Do Soil Chemical Changes Contribute to the Dominance of Blady Grass (<i>Imperata cylindrica</i>) in Surface Fire-Affected Forests?

• Main Authors: Orpheus M. Butler, Tom Lewis, Chengrong Chen
• Format: Article
• Language: English
• Published: MDPI AG 2021-05-01
• Series: Fire
• Subjects: burning; stoichiometry; nutrient limitation; phosphorus; nitrogen; alang-alang
• Online Access: https://www.mdpi.com/2571-6255/4/2/23

<i>Imperata cylindrica</i> is a perennial grass that often proliferates in fire-affected forests. Recent fire events have been consistently associated with a lowering of soil nitrogen (N) to phosphorus (P) ratios. Thus, <i>I. cylindrica</i> might have a tendency toward P-limited growth and/or tolerance for low soil N availability that confers a competitive advantage post-fire. We contrasted soil and <i>I. cylindrica</i> chemistry between recently burned and unburned areas in eastern Australia. <i>Imperata cylindrica</i> foliar N:P ratios were 21% lower in burned areas than in unburned areas, reflecting an increase in the uptake of P, but not N, post-fire, consistent with P-limitation. We then grew <i>I. cylindrica</i> seedlings in soils with differing fire-exposure histories and subjected them to various resource amendments (including N and P addition). Survival of <i>I. cylindrica</i> seedlings was not affected by the fire-exposure history of soil, but was reduced by 66% through N-addition. Soil fire history did not significantly affect <i>I. cylindrica</i> growth, but addition of P greatly enhanced <i>I. cylindrica</i> growth, particularly on unburned soils. Our results indicate that the association between <i>I. cylindrica</i> and forest fire regime could be facilitated, in part, by the short-term positive effect of fire on soil phosphorus and the long-term positive effect of fire-exclusion on soil nitrogen, particularly on well-weathered soils.