The Geomunoreum Lava Tube System, declared as a UNESCO World Heritage Site, has a unique natural ecosystem. The information available about this ecosystem, which contains lava caves with secondary carbonate speleothems, is sparse. Hence, extensive research is warranted for establishing a conservation standard. We commenced microbial research on the system and have been studying the microorganisms coating the lava tube wall to acquire fundamental information for understanding the lava cave ecology of Jeju Island. Samples were collected from yellow-colored walls in six caves that are part of the system―the Bengdwi, Utsanjeon, Bukoreum, Manjang, Gimnyeong, and Yongcheon caves. This study focused on yellow walls as it is the most easily distinguished color. According to previous studies, the color of cave walls is attributed to microorganisms or their components. To determine whether the yellow mats from the Jeju lava tube walls are caused by microorganisms, we examined samples at the microscopic scale, by staining mats and analyzing bacterial isolates from glitter particles. As a result, we found that the yellow walls of lava tubes are comprised of microbial mats.

The effect of biofertilizer (compound of microbial inoculants or groups of micro-organisms) on growth and yield of rice was investigated. The experiment was carried out in a randomized complete block design with 3 replications and 7 treatments namely: RF=N-P2O5-K2O (11-5.5-4.8 kg 10a-1 ); half of the recommended fertilizer rate, HRF=N-P2O5-K2O (5.5-2.75-2.4 kg 10a-1 ); HRF+Bio 250=HRF combined with 250 kg biofertilizer 10a-1 ; HRF+Bio 500=HRF combined with 500 kg biofertilizer 10a-1 ; Bio 250=250 kg biofertilizer 10a-1 ; Bio 500=500 kg biofertilizer 10a-1 ; and NF = No Fertilizer. Results showed that the recorded values of plant height, tiller number and chlorophyll content at 40 to 60 days after transplanting (DAT) in HRF+Bio 500 were significantly higher than those recorded in the RF treatment. Similar observations between these two treatments were only recorded from 60 DAT onwards. Yield components were also superior in HRF+Bio 500 treatment and comparable to that of RF. The highest grain yield obtained in HRF+Bio 500 treatment (785.8 kg 10a-1 ) was statistically similar to that of RF (739.8 kg 10a-1 ) but significantly higher than that of NF (506.7 kg 10a-1 ). Finally, head grain recovery (90.9) was low while chalkiness (0.03) was high at HRF+Bio 500 treatment as compared with RF, which were (96.1) and (0.3), respectively. Results showed that combined treatment of HRF and 500 kg biofertilizer 10a-1 has similar effects on the growth and yield of rice with that of RF.