Evaluation of hydroxyl radical-scavenging property of purpurogallin using high pressure liquid chromatography

Purpurogallin (PPG) has been used as an additive to edible and non-edible oils or fats to retard oxidation. Its antioxidant mechanism is not known. We investigated the ability of PPG to scavenge exogenously generated hydroxyl radicals (·OH) using a sensitive high pressure liquid chromatographic (HPLC) method. ·OH was generated by photolysis of H₂O₂ (1.25–10 moles) with UV light and was trapped with salicylic acid (500 nmoles). Salicylic acid is hydroxylated to produce ·OH adduct products 2,3-and 2,5-dihydroxybenzoic acid (DHBA). H₂O₂ produced concentration-dependent ·OH as estimated by generation of 2,3- and 2,5-DHBA. PPG (100, 200, 300, 400, 500 and 600 nmoles) produced concentration-dependent decreases in ·OH adduct products (approximately 70% inhibition with 600 nmoles of PPG). It did not affect the peak of standard 2,3- and 2,5-DHBA indicating that the decrease in the adduct product generated by H₂O₂ is due to scavenging of ·OH. These results indicate that photolysis of H₂O₂ by UV light produces ·OH and that PPG scavenges ·OH.     

Quantitative detection of 4-hydroxyequilenin–DNA adducts in mammalian cells using an immunoassay with a novel monoclonal antibody

Estrogen–DNA adducts are potential biomarkers for assessing the risk and development of estrogen-associated cancers. 4-Hydroxyequilenin (4-OHEN) and 4-hydroxyequilin (4-OHEQ), the metabolites of equine estrogens present in common hormone replacement therapy (HRT) formulations, are capable of producing bulky 4-OHEN–DNA adducts. Although the formation of 4-OHEN–DNA adducts has been reported, their quantitative detection in mammalian cells has not been done. To quantify such DNA adducts, we generated a novel monoclonal antibody (4OHEN-1) specific for 4-OHEN–DNA adducts. The primary epitope recognized is one type of stereoisomers of 4-OHEN–dA adducts and of 4-OHEN–dC adducts in DNA. An immunoassay with 4OHEN-1 revealed a linear dose–response between known amounts of 4-OHEN–DNA adducts and the antibody binding to those adducts, with a detection limit of approximately five adducts/10⁸ bases in 1 µg DNA sample. In human breast cancer cells, the quantitative immunoassay revealed that 4-OHEN produces five times more 4-OHEN–DNA adducts than does 4-OHEQ. Moreover, in a mouse model for HRT, oral administration of Premarin increased the levels of 4-OHEN–DNA adducts in various tissues, including the uterus and ovaries, in a time-dependent manner. Thus, we succeeded in establishing a novel immunoassay for quantitative detection of 4-OHEN–DNA adducts in mammalian cells.     

Lack of contribution of covalent benzo[a]pyrene-7,8-quinone–DNA adducts in benzo[a]pyrene-induced mouse lung tumorigenesis

