Oral Session # 49: Invasive Species IV: Grasslands; Wetlands.
Presiding: F Hughes
Wednesday, August 6. 8:00 AM to 11:30 AM, SITCC Meeting Room 204.

Compensatory growth response across two nutrient regimes by invasive Arundo donax.

Sher, Anna*,, Spencer, Dave, Sweet, Sara , DiTomaso, Joe,

ABSTRACT- Arundo donax (giant reed) is a pervasive invader of riparian systems and is currently a candidate for biological control. We investigated response to simulated herbivory for one year (2/02-2/03) of twelve Arundo individuals grown in 1.86 m3 containers with horizontal mini-rhizotrons at 30 cm intervals. Plants received one of four treatments: either uncut or subjected to cuttings that removed half of the above ground biomass, with either high or low nutrient levels (approx. 24 mg/wk inorganic N vs. 1.6 mg/wk). We monitored growth and architecture above ground with a 3-D digitizer, and below ground with a mini-rhizotron camera. Photosynthesis and transpiration rates were measured using a LI-6400. A less-detailed, companion study in the field on 8 pairs of plants (cut and uncut) was simultaneously conducted. All 12 potted plants had roots >1 m deep within 5 months. Cut plants had the highest rates of branching and the highest relative growth rate (RGR) as measured by shoot height and number, leaf number, and increase in mean diameter of new shoots. Nutrient treatment had no effect on branching rates or RGR in most cases. Cut plants also had higher photosynthetic rates than uncut plants, as did high nutrients relative to low nutrients. The same photosynthetic patterns were seen for field plants. Our results suggest that A. donax is capable of vigorous compensatory growth in response to above ground herbivory, even under low nutrient conditions.

Key words: invasive , giant reed grass, Arundo donax, riparian