Plant-Based Biostimulants Influence the Agronomical, Physiological, and Qualitative Responses of Baby Rocket Leaves under Diverse Nitrogen Conditions

Abstract

Nitrogen is the primary technical means responsible for food production increase, but on the other hand, wise management is needed because its excessive use can have a negative impact on the environment and on green leafy vegetable quality, such as that rocket. Rocket has the characteristics of accumulating nitrate in leaves with possible impacts on human health. In order to overcome this issue, researchers are focusing their attention on the use of alternative means, such as plant biostimulant application. The scope of this study was to assess the effect of legume-derived protein hydrolysate(LDPH) and tropical plant extract(TPE), combined with various doses of nitrogen (0 kg ha−1 non-fertilized; N0); 60 kg ha−1 (sub-optimal; N1); 80 kg ha−1 (optimal; N2); and 100 kg ha−1 (supra-optimal; N3)), in order to reduce nitrogen use, boost yield, and enhance the chemical and nutritional value of leaves without significantly accumulating nitrate. Both vegetal-based plant biostimulants enhanced plant growth, boosted the marketable yield (especially at N0 and N1 levels, by 38.2% and 28.2%, respectively, compared to the non-treated control), and increased the SPAD (Soil Plant Analysis Development) index and leaf pigments content, such as chlorophyll and carotenoids, especially in treated-LDPH rocket. The plant-based biostimulants also produced a major amplification in lipophilic antioxidant activity (+ 48%) and total ascorbic acid content (average + 95.6%), especially at low nitrogen fertilization levels, and maintained nitrate content under the legal European Comission limits.

Nitrogen Use and Uptake Efficiency and Crop Performance of Baby Spinach (Spinacia oleracea L.) and Lamb’s Lettuce (Valerianella locusta L.) Grown under Variable Sub-Optimal N Regimes Combined with Plant-Based Biostimulant Application

“…This was the case in the current study, whereby baby spinach and lamb's lettuce cultivated under N100% negatively modulated the synthesis and accumulation of antioxidant molecules such as total phenols and ascorbic acid along with low antioxidant activity. Similar trends were reported recently by Di Mola et al [42,43] on baby lettuce and rocket grown under optimal and supra-optimal N regimes.…”

“…The plant-based biostimulant used in this test was Trainer ® , a legume-derived protein hydrolysate (containing free amino acids and signaling molecules such as small soluble peptides), for which previous researches have already demonstrated its ability to boost crops' resources use efficiency (RUE) [15,52]-especially N uptake and assimilation [39]-as well as productivity [6,32] and quality [53,54]. Our results highlighted the ability of LDPH to enhance yield of both baby spinach and lamb's lettuce (+24.6% and +13.5% for plant sprayed with Trainer ® compared to control plants, respectively), which is in line with Carillo et al's [35] findings on spinach, and Di Mola et al [42,43] on other two important leafy greens (lettuce and baby leaf rocket) cultivated under variable N regimes. The positive effects of the foliar application of LDPH, irrespective of the N fertilization treatments, were more pronounced in spinach than in lamb's lettuce, demonstrating a species-specific response [15,55], especially that the same commercial plant-based biostimulant was used.…”

“…Interestingly, in our study the marketable fresh yield of LDPH-treated spinach and lamb's lettuce grown under N50% was similar to those grown under N100% (especially the non-treated plants). A number of biochemical and physiological aspects may have contributed to this result, including (i) a higher chlorophyll content (a, b and total) and SPAD index in biostimulant-treated than in non-treated plants, and (ii) improved leaf status in terms of nitrate content, triggering a more efficient translocation of assimilates to potential photosynthetic sinks, thus boosting plant growth and yield [35,42,43]. Moreover, several authors attributed the stimulation action and the increased N assimilation in response to LDPH application to multiple mechanisms of action involving (i) the hormones-like activities (i.e., auxin and giberrellins-like activities), (ii) the increase in the activity of the key enzymes glutamine synthetase and nitrate reductase, and (iii) the upregulation of specific genes responsible in N assimilation and pigment synthesis [27,33,[56][57][58].…”

Changes in Biochemistry and Yield in Response to Biostimulants Applied in Bean (Phaseolus vulgaris L.)

“…The beneficial effect of biostimulants with seaweed extracts or amino acids on plant growth and development, and on the quantity and quality of the yield, regardless of its developmental stage, was confirmed in numerous studies [13,34,35,[39][40][41][57][58][59][60][61][62]. An interesting solution is to combine these two components in a single preparation, as in the case of the Fylloton biostimulant (Biolchim Poland), which contains the extract of Ascophyllum nodosum (L.) Le Jolis, as well as vegetal amino acids.…”

“…Due to the presence of specific peptides and precursors of phytohormone biosynthesis (tryptophan, which is the main precursor of IAA (Indole-3-acetic acid) biosynthesis and bioactive peptides), protein hydrolysates affect the hormonal balance of plants, which is related to stimulating plant growth [53]. The use of these biopreparations positively impacts the quality of agricultural produce, increasing the content of carotenoids, flavonoids, polyphenols, and ascorbic acid [54][55][56][57], and reducing the amount of undesirable compounds, e.g., nitrates [56].…”