Influence of Shade, Media and Fertility on Growth of Taxus

Root dry weight

Fertilizer rates and the interaction between media and fertilizer were significant at 5% level. Under natural lighting root growth was the same under all nutrient additions in the 2:1 soil:perlite medium.   With   3:2:2 soil:peat:perlite medium 380 ppm N additions proved excessive (Fig. 1A) and over 67% of the plants were killed due to high soluble salts levels (Table 1).   Soil tests (Table 1), also indicated relatively high soluble salt levels for the 2:1 medium, but all plants survived. The nutrient and water retention capacity of the 3:2:2 medium was greater than that of the 2:1 medium.

Root growth of plants under 50% shade was similar to that under natural lighting (Fig. 1A) where 120 and 192 ppm N was used. The highest rate of 20-20-20 solution also resulted in 66% mortality of plants in   soil:peat:perlite. However,   plants grown in soil:perlite, which is more easily leached, were not damaged.

Shoot dry weight

At 50% shading total shoot dry weight was greater than at ambient light (Fig. 1B). Shoot growth was equal in both media at all fertilizer rates, except with the highest application in the 3:2:2 mixture (Fig. 1B).   This drastic decline in growth is likely attributed to high soluble salts levels in the root zone (Table 1).

Under 50% and no shading the amount of shoot growth with 120 ppm N was approximately equal (7.9 and 7.57 g) regardless of the soil medium (Fig. 1B). Shoot growth increased as the nutrient levels increased to 192 ppm. With the highest nutrient addition shoot growth declined in both media, but the extent of decrease was greater in soil:peat:perlite.

Shoot length

Statistical analysis of total shoot length indicated a significant interaction between light and fertilizer treatments. Under natural lighting shoots made equal length growth with 120 and 192 ppm applications (Fig. 1C). However, with the 384 ppm application shoot length significantly declined in 3:2:2 but not in 2:1 medium. The sharp decline in the former is likely due to soluble salt build-up (Table 1).

Shoots under 50% shade were longer than those under natural light regardless of the medium or fertilizer treatment (Fig. 1C). Under shade, the shoots grew maximally (213 cm) in 3:2:2 medium with 192 ppm N additions (Fig. 1C).

Shade grown Taxus are produced in commercial nurseries and frequently encountered in the landscape. Native Taxus are found in Canada where ample shading by the forest canopy is available. This study indicates greater shoot length will result from shading regardless of the growing media. Media selection is important, however, to obtain maximum plant growth.

Plants grown in the soil:perlite mixture tolerated the high salt levels arising from the highest fertilizer applications and produced greater amounts of shoot and root dry matter as compared to the soil:peat:perlite mixture.   In   the   latter   mixture, some plants were killed due to high soluble salts. Soil test results (Table 1) showed that the total soluble salt content of the soil:peat:perlite mixture was 200 m mhos as compared to 121 m mhos for soil:perlite mixture. The differences in electrical conductivity of the mixtures are related to their texture, leaching ability, moisture holding capacity and pore spaces.   The soil:perlite mixture had a coarse texture, more large pores and possessed a greater leaching ability and lower water holding capacity.   There was no significant growth differences between the two media with the 120 and 192 ppm N treatments.