DROUGHT ASSESSMENT OF AUXIN-BOOSTED BIOSOLIDS

The presence of biologically active substances such as plant hormones in certain biosolids may enhance plant stress resistance by providing hormones directly or by stimulating the activity of microbes that supply substrates and hormones. This study was conducted to investigate if auxin-boosted biosolids increase physiological fitness and drought stress resistance of Kentucky bluegrass (KBG; Poa pratensis L.) under greenhouse conditions. Calcined clay-filled containers were amended with auxin-boosted biosolids, non-treated biosolids, and indole butyric acid (IBA) at three rates. The control received inorganic N (202 kg ha−1) only. The KBG subjected to each treatment was grown under well-watered (80–90% field capacity (FC)) and drought stress (40–50% FC) conditions. Root and shoot growth, visual quality, visual estimates of leaf wilting, canopy photochemical efficiency (PEc), leaf proline, cytokinin, and antioxidant enzyme activities were measured. The grass treated with auxin-boosted biosolids or IBA had greater root mass under drought stress compared to either the control or non-dosed biosolids treatments. Auxin-boosted biosolids improved turfgrass quality and delayed leaf wilting. The KBG amended with auxin boosted biosolids or IBA had greater PEc, leaf proline content, cytokinin trans-zeatin riboside (t-ZR) content, and antioxidant superoxide dismutase (SOD) activity under drought stress conditions when compared to the control. These data suggest that auxin-boosted biosolids may enhance defense chemical responses during limited soil moisture conditions, improving drought resistance. The beneficial effects of auxin-boosted biosolids may be closely associated with their increased activity of hormones such as auxin.