Effect of Sulfur and Nod Factors (LCOs) on Some Physiological Features and Yield of Pea (Pisum sativum L.)

Abstract

The response of pea var. Medal to treatment with Nod factors (LCOs) and mineral sulfur was estimated in a pot experiment with a completely randomized design. Foliar spraying of plants was performed at the 5–6 leaf stage (BBCH 15) at concentrations of 10⁻¹² M dm⁻³ and 12 g S dm⁻³ for LCOs and sulfur, respectively. The use of these factors, both individually and in combination, caused an increase in leaf area and “greenness” (SPAD), gas exchange parameters, straw and seed yields and in the root system. The number of nodules and respective nodule dry weight also increased with these treatments. A significant increase in seed yield resulted from the beneficial effects of LCOs and sulfur with an increase in the number of pods and seeds per plant compared to control plants, is clearly significant from the agricultural point of view. Although each factor improved the traits studied, the best results were achieved in the case of plants treated with both LCOs and sulfur.

These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Leguminous plants have a great importance in agriculture for the production of valuable seeds, which are used as food for human and fodder for animals. However, a relatively low and variable seed yield has led to a decrease in their cultivation (Graham and Vance 2003). Therefore scientists are looking at factors, which may improve the yield of legume s. Some of these studies are focused on the legumes’ ability for biological nitrogen fixation (BNF) by forming a relationship with specialized nitrogen-fixing bacteria called rhizobia (van Hameren et al. 2013). The rhizobia convert atmospheric di-nitrogen into forms of nitrogen usable for the plant, whilst being housed in novel root organs – nodules. Optimizing BNF processes, such as nodulation, has the potential to increase crop yields and enhance soil fertility whilst reducing farming costs and harmful environmental impacts (van Hameren et al. 2013). Research into legume-rhizobia symbioses has identified numerous plant and bacterial metabolites, which are essential for the establishment of symbiosis and development of root nodules (Brewin 2004). This group of metabolites includes bacterial Nod factors (lipochitooligosaccharides-LCOs), which are bacteria-to-plant signals required for the establishment of rhizobia-legume nitrogen fixing symbioses (Cullimore et al. 2001). LCOs induce the formation of root nodules (Geurts et al. 2005; Podleśny et al. 2014a) and improve plant germination, growth and yield (Podleśny et al. 2014b) so they could be used as biofertilizers (Bhardwaj et al. 2014; Kidaj et al. 2012). On the other hand, BNF is particularly sensitive to environmental stresses such as nutrient deficiency (Divito and Sadras 2014). Varin et al. (2010) showed that sulfur has an important role in this process by demonstrating that its deficiency reduces nitrogen fixation in pea (Pisum sativum L.) and lucerne (Medicago sativa L.). Some Rhizobium-legume symbiotic interactions are mediated by Nod factor s (LCOs), which can be sulfated (Snoeck et al. 2003). Moreover sulfur, as glutathione or ascorbate-glutathione cycle enzymes, is essential for the establishment of legume-rhizobia symbiosis, regulation of the cell cycle and growth, and for root meristem activity (Groten et al. 2005). However, the amount of sulfur in the soil profile is frequently not sufficient to fulfill the nutritional needs of legumes (Cazzato et al. 2012; Szulc et al. 2014). The aim of the present study was the evaluation of LCOs, mineral sulfur and the combined application of both factors on physiological and agricultural parameters of pea yield.

An experiment was conducted in the greenhouse, in Mitscherlich pots, which contained a mixture of soil (5 kg) and sand (2 kg) and which were planted with pea var. Medal (afila type). The plants were sprayed with: 1, control (distilled water); 2, LCOs/Nod factors (concentration: 10⁻¹² M dm⁻³); 3, sulfur (concentration: 12 g S dm⁻³); and 4, LCOs and sulfur in the above-mentioned concentrations. Rhizobial Nod factors (LCOs) were isolated from liquid cultures of Rhizobium leguminosarum bv. viciae GR09 (Rlv GR09) strain induced by a plant flavonoid extract (Wielbo et al. 2007). Foliar spraying (25 ml per pot of five plants) was performed in the 5–6 leaf phase of growth (BBCH 15). Plants were harvested at three developmental phases: flowering (BBCH 60), fruit development (BBCH 75) and full maturity (BBCH 89). Dry matter of specific plant organs and seed yield were measured (Fig. 1).

