Nutrients Stimulate Leaf Breakdown Rates and Detritivore Biomass: Bottom-Up Effects via Heterotrophic Pathways

• Published in: Oecologia Vol. 151; no. 4; pp. 637 - 649
• Main Authors: Greenwood, Jennifer L., Rosemond, Amy D., Wallace, J. Bruce, Cross, Wyatt F., Weyers, Holly S.
• Format: Journal Article
• Language: English
• Published: Berlin Springer 01-04-2007; Springer Nature B.V
• Subjects: Acer - metabolism; Acer rubrum; Animal and plant ecology; Animal, plant and microbial ecology; Animals; Aquatic environment; Biological and medical sciences; Biomass; Carbon - metabolism; Creeks & streams; Ecosystem; Ecosystem Ecology; Fertilizers; Food webs; Fresh water ecosystems; Freshwater ecology; Fundamental and applied biological sciences. Psychology; General aspects; Invertebrates; Invertebrates - metabolism; Land use; Leaves; Macroinvertebrates; Microbial activity; Nitrogen - metabolism; Nutrient concentrations; Nutrient content; Nutrient flow; Nutrients; Plant Leaves - metabolism; Plant Leaves - microbiology; Respiration; Rhododendron; Rhododendron - metabolism; Rhododendron maximum; Soil - analysis; Soil Microbiology; Streams; Synecology; Detritus; Plant leaf; Nutrient enrichment; Biomass; Abscission; Bottom up control; Medium enrichment; Stream macroinvertebrates; Quality; Nutrient; Stream; Leaf quality; Detritivorous; Invertebrata; Headwater stream
• ISSN: 0029-8549; 1432-1939
• DOI: 10.1007/s00442-006-0609-7

Most nutrient enrichment studies in aquatic Systems have focused on autotrophic food webs in Systems where primary producers dominate the resource base. We tested the heterotrophic response to longterm nutrient enrichment in a forested, headwater stream. Our study design consisted of 2 years of pretreatment data in a reference and treatment stream and 2 years of continuous nitrogen (N) + phosphorus addition to the treatment stream. Studies were conducted with two leaf species that differed in initial C:N, Rhododendron maximum (rhododendron) and Acer rubrum (red maple). We determined the effects of nutrient addition on detrital resources (leaf breakdown rates, litter C:N and microbial activity) and tested whether nutrient enrichment affected macroinvertebrate consumers via increased biomass. Leaf breakdown rates were ca. 1.5 and 3x faster during the first and second years of enrichment, respectively, in the treatment stream for both leaf types. Microbial respiration rates of both leaf types were 3x higher with enrichment, and macroinvertebrate biomass associated with leaves increased ca. 2-3x with enrichment. The mass of N in macroinvertebrate biomass relative to leaves tended to increase with enrichment up to 6x for red maple and up to 44x for rhododendron leaves. Lower quality (higher C:N) rhododendron leaves exhibited greater changes in leaf nutrient content and macroinvertebrate response to nutrient enrichment than red maple leaves, suggesting a unique response by different leaf species to nutrient enrichment. Nutrient concentrations used in this study were moderate and equivalent to those in streams draining watersheds with altered land use. Thus, our results suggest that similarly moderate levels of enrichment may affect detrital resource quality and subsequently lead to altered energy and nutrient flow in detrital food webs.