T. Aziz

Influence of inorganic N on mycorrhizal activity, nodulation, and growth ofLeucaena leucocephalain an oxisol subjected to simulated erosion

Abstract The influence of inorganic N on the development of mycorrhizal symbiosis inLeucaena leucocephala(Lam.) de Wit was studied in an Oxisol subjected to simulated erosion. The plants were grown in pots containing soil samples inoculated with the VAM fungusGlomus aqgregatumand amended with 0, 25, 50 or 100 ppm N. The extent of VAM colonization of roots increased with increasing levels of N in both eroded and uneroded soils. However, the level of infection was significantly higher in the eroded soil than in the uneroded one. Mycorrhizal activity monitored in terms of P content of leucaena subleaflets increased significantly in the eroded soil when it was amended with 25 ppm N and became similar to that observed in the uneroded soil. Nodule dry matter production and shoot N concentration increased significantly with N application upto 50 ppm. Above this level of N, nodule dry weight declined while N concentration did not change. Application of 25 ppm N to the eroded soil also significantly increased shoo...

Enhancement of endomycorrhizal activity through nitrogen fertilization in cowpea grown in an oxisol subjected to simulated erosion.

Abstract The influence of inorganic nitrogen on the development of mycorrhizal symbiosis in Vigna unguiculata (L.) Walp cv. California Blackeye No. 5 (cowpea) was studied in a noneroded oxisol and an oxisol subjected to simulated erosion. Plants were grown in pots containing soil inoculated with the vesicular‐arbuscular mycorrhizal (VAM) fungus Glomus aggregatum and amended with 0–100mg N kg‐1 soil. Vesicular‐arbuscular mycorrhizal colonization of roots, shoot P and N status, and shoot, root, and nodule dry weights were significantly stimulated by amendment of the eroded soil with N. However, the response of root colonization, shoot P concentration, and nodule dry weight to N application of the noneroded soil was not significant. The relationship of N with root colonization and shoot P status was described by a linear model while the relationships between N and other variables measured were described by quadratic equations. The results illustrate the potential benefits of starter N in the establishment of...

The sensitivity of three vesicular-arbuscular mycorrhizal species to simulated erosion

Abstract A greenhouse experiment was conducted to determine the effectiveness of three vesicular‐arbuscular mycorrhizal (VAM) species in an Oxisol subjected to simulated erosion using Leucaena leucocephala as an indicator host. The extent of colonization of leucaena roots increased significantly due to VAM inoculation of the eroded and uneroded soils. The highest level of VAM colonization was observed when leucaena was grown in association with Glomus aggregatum. followed by G. mosseae and G. etunicatum. Increased infection associated with inoculation of the eroded soil did not result in enhanced mycorrhizal effectiveness. Inoculation of the uneroded soil, however, led to significant improvement in root colonization as well as in symbiotic effectiveness. Suppression in expression of mycorrhizal effectiveness in the eroded soil appears to be a result of nutrient deficiency. The results suggest the importance of restoring lost nutrients before differences in VAM species could be effectively exploited for a ...

Relative importance of Ca, N, and P in enhancing mycorrhizal activity in Leucaena leucocephala grown in an oxisol subjected to simulated erosion

Abstract Pot experiments were conducted in the greenhouse to determine the combined effects of lime, nitrogen and phosphorus and the relative importance of each of these nutrients in establishing nodulated and mycorrhizal Leucaena leucocephala (Lam.) de Wit Var. K8 in an oxisol subjected to simulated erosion. Leucaena was grown in the soil inoculated or not with the vesicular‐arbuscular mycorrhizal fungus Glomus aggregatum Schenck and Smith emend Koske, with or without a basal nutrient (basal) consisting of K, Mg, S, Zn, Cu, and B plus lime, N, and P (complete) or one of the latter three supplements. The extent of mycorrhizal colonization of roots as well as mycorrhizal effectiveness, as measured by pinnule P content increased when the eroded soil was amended with combinations of all the nutrients and inoculated with G. aggregatum. Similar trends were observed when symbiotic effectiveness was measured in terms of shoot P, Cu, and Zn status and dry matter yield. Nodule dry matter was also responsive to ame...

