High‐frequency fire alters C : N : P stoichiometry in forest litter

Abstract

Fire is a major driver of ecosystem change and can disproportionately affect the cycling of different nutrients. Thus, a stoichiometric approach to investigate the relationships between nutrient availability and microbial resource use during decomposition is likely to provide insight into the effects of fire on ecosystem functioning. We conducted a field litter bag experiment to investigate the long-term impact of repeated fire on the stoichiometry of leaf litter C, N and P pools, and nutrient-acquiring enzyme activities during decomposition in a wet sclerophyll eucalypt forest in Queensland, Australia. Fire frequency treatments have been maintained since 1972, including burning every 2 years (2yrB), burning every 4 years (4yrB) and no burning (NB). C : N ratios in freshly fallen litter were 29-42% higher and C : P ratios were 6-25% lower for 2yrB than NB during decomposition, with correspondingly lower 2yrB N : P ratios (27-32) than for NB (34-49). Trends in litter soluble and microbial N : P ratios were similar to the overall litter N : P ratios across fire treatments. Consistent with these, the ratio of activities for N-acquiring to P-acquiring enzymes in litter was higher for 2yrB than NB, whereas 4yrB was generally intermediate between 2yrB and NB. Decomposition rates of freshly fallen litter were significantly lower for 2yrB (72 AE 2% mass remaining at the end of experiment) than for 4yrB (59 AE 3%) and NB (62 AE 3%), a difference that may be related to effects of N limitation, lower moisture content, and/or litter C quality. Results for older mixed-age litter were similar to those for freshly fallen litter although treatment differences were less pronounced. Overall, these findings show that frequent fire (2yrB) decoupled N and P cycling, as manifested in litter C : N : P stoichiometry and in microbial biomass N : P ratio and enzymatic activities. Furthermore, these data indicate that fire induced a transient shift to N-limited ecosystem conditions during the postfire recovery phase.

Flexible Carbon-Use Efficiency across Litter Types and during Decomposition Partly Compensates Nutrient Imbalances—Results from Analytical Stoichiometric Models

“…With these values at the beginning and at the end of the decomposition process, the slope is found as β = −0.04. This trend implies an increasing microbial biomass N:C as decomposition progresses and litter N:C ratio increases, as suggested by data (Wagener and Schimel, 1998; van Meeteren et al, 2008; Brandstäetter et al, 2013; Toberman et al, 2014). Moreover, with this parameterization of model III, the value of r B at x = 0.5 is consistent with the long-term average r B = 0.1 assumed for models I and II.…”

“…However, in decomposing litter undergoing strong nutrient enrichment, some trends in microbial biomass N:C have been found. In some studies, microbial N:C increases with increasing litter N:C as decomposition progresses (Wagener and Schimel, 1998; van Meeteren et al, 2008; Brandstäetter et al, 2013; Toberman et al, 2014), but in others no trends are apparent (Mooshammer et al, 2014a). Along the extreme stoichiometric gradient between a decaying log and the nearby soil (assuming that the latter is representative of the final phases of wood decomposition), only small differences in microbial biomass elemental composition were found, despite the four-fold increase in N:C ratio (Hart, 1999).…”

Soil fungal communities respond compositionally to recurring frequent prescribed burning in a managed southeastern US forest ecosystem

“…Most commonly in forest ecosystems, fires tend to reduce soil organic matter and nutrient availability in the short term, although the addition of burnt plant material can increase these parameters in the long-term (PrietoFernández et al, 2004;Certini, 2005). Williams et al (2011) andToberman et al (2014) observed that a greater frequency in prescribed fires lead to greater loss in available soil nutrients in the long-term. We observed no, or only minimal, differences in the soil parameters (pH, total N, and total C) across the different burn treatments, even though our experimental manipulations have been in place for two decades.…”

The stoichiometric legacy of fire regime regulates the roles of micro‐organisms and invertebrates in decomposition

“…Each treatment consisted of 4 randomized burning plots (as described by Toberman et al. ), with 12 burning plots in total. Each of these burning plots was ca.…”

“…Recent or repeated fire events are often associated with N‐depleted and P‐enriched stoichiometry (i.e., lower N : P and C : P) in soil and plant material (Toberman et al. , Muqaddas et al. , Butler et al.…”