Effect of Irradiance, Temperature, and Spore Sowing Density on Propagation and Growth in Adiantum Species Native to Taiwan

Adiantum is one of the most popular ferns worldwide. However, native Adiantum species are rare seen in the market due to the lack of information on propagation and production. Thus, the objectives of this thesis were to study the effects of irradiance, temperature, spore sowing density on spore germination, and gametophyte and sporophyte growth and development of several Adiantum species native to Taiwan.

Effects of various irradiance levels (0, 30, 60, 90, 120 μmol•m-2•s-1 photosynthetic photon flux, PPF) on spore germination and gametophyte development were determined at 27±3ºC under a 12-hour photoperiod provided from fluorescent lamps. Spores of A. hispidulum, A. capillus-veneris and A. soboliferun germinated well under 30 μmol•m-2•s-1 PPF, with 70%, 88%, and 80% germination rate, respectively. Spores of A. capillus-veneris could germinate in the dark conditions. In contrast, spores of A. philippense had a higher germination rate (56%) under 120 μmol•m-2•s-1 PPF condition. A. hispidulum, A. capillus-veneris, A. philippense and A. soboliferun produced the first frond after spore sowing for 8, 9, 16, and 16 weeks, respectively under 30 μmol•m-2•s-1, while higher irradiances (> 30 μmol•m-2•s-1) resulted in lower germination rate, and slower germination and gametophyte development.

Effects of day/night temperature of 30/25, 25/20, 20/15 or 15/13 ℃ on spore germination were studied under greenhouse conditions with an average noon PPF of 197 μmol•m-2•s-1. Spore germination rates at 30/25 ℃ of A. hispidulum, A. capillus-veneris, and A. soboliferun were 79%, 85%, 86%, respectively, higher than those at lower at temperature. In contrast, the highest spore germination (81%) of A. philippense was observed at 25/20 ℃. Under 30/25 ℃ conditions, A. hispidulum, A. capillus-veneris, and A. soboliferun produced the first frond after spore sowing for 9, 7, 10, 12 weeks, respectively. Lower temperature (< 30/25 ℃) resulted in slower and lower spores germination, and stunt gametophyte growth.

A. hispidulum and A. philippense exhibited apogamy, and thus reached sporophytic growth earlier than A. capillus-veneris and A. soboliferun which had a bisexual propagation.

Spore suspension was prepared with 63, 39, 31, 25, and 21 spores per cm2 to determine the effects of spore sowing density on spore germination and gametophyte growth. The germination was carried out in a growth room at 25±2ºC and 30μmol•m-2•s-1 PPF under a 12-hour photoperiod. All spores of the tested ferns germinated 4 weeks after sowing with an average of 82.4% germination rate, regardless of sowing density. Hermaphroditic gametophytes were majoly seen in all sowing density treatments. The number of asexual gametophytes decreased as the spore sowing density increased. No male gametophytes was observed with the low sowing density (21 spores per cm2). While no female gametophytes was observed with the high density treatment (63 spores per cm2). Hermaphroditic gametophytes had the largest size, followed by female gametophytes, and than asexual and male gametophytes.

Shading would affect the plant growth of A. capillus-veneris and A. hispidulum.Effect of 0%, 31%, 55%, 82%, or 88% shade in a greenhouse were studied on growth and photosynthesis. A. capillus-veneris veneris had the highest net photosynthetic rate of 7.22 μmol•m-2•s-1 with 82% shade. A. hispidulum had the highest net photosynthetic rate of 5.4 μmol•m-2•s-1 under 88% shading.

For both ferns, plant fresh and dry weights, frond area, stomatal number, and SPAD-502 values decreased as irradiance increased. A. capillus-veneris produced fewer, but A. hispidulum had more, fronds with sorias irradiance increased. Yellow and necrotic fronds were observed in both ferns under 0% or 30% shading conditions.

Interior performance was evaluated in plants grown under various shading in a greenhouse followed by 3-month indoor conditions. A. capillus-veneris had the lowest light compensation point and had the best interior performance when grown previously under 55% or 88% shading conditions. A. hispidulum performed best when grown under 31% or 55% shadings.