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

Date Published: July 12, 2017

Publisher: Public Library of Science

Author(s): Bao-Qiang Zheng, Long-Hai Zou, Kui Li, Xiao Wan, Yan Wang, Zhong-Jian Liu.

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

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.

Partial Text

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. Moreover, these orchids are experiencing habitat reduction because of biological resource use and agricultural activities, such as deforestation and overgrazing. To date, most Cypripedium species have been identified as vulnerable, threatened or endangered in the IUCN Red List of Threatened Species [3]. C. tibeticum is characterized by a large, broad labellum with a white-margined rim and dark purple flowers; it is distributed in southwest China, Sikkim, Bhutan, and India [1,4]. 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]. Although these species are distributed over a wide range of habitats, its populations are suffering a decline throughout the wild [6].

 

Source:

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

 

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