Responses of microbial components of the rhizosphere to plant management strategies in a semiarid rangeland

Abstract

Rhizosphere microbial responses to herbage removal and irrigation were assessed in a semi-arid rangeland by determining phosphatase and dehydrogenase activity, ATP, and fluorescein diacetate (FDA)-stained and total hyphal lengths. In four sequential one-week experiments (15 sample dates), irrigation resulted in significant decreases in dehydrogenase activity on 53% of the sample dates, while with herbage removal such decreases were only observed on only 7% of the sample dates. The combined treatment (herbage removal and irrigation) gave intermediate responses, with dehydrogenase decreasing on 33% of the dates, which indicated that herbage removal mitigated the reduction of rhizosphere microbial activiy caused by irrigation. In contrast to these decreases, total hyphal lengths increased on 47 and 33% of the dates in the combined and irrigated treatments, respectively. However, in both treatments active hyphae decreased on 47% of the dates. Comparison of dehydrogenase activity with hyphal length responses suggested that overall microbial activity, as opposed to the fungal component, was preferentially stimulated by herbage removal, while irrigation caused a decrease in both microbial activity and degradation of fungal hyphae. Increases in dehydrogenase activity were observed within 24 hr of herbage removal in 3 of 4 weeks. An increase in dehydrogenase activity was also observed upon initiation of irrigation, but dehydrogenase activity decreased with continued irrigation. These results indicated that manipulation of range plants by herbage removal and irrigation would lead to distinct changes in fungal populations and microbial activities in the rhizosphere. The relationship between plant management and rhizosphere microbial responses can be studied under field conditions to provide better understanding of plant-soil interactions with the ultimate goal of improving productivity of semiarid ecosystems.