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

M Zhang,J Zhu,Q Yan

doi:10.5424/fs/2012213-02721

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.

Highlights

As one of the most important five-leaved pine species in the northern hemisphere, Korean pine (Pinus koraiensis Siebold & Zucc.) is mainly distributed throughout Northeast Asia’s (Ma and Zhuang, 1992) mixed broadleaved Korean pine forests (MBKPF)
The results indicated that the germination percentage was distinct among forest stands under leaf canopy and leafless canopy, as well as in shade houses
It is clear that light conditions affect seed germination of P. koraiensis

Summary

Introduction

As one of the most important five-leaved pine species in the northern hemisphere, Korean pine (Pinus koraiensis Siebold & Zucc.) is mainly distributed throughout Northeast Asia’s (Ma and Zhuang, 1992) mixed broadleaved Korean pine forests (MBKPF). Due to an intense amount of human disturbance, as well as abnormally extreme, natural disasters, most of the MBKPF (accounting for 52.5% of Northeast China) have been destroyed and replaced by secondary forests (Wu et al, 2004). Based on our preliminary investigation (Yu et al, 2006), regenerated P. koraiensis seedlings emerged from deciduous secondary forests with heterogeneous distribution patterns. This phenomenon may largely be due to the responses of seed germination and/or seedling survival of environmental variations induced by the shading degree and seed positioning in the soil. As P. koraiensis seedlings are capable of surviving under dense canopies (Hao et al, 2007), the regeneration pattern of P. koraiensis seedlings may be primarily due to seed germination variations under different environmental conditions

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