Meta-analysis of the detection of plant pigment concentrations using hyperspectral remotely sensed data

Passive optical hyperspectral remote sensing of plant pigments offers potential for understanding plant ecophysiological processes across a range of spatial scales. Following a number of decades of research in this field, this paper undertakes a systematic meta-analysis of 85 articles to determine whether passive optical hyperspectral remote sensing techniques are sufficiently well developed to quantify individual plant pigments, which operational solutions are available for wider plant science and the areas which now require greater focus. The findings indicate that predictive relationships are strong for all pigments at the leaf scale but these decrease and become more variable across pigment types at the canopy and landscape scales. At leaf scale it is clear that specific sets of optimal wavelengths can be recommended for operational methodologies: total chlorophyll and chlorophyll a quantification is based on reflectance in the green (550–560nm) and red edge (680–750nm) regions; chlorophyll b on the red, (630–660nm), red edge (670–710nm) and the near-infrared (800–810nm); carotenoids on the 500–580nm region; and anthocyanins on the green (550–560nm), red edge (700–710nm) and near-infrared (780–790nm). For total chlorophyll the optimal wavelengths are valid across canopy and landscape scales and there is some evidence that the same applies for chlorophyll a

A novel pattern of leaf movement: The case of Capparis spinosa L.

A novel type of heliotropic leaf movement is presented for Capparis spinosa L., a summer perennial shrub of Mediterranean and arid ecosystems. In contrast to plants that demonstrate uniform diaheliotropic and/or paraheliotropic movement for all their foliage, the alternate leaves of C. spinosa follow different movement patterns according to their stem azimuth and the side of the stem that they come from (cluster). Additionally, leaf movement for each cluster may not be uniform throughout the day, showing diaheliotropic characteristics during half of the day and paraheliotropic characteristics during the rest of the day. In an attempt to reveal the adaptive significance of this differential movement pattern, the following hypotheses were tested: (i) increase of the intercepted solar radiation and photosynthesis, (ii) avoidance of photoinhibitory conditions, (iii) amelioration of water-use efficiency and (iv) adjustment of the leaf temperature microenvironment. No evidence was found in support of the first two hypotheses. A slight difference toward a better water use was found for the moving compared with immobilized leaves, in combination with a better cooling effect. © 2016 The Author 2016. Published by Oxford University Press. All rights reserved

Climatic Drivers of the Complex Phenology of the Mediterranean Semi-Deciduous Shrub Phlomis fruticosa Based on Satellite-Derived EVI

A 21-year Enhanced Vegetation Index (EVI) time-series produced from MODIS satellite images was used to study the complex phenological cycle of the drought semi-deciduous shrub Phlomis fruticosa and additionally to identify and compare phenological events between two Mediterranean sites with different microclimates. In the more xeric Araxos site, spring leaf fall starts earlier, autumn revival occurs later, and the dry period is longer, compared with the more favorable Louros site. Accordingly, the control of climatic factors on phenological events was examined and found that the Araxos site is mostly influenced by rain related events while Louros site by both rain and temperature. Spring phenological events showed significant shifts at a rate of 1–4.9 days per year in Araxos, which were positively related to trends for decreasing spring precipitation and increasing summer temperature. Furthermore, the climatic control on the inter-annual EVI fluctuation was examined through multiple linear regression and machine learning approaches. For both sites, temperature during the previous 2–3 months and rain days of the previous 3 months were identified as the main drivers of the EVI profile. Our results emphasize the importance of focusing on a single species and small-spatial-scale information in connecting vegetation responses to the climate crisis. © 2022 by the authors. Licensee MDPI, Basel, Switzerland

Without exceeding the limits: industrial soil rich in Zn and Cd has no effect on purslane and lettuce but promotes geranium growth

The aims of the study were (a) the assessment of growth and physiological response of a weed/alternative crop (purslane), an ornamental plant (geranium) and an edible vegetable (lettuce) to Zn- and Cd-contaminated industrial soil and (b) the investigation of the possible exclusion or accumulation process of these plants concerning Zn and Cd, evaluating thus their phytoremediation potential. Both Zn and Cd concentrations increased significantly in all three plant species in the contaminated soil compared to the uncontaminated control. Metal soil-to-plant transfer coefficient was lower in the first soil compared to control, indicating slower metal uptake with increased metal concentrations in soil. Geranium exhibited a growth promotion along with a better photosynthetic performance in the industrial soil. Purslane displayed an altered architecture and a more massive old leaf cohort, but its overall growth remained unaffected by increased [Zn] and [Cd], similarly to lettuce. No effects on PSII photochemical efficiency and photosynthetic pigments of all studied species were recorded. We conclude that metal uptake by plants remained within the limits of favorable growth and metal bioavailability was determined by (a) the fact that metals were deposited over long periods and were thus strongly retained by soil colloidal phases and (b) Cd/Zn antagonism. The results highlight the importance of soil history component in shaping heavy metal behavior, determining thus their bioavailability. © 2016, Springer-Verlag Berlin Heidelberg

