Seed germination of Pinus koraiensis in response to light regimes caused by shading and seed positions

Abstract

Pinus koraiensis Siebold & Zucc. (Korean pine), the dominant tree species in the mixed broadleaved Korean pine forests (regional climax), is severely restricted by its regeneration failure. To determine the effects of light regimes on P. koraiensis regeneration, the seed germination process was examined in shade houses and forest stands (before and after leaf expansion) with various light levels created by shading and seed positions. Despite the large size of P. koraiensis seeds (500-600 mg), both light intensity and quality significantly affected the germination percentage in both shade houses and forests. Substantial changes in light intensity and quality led the majority of seeds (80%) to germinate in leafless forests and shade houses, while only a minority (≤ 20%) germinated after leaf expansion in the forests. Moreover, seed germination in shade houses and leafless forests exhibited similar patterns; they consistently reached a 70% shading degree, which was optimal for the seed germination of P. koraiensis on topsoil. Seed positioning significantly affected germination for each shading degree, especially when litter and soil coverings drastically inhibited germination. In conclusion, (1) when seeds were not stressed by temperature and moisture, light irradiance played a critical role in the seed germination of P. koraiensis; (2) seed positioning, in relation to alterations in light intensity and quality, affected the germination of P. koraiensis; (3) a shade house experiment using neutral cloth provided an applicable and controllable way to monitor the P. koraiensis seed germination in early spring before leaf expansion. The light requirement for the germination of P. koraiensis played a key role in the regeneration of P. koraiensis throughout the temperate secondary forests.

Optimum light transmittance for seed germination and early seedling recruitment of Pinus koraiensis: implications for natural regeneration

“…Thus, early spring seem a favorable period for seed germination of P. koraiensis. This result clearly confirms the findings of our previous field experiment (Zhang et al 2012), in which 80% of P. koraiensis seeds germinated prior to leaf expansion.…”

“…According to our field observations, 30% light transmittance occurred in broadleaved secondary forest stands in the early spring prior to leaf expansion (see Fig. 1 in Zhang et al 2012). Thus, early spring seem a favorable period for seed germination of P. koraiensis.…”

“…Such uncoupled light requirements have also been reported for other tree species which can germinate under closed canopy, but need higher light at the seedling stage (Kyereh et al 1999, Fady et al 2004, Parker et al 2004, 2006, Ganatsas & Tsakaldimi 2007. Moreover, the germination of most seeds of P. koraiensis occurs in early spring before leaf expansion in the secondary forest (Zhang et al 2012). The subsequent reduction in light transmittance after leaf expansion would be disadvantageous to seedling growth of P. koraiensis.…”

“…Pulinets (1986) studied the development of P. koraiensis under different light intensities created by the shading of shrubs, and concluded that the light requirements varied greatly across the entire growth period. Zhang et al (2012) found that 30% of the full sunlight was optimum for seed germination of P. koraiensis in both shade houses and field conditions. To our knowledge, 60% of full light was the most favorable environment for the growth of 5-year-old P. koraiensis seedlings (Zhu et al 2014).…”

Growth, Nutrient Assimilation, and Carbohydrate Metabolism in Korean Pine (Pinus koraiensis) Seedlings in Response to Light Spectra

“…In secondary forests where Korean pine trees dwell, illumination conditions of light intensity and quality can both significantly affect seed germination, seedling photosynthesis, and tree growth in this species [2,15,16]. The seeds of Korean pine require a light transmittance lower than 60% for germination, but its seedlings require a higher transmittance and at least a minimum 7% canopy openness [2,15].…”