Soil insects alter fine root demography in peach (Prunus persica)

Minirhizotrons were used to assess the effects of soil insect suppression on the demography of peach fine roots (<1 mm diameter) over two growing seasons. The experiment was conducted at the USDA-ARS Appalachian Fruit Research Station in Kearneysville, WV, USA using six 15-year-old peach trees. Clear butyrate minirhizotrons were installed beneath each tree in April 1996. Soil drench treatments were applied around individual minirhizotron tubes at monthly intervals and consisted of 1 L of water or 250 μL of a broad-spectrum insecticide in 1 L of water. Roots were videotaped at 2- to 4-week intervals during the 1996 and 1997 growing seasons. Insecticide application was associated with a significant increase in fine root longevity: the median lifespans of insecticide-treated roots were 46-125 d longer than those of control roots. In addition, the development of brown pigmentation was significantly delayed in insecticide-treated roots. Insecticide application did not appear to increase soil fertility, as accumulation of NO₃^-, NH₄⁺, and PO₄²- on mixed bed ion-exchange resin was similar in treated and untreated soil. These results suggest that interactions with below-ground insects can significantly influence root longevity and may alter the rate at which roots undergo developmental changes in anatomy and physiology.