Department of Integrative Biology, University of California, Berkeley, CA 94720, USA
Department of Neurobiology, Physiology, and Behavior, University of California, Davis, CA 95616, USA.
J Exp Biol. 2019 Feb 25;222(Pt 4):jeb190595. doi: 10.1242/jeb.190595.
The resistance of macroalgae to damage by hydrodynamic forces depends on the mechanical properties of their tissues. Although factors such as water-flow environment, algal growth rate and damage by herbivores have been shown to influence various material properties of macroalgal tissues, the interplay of these factors as they change seasonally and affect algal mechanical performance has not been worked out. We used the perennial kelp to study how the material properties of the rachis supporting a frond changed seasonally over a 2 year period, and how those changes correlated with seasonal patterns of the environment, growth rate and herbivore load. Rachis tissue became stiffer, stronger and less extensible with age (distance from the meristem). Thus, slowly growing rachises were stiffer, stronger and tougher than rapidly growing ones. Growth rates were highest in spring and summer when upwelling and long periods of daylight occurred. Therefore, rachis tissue was most resistant to damage in the winter, when waves were large as a result of seasonal storms. Herbivory was greatest during summer, when rachis growth rates were high. Unlike other macroalgae, did not respond to herbivore damage by increasing rachis tissue strength, but rather by growing in width so that the cross-sectional area of the wounded rachis was increased. The relative timing of environmental factors that affect growth rates (e.g. upwelling supply of nutrients, daylight duration) and of those that can damage macroalgae (e.g. winter storms, summer herbivore outbreaks) can influence the material properties and thus the mechanical performance of macroalgae.
海藻对水力破坏的抵抗力取决于其组织的机械性能。尽管水流动环境、藻类生长速度和食草动物的损害等因素已经表明会影响海藻组织的各种材料特性，但这些因素在季节性变化时的相互作用以及它们如何影响藻类的机械性能尚未被研究清楚。我们使用多年生海藻来研究支撑叶片的中轴的材料特性如何在两年的时间内随季节变化，以及这些变化如何与环境、生长速度和食草动物负荷的季节性模式相关。中轴组织随着年龄（距离茎尖的距离）的增长而变得更加坚硬、更强壮和更具弹性。因此，生长缓慢的中轴比生长迅速的中轴更坚硬、更强壮和更坚韧。当上升流和长时间的白天出现时，生长速度在春季和夏季最高。因此，中轴组织在冬季最能抵抗波浪大的季节性风暴的破坏，而冬季是波浪最大的时候。食草动物在夏季最为活跃，此时中轴的生长速度最高。与其他海藻不同的是，海藻并不会通过增加中轴组织的强度来应对食草动物的损害，而是通过增宽来生长，从而增加受伤中轴的横截面积。影响生长速度的环境因素（例如上升流供应的营养物质、白天持续时间）和可能损害海藻的因素（例如冬季风暴、夏季食草动物爆发）的相对时间可以影响海藻的材料特性，从而影响海藻的机械性能。
