Showing papers by "Jane C. Marks published in 2009"

Early bacterial and fungal colonization of leaf litter in Fossil Creek, Arizona

Abstract: Microbes are important in stream ecosystem processes and ubiquitous in stream environments, but limitations of study techniques have left most of these microbial communities poorly described. In stream ecosystems, fungal and bacterial communities play critical roles in leaf decomposition and release energy and nutrients to higher trophic levels of the food web. Our research examined microbial communities in Fossil Creek, Arizona, USA, to elucidate effects of litter quality and abiotic habitat characteristics on early microbial colonizers of leaves. High- and low-quality leaf litter was placed in the creek at 5 study sites with heterogeneous environmental conditions (including differing stream morphology, water flow, water chemistry, and travertine deposition). Microbial assemblages that colonized the decomposing leaves were characterized using terminal-restriction fragment length polymorphism analysis and clone library comparisons. Our study revealed differences in microbial community structure along environmental gradients and, to some extent, between high- and low-quality litter in Fossil Creek. Leaf decomposition rates were strongly influenced by both litter quality and abiotic site characteristics, but microbial communities were more strongly influenced by site than by litter quality. Bacterial and fungal communities differed with incubation times: bacterial diversity increased between 2-d and 8- to 9-d incubations, whereas fungal diversity decreased. Fungal community diversity was negatively correlated with decomposition rates after incubation in the creek for 2 d when the community still included nonaquatic fungi, but this relationship did not exist after longer incubation. Bacterial community diversity was not related to litter quality or decomposition rates.

Genetic and environmental controls of microbial communities on leaf litter in streams

Abstract: Summary 1. Despite the importance of microorganisms for leaf litter decomposition in streams, little is known about which factors affect community composition of bacterial and fungal communities. Standard morphological techniques probably underestimate microbial diversity. 2. We used terminal restriction fragment length polymorphisms of the ITS regions for fungi, and the 16S region for bacteria, to compare fungal and bacterial communities on four cross types of cottonwood leaves (Populus fremontii, P. angustifolia, and their naturally occurring F1 and backcross hybrids). Decomposing leaves were studied in two Arizona rivers that differ in water chemistry and macroinvertebrates. 3. Hybridising cottonwoods are an ideal model system to test how genetic differences in leaf litter chemistry affect microbial communities because cross types have different decomposition rates and leaf litter chemistry. Leaves were incubated in litter bags for 2 weeks and brought to the laboratory for genetic analysis. Communities were analysed using non-metric multi dimensional scaling (NMDS) and diversity indices. 4. Fungal and bacterial communities differed between the two rivers, even when growing on identical substrates. There were also significant differences in microbial communities among the four cross types, indicating that genetically based differences in leaf litter translate to differences in microbial communities. 5. Diversity increased along the hybridising complex from P. fremontii to P. angustifolia, with hybrids showing intermediate values. Fungal and bacterial diversity were significantly higher on cross types with higher tannin concentrations and slower decomposition rates. 6. Environmental conditions most strongly structured microbial communities, but within an environment, genetic-based differences in leaf litter quality yielded differences in diversity and community structure. 7. Molecular tools are making it possible to understand patterns of microbial diversity in river ecosystems, paving the way for a better understanding of how differences in microbial species affect ecosystem processes and higher trophic levels.

Short-term responses of decomposers to flow restoration in Fossil Creek, Arizona, USA

Abstract: Dam decommissioning projects, although numerous, rarely include complete sets of data before and after restoration for evaluating the ecological consequences of such projects. In this study, we used a before-after control-impact (BACI) design to assess changes in leaf litter decomposition and associated macroinvertebrate and fungal decomposers following dam decommissioning in Fossil Creek, Arizona, USA. Leaf litterbags were deployed in a relatively pristine site above the dam and a highly disturbed site below the dam where over 95% of the flow was previously diverted for hydropower generation. Leaf litter decomposition was significantly slower below the dam both measurement years (pre- and post- restoration) with no site-year interaction, indicating that decomposition in this stream section was not affected by increased flow. In contrast, both macro- invertebrates and fungi differed significantly above and below the dam prior to restoration but were similar post-restoration, supporting the concept that decomposer communities can quickly rebound fol- lowing reintroduction of full flow. Our results indicate that some aquatic ecosystem variables can return to a more natural state following ecological restoration activities such as water flow restoration.

Effects of travertine and flow on leaf retention in Fossil Creek, Arizona

Abstract: Leaf retention is important in transferring energy from riparian trees to stream food webs. Retention increases with geomorphic complexity such as substrate coarseness, sinuosity, and the presence of debris dams. High discharge can reduce retention, particularly when streams lack physical trapping features. Travertine formations, caused by calcium carbonate deposition, can alter stream morphology. To date, however, we know of no study testing the effect of travertine on leaf retention. This study capitalized on a river restoration project in Fossil Creek, Arizona, where water was returned to the channel after a century of diversion. We examined how the fixed factors Flow (before and after restoration) and Morphology (travertine and riffle-pool sites) affected leaf retention. Leaf retention was higher in sites where travertine forms barriers across the river, relative to sites with riffle-pool morphology. Most leaves retained in travertine reaches were concentrated at the bottom of pools formed between dams. Although flow restoration did not alter retention rates across all sites, it diminished them at travertine sites, indicating an interaction between stream flow and morphology. We conclude that stream complexity and leaf retention are enhanced by travertine deposition but that high discharge can reduce the retentive capacity of in-stream structures.