Departamento de Ecologia, Instituto de Biologia Roberto Alcântara Gomes, Universidade do Estado do Rio de Janeiro, Rua São Francisco Xavier 524, Rio de Janeiro, RJ, 20550-900, Brazil.
MARETEC, Instituto Superior Técnico, Universidade Técnica de Lisboa, Av. Rovisco Pais, 1049-001, Lisbon, Portugal.
BMC Ecol. 2019 Jan 31;19(1):6. doi: 10.1186/s12898-019-0218-z.
As plants, algae and some sessile invertebrates may grow in nearly monospecific assemblies, their collective biomass increases and if they compete hard enough some die, freeing up space. The concurrent increase in biomass and decrease in density is called self-thinning, and its trajectory over time or maximum values represent a boundary condition. For a single stand developing over time the boundary defines the carrying capacity of the environment but the most extreme trajectories emulate the efficiency of species in packing biomass into space.
Here we present a meta-analysis of compiled data on biomass and density from 56 studies of 42 species of seaweeds from 8 orders within 3 phyla scattered through the world's oceans. Our analysis shows that, with respect to biomass, seaweeds are the most efficient space occupiers on Earth because they transgress previously fixed limits derived from land plants. This is probably because seaweeds are not limited by water and do not need structures for its transport or for transpiration; they photosynthesise and uptake nutrients over their entire surface; they are attached to the substrate by holdfasts that are small proportional to their volume or weight compared to roots; water provides them better support, reducing the need for tissues for rigidity. We also identified a biomass concentration common to plants and seaweeds which represents the threshold that no life on the planet can pass. Using each stand's distance to the biomass-density boundary, we determined that within the seaweeds the efficiency of space occupation differed amongst taxonomic and functional groups as well as with clonality and latitude.
Algae occupy space more efficiently than plants, most likely because the watery environment facilitates the physical processes and integration of space occupation. The distance-to-the-boundary proves a good metric to discriminate among groups and may be useful for comparison of the most efficient biomass producing systems, or for the identification of systems impacted by pollution.
由于植物、藻类和一些固着无脊椎动物可能以近乎单种的组合生长，它们的集体生物量增加，如果它们竞争得足够激烈，一些生物就会死亡，从而腾出空间。生物量的同时增加和密度的降低称为自疏，其随时间的轨迹或最大值代表一个边界条件。对于随时间发展的单一林分，边界定义了环境的承载能力，但最极端的轨迹模拟了物种将生物量装入空间的效率。
在这里，我们对来自 3 个门的 8 个纲的 42 种海藻的 56 项研究的生物量和密度汇总数据进行了荟萃分析，这些研究分布在世界各地的海洋中。我们的分析表明，就生物量而言，海藻是地球上最有效的空间占据者，因为它们超越了以前从陆地植物得出的固定限制。这可能是因为海藻不受水的限制，不需要用于运输或蒸腾的结构；它们可以在整个表面进行光合作用和吸收营养；它们通过相对于根小得多的固着器附着在基质上；水为它们提供了更好的支撑，减少了对组织刚性的需求。我们还确定了一个植物和海藻共有的生物量浓度，这代表了地球上任何生命都无法逾越的阈值。利用每个林分与生物量-密度边界的距离，我们确定在海藻中，空间占据效率在分类和功能群以及克隆性和纬度之间存在差异。
藻类比植物更有效地占据空间，这很可能是因为水生环境促进了物理过程和空间占据的整合。距离边界证明是区分群体的一个很好的指标，可用于比较最有效的生物量生产系统，或识别受污染影响的系统。
