It is important, however, to recognize that once nodules are formed, rhizobia exist inside a plant membrane and are protected from the direct effects of external soil and environmental stresses.

• 然而，必须认识到一旦根瘤形成，根瘤菌便在植物膜内存在，并受到保护以免受外界土壤及环境胁迫的影响。