Shoot density of Miscanthus sinensis populations in different habitats and their maintenance mechanisms in relation to shoot growth.

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.

Ontogenetic changes in accumulation of rhizomes in monoclonal patch of Miscanthus sinensis Anderss. in warm temperate region of Japan.

To determine the main benefits of clonal expansion of Miscanthus sinensis patches (monoclones), we observed the annual pattern of the areal expansion of a number of M. sinensis patches and examined how the quantity of rhizomes in such patches is related to changes in their basal area. To forage for nutriments, a patch must continuously widen its habitat. Patches annually expanded centrifugally by sympodial branching of short rhizomes, which originated in tillering that occurred more than once a year. However, the basal area of the patches approached a ceiling as the patches aged. Both the number and the weight of rhizomes in the patches continued to increase as long as the basal area expanded. The mean weight of rhizomes in patches also initially increased quickly, but then reached a ceiling as the clones expanded. Similarly, the amount of reserve substance per shoot in the patches increased asymptotically along with the clonal expansion, depending on the rhizome mass allotted to each shoot. These results suggest that, in the clonal growth of M. sinensis patches, the accumulation of reserve matter in the rhizomes is more important than foraging in new areas.

Shoot population dynamics of persisting clones of Miscanthus sinensis in the warm-temperate region of Japan.

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.