Impact of biosolids on hormone metabolism in drought-stressed tall fescue
The presence of biologically active substances (BAS) in biosolids may enhance plant stress tolerance and growth, but the underlying mechanisms are not well understood. This greenhouse study investigated the effects of untreated biosolids, containing 2.1 µg indole-3-acetic acid (IAA) g–1, and tryptophan-treated biosolids, containing 15.4 µg IAA g–1, on tall fescue [Lolium arundinaceum (Schreb.) Darbysh.] drought resistance. Treatments included a fertilizer control, indole-3-butyric acid (IBA) at 2 µM (hormone control), treated biosolids (2.95 g kg–1 soil), and untreated biosolids (2.97 g kg–1 soil). Nitrogen availability was equalized among treatments, and tall fescue physiological responses were measured under well-watered or moisture stress conditions. Treated biosolids improved turfgrass quality and root mass under both soil moisture regimes and delayed leaf wilting under moisture stress. At the end of the second drought cycle (2 February), treated biosolids improved quality and photochemical efficiency by 18 and 26% relative to the control. Treated biosolids increased leaf IAA by 122 and 52%, respectively, and trans-zeatin riboside by 100 and 189%, respectively, during each of two maximum drought periods. Leaf tissue increases of IAA and cytokinin were associated with greater content of these hormones in the soil. The data suggest that biosolids application may alter growth hormone (IAA and cytokinin) content and improve plant drought resistance.