Benzo[a]pyrene (B[a]P) is a potent human and rodent lung carcinogen. This activity has been ascribed in part to the formation of anti-trans-7,8-dihydroxy-7,8-dihydroB[a]P-9,10-epoxide (BPDE)-DNA adducts. Other carcinogenic mechanisms have been proposed: (1) the induction of apurinic sites from radical cation processes, and (2) the metabolic formation of B[a]P-7,8-quinone (BPQ) that can form covalent DNA adducts or reactive oxygen species which can damage DNA. The studies presented here sought to examine the role of stable BPQ-DNA adducts in B[a]P-induced mouse lung tumorigenesis. Male strain A/J mice were injected intraperitoneally once with BPQ or trans-7,8-dihydroxy-7,8-dihydroB[a]P (BP-7,8-diol) at 30, 10, 3, or 0 mg/kg. Lungs and livers were harvested after 24 h, the DNA extracted and subjected to ³²P-postlabeling analysis. Additional groups of mice were dosed once with BPQ or BP-7,8-diol each at 30 mg/kg and tissues harvested 48 and 72 h later, or with B[a]P (50 mg/kg, a tumorigenic dose) and tissues harvested 72 h later. No BPQ or any other DNA adducts were observed in lung or liver tissues 24, 48, or 72 h after the treatment with 30 mg/kg BPQ. BP-7,8-diol gave BPDE-DNA adducts at all time points in both tissues and B[a]P treatment gave BPDE-DNA adducts in the lung. In each case, no BPQ-DNA adducts were detected. Mouse body weights significantly decreased over time after BPQ or BP-7,8-diol treatments suggesting that systemic toxicity was induced by both agents. Model studies with BPQ and N-acetylcysteine suggested that BPQ is rapidly inactivated by sulfhydryl-containing compounds and not available for DNA adduction. We conclude that under these treatment conditions BPQ does not form stable covalent DNA adducts in the lungs or livers of strain A/J mice, suggesting that stable BPQ-covalent adducts are not a part of the complex of mechanisms involved in B[a]P-induced mouse lung tumorigenesis.     

Transition-state analogues as inhibitors of L-dopa decarboxylase

1. A series of compounds has been prepared which are analogues of the transition state of the reaction catalysed by L-dopa decarboxylase (EC 4.1.1.28). 2. These compounds are reduced adducts of the substrate (L-dopa) and coenzyme (pyridoxal phosphate), as well as analogues of these substances (D-dopa, pyridoxal and salicaldehyde). 3. Compounds were also prepared with an oxazine link between the 3'-oxygen and the nitrogen attached to the 4'-carbon of the aldehyde moiety. 4. None of the D-dopa adducts produced any significant inhibition, but the L-dopa adducts were all active at millimolar levels, with the oxazine derivatives being more active than their parent compounds. 5. Inhibition was competitive with respect to L-dopa, but was neither competitive nor non-competitive with respect to pyridoxal phosphate. 6. The most active compound tested was the oxazine derivative of the L-dopa/salicaldehyde adduct, with an estimated Ki of 58.0 microM. 7. Increased inhibitory activity was observed when enzyme depleted of pyridoxal phosphate was used.     

Heterogeneous distributions and dispersive photodissociation rates of benzo[a]pyrene diol-epoxide enantiomer-DNA and -poly(dG-dC).poly(dG-dC) adducts.

Two types of heterogeneity of adducts are illustrated and discussed utilizing non-line narrowed (S2----S0 laser excitation) and line-narrowed (excitation into the (0,0) origin band) fluorescence spectra at low temperatures. The first type (type A) is due to structurally distinct and/or energetically inequivalent conformers. The second one (type B) is provided by an inhomogeneous environment of DNA and polynucleotides. In light of the above, the non-exponential photodissociation kinetics of the (+/-)-anti-BPDE-DNA and -polynucleotide adducts have been reanalyzed in terms of a dispersive first order chemical reaction, where the inhomogeneous effects are explicitly included. It is demonstrated that the DNA structure shows considerable inhomogeneous broadening, and that type B heterogeneity is responsible for the dispersive photodissociation process. The latter is accounted for by a Gaussian distribution of activation energies, with the center of the distribution at approximately 600 meV and the full width at half-maximum equal to approximately 50 meV (approximately 2 kT). Photolabile (+/-)-anti-BPDE-DNA and -polynucleotide adducts are identified as quasi-intercalated (site I) (+)- and (-)-cis-BPDE. The calculated concentrations of cis-BPDE adducts in DNA and polynucleotides from the kinetic data are in very good agreement with the cis-BPDE adduct concentrations obtained from the spectral and/or chemical analysis. The average photodissociation rate and the photodissociation quantum yield of cis- and trans-BPDE adducts are also estimated.     

