Gopher mound soil reduces growth and affects ion uptake of two annual grassland species

Portions of an annual serpentine grassland community in California are subject to frequent gopher mound formation. Consequently, studies were undertaken to characterize the effects of mound soils on plant growth and ion uptake. For two of the dominant annual species (Bromus mollis L. and Plantago erecta Morris), growth was reduced in gopher mound soil relative to that in inter-mound soil. A similar reduction in growth was found for plants grown in soils collected at a depth corresponding to the depth of gopher burrowing. This reduction in growth was associated with lower total P and N contents of the soil which were reflected in lower shoot contents of N and P. Additional experiments, however, showed that reduced N and P availabilities in mound soil were not entirely responsible for the growth reduction. Similarly, shoot Ca/Mg ratios were reduced in mound soil but additions of Ca improved the Ca/Mg ratio without improving growth. Growth reductions were associated with altered shoot concentrations of microelements, particularly elevated levels of Mn. A competition experiment between Plantago and Bromus showed that Bromus was more competitive than Plantago in mound and inter-mound soils and that soil type had only small affects on the nature of the interaction between the two species.