Nutrient pulses after prescribed winter fires and preferential patterns of N uptake may contribute to the expansion of Brachypodium pinnatum (L.) P. Beauv. in highland grasslands

Abstract

Question Do prescribed winter fires – authorized to prevent shrub encroachment and control necromass accumulation in protected grassland communities – promote significant changes in soils and in the pool of nutrients available to plants? Does Brachypodium pinnatum, an expanding native grass, take better advantage of the most dynamic nutrient pulse, that of N, than other dominant native grasses? Location Aezkoa commons, western Pyrenees. Methods We scheduled experimental winter burnings in three semi‐natural grasslands with incipient shrub encroachment and tracked the short‐term physical–chemical changes produced in the soil. During the peak biomass period, we performed a stable isotope field experiment in order to follow the fate of three different chemical forms of labelled N (15NO3−, 15NH4+ and 13C2‐15N‐glycine) in 48 undisturbed stands of B. pinnatum and Festuca gr. rubra. Results The soil pools of available phosphorus, potassium and ammonium significantly increased after the fire. Four months later, a pulse of nitrate was also recorded. The isotopic labelling experiment revealed that, although the three forms of N were absorbed by the grasses, significant differences in 15N tissue enrichment appeared after 48 h. Altogether, the results indicated a higher response of B. pinnatum to the NH4+ pulse than F. rubra, although the latter was able to absorb intact glycine, unlike B. pinnatum. Conclusions Controlled winter burnings, despite being low intensity, cause a significant release of the main nutrients associated with plant growth. This makes the plant community more susceptible to floristic changes. The field experiment suggests that B. pinnatum may make better use of the post‐fire NH4+ pulse than F. rubra. This preferential uptake, together with other competing mechanisms of the species, may trigger the expansion of B. pinnatum in burned areas.

Does disturbance enhance the competitive effect of the invasive Solidago canadensis on the performance of two native grasses?

“…Therefore, fire can eliminate all aboveground plant parts with active meristematic tissues, and may also reduce the viability and/or activation of axillary buds of perennial grasses (Busso et al 1993). However, burning might have several advantages for grasses: fire accelerates the mineralization of organic matter thus increasing nutrient availability (Canals et al 2014); fire may stimulate resprouting and promote growth by depleting allelopathic substances (Vilà et al 2001), and also reduce pathogen density in soil (Keeley and Fotheringham 2000). Despite these potential effects, our experimental burning had no impact on the vegetative performance and allocation of B. pinnatum grown without competition.…”

Disturbance maintains native and exotic plant species richness in invaded grassy woodlands

“…), provide a temporary nutrient pulse (Canals et al. ), reduce pathogens (Roy et al. ), reduce litter (Guthrie et al.…”

“…However, fire has effects beyond biomass removal, which may influence the outcome for restoration. Fire can stimulate soil seed banks (Potts & Stephens 2009;Gomez-Gonzalez et al 2011), provide a temporary nutrient pulse (Canals et al 2014), reduce pathogens (Roy et al 2014), reduce litter (Guthrie et al 2016) and drive overall nutrient losses (Kauffman et al 1995;Holdo et al 2007).…”

Land use change effects on carbon and nitrogen stocks in the Pyrenees during the last 150 years: A modeling approach

“…Nutrient demands were also obtained from literature sources (Dordas, 2012;Duke, 1983). Data on pastures came from field observations by the authors (Canals et al, 2014;Canals and San Emeterio, unpub. data).…”

“…These effects include, but are not limited to: (1) substantial nutrient removals in harvested timber, influencing the balance of remaining plantavailable nutrients in the long term (Blanco et al, 2005); (2) physical effects of ploughing, which changes soil structure, influencing soil oxygenation, water retention, and water flow, which in turn affects mineralization rates of soil organic matter (SOM) (Ballard, 2000); (3) canopy removal during thinning or harvesting, affecting soil temperature and moisture regimes (Blanco, 2004); (4) prescribed fire or slash burning, resulting in substantial nutrient pulses (Canals et al, 2014), which may be used by the new vegetation or may be lost from the system through volatilization (notably of N and S) and, in some cases, fly-ash losses (Kimmins, 1997); and (5) changes in nutrient content and availability by fertilization, which is some cases could result in soil acidification from nitrification (Ballard, 2000). All these effects have a direct translation into reducing soil fertility in the long-term, affecting ecosystem productivity and C storage capacity (Morris et al, 1997;Wei and Blanco, 2014).…”