Effectiveness of some iron phosphates as sources of phosphorus for plants

Summary Two well-characterized crystalline ferric phosphates, two colloidal ferric phosphates, and fluorapatite were tested under greenhouse conditions as sources of phosphorus for corn over a 3-cropping period. The selected compounds are representative of those expected to form in soils as reaction products from more soluble phosphate fertilizers.Strengite, FePO₄·2H₂O, was completely unavailable in acid soils and gave only a slight phosphorus response on soils limed to pH 7.6. Uptake of P from hydrogen ammonium ferric phosphate, H₈NH₄Fe₃(PO₄)₈·6H₂O, was approximately 70 per cent that from MCP, and increased with cropping.The colloidal ferric phosphates were approximately 78 per cent as available as MCP and became more available with liming and cropping. In the soil limed to pH 6.5, their effectiveness increased from 47 per cent that of MCP in the first crop to 100 per cent as effective by the third crop.Fluorapatite, included as an insoluble calcium phosphate source, was completely unavailable.     

Isolation,purification and characterization of phytase from germinating mung beans

Phytase isolated from mung bean cotyledons was purified about 80-fold with a recovery of 28%. The enzyme is stable at 0°, has a pH optimum at 7·5 and optimal temperature of 57°. The energy of activation is approximately 8500 cal/mole between 37° and 57°. Inhibition by P_i has been found to be competitive, the K_i value being 0·40–0·43 × 10⁻³ M; the K_m value with phytate is 0·65 × 10⁻³ M. Divalent cations are not required for activity. Lower members of inositol phosphates are better substrates, as shown by their V_max and K_m values. When subjected to polyacrylamide gel electrophoresis two bands have been resolved; one (major) corresponds to phytase and the other (minor) to phosphatase and pyrophosphatase activity. Filtration through Biogel P-200 partially resolves phytase from phosphatase and pyrophosphatase. The molecular weight of phytase is approximately 160,000.     

Model studies of the (6-4) photoproduct photoreactivation: synthesis and photosensitized splitting of uracil oxetane adducts

Uracil oxetane adducts, which are model compounds for the oxetane intermediates generated during the formation of (6-4) photoproducts or in their photoenzymatic repair, have been synthesized using 1,3-dimethyluracil with carbonyl compounds. On the basis of fluorescence measurements and photolysis experiments, it is demonstrated that the oxetane adducts can be split into the nucleotide base and carbonyl compounds via an electron transfer reaction from photosensitizer. The reaction is more efficient for a stronger electron donor.     

Nutrition and burrowing energetics of the Cape mole-rat Georychus capensis

Summary At 22°C the resting oxygen consumption of G. capensis is 1.13±0.05 cm³O₂·g^-1·h^-1 (mean± S.E.). In loose sandy soil the burrowing metabolic rate was approximately three times that of resting (3.41±0.19 cm³O₂·g^-1· h^-1). Rate of oxygen consumption while burrowing bears a linear relationship with rate of burrowing. The equation of the regression line describing this relationship was used to construct a model for calculating energy expenditure of burrowing in free-living mole-rats. The diet of G. capensis consists of some green plant material and geophyte corms. The latter has a mean gross energy content of 16.36 kJ·g^-1 dry weight. The digestibility coefficient for captive G. capensis fed on sweet potato, was 97.42±0.41%. Data collected from an excavated burrow system revealed that the total energetic cost of constructing the burrow amounted to 79% of the estimated digestible energy available from geophyte corms in the area. A food store in the same burrow system was sufficient to meet the maintenance requirements of an adult G. capensis, resting at 22°C, for approximately 80–85 days. Soil samples taken at random adjacent to the burrow contained corms with a mean estimated digestible energy value of 2084 kJ per m³ of soil. A comparison of energetic cost of burrowing and randomly available digestible energy in the field suggests that foraging patterns are not random.     

