Effects of the Herbicide Diuron on Cordgrass (Spartina foliosa) Reflectance and Photosynthetic Parameters

Abstract

Early indicators of salt marsh plant stress are needed to detect stress before it is manifested as changes in biomass and coverage. We explored a variety of leaf-level spectral reflectance and fluorescence variables as indicators of stress in response to the herbicide diuron. Diuron, a Photosystem II inhibitor, is heavily used in areas adjacent to estuaries, but its ecological effects are just beginning to be recognized. In a greenhouse experiment, we exposed Spartina foliosa, the native cordgrass in California salt marshes, to two levels of diuron. After plant exposure to diuron for 28 days, all spectral reflectance indices and virtually all fluorescence parameters indicated reduced pigment and photosynthetic function, verified as reduced CO 2 assimilation. Diuron exposure was not evident, however, in plant morphometry, indicating that reflectance and fluorescence were effective indicators of sub-lethal diuron exposure. Several indices (spectral reflectance index ARI and fluorescence parameters EQY, Fo, and maximum rETR) were sensitive to diuron concentration. In field trials, most of the indices as well as biomass, % cover, and canopy height varied predictably and significantly across a pesticide gradient. In the field, ARI and Fo regressed most significantly and strongly with pesticide levels. The responses of ARI and Fo in both the laboratory and the field make these indices promising as sensitive, rapid, nondestructive indicators of responses of S. foliosa to herbicides in the field. These techniques are employed in remote sensing and could potentially provide a link between landscapes of stressed vegetation and the causative stressor(s), which is crucial for effective regulation of pollution.

Effects of cadmium and salicylic acid on growth, spectral reflectance and photosynthesis of castor bean seedlings

“…4) and significantly lower average mSR 705 , chl NDI, and REP values than did the control plants (Table 3). Similar spectral shifts have been reported in the spectra of leaves subject to a variety of stressors (Poulos et al 2007;Thorhaug et al 2006;Williams et al 2009). As mSR 705 and REP were effective in describing changes in chlorophyll content, and chl NDI is usually correlated with Chl a concentration (Sims and Gamon 2002), these results indicate a reduction in chlorophyll content, a manifestation of toxicity by Cd.…”

Time course of the photochemical reflectance index during photosynthetic induction: its relationship with the photochemical yield of photosystem II

“…) is consistent with this hypothesis and an earlier study (Gamon et al ), which reported that DCMU nullified a change in R 531 . To the best of our knowledge, only one study (Williams et al ) has directly assessed the effect of DCMU on PRI. Williams et al () supplied weak DCMU solutions (250 and 400 μg l −1 –1.07 and 1.72 μM, respectively) to cordgrass plants ( Spartina foliosa ) and found that DCMU treatment reduced the PRI response to irradiation by 50% compared with the controls.…”

Glyphosate-dependent effects on photosynthesis of Solanum lycopersicum L.—An ecophysiological, ultrastructural and molecular approach

“…Actually, when plants were exposed to light intensities similar to those experienced during growth, the values of ΦPSII and rETR were increased in response to GLY treatments, suggesting that the observed decrease in chlorophyll content, as well as the depletion of gene expression of D1 and CP47, did not result in photochemical damage, at least under these conditions. Although the rETR (rETR = ΦPSII × PPFD) does not reflect the absolute electron flow across thylakoids membrane, this formula has been widely used in stress physiology studies to report the electron transport rate occurring at a given light intensity in different photoautotrophic organisms and types of samples (Garrido et al, 2019;Masojídek et al, 2001;Ritchie, 2012;Williams et al, 2009;Zivcak et al, 2013), and more specifically on studies dealing with effects of GLY on photosynthesis (Gomes et al, 2017;Yanniccari et al, 2012;Zobiole et al, 2010a;Gomes et al, 2016b;Vital et al, 2017). Besides, even if it is conceivable that GLY, as other stress signals (Sukhova et al, 2018), could have affected p (fraction of PPFD absorbed by leaves) and dII (multiplication factor since the transport of a single electron requires the absorption of two photons), ETR is largely determined by ΦPSII (Genty et al, 1989).…”