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

Authors: Reinhart, Kurt; DANGI, SADIKSHYA - Retired ARS Employee; Vermeire, Lance

Submitted to: Plant and Soil
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/8/2016
Publication Date: 7/1/2016
Publication URL: http://handle.nal.usda.gov/10113/5642502
Citation: Reinhart, K.O., Dangi, S.R., Vermeire, L.T. 2016. The effect of fire intensity, nutrients, soil microbes, and spatial distance on grassland productivity. Plant and Soil. 409:203-216 doi:10.1007/s11104-016-2957-3.

Interpretive Summary: • Problem- Understanding fire effects on rangelands depends partly on knowing the effect of fire on soil nutrients and knowing which nutrients limit plant biomass production. • Prediction- We assumed nitrogen limited biomass production and that shortly after fires nitrogen would be pulsed and result in increased plant production. • Accomplishment- Among 11 potential limiting nutrients, we found that manganese and phosphorus (P) likely limited semiarid rangeland biomass production. Nitrogen levels appeared adequate and did not limit plant productivity. These results may be specific to our field study in eastern Montana, however, other grasslands are known to be limited by P.

Technical Abstract: 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.