Environmental hormesis of non-specific and specific adaptive mechanisms in plants

Agricultural systems in the EU have become more vulnerable and less sustainable due to an overreliance on herbicides and the tremendous increase in herbicide-resistant weeds. The EU Green Deal aims to reduce the use and risk of chemical pesticides by 50% by 2030, although it is still undefined whether a reduction in herbicide use could be feasible in different farming systems and situations. This review aims to provide a holistic framework for sustainable crop and weed management to reduce the herbicide input and ensure crop protection. Current and future dilemmas and policies that need to be handled to ensure the agroecological transition of the EU’s agricultural systems are also discussed. The integration of non-chemical alternatives for integrated weed management is feasible and includes novel cultivation techniques (e.g., intercropping, false seedbed, reduced tillage, crop rotation and diversification, adjustments on sowing densities and dates), non-chemical tools (e.g., flaming, seed coating, beneficial microorganisms, mechanical weeding, biocontrol agents and natural herbicides), competitive plant material (hybrids and cultivars, cover crops, service crops), and new technologies and precision agriculture tools (e.g., Decision Support Systems, robots, remote sensing, UAVs, omics and nanotechnology). A special focus should be appointed to agroecology and biodiversity conservation.

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Sustainable Crop and Weed Management in the Era of the EU Green Deal: A Survival Guide

The recent recognition that low doses of herbicides, human and veterinary antibiotics, metallic elements, micro/nano-plastics, and various other types of environmental pollutants widely enhance chlorophylls in the framework of hormesis created the need to further evaluate the response of photosynthetic pigments and gas exchange to low doses of stresses. An analysis of about 370 values of maximum stimulatory response (MAX; percentage of control response, %) of chlorophylls in higher plants, algae and duckweeds, and other photosynthesizing organisms, mined from published literatures, revealed a greater MAX for higher plants (median = 139.2%) compared to algae and duckweeds (median = 119.6%). However, an analysis of about 50 mined values of MAX of carotenoids revealed no significant difference in the median MAX between higher plants (median = 133.0%) and algae-duckweeds (median = 138.1%). About 70 mined values of MAX were also concentrated for photosynthetic rate (median MAX = 129.2%) and stomatal conductance (median MAX = 124.7%) in higher plants. Within higher plants, there was no significant difference in the median MAX among chlorophylls, carotenoids, photosynthetic rate, and stomatal conductance. Similarly, there was no significant difference in the median MAX between chlorophylls and carotenoids of pooled algae and duckweeds. The results suggest that the MAX is typically below 160% and as a rule below 200% of control response, and does not differ among chlorophylls, carotenoids, photosynthetic rate, and stomatal conductance. New research programs with improved experimental designs, in terms of number and spacing of doses within the “low-dose zone” of the hormetic dose–response relationship, are needed to study the molecular/genetic mechanisms underpinning the low-dose stimulation of photosynthesis and its ecological implications.

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José Carlos de Oliveira Junior

Papers

Hormesis in plants: Physiological and biochemical responses.