CONICET | Buscador de Institutos y Recursos Humanos

In the context of HYPERNETS project, which has developed the relatively low cost hyperspectral radiometer HYPSTAR® (and associated pointing system) for automated measurement of water and land bidirectional reflectance, the tidal coastal marsh in the Mar Chiquita (Argentina) lagoon was characterized as a test site for validation of radiometric variables [Piegari 2020]. This site is a coastal habitat that provides ecosystem services essential to people and the environment [Assessment, Millennium Ecosystem 2005] and the vegetation is dominated by Sporobolus densiflorus [Trilla 2016]. There is evidence that growth and photosynthetic apparatus of this species is negatively affected by the herbicide glyphosate [Mateos-Naranjo 2009], which is extensively used in the Argentinean agricultural production [Aparicio 2013]. Previous studies have shown the potential of remote sensing to monitor plant injury from glyphosate using hyperspectral data [Huang 2012, Zhao 2014]. In particular, NDVI (Normalized Difference Vegetation Index) and PRI (Photochemical Reflectance Index, an indicator of photosynthesis activity) are spectral indices typically used to evaluate plant conditions. In this context, the HYPSTAR® instrument will provide high quality in situ reflectance, at fine spectral resolution (10 nm FWHM) in the 400-1700nm range with automated measurements every 30 mins, useful for the validation of surface reflectance data from all present and future earth observation missions and to monitor the health status of the vegetation. Thus, allowing to further explore if herbicides effects can be detected using spectral indices (designed for green vegetation) in natural environments characterized by the presence of a large fraction of standing litter - such as the Buenos Aires Atlantic coastal marshes.In this study we sought to determine if it is possible to detect the effect of glyphosate on S. densiflorus spectral response using chlorophyll fluorescence and hyperspectral data. To achieve this, samples of S. densiflorus adult clumps were taken in Puntas Piedras (35°34´40.1"S 57°15´11.9"W Buenos Aires, Argentina). Clumps of about 18 cm diameter were planted in 21 individual plastic pots, with a diameter and height of 24 cm and 28 cm, resp., filled with marsh soil. Pots were randomly separated in three sets (seven pots per treatment) according to two doses of Glyphosate-based herbicide (GlacoXAN TOTAL; 43,8 g active ingredient/100 ml, Argentina) with 876 g a.i./ha and 7200 g a.i./ha and an untreated control. The herbicide was administered homogeneously over the leaves surface, early in the morning and in absence of wind, using a pulverizer (250 ml of spray volume). Photosynthetic parameters were acquired in random fully developed leaves attached to the plants using a portable fluorometer PAR-FluorPen FP 100-MAX-LM of Photon Systems Instruments (Czech Republic). Leaves were dark-adapted for 20 min and then measurements were performed following the OJIP protocol [Stirbet 2011]. Radiometric measurements were obtained using a field spectrometer FieldSpec3® Analytical Spectral Devices (ASD), Inc. (Boulder, Colorado), which covers the spectral range between 350 and 2500 nm. Reflectance spectra at leaf level were acquired with a Plant Probe and Leaf Clip accessories (ASD) and with 7 pots per scene at canopy level were carried out, swapping the pots so that each of the 7 were placed in the center to generate 7 different scenes per treatment. The photosynthetic parameters derived from OJIP test and reflectance measurements at leaf and canopy levels were obtained for the three treatments 1, 8 and 15 days after treatment (DAT). Analysis of variance (ANOVA) tests were performed together with a LSD Fisher test to evaluate significant differences. Results show that by means of photosynthetic parameters and spectral indices, crop injury of glyphosate in S. densiflorus could be early detected. The maximum quantum yield of photosystem II (Fv/Fm), which is considered to be a sensitive indicator of plant photosynthetic performance, shows differences between the control and low and high dose treatments (p