Trends of population density of standing tillers, and developmental morphology of stolons and aerial-tillers in Japanese Iawn grass (Zoysia japonica Steud.) growing in sward conditions.

日本结缕草（Zoysia japonica Steud.）种群数量通常保持在15，000个/平方米左右的非常高的水平，与日本栽培的针茅草原形成了鲜明的对比，日本栽培的针茅草原的初始植物密度往往在建立后的活跃生长期迅速下降。此外，结缕草在频繁落叶条件下也能获得较高的产量，构成结缕草密集种群的气生分蘖主要是由匍匐茎多节下部节旺盛产生的Ta分蘖组成。与此相反，经常出现的Tb分蘖位于一个节点以上的Ta分蘖似乎是罕见的，作为一个更大的部分（近80%）的Tb芽保持休眠较长的时间在季节。在本研究所进行的高频率落叶条件下，二、三级分蘖从老化和衰老的Ta和Tb分蘖的叶腋中相当自由地出现，因此它们补充了现存分蘖总数的20 ~ 30%，在草地条件下生长的每根匍匐茎的多节形成和伸展生长比单株受到强烈抑制;平均每年形成的多节数约为1000个。匍匐茎总伸长量在30 cm左右。在本研究的解剖学研究中，在每个匍匐茎顶端附近的Ta和Tb芽之间的发育明显不同。Ta和Tb分蘖芽分化起始于同一多节位，这可能是导致Ta和Tb分蘖芽分化的原因之一。

Standing tiller densities in frequently defoliated Japanese lawn grass (Zoysia japonica Steud.) populations were generally kept at very high level around 15,000/m^2, and revealed quite excellent contrast to those of Festucoid grasslands cultivated in Japan where initial plant densities tend to decrease quickly during actively growing periods after the establishment. Besides, Zoysia swards examined often showed their ability to realize relatively prominent yield even under frequent defoliations.Principal part of aerial-tillers that constructed the above mentioned dense population of Zoysia was composed of so-called Ta tillers which vigorously generated from the lower nodes of every multiple-node of stolons. In contrast with this, regular emergence of Tb tillers which located one node above the Ta tillers seemed to be rare, as a larger part (nearly 80%) of Tb buds stayed dormant for a longer period during the seasons. Under highly frequent defoliations as conducted in the present study, secondary and tertiary tillers appeared rather freely from the leaf axils of aged and senescing Ta and Tb tillers, and so they supplemented 20 to 30% of total existing tillers.The formation of multiple-node and extension growth in each stolon growing under a sward condition was suppressed strongly as compared with those of single-plants ; average number of multiple-nodes formed per year was ca. 20 and total stolon elongation was around 30 cm. In anatomical investigation in this study, a distinct difference of development was clearly observed between Ta and Tb buds near the apex of each stolon. The differential tiller bud initiation commenced in Ta and Tb tiller buds, both attaching to the same multiple-node, seems to be one reason to result the following diverse development of Ta and Tb tillers.