Li 6400xt photosynthesis measurement system

The net photosynthetic rate (μmol m^–2 s^–1), stomatal conductance (g_s, mol m^–2 s^–1), and transpiration rate (E, mmol m^–2 s^–1) were measured at 9:00–11:00 a.m. with a portable LI-6400XT photosynthesis measurement system (LI-COR Inc., Lincoln, NE, United States). WUE_i (μmol mmol^–1) was calculated according to the following equation:
The chlorophyll contents were determined by using the method described by Jawale et al. (2017) (link). Plant height was determined by tapeline and the unit was cm, stem diameter was determined by using a Vernier caliper and the unit was mm, the measurement was conducted on the junction of root and stem, and leaf area was determined by using a leaf area meter (handheld laser leaf area meter, CI, 203) and the unit was cm². The dry weights of the plants were measured at the end of the treatment. The plants were dried in an oven at 80°C. Plant dry weights of aboveground (DW_a) and underground parts (DW_u) were determined using an electronic analytical balance. The root/shoot ratio (R/S) was calculated as follows: R/S = DW_a/DW_u. The single fruit weight and fruit weight per plant were determined using an electronic analytical balance after the fruit was ripe. The economic water-use efficiency (WUE_e, g L^–1) and biomass water-use efficiency (WUE_b, g L^–1) were calculated according to the following equations:

Healthy leaves of the same orientation were selected on 9 May to measure their photosynthesis parameters according to Chen et al. [39 (link)] and Zhang et al. [41 (link)]. The photosynthetic rate (Pn), transpiration rate (Tr), stomatal conductance (Gs), intercellular carbon dioxide concentration (Ci), and water use efficiency (WUE) were monitored using a portable LI-6400XT photosynthesis measurement system (LI-COR Inc., Lincoln, NE, USA) with photosynthetically active radiation of 1000 μmol m⁻² s⁻¹ at 8:00~10:00 a.m. Meanwhile, the chlorophyll a and chlorophyll b contents of P. heterophylla leaves were determined with acetone–ethanol (v/v, 2:1) extraction using a UV-5800PC spectrophotometer at 663 nm and 645 nm, respectively. The chlorophyll content in P. heterophylla leaves was the sum of the chlorophyll a and chlorophyll b contents.

Fifteen P. ternata plants, on the east, west, south, north, and in the middle of each plot, were randomly selected at the vigorous growth period (May 15) for investigation of their photosynthesis parameters. The chlorophyll content of the fully-expanded leaves of P. ternata was monitored by a SPAD-502Plus chlorophyll meter (Konica Minolta Inc., Osaka, Japan). Meanwhile, their Pn, Ci, Gs, and Tr contents were monitored by a portable LI-6400XT photosynthesis measurement system (LI-COR Inc., Lincoln, NE, USA), with the photosynthetically active radiation of 1000 μmol m⁻² s⁻¹ at 8:00–10:00 a.m. [27 (link),28 (link)].