著者

森田 脩

出版者

三重大学生物資源学部

雑誌

三重大学生物資源学部紀要 (ISSN:09150471)

巻号頁・発行日

no.4, pp.p1-72, 1990-03

被引用文献数

9

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Sod- and over-seeding methods have been considerabty employed on grassland development, especially in mountainous area of Japan. On the surface of untilled land, however , seed germination and seedling establishment seem variable depending on the ecosystematically combined conditions of vegetation, soil, and weather. In the present study the germinating process and behavior of surface-sown seeds of temperate grass species was, on a laboratory scale, investigated in relationship to thefunction of coleorhiza hairs in seedling establishment under several different conditions of soil and temperature.I. Characteristics of Germination and Establishment of Surface-sown Grass seeds1) Germination process and behavior In the germination process of tall fescue seed placed embryo downward on the soil of the seedbed, the coleorhiza appeared at the basal portion of the lemma and developed numerous hairs around the tip of that organ first. The coleorhiza hairs adhered to the soil surface, entered the soil and thenbound soil particles. This anchoring action of the coleorhiza and its hairs was followed by the appearance and penetration of the seminal root. The germination process of the coleorhiza phase was identical for different conditions of soil and environment, while the process of seminal root penetration was variable depending on the adhering strength of coleorhiza hairs equivalent to the maximum tensile load to pull seed out of the soil surface. To measure these values, an apparatus was devised in the present study. Germinating behavior was classified as three different types as follows:TYPE I (Lying type); Coleorhiza hairs of the seed adhered to, and were anchored in the soil, and theseed germinated in the same lying posture as it was placed.TYPE II (Rising type); Coleorhiza hairs grasped the soil well, and seed germinated in rising posture.TYPE Ⅲ (Exposed-root type); Colerohiza hairs failed to grasp the soil particles, and the seminal root could not directly penetrate into the soil adequatly. Seminal roots in most of the seeds were heldup and exposed over the soil surface.\n2) The variations in germinating behavior and adhering strength of coleorhiza hairs of six temperate grass species Orchardgrass, tall fescue, and Kentucky bluegrass had a relatively higher percentage of rising typein germinating behavior and of penetration of seminal root than did meadow fescue, perennial ryegrass and Italian ryegrass. The adhering strength of coleorhiza hairs was higher at the level of 2 gr per seedfor orchardgrass, tall fescue, and Kentucky bluegrass than at that of 1 gr per seed for the other grass species tested. Within each of grass species, the adhering strength of coleorhiza hairs was found to beclosely related to the percentage of rising type in germinating behavior (r=0.96, p<0.01). Overall six grass species examined, however, there was not relationship between those two measurements, probably reflecting in their differences in the shape and weight of seeds. Coleorhiza hairs, and especially their adhering strength, are a very important factor associated with seedling establishment of surface-sown seeds. From this perspective, there were some advantages insod- and over-seeding were for tall fescue, orchardgrass and Kentucky bluegass. Ⅱ. Effects of Environmental Conditions of Temperature and Soil on Germinating Behavior and Adhering Strength of Coleorhiza hairs1) Temperature The germinating behavior and the adhering strength of coleorhiza hairs of the surface-sown tall fescue were investigated under different temperature conditions. The best germination process wasobserved at the temperatures of 15- 25℃ which have been known as the favorable range of growthtemperatures for temperate grass species. Within that temperature range the coleorhiza hairsappeared,grew vigorously and adhered strongly to the soil surface,and the percentage of the rising type in germinating behavior was considerably higher as compared with other temperatures, such as5℃ and 35℃. At the unfavorable temperatures, the exposed root type was observed more frequently, reflecting the weak adherence of coleorhiza hairs which was associated with lower number andlength of the hairs. The lying type was infrequent throughout all temperature conditions tested. Theadhering strength of coleorhiza hairs was closely correlated with number and length of those hairs and with the percentage of rising type (r =0.89, p<0.01 and r=0.92, p<0.01).\n2) Soil type, moisture and hardness The germinating behavior and the adhering strength of coleorhiza hairs of surface-sown tall fescueseed in a yellow paddy field soil and in three different types (sampled from Takanoo, Kawatabi, and Nishinasuno areas) of Kuroboku soil treated with 7 or 6 moisture levels (40- 90%) were observed.With all soil types and moisture levels, the lying type was rernarkably dominant below the hardness value of 3 gr which was determined on the soil surface by the silk needle method. The percentages of the rising type and the exposed-root type were increased with increasing soil hardness related to the decreasing moisture content. The highest percentage of the rising type was obtained at 40% and 85%moisture contents for paddy field soil and for the Kuroboku soils respectivety,indicating that the adhering of coleorhiza hairs was very variable in different physical structures of soil.\n3) Forms of organic litter on the soil surface As for with the germination rate and percentage of tall fescue sown on the soil surface, thosevalues of that grass were not influenced by three different forms of organic litter placed on the soil surface (the leaf litter layer, the decomposed layer, and the ash layer), except for a lower germination ratewith the leaf litter layer. The rising type tended to be higher for the decomposed matter than the leaflitter form, although all percentages were considerably higher in the exposed-root type. The adheringstrength of the coleorhiza was, as the result of combining adhering potentiality of the hairs and physicalstructure of soil or organic matter, lower with the decomposed matter and ash layers as compared withthe yellow paddy field soils.\nIII. Effects of Soil Amendment matter and Seed Pressing on the Seed Germination and Seedling Establishrnent1) Application of soil amendment matter The germination behavior of surface-sown tall fescue was investigated at the different pH conditions of each of the yellow paddy field soils and the Takanoo Kuroboku soils treated with applications ofsoil amendment matter. The rising type in germinating behavior was dominant at the pH values of 5to 8 in the paddy field soils and at the values of 5 to 6 in the Kuroboku soils. An application of fused magnesium phosphate was more effective in improving the p.H value of the acid Kuroboku soils and the germinating behavior in that soil than was that of superphosphate.\n2) Seed pressing Cattle trampled surface-sown seeds into the soil induced more favorable germination, such as higher percentage and higher initial growth of plant. Without trampling, most of seeds were lost during unsettled conditions. The adhering strength of coleorhiza hairs of surface-sown seeds was increased by seed pressing to about 1.4-2.4 times as much as no pressing, showing a higher percentage of the rising type which was superior in the initial growth to the exposed-root type. By inserting the embryo part of the seed intothe soil to about 2 mm depth, or by pressing seeds at the force of about 1 gr, good penetration of the seminal root and good seedling establishment were highly achieved even for the Kuroboku soils in which the exposed-root type was normally dominant.\n In the present study adhesion of coleorhiza hairs to the soil surface was found to aid favorablepenetration of the seminal root and thereby to induce favorable seed germination and seedling establish-ment because such anchoring action could protect seeds from being held by the penetration of the semi-nal root, The strength of coleorhiza hairs was found to be positively related to the percentage of therising type in germinating behavior observed during such initially critical stage of germination. The rising type in germinating behavior resulted in good seedling establishment, while the exposed-root typedid not survive. With the sod- and over-seeding establishment tested here, the percenhge of the rising type was variable depending on grass species, soil type and moisture level, hardness of soil surface,form of organic litter, application of soil amendment matter, and seed pressing. Frorn the viewpoint ofthe adhering function of coleorhiza hairs, application of soil amendment matter and seed pressing werefound to be effective methods to improve seed germination and seedling establishment, especially foracid Kuroboku soils which weakened the adhering strength of coleorhiza hairs.