Soil ecosystem functioning under global change: extreme weather events and exotic herbaceous species alter soil microbial communities and nutrient cycling in southern California
Soil biological and physicochemical responses to global change drivers represent a major source of uncertainty in current and future ecosystem services. In this dissertation, I tested the hypothesis that shifts in weather patterns and invasions of exotic herbaceous species can alter soil functions in Southern California’s shrublands. Chapter 1 shows that severe droughts reduce microbial biomass and shift microbial community composition towards osmotic stress life- strategies. Exotic herbaceous species altered the soil microclimate and stimulated microbial activity. These findings indicate that severe droughts and plant invasions can produce a smaller C pool vulnerable to gaseous losses. Chapter 2 shows exotic plants enhancing rewetting CO! pulses through greater sensitivity to temperature, antecedent soil moisture, and rainfall event size. These results compliment Chapter 1 by providing evidence that invasions can exacerbate ecosystem’s C losses. Chapter 3 examines N cycling in the system and found that soil inorganic N accumulation and leaching losses increase under exotics when compared to soils under native woody species. This suggests that severe droughts and invasions can produce larger soil N pools that are vulnerable to leaching losses. In summary, this dissertation shows that soil responses to extreme weather events and plant invasions, as measured through microbial biomass, activity, community structure and metabolic composition, N and C pools and fluxes, may increase the vulnerability of ecosystem functioning through soil C and N losses and positive feedbacks to global change drivers.