A mathematical model for intracellular effects of toxins on DNA adduction and repair

The processes by which certain classes of toxic compounds or their metabolites may react with DNA to alter the genetic information contained in subsequent generations of cells or organisms are a major component of hazard associated with exposure to chemicals in the environment. Many classes of chemicals may form DNA adducts and there may or may not be a defined mechanism to remove a particular adduct from DNA independent of replication. Many compounds and metabolites that bind DNA also readily bind existing proteins; some classes of toxins and DNA adducts have the capacity to inactivate a repair enzyme and divert the repair process competitively. This paper formulates anintracellular dynamic model for one aspect of the action of toxins that form DNA adducts, recognizing a capacity for removal of those adducts by a repair enzyme combined with reaction of the toxin and/or the DNA adduct to inactivate the repair enzyme. This particular model illustrates the possible saturation of repair enzyme capacity by the toxin dosage and shows that bistable behavior can occur, with the potential to induce abrupt shifts away from steady-state equilibria. The model suggests that bistable behavior, dose and variation between individuals or tissues may combine under certain conditions to amplify the biological effect of dose observed as DNA aduction and its consequences as mutation. A model recognizing stochastic phenomena also indicates that variation in within-cell toxin concentration may promote jumps between stable equilibria.     

Antioxidant activity of allicin,an active principle in garlic

Garlic has been claimed to be effective against diseases, in the pathophysiology of which oxygen free radicals (OFRs) have been implicated. Effectiveness of garlic could be due to its ability to scavenge OFRs. However, its antioxidant activity is not known. We investigated the ability of allicin (active ingredient of garlic) contained in the commercial preparation Garlicin to scavenge hydroxyl radicals (·OH) using high pressure liquid chromatographic (HPLC) method. ·OH was generated by photolysis of H₂O₂ (1.25–10 moles/ml) with ultraviolet light and was trapped with salicylic acid which is hydroxylated to produce ·OH adduct products 2,3- and 2,5-dihydroxybenzoic acid (DHBA). H₂O₂ produced a concentration-dependent ·OH as estimated by ·OH adduct products 2,3-DHBA and 2,5-DHBA. Allicin equivalent in Garlicin (1.8, 3.6, 7.2, 14.4, 21.6, 28.8 and 36 g) produced concentration-dependent decreases in the formation of 2,3-DHBA and 2,5-DHBA. The inhibition of formation of 2,3-DHBA and 2,5-DHBA with 1.8 g/ml was 32.36% and 43.2% respectively while with 36.0 g/ml the inhibition was approximately 94.0% and 90.0% respectively. The decrease in ·OH adduct products was due to scavenging of ·OH and not by scavenging of formed ·OH adduct products. Allicin prevented the lipid peroxidation of liver homogenate in a concentration-dependent manner. These results suggest that allicin scavenges ·OH and Garlicin has antioxidant activity.     

Interaction between fulvic acids of different origins and active oxygen radicals

Using the spin trapping technique, the interaction between fulvic acids (FAs) of different origins and the active oxygen radicals was studied. The active oxygen radicals under study included superoxide anion (O2 · -) produced by xanthine oxidase (XOD) and stimulated polymorphonuclear leukocytes (PMN) of human being and hydroxyl radical ( ·OH) produced from Fenton's reaction. It has been found that the FAs from both Kaschin-Beck disease (KBD) region and non-KBD region can accelerate the production of ·OH and scavenge O2 ·- . FA from peat can scavenge both O2·- and ·OH. The results show that the behavior of KBD and non-KBD FAs differs clearly from peat FA. It has been concluded that the superoxidation damage of KBD induced by FA is mainly due to hydroxyl radical reaction initiated in biological system.     

