ФИЗИОЛОГИЯ РАСТЕНИЙ, 2012, том 59, № 2, с. 251-261
ЭКСПЕРИМЕНТАЛЬНЫЕ СТАТЬИ
УДК 581.1
Canopy and Leaf Photosynthetic Characteristics and Water Use Efficiency of Sweet Sorghum under Drought Stress1 © 2012 T. Xie, P. Su
Linze Inland River Basin Research Station, Plant Stress Ecophysiology and Biotechnology Laboratory, Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, Lanzhou, China
Received February 24, 2011
The objective of this paper was to examine the relationship between Water Use Efficiency (WUE) at the canopy and leaf levels, to determine soil moisture conditions, which can optimize yield, and WUE of sweet sorghum, thus providing some theoretical foundation for using marginal land effectively and developing production of sweet sorghum (Sorghum bicolor (Linn.) Moench). Three levels of soil moisture conditions were established, and photosynthetic characteristics and yield were measured. The canopy apparent photosynthetic rate (CAP) and leaf photosynthetic rate (PN) were reduced gradually with increased drought stress, and the CAP was lower than the PN under every soil moisture condition. The PN had a midday depression phenomenon, but the CAP did not exhibit this midday depression phenomenon under severe drought stress. The linear regression relationship of CAP and PN was CAP = 1.5945 + 0.1496 PN. The canopy apparent WUEC and leaf WUEl were the highest under moderate drought stress. It was 5.3 and 5.8 times higher than the WUEL in mid-July and late August, respectively. The stem fresh biomass yield was 77 tons/ha under moderate drought stress, and WUE of aboveground biomass yield (WUEB) was also the highest. Our results show that moderate drought stress did not result in a significant reduction in biomass yield but increased WUE significantly.
Keywords: Sorghum bicolor - crop energy - assimilation chamber - canopy apparent photosynthesis - water use efficiency - biomass yield
INTRODUCTION
Water is the main factor, which affects plant growth and reproduction as well as plant distribution and production in terrestrial ecosystems. Because of the huge difference in precipitation and potential evapotranspiration, many plants may be under drought stress conditions in arid regions. At present, many researchers have focused on the responses of plants to drought environment [1, 2]. Sweet sorghum is a C4 crop with a high net photosynthetic rate and is also known to show high drought and water logging resistance and salinity tolerance [3]. It is of particular interest because its biomass is variously used for the production of energy, fibers, or paper, as well as for syrup and animal feed. Research on sweet sorghum has focused on its shoot chemical composition [4], biomass yield, sugar con-
1 This text was submitted by the authors in English.
Abbreviations'. Ca - ambient CO2 concentration; CAP - canopy apparent photosynthetic rate; CAT - canopy apparent transpiration rate; Gs - stomatal conductance; MD - moderate drought stress; NW - normal water supply; PN - leaf photosynthetic rate; RH - relative humidity; SD - severe drought stress; Tr - leaf transpiration rate; PFD - photon flux density; WUE - water use efficiency.
Corresponding author. Tingtong Xie. Linze Inland River Basin Research Station, Plant Stress Ecophysiology and Biotechnology Laboratory, Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, 730000 Lanzhou, China. E-mail. xieting1026@126.com
tent [5, 6], hereditary diversity, and breeding [7], and physiological characteristics [8, 9] to serve as an energy crop, which does not compete with food production. Little research has focused on canopy and leaf photosynthetic characteristics, especially with regards to the relationship between canopy and leaf levels, especially under drought stress. Research on carbon assimilation and water use by crops is critical to understand the processes leading to their carbon and water balance, and it is commonly divided into canopy and leaf levels [10].
Canopy photosynthesis is understood as originating from groups of leaves or individual plants. The canopy of a plant, particularly its leaf area, is a reflection of the material source. Canopy photosynthesis also reflects the photosynthetic capacity of the material source. Therefore, canopy photosynthesis can be used to represent photosynthetic activity for different leaf morphologies and canopy structures [11]. Many studies indicate that canopy photosynthesis is a complex process, which was affected by various environmental and plant factors [12]. The accurate determination of canopy CO2 and H2O fluxes is the key premise for understanding the environmental adaptability of plants.
The canopy chamber with an infrared gas analyzer can directly measure the CO2 and H2O fluxes at the canopy level [13], but there are some limitations in the currently used canopy chambers, such as the microcli-
Table 1. Soil moisture content of sweet sorghum under different water regimes
Treatment Field moisture capacity, % Soil moisture content, %
NW 70 ± 5 16.2 ± 1.0
MD 50 ± 5 11.6 ± 1.0
SD 30 ± 5 6.. ± 1.0
matic differences between the chamber and the environment when the chamber is closed [14]; the walls alter the radiation amount and quality inside the chamber [15]. The canopy chamber, which was used in this study, had significant improvements to overcome these limitations. Firstly, cooling components inside the chamber, which can