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Diurnal and seasonal trends of water relations in five co-occurring chasmophytic species

机译：5种同时存在的苔藓植物物种水关系的昼夜变化

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The present study examines the seasonal and diurnal patterns of water management by plant species inhabiting the wall fissures of the ancient castle of Patras. Their water status (water potential), stomatal behaviour (leaf resistance and transpiration rate) as well as tissue water relations (turgor loss point, osmoregulation capability and cell wall elasticity) were recorded in relation to season, daytime and respective environmental conditions. Despite some minor deviations, all five species exhibited a water spending strategy with high diurnal transpiration rates through seasons, limited only by the generally low light intensities prevailing at the northwest-facing vertical walls. Progressive shortage of water during summer resulted in the reduction of transpiration in four species. Diurnal water losses caused a reduction of water potential until midday or dusk, which further decreased with the progress of the dry period. However, predawn water potential remained high through all seasons. The above finding, together with the high transpiration, was unexpected for species growing in a very hostile environment as far as water supply is regarded. It could be partly explained by the recently found ability of all five species to absorb dew from leaf surfaces. However, such plants should also possess mechanisms to take up water efficiently from a rather dry substrate. Indeed, pressure-volume analysis revealed substantial seasonal changes in osmoregulatory capacity and minor changes in cell wall elasticity of leaf tissue. Both changes facilitate (the mechanism differs) water uptake from the wall-fissure substrate during the dry period. Although the relative contribution of the two mechanisms was different, they both allowed plants to maintain turgor and thus growth throughout their growing season. (C) 2007 Elsevier GmbH. All rights reserved.
机译：本研究考察了居住在帕特雷古城堡墙体裂缝中的植物物种对水管理的季节性和昼夜模式。记录它们的水状态（水势），气孔行为（叶抵抗力和蒸腾速率）以及组织水的关系（充盈损失点，渗透压调节能力和细胞壁弹性）与季节，白天和各个环境条件的关系。尽管有一些细微的差异，但所有五个物种均表现出节水策略，整个季节的日蒸腾速率较高，仅受西北垂直壁普遍存在的低光照强度的限制。夏季逐渐缺水，导致四种物种的蒸腾作用减少。白天的水损失导致中午或傍晚的水势降低，并随着干旱时期的进行而进一步减少。但是，整个季节之前，黎明前的水势仍然很高。就在考虑到供水的情况下，上述发现以及高蒸腾作用对于在非常不利的环境中生长的物种而言是出乎意料的。这可以部分归因于最近发现的所有五个物种吸收叶片表面露水的能力。但是，此类植物还应具有从相当干燥的基质中有效吸收水分的机制。实际上，压力-体积分析显示渗透压调节能力发生了实质性的季节性变化，叶片组织的细胞壁弹性发生了细微变化。两种变化都有助于（机理不同）在干燥期间从壁裂基质吸收水分。尽管这两种机制的相对作用不同，但它们都使植物得以维持膨大，从而在整个生长季节中生长。 （C）2007 Elsevier GmbH。版权所有。

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