Mulga log mounds: Fertile patches in the semi-arid woodlands of eastern Australia

In the semi-arid woodland of eastern Australia, soil mounds are often associated with fallen mulga (Acacia aneura) trees. Measurements of the physical and chemical properties of the soils in these mounds compared with surrounding soils, together with differences in herbage growth responses, indicate that these mounds are fertile patches, with possible importance as habitats for soil fauna and as refugia for a range of organisms during drought. The mound soil material may accumulate by fluvial, aeolian or rain-splash deposition about the fallen log, however, some of the mound material was derived from termite feeding gallery structures. The surface feeding gallery material may be comprised of soil particles from within the mound or from tunnels and storage galleries below the mound, and probably depends on the termite species.     

Effects of actinobacteria on plant disease suppression and growth promotion

Biological control and plant growth promotion by plant beneficial microbes has been viewed as an alternative to the use of chemical pesticides and fertilizers. Bacteria and fungi that are naturally associated with plants and have a beneficial effect on plant growth by the alleviation of biotic and abiotic stresses were isolated and developed into biocontrol (BCA) and plant growth-promoting agents (PGPA). Actinobacteria are a group of important plant-associated spore-forming bacteria, which have been studied for their biocontrol, plant growth promotion, and interaction with plants. This review summarizes the effects of actinobacteria as BCA, PGPA, and its beneficial associations with plants.     

Methylotrophic bacteria in sustainable agriculture

Excessive use of chemical fertilizers to increase production from available land has resulted in deterioration of soil quality. To prevent further soil deterioration, the use of methylotrophic bacteria that have the ability to colonize different habitats, including soil, sediment, water, and both epiphytes and endophytes as host plants, has been suggested for sustainable agriculture. Methylotrophic bacteria are known to play a significant role in the biogeochemical cycle in soil ecosystems, ultimately fortifying plants and sustaining agriculture. Methylotrophs also improve air quality by using volatile organic compounds such as dichloromethane, formaldehyde, methanol, and formic acid. Additionally, methylotrophs are involved in phosphorous, nitrogen, and carbon cycling and can help reduce global warming. In this review, different aspects of the interaction between methylotrophs and host plants are discussed, including the role of methylotrophs in phosphorus acquisition, nitrogen fixation, phytohormone production, iron chelation, and plant growth promotion, and co-inoculation of these bacteria as biofertilizers for viable agriculture practices.     

Differences between bacterial communities in the gut of a soil-feeding termite (Cubitermes niokoloensis) and its mounds

In tropical ecosystems, termite mound soils constitute an important soil compartment covering around 10% of African soils. Previous studies have shown (S. Fall, S. Nazaret, J. L. Chotte, and A. Brauman, Microb. Ecol. 28:191-199, 2004) that the bacterial genetic structure of the mounds of soil-feeding termites (Cubitermes niokoloensis) is different from that of their surrounding soil. The aim of this study was to characterize the specificity of bacterial communities within mounds with respect to the digestive and soil origins of the mound. We have compared the bacterial community structures of a termite mound, termite gut sections, and surrounding soil using PCR-denaturing gradient gel electrophoresis (DGGE) analysis and cloning and sequencing of PCR-amplified 16S rRNA gene fragments. DGGE analysis revealed a drastic difference between the genetic structures of the bacterial communities of the termite gut and the mound. Analysis of 266 clones, including 54 from excised bands, revealed a high level of diversity in each biota investigated. The soil-feeding termite mound was dominated by the Actinobacteria phylum, whereas the Firmicutes and Proteobacteria phyla dominate the gut sections of termites and the surrounding soil, respectively. Phylogenetic analyses revealed a distinct clustering of Actinobacteria phylotypes between the mound and the surrounding soil. The Actinobacteria clones of the termite mound were diverse, distributed among 10 distinct families, and like those in the termite gut environment lightly dominated by the Nocardioidaceae family. Our findings confirmed that the soil-feeding termite mound (C. niokoloensis) represents a specific bacterial habitat in the tropics.     

