Molecular Soil Biology 2024, Vol.15, No.2, 74-86 http://bioscipublisher.com/index.php/msb 78 efficiency. For instance, Bradyrhizobiumspecies are the exclusive symbionts for legumes in the Caesalpinioideae sub-family, while Mesorhizobiumand Burkholderia are prevalent in the Fynbos region of South Africa (Lemaire et al., 2015; Andrews and Andrews, 2016). Figure 2 Split-root systems to characterize the control of nitrogen-fixing symbiosis by systemic N signaling of the plant N demand (Adopted from Lepetit and Brouquisse, 2023) Image caption: (A) Split root systems used to study the control of nodule formation by plant N demand. Non symbiotic plants are used. Contrasted mineral N supply applied to half-root systems may either fully satisfy the plant N demand (N satiety) or results in plant N limitation (N deficit). The response to inoculation by rhizobium in untreated roots strongly relies on the level of N supply of the plant revealing the strong systemic control of nodule formation by systemic signaling of the plant N demand. (B) Split root systems used to study the control of mature nodules by the plant N demand. Symbiotic plants supplied with air as a unique N source through the function of mature N2 fixing nodules are used. N treatment applied to a half-root system may either fully satisfy the plant N demand (N satiety) or result in plant N limitation (N deficit). Plant N satiety resulted in nodule senescence whereas plant N limitation stimulates the expansion of mature nodules. The development of the nodules in untreated roots is strongly dependent on the level of supply of the whole plant, revealing the control by the systemic signaling of the whole plant N demand (Adopted from Lepetit and Brouquisse, 2023) 5.2 Host range and specificity factors The host range and specificity of rhizobia are influenced by both genetic and environmental factors. Some legumes exhibit promiscuity, nodulating with a wide range of rhizobial species, while others are highly specific. For example, Mimosa species in Brazil show specificity towards Burkholderia, whereas in Mexico, they prefer Rhizobium/Ensifer. Similarly, Cicer arietinum (chickpea) specifically nodulates with Mesorhizobium species (Andrews and Andrews, 2016). Environmental factors such as soil acidity and site elevation also play a role in
RkJQdWJsaXNoZXIy MjQ4ODYzMg==