Characterization of bifunctional adducts produced in DNA by trans-diamminedichloroplatinum(II)

The cancer chemotherapeutic drug cis-diamminedichloroplatinum(II) (cis-DDP) produces bifunctional reactions with DNA which appear critical to its toxic action. The relative inefficacy of the isomer trans-DDP results from its production of predominantly monofunctional adducts in DNA. However, trans-DDP is also toxic and this is presumed to result from bifunctional reaction. These reactions have been characterized by platinating pure DNA followed by enzyme digestion, HPLC separation and analysis by atomic absorption and nuclear magnetic resonance (NMR). Bifunctional adducts occur between deoxyguanosine (dG) and either deoxyadenosine (dA), deoxycytidine (dC) or another dG. Although dG-Pt-dG occurs in both double-stranded (approximately 40% of total adducts) and single-stranded DNA (approximately 60%) there is a marked preference for formation of dG-Pt-dC in double-stranded DNA (approximately 50%) and dG-Pt-dA in single-stranded DNA (approximately 35%). Only dG-Pt-dG forms rapidly; the other adducts derive from rapid formation of a monofunctional dG-Pt and further reaction with dA or dC over many hours.     

Characterization of glycated proteins by 13C NMR spectroscopy. Identification of specific sites of protein modification by glucose

13C NMR spectroscopy has been used to characterize Amadori (ketoamine) adducts formed by reaction of [2-13C]glucose with free amino groups of protein. The spectra of glycated proteins were acquired in phosphate buffer at pH 7.4 and were interpreted by reference to the spectra of model compounds, N alpha-formyl-N epsilon-fructose-lysine and glycated poly-L-lysine (GlcPLL). The anomeric carbon region of the spectrum (approximately 90-105 ppm) of glycated cytochrome c was superimposable on that of N alpha-formyl-N epsilon-fructose-lysine, and contained three peaks characteristic of the alpha- and beta-furanose and beta-pyranose anomers of Amadori adducts to peripheral lysine residues on protein (pK alpha approximately 10.5). The spectrum of GlcPLL yielded six anomeric carbon resonances; the second set of three was displaced about 2 ppm to lower shielding of the first and was assigned to the Amadori adduct at the alpha-amino terminus (pK alpha approximately 7.5). The spectrum of glycated RNase was similar to that of GlcPLL, but contained a third set of three signals attributable to modification of active site lysine 41 (pK alpha approximately 8.8). The assignments for RNase were confirmed by analysis of spectra taken at pH 4 and under denaturing conditions. The spectrum of glycated hemoglobin was comparable to that of GlcPLL, and distinct resonances could be assigned to Amadori adducts at amino-terminal valine and intrachain N epsilon-lysine residues. Chemical analyses were performed to measure the relative extent of alpha- and epsilon-amino group modification in the glycated macromolecules, and the results were compared with estimates based on integration of the NMR spectra.     

Covalent adduction of human serum albumin by 4-hydroxy-2-nonenal: kinetic analysis of competing alkylation reactions

The electrophilic lipid oxidation product 4-hydroxy-2-nonenal (HNE) reacts with proteins to form covalent adducts, and this damage has been implicated in pathologies associated with oxidative stress. HNE adduction of blood proteins, such as human serum albumin (HSA), yields adducts that may serve as markers of oxidative stress in vivo. We used liquid chromatography-tandem mass spectrometry (LC-MS-MS) and the P-Mod algorithm to map the sites of 10 adducts formed by reaction of HNE with HSA in vitro. The detected adducts included Michael adducts formed at histidine and lysine residues. The selectivity of HNE in competing adduction reactions was evaluated by analysis of kinetics for HNE Michael adduction at six targeted HSA histidine residues. Reaction kinetics were analyzed by selected reaction monitoring in LC-MS-MS using stable isotope tagging with phenyl isocyanate. Rate constants ranged over 4 orders of magnitude, with the order of reactivity being H242 > H510 > H67 > H367 > H247 approximately K233. The most reactive target, H242, is located in a fatty acid- and drug binding cavity in subdomain IIa of HSA and appears to be a hot-spot for HNE modification. Analysis of adduction kinetics together with HSA structure and target residue pK(a) values suggest that location in the hydrophobic binding cavity and low predicted pK(a) of H242 account for its high reactivity toward HNE. H242 adducts may be preferred products of adduction by lipophilic electrophiles and may comprise a family of biomarkers for oxidative stress.     

