Defoliation effects on resource allocation in Arizona cottontop (Digitaria californica) and Lehmann lovegrass (Eragrostis lehmanniana)

Abstract

Arizona cottontop (Digitaria californica), a bunchgrass native to the Chihuahuan and Sonoran Deserts in North America, and Lehmann lovegrass (Eragrostis lehmanniana), a bunchgrass introduced to the southwestern USA from southern Africa, were defoliated and examined for above‐ and below‐ground productivity, nitrogen and phosphorus allocation, and photosynthetic potential. Stems plus sheaths from which leaf blades have been removed may be important to Lehmann lovegrass because this tissue is photosynthetically active and contains nitrogen and phosphorus reserves. After defoliation, Arizona cottontop re‐established a canopy more quickly than Lehmann lovegrass but differences were due to greater numbers and growth rates of Arizona cottontop leaves. Rapid Arizona cottontop leaf growth was followed by a 50% decline in below‐ground biomass. Lehmann lovegrass had a lower investment in above‐ and below‐ground biomass, nitrogen and phosphorus per plant. Grazing tolerance associated with Lehmann lovegrass may be related to the prostrate form of regrowing leaves and a dense but shallow root system.