Leaf litter identity alters the timing of lotic nutrient dynamics

The effects of resource quality on ecosystems can shift through time based on preferential use and elemental needs of biotic consumers. For example, leaf litter decomposition rates are strongly controlled by initial litter quality, where labile litter is processed and depleted more quickly than reca...

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Bibliographic Details
Published in:Freshwater biology 2019-12, Vol.64 (12), p.2247-2259
Main Authors: Robbins, Caleb J., Matthaeus, William J., Cook, Stephen C., Housley, Lauren M., Robison, Sarah E., Garbarino, Matt A., LeBrun, Erick S., Raut, Swastika, Tseng, Chi‐Yen, King, Ryan S.
Format: Article
Language:English
Subjects:
Additives
biodiversity–ecosystem function
Composition effects
Decomposition
Dynamics
Ecosystem assessment
Ecosystems
Environmental changes
Immobilization
Leaf litter
Leaves
Mesocosms
Microorganisms
Mineral nutrients
mineralisation
Mineralization
Nutrient content
Nutrient dynamics
Nutrient requirements
Nutrient status
Nutrient uptake
Nutrients
Oak
Phosphates
Platanus occidentalis
Populus deltoides
Quercus macrocarpa
resource quality
Rivers
Species composition
Streams
Uptake
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Summary:The effects of resource quality on ecosystems can shift through time based on preferential use and elemental needs of biotic consumers. For example, leaf litter decomposition rates are strongly controlled by initial litter quality, where labile litter is processed and depleted more quickly than recalcitrant litters. We examined the effect of this processing continuum on stream nutrient dynamics. We added one of four different litter compositions differing in litter quality (cottonwood [Populus deltoides], labile; sycamore [Platanus occidentalis], recalcitrant; bur oak [Quercus macrocarpa], recalcitrant; and mixed [equivalent mixture of previous three species]) to 12 large (c. 20 m long, with riffle, glide and pool sections) outdoor stream mesocosms to assess the effect of litter species composition on whole‐stream nutrient uptake. Nutrients were dosed once weekly for 8 weeks to measure uptake of NH4–N, NO3–N, and PO4–P. We also measured changes in litter C, N, and P content on days 28 and 56 of the study. Nutrient uptake rates were highly variable, but occasionally very different among litter treatments (c. 5× between highest and lowest uptake rates by species). Uptake rates were generally greatest in cottonwood (labile) streams early in the study. However, during the last 4 weeks of the study, bur oak streams (recalcitrant) took up more nutrients than cottonwood streams, resulting in more cumulative NO3–N uptake in bur oak than in cottonwood streams. Cumulative NO3–N uptake was greater in mixed streams than expected (non‐additive) on two dates of measurement, but was generally additive. Changes in litter nutrient content largely corroborated nutrient uptake patterns, suggesting strong N immobilisation early in the study and some N mineralisation later in the study. P was strongly retained by most litters, but especially bur oak. Nutrient content of litter also largely changed additively, suggesting minimal evidence for non‐additive diversity effects on nutrient source/sink status. Our results demonstrate that litter species identity can have whole‐ecosystem effects on stream nutrient dynamics, with important implications for the form and fate of nutrients exported downstream. Further, diverse litter assemblages may serve as temporal stabilisers of ecosystem processes, such as nutrient sequestration, due to microbial nutrient requirements and differential decomposition rates, or the classic litter processing continuum.
ISSN:0046-5070
1365-2427
DOI:10.1111/fwb.13410