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