平潭岛典型海岸草丛沙堆植物群落水势日变化特征及其影响因素

Diurnal variations of water potential and its influencing factors in typical plant communities on coppice dunes of pingtan island

水势是反映植物受到环境胁迫的重要指标之一,可用来确定其受胁迫的程度和适应能力大小。以福建省平潭岛海岸典型沙生植物老鼠艻(Spinifex littoreus)形成的草丛沙堆为研究对象,选取晴朗无云的天气,采用PSYPRO水势测量系统对其植物叶、茎水势及其所形成的沙堆土壤水势进行测定,同时采用HUMIPORT10手持式温湿度计对当日的气象要素进行同步观测。结果表明:(1)老鼠艻的叶水势呈现出与早晚高午间低相反的反梯度现象,叶、茎水势的日变化均表现为"M"型变化趋势,除18:00后,其它时间均表现为叶片水势下降、茎干水势上升,并且发现叶、茎水势的变化趋势存在位相后移现象;(2)老鼠艻的叶、茎水势在10:00时差异达到最大的0.65MPa,且茎水势高于叶水势,在14:00左右,植物茎水势出现低于叶水势的反常现象,在18:00时叶、茎水势趋于相同;(3)除表层30cm外,其它层土壤水势日变化特征总体表现为从早晨开始下降,14:00达到最低,但总体变化不明显;(4)随着深度增加,草丛沙堆土壤水势呈现为依次增加的趋势,但80cm以下土壤水势变化不显著(P>0.1);(5)叶水势与大气水势具有较好的相关性,且变化显著(P<0.1),与茎水势及浅层土壤水势有一定相关性,但变化不显著(P>0.1),与50cm以下土壤水势均无相关性。

Water potential is one of the most important factors that reflect environmental stress on plants, and can be used to identify the level of stress a plant experiences and its adaptation ability. This study focused on the coppice dunes formed by the psammophyte Spinifex littoreus on Pingtan Island, Fujian province. The PSYPRO Water Potential System was used to determine the water potential of the leaves, stems, and soil, and a HUMIPORT10 hand-held hygrometer was used to simultaneously measure the meteorological variables on cloudless, sunny days. Spinifex littoreus showed an opposite pattern of leaf water potential, which is in contrast to the normal phenomenon of increased leaf water potential in the morning and evening compared to that at midday. The diurnal variations of leaf and stem water potential all demonstrated an ＇ M＇ curve pattern, indicating a decrease of leaf water potential and increase of stem water potential in daytime, until 18：00. Furthermore, we found that the changes of leaf water potential occurred later than those of stem water potential. The biggest discrepancy between stem and leaf water potential, reaching 0.65MPa, appeared at 10：00, when stem water potential was higher than leaf water potential. At about 14：00, an abnormal phenomenon appeared, in which leaf water potential was higher than stem water potential, but at about 18：00, leaf and stem water potential tended to be the same. With the exception of soil water potential at 30cm, the diurnal variation of soil water potential showed a decrease starting in the morning, which reached the minimum at 14：00; however, this tendency was not statistically significant （P〉O. 1 ）. With increasing depth, the soil water potential showed a tendency to increase, but this trend disappeared below a depth of 80cm. Strong correlations and significant changes （P 〈 O. 1 ） in water potential were observed between the atmosphere water potential and leaf. Leaf, stem, and 30-cm-deep soil water potential showed some correlations, but the variations were not statistically significant （P〉0. 1 ）. Leaf water potential was not correlated with the water potential of soil at other depths.