Deciphering earth mound origins in central Brazil

Mound fields are a common landscape throughout the world and much of the evidence for their origin has been of a circumstantial nature. It has been hypothesized that earth mounds emerge over grasslands by termite activity; alternatively, they might be formed after erosion. We tested whether a mound field in central Brazil was generated by termite activity or erosion. We used soil organic matter isotopic composition, soil chemical, physical and floristic composition to determine the origin of a mound field. If the mounds emerged by termite activity in an established grassland the soil organic matter below the mound should have the isotopic signature of C₄ dominated grassland, which contrasts with savanna C₃ + C₄ signature. Additionally, soil traits should resemble those of the grassland. All markers indicate that the mounds were formed by erosion. The soil isotopic composition, chemical traits and texture below the mound resembled those of the savanna and not those of the grassland. Moreover, most of the species present in the mound were typical of savanna. Concrete evidence is provided that mound fields in the studied area were produced by erosion of a savanna ecosystem and not termite activity. The use of the techniques applied here would improve the assessments of whether analogous landscapes are of a biogenic nature or not.     

Differences between Bacterial Communities in the Gut of a Soil-Feeding Termite (Cubitermes niokoloensis) and Its Mounds

In tropical ecosystems, termite mound soils constitute an important soil compartment covering around 10% of African soils. Previous studies have shown (S. Fall, S. Nazaret, J. L. Chotte, and A. Brauman, Microb. Ecol. 28:191-199, 2004) that the bacterial genetic structure of the mounds of soil-feeding termites (Cubitermes niokoloensis) is different from that of their surrounding soil. The aim of this study was to characterize the specificity of bacterial communities within mounds with respect to the digestive and soil origins of the mound. We have compared the bacterial community structures of a termite mound, termite gut sections, and surrounding soil using PCR-denaturing gradient gel electrophoresis (DGGE) analysis and cloning and sequencing of PCR-amplified 16S rRNA gene fragments. DGGE analysis revealed a drastic difference between the genetic structures of the bacterial communities of the termite gut and the mound. Analysis of 266 clones, including 54 from excised bands, revealed a high level of diversity in each biota investigated. The soil-feeding termite mound was dominated by the Actinobacteria phylum, whereas the Firmicutes and Proteobacteria phyla dominate the gut sections of termites and the surrounding soil, respectively. Phylogenetic analyses revealed a distinct clustering of Actinobacteria phylotypes between the mound and the surrounding soil. The Actinobacteria clones of the termite mound were diverse, distributed among 10 distinct families, and like those in the termite gut environment lightly dominated by the Nocardioidaceae family. Our findings confirmed that the soil-feeding termite mound (C. niokoloensis) represents a specific bacterial habitat in the tropics.     

Effects of Erosion from Mounds of Different Termite Genera on Distinct Functional Grassland Types in an African Savannah

A key aspect of savannah vegetation heterogeneity is mosaics formed by two functional grassland types, bunch grasslands, and grazing lawns. We investigated the role of termites, important ecosystem engineers, in creating high-nutrient patches in the form of grazing lawns. Some of the ways termites can contribute to grazing lawn development is through erosion of soil from aboveground mounds to the surrounding soil surface. This may alter the nutrient status of the surrounding soils. We hypothesize that the importance of this erosion varies with termite genera, depending on feeding strategy and mound type. To test this, we simulated erosion by applying mound soil from three termite genera (Macrotermes, Odontotermes, and Trinervitermes) in both a field experiment and a greenhouse experiment. In the greenhouse experiment, we found soils with the highest macro nutrient levels (formed by Trinervitermes) promoted the quality and biomass of both a lawn (Digitaria longiflora) and a bunch (Sporobolus pyramidalis) grass species. In the field we found that soils with the highest micro nutrient levels (formed by Macrotermes) showed the largest increase in cover of grazing lawn species. By linking the different nutrient availability of the mounds to the development of different grassland states, we conclude that the presence of termite mounds influences grassland mosaics, but that the type of mound plays a crucial role in determining the nature of the effects.     

