Abstract: It is important for legumes to germinate and form nodules successfully under adverse soil conditions. In the current study, four summer legume crops used for green manure; Phaseolus calcaratns, Vigna radiata, Sesbania cannabina and Vigna unguiculata were utilised to investigate the responses of seed germination and the antioxidative enzyme activities of their rhizobia to soil acidity and NaCl stress. Four pH levels (4, 5, 6, 7), four Al³⁺ levels (0, 50, 100 and 200 mg·L^-1), and four NaCl levels (0, 40, 120 and 200 mmol·L^-1) were assessed for their effects on seed germination. Similarly, four pH levels (4, 5, 6, 7), five Al³⁺ levels (0, 25, 50, 75 and 100 μmol·L^-1), and five NaCl levels (0, 10, 20, 30 and 40 g·L^-1) were assessed for the influence on antioxidative enzymes. The results indicated that the seed germination and rhizobia antioxidative enzyme activities were significantly influenced by low soil pH and increased concentrations of Al³⁺ and NaCl. Overall, the antioxidative enzyme activities of rhizobia were more sensitive than seed germination to these stresses. Among the four plant species, seed germination and rhizobia of S. rostrat were comparatively sensitive to soil pH and Al³⁺ but was relatively tolerant to NaCl stress; those of P. calcaratns, V. radiate and V. unguiculata were relatively tolerant to low levels of NaCl and high levels of soil pH, whereas those of all plant species were sensitive to increased Al³⁺ concentrations. In acid or alkaline soils, higher concentrations of H⁺ and Al³⁺ or NaCl inhibited seed germination, retarded rhizobia growth, reduced the oxidation resistance of rhizobia, and limited the early growth of legume seedlings.

Key words: legume green manure, seed germination, rhizobium, adverse environments, antioxidative enzyme