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Contrasting physiological responses to excess heat and irradiance in two tropical savanna sedges

机译：两种热带稀树草原莎草对过热和辐照度的生理反应不同

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Tropical hyperseasonal savannas provide a rare example of a tropical climax community dominated by graminoid species. Species living in such savannas are frequently exposed to excess heat and light, in addition to drought and waterlogging, and must possess traits to avoid or tolerate these stress factors. Here we examine the contrasting heat and light stress adaptations of two dominant savanna sedges: Lagenocarpus guianensis, which is restricted to the sheltered forest edge, and Lagenocarpus rigidus, which extends from the forest edge to the open savanna. An ecotone extending from the forest edge to the open savanna was used to assess differences in a range of physiological traits (efficiency of photosystem II, cell membrane thermostability, stomatal conductance, leaf surface reflectance and canopy temperature depression) and a range of leaf functional traits (length : width ratio, specific leaf area and degree of folding). Lagenocarpus guianensis showed significantly less canopy temperature depression than L. rigidus, which may explain why this species was restricted to the forest edge. The range of leaf temperatures measured was within the thermal tolerance of L. guianensis and allowed photosystem II to function normally, at least within the cool forest edge. The ability of L. rigidus to extend into the open savanna was associated with an ability to decouple leaf temperature from ambient temperature combined with enhanced cell membrane thermostability. The high degree of canopy temperature depression seen in L. rigidus was not explained by enhanced stomatal conductance or leaf reflectance, but was consistent with a capacity to increase specific leaf area and reduce leaf length: width ratio in the open savanna. Plasticity in leaf functional traits and in cell membrane thermostability are key factors in the ability of this savanna sedge to survive abiotic stress.
机译：热带的超季节稀树草原提供了一个罕见的例子，说明以类粒动物为主的热带高潮群落。除干旱和涝灾外，生活在这种热带稀树草原上的物种还经常暴露于过多的热量和光照下，并且必须具有避免或忍受这些压力因素的特征。在这里，我们研究了两种主要热带稀树莎草的热和光胁迫的适应性变化：Lagenocarpus guianensis只限于庇护林边缘，而Lagenocarpus刚草则从森林边缘延伸到开阔的稀树草原。一个从森林边缘延伸到热带稀树草原的过渡带被用来评估一系列生理特征（光系统II的效率，细胞膜热稳定性，气孔导度，叶片表面反射率和冠层温度降低）的差异以及一系列叶片功能性状（长度：宽度比，比叶面积和折叠度）。圭亚那古猿表现出的冠层温度下降幅度比僵硬李子要小得多，这可以解释为什么这种树种被限制在森林边缘。测得的叶子温度范围在gu.ensis的热耐受性之内，并使光系统II至少在凉爽的森林边缘正常运行。僵硬杆菌扩展到开放大草原的能力与将叶片温度与环境温度解耦的能力以及增强的细胞膜热稳定性相关。僵硬的高冠层温度下降的程度不能通过气孔导度或叶片反射率的增强来解释，但与增加比叶面积和减少开放大草原中叶长：宽比的能力是一致的。叶片功能性状和细胞膜热稳定性的可塑性是该热带稀树莎草在非生物胁迫下生存的关键因素。

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