Termite mounds contain soil-derived methanotroph communities kinetically adapted to elevated methane concentrations

Termite mounds have recently been confirmed to mitigate approximately half of termite methane (CH₄) emissions, but the aerobic CH₄ oxidising bacteria (methanotrophs) responsible for this consumption have not been resolved. Here, we describe the abundance, composition and CH₄ oxidation kinetics of the methanotroph communities in the mounds of three distinct termite species sampled from Northern Australia. Results from three independent methods employed show that methanotrophs are rare members of microbial communities in termite mounds, with a comparable abundance but distinct composition to those of adjoining soil samples. Across all mounds, the most abundant and prevalent methane monooxygenase sequences were affiliated with upland soil cluster α (USCα), with sequences homologous to Methylocystis and tropical upland soil cluster (TUSC) also detected. The reconstruction of a metagenome-assembled genome of a mound USCα representative highlighted the metabolic capabilities of this group of methanotrophs. The apparent Michaelis–Menten kinetics of CH₄ oxidation in mounds were estimated from in situ reaction rates. Methane affinities of the communities were in the low micromolar range, which is one to two orders of magnitude higher than those of upland soils, but significantly lower than those measured in soils with a large CH₄ source such as landfill cover soils. The rate constant of CH₄ oxidation, as well as the porosity of the mound material, were significantly positively correlated with the abundance of methanotroph communities of termite mounds. We conclude that termite-derived CH₄ emissions have selected for distinct methanotroph communities that are kinetically adapted to elevated CH₄ concentrations. However, factors other than substrate concentration appear to limit methanotroph abundance and hence these bacteria only partially mitigate termite-derived CH₄ emissions. Our results also highlight the predominant role of USCα in an environment with elevated CH₄ concentrations and suggest a higher functional diversity within this group than previously recognised.Subject terms: Soil microbiology, Biogeochemistry     

Termite Mounds as Nutrient–Rich Food Patches for Elephants

This study compared elephant use of woody vegetation on termite mounds with surrounding woodlands in western Zimbabwe. Twelve sites consisting of paired plots on termite mounds and in woodlands were selected. At each site, soil and vegetation samples (leaf and stem) were collected for chemical analysis. Both soil and plant samples were analyzed for calcium, magnesium, potassium, sodium, and phosphorus, and plant samples were also analyzed for crude protein concentration. Two indices of elephant feeding damage were computed: the median number of stems and branches removed per plant, and the mass of stems and branches removed by elephants per unit area. Termite mound soils had higher concentrations of all elements tested than soils from woodlands, and termite mounds differed from woodland plots in terms of plant species composition. Trees growing on termite mounds had higher concentrations of all nutrients except sodium and crude protein, and were subjected to more intense feeding by elephants than trees from the surrounding vegetation matrix. Termite mounds may play an important role in determining food availability and spatial feeding patterns by elephants and other herbivores.     

Role of termites in the restoration of soils and plant richness on bowé in West Africa

Bowé (hardened ferricrete soils formed by erosion, drought or deforestation) are often associated with termite mounds, but little is known about these mounds and their role in the restoration of soils and plant biodiversity on bowé. This study examined termite mounds on bowé and their effects on soil depth and plant richness. Sixty-four sampling plots were laid out randomly on bowé sites with mounds and on adjacent bowé sites without mounds. The height and circumference of each mound were measured. Species inventories were made and soil depth measured in each plot. Linear mixed effects and generalised mixed effects models with Poisson error distribution were used to assess the variation in soil depth and plant species richness in mound and nonmound microsites. Two types of mounds (small vs. large) associated with different termite species were observed on bowé, with the small mounds being most common. Plots with either large or small mounds had deeper soils and higher plant richness than the adjacent plots without mounds. Conservation of termite mounds is important for restoring soils and plant richness on bowé, and termite mounds should be taken into consideration in biodiversity and soil management strategies for bowé.     

Promotion of plant growth, biological control and induced systemic resistance in maize by Pseudomonas aurantiaca JD37

Some Pseudomonas aurantiaca strains have been found to facilitate plant growth. A P. aurantiaca JD37 strain isolated from a suburb of Shanghai, China, was found to effectively colonize the rhizosphere soil and internal roots of maize (Zea mays L.) and promote maize growth. Agar diffusion assays and biocontrol effect experiments showed that strain JD37 had significant antagonistic activity against Bipolaris maydis, as well as a high biocontrol effect on southern maize leaf blight caused by B. maydis. PCR detection, associated with reverse-phase high-performance liquid chromatography assays, showed that strain JD37 might produce a number of important antibacterial substances, such as phenazine-1-carboxylic acid, pyrrolnitrin and 2,4-diacetylphloroglucinol. The crude bacterial extracts and the cell-free supernatant of strain JD37 were found to induce resistance in maize against B. maydis and reduce plant disease. Our results indicate the potential of some bacteria for producing bacterial compounds that serve as inducers of disease resistance, which is an attractive alternative to the application of chemical fertilizers, pesticides and supplement in agricultural practices.     

