F’0, F0: Minimal fluorescence from dark- and light-adapted leaf, respectively (PSII centers open).; F’m, Fm: Maximal fluorescence from dark- and light-adapted leaf, respectively (PSII centers closed).; F’v, Fv: Variable fluorescence from dark- and light-adapted leaves, respectively (QA reduction).; Fv/Fm: Maximum quantum yield of PSII photochemistry.; F’v/F’m: PSII maximum efficiency, provides an estimate of the maximum efficiency of PSII photochemistry at a given PPFD, which is the PSII operating efficiency if all the PSII centers were open (QA oxidized).; NPQ: Non-photochemical quenching.; ETR: Electron transport rate.; q0: Relative changes of minimum fluorescence of chlorophyll a.; qP: Photochemical quenching coefficient.; qA: Absolute quenching.; Rfd: Ratio of chlorophyll fluorescence decrease to steady-state or vitality index.; SV0: Non-photochemical quenching of minimum fluorescence of chlorophyll a
TABLE 3 The effects of redroot pigweed leachate on photosynthetic gas exchange parameters of cucumber and wheat plants. The data represent the mean of three replications ± SD and different letters in each parameter for each species indicate significantly different values at p ≥0.01