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Growth and Photosynthetic Performance of Seedlings of Two Larch Species Grown in Shaded Conditions

To study the regeneration pattern of the Japanese larch (Larix kaempferi Sarg.) and its hybrid larch (Larix gmelinii x L. kaempferi), we compared the growth and photosynthetic performance of two larch seedlings under differing light levels (8%, 16%,32% shade conditions, with 100% light as control) and fertilizer regimes (5mg and 25mg per seedling). The total dry mass of the shaded seedlings was smaller than for the control seedlings after 12 weeks of the growing period in both larch species. The lowest needle area was observed in seedlings grown under 8% light level. The specific leaf area (SLA, needle area per unit dry mass) of seedlings grown at 100% light was significantly lower than in seedlings grown in 8% light. However, there was no significant difference in dry mass allocation for either larch species in the two nutrient treatments. Fertilizer regimes did not affect the needle area of either species. The total chlorophyll content per unit leaf area increased with increasing irradiance, due mainly to the reduction in SLA. Seedlings of both species grown at 100% light have a significantly higher light-saturated rate of net CO2 assimilation (Amax) and higher Vcmax (maximum rate of carboxylation) than for the other light treatments given the same fertilizer level. The Japanese larch displayed greater changes in response to decreasing PPFD, as a result of its remarkable change in SLA. However, Japanese larch seedlings treated with high nutrient fertilizer were suppressed in shady conditions. These results suggest that the hybrid larch would be more dominant in slightly shaded conditions on infertile soil.