Fig. 1

Impact of LCOs (10⁻¹² M dm⁻³) and sulfur (12 g S dm⁻³) on yield of pea plants. The weight of straw, seeds and root system was determined upon harvest at full maturity (BBCH 89). Seed yield was calculated for 14 % moisture content and expressed per pot. Roots were rinsing in dense metal sieves, dried and weighed. Different letters indicate significant differences between treatments (p ≤ 0.05, Tukey’s test)

Both LCOs, sulfur, and their combined use had an effect on the parameters measured. Firstly, an increase in leaf area during the flowering and green pod phases of pea growth in comparison to control plants (treated with distilled water) was observed (Table 1). Moreover, these leaves also demonstrated an increased leaf greenness index (SPAD). The application of LCOs and sulfur increased the values of the main gas exchange parameters in the pea leaves (Table 2). It is probable that these changes of photosynthesis (Pn) and transpiration (E) intensity were the result of greater leaf area and greater concentration of chlorophyll in leaves as an effect of plants treated with LCOs, sulfur or both these factors. The best results of studied traits were achieved in plants treated with both LCOs and sulfur, and were lower in plants treated with LCOs (leaf area and SPAD) and with sulfur (Pn, net photosynthesis and E, transpiration intensity). Similar responses of peas to LCOs were observed earlier (Kidaj et al. 2012; Podleśny et al. 2014a, b). The same trends in the effect of LCOs on soybean were found by Almaraz et al. (2007), who observed a 13 % increase in photosynthesis over controls which was accompanied by increase in stomatal conductance. Previous studies have suggested that Nod factors sprayed onto shoots stimulate carbon sink strength by increasing early cell division in meristems and this may trigger an increase in photosynthetic rate, based on photosynthetic regulation by carbon sinks. Moreover, the observed increase in stomatal conductance may indicate that Nod factors improved photosynthetic rate by increasing the CO₂ supply for photosynthesis (Almaraz et al. 2007). Applied sulfur also showed a beneficial effect on gas exchange parameters, indicating that this nutrient plays an important role in these processes. According to Mazid et al. (2011) the photosynthetic apparatus is severely affected under S deficiency, mainly by the reduction of chloroplast and Rubisco content. As the largest increase in leaf area, photosynthetic activity and transpiration was observed with combined use of LCOs and sulfur, it may indicate that the use of these both factors increases their beneficial effect. Similarly, observation of the roots showed that the use of LCOs and sulfur, and particularly their use in combination, had a significant effect on the number of root nodules and their total dry matter (Table 3). The results obtained are in agreement with the findings of Kidaj et al. (2012) and Podleśny et al. (2014a, b) in relation to plants response to LCOs and with observations of Scherer et al. (2006) and Zhao et al. (1999) in relation to sulfur. The earlier studies of Podleśny et al. (2014a, b) found that LCOs slightly accelerated pea growth from the first developmental phases and stimulated the growth of vegetative and generative organs. Scherer et al. (2006) showed an effect of sulfur on the amount of sucrose and glucose in shoots and nodules of pea. According to these authors, when S is limiting, protein synthesis is inhibited resulting in lower yields. Moreover, pea plants fertilized with sulfur fixed more nitrogen than control plants (S0). The analysis of yield structure demonstrated the beneficial effect of LCOs and sulfur in increasing the number of pods and seeds per plant (Table 4). It can be supposed that plants sprayed with LCOs improved nitrogen fixation and additionally sprayed with sulfur more effectively used it as sulfur deficiency decrease nitrogen use efficiency (Fismes et al. 2000).

Table 1 Impact of LCOs (10⁻¹² M dm⁻³) and sulfur (12 g S dm⁻³) on chosen pea leaf indices during growth

Table 2 Impact of LCOs (10⁻¹² M dm⁻³ of water) and sulfur (12 g S dm⁻³) on gas exchange parameters of pea leaves

Table 3 Impact of LCOs (10⁻¹² M dm⁻³ of water) and sulfur (12 g S dm⁻³) on number and dry matter of root nodules (mg plant⁻¹) and dry matter of 1 nodule (mg) during flowering (BBCH 60) and green pod (BBCH 75) stages of pea growth

Table 4 Impact of LCOs (10⁻¹² M dm⁻³) and sulfur (12 g S dm⁻³) on pea yield structure features