Optimal environmental range for Juncus effusus, an important plant species in an endangered insect species (Nannopya pygmaea) habitat in Korea

Juncus effusus is mostly found in freshwater wetlands and is widely used for landscaping and creating artificial wetlandsdue to its high ecological value. J. effusus tends to dominate during the early stage (3-10 years) of the second successionin abandoned paddy fields. This study focused on the environmental characteristics of J. effusus to create habitat for anendangered species, Nannopya pygmaea, which lives in wetlands dominated by J. effusus. Considering the distributionof J. effusus and N. pygmaea, 63 quadrats at eight wetlands were investigated between May and June 2006 during thecritically dry period. Fifty-three species from 28 families co-occurred with J. effusus, and Persicaria thunbergii was themost abundant (63.5%). The optimal ranges of distribution (ORD) for the water variables were water depth, -2 to 10 cm;dissolved oxygen, 0.99-3.55 mg/kg, conductivity (CON), 23.40-115.40 μs/cm, total dissolved solid, 12.53-57.60 mg/L;pH, 5.00-6.87; K+, 0.11-1.46 mg/L; Ca2+, 1.53-5.85 mg/L; Na+, 3.16-7.47 mg/L; Mg2+, 0.11-1.96 mg/L; NO3-N, < 0.001-0.072mg/L; NH4-N, 0.005-0.097 mg/L; and PO4-P, 0.006-0.047 mg/L. ORDs for the soil variables were water content, 1.05-2.96%; loss-on ignition method (LOI), 5.07-7.81%; CON, 23.70-59.70 μs/cm; pH, 4.40-5.16; extracted (e) K+, 4.34-15.73cmol/kg; eCa2+, 31.56-191.56 cmol/kg; eNa+, < 0.01-2.61 cmol/kg; eMg, 0.04-19.82 cmol/kg; eNO3-N, 0.514-1.175 mg/kg;eNH4-N, 0.033-0.974 mg/kg, ePO4-P, 0.491-11.552 mg/kg; total nitrogen, 0.016-0.200%; and total carbon, 1.06-2.37%. Theappearance of rush during early succession indicated relatively lower levels of these physicochemical parameters, andthat ORDs should be maintained for the J. effusus community.