Occupational dose from natural radionuclides in phosphate fertilizers

Summary In this investigation the occupational exposure of single persons due to the gamma radiation of the natural radionuclides in rock phosphates and phosphate fertilizers and their contribution to the population dose in the FRG has been determined. The exposure rates in the working fields production, transport, loading and storage of rock phosphates and phosphate fertilizers and due to their application in agriculture have been measured by means of scintillation dose rate meters or LiF-thermoluminescence dosemeters or have been estimated from specific activities.Mean additional exposure rates of 2–26 µR/h, with local maximum values up to 190 µR/h, were observed. From these values, together with statistical data for the number of occupied persons and annual working times in the various working fields, the mean and maximum annual dose of individuals and the contribution to the mean population dose have been estimated. The results show that a maximum annual dose to individuals from 0.4 mrem/y (agriculture) up to 45 mrem/y (production plants or storehouses) can occur. The corresponding mean annual doses are 0.05–20 mrem/y. The contribution of the occupational radiation exposure due to rock phosphates and phosphate fertilizers to the mean population dose is 174 man · rem/y related to whole body. To this, fertilizer production contributes 40 man · rem/y, transport and loading 45 man · rem/y, agricultural storehouses 31 man · rem/y, and agriculture 58 man · rem/y.Altogether, this investigation shows that an occupational radiation exposure of individuals may occur which corresponds to the mean terrestrial radiation exposure in the FRG. The contribution of the occupational collective doses due to phosphates to the population dose, however, is negligibly small.     

Reactions of platinum(IV) amine compounds with 9-methylhypoxanthine at high temperature result in both platinum(II) and platinum(IV) amine adducts

The products obtained from the reaction of Pt(IV)Cl₄(LL) compounds (LL denotes the chelating ligands ethylenediamine (en) and 2,2-dimethyl-1,3-diaminopropane (dmdap), or two cis- or trans-coordinated ammines) with 9-methylhypoxanthine (mHyp) at high temperature (80°C) have been characterized by proton NMR spectroscopy. It appeared that both platinum(II) and platinum(IV) adducts were present in the reaction mixtures. After cation-exchange chromatography, the Pt(II) compound could be characterized as Pt(II)(LL)(mHyp)₂, whereas the Pt(TV) fractions appeared to contain mainly one or two adducts for the chelating diamine compound but more adducts for the ammine compounds. A ³J(¹⁹⁵Pt-¹H) coupling was observed for the Pt(IV), but not for the Pt(II) compounds at the used spectrometer frequency. This supplies a useful tool to discriminate between these two types of platinum adducts.     

Neodymium β-diketonate glyme complexes: Synthesis and characterization of volatile precursors for MOCVD applications

The monoglyme [CH₃OCH₂CH₂OCH₃] and diglyme [CH₃O(CH₂CH₂O)₂CH₃] adducts of the neodymium tris-hexafluoroacetylacetonato [Nd(hfa)₃·monoglyme·H₂O and Nd(hfa)₃·diglyme] have been synthesised in a single step reaction. They have been characterized by elemental analyzes, mass spectrometry, and IR spectroscopy. Single crystal X-ray diffraction studies provide evidence of a mononuclear nine-coordinated complex with a monocapped square antiprismatic structure for the Nd(hfa)₃·diglyme (monoclinic system, space group P2₁/n; a = 9.7717(2), b = 15.5723(4), c = 20.5620(5) Å, β = 103.668(2)°; Z = 4). The Nd(hfa)₃·monoglyme·H₂O consists of asymmetric units containing two similar molecules (monoclinic system, space group = C2; a = 16.7057(4), b = 12.2579(4), c = 29.3734(5) Å, β = 101.170(3)°, Z = 8).The mass transport properties of these adducts have been investigated by thermogravimetric analysis which revealed high volatility and good thermal stability with a residue left lower than 3%. The Nd(hfa)₃·diglyme has been successfully applied to the low-pressure metal organic chemical vapor deposition (MOCVD) of NdBa₂Cu₃O_7−δ thin films.     

