Title : Fish hydrolysates as effective biostimulants for plants
Abstract:
Climate change poses significant challenges to plant health, affecting their resistance to various stresses. Several strategies are used to increase plant resilience in the face of climate change. Among them is the use of biostimulants, which can help plants withstand stressful conditions while promoting growth and productivity. The biostimulants produced from fish waste may be a promising innovative solution for increasing crop yields by stimulating plant growth and development, as well as increasing their resistance to abiotic and biotic factors. Due to their high nutrient content, fish waste and by-products are among the most promising candidates for the production of alternative fertilizer products, such as plant biostimulants. Moreover, it can be a way to solve the problem of waste disposal. This approach is in line with the principles of the circular economy and is fully justified from both an economic and environmental point of view. Thus, the aim of the study was to develop an optimal method for the production of fish hydrolysates and test their effectiveness as plant biostimulants for important crops such as corn and beans. Rainbow trout (Oncorhynchus mykiss) fish waste was hydrolysed using proteolytic enzymes from trout entrails. Hydrolysate I consists only of homogenised fish viscera. Hydrolysate II consists of homogenised bones/heads and fish viscera in a ratio of 3:1. All samples were placed in a water bath at +37°C (12 hours) and then boiled for 1 hour. Common bean seeds (Phaseolus vulgaris L.) were planted in soil and watered once with 1%, 2% or 5% solutions of fish hydrolysates I and II. The control group was watered with water. The effect of hydrolysates on the germination and growth of beans, chlorophyll and carotenoid content was determined. It was found that treatment with a 1% concentration of fish hydrolysates is more optimal for beans, while at a concentration of 5%, hydrolysate I inhibited germination, and after treatment with 5% hydrolysate II, not a single seed germinated. Therefore, in the group of plants treated with 5 % fish hydrolysates, biochemical studies of photosynthetic pigments were not carried out. The treatment of beans with 1% hydrolysate I showed almost twofold growth stimulation. This hydrolysate was obtained only from the entrails, so the amount of enzymes in this sample is quite significant. The higher amount of enzymes could contribute to a better breakdown of proteins into low molecular weight peptides, which, accordingly, facilitated their assimilation by plants. On the other hand, hydrolysate II, which contained a lot of bones in the raw material, contains a correspondingly large amount of calcium, an excess of which can cause chlorosis. According to our data, hydrolysate I in both doses did not have a negative effect on the pigments of the photosynthetic system, while hydrolysate II had a destructive effect on the chlorophyll a content, even in low concentrations It is also known that calcium plays an important role in symbiotic signaling between the root system of legumes and nitrogen-fixing bacteria, so it is likely that an excess of calcium can additionally negatively affect this interaction. Consequently, it was found that for beans, a hydrolysate of fish entrails alone at a concentration of 1% is more effective as a plant biostimulant.
