Evaluate the photosynthesis and chlorophyll fluorescence of Epimedium brevicornu Maxim

All methods were performed in accordance with the local relevant guidelines, regulations and legislation.

Instruments

LI-6400 photosynthesis system (LI-6400 Inc., Lincoln, NE, USA) and PAM-2500 portable chlorophyll fluorescence apparatus (PAM-2500, Walz, Germany) were used in the study.

Materials

About 90 living E. brevicornu plants were collected from Taihang Mountains in October 2018. The E. brevicornu was not in endangered or protected. The collection of these E. brevicornu plants was permitted by local government. These plants were averagely planted in nine plots of 2 m². The roots of E. pubescens were planted 6–8 cm below ground. These plots were placed on farmland near Taihang Mountains and covered with sunshade net (about 70% light transmittance). These plants were timely irrigated after planting to ensure that they grew well but not fertilized.

Determination of photosynthetic characteristics

The photosynthetic characteristics of mature leaves on the E. brevicornu plants were determined between June 6–8, 2019 with the Li-6400 photosynthesis system. The diurnal variation of photosynthesis in three leaves of three plants was determined. When the light response curve was determined, the temperature of the leaf chamber was set at 28 °C, and the concentration of CO₂ in the leaf chamber was set at 400 µmol mol⁻¹. When determining the CO₂ response curve, the light intensity in the leaf chamber was set at 1000 µmol m⁻² s⁻¹, and the temperature of the leaf chamber was set at 28 °C. The light response curve and CO₂ response curve were determined three times in three leaves of three different plants.

Determination of chlorophyll fluorescence characteristics

The fluorescence characteristics of chlorophyll in E. brevicornu leaves were determined with PAM-2500 portable chlorophyll fluorescence apparatus between June 8–9, 2019. The leaves underwent dark adaptation for 30 min before determining slow kinetics of chlorophyll fluorescence. Then the light curves of chlorophyll fluorescence were determined. All of these determinations were repeated three times on three mature leaves of three plants.

The data was analysed with SPSS (Statistical Product and Service Solutions, International Business Machines Corporation, USA). The light response curves were fitted with following modified rectangular hyperbola model^11,12.

PAR is the value of light intensity in leaf chamber of Li-6400 photosynthesis system. Photo is net photosynthetic rate. LCP is the light compensation point. E is the apparent quantum yield. M and N are parameters. The dark respiration rate under the LCP is calculated according to E·LCP. The light saturation point (LSP) is calculated according to (((M + N) ·(1 + N·LCP)/M)^½)/−1)/N.

The net photosynthetic rate under the light saturation point (LSP) can be calculated according to the above model.

The CO₂ response curves were fitted with below modified rectangular hyperbola model^11,12.

PAR is the value of light intensity in leaf chamber of Li-6400 photosynthesis system. Photo is net photosynthetic rate. CCP is CO₂ compensation point. E is also the apparent quantum yield. M and N are parameters. The dark respiration rate under the CO₂ calculated according to E·CCP. The CO₂ saturation point (CSP) is calculated according to (((M + N) ·(1 + N·CCP)/M)^½)/−1)/N.

The net photosynthetic rate under the CO₂ saturation point (CSP) can be alternatively calculated according to the above model.

The light curves of chlorophyll fluorescence were fitted according to the below model of Eilers and Peeters^12,13.

ETR is the electron transport rate of photosynthetic system II. PAR is fluorescence intensity. The letters a, b and c are parameters.

Source: Ecology - nature.com