Studies on Weed Vegetation in Non-cultivated Paddy Fields : II. The relation between the ecological distribution of Gramineous C3- and C4- weeds and the soil moisture condition in non-cultivated paddy fields

摘要

We reported earlier that the weed vegetation of non-cultivated paddy fields, which had lain waste for years, varied with the difference of soil moisture. On the other hand, there is a well-known fact that higher plants can be divided into major two groups, C3- and C4-species, with distinct photosynthetic pathway. Recently, it is also reported that these two groups are dissimilar in their habitat affected by environmental factors such as temperature, precipitation and so on. In this investigation, in order to find out the difference of ecological distribution between C3- and C4-weeds according to soil moisture of non-cultivated paddy fields, the authors tried to compare the value of Summed Dominance Ratio (SDR2) in two weed groups of the Gramineae. The data of SDR2 used in this paper are the same ones which have been examined in the previous paper. Results are as follows: 1. The distribution of two weed groups within the Gramineae varied with the difference of soil moisture conditions in non-cultivatcd paddy fields, that is, the percentage of SDR2 in C3-weeds to total SDR2 was higher in lowland conditions than in upland ones. However, that of C4-weeds was in the reverse tendency. This relationship between ecological distribution and soil moisture condition was more apparent in paddy fields of long-year non-cultivation than in those of short-year non-cultivation. (Table 2, 3, 4) 2. It was observed that some species were distinctive in distribution pattern to soil moisture condition. Arthraxon hispidus, Hemarthria sibirica of C4-species and Panicum bisulcatum of C3-species showed a more adaptive characteristic to wide range of soil moisture condition than other specics. Echinochloa spp., Leptochloa chinensis and Paspalum distichum showed rather a well-growing characteristic under wet condition than other C4-species. And in some plots where these particular C4-species were in more invasive, SDR2 percentage of C4-species were higher than that of C3-species even under lowland condition. 3. The close relation was recognized between the ecological distribution of C3-, C4-species to soil moisture condition and their systematical situation judged from the systematics of the Gramineae which was proposed by TATEOKA. (Table 5)