| Summary: | 碩士 === 國立屏東科技大學 === 森林系所 === 103 === The purpose of this study is to understand the distribution of two Gramineae wetland plants Leersia hexandra and Panicum repens in different water level microhabitats of Nanjen Lake, and investigate the reason why L. hexandra was replaced by P. repens in non-flooded areas. To achieve this purpose, we observed the coverage of L. hexandra and P. repens in different water level microhabitats of Nanjen Lake, measured their photosynthetic characteristics in NPUST nursery, as well as compared their growth performances in different seasons and water levels with artificially submerged experiments.
The results showed that, in monopolized community of either L. hexandra or P. repens in the grassy marsh area of Nanjen Lake, the coverage of each species was negatively related to water levels. While in mixed community of both species, the relationship between coverage and water levels was significantly positive for L. hexandra but negative for P. repens. The coverage of P. repens was significantly higher than that of L. hexandra in shallower water levels. In Nanjen Lake, we also observed that P. repens would wither in substantial amount in autumn and re-sprout in spring. An artificially submerged experiment was conducted in autumn, 2014, at nursery of NPUST. Results showed that when each species was mono-planted, the biomass of L. hexandra was significantly higher at 30 cm water level than the biomass at other water levels. On the other hand, the biomass of P. repens was highest in non-flooded treatment. When the two species were mix-planted, biomass of the two species showed no significant difference in non-flooded treatment, while the biomass of L. hexandra was significantly higher than that of P. repens when water level was 30 cm or deeper. Another submerged experiment was conducted in spring, 2015. The results showed that, when mono-planted, biomass of L. hexandra or P. repens was significantly higher in non-flooded treatment than their biomass at any other water levels. Yet when mix-planted, P. repens was advantageous in non-flooded treatment while the two species were equally competitive at 15 and 30 cm water levels. According to the above results, P. repens showed higher competiveness than L. hexandra under non-flooded condition in spring but not in autumn. It might due to the phonological nature of P. repens. This species would become weak and wither in autumn, so that its growth and competiveness against L. hexandra would decline. In addition, the photosynthetic capacity of both species measured in NPUST nursery indicated that P. repens was significantly higher than L. hexandra (29.4 vs. 18.8 µmol CO2 m-2 s-1). The net photosynthesis rates of both species were significantly higher under non-flooded condition than under 15-cm submerged condition. However, both species could still maintain their net photosynthetic rates under flooded conditions at above 75% of net photosynthesis under non-flooded condition.
The above results supported our hypothesis that " P. repens has the ability to competitively exclude L. hexandra under non-flooded condition." Therefore, P. repens is capable of competitively excluding L. hexandra under non-flooded condition in Nanjen Lake, but L. hexandra will dominate at habitat with deeper water levels.
Keywords：Competition, Leersia hexandra, Nanjen Lake, Panicum repens, Photosynthesis, Submerge experiments, Water levels.
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