Decomposing organic matter forms a substantial resource base, fueling the biogeochemical function and secondary production of most aquatic ecosystems. However, detrital N (nitrogen) and P (phosphorus) dynamics remain relatively unexplored in aquatic ecosystems relative to terrestrial ecosystems, despite fundamentally linking microbial processes to ecosystem function across broad spatial scales. We synthesized 217 published time series of detrital carbon (C), N, P, and their stoichiometric ratios (C:N, C:P, N:P) from stream ecosystems to analyze the temporal nutrient dynamics of decomposing litter using generalized additive models. Model results indicated that detritus was a net source of N (irrespective of inorganic or organic form) to the environment, regardless of initial N content. In contrast, P sink/source dynamics were more strongly influenced by the initial P content, in which P‐poor litters were sinks for nutrients until these shifted to net P mineralization after ~40% mass loss. However, large variations surrounded both the N and P predictions, suggesting the importance of nonmicrobial factors such as fragmentation by invertebrates. Detrital C:N ratios converged and became more similar toward the end of the decomposition, suggesting predictable microbial functional effects throughout detrital ontogeny. C:P and N:P ratios also converged to some degree, but these model predictions were less robust than for C:N, due in part to the lower number of published detrital C:P time series. The explorations of environmental covariate effects were frequently limited by a few coincident covariate measurements across studies, but temperature, N availability, and P tended to accelerate the existing ontogenetic patterns in C:N. Our analysis helps to unite organic matter decomposition across aquatic–terrestrial boundaries by describing the basic patterns of elemental flows catalyzed by decomposition in streams, and points to a research agenda with which to continue addressing gaps in our knowledge of detrital nutrient dynamics across ecosystems.
Elevated deposition of atmospheric nitrogen (N) has shifted nutrient availability in terrestrial and aquatic habitats of ecosystems, but rarely are ecosystem processes in those components examined simultaneously. We used a multi-decadal, whole, paired watershed experiment to determine how chronic N enrichment with (NH4)2SO4alters litter decomposition in terrestrial and stream systems. We also used short-term phosphorus (P) enrichment experiments within both watersheds to determine whether chronic N enrichment enhances P limitation of decomposition. Leaves from N-treated and reference watersheds were used in a reciprocal design to parse effects of altered nutrient availability in leaves and in the environment. We found divergent responses of terrestrial and stream decomposition to altered nutrient regimes. Chronic experimental N enrichment increased N and P concentrations in post-abscission leaves which decayed faster than leaves from the reference watershed in the terrestrial environment. Experimental N enrichment also did not induce P limitation of terrestrial decomposition. In contrast, litter decomposition rate in the two streams was not enhanced by elevated N in stream water or by altered leaf chemistry. Instead, chronic experimental N enrichment shifted decomposition in streams from co-limitation to strong P limitation. Microbial respiration and extracellular enzyme production responded to altered nutrient availability in a manner consistent with resource allocation models. Divergent responses of terrestrial and aquatic decomposition to elevated N deposition likely arise from differences in water bioavailability. Our work highlights the value of simultaneously considering ecosystem processes in terrestrial and aquatic systems to understand the consequences of integrated landscape processes operating on large spatial scales.
more » « less- NSF-PAR ID:
- 10363501
- Publisher / Repository:
- Springer Science + Business Media
- Date Published:
- Journal Name:
- Ecosystems
- Volume:
- 26
- Issue:
- 1
- ISSN:
- 1432-9840
- Page Range / eLocation ID:
- p. 72-85
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Human activities have dramatically altered global patterns of nitrogen (N) and phosphorus (P) availability. This pervasive nutrient pollution is changing basal resource quality in food webs, thereby affecting rates of biological productivity and the pathways of energy and material flow to higher trophic levels.
Here, we investigate how the stoichiometric quality of basal resources modulates patterns of material flow through food webs by characterizing the effects of experimental N and P enrichment on the trophic basis of macroinvertebrate production and flows of dominant food resources to consumers in five detritus‐based stream food webs.
After a pre‐treatment year, each stream received N and P at different concentrations for 2 years, resulting in a unique dissolved N:P ratio (target range from 128:1 to 2:1) for each stream. We combined estimates of secondary production and gut contents analysis to calculate rates of material flow from basal resources to macroinvertebrate consumers in all five streams, during all 3 years of study.
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This study suggests that ongoing global increases in N and P supply will increase organic matter flows to metazoan food webs in detritus‐based ecosystems by reducing stoichiometric constraints at basal trophic levels. However, the extent to which those flows are propagated to the highest trophic levels likely depends on responses of individual prey taxa and their relative susceptibility to predation.
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