Rhizobial–Host Interactions and Symbiotic Nitrogen Fixation in Legume Crops Toward Agriculture Sustainability

Abstract

Symbiotic nitrogen fixation (SNF) process makes legume crops self-sufficient in nitrogen (N) in sharp contrast to cereal crops that require an external input by N-fertilizers. Since the latter process in cereal crops results in a huge quantity of greenhouse gas emission, the legume production systems are considered efficient and important for sustainable agriculture and climate preservation. Despite benefits of SNF, and the fact that chemical N-fertilizers cause N-pollution of the ecosystems, the focus on improving SNF efficiency in legumes did not become a breeder’s priority. The size and stability of heritable effects under different environment conditions weigh significantly on any trait useful in breeding strategies. Here we review the challenges and progress made toward decoding the heritable components of SNF, which is considerably more complex than other crop allelic traits since the process involves genetic elements of both the host and the symbiotic rhizobial species. SNF-efficient rhizobial species designed based on the genetics of the host and its symbiotic partner face the test of a unique microbiome for its success and productivity. The progress made thus far in commercial legume crops with relevance to the dynamics of host–rhizobia interaction, environmental impact on rhizobial performance challenges, and what collectively determines the SNF efficiency under field conditions are also reviewed here.

Biofertilizers: An ecofriendly technology for nutrient recycling and environmental sustainability

“…Another important aspect of nitrogen fixation is leghemoglobin formation in nodules, which helps in maintaining a low concentration of oxygen necessary for the activity of oxygen-sensitive nitrogenase ( Marchal, and Vanderleyden, 2000 ). The process of nitrogen fixation carried out by Rhizobium enables the legumes to be less dependent on chemical fertilizers as compared to the non-leguminous plants ( Goyal et al, 2021 ).…”

Enhanced Soybean Productivity by Inoculation With Indigenous Bradyrhizobium Strains in Agroecological Conditions of Northeast Germany

“…The soils for both greenhouse experiments were collected from the same site where the field trial was conducted. However, significantly higher nodulation and shoot N uptake were observed in the greenhouse compared with the field conditions, indicating the strong influence of abiotic variables on nodulation and soybean growth (Hungria and Vargas, 2000;Goyal et al, 2021). The observed low mean temperature (11.4 • C) in field conditions in early May translated into a low root zone temperature (Schmidt et al, 2015), and low precipitation (5 mm, i.e., only 20% of total precipitation) during germination and seedling establishment of soybean plants likely influenced the symbiotic performance of the strains.…”

“…Environmental stress factors such as temperature, drought, salinity, pH, biotic competition, etc. affect both the host and rhizobium response, leading to a reduction in BNF efficiency ( Laranjo and Oliveira, 2011 ; Goyal et al, 2021 ). According to Cernay et al (2015) , the high susceptibility of BNF to environmental stress factors is one of the major drivers of the high grain legume yield variability in Europe.…”

Impact of Two Strains of Rhizobium leguminosarum on the Adaptation to Terminal Water Deficit of Two Cultivars Vicia faba

“…Drought stress constraints plants and rhizobia act symbiotically to perform optimally [3]. Climate change is expected to aggravate the periods and intensity of water stress, including drought stress.…”

“…Legumes are an important source of protein suitable for livestock feed and human consumption [1]. Additionally, their ability to establish a symbiosis with specific Rhizobium bacteria that enzymatically convert atmospheric nitrogen into organic form in the host roots, provides the benefit of reduced fertilizer input and enhanced soil biological activity which helps in improving and sustaining the soil productivity [2,3]. Faba bean (Vicia faba L.) is one of the most important legume crops globally [2], owing to its high protein content (up to 35% in dry seeds), carbohydrates, fiber, and vitamins [1,4].…”