. Taken together, our results demonstrate that high PAR-mediated induction of trichome-associated chemical defenses plays a prominent role in tomato-thrips interactions.

Thrips advisor: exploiting thrips-induced defences to combat pests on crops.

Plants have developed diverse defence mechanisms to ward off herbivorous pests. However, agriculture still faces estimated crop yield losses ranging from 25% to 40% annually. These losses arise not only because of direct feeding damage, but also because many pests serve as vectors of plant viruses. Herbivorous thrips (Thysanoptera) are important pests of vegetable and ornamental crops worldwide, and encompass virtually all general problems of pests: they are highly polyphagous, hard to control because of their complex lifestyle, and they are vectors of destructive viruses. Currently, control management of thrips mainly relies on the use of chemical pesticides. However, thrips rapidly develop resistance to these pesticides. With the rising demand for more sustainable, safer, and healthier food production systems, we urgently need to pinpoint the gaps in knowledge of plant defences against thrips to enable the future development of novel control methods. In this review, we summarize the current, rather scarce, knowledge of thrips-induced plant responses and the role of phytohormonal signalling and chemical defences in these responses. We describe concrete opportunities for breeding resistance against pests such as thrips as a prototype approach for next-generation resistance breeding.

Induction of Jasmonic Acid-Associated Defenses by Thrips Alters Host Suitability for Conspecifics and Correlates with Increased Trichome Densities in Tomato.

Plant defenses inducible by herbivorous arthropods can determine performance of subsequent feeding herbivores. We investigated how infestation of tomato (Solanum lycopersicum) plants with the Western flower thrips (Frankliniella occidentalis) alters host plant suitability and foraging decisions of their conspecifics. We explored the role of delayed-induced jasmonic acid (JA)-mediated plant defense responses in thrips preference by using the tomato mutant def-1, impaired in JA biosynthesis. In particular, we investigated the effect of thrips infestation on trichome-associated tomato defenses. The results showed that when offered a choice, thrips preferred non-infested plants over infested wild-type plants, while no differences were observed in def-1. Exogenous application of methyl jasmonate restored the repellency effect in def-1. Gene expression analysis showed induction of the JA defense signaling pathway in wild-type plants, while activating the ethylene signaling pathway in both genotypes. Activation of JA defenses led to increases in type-VI leaf glandular trichome densities in the wild type, augmenting the production of trichome-associated volatiles, i.e. terpenes. Our study revealed that plant-mediated intraspecific interactions between thrips are determined by JA-mediated defenses in tomato. We report that insects can alter not only trichome densities but also the allelochemicals produced therein, and that this response might depend on the magnitude and/or type of the induction.

Towards eco-friendly crop protection: natural deep eutectic solvents and defensive secondary metabolites.

With mounting concerns over health and environmental effects of pesticides, the search for environmentally acceptable substitutes has amplified. Plant secondary metabolites appear in the horizon as an attractive solution for green crop protection. This paper reviews the need for changes in the techniques and compounds that, until recently, have been the mainstay for dealing with pest insects. Here we describe and discuss main strategies for selecting plant-derived metabolites as candidates for sustainable agriculture. The second part surveys ten important insecticidal compounds, with special emphasis on those involved in human health. Many of these insecticidal metabolites, however, are crystalline solids with limited solubility which might potentially hamper commercial formulation. As such, we introduce the concept of natural deep eutectic solvents for enhancing solubility and stability of such compounds. The concept, principles and examples of green pest control discussed here offer a new suite of environmental-friendly tools designed to promote and adopt sustainable agriculture.

Parallel evolution in an invasive plant: effect of herbivores on competitive ability and regrowth of Jacobaea vulgaris.

A shift in the composition of the herbivore guild in the invasive range is expected to select for plants with a higher competitive ability, a lower regrowth capacity and a lower investment in defence. We show here that parallel evolution took place in three geographically distinct invasive regions that differed significantly in climatic conditions. This makes it most likely that indeed the shifts in herbivore guilds were causal to the evolutionary changes. We studied competitive ability and regrowth of invasive and native Jacobaea vulgaris using an intraspecific competition set-up with and without herbivory. Without herbivores invasive genotypes have a higher competitive ability than native genotypes. The invasive genotypes were less preferred by the generalist Mamestra brassicae but more preferred by the specialist Tyria jacobaeae, consequently their competitive ability was significantly increased by the first and reduced by the latter. Invasive genotypes showed a lower regrowth ability in both herbivore treatments.

Revisiting the dilution procedure used to manipulate microbial biodiversity in terrestrial systems.

It is hard to assess experimentally the importance of microbial diversity in soil for the functioning of terrestrial ecosystems. An approach that is often used to make such assessment is the so-called dilution method. This method is based on the assumption that the biodiversity of the microbial community is reduced after dilution of a soil suspension and that the reduced diversity persists after incubation of more or less diluted inocula in soil. However, little is known about how the communities develop in soil after inoculation. In this study, serial dilutions of a soil suspension were made and reinoculated into the original soil previously sterilized by gamma irradiation. We determined the structure of the microbial communities in the suspensions and in the inoculated soils using 454-pyrosequencing of 16S rRNA genes. Upon dilution, several diversity indices showed that, indeed, the diversity of the bacterial communities in the suspensions decreased dramatically, with Proteobacteria as the dominant phylum of bacteria detected in all dilutions. The structure of the microbial community was changed considerably in soil, with Proteobacteria, Bacteroidetes, and Verrucomicrobia as the dominant groups in most diluted samples, indicating the importance of soil-related mechanisms operating in the assembly of the communities. We found unique operational taxonomic units (OTUs) even in the highest dilution in both the suspensions and the incubated soil samples. We conclude that the dilution approach reduces the diversity of microbial communities in soil samples but that it does not allow accurate predictions of the community assemblage during incubation of (diluted) suspensions in soil.