Variation in nitrogen deposition and available soil nitrogen in a forest–grassland ecotone in Canada

Summary1 Herbivores can play a key role in affecting ecosystem function, but their direct and indirect effects are often confounded with each other and have rarely been dissected. Predictions for open systems, i.e. those with cross-habitat nutrient fluxes and dispersal, may differ from those expected in closed systems, where no such transfers occur, but these differences have only recently begun to be characterized. 2 We present a theoretical model of plant productivity and soil nitrogen (N) based on the Serengeti ecosystem in order to investigate the interplay among herbivore movement, nutrient transport across habitats (spatial subsidies), the fire regime and the effects of herbivores on N cycling. 3 Model results suggest that the fire regime and herbivore migration are key determinants of primary productivity and fertility, and that the impact of these factors depends on grazing intensity. At low intensity, high grass biomass leads to extensive fires and N volatilization, but this effect is reduced at high grazing intensity. Without migration, the model predicts that primary productivity and fertility initially increase, then decline with increasing grazing intensity. Conversely, seasonal migration decouples the growing and grazing seasons, leading to a monotonic increase in productivity with grazing intensity. Cross-habitat N transport has a relatively modest effect on N dynamics, and the magnitude of the seasonality effect outweighs the spatial subsidy effect. 4 Our model suggests that herbivores and fire may play key interactive roles in regulating producers and determining ecosystem functional properties in grazing systems, both through consumption and via indirect effects on nutrient availability. The direction and magnitude of these effects could potentially vary greatly among ecosystems with resident vs. migratory herbivores, suggesting that spatial coupling through animal movement can be important at both the population and ecosystem levels. 5 This study suggests that the degree to which trophic interactions influence ecosystem function may be strongly modulated by whether systems are open or closed. It also suggests that direct and indirect effects of consumers on their resources (top-down effects) may be far more important than nutrient subsidies in open terrestrial systems.

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“…1999; Knapp et al . 1999; Kochy & Wilson 2005) and community structure and composition (Collins et al . 1998).…”

Section: Discussionmentioning

confidence: 99%

Plant productivity and soil nitrogen as a function of grazing, migration and fire in an African savanna

et al. 2006

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“…Treatments were applied in a 2 · 2 factorial design of fertilizer (+F = fertilizer added, -F = no fertilizer) and plant litter (-L = litter removed, +L = litter left in situ after yearly mowing) with the control plots characterized as no fertilization and plant litter left in situ (+L/-F), resulting in six replicates per treatment. In April 2002 and continuing each April through 2005, Scotts brand Osmocote 8-9 month Slow Release Fertilizer 19-6-12 (NPK; Scotts, Marysville, OH, USA) was applied at 200 kg N ha -1 (20 g N m -2 ) in fertilized plots, well above the Köchy and Wilson (2005) 15 g N m -2 yr -1 threshold necessary to induce a eutrophication effect in grasslands and other habitats. We could not exclude ambient wet/dry atmospheric N deposition, though deposition rates from 1990 to 2005 were relatively low at approximately 10.1 kg N ha -1 yr -1 (1.01 g N m -2 yr -1 ) at a nearby monitoring site in Lykens (162 km west of our study site), OH, USA, and approximately 9.3 kg N ha -1 yr -1 (0.93 g N m -2 yr -1 ) at another nearby monitoring site in Mercer Co. (G. K. Goddard site; 96 km east of our study site), PA, USA (US EPA 2005).…”

Section: Study Site and Experimental Designmentioning

confidence: 99%

Large-scale manipulation of plant litter and fertilizer in a managed successional temperate grassland

2007

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Plant litter may play an important role in herbaceous plant communities by limiting primary production and influencing plant species richness. However, it is not known how the effect of litter interacts with fertilization. We tested for the role of litter and fertilization in a large-scale experiment to investigate effects on diversity and biomass of plant species, growth forms, native vs. non-native groups, and abiotic ecosystem components (e.g., soil moisture, PAR). We manipulated plant litter (removed vs. left in situ) and nutrient availability (NPK-fertilized vs. unfertilized) for 4 years in 314-m 2 plots, replicated six times, in an old-field grassland. While many of our species-level results supported previously published studies and theory, our plant group results generally did not. Specifically, grass species richness and forb biomass was not affected by either fertilization or plant litter. Moreover, plant litter removal significantly increased non-native plant species richness. Relative to native plant species, all of our experimental manipulations significantly increased both the biomass and the species richness of nonnative plant species. Thus, this grassland system was sensitive to management treatments through the facilitation of non-native plant species. We coupled biotic and abiotic components within a nonmetric multidimensional scaling (NMS) analysis to investigate treatment effects, which revealed that specific treatments altered ecosystem development. These results suggest that fertilization and plant litter may have larger impacts on plant communities and on ecosystem properties than previously understood, underscoring the need for larger-scale and longerterm experiments.

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“…Thirdly, extremely arid croplands are subject to substantial drying and wetting and freezing and thawing cycles than other locations due to the high frequency of irrigation and longer winters (November to April). Numerous studies have demonstrated that alternating drying and wetting and freezing and thawing can accelerate the mineralization of soil organic matter [39–40]. This could lead an increase in N min derived from the mineralization of soil organic matter.…”

Section: Discussionmentioning

confidence: 99%

Highly Arid Oasis Yield, Soil Mineral N Accumulation and N Balance in a Wheat-Cotton Rotation with Drip Irrigation and Mulching Film Management

Liu

Wang

et al. 2016

PLoS ONE

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Few systematic studies have been carried out on integrated N balance in extremely arid oasis agricultural areas. A two-year field experiment was conducted to evaluate the N input and output balances under long-term fertilization conditions. Five treatments were chosen, namely CK (no fertilizer), NPK, NPKS (10% straw return N and 90% chemical N), NPKM (one third urea-N, two thirds sheep manure) and NPKM+ (1.5 times NPKM). The results show an abundance of dry and wet N deposition (33 kg N ha-1 yr-1) in this area. All treatments (excluding CK) showed no significant difference in wheat production (P>0.05). NPKM gave higher cotton yields (P<0.05). In both crops, NPKM and NPKS treatments had a relatively higher N harvest index (NHI). 15N-labeled results reveal that the fertilizer N in all N treatments leached to<1 m depth and a high proportion of fertilizer-N remained in the top 60 cm of the soil profile. The NPKM+ treatment had the highest residual soil mineral N (Nmin, 558 kg Nd ha-1), and NPKM and NPKS treatments had relatively low soil Nmin values (275 and 293 kg N ha-1, respectively). Most of the treatments exhibited very high apparent N losses, especially the NPKM+ treatment (369kg N ha-1). Our arid research area had a strikingly high N loss compared to less arid agricultural areas. Nitrogen inputs therefore need careful reconsideration, especially the initial soil Nmin, fertilizer N inputs, dry and wet deposition, and appropriate organic and straw inputs which are all factors that must be taken into account under very arid conditions.

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Variation in nitrogen deposition and available soil nitrogen in a forest–grassland ecotone in Canada

Cited by 13 publications

References 56 publications

Plant productivity and soil nitrogen as a function of grazing, migration and fire in an African savanna

Plant productivity and soil nitrogen as a function of grazing, migration and fire in an African savanna

Large-scale manipulation of plant litter and fertilizer in a managed successional temperate grassland

Highly Arid Oasis Yield, Soil Mineral N Accumulation and N Balance in a Wheat-Cotton Rotation with Drip Irrigation and Mulching Film Management

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