Crushed maize seeds enhance soil biological activity and salt tolerance in caper (Capparis spinosa L.)

Highlights

• Applying biostimulant increased plant biomass and proline.

• Applying biostimulant significantly enhanced soil enzymes activity.

• Using biostimulant significantly increased the rutin bioflavonoid of caper.

• Applying biostimulant increased the phenol content of caper.

Abstract

Caper (Capparis spinosa L.) is an ancient plant with ecological, industrial, medicinal and economical benefits which at its primary growth phase is sensitive to salt stress. This study was conducted to investigate the biostimulant effect of supplementing crushed maize (Zea mays L.) seeds (CMS) (0, 10 and 20 %) into growing media on caper salt tolerance and soil biological activity under different salinity level (0, 5, 10 and 15 dS/m). Applying 20 % biostimulant increased the number of leaves and roots by 200.0 and 56.0 %, respectively, compared with untreated seedlings at the same salinity level. The application of 20 % biostimulant also enhanced the proline content (by 40.5 %), total phenolic contents (34.0 %), rutin (356.4 %) and leaf K content (29.8 %) of treated capers compared with untreated seedlings. Applying 20 % biostimulant also significantly increased the soil enzymes activity including urease, dehydrogenase, and phosphatase as well as soil bacteria population. Whereas, using biostimulant significantly decreased the content of Na in different caper’s organs. However, the total flavonoid content, soil fungi population and most of the morphological parameters of caper were not significantly affected by the application of CMS. In total, the soil application of CMS had a substantial effect on physiological and biochemical parameters of salinized capers and soil biological activity based on principal component analysis (PCA). In conclusion, using CMS as a soil supplement can be recommended as a safe and natural biostimulant to alleviate the negative impacts of salt stress in caper seedlings.

Introduction

Caper (Capparis spinosa L.), locally known as “Kavar” or “Kabbar”, is a perennial bush plant which is highly adaptive to a warm and dry climate. Based on the evidenced documents, caper is originated from the west and central regions of Asia and the date of its consumption in Middle East back to 2400–1400 B.C (Van Zeist and Bakker-Heeres, 1985). In folk medicine, it has been used as an antidote for a scorpion sting, anti-inflammatory, astringent, diuretic, tonic, and analgesic (Jiang et al., 2007). Based on the recent studies, different Capparis species have remarkable biological activities such as antimicrobial, antioxidant, antiplaque, and hepatoprotective activity. Moreover, C. spinose is an efficient and industrial source of important bioflavonoids such as rutin and quercetin (Gull et al., 2015). The commercial parts of caper are flower buds and unripe fruits which due to their strong flavor and special organoleptic properties are considered as popular condiment and salad seasoning in Mediterranean cuisines mainly (Sadeghi et al., 2012; Chedraoui et al., 2017). Morocco and Turkey are the largest exporters of caper while the United States of America (USA) is the leading importer where the price is about 25 US$ per kg. In some of Mediterranean and European countries, Australia and China caper is considered as an economic and valuable plant with low production cost (Chedraoui et al., 2017).

Caper plant has a high tolerance to the harsh environmental conditions such as high (>40 °C) and cold (−8 °C) temperature, drought, salinity, alkaline, and poor soil nutrition (Al-Yemeni and Zayed, 1999; Sozzi and Vicente, 2006). Moreover, its high soil covering ability (creeping vegetative parts) as well as deep root system make it a suitable species for increasing greenery and decreasing soil erosion in arid and semi-arid areas (Andrade et al., 1997; Chedraoui et al., 2017; Sadeghi and Rostami, 2016). Therefore, because of its high stress-tolerant characteristics as well as ecological and economic benefits, the cultivation of this plant in marginal and xeric areas of Asia as an alternative crop has been widely increased in recent years (Chedraoui et al., 2017; Al-Safadi and Elias, 2011; Sadeghi and Rostami, 2017). However, the large scale propagation of caper is limited by low germination percentage, rooting percentage of cuttings, and survival rate (<30 %) (Al-Safadi and Elias, 2011; Chedraoui et al., 2017). On the other hand, C. spinosa at its primary growth phase is sensitive to salt stress which significantly reduced the survival rate and successful establishment of young seedlings (Rostami et al., 2016). Therefore, in order to promote the cultivation of caper in xeric and saline condition, the growth rate, vigor, tolerance, and establishment of young seedlings should be meliorated (Ramezani-Gask et al., 2008).

One of the newest strategies to improve stress-tolerance, growth rate, yield, and performance of plants is the applying natural biostimulants. Natural biostimulants are organic product derived from animal or plant sources and contain a wide variety of biomolecules such as polysaccharides, amino acids, antioxidants, phytohormones, phenolic compounds and minerals which are easily assimilated by plants and soil microbial community. It also has been proven that they have significant effects on growth and yield attributes, nutrient uptake, metabolic processes, strength of crops under stress condition and soil biological activities. (Abdel Latef et al., 2017; du Jardin, 2015; Tejada et al., 2018; Rehman et al., 2018).

Due to the recent reports relating the phytotoxic effect of animal-origin biostimulants and the restrictive regulation of the European Union (EU) regarding the application of these biostimulants during the production of edible crops with “organic” label, using of plant derived biostimulants has received more attention (Nardi et al., 2016; Colla et al., 2015; du Jardin, 2015).

Among plant-based biostimulants, maize seed (as extract or soil supplement) is an organic, inexpensive, safe, non-toxic, and valuable source of plant hormones, minerals, proteins, and antioxidants which was exploited to enhance the growth attributes, nutrient uptake, growth hormone level, water content as well as the tolerance of stressed plants (Rady and ur Rehman, 2016; Rehman et al., 2018; Semida and Rady, 2014). In this respect, Rehman et al. (2018) observed that seed soaking of sunflower in maize grain extract significantly increased growth traits, membrane stability, the content of chlorophyll, carotenoids, soluble sugars, proline as well as up taking nitrogen, phosphorus, and potassium. Also, it was reported that the extract of maize seeds alleviated the negative impacts of salt stress in common bean (Rady et al., 2019; Semida and Rady, 2014) as well as improving cadmium tolerance in wheat plants (Alzahrani and Rady, 2019). However, there is only one report (Rady and ur Rehman, 2016) concerning the biostimulant effects of supplementing crushed maize seeds into growing media and no study regarding its potential effects on soil biological activities.

Based on the latest published statistics and soil maps, the area of saline and alkaline lands of Iran is more than 34 million hectares (20 % of total lands). Moreover, about 11 % of Iran’s water resources contain more than 1500 mg/L mineral content (Ranjbar and Pirasteh-Anosheh., 2015). On the other hand, caper is usually cultivated in marginal, dry and saline lands of Mediterranean countries with a poor soil fertility where salinity imposes a severe stress on young seedlings and led to the significant reduction of growth and survival rate (Chedraoui et al., 2017). To the best of author’s knowledge there are no studies concerning the use of natural biostimulants on caper plant under saline or normal condition. Therefore, the present investigation was conducted in order to assess the effect of crushed maize seeds on caper plant (in terms of growth attributes, photosynthesis pigments, proline, total phenolic and flavonoids, rutin, Na, and K concentration) and soil biological activities (in terms of soil enzymes activity and microbial community) under saline and normal condition.