Plant Community and Soil Microbial Carbon and Nitrogen Responses to Fire and Clipping in a Southern Mixed Grassland

Abstract

Disturbances, such as fire and grazing, play important roles in determining grassland plant community composition and soil microbial dynamics, as well as regulating the flows of carbon (C) and nitrogen (N) between the two groups of organisms. In a mixed grassland of the southern Great Plains, we tested the hypotheses that spring-season fire would increase the absolute biomass and relative proportion of C 4 grasses in the plant community, and decrease soil microbial biomass N, thereby increasing microbial C:N ratios. We also tested the hypothesis that clipping (to simulate grazing) would reduce effects of fire, with a greater reduction of fire effect corresponding to an increased frequency of clipping. Contrary to our hypothesis, C 4 grasses showed no significant treatment responses. Treatment effects were limited to C 3 grasses, and clipping was more important than fire in terms of effects on plant community composition. However, because of its greater capacity to reduce aboveground litter, fire had the greater impact on soil microbial C. Contrary to the hypothesized outcome, no significant effects of disturbance on soil microbial N were observed. This suggests that control of N cycling in this ecosystem is primarily microbial in nature, though dependent on inputs of plant C via litter. Interactions between fire and clipping were observed in litter mass, highlighting the importance of litter inputs for plant-soil nutrient feedbacks. Resumen Perturbaciones, tales como el fuego y el pastoreo, juegan roles importantes en determinar la composición en las comunidades de pastizales y en las dinámicas microbianas del suelo, así como en la regulación del flujo de C y N entre los dos grupos de organismos. En unos pastizales mixtos de las Grandes Planicies del Sur, nosotros probamos la hipótesis de que los fuegos de primavera aumentarían la biomasa absoluta y la proporción relativa de hierbas C 4 en las comunidades de plantas, y disminuiría el N en la biomasa microbiana del suelo, de ese modo se incrementaría las raciones microbianas de C:N. Nosotros también pusimos a prueba la hipótesis de que el corte (para estimular el pastoreo) podría reducir los efectos del fuego, con una reducción mayor del efecto del fuego correspondería a un aumento en la frecuencia de recorte. Contrario a nuestra hipótesis, las gramas C 4 mostraron respuestas no significativas al tratamiento. Los efectos del tratamiento se limitaron a los gramas C 3 , donde el corte fue más importante que el fuego en términos de efectos de la composición en comunidad vegetal. Sin embargo, debido a su mayor capacidad para reducir la hojarasca superficial, el fuego tiene el mayor impacto en el C microbiano del suelo. Contrario a la hipótesis propuesta, no se observaron efectos de perturbación significativa en el N microbiano del suelo. Esto sugiere que el control del ciclo de N en este ecosistema es principalmente microbiano en naturaleza, aunque

Net Carbon Fluxes Over Burned and Unburned Native Tallgrass Prairie

“…For example, a number of studies have reported decreases in soil organic C following fire (Ajwa et al 1999;Harris et al 2008), particularly in dry years (Garcia and Rice 1994), which supports results from our study. Other researchers, however, have reported increases in soil organic C in response to fire Dai et al 2006), while others reported no change in soil organic content after fire (Fynn et al 2003).…”

Incorporating Biodiversity Into Rangeland Health: Plant Species Richness and Diversity in Great Plains Grasslands

“…Although some studies have investigated how short-and mixed-grass prairie plant assemblages in GPG respond to fire in combination with ungulate grazing (e.g., Erichsen-Arychuk et al 2002;Harris et al 2008), we found none that reported plant species richness or diversity. Similarly, although prairie dog colonies tend to expand more quickly into burned than unburned areas (Milne-Laux and Sweitzer 2006;Augustine et al 2007), we found no studies investigating their interactive effects on plant richness and diversity.…”

Effect of fires on soil organic carbon pool and mineralization in a Northeastern China wetland

“…This result is accordance with Kara and Bolat (2009) who also found no significant differences in MBC between the burned and unburned soils. In other studies, however, it was reported that soil MBC was reduced after burning (Harris et al, 2008;Palese et al, 2004), because of decreased above-ground litter, lower burning intensity, and cold and rainy weather over these study areas. Similarly, Choromanska and DeLuca (2002) observed that repeated burning can diminish MBC relative to soils that have been only burnt once.…”