[The responses of photosynthesis to strong light in the medicinal plants Anisodus tanguticus (Maxim.) Pascher and Rheum tanguticum Maxim. on the Qinghai-Tibet Plateau].
Photosynthetic electron transport and light energy allocation were studied in the alpine plants Anisodus tanguticus (Maxim.) Pascher and Rheum tanguticum Maxim. ex Balf on the Qinghai-Tibet Plateau by using gas exchange and chlorophyll fluorescence. The results indicated that apparent quantum yield (AQY) of leaves of A. tanguticus was marginally higher than that of R. tanguticum although it had a lower maximum net photosynthetic rate (Pmax). The net photosynthetic rate (P(n)) of A. tanguticus was higher than R. tanguticum within the range of middle photosynthetic photon flux density (PPFD). However, the P(n) in R. tanguticum increased concomitantly with PPFD and did not appear to show light saturation of P(n) even under 2000 micromol m(-2) s(-1) which is similar to full light in summer (Fig.1). Increasing the PPFD to 1200 micromol m(-2) s(-1) decreased the ratio of carboxylation rate to total photosynthetic electron flow rate (J(C)/J(F)) although increased the ratio of photorespiration (J(O)/J(F)) for both species. Both J(C)/J(F) and J(O)/J(F) stabilized with a PPFD of more than 1200 micromol m(-2) s(-1) (Fig.2). The changes in the ratios of Rubisco oxygenation to carboxylation (V(O)/V(C)) were similar to changes to J(O)/J(F) (Fig.3). The increase of thermal energy dissipation (D) in A. tanguticus was higher than R. tanguticum with increased PPFD (Fig.4). It can be concluded that the two species adopt different mechanisms to cope with increased solar radiation. Increasing the fractions of PSII thermal energy dissipation and electron transport through photorespiration were the main adaptations in A. tanguticus. Enhancement of photosynthetic capacity with increased PPFD to balance the higher light energy absorbed by leaves is considered the main adaptation for R. tanguticum.
Shi
Sheng-Bo
SB
Northwest Institute of Biology Plateau, Chinese Academy of Sciences, Xining 810001, China. sbshi@mail.nwipb.ac.cn
Wang
Xue-Ying
XY
Li
Hui-Mei
HM
Han
Fa
F
D004579:Electron Transport / Q000502:physiology / Q000528:radiation effects; D008027:Light; D010788:Photosynthesis / Q000502:physiology / Q000528:radiation effects*; D010946:Plants, Medicinal / Q000502:physiology / Q000528:radiation effects; D012250:Rheum / Q000502:physiology / Q000528:radiation effects*; D019657:Solanaceae / Q000502:physiology / Q000528:radiation effects*; D018609:Tibet