Patterns of Growth and Soil-water Utilization in some Exotic Annuals and Native Perennial Bunchgrasses of California

In western California, exotic cool-season annuals appear tohave widely replaced native perennial bunchgrasses as the herbaceouscommunity dominants in grasslands, oak savannas, and oak woodlands.We argue that because these two herbaceous plant types possessvery different life histories, this invasion may have correspondinglyaltered seasonal patterns of soil-water availability. To beginto assess this hypothesis, in this study we compared exoticcool-season annuals and native perennial bunchgrasses in termsof growth, biomass allocation, rooting distribution, root morphology,and soil-water utilization. Exotic cool-season annuals completed their life cycle earlyin the dry season through rapid growth apparently made possibleby a high proportional allocation to shoots in combination withthe efficient production of roots of high specific root length.Further, annuals tended to concentrate root growth and soil-waterutilization in the upper soil profile. In contrast, native perennialbunchgrasses allocated a high proportion of their biomass tothe production of a deep root system, which allowed them tocontinue soil-water utilization well into the dry season andcontribute to the formation of a very dry soil profile. Takentogether, these contrasting patterns suggest that the invasionof exotic cool-season annuals might have produced a correspondingincrease in the amount of water present at depth in the soilprofile during the dry season. Brachypodium distachyon ; Bromus diandrus ; Cynosurus echinatus ; Elymus glaucus ;Nassella pulchra ; Trifolium hirtum ; soil-water utilization; specific root length; growth analysis; rooting depth