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Abstract Nitrogen (N) is a limiting nutrient for primary productivity in most terrestrial ecosystems, but whether N limitation is strengthening or weakening remains controversial because both N sources and sinks are increasing in magnitude globally. Temperate marshes are exposed to greater amounts of external N inputs than most terrestrial ecosystems and more than in preindustrial times owing to their position downstream of major sources of human‐derived N runoff along river mouths and estuaries. Simultaneously, ecosystem N demand may also be increasing owing to other global changes such as rising atmospheric [CO2]. Here, we used interannual variability in external drivers and variables related to exogenous supply of N, along with detailed assessments of plant growth and porewater biogeochemistry, to assess the severity of N‐limitation, and to determine its causes, in a 14‐year N‐addition × elevated CO2experiment. We found substantial interannual variability in porewater [N], plant growth, and experimental N effects on plant growth, but the magnitude of N pools through time varied independently of the strength of N limitation. Sea level, and secondarily salinity, related closely to interannual variability in growth of the dominant plant functional groups which drove patterns in N limitation and in porewater [N]. Experimental exposure of plants to elevated CO2and years with high flooding strengthened N limitation for the sedge. Abiotic variables controlled plant growth, which determined the strength of N limitation for each plant species and for ecosystem productivity as a whole. We conclude that in this ecosystem, which has an open N cycle and where N inputs are likely greater than in preindustrial times, plant N demand has increased more than supply.
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Element stoichiometry and nutrient limitation in bog plant and lichen species
Abstract Ombrotrophic bogs receive new inputs of elements solely through atmospheric deposition, except for N where inputs are predominantly through N 2 -fixation, at least in low N deposition environments. At various locations across the globe, including the Athabasca Oil Sands Region (AOSR) of northern Alberta, Canada, element atmospheric deposition has increased as a result of anthropogenic activities. Regional and/or global deposition gradients offer an opportunity to examine questions related to nutrient limitation and element stoichiometry, i.e., the maintenance of relatively constant element ratios in bog lichen/plant tissues despite differing element deposition/availability. Using a dataset of tissue element concentrations in eight lichen/plant species in six AOSR bogs, supplemented with literature data from other sites globally, this synthesis asks: is there evidence of element stoichiometric homeostasis in lichen or plant species in AOSR bogs; if so, do stoichiometric homeostasis relationships extend globally beyond the AOSR, and; do element ratios provide insight into element limitation for the eight species? Mean element ratios and their coefficients of variation, ternary NPK and CaMgK plots, and scaling coefficients revealed widespread evidence of stoichiometric homeostasis. Stoichiometric relationships generally were unaffected by differences in element deposition among the AOSR bogs. Stoichiometric relationships sometimes extended to a species globally, but sometimes did not. Element ratios and ternary diagrams suggested a combination of N-, P-, and K-limitation, both within and beyond the AOSR bogs. Regionally high atmospheric N deposition may have shifted some species from N-limitation prior to the Industrial Revolution to P- or K-limitation today.
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- Award ID(s):
- 1726705
- PAR ID:
- 10398701
- Date Published:
- Journal Name:
- Biogeochemistry
- Volume:
- 160
- Issue:
- 3
- ISSN:
- 0168-2563
- Page Range / eLocation ID:
- 355 to 379
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1007/s10533-022-00968-y