Repair kinetics of trans-4-hydroxynonenal-induced cyclic 1,N2-propanodeoxyguanine DNA adducts by human cell nuclear extracts

trans-4-Hydroxynonenal (HNE) is a major peroxidation product of omega-6 polyunsaturated fatty acids. The reaction of HNE with DNA produces four diastereomeric 1,N(2)-gamma-hydroxypropano adducts of deoxyguanosine (HNE-dG); background levels of these adducts have been detected in tissues of animals and humans. There is evidence to suggest that these adducts are mutagenic and involved in liver carcinogenesis in patients with Wilson's disease and in other human cancers. Here, we present biochemical evidence that in human cell nuclear extracts the HNE-dG adducts are repaired by the nucleotide excision repair (NER) pathway. To investigate the recognition and repair of HNE-dG adducts in human cell extracts, we prepared plasmid DNA substrates modified by HNE. [(32)P]-Postlabeling/HPLC determined that the HNE-dG adduct levels were approximately 1200/10(6) dG of plasmid DNA substrate. We used this substrate in an in vitro repair-synthesis assay to study the complete repair of HNE-induced DNA adducts in cell-free extracts. We observed that nuclear extracts from HeLa cells incorporated a significant amount of alpha[(32)P]dCTP in DNA that contained HNE-dG adducts by comparison with UV-irradiated DNA as the positive control. Such repair synthesis for UV damage or HNE-dG adducts did not occur in XPA cell nuclear extracts that lack the capacity for NER. However, XPA cells complemented with XPA protein restored repair synthesis for both of these adducts. To verify that HNE-dG adducts in DNA were indeed repaired, we measured HNE-dG adducts in the post-repaired DNA substrates by the [(32)P]-postlabeling/HPLC method, showing that 50-60% of HNE-dG adducts were removed from the HeLa cell nuclear extracts after 3 h at 30 degrees C. The repair kinetics indicated that the excision rate is faster than the rate of gap-filling/DNA synthesis. Furthermore, the HNE-dG adduct isomers 2 and 4 appeared to be repaired more efficiently at early time points than isomers 1 and 3.     

Nutrient cycling by the subterranean termite Gnathamitermes tubiformans in a Chihuahuan desert ecosystem

Summary We estimated the density of subterranean termites Gnathamitermes tubiformans at 800,000 · ha^-1 for a standing crop biomass of 2 kg · ha^-1 Predation losses were estimated to be 5,73 kg · ha^-1 · yr^-1 representing the major release of nutrients from termites to surficial soil layers. Nutrient fluxes from termites to predators amounted to 410g N·ha^-1·yr^-1, 33 g S · ha^-1 · yr^-1 and 19 g P · ha^-1 · yr^-1. These fluxes account for 8% of the litter N, 1.5% of the litter P and 2.9% of the litter S. The termites fixed an estimated 66 g · ha^-1 · yr^-1 atmospheric N and returned an estimated 100 g · ha^-1 · yr^-1 in the surface gallery carton. Since losses of elements from subterannean termites were greater than standing crops, we estimated an annual turnover of N at 3.5 times per year, P of 2.5 times per year, and S of 2.5 per times per year.Since surface foraging, predation and alate flights are pulse regulated by rainfall, nutrient flows through subterranean termites are episodic and releases of nutrients accumulated in termite biomass preceeds or is coincident with productivity pulses of some shallow rooted plants. We propose that subterranean termites are important as regulators in desert nutrient cycles.