Soil microorganisms and plants produce enzymes thatmineralize organically bound nutrients When nutrientavailability is low, the biota may be able to increase production ofthese enzymes to enhance the supply of inorganicnitrogen (N) and phosphorus (P) Regulation of enzyme productionmay be a point where N and P cyclesinteract We measured acid phosphatase and chitinase(N-acetyl s-D-glucosaminide) activity in soilacross a chronosequence in Hawaii where N and Pavailability varies substantially among sites and longterm fertilizer plots had been maintained for over 4years Phosphatase activity was high at all sites Chitinaseactivity decreased significantly as age and Navailability increased across the chronosequencePhosphorus addition suppressed phosphatase activity atall sites, while N addition increased phosphataseactivity at the young, N-limited site In contrast,N addition repressed chitinase activity only at the Nlimited young site, and P additions had no effect onchitinase activity These results suggest that theregulatory relationship between nutrient supply andnutrient mineralization are asymmetric for N and P,and that the differences could help to explaindifferences observed in patterns of N and Pavailability

Regulation of soil phosphatase and chitinase activity by N and P availability

https://andrewsforest.oregonstate.edu/pubs/pdf/pub4056.pdf

Enzyme activities as a component of soil biodiversity: A review

Chitin is the (1→4)-β-linked homopolymer of N-acetyl-D-glucosamine (Fig. 1). The individual polymer chains can be thought of as helices, as each sugar unit is inverted with respect to its neighbors. This leads to their stabilization as rigid ribbons by 03—H … 05 and 06—H … 07 hydrogen bonds. The commonest form of chitin is α-chitin. Its unit cell is of two N,N‵-diacetylchitobiose units of two chains in an antiparallel arrangement. Thus, adjacent polymer chains run in opposite directions, held together by 06—H … 06 hydrogen bonds, and the chains are held in sheets by 07 … H—N hydrogen bonds (Minke and Blackwell, 1978). This gives a statistical mixture of CH2OH orientations, equivalent to half oxygens on each residue, each forming inter- and intramolecular hydrogen bonds. This results in two types of amide groups; all are involved in the interchain C=O … H—N bonds, while half of the groups also serve as acceptors for 06—H … O=C intramolecular bonds. This extensive intermolecular hydrogen bonding leads to a very stable structure, the individual polymer chains eventually giving rise to microfibrils if allowed to crystallize (Gooday, 1983). A less common form of chitin is β-chitin, in which the unit cell is of one N,N‵diacetylchitobiose unit, giving a polymer stabilized as a rigid ribbon, as for α-chitin, by 03—H … 05 intramolecular bonds (Gardner and Blackwell, 1975). Chains are then held together in sheets by C=O … H—N hydrogen bonding of the amide groups and by the CH2OH side chains, forming intersheet hydrogen bonds to the carbonyl oxygens on the next chains (06—H … 07). This gives a structure of parallel poly-N-acetylglucosamine chains with no intersheet hydrogen bonds.

The Ecology of Chitin Degradation

Microorganisms are able to utilize nitrogen (N) from a wide range of organic and mineral compounds. In this paper, we review the current knowledge about the regulation of the enzyme systems involved in the acquisition of N and propose a conceptual model on the factors affecting the relative importance of organic and mineral N uptake. Most of the N input into soil is in the form of polymers, which first have to be broken down into smaller units by extracellular enzymes. The small organic molecules released by the enzymes can then be taken up directly or degraded further and the N taken up as ammonium (NH4+). When NH4+ is available at high concentrations, the utilization of alternative N sources, such as nitrate (NO3−) and organic molecules, is generally repressed. In contrast, when the NH4+ availability is low, enzyme systems for the acquisition of alternative N sources are de-repressed and the presence of a substrate can induce their synthesis. These mechanisms are known as N regulation. It is often assumed that most organic N is mineralized to NH4+ before uptake in soil. This pathway is generally known as the mineralization-immobilization-turnover (MIT) route. An advantage of the MIT route is that only one transporter system for N uptake is required. However, organic N uptake has the advantage that, in addition to N, it supplies energy and carbon (C) to sustain growth. Recent studies have shown that the direct uptake of organic molecules can significantly contribute to the N nutrition of soil microorganisms. We hypothesize that the relative importance of the direct and MIT route during the decomposition of residues is determined by three factors, namely the form of N available, the source of C, and the availability of N relative to C. The regulation system of soil microorganisms controls key steps in the soil N cycle and is central to determining the outcome of the competition for N between soil microorganisms and plants. More research is needed to determine the relative importance of the direct and MIT route in soil as well as the factors affecting the enzyme systems required for these two pathways.

Pathways of nitrogen utilization by soil microorganisms - a review.

Mechanisms of nematode suppression by organic soil amendments—A review

Organic matter amendments to soil can be used to manage phytoparasitic nematodes. The most effective amendments are those with narrow C:N ratios and high protein or amine-type N content. For soil with 1.0% (w/w) organic matter amendment there is a direct relation between extent of nematode control and the N content of amendments. A special group of amendments are those containing chitinous materials. Chitin addition to soil results in stimulation of a select microflora capable of degrading the polymer. Several microbial species are known to destroy the eggs of phytonematodes (Meloidogyne spp.). Organic matter can be modified by addition of specific compounds or by inoculation with particular microbial species to produce an amendment that will induce suppressiveness.

