Transpiration And Water Consumption Characteristics Of Major Plant Species Of Shrub And Grass Communities In The Loess Hilly Region

Water deficit is the most problem for vegetable growth in arid and semi-arid region. With Li-6400 portable photosynthesis system, we studied photosynthetic rate, transpiration rate, water use efficiency and their affecting factors of the seven plant species in loess hilly region to enhance the water use efficiency of plant. The daily water consumption were estimated on Camgana korshinskii,Sophora viciifolia,Hippophae rhamnoides and Artemisia gmelinii. Besides, we also analyzed and discussed transpiration characteristics and the water consumption regulations of different plant species. The main results are as follows:(1)The diurnal changes of net photosynthetic rate of every plant species were mostly single-peak curves and bimodal curves, and the peaks appeared at the different period of day in different months in loess hilly region. The diurnal changes of photosynthetic rate of Hippophae rhamnoides and Potentilla discolor presented V notch curves in June, and that of Periploca sepium and Potentilla discolor were declining alone from 8:00 to 18:00. Besides, each plant species displayed the same phenomenon that the photosynthesis midday depression to some degree in certain months. Average photosynthetic rate of the seven plants from May to September were ranked in the order as follows: Camgana korshinskii>Glycyrrhiza uralensis>Sophora viciifolia>Artemisia gmelinii>Hippophae rhamnoides>Periploca sepium>Potentilla discolor.(2)The diurnal variations of transpiration rate of five plants were one-peak curves and bimodal curves also, which included Camgana korshinskii,Glycyrrhiza uralensis,Periploca sepium,Artemisia gmelinii and Potentilla discolor, and that of Sophora viciifolia were one-peak curves. Otherwise the Hippophae rhamnoides's transpiration rate presented one-peak curves and three-peaks curves. All seven species belonged to non-transpiration midday depression type. Daily average transpiration rate of Camgana korshinskii and Artemisia gmelinii were higher in June,July and September,but other five plants were higher in May,July and September. Average photosynthetic rate from May to September were ranked in the order as follows: Camgana korshinskii>Glycyrrhiza uralensis>Potentilla discolor>Artemisia gmelinii>Periploca sepium>Sophora viciifolia>Hippophae rhamnoides.(3)The water use efficiency in Camgana korshinskii,Hippophae rhamnoides and Potentilla discolor was decreased first and then increased, and declined again from May to October. That of Artemisia gmelinii was nearly a straight line, but for another three plants that were one-peak curves and the peak appeared in August. The decreasing orders of the max. daily average water use efficiency were as follows: Sophora viciifolia(8.34mmol·mol-1),Hippophae rhamnoides(8.07mmol·mol-1),Periploca sepium(5.66mmol·mol-1),Glycyrrhiza uralensis(5.38mmol·mol-1),Camgana korshinskii(4.47mmol·mol-1),Potentilla discolor(3.96mmol·mol-1)and Artemisia gmelinii(1.59mmol·mol-1). The average water use efficiency from May to September were ranked as follows: Hippophae rhamnoides>Sophora viciifolia>Periploca sepium>Glycyrrhiza uralensis>Camgana korshinskii>Potentilla discolor>Artemisia gmelinii.(4)Because many environmental factors and physiological factors together affect on the physiological process of plants, the key affecting factors of photosynthetic rate or transpiration rate were changing in different months and growth stages. Through the methods of stepwise regression analysis and correlation analysis, it was known that the key affecting factors of photosynthetic rate included stomatal conductance,photosynthetic active radiation and air CO2 concentration. The key factors of different plants'transpiration were different too, mainly including stomatal conductance,stomata limiting value,photosynthetic active radiation,air temperature and soil water content and so on.(5)The light compensation points (LCP) of Artemisia gmelinii and Potentilla discolor were 44.1μmol·m-2·s-1 and 51.4μmol·m-2·s-1, the light saturation points (LSP) were 351μmol·m-2·s-1 and 527μmol·m-2·s-1, respectively. With increasing PAR, their transpiration rates were increasing along. The water use efficiency of Artemisia gmelinii and Potentilla discolor abided by a parabola model while increasing PAR. Both the two have high water use ability at each time interval in survey day. Artemisia gmelinii was a sunny plant and not a typical sun plant, and Potentilla discolor was a typical sunny plant.(6)Daily single-plant's transpiration of Camgana korshinskii was higher in June and July. Daily single-plant's transpiration of Sophora viciifolia and Hippophae rhamnoides were higher in May,July and September. The peak of the three single-plant species's daily water consumption appeared in July, and orders of that was: Camgana korshinskii(8.523kg)>Sophora viciifolia(4.20kg)>Hippophae rhamnoides(3.540kg). The average daily single-plant's transpiration in growth season(from May to September) were ranked as follows: Camgana korshinskii(4.48kg)>Hippophae rhamnoides(2.839kg)>Sophora viciifolia(2.799kg). (7)The monthly community transpiration had difference for Camgana korshinskii,Sophora viciifolia and Hippophae rhamnoides. The max daily community transpiration of Camgana korshinskii,Hippophae rhamnoides and Sophora viciifolia were in July respectively at 24.04mm,14.16mm and 3.82mm. The daily transpiration of Artemisia gmelinii community was a one-peak curve. Daily transpiration was highest in June and the maximum was 6.7mm. Average daily transpiration from May to September were ranked in a descending order as follows: Camgana korshinskii community,Hippophae rhamnoides community,Artemisia gmelinii community and Sophora viciifolia community.(8)Camgana korshinskii and Glycyrrhiza uralensis had the characteristics of high photosynthesis,high transpiration and high water use efficiency. Artemisia gmelinii and Potentilla discolor were the herbage plants with high photosynthesis,high transpiration and low water use efficiency. Hippophae rhamnoides and Sophora viciifolia were the shrub tree species with high water use efficiency and low water consumption. Periploca sepium belonged to shrub species with low transpiration and high water use efficiency.