Ectomycorrhizal fungi reduce the light compensation point and promote carbon fixation of Pinus thunbergii seedlings to adapt to shade environments

Liang Shi,Binhao Liu,Kazuhide Nara,Yan Xia,Yahua Chen,Jie Wang,Chunlan Lian,Zhenguo Shen

doi:10.1007/s00572-017-0795-7

Liang Shi, Binhao Liu + Show 6 more

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https://doi.org/10.1007/s00572-017-0795-7

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Abstract

We examined the effects of three ectomycorrhizal (ECM) symbionts on the growth and photosynthesis capacity of Japanese black pine (Pinus thunbergii) seedlings and estimated physiological and photosynthetic parameters such as the light compensation point (LCP), biomass, and phosphorus (Pi) concentration of P. thunbergii seedlings. Through this investigation, we documented a new role of ectomycorrhizal (ECM) fungi: enhancement of the survival and competitiveness of P. thunbergii seedlings under low-light condition by reducing the LCP of seedlings. At a CO2 concentration of 400 ppm, the LCP of seedlings with ECM inoculations was 40–70 μmol photons m−2 s−1, significantly lower than that of non-mycorrhizal (NM) seedlings (200 μmol photons m−2 s−1). In addition, photosynthetic carbon fixation (Pn) increased with light intensity and CO2 level, and the Pn of ECM seedlings was significantly higher than that of NM seedlings; Pisolithus sp. (Pt)- and Laccaria amethystea (La)-mycorrhizal seedlings had significantly lower Pn than Cenococcum geophilum (Cg)-mycorrhizal seedlings. However, La-mycorrhizal seedlings exhibited the highest fresh weight, relative water content (RWC), and the lowest LCP in the mycorrhizal group. Concomitantly, ECM seedlings showed significantly increased chlorophyll content of needles and higher Pi concentrations compared to NM seedlings. Overall, ECM symbionts promoted growth and photosynthesis while reducing the LCP of P. thunbergii seedlings. These findings indicate that ECM fungi can enhance the survival and competitiveness of host seedlings under low light.

Highlights

Mycorrhizal fungi play crucial roles in shaping the development of forest ecosystems (Clark and St Clair 2011)
Our objectives were to determine (1) whether inoculation with ECM fungi improves the capacity of P. thunbergii seedlings to utilize low light; (2) how ECM fungal inoculation enhances the shade tolerance of P. thunbergii seedlings; and (3) the effects of ECM fungi on the carbon fixation (Pn) of P. thunbergii seedlings
1200 ppm, the photosynthetic carbon fixation (Pn) values of Cenococcum geophilum (Cg), Laccaria amethystea (La), and Pisolithus sp. (Pt)-mycorrhizal seedlings were 4.8, 3.3, and 2.7 times higher than that of NM seedlings, respectively. These findings indicate that ECM fungi inoculation significantly improve the CO2 fixation (Pn) of P. thunbergii seedlings under different CO2 concentrations

Summary

Introduction

Mycorrhizal fungi play crucial roles in shaping the development of forest ecosystems (Clark and St Clair 2011). In forests, light is the greatest limiting factor for seedling survival and growth (Kolb et al 1990). Mycorrhiza (2017) 27:823–830 stock, primarily due to shade intolerance and slow initial growth rates (Kabrick et al 2015). In old-growth forests of Eastern Asia, Taiwania cryptomerioides is a shade-intolerant and long-lived conifer that experiences intense light competition, yet eventually emerges from the canopy (40–70 m), which comprises more shade-tolerant evergreen broadleaved trees (He et al 2015). Paper birch competes well for light and inhibits the growth of shade-intolerant conifers (Callaway and Walker 1997). These previous studies indicate that some conifer species do not possess a competitive advantage in forest ecosystems under natural conditions. The protection and restoration of shade-intolerant conifers remain challenging but essential endeavors

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