Biological control of nematodes: Soil amendments and microbial antagonists

Chitinase activity was determined by incubating a mixture of toluene-treated soil with 1% (w/w) colloidal chitin suspension for 18 h at 37°C and then, after dilution, assaying the amount of N-acetyl-glucosamine released. Maximal chitinase activity was observed at 45°C and optimal pH for enzymatic reaction was 5.0–5.5. Soil chitinase activity decreased with increasing soil depth and was significantly affected by crop cover and fertilization regime. Chitin added to soil stimulated chitinase activity. Enzyme activity was correlated with the soil fungal population but not with numbers of actinomycetes or bacteria. A specialized mycoflora was associated with chitin decomposition.

The determination of soil chitinase activity: Conditions for assay and ecological studies

The effect of chitin on soil microflora and on nematodes was studied in microplots containing a sandy loan [pH = 6.0 and organic matter content 1% (w/w)] infested with Meloidogyne arenaria (Neal) Chitwood. Ground chitin was added to soil at rates of 0-4.0% (w/w). The chitin was allowed to decompose for 10 weeks, during which time soil samples were collected every 15 days. After 10 weeks, soil from each plot was transferred to the greenhouse and planted with 'Summer Crookneck' squash (Cucurbita pepo L.) to assess degree of root galling caused by the nematode. Chitin treatments at rates of 0.4% and above reduced root galling; however, at rates 0.8%, chitin amendments were phytotoxic to the plants. Chitin amendments at rates of 1% and above resulted in an increase in pH, conductivity, nitratenitrogen, ammoniacal-nitrogen and chitinase activity. Fungal populations were stimulated by chitin amendments at rates of 1% and above. Elements of a mycoflora previously associated with parasiti

/pdf/chitin-amendments-for-control-of-meloidogyne-arenaria-in-4easct9m4p.pdf

Chitin Amendments for Control of Meloidogyne arenaria in Infested Soil. II. Effects on Microbial Population

The effect of amending soil with chitin on Meloidogyne arenaria (Neal) Chitwood was studied in a greenhouse experiment using silt loam [pH 6.5, org. matter 1% (w/w)] from an infested peanut (Arachis hypogaea L.) field. Chitin was added to soil at rates of 0.5-4.0% (w/w). The chitin was allowed to decompose for 3 weeks, then the soil was planted with summer crookneck squash (Cucurbita pepo L.). After 6 weeks of growth, squash plants were examined to determine the level of root galling and the soil was analyzed for soil enzymic activity and microbial populations. No galls were found on plants from soil with 1% or more of chitin. Soils with 0.5 to 2.0% chitin produced plants which were significantly taller and with heavier shoots than those from untreated soil or from soil with 4.0% chitin. Chitin treatments of 2.0% or higher significantly reduced germination of seed, and chitin at rates above 1.0% resulted in a significant reduction in root weight. Chitin amendments resulted in incre

/pdf/chitin-amendments-for-control-of-meloidogyne-arenaria-in-1rm8hf3rqw.pdf

Chitin Amendments for Control of Meloidogyne arenaria in Infested Soil

The degree of parasitism of 14 fungal species isolated from cysts and eggs of Heterodera glycines Ichinohe against eggs of H. glycines, and of Meloidogyne arenaria (Neal) Chitwood was tested in vitro. The fungi were: Chaetomium indicum Corda, Codinaea heteroderae Morgan-Jones, Fusarium oxysporum Schlecht, F. solani (Mart.) Sacc., Gliocladium catenulatum Gilman & Abbot, G. roseum Bain, Neocosmospora vasinfecta E.F. Smith, Phoma macrostoma Mont., P. multirostrata (Mathur, Menon & Thirum) Dorenb. & Boerema, Stagonospora heteroderae Morgan-Jones, Verticillium lamellicola (R.E.V. Smith) Gams, V leptobactrum Gams, and Thielavia terricola (Gilman & Abbott) Emmons. The fungi were cultured in a chitin-mineral salts agar medium and nematode eggs were added to actively growing cultures to assess the ability of the fungal species to parasitize them. The cultures that showed the highest percent of parasitized eggs were those with V. lamellicola, V. leptobactrum, P macrostoma and P. multirostrata.

/pdf/parasitism-of-eggs-of-heterodera-glycines-and-meloidogyne-30cwimgq38.pdf

G. Morgan-Jones

Papers

Biological control of nematodes: Soil amendments and microbial antagonists

The determination of soil chitinase activity: Conditions for assay and ecological studies

Chitin Amendments for Control of Meloidogyne arenaria in Infested Soil. II. Effects on Microbial Population

Chitin Amendments for Control of Meloidogyne arenaria in Infested Soil

Parasitism of Eggs of Heterodera glycines and Meloidogyne arenaria by Fungi Isolated from Cysts of H. glycines