Photosynthesis,respiration, and carbon allocation of two cool-season perennial grasses in response to surface soil drying

The study was conducted to investigate carbon metabolic responses to surface soil drying for cool-season grasses. Kentucky bluegrass (Poa pratensis L.) and tall fescue (Festuca arundinaceae Schreb.) were grown in a greenhouse in split tubes consisting of two sections. Plants were subjected to three soil moisture regimes: (1) well-watered control; (2) drying of upper 20-cm soil (upper drying); and (3) drying of whole 40-cm soil profile (full drying). Upper drying for 30 d had no dramatic effects on leaf water potential (Ψ_leaf) and canopy photosynthetic rate (P_n) in either grass species compared to the well-watered control, but it reduced canopy respiration rate (R_canopy) and root respiration rate in the top 20 cm of soil (R_top). For both species in the lower 20 cm of wet soil, root respiration rates (R_bottom) were similar to the control levels, and carbon allocation to roots increased with the upper soil drying, particularly for tall fescue. The proportion of roots decreased in the 0-20 cm drying soil, but increased in the lower 20 cm wet soil for both grass species; the increase was greater for tall fescue. The Ψ_leaf, P_n, R_canopy, R_top, R_bottom, and carbon allocation to roots in both soil layers were all significantly higher for upper dried plants than for fully dried plants of both grass species. The reductions in R_canopy and R_top in surface drying soil and increases in root respiration and carbon allocation to roots in lower wet soil could help these grasses cope with surface-soil drought stress. This revised version was published online in June 2006 with corrections to the Cover Date.