Ascophyllum nodosum-Based Biostimulants: Sustainable Applications in Agriculture for the Stimulation of Plant Growth, Stress Tolerance, and Disease Management
- 1Marine Bio-products Research Laboratory, Department of Plant, Food and Environmental Sciences, Dalhousie University, Truro, NS, Canada
- 2Research & Development, Acadian Seaplants Limited, Dartmouth, NS, Canada
Abiotic and biotic stresses limit the growth and productivity of plants. In the current global scenario, in order to meet the requirements of the ever-increasing world population, chemical pesticides and synthetic fertilizers are used to boost agricultural production. These harmful chemicals pose a serious threat to the health of humans, animals, plants, and the entire biosphere. To minimize the agricultural chemical footprint, extracts of Ascophyllum nodosum (ANE) have been explored for their ability to improve plant growth and agricultural productivity. The scientific literature reviewed in this article attempts to explain how certain bioactive compounds present in extracts aid to improve plant tolerances to abiotic and/or biotic stresses, plant growth promotion, and their effects on root/microbe interactions. These reports have highlighted the use of various seaweed extracts in improving nutrient use efficiency in treated plants. These studies include investigations of physiological, biochemical, and molecular mechanisms as evidenced using model plants. However, the various modes of action of A. nodosum extracts have not been previously reviewed. The information presented in this review depicts the multiple, beneficial effects of A. nodosum-based biostimulant extracts on plant growth and their defense responses and suggests new opportunities for further applications for marked benefits in production and quality in the agriculture and horticultural sectors.
The global effects of negative climatic changes have manifested as desertification, increased atmospheric CO2and temperature, soil salinization, and nutrient imbalances (e.g., mineral toxicity and deficiency) and have caused dramatic effects on agricultural production and the quality of crops (dos Reis et al., 2012). Such abiotic stresses have reduced the growth, development, productivity, and quality of plants and, in extreme conditions, resulted in death and local extinction of species (Matesanz et al., 2010; Anderson et al., 2011). Abiotic stresses are reported to have led to an average yield loss greater than 50% in most crops (Boyer, 1982; Vinocur and Altman, 2005). Rice yields declined 15% per 1°C rise in mean growing season temperature, measured from 1979 to 2003 (Peng et al., 2004). Additionally, changing climatic conditions can increase plant susceptibility to pathogens (West et al., 2012; Elad and Pertot, 2014), further increasing adverse growing conditions for plants.
The global amount of cultivable land available for agriculture is continuously shrinking due to urbanization and the adverse effects of climate change. In order to meet the ever-increasing demands of the growing human population, world food production must double by the year 2050 (Qin et al., 2011; Voss-Fels and Snowdon, 2016). To address the pressures associated with increasing agricultural productivity to subsequently meet the rising demands for food, producers have turned to excessive applications of synthetic (chemical) fertilizers and pesticides. These harmful chemicals pose both short- and long-term threats to the health of the entire biosphere (Damalas and Koutroubas, 2016). Therefore, an effective, biological-based alternative is required in order to reduce dependency on synthetic fertilizers and pesticides. Plant biostimulants are a new class of crop input, offering a potential alternative to traditional, agro-chemical inputs, and, in most cases, can reduce the application rates of synthetic fertilizers and pesticides by enhancing their efficacy (Calvo et al., 2014; Van Oosten et al., 2017; Yakhin et al., 2017).
According to the European Biostimulants Industry Council (EBIC), “plant biostimulants contain substance(s) and/or micro-organisms whose function when applied to plants or the rhizosphere is to stimulate natural processes to enhance/benefit nutrient uptake, nutrient efficiency, tolerance to abiotic stresses, and crop quality”1. The concept of biostimulants has been researched since 1933 (Yakhin et al., 2017) but has gained attention in more recent years as a potential solution to mitigate the negative impacts of a changing climate on agriculture. It should be noted that seaweed extracts are but one of the inputs that are classed as biostimulants.
Seaweeds are multi-cellular, macroscopic organisms found in coastal, marine ecosystems and are a rich source of polysaccharides, polyunsaturated fatty acids (PUFAs), enzymes, and bioactive peptides among others (Courtois, 2009; De Jesus Raposo et al., 2013; Ahmadi et al., 2015; Shukla et al., 2016; Okolie et al., 2018). In particular, inter-tidal seaweeds may be exposed to unfavorable conditions including extreme variations in temperature, salinity, and light. Seaweeds, as compared to terrestrial organisms, produce different stress-related compounds that are essential for their survival in these environments (Shukla et al., 2016). As such, selected seaweed resources are important sources of plant biostimulants and are widely used to promote agricultural productivity (Khan et al., 2009; Sharma et al., 2014; du Jardin, 2015; Van Oosten et al., 2017). The most widely researched seaweed, used as a source for industrial and commercial plant biostimulants, is the brown, inter-tidal seaweed Ascophyllum nodosum. Various commercial extracts from A. nodosum have been demonstrated to improve plant growth, mitigate some abiotic and biotic stresses while also improving plant defenses by the regulation of molecular, physiological, and biochemical processes. Of all sources of seaweed-based biostimulants, those manufactured from A. nodosum are perhaps the best studied with various modes of action being proposed (Figure 1). This review focuses on accumulating current knowledge of the bioactive compounds presents in A. nodosum extracts and their modes of action in promoting plant growth in the presence of abiotic and biotic stresses.