Publications (4)80.48 Total impact
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Article: Resource-based niches provide a basis for plant species diversity and dominance in arctic tundra.
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ABSTRACT: Ecologists have long been intrigued by the ways co-occurring species divide limiting resources. Such resource partitioning, or niche differentiation, may promote species diversity by reducing competition. Although resource partitioning is an important determinant of species diversity and composition in animal communities, its importance in structuring plant communities has been difficult to resolve. This is due mainly to difficulties in studying how plants compete for below-ground resources. Here we provide evidence from a 15N-tracer field experiment showing that plant species in a nitrogen-limited, arctic tundra community were differentiated in timing, depth and chemical form of nitrogen uptake, and that species dominance was strongly correlated with uptake of the most available soil nitrogen forms. That is, the most productive species used the most abundant nitrogen forms, and less productive species used less abundant forms. To our knowledge, this is the first documentation that the composition of a plant community is related to partitioning of differentially available forms of a single limiting resource.Nature 02/2002; 415(6867):68-71. · 36.28 Impact Factor -
Article: Resource-based niches provide a basis for plant species diversity and dominance in arctic tundra
[show abstract] [hide abstract]
ABSTRACT: Ecologists have long been intrigued by the ways co-occurring species divide limiting resources. Such resource partitioning, or niche differentiation, may promote species diversity by reducing competitionNature 01/2002; 415(6867):68-71. · 36.28 Impact Factor -
Article: NITROGEN BIOGEOCHEMISTRY IN THE OLIGOHALINE ZONE OF A NEW ENGLAND ESTUARY
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ABSTRACT: We investigated nitrogen cycling in the oligohaline zone (the low-salinity region where river water first enters the estuary) of the Parker River estuary in northeastern Massachusetts. We introduced an isotopic tracer (15 N-NO 3 ï¿¿) for 27 days in August 1996 to help determine how watershed-derived nitrogen moves through the upper estuary. The amount of tracer added was sufficient to enrich nitrate isotopically by ï¿¿100‰ in the vicinity of the addition but did not influence nitrate concentration appreciably. During typical sum-mer low-flow conditions as occurred during the addition period, essentially all riverine nitrate (including the nitrate tracer) was rapidly removed from the water column by the planktonic diatom Actinocyclus normanii. Export of tracer down-estuary was low during the isotope addition period, in part because of low river discharge. Instead, most of the nitrogen originally assimilated by A. normanii was transferred to sediments in the oligo-haline zone. Nitrogen demand by phytoplankton during summer exceeded riverine supply by an order of magnitude. The additional nitrogen came mainly from the regeneration of benthic nitrogen, although some may have come from groundwater. The whole-ecosystem isotope tracer approach applied here was a powerful means of investigating the fate of watershed-derived nitrogen in the upper estuary.Ecology 01/2000; 81:416-432. · 4.85 Impact Factor -
Article: Effects of sulfate concentration in the overlying water on sulfate reduction and sulfur storage in lake sediments
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ABSTRACT: We investigated the effects of sulfate concentration on sulfate reduction and net S storage in lake sediments using34S as a tracer. The water overlying intact sediment cores from the hypolimnion of Mares Pond, MA, was replaced with two Na2 34SO4 solutions at either ambient (70 M) or elevated (260 M) sulfate concentrations. The 34S of the added sulfate was 4974 . Over two months, the net sulfate reduction rate in the ambient sulfate treatment was zero, while the net rate for the high sulfate treatment was 140 moles/m2/d. The water overlying the cores was kept under oxic conditions and the sediment received no fresh carbon inputs, thus the net rate reported may underestimate the in situ rate. Gross sulfate reduction rates calculated by isotope dilution were approximately 350 moles/m2/d for both treatments. While the calculation of gross sulfate reduction rates in intact sediment cores can be complicated by differential diffusion of34S and32S, isotopic fractionation, and the possible formation of ester sulfates, we believe these effects to be small. The results suggest that sulfate reduction is not strongly sulfate-limited in Mares Pond. The difference in net sulfate reduction rates between treatments resulted from a decrease in sulfide oxidation and suggests the importance of reoxidation in controlling net S storage in lake sediments. In both treatments the CRS and organic S fractions were measurably labelled in34S. Below the sediment surface, the CRS fraction was the more heavily labelled storage product for reduced sulfides.Biogeochemistry 12/1993; 24(3):129-144. · 3.07 Impact Factor