Residual toxicity of soil-applied chlorothalonil on mycorrhizal symbiosis in Leucaena leucocephala

The residual effect of the fungicide chlorothalonil on the vesicular-arbuscular mycorrhizal (VAM) symbiosis was evaluated in a greenhouse experiment. The soil used was an oxisol (Tropeptic Eutrustox) treated with P to obtain target levels near-optimal for VAM activity or sufficient for nonmycorrhizal host growth. In the uninoculated soil treated with the former P level, the fungicide reduced VAM colonization of roots and completely suppressed symbiotic effectiveness measured in terms of pinnule P content. When this soil was inoculated with Glomus aggregatum, symbiotic effectiveness was significantly reduced but not eliminated by 50 mg of the fungicide kg−1. At higher chlorothalonil levels, VAM effectiveness but not VAM colonization was completely suppressed in the inoculated soil. The pattern with which chlorothalonil influenced tissue P content and dry matter yield at the time of harvest closely paralleled its effect on VAM effectiveness. In the soil treated with P level sufficient for nonmycorrhizal host growth, the adverse effect of the fungicide on the above variables was appreciably milder than when the host relied on VAM fungi for its P supply. The toxic effect of the fungicide, therefore, was partly offset by P fertilization, suggesting that VAM fungi were more sensitive to chlorothalonil than the host. Our results demonstrate that although the toxic effect of chlorothalonil declined as a function of time, a significant level of toxicity persisted 12.5 weeks after the chemical was applied to soil.

Inhibition of mycorrhizal symbiosis in Leucaena leucocephala by chlorothalonil

The effect of the fungicide, chlorothalonil, on vesicular-arbuscular mycorrhizal (VAM) symbiosis was studied in a greenhouse using Leucaena leucocephala as test plant. Chlorothalonil was applied to soil at 0, 50, 100 and 200 μg g−1. The initial soil solution P levels were 0.003 μg mL−1 (sub-optimal) and 0.026 μg mL−1 (optimal). After 4 weeks, the sub-optimal P level was raised to 0.6 μg mL−1 (high). The soil was either uninoculated or inoculated with the VAM fungus, Glomus aggregatum. The fungicide reduced mycorrhizal colonization of roots, development of mycorrhizal effectiveness, shoot P concentration and uptake and dry matter yields at all concentrations tested, although the highest inhibitory effect was noted as the concentration of the fungicide was increased from 50 to 100 μg g−1. Phosphorus applied after four weeks tended to partially offset the deleterious effects of chlorothalonil in plants grown in the inoculated and uninoculated soil which suggests that the fungicide was interfering with plant P uptake. The results suggest that the use of chlorothalonil should be restricted to levels below 50 μg g−1 if the benefits of mycorrhizal symbiosis are to be expected.

Stimulation of mycorrhizal activity in Vigna unguiculata through low level fertilization of an oxisol subjected to imposed erosion

Abstract A greenhouse experiment was conducted to determine the combined effects of lime, nitrogen and phosphorus on mycorrhizal activity in an oxisol subjected to imposed erosion using Vigna unquiculata (L.) Walp cv. ‘California Blackeye No. 5’ (cowpea) as a test plant. Cowpea was grown in the soil in the presence or absence of the vesicular‐arbuscular mycorrhizal fungus Glomus aqgregatum (Schenck & Smith emend. Koske) with or without a basal nutrient (basal) consisting of K, Mg, S, Zn, Cu and B; and with basal nutrients plus lime, N and P (complete). The extent of mycorrhizal colonization of roots as well as mycorrhizal effectiveness measured in terms of leaf disc P content increased significantly when the eroded soil was amended with a combination of all of the nutrients and inoculated with Glomus aggregatum. Vesicular‐arbuscular mycorrhizal inoculation and nutrient amendment was also accompanied by significant increase in shoot P, Cu, Zn and N content, and nodule, shoot and root dry matter yield. The ...