Photosynthetic, morphological, and reproductive variations in Cypripedium tibeticum in relation to different light regimes in a subalpine forest.

Bao-Qiang Zheng,Kui Li,Yan Wang,Xiao Wan,Long-Hai Zou

doi:10.1371/journal.pone.0181274

Bao-Qiang Zheng, Kui Li + Show 3 more

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https://doi.org/10.1371/journal.pone.0181274

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Abstract

Cypripedium tibeticum, a subalpine orchid species, inhabits various habitats of subalpine forests, mainly including the forest edge (FE), forest gap (FG), and understory (UST), which have significantly different light intensities (FE > FG > UST). However, the ecological and physiological influences caused by different light regimes in this species are still poorly understood. In the present study, photosynthetic, morphological, and reproductive characteristics were comprehensively studied in plants of C. tibeticum grown in three types of habitats. The photosynthetic capacities, such as the net photosynthetic rate, light-saturated photosynthesis (Pmax), and dry mass per unit leaf area (LMA), were higher in FE and FG than in UST according to light availability. Compared with FG, the populations in FE and UST suffer from excessively strong and inadequate radiation, respectively, which was further corroborated by the low Fv/Fm in FE and high apparent quantum yield (AQY) in FG. The leaves of the orchids had various proportions of constituents, such as the leaf area, thickness and (or) epidermal hair, to reduce damage from high radiation (including ultraviolet-b radiation) in FE and capture more light in FG and UST. Although the flower rate (FR) was positively correlated to both Pmax and the daily mean PAR, fruit-set only occurred in the populations in FG. The failures in FE and UST might be ascribed to changes in the floral functional structure and low biomass accumulation, respectively. Moreover, analysis of the demographic statistics showed that FG was an advantageous habitat for the orchid. Thus, C. tibeticum reacted to photosynthetic and morphological changes to adapt to different subalpine forest habitats, and neither full (under FE) nor low (UST) illumination was favorable for population expansion. These findings could serve as a guide for the protection and reintroduction of C. tibeticum and emphasize the importance of specific habitats for Cypripedium spp.

Highlights

The genus Cypripedium L., which includes 52 species, belongs to the group of slipper orchids (Orchidaceae: Cypripedioideae) [1]
The photosynthetic active radiation (PAR) of both forest gap (FG) and UST remained at a much lower level than forest edge (FE) before 1100 HR, and the PARs differed between FG and UST
The dynamics of PAR recorded on several sunny days (Fig 2A and S1 Fig) demonstrated that there were heterogeneous light regimes corresponding to the three habitats

Summary

Introduction

The genus Cypripedium L., which includes 52 species, belongs to the group of slipper orchids (Orchidaceae: Cypripedioideae) [1]. Due to their high ornamental and medical values [2], Cypripedium species have been poached ruthlessly in the wild. C. tibeticum inhabits sparse forests, forest margins, scrubby slopes, and grassy slopes which are found at altitudes of 2,300 to 4,600 m [5]. These species are distributed over a wide range of habitats, its populations are suffering a decline throughout the wild [6]

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