Varying concentrations of soil chromium (VI) for the exploration of tolerance thresholds and phytoremediation potential of the oregano (Origanum vulgare)

Varying concentrations of soil Cr(VI) were used in order to explore the tolerance thresholds and phytoremediation potential of Greek oregano (Origanum vulgare), in a pot experiment conducted outdoors. Oregano exhibited a rather exceptional capacity to bioaccumulate Cr in both the aerial part (up to 1200 mg of total Cr kg −1 DM) and the root—reaching 4300 mg kg −1 DM when grown in soil [Cr(VI)] of 150–200 mg kg −1 . Plant responses indicated that there was a threshold set at 100 mg Cr(VI) kg −1 in the soil, above which the following results were recorded: (i) a restriction of Cr translocation from below- to above-ground plant part, (ii) a raise of the soil-to-root Cr transfer, and (iii) the Cr(III) evolution from the reduction of Cr(VI) was significantly decelerated in the root and accelerated in the aerial part. Soil [Cr] that surpassed this threshold challenged plant tolerance, resulting in a dose-dependent reduction of growth and antioxidant phenolics pool. Nonetheless, the significant Cr uptake capacity at plant level accounted for the considerably short remediation time (i.e., 29 years at soil [Cr(VI)] of 150 mg kg −1 ) calculated according to these results. The overall performance of oregano indicated that phytoremediation would be feasible at sites with Cr contamination levels ranging within the above-defined thresholds. © 2018, Springer-Verlag GmbH Germany, part of Springer Nature

Insecticidal effect of Dittrichia viscosa lyophilized epicuticular material against four major stored-product beetle species on wheat

We examined the insecticidal effect of lyophilized epicuticular material of the ruderal species Dittrichia viscosa in four major stored-product beetle species. Furthermore, the potential of this material in progeny production suppression was also evaluated. The water-soluble extract was derived from plants that had been harvested in September 2016, through freeze-drying, in order to create a fine powder formulation. In our bioassays, the powder was applied in four doses on wheat: 0 (control), 1000, 3000 and 5000 ppm and mortality of the exposed individuals was measured after 1, 3, 7, 14 and 21 days of exposure, while progeny production capacity was recorded 65 days later. Among the species tested, Oryzaephilus surinamensis was found to be the most susceptible, followed by Tribolium confusum and Sitophilus oryzae, while Rhyzopertha dominica was not practically affected. Progeny production was particularly reduced for all species relative to the controls. Indicatively, for O. surinamensis, at the highest dose rate, there were only 0.2 adults per vial, while the respective figures for the control exceeded 40 adults per vial. To our knowledge, this study is the first that examined the insecticidal effect of epicuticular material of D. viscosa for the control of stored-grain insect species. Additional experimentation is required to indicate the rationale of using this natural resource-based material under a non-chemical control strategy at the post-harvest stages of agricultural commodities. © 2020 Elsevier Lt

Basil as secondary crop in cascade hydroponics: Exploring salinity tolerance limits in terms of growth, amino acid profile, and nutrient composition

In a cascade hydroponic system, the used nutrient solution drained from a primary crop is directed to a secondary crop, enhancing resource-use efficiency while minimizing waste. Nevertheless, the inevitably increased EC of the drainage solution requires salinity-tolerant crops. The present study explored the salinity-tolerance thresholds of basil to evaluate its potential use as a secondary crop in a cascade system. Two distinct but complemented approaches were used; the first experiment examined basil response to increased levels of salinity (5, 10 and 15 dS m-1, compared with 2 dS m-1 of control) to identify the limits, and the second experiment employed a cascade system with cucumber as a primary crop to monitor basil responses to the drainage solution of 3.2 dS m-1. Growth, ascorbate content, nutrient concentration, and total amino acid concentration and profile were determined in both experiments. Various aspects of basil growth and biochemical performance collectively indicated the 5 dS m??1 salinity level as the upper limit/threshold of tolerance to stress. Higher salinity levels considerably suppressed fresh weight production, though the total concentration of amino acids showed a sevenfold increase under 15 dS m-1 and 4.5-fold under 5 and 10 dS m-1 compared to the control. The performance of basil in the cascade system was subject to a compromise between a reduction of fresh produce and an increase of total amino acids and ascorbate content. This outcome indicated that basil performed well under the conditions and the system employed in the present study, and might be a good candidate for use as a secondary crop in cascade-hydroponics systems. © 2021 by the authors. Licensee MDPI, Basel, Switzerland

