Soil N and Plant Responses to Fire, Topography, and Supplemental N in Tallgrass Prairie

Abstract

Tallgrass prairie in the Flint Hills region of Kansas is characterized by considerable topographic relief coupled with variation in soil properties. These topoedaphic gradients, together with variation in fire regimes, result in temporal and landscape‐level variability in soil resource availability and plant responses. Nitrogen usually is considered to be the nutrient most limiting to primary productivity in tallgrass prairie, but few studies have addressed how N availability varies seasonally, or across the landscape and with fire frequency. We measured soil inorganic N, in situ net N mineralization, aboveground net primary productivity (ANPP), and N mass on plots either fertilized with N in 1993 or in 1994, or unfertilized, in uplands and lowlands of two annually burned and two long‐term unburned sites during the 1994 growing season. In addition, our study was conducted in the year following record rainfall, allowing us to assess the potential for high precipitation amounts to affect subsequent N cycling and plant production. Both fire treatment and topography affected soil N availability. In general, N mineralization was greater on unburned than on burned sites and was up to five times greater on uplands than lowlands. Total extractable soil N was highest early in the season and least at midseason, and it also tended to be higher in unburned sites than burned sites on unfertilized plots. Added N increased ANPP, but there were no differences between plots fertilized in 1994 and those fertilized in 1993. In general, patterns of ANPP on control plots were consistent with known production responses to topography and burning (higher in annually burned sites and in lowland sites) but were inversely related or unrelated to patterns of N availability (higher in unburned sites and at upland topographic positions). Potential loss of N by volatilization during spring burning was greater than in years with normal rainfall amounts and represented a significant portion of aboveground plant N mass. Potential N losses did not appear to limit ANPP or N availability in the current growing season. Our results suggest that different factors control soil N mineralization and plant productivity, which explains, in part, why patterns of ANPP are not well correlated with patterns of N availability in tallgrass prairie ecosystems.

Nitrogen and carbon dynamics in prairie vegetation strips across topographical gradients in mixed Central Iowa agroecosystems

“…Regarding mowing and spring burning, these stimulate plant productivity of prairie vegetation, influence biotic N incorporation into vegetative tissue of plants, and alter species composition (Carter et al, 2000;Turner et al, 1997). Thus, these two common restoration tools may increase the capacity of PVS to take up additional N from fertilizer applied into the crop areas between the strips.…”

“…For example, although mowing and burning influencing the presence of forbs, burning declined plant richness (Carter et al, 2000). With respect to N cycling, Maron and Jefferies (2001) found substantially greater amounts of N in prairie soils with mowing, while fire reduced net N mineralization, N availability, and plant uptake, while promoting immobilization of existing N in the organic fraction of soil from turnover of organic matter of lower quality (low N content and high C:N ratio; Anderson et al, 2006;Blair, 1997;Turner et al, 1997).…”

“…Research conducted in restored and native tallgrass prairie ecosystems showed that both N cycling and availability Turner et al, 1997), as well as plant N uptake and C storage (Knapp et al, 1993;Nippert et al, 2011;Turner et al, 1997) varied by slope position. However, knowledge about the specific mechanisms that control spatio-temporal fluxes of N and C within PVS located in different landscape positions and embedded within a matrix of annual crops is lacking (Lovell and Sullivan, 2006).…”

Macroinvertebrates in North American tallgrass prairie soils: effects of fire, mowing, and fertilization on density and biomass

“…Nitrogen is generally considered to be the nutrient most limiting to plant productivity in these grasslands (Seastedt et al, 1991;Turner et al 1997), though soil P availability is also low and can influence plant community composition via plantmycorrhizal interactions (Hartnett and Wilson, 1999). Frequent fires result in large N losses due to combustion of plant tissues and associated volatilization of N (Ojima et al, 1994;Blair et al, 1998).…”

Relação entre distribuição de espécies arbóreas e topografia em um gradiente florestal na Estação Ecológica do Panga (Uberlândia, MG)

“…Benincasa et al (1983) e Basnet (1992) destacam a diversidade de microclimas no gradiente topográfico, variando conforme o tipo de solo, regimes de umidade, formação geológica e altitude, sendo respondido pelos vegetais pela variação da área foliar e diferença de produção, em compensação à quantidade de energia incidente. Turner et al (1997), Fisk et al (1998) e Loreti & Oesterheld (1996) mostram que os processos de ciclagem de nutrientes estão relacionados com variações espaciais de umidade entre as áreas elevadas, que tendem a ser mais secas, e as partes baixas, onde a umidade tende a ser maior. Para Dwyer & Merrian (1981), Vivian-Smith (1997) e Eldridge et al (1991), as variações microtopográficas são responsáveis pela captura de matéria orgânica e sementes, gerando microambientes que determinam a intensidade de ocorrência de microorganismos, germinação, estabelecimento e mortalidade de plântulas.…”