Soil Composition and Function as Insight for Understanding Native Grassland Success

Includes bibliographical references (pages 39-42).Due to ever-increasing human activity and connectivity, non-native annual plants have increased in range and influence over the past century. Invasive plants employ a wide range of species-specific mechanisms to establish themselves in foreign soil, including enhanced competitive ability, phenotypic plasticity and modification of soil processes. Biologists have applied a variety of restoration techniques to combat the spread of invasive plants. Many restoration plans, however, are ineffective, expensive, time consuming or a combination of the three. Few studies have examined the effect restoration techniques have on belowground soil processes even though soil characteristics have been shown to have strong influence on the composition of aboveground plant communities. This study seeks to establish a link between native plant restoration and belowground soil process. In a field experiment, three restoration techniques were applied to a recently burned California grassland. Plant community composition, soil nitrogen, pH, moisture, texture and enzymatic activities were measured. The experiment showed no effect of restoration technique on the plant community and soil processes. Results, however, showed strong linkages between soil characteristics and the identity of aboveground plant species. Additionally, in a greenhouse experiment, seed mixes of either native grassland or non-native grassland plant species were grown in separate pots to display the effect of early germination on later growing plants. After five weeks of growth, seed mixes were sewn into the old pots and allowed to grow. Results of the greenhouse experiment showed a strong negative effect on the biomass of later germinating plants due to early germination regardless of the identity of the early germinating plant group. The negative effect on biomass was observed even when the aboveground growth of the early germinating plant was removed. This work shows the importance of understanding soil processes and invasive mechanisms when designing restoration plans