Leaf silicification provides herbivore defence regardless of the extensive impacts of water stress

Silicon nanoparticles: Comprehensive review on biogenic synthesis and applications in agriculture

Recent advancements in nanotechnology have opened new advances in agriculture. Among other nanoparticles, silicon nanoparticles (SiNPs), due to their unique physiological characteristics and structural properties, offer a significant advantage as nanofertilizers, nanopesticides, nanozeolite and targeted delivery systems in agriculture. Silicon nanoparticles are well known to improve plant growth under normal and stressful environments. Nanosilicon has been reported to enhance plant stress tolerance against various environmental stress and is considered a non-toxic and proficient alternative to control plant diseases. However, a few studies depicted the phytotoxic effects of SiNPs on specific plants. Therefore, there is a need for comprehensive research, mainly on the interaction mechanism between NPs and host plants to unravel the hidden facts about silicon nanoparticles in agriculture. The present review illustrates the potential role of silicon nanoparticles in improving plant resistance to combat different environmental (abiotic and biotic) stresses and the underlying mechanisms involved. Furthermore, our review focuses on providing the overview of various methods exploited in the biogenic synthesis of silicon nanoparticles. However, certain limitations exist in synthesizing the well-characterized SiNPs on a laboratory scale. To bridge this gap, in the last section of the review, we discussed the possible use of the machine learning approach in future as an effective, less labour-intensive and time-consuming method for silicon nanoparticle synthesis. The existing research gaps from our perspective and future research directions for utilizing SiNPs in sustainable agriculture development have also been highlighted.

Field application of silicon alleviates drought stress and improves water use efficiency in wheat

Detrimental impacts of drought on crop yield have tripled in the last 50 years with climate models predicting that the frequency of such droughts will intensify in the future. Silicon (Si) accumulation, especially in Poaceae crops such as wheat (Triticum aestivum L.), may alleviate the adverse impacts of drought. We have very limited information, however, about whether Si supplementation could alleviate the impacts of drought under field conditions and no studies have specifically manipulated rainfall. Using field-based rain exclusion shelters, we determined whether Si supplementation (equivalent to 39, 78 and 117 kg ha^-1) affected T. aestivum growth, elemental chemistry [Si, carbon (C) and nitrogen (N)], physiology (rates of photosynthesis, transpiration, stomatal conductance, and water use efficiency) and yield (grain production) under ambient and drought (50% of ambient) rainfall scenarios. Averaged across Si treatments, drought reduced shoot mass by 21% and grain production by 18%. Si supplementation increased shoot mass by up to 43% and 73% in ambient and drought water treatments, respectively, and restored grain production in droughted plants to levels comparable with plants supplied with ambient rainfall. Si supplementation increased leaf-level water use efficiency by 32-74%, depending on Si supplementation rates. Water supply and Si supplementation did not alter concentrations of C and N, but Si supplementation increased shoot C content by 39% and 83% under ambient and drought conditions, respectively. This equates to an increase from 6.4 to 8.9 tonnes C ha^-1 and from 4.03 to 7.35 tonnes C ha^-1 under ambient and drought conditions, respectively. We conclude that Si supplementation ameliorated the negative impacts of drought on T. aestivum growth and grain yield, potentially through its beneficial impacts on water use efficiency. Moreover, the beneficial impacts of Si on plant growth and C storage may render Si supplementation a useful tool for both drought mitigation and C sequestration.

Functions of silicon in plant drought stress responses

Silicon (Si), the second most abundant element in Earth's crust, exerts beneficial effects on the growth and productivity of a variety of plant species under various environmental conditions. However, the benefits of Si and its importance to plants are controversial due to differences among the species, genotypes, and the environmental conditions. Although Si has been widely reported to alleviate plant drought stress in both the Si-accumulating and nonaccumulating plants, the underlying mechanisms through which Si improves plant water status and maintains water balance remain unclear. The aim of this review is to summarize the morphoanatomical, physiological, biochemical, and molecular processes that are involved in plant water status that are regulated by Si in response to drought stress, especially the integrated modulation of Si-triggered drought stress responses in Si accumulators and intermediate- and excluder-type plants. The key mechanisms influencing the ability of Si to mitigate the effects of drought stress include enhancing water uptake and transport, regulating stomatal behavior and transpirational water loss, accumulating solutes and osmoregulatory substances, and inducing plant defense- associated with signaling events, consequently maintaining whole-plant water balance. This study evaluates the ability of Si to maintain water balance under drought stress conditions and suggests future research that is needed to implement the use of Si in agriculture. Considering the complex relationships between Si and different plant species, genotypes, and the environment, detailed studies are needed to understand the interactions between Si and plant responses under stress conditions.