Root vegetables bioaccumulate microcystins-LR in a developmental stage-dependent manner under realistic exposure scenario: The case of carrot and radish

Cyanotoxins are secondary metabolites of the ubiquitous cyanobacteria and exert their toxicity to plants and humans. Human health can be impacted by cyanotoxin bioaccumulation in crops via irrigation from contaminated water reservoirs. In the present study we conducted an ecologically relevant experiment in terms of toxin dose, cultivation time and the use of agricultural soil and naturally contaminated irrigation water. We investigated the growth response, protection potential, bioaccumulation profile and the related health risk of two widely consumed root vegetables, radish and carrot, when the exposure to microcystins-rich water commences at different developmental stages, from seed to 4 true leaves stage. Additionally, carrot was subjected to a prolonged depuration phase in order to evaluate its recovery potential. The results indicate a developmental stage-dependent profile of all measured parameters. Severe growth reduction was evident for plants receiving degraded water from the seed stage which reached 50% and 70% for radish and carrots, respectively. The impact was less pronounced when degraded water was first received at subsequent developmental stages. The protection response, in terms of phenolic content, was considerably insufficient to mitigate the stress at the tissue level. The earlier in its life cycle a plant confronts the exposure, the greater microcystins content occurs in its tissue, particularly in the edible parts, posing considerably high health risk for humans upon consumption. Estimated daily toxin intake after consuming treated taproots exceeded the World Health Organization safety threshold by 4 and 5 times for adults and children, respectively. The experimental depuration in carrot only partially alleviated the problem of bioaccumulation and growth impairment, thus, pointing to irreversible hazards. The results highlight the importance of monitoring the major cyanotoxins content in irrigation water and emphasize the necessity to re-visit the regulation/guidelines concerning the origin and quality of the irrigation water in the frame of effective agricultural water management. © 2020 Elsevier B.V

Spray irrigation with microcystins-rich water affects plant performance from the microscopic to the functional level and food safety of spinach (Spinacia oleracea L.)

Irrigation water coming from freshwater bodies that suffer toxic cyanobacterial blooms causes adverse effects on crop productivity and quality and raises concerns regarding food contamination and human exposure to toxins. The common agricultural practice of spray irrigation is an important exposure route to cyanotoxins, yet its impact on crops has received little attention. In the present study we attempted an integrated approach at the macro- and microscopic level to investigate whether spray or drip irrigation with microcystins (MCs)-rich water differently affect spinach performance. Growth and functional features, structural characteristics of stomata, and toxin bioaccumulation were determined. Additionally, the impact of irrigation method and water type on the abundance of leaf-attached microorganisms was assessed. Drip irrigation with MCs-rich water had detrimental effects on growth and photosynthetic characteristics of spinach, while spray irrigation ameliorated to various extents the observed impairments. The stomatal characteristics were differently affected by the irrigation method. Drip-irrigated spinach leaves showed significantly lower stomatal density in the abaxial epidermis and smaller stomatal size in the adaxial side compared to spray-irrigation treatment. Nevertheless, the latter deteriorated traits related to fresh produce quality and safety for human consumption; both the abundance of leaf-attached microorganisms and the MCs bioaccumulation in edible tissues well exceeded the corresponding values of drip-irrigated spinach with MC-rich water. The results highlight the significance of both the use of MCs-contaminated water in vegetable production and the irrigation method in shaping plant responses as well as health risk due to human and livestock exposure to MCs. © 2021 Elsevier B.V

Multi-Year Monitoring of Deciduous Forests Ecophysiology and the Role of Temperature and Precipitation as Controlling Factors

Two deciduous forest ecosystems, one dominated by Fagus sylvatica and a mixed one with Quercus cerris and Quercus frainetto, were monitored from an ecophysiological perspective during a five-year period, in order to assess seasonal fluctuations, establish links between phenology and ecophysiology, and reveal climatic controls. Field measurements of leaf area index (LAI), chlorophyll content, leaf specific mass (LSM), water potential (Ψ) and leaf photosynthesis (Aleaf) were performed approximately on a monthly basis. LAI, chlorophylls and LSM fluctuations followed a recurrent pattern yearly, with increasing values during spring leaf burst and expansion, relatively stable values during summer and decreasing values during autumn senescence. However, pre-senescence leaf fall and chlorophyll reductions were evident in the driest year. The dynamically responsive Aleaf and Ψ presented considerable inter-annual variation. Both oak species showed more pronounced depressions of Aleaf and Ψ compared to beech, yet the time-point of their appearance coincided and was the same for all species each year. Spring temperature had a positive role in the increasing phase of all ecophysiological processes while rising autumn temperature resulted in retarded senescence. Precipitation showed asymmetric effects on the measured ecophysiological parameters. The between-species differences in responses, climate sensitivity and climate memory are identified and discussed. © 2022 by the authors