Mycorrhizal fungi colonize many terrestrial plants and often result in an increased uptake of P and several micronutrients. Little information is available on the relationships among vesicular-arbuscular endomycorrhizae (YAM), aquatic plants, and plant P concentrations. The major objectives of this study were to measure the degree of YAM colonization of wetland plants, and to determine the relationship between colonization and plant P concentrations when sampled from two contrasting water regimes (hydric soil with no surface water and hydric soil with a minimum of 10 cm of surface water). Two semipermanent wetlands in Lake County, South Dakota, were chosen for the study. Water regime did not have a significant effect on total or organic soil P concentration. Vesicular-arbuscular endomycorrhizal spore samples collected from wet soils averaged 5000 spores kg"' compared with 2740 spores kg"' in dry soils. The eight plant species evaluated to determine VAM colonization were reed canarygrass (Phalaris arundinacea L.), slough sedge (Carex atherodes Spreng.), river bulrush [Scirpus fluviatilis (Torr.) Gray], slender rush (Juncus tenuis Willd.), dogbane (Apocynum cannabinum L.), water smartweed (Polygonum amphibium L.), cattail (Typha Xglauca Godr.), and wild licorice (Glycyrrhiza lepidota (Nutt.) Pursh). Vescular-arbuscular endomycorrhizal colonization ranged from 78% (wild licorice) to none (slough sedge and slender rush). Roots from dry areas averaged 27% colonization compared with less than 1% in wet areas. Colonization levels of dogbane and reed canarygrass in dry zones were highly correlated to plant P concentrations. The results of this study indicate that several wetland plant species develop substantial mycorrhizal associations, particularly in relatively dry environments.

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Nitrogen mineralization, nitrification potentials, pH, total N, C, extractable P and cations were measured in soils under 4-year-old, mono-specific stands of six fast-growing, native tree species, an abandoned pasture, and a 20-year-old secondary forest, as part of a study on the use of indigenous tree species for rehabilitation of soil fertility' on degraded pastures at the La Selva Biological Station in the Atlantic humid lowlands of Costa Rica. Soil net nitrification potential rates were higher under two N-fixing, leguminous species, Stryphnodendron microstachyum Poepp. et Endl. (1.1-1.9 mg kg -1 day -1) and Dalbergia tucurensis Donn. Smith (0.7-1.5 mg kg-lday-1), than under the non-N-fixing trees in the plantation, Vochysia guatemalesis Don. Sm., Vochysiaferruginea Mart, Dipteryx panamensis (Pittier) Record and Mell and Hyeronima alchorneoides Fr. Allemao (0.2-0.8 mg kg-1 day-1). Values under the N-fixing trees were comparable to those found in secondary forest. There were no statistically significant: differences in soil total N or in other nurtients between the species. Results of pH measurements done before and after incubation did not show any clear evidence of a pH drop attributable to nitrification.