# Effect of Plant Biostimulants on Nutritional and Chemical Profiles of Almond and Hazelnut
## 1 Introduction  
There has been an increasing interest in the functional characteristics of nuts, as these are a relevant source of bioactive constituents. Hazelnut (_Corylus avellama_ L.) is the most important cultivated species in the _Corylus_ genus (Bettalaceae). It is widely spread from the Himalayas to the far north of Canada [1]. Turkey is the world's largest producer, followed by Italy and the United States of America [2]. Likewise, almond [_Prunus dulcis_ (Mill.) [PERSON], Rosaceae] is one of the most popular nuts in the world, standing out in first place in what concerns production levels, mainly due to the contribution of California, the world's largest producer of this species [3, 4]. The benefits of including these nuts in the human diet are partly related to their monosaturated fatty acids (MUFA), particularly oleic acid, and polyunsaturated fatty acids (PUFA), namely linoleic acid, tocoperhools (e.g., \(\alpha\)-tocopherol), and phytosterols (e.g., \(\beta\)-sitosterol) [5, 6, 7, 8]. These liposoluble components have been recognized for their essential contribution to prevent dyslipidemia [9, 10, 11, 12], by specifically reducing the total plasma concentrations of LDL-cholesterol [13, 14, 15, 16, 17].  
Tocombrends are also recognized as antioxidants due to their ability to protect cell membranes from oxidative damage induced by free radicals [18, 19, 20], in addition to having anti-inflammatory potential [21].  
Almond and hazelnut crops are very important, particularly among countries with high production levels, such as Portugal, owing to their interesting nutritional/functional value. The chemical profile of these nuts may vary due to edapoclimatic factors, which can also modulate the corresponding production yields, for instance due to frost damage, by hampering the entomophile pollination, or disordered flowering and flower degeneration. Using biostimulants might be an effective way to improve nutrients uptake from the soil, as well as increasing photosynthesis levels, thereby representing a useful treatment for different crops like almond and hazelnut [2; 22; 23].  
Because of their potential health benefits, almond and hazelnut are being progressively included in healthy diets, demanding higher production levels worldwide. Nonetheless, there is a general concern towards the practice of agriculture less harmful to the environment, which raises the need for ecological alternatives to fertilizers or pesticides. The search for biostimulants has been an active research field, but the maintenance, or ideally the improvement, of the products obtained when using these growing adjuvants must be verified [2; 22; 23]. Studies report that the use of marine bioactive substances extracted from algae in agricultural and horticultural crops has many beneficial effects in terms of increased yield and quality [24; 25]. Seaweed extracts contain primary and secondary nutrients, amino acids, vitamins, cytokins, auxin, and abscisic acid [26], among other substances that stimulate plant growth and performance [27], help develop tolerance to environmental stress [28; 29], increase nutrient uptake from soil [30; 31], and increase antioxidant properties [31; 32].  
It is a fact that the chemical profile of nuts can have a slight, although natural, variability within each species. Besides the edapoclimatic conditions, these fluctuations might be due to the cultivar or agricultural factors, such as the use of plant biostimulants [12; 33; 34]. The best biostimulant application intends to improve the plant's nutrient use efficiency and enhance tolerance to biotic and abiotic stresses. Bearing this in mind, we tested the influence of two plant biostimulants (seaweed extract and free amino acids) in combination with soil and foliar boron (in almond), and with or without using a basal NPK (nitrogen, phosphorus, and potassium) fertilization program (in hazelnut), in the chemical (moisture, total fat, proteins, carbohydrates, and ash) and phytochemical (fatty acids, tocopherols, sterols) properties of almond and hazelnut.