Light reduction and moisture stress: effects on growth and water relations of western larch seedlings.

Ten-week-old Larix occidentalis seedlings were grown under 70, 37, and 27% full sunlight from late July to early October. In August, seedlings under each light treatment were repetitively water stressed until predawn leaf water potential reached 1 of 3 levels: no stress (> -0.4 MPa), moderate stress (-0.7 to -1.0 MPa), and severe stress (-1.5 to -1.8 MPa). Moisture stressing significantly reduced height and diameter of seedlings grown under 70% light. Light reduction reduced shoot and root biomass accumulation. A positive linear relation was found between root dry weight and light intensity. Largest seedlings (weight basis) received the highest light, were unstressed, and had the lowest shoot/root ratios. Terminal bud set was not affected by light reduction or moisture stressing but occurred under a 14-h photoperiod and reduced nighttime temperatures. -from Authors