Carry-over effects of water and nutrient supply on water use of Pinus taeda

A study of the effects of nutrients and water supply (2 x 2 factorial exper iment) was conducted in a 12-yr-old stand of loblolly pine (Pinus taeda L.) during a period in which soil moisture was not augmented by irrigation bec ause of frequent rain events. Information on the responses of sapwood-to-le af area ratio and early-to-late wood ratio, to four years of treatments led to the hypothesis that the combination of increased nutrient and water sup ply (IF treatment) will increase tree transpiration rate per unit leaf area (E-C,E-1) above E-C,E-1 in the control (C), as well as increasing E-C,E-1 above that when either the supply of water (I) or of nutrients (F) is incre ased. We further hypothesized that canopy transpiration (E-C) will rank IF > F > I = C, based on the ranking of leaf area index (L) and assuming that the ranking of E-C,E-1 is as first hypothesized. We rejected our first hypo thesis, because F had lower E-C,E-1 than the other treatments, rather than IF having higher values. We could not reject the second hypothesis; the ran king of average daily E-C was 1.8 mm for IE 1.2 mm for F, and 0.7 mm for bo th C and I (SE < 0.1 mm for all treatments). Thus, it was the lower E-C,E-1 of the F treatment, relative to IF, that resulted in ranking of E-C simila r to that hypothesized. Lower E-C,E-1 in F trees was found to relate to low er canopy stomatal conductance, even though soil moisture conditions during the time of the study were similar in all treatments. Only trees in the F treatment absorbed a substantial amount of water (25%) below 1 m in the soi l. These results indicate a "carry-over" effect of irrigation when combined with fertilization that increases E-C in irrigated trees, relative to unir rigated trees, even under conditions when soil moisture is high and similar in all treatments.