LAUSR

Abstract To estimate the salt tolerance and drought tolerance of Lycium ruthenicum Murr, we designed a pot experiment to measure the physiological and biochemical photosynthetic mechanisms of this species by establishing a range of NaCl concentrations (0, 50, 100, 200 and 400 mM) and degrees of drought stress (30%, 60%, 75% and 100% of field capacity). The results showed that the net photosynthetic rate (Pn), transpiration rate (Tr), stomatal conductance (Gs), chlorophyll (Chl), carotenoids (Cars), maximal fluorescence (Fm), optimal quantum yield of photosystem II (PSII) (Fv/Fm), performance index (PIABS), activity of the water-splitting complex (Fv/Fo), actual photochemical efficiency of PSII (ΦPSII) and photochemical quenching (qP) were stimulated by moderate salinity (0–100 mM) and low water deficit (75–100%) and inhibited by high salinity (200–400 mM) and severe water deficit (30–60%). The changes in minimal fluorescence (Fo) and nonphotochemical quenching (qN) were opposite. Furthermore, the contents of malondialdehyde (MDA), proline, superoxide dismutase (SOD), and peroxidase (POD) significantly increased with increasing stress levels. In summary, salt and drought stress can separately enhance the photosynthetic capability to some extent because of increases in Gs and PSII activity. With an increase in stress, nonstomatal limitations, inhibition of electron transport and the activity of PSII can lead to reductions in photosynthetic capability. In addition, increases in osmotic substances and antioxidant enzymes can increase photosynthesis to some extent, but the physiological photosynthetic mechanisms are not protected from damage as these substances and enzymes continually increase. In summary, the resulting information can provide a theoretical basis and reference for construction of the ecological environment of the Qaidam area and the popularization and cultivation of Lycium ruthenicum Murr, thereby increasing ecological, social and economic benefits.