基于“三温模型”的珍稀濒危荒漠植物半日花蒸腾速率研究

利用远红外热成像技术获取半日花叶温,并根据"三温模型"原理测定半日花的蒸腾速率,结果表明:在晴朗天气条件下,测定时间段内半日花蒸腾速率的日变化曲线呈"单峰型",且峰值出现在15:00,最低值出现在17:00;叶温在测定时间内均高于气温,叶温与气温差最大为9.58 K,最小为0.71 K;在半日花所测冠幅范围内,冠幅越大,其蒸腾速率越大,蒸腾扩散系数越小。样本中,最大冠幅半日花测定时间内的蒸腾速率均值最高,为9.42×10-6MJ m-2d-1,蒸腾扩散系数最低,为0.41;最小冠幅半日花测定时间内的蒸腾速率均值最低,为4.18×10-6MJ m-2d-1,蒸腾扩散系数最高,为0.76。试验测定结果与传统测定技术结果相比较表明:利用远红外热成像技术非接触无损伤测定半日花蒸腾速率具有可行性。

Transpiration rate change in the rare and endangered eremophyte Helianthemum Songaricum schrenk based on the "Three-Temperature Model"

Helianthemum songaricum Schrenk is an ancient relic plant mainly distributed in the Dzungaria of Xinjiang Uygur Autonomous Region and the western Ordos of Inner Mongolia Autonomous Region. H. songaricum Schrenk is an important source of scientific information to study the origin and migration of desert plants in central Asia. However, due to environmental degradation caused by human activities, such as overgrazing during the past decades, its population and distribution area has declined rapidly, with substantial changes in the plant community structure. In order to gather information on its transpiration rate through contactless and non-invasive methods, we measured H. songaricum Schrenk leaf temperature using infrared thermal imaging technology and assessed the transpiration rate of the species by applying the "Three-temperature model". The sample area was set up at a typical H. songaricum Schrenk community, covering an area of about 1106.857 m² in the Western Ordos National Nature Reserve. In this sample area, we selected three plant sizes (large, medium and small), with five strains per plant size, making a total of fifteen plants as the sample group. The FLUKE-Ti55 far infrared thermal imager has been applied to the determination of H. songaricum Schrenk leaf temperature. The experimental results were summarized as follows: the diurnal variation pattern of transpiration rate (Tr) was a one-peak curve with the maximum Tr value at 15:00 and the minimum at 17:00. Different crown breadths of H. songaricum Schrenk had different Tr values, but followed the same pattern. The Tr value was smaller for the smaller H. songaricum Schrenk plants. The Tr value of the larger H. songaricum Schrenk was greater than the smaller one, with an increase of 125.37%. The leaf temperature was higher than the ambient air temperature with the difference reaching a maximum of 9.58 K and a minimum of 0.71 K. The leaf temperature with treatments of large, medium and small H. songaricum Schrenk was 306.14, 306.58, and 308.62, respectively. The leaf temperature of the smaller H. songaricum Schrenk is greater than the larger plant by 2.48 K. The transpiration transfer coefficient of the different canopy plant H. songaricum Schrenk were different showing it was inversely proportional to its crown size, with transpiration transfer coefficient decreasing with increasing canopy. The transpiration transfer coefficient of the large, medium and small H. songaricum Schrenk were 0.41, 0.48, and 0.76, respectively, with the transpiration transfer coefficient of the smaller plant recording higher levels than the larger one, with an increase of 85%; There was an inverse relationship between the diurnal variation pattern of the transpiration rate and the transpiration transfer coefficient. The smaller the crown breadth of H. songaricum Schrenk, the worse the root area water condition was, and the harder the water stress. The highest transpiration rate was recorded as 9.42×10^-6 MJ m^-2 d^-1 when the plant''s crown size was the largest and at 15:00, its Tr value reached a maximum of 1.42×10^-5 MJ m^-2 d^-1. In addition, the lowest transpiration transfer coefficient was 0.41. To summarize, this paper proved that non-invasive and contactless measurement techniques for determination of transpiration rates of H. songaricum Schrenk are feasible.