Nitrogen limitation of many temperate plant communities makes the impacts of fossorial mammal activity on soil N dynamics an interesting and potentially important topic. We determined the effects of gopher mound building on soil N transformations by measuring gross rates of N mineralization and nitrification using short‐term 15N pool dilution methods, net rates of mineralization and nitrification using longer‐term buried‐bag determinations, inorganic N pools, and soil physical characteristics in gopher‐disturbed soil, bare soil, and intact vegetated soil in a California annual grassland during the spring growing season. Soil bulk densities were lower and temperatures were higher in gopher mound material. Neither gross nor net rates of N mineralization or nitrification were statistically distinguishable among gopher‐disturbed, bare, and vegetated soils. However, larger pools of NH4 and NO3 were present in mound and bare soils than in vegetated soils, nitrification potential was higher in mound soils than in vegetated soils, and the rate constant for microbial NO3 consumption was higher in vegetated soil than in bare or gopher‐mound soil. Gopher removal of plants from this annual grassland was the primary mechanism of impact on N cycling through both elimination of plant uptake of inorganic N and by reduction of root‐enhanced microbial immobilization of NO3‐N. Corresponding Editor: M. E. Ritchie.

In Mediterranean areas, the establishment of multispecies pastures for extensive livestock use is an alternative to the growing of traditional cereal crops. Lolium rigidum Gaud. is one of the most valuable forage grasses adapted to semiarid environments but its performance in mixtures is not fully understood. Field observations suggest that the species exerts allelopathic effects, although there is no evidence in the literature to support this assumption. The objective of the study was to determine whether L. rigidum affects the germination and seedling growth of common forage species by allelopathic means. Two bioassays were conducted to test for the allelopathic potential of seeds and adult (shoot and root) tissues of L. rigidum on two grasses, Lolium multiflorum Lam. and Dactylis glomerata L., and a legume, Medicago sativa L. The three species showed different degrees of sensitivity to L. rigidum with L. multiflorum being particularly sensitive to allelopathy. Positive and negative effects of L. rigidum on seedling development were noted. Shoot extracts of L. rigidum displayed the most consistent negative effects by inhibiting elongation of the radicle of the three target species. The significance of the results is that in drought-prone environments and where water resources are scarce poor root development decreases the ability of the plants to grow and survive.

Abstract. The hypothesis that mole burrowing activity alters soil nutrient fluxes and that, as a response to the new conditions, a specialized guild of species develops on the molehills, was tested in an area located in the southwestern Spanish Pyrenees, on a spectrum of montane grassland communities that varies from xeric to temporally waterlogged. Evidence for an association between disturbance and nutrient availability was reported for nitrogen. Mole‐disturbed soils had elevated amounts of inorganic nitrogen compared to soils in surrounding pastures. At the first stages of mound revegetation, changes in nitrate flushes and in species competitive relationships following disturbance appeared to facilitate the establishment of ruderal and non‐mycorrhizal species. The diversity of the whole grassland was enhanced by the existence of these sets of species, abundant on mounds and rarer in the pasture. However, the difference was mainly quantitative, as exclusive colonizers of molehills were not found.

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