Instituto de Investigación en Biodiversidad y Medioambiente (INIBIOMA) , Quintral 1250, (8400) Bariloche , Argentina.
AoB Plants. 2010;2010:plq019. doi: 10.1093/aobpla/plq019. Epub 2010 Oct 25.
Plants are regarded as populations of modules such as axes and growth units (GUs, i.e. seasonally produced axis segments). Due to their dense arrays of GUs, cushion plants may resemble crowded plant populations in the way the number of components (GUs in plants, individuals in populations) relates to their individual sizes.
The morphological differentiation of GUs and its relationship with biomass accumulation and plant size were studied for the cushion subshrub Mulinum spinosum (Apiaceae), a widespread species in dry areas of Patagonia. In 2009, GUs were sampled from one-quarter of each of 24 adult plants. Within- and between-plant variations in GU length, diameter, number of nodes and biomass were analysed and related to whole-plant size.
Each year, an M. spinosum cushion develops flowering GUs and vegetative GUs. Flowering GUs are larger, twice as numerous and contain two to four times more dry mass (excluding reproductive structures) than vegetative GUs. The hemispherical area of the cushions was positively correlated with the biomass of last-year GUs. The biomass of flowering GUs was negatively correlated with the density of GUs. Mulinum spinosum plants exhibited a notable differentiation between flowering and vegetative GUs, but their axes, i.e. the sequences of GUs, were not differentiated throughout the plants. Flowering GUs comprised a major proportion of each plant's photosynthetic tissues.
A decrease in the size of flowering GUs and in their number relative to the total number of GUs per plant, parallel to an increase in GU density, is predicted as M. spinosum plants age over years. The assimilative role of vegetative GUs is expected to increase in summer because of their less exposed position in the cushion. These GUs would therefore gain more from warm and dry conditions than flowering GUs.
植物被视为模块群，如轴和生长单位（GU，即季节性产生的轴段）。由于其密集的 GU 阵列，垫状植物可能类似于密集的植物种群，因为组件的数量（植物中的 GU，种群中的个体）与它们的个体大小有关。
本研究以广泛分布于巴塔哥尼亚干旱地区的伞形科垫状小灌木刺状 Mullinum（Mulinum spinosum）为研究对象，研究了 GU 的形态分化及其与生物量积累和植物大小的关系。2009 年，从 24 株成年植物的四分之一中采集了 GU。分析了 GU 长度、直径、节数和生物量的个体间和个体内变异，并与整株植物的大小相关。
每年，一个 Mullinum 垫状植物发育出开花 GU 和营养 GU。开花 GU 更大，数量是营养 GU 的两倍，并且包含的干物质（不包括生殖结构）是营养 GU 的两倍到四倍。垫状植物的半球形面积与去年 GU 的生物量呈正相关。开花 GU 的生物量与 GU 的密度呈负相关。Mullinum spinosum 植物在开花 GU 和营养 GU 之间表现出明显的分化，但它们的轴，即 GU 的序列，在整个植物中没有分化。开花 GU 构成了每个植物光合作用组织的主要部分。
随着 Mullinum spinosum 植物年龄的增长，预计开花 GU 的大小及其相对于每个植物的 GU 总数的数量会减少，而 GU 密度会增加。由于在垫状植物中处于较不暴露的位置，营养 GU 的同化作用预计会在夏季增加。因此，这些 GU 将比开花 GU 从温暖和干燥的条件中获得更多的收益。