Application of 13C NMR to investigate the transformations and biodegradation of organic materials by wood- and soil-feeding termites, and a coprophagous litter-dwelling dipteran larva

Solid-state 13C nuclear magnetic resonance spectroscopy has been used to characterize the C in samples of the food (wood), gut contents and faeces from the wood-feeding termite, Microcerotermes parvus; soil in the guts and mound material from the soil-feeding termite, Thoracotermes macrothorax; and the food and faeces from the litter-feeding, coprophagous larvae of the dipteran fly, Bibio marci. Spectra from the wood-feeding termite indicated preferential loss of polysaccharide and accumulation of lignin with some modification to the O-aromatic-C and methoxyl-C (O-methyl-C) components during passage through the gut. Spectra for the soil-feeding termite indicated little change in the distribution of 13C between resonances following passage through the gut, except for some evidence of preferential polysaccharide loss. Interpretation of the spectra from these organisms was restricted by the relatively low C content of the soils and mound material, and by the large contribution to the NMR spectra from the gut tissue rather than the gut contents. Spectra for the litter-feeding dipteran larvae indicated preferential feeding on the polysaccharide-rich component of the litter and then overall loss of polysaccharide-C and accumulation of both aromatic-C and methoxyl-C in the gut. These changes were greater for the second passage than for the first passage through the gut, suggesting that principally mechanical and physical changes occurred initially and that chemical digestion was prevalent during the second passage.     

Mound-building termites and soil microbial biomass: An interaction influencing termite abundance

Termites are more abundant in the warmer lower latitudinal regions of the earth. Within these broad geographic regions, however, the precise nature of the factors influencing termite abundance is poorly understood. In this paper I have examined the abundance of detritivorous, mound-building termites and certain aspects of the climate, soils and vegetation at 14 sites in tropical northeastern Australia. No relationship between termite mound density and the particle-size characteristics of surface soil horizons, plant available phosphorous or rainfall was found. Microbial biomass carbon level of the surface soil was found to have a strong negative relationship with termite mound numbers. The negative interaction between the soil microbial population and termites may be due to the limiting effect of the organic matter processing capacity of the soil microbial population on the success of termites in occupying the decomposer niche in any particular area. Microbial biomass may therefore be a major factor influencing termite abundance in tropical Australian landscapes and elsewhere.     

Antibiotic production by bacterial biocontrol agents

Interest in biological control of plant pathogens has been stimulated in recent years by trends in agriculture towards greater sustainability and public concern about the use of hazardous pesticides. There is now unequivocal evidence that antibiotics play a key role in the suppression of various soilborne plant pathogens by antagonistic microorganisms. The significance of antibiotics in biocontrol, and more generally in microbial interactions, often has been questioned because of the indirect nature of the supporting evidence and the perceived constraints to antibiotic production in rhizosphere environments. Reporter gene systems and bio-analytical techniques have clearly demonstrated that antibiotics are produced in the spermosphere and rhizosphere of a variety of host plants. Several abiotic factors such as oxygen, temperature, specific carbon and nitrogen sources, and microelements have been identified to influence antibiotic production by bacteria biocontrol agents. Among the biotic factors that may play a determinative role in antibiotic production are the plant host, the pathogen, the indigenous microflora, and the cell density of the producing strain. This review presents recent advances in our understanding of antibiotic production by bacterial biocontrol agents and their role in microbial interactions. This revised version was published online in August 2006 with corrections to the Cover Date.     

Multicellular behaviour and production of a wide variety of toxic substances support usage of Bacillus subtilis as a powerful biocontrol agent

