The shoot configuration of each monoclonal patch of phalanx‐forming tallgrass, Miscanthus sinensis, is characterized by the formation of a ‘fairy ring’, which forms as the result of developing vacant inner areas. One large‐sized M. sinensis patch (patch L), observed over a 9‐year survey period, underwent lateral expansion in almost all directions as a result of peripheral shoot births. In the year after the shoots in each part of patch L reached a maximum density (Dmax), the number of shoots decreased by approximately 20% per year. However, the overall number of within‐patch shoots was stable during the survey because the patch area increased at the periphery. Twelve patches (>900 cm2 in area) with orthotropic shoots were selected to observe the distribution pattern of within‐patch shoots, and the patch areas were divided into three parts: the exterior, intermediate and interior areas. In 10 of these 12 patches, shoot densities were lowest in the interior areas and highest in the exterior areas, which led to ring formation. The shoot density of each subarea was inversely related to the age of the subarea. This raises the possibility that in any part of these patches, shoot densities decrease annually from Dmax in a similar way.
Abstract:Two gramineous weeds, early watergrass (Echinochloa wyzicola Vasing) and foxtail (Setaria viridis (L.) Beauv.), and rice (Oryza sativa L. cv. Nipponbare) were exposed to salinity stress. The leaf water status, levels of amino acid, proline, and glycinebetaine of seedlings during the 7 days following root treatment of 50 and 100mMNaCI were measured. Foxtail and early watergrass were able to maintain a high turgor and high relative water content under the salinity condition. Proline content in leaves was also increased by salt stress in these plants, but this was lower in rice than in foxtail or early watergrass. Glycinebetaine content was also increased by salinity in the two weeds. However, glycinebetaine was not
The population dynamics of annual shoots in four clonal patches of Miscanthus sinensis was surveyed in terms of clone persistence. Over a study period of 3 years, a stable net shoot number was attained through a balanced replacement of old shoots by tillering 2-3 times a year. The birth rate was significantly correlated with the average monthly temperature. This suggests that a warm climate advances the date of tillerings, and shoots become taller as they emerge earlier. Five cohorts were identified, corresponding to shoots that were born in spring, early summer, summer, autumn and early winter. The autumn cohorts were more numerous and had a greater longevity than the other cohorts; they were thus were best suited for overwintering and, consequently, maintaining the population from one generation to the next. The shoots of earlier cohorts grew too tall to survive the cold of winter, which might cause freezing injury, while later cohorts' shoots excelled in overwintering because of their shortness. However, if the delayed shoots are very short, they will also have difficulty in surviving the early season of growth. Therefore, M. sinensis shoots have an optimum size for survival.
How perennial grass populations are maintained in different climates is poorly understood at the level of individual shoots (ramets). During the years 1982-1987 and 1991-1993, measurements of shoot dynamics and growth in populations of a clonal grass, Miscanthus sinensis, were made at two sites in Japan that differed by approximately 5 °C in mean temperature. While annual shoot births were very stable during the period 1982-1987 at both sites, the number of flowering shoots fluctuated cyclically every year. The clonal propagation of shoots was size-independent, whereas the reproduction (flowering) of shoots was size-dependent and negatively affected their own offspring size. Shoot size negatively affected the overwintering of shoots. In the warm climate with a long growing period (9 months), both early-emerging shoots and the subsequent high order tillering shoots developed in large numbers. In the cool climate with a short growing period (6 months), more than half of the annual births occurred in August and September. Nevertheless, average longevity and wintering competency of shoots were not greatly different between the two populations. In response to a warmer climate, tillerings started earlier. This appeared to increase the total number of new shoots that would die within the year; nevertheless, the shoot densities remained much higher because a longer growing season would increase the number of high order tillerings. There was thus a trade-off between the annual survival ratio of new shoots and the number of annual shoot births.
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