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The effect of fire intensity, nutrients, soil microbes, and spatial distance on grassland productivity

Kurt O. Reinhart, Sadikshya R. Dangi, Lance T. Vermeire
Plant and soil 2016 v.409 no.1-2 pp. 203-216
copper, ecological competition, fire ecology, fire intensity, fire season, grasslands, growing season, ion exchange resins, iron, magnesium, manganese, microbial biomass, models, nitrification, nitrogen, nutrients, phospholipid fatty acids, phosphorus, phytomass, potassium, primary productivity, soil microorganisms, soil nutrients, sulfur
Understanding nutrient limitation is essential for interpreting grassland dynamics and responses to disturbance(s). Effects of fire on the biomass of grassland plants and soil microbes is likely mediated by short-term pulses of limiting resources. We used a replicated fire ecology experiment with eight fire season and history treatments to interpret the nutrients that limit plant and soil microbe biomasses. We quantified plant biomass and living microbial biomass at peak plant productivity the first growing season after fire treatments in a semiarid and temperate grassland. Total microbial biomass was determined by phospholipid fatty acid (PLFA) analysis. During the two month period prior to biomass sampling, we measured flux in 11 soil nutrients with ion exchange resins. We used a pattern analysis approach to identify useful associations between soil nutrients and plant and microbial biomasses. We hypothesized the grassland plants and microbes would be limited mainly by nitrogen (N). Across the sampled gradient, moderate amounts of variation in annual net primary productivity (ANPP) was best explained by a model with magnesium (Mg), manganese (Mn), phosphorus (P), and sulfur (S). We determined that most of this variation was explained by Mn followed by P, S, and Mg. ANPP was positively associated with Mn and P (negatively associated with S and Mg) thereby suggesting that ANPP was limited by Mn and P. We then determined that moderate amounts of variation in surface microbial biomass were explained by iron (Fe), potassium (K), Mg, N, and P. Surface microbial biomass was positively associated with P and Fe (negatively associated with Mg, N, and K). Subsurface microbial biomass was explained by copper, Mg, N, and P. We determined that most of the variation in microbial biomass was explained by Mg and P. Microbial biomass was positively associated with P (negatively associated with Mg) thereby suggesting microbial biomass was also limited by P. Surface and subsurface microbial biomasses were negatively associated with N suggesting elevated levels of microbial biomass have temporarily immobilized N and/or contributed to N losses (i.e. nitrification). These findings indicate that multiple nutrients limit plant and microbial biomasses and the possibility for competition between plants and microbes for P.