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N Enrichment (n + enrichment)
Selected AbstractsTradeoffs and thresholds in the effects of nitrogen addition on biodiversity and ecosystem functioning: evidence from inner Mongolia GrasslandsGLOBAL CHANGE BIOLOGY, Issue 1 2010YONGFEI BAI Abstract Nitrogen (N) deposition is widely considered an environmental problem that leads to biodiversity loss and reduced ecosystem resilience; but, N fertilization has also been used as a management tool for enhancing primary production and ground cover, thereby promoting the restoration of degraded lands. However, empirical evaluation of these contrasting impacts is lacking. We tested the dual effects of N enrichment on biodiversity and ecosystem functioning at different organizational levels (i.e., plant species, functional groups, and community) by adding N at 0, 1.75, 5.25, 10.5, 17.5, and 28.0 g N m,2 yr,1 for four years in two contrasting field sites in Inner Mongolia: an undisturbed mature grassland and a nearby degraded grassland of the same type. N addition had both quantitatively and qualitatively different effects on the two communities. In the mature community, N addition led to a large reduction in species richness, accompanied by increased dominance of early successional annuals and loss of perennial grasses and forbs at all N input rates. In the degraded community, however, N addition increased the productivity and dominance of perennial rhizomatous grasses, with only a slight reduction in species richness and no significant change in annual abundance. The mature grassland was much more sensitive to N-induced changes in community structure, likely as a result of higher soil moisture accentuating limitation by N alone. Our findings suggest that the critical threshold for N-induced species loss to mature Eurasian grasslands is below 1.75 g N m,2 yr,1, and that changes in aboveground biomass, species richness, and plant functional group composition to both mature and degraded ecosystems saturate at N addition rates of approximately 10.5 g N m,2 yr,1. This work highlights the tradeoffs that exist in assessing the total impact of N deposition on ecosystem function. [source] Beyond biomass: measuring the effects of community-level nitrogen enrichment on floral traits, pollinator visitation and plant reproductionJOURNAL OF ECOLOGY, Issue 3 2010Laura A. Burkle Summary 1.,Nitrogen (N) limits primary productivity in many systems and can have dramatic effects on plant,herbivore interactions, but its effects on mutualistic interactions at the community level are not well-understood. The reproduction of many plants depends on both soil N and pollination, and N may affect floral traits, such as flower number or size, which are important for pollinator attraction to plant individuals and communities. 2.,Thus, N may influence plant biomass and reproduction directly as well as indirectly via changes in pollination. The degree to which the effects of N enrichment scale from plant individuals to assemblages through emerging community-level changes in species interactions, like pollination, is relatively unknown. 3.,For 4 years, we tested how N addition to subalpine plant assemblages in Colorado, USA, affected primary productivity and species diversity, floral traits and plant,pollinator interactions, and components of female and male plant reproduction. 4.,At the community level, we found that high-N addition favoured the biomass and seed production of grasses, whereas low-N addition promoted forb growth, flower production and pollinator visitation. However, using a pollen supplementation experiment, we found no evidence that N addition altered patterns of pollen limitation of seed production. Pollinators distributed themselves evenly across floral resources such that per-flower visitation rate did not differ among N treatments. Thus, individual plants did not incur any extra benefit or cost from community-level changes in plant,pollinator interactions that resulted from N enrichment, and the effects of N on forb reproduction were direct. 5.,Synthesis. Understanding how mutualistic and antagonistic species interactions influence individual and community responses to abiotic resources may provide insight to the dominant forces structuring communities and is especially important in the context of predicting the effects of environmental change. In this case, the direct effects of N addition on plants were stronger than the indirect effects mediated through plant,pollinator interactions, thus supporting the concept of bottom-up resource limitation controlling plant response. [source] NITROGEN ENRICHMENT OF PORPHYRA PERFORATA THROUGH HIGH DOSE PULSE FERTILIZATIONJOURNAL OF PHYCOLOGY, Issue 2001Article first published online: 24 SEP 200 Zertuche-González, J. A1., Chanes-Miranda L2., Carmona, R3., Kraemer G4., Chopin T.5 & Yarish, C3 1Universidad Autonoma de Baja California, Instituto de Investigaciones Oceanologicas, PO Box #453, C.P. 22830, Ensenada, Baja California, Mexico. 2CBTIS-41, Km 115 Carretera Transpeninsular, Ensenada, BC Mexico. 3University of Connecticut, Department of Ecology and Evolutionary Biology, 1 University Place, Stamford, CT, 06901-2315, USA. 4State University of New York, Purchase College, Div. of Nat. Sciences, Purchase, NY, 10577, USA. 5University of New Brunswick, Centre for Coastal Studies and Aquaculture and Centre for Environmental and Molecular Algal Research, P.O. Box 5050, Saint John, New Brunswick, E2L 4L5, Canada Porphyra perforata is a highly preferred seaweed used as fodder in abalone culturing due to its relatively high nutritional value. High growth rates of abalone, particularly in the early stages, are suspected to be due the high protein-aminoacid and low water content of the Porphyra. Also, high NO3 content may be important to improve the bacterial flora in the animals, which in turn may favor more efficient digestion. Changes in the composition of Porphyra, however, can occur rapidly due to environmental conditions decreasing the nutritional value of the plant. Short term N pulse fertilization were performed on P. perforata in order to evaluate the feasibility to increase its nutritional value. Enrichment was performed under low light conditions (<5 ,E m -2 s -1) to inhibit growth and promote higher N enrichment per unit of biomass. Tissue N in the form of NO3, NH4 and total organic N were measured, after 3,6,12 and 24 hrs, in tissue exposed to 500 ,M of N. Results indicated a rapid N tissue enrichment particularly in the form of NO3. Nitrate accumulation occurs continuously, up to 24 hrs. Total organic N is maximum after 12 hrs and tends to decrease after that. Fertilization with NH4 promotes NO3 accumulation. These results suggest the feasibility to improve the nutritional value of P. perforata by short-term pulse fertilization. The capacity of this species to uptake NH4 under low light conditions (similar to those use in abalone culturing) makes it also ideal for integrated aquaculture. [source] Understorey plant and soil responses to disturbance and increased nitrogen in boreal forestsJOURNAL OF VEGETATION SCIENCE, Issue 2 2009O.H. Manninen Abstract Question: How do N fertilization and disturbance affect the understorey vegetation, microbial properties and soil nutrient concentration in boreal forests? Location: Kuusamo (66°22,N; 29°18,E) and Oulu (65°02,N; 25°47,E) in northern Finland. Methods: We conducted a fully factorial experiment with three factors: site (two levels), N fertilization (four levels) and disturbance (two levels). We measured treatment effects on understorey biomass, vegetation structure, and plant, soil and microbial N and C concentrations. Results: The understorey biomass was not affected by fertilization either in the control or in the disturbance treatment. Fertilization reduced the biomass of deciduous Vaccinium myrtillus. Disturbance had a negative effect on the biomass of V. myrtillus and evergreen Vaccinium vitis-idaea and decreased the relative proportion of evergreen species. Fertilization and disturbance increased the biomass of grass Deschampsia flexuosa and the relative proportion of graminoids. The amount of NH4+ increased in soil after fertilization, and microbial C decreased after disturbance. Conclusions: Our results suggest that the growth of slow-growing Vaccinium species and soil microbes in boreal forests are not limited by N availability. However, significant changes in the proportion of dwarf shrubs to graminoids and a decrease in the biomass of V. myrtillus demonstrate the susceptibility of understorey vegetation to N enrichment. N enrichment and disturbance seem to have similar effects on understorey vegetation. Consequently, increasing N does not affect the rate or the direction of recovery after disturbance. Moreover, our study demonstrates the importance of understorey vegetation as a C source for soil microbes in boreal forests. [source] | ||||||||||