Intensive cultivation of plants in the monoculture field system in order to feed the continuously growing human population creates a need for their protection from the variety of natural competitors such as: bacteria, fungi, insects as well as other plants. The increase in the use of chemical substances in the 20th century has brought many effective solutions for the agriculture. However, it was extremely difficult to obtain a substance, which would be directed solely against a specific plant pathogen and would not be harmful for the environment. In the late 1900's scientists began trying to use natural antagonisms between resident soil organism to protect plants. This phenomenon was named biocontrol. Biological control of plants by microorganisms is a very promising alternative to an extended use of pesticides, which are often expensive and accumulate in plants or soil, having adverse effects on humans. Nonpathogenic soil bacteria living in association with roots of higher plants enhance their adaptive potential and, moreover, they can be beneficial for their growth. Here, we present the current status of the use of Bacillus subtilis in biocontrol. This prevalent inhabitant of soil is widely recognized as a powerful biocontrol agent. Naturally present in the immediate vicinity of plant roots, B. subtilis is able to maintain stable contact with higher plants and promote their growth. In addition, due to its broad host range, its ability to form endospores and produce different biologically active compounds with a broad spectrum of activity, B. subtilis as well as other Bacilli are potentially useful as biocontrol agents.     

长期施用化肥及秸秆还田对砂姜黑土细菌群落的影响

【目的】在施用化肥的基础上进行秸秆还田是提高砂姜黑土肥力的有效措施,以往的研究只注重秸秆还田对土壤结构、肥力等物理化学性状方面的研究,缺少施肥对砂姜黑土微生物群落影响的研究。本研究以安徽蒙城典型的砂姜黑土为研究对象,以期揭示长期施用化肥和秸秆还田对砂姜黑土细菌群落的影响。【方法】采用454高通量测序对砂姜黑土不同农业施肥措施下的细菌群落进行分析研究,并通过生物信息学的分析方法揭示影响砂姜黑土细菌群落的主要因素。【结果】通过对454高通量测序数据的分析,发现砂姜黑土主要的细菌门类为放线菌、变形菌、酸杆菌、绿弯菌和拟杆菌。长期施用化肥显著提高了砂姜黑土肥力和作物产量,但导致了细菌群落结构的显著变化和多样性的显著降低。秸秆还田有利于土壤肥力的进一步提高,但是并没有缓解长期施用化肥对土壤细菌群落产生的不利影响。分析发现土壤pH的变化是导致土壤细菌群落变异的主要因素。【结论】在施用化肥的基础上进行秸秆还田有利于砂姜黑土肥力的提升,然而并没有缓解由施肥导致的土壤酸化对土壤细菌群落组成和多样性产生的不利影响。这暗示秸秆还田可能并未对砂姜黑土微生物生态产生根本性的有益影响,对于秸秆农田的利用方式还需要进一步研究,以达到农业生产效益和生态效益的并重。     

AM真菌在有机农业发展中的机遇

在农田生态系统中,许多农作物均为丛枝菌根(AM)真菌的优良宿主植物,当AM真菌与这些宿主植物建立共生关系之后,AM真菌的存在有益于宿主植物的生长。然而,传统农业耕作模式中化学肥料和农药的施用、耕作制度的不断调整和非宿主植物的种植等都不利于AM真菌的建植。有机农业生态系统排除了化学肥料和农药的施用,减少了对AM真菌生长不利的因素,促进了土壤中AM真菌数量的增加和群落多样性的提高。同时,AM真菌可以通过多种方式改善土壤物理结构、提高农作物对干旱胁迫的耐受能力以及宿主植物对病虫害的抗性/耐性、抑制杂草生长、促进营养物质的吸收,进而提高植物的生长和改善产品的品质。基于此,围绕AM真菌在有机农业发展中的生态学功能展开论述,分析当前有机农业生态系统存在的问题,探讨利用AM真菌发展有机农业的可行性及其发展的机遇,以期促进AM真菌在有机农业发展中的应用。     

Influence of large termitaria on soil characteristics, soil water regime, and tree leaf shedding pattern in a West African savanna

Termitaria are major sites of functional heterogeneity in tropical ecosystems, through their strong influence on soil characteristics, in particular soil physico-chemical properties and water status. These factors have important consequences on nutrient availability for plants, plant spatial distribution, and vegetation dynamics. However, comprehensive information about the influence of termite-rehandled soil on soil water regime is lacking. In a humid shrubby savanna, we characterized the spatial variations in soil texture, soil structure and maximum soil water content available for plants (AWC max) induced by a large termite mound, at three deepths (0–0.10, 0.20–0.30 and 0.50–0.60 m). In addition, during a three month period at the end of the rainy season, soil water potential was surveyed by matrix sensors located on the termite mound and in the surrounding soil at the same depths and for the 80–90 cm layer. Concurrently, the leaf shedding patterns of two coexisting deciduous shrub species exhibiting contrasted soil water uptake patterns were compared for individuals located on termite mounds and in undisturbed control areas. For all the soil layers studied, clay and silt contents were higher for the mound soil. Total soil clods porosity was higher on the mound than in control areas, particularly in the 0.20-0.60 m layer, and mound soil exhibited a high shrinking/swelling capacity. AWC_max of the 0-0.60 m soil layer was substantially higher on the termite mound (112 mm) than in the surroundings (84 mm). Furthermore, during the beginning of the dry season, soil water potential measured in situ for the 0.20-0.90 m soil layer was higher on the mound than in the control soil. In contrast, soil water potential of the 0-0.10 m soil layer was similar on the mound and in the control soil. In the middle of the dry season, the leaf shedding pattern of Crossopteryx febrifuga shrubs (which have limited access to soil layers below 0.60 m) located on mounds was less pronounced than that of individuals located on control soil. In contrast, the leaf shedding pattern of the shrub Cussonia barteri (which has a good access to deep soil layers) was not influenced by the termite mound. We conclude that in this savanna ecosystem, termite mounds appear as peculiar sites which exhibit improved soil water availability for plants in upper soil layers, and significantly influence aspects of plant function. Implications of these results for understanding and modelling savanna function and dynamics, and particularly competitive interactions between plant species, are discussed.     

Allelopathy as a Tool in the Management of Biotic Resources in Agroecosystems

In modern agriculture, natural plant communities may be replaced by a single crop species. Weeds, some microorganisms, and viruses, as well as some herbivores are organisms that should be eliminated. Pesticides and fertilizers not only affect the pests and crops, but soil, non-pest species, water, food, and humans. In traditional agriculture weeds are components with an important ecological role in the maintenance of the system. Some weeds have been used as tools to control the growth of other weeds in traditional agroecosystems. Researchers on sustainable and organic agriculture get valuable information from traditional agriculture and currently are conducting research on plant breeding, soil fertility and tillage, crop protection, and cropping systems. Allelopathy and chemical ecology are directly involved in each of these fields and can play an important role in crop productivity, conservation of genetic diversity, and maintenance of ecosystems stability. Allelopathy has been shown to be related with problems of chemical interference between crops and weeds, crops and crops, toxicity of crops and weeds residues, and/or crops and weeds exudates. Problems of autotoxicity, orchard replanting, and forest regeneration are also referred as allelopathic. Allelopathy is strongly coupled with other stresses of the environment, including insects and disease, temperature extremes, nutrient and moisture variables, radiation, and herbicides. These stress conditions often enhance allelochemical production and increase the potential for allelopathic interference. Allelopathy offers potential for weed control through the production and release of allelochemicals from plants. Allelochemicals may impact the availability of nutrients through effects on the symbiotic microbes. Destruction and changes in the use of soils in the tropics have decreased biodiversity, bringing about the loss of valuable natural products. Many different types of useful products such as natural pesticides and drugs can arise from allelopathy studies. New methods must be generated for allelopathy as a part of the biotic resources management strategies.     

Phosphorus and phosphate solubilizing bacteria: Keys for sustainable agriculture

Abstract

Phosphorus (P) is one of the most important minerals required for plant growth occupying a strong position among soil macro nutrients. Soil P deficiency is often fulfilled by phosphate fertilizers. P deficiency in soils is due to less total P contents in the soil and fixation of added P from chemical fertilizers as well as other organic sources like manures. The response of plant under P stress or even when it is present in adequate amount is very mild. The basic constraint in the availability of P is its solubilization as it gets fixed both in acidic and alkaline soil. Soil fixed P can only be solubilized by phosphate solubilizing microorganisms (PSMs).These bacteria released different types of organic acids in the soil which make P soluble and available to plants. The potential of these PSMs to solubilize P varies and mainly depends upon mechanism adopted for solubilization, their molecular genetics as well as their ability to release P in soil. The PSMs, having all the characteristics of phytohormone production, nitrogen fixation, as well as, heavy metal decontamination and creating salt stress tolerance in plants, are quite rare for sustainable agriculture. Application of this environment friendly approach for increasing crop productivity as well as its impact on soil and plant health is discussed in this review which will not only open new avenues of research but also provide fruitful information about phosphate solubilizing microbes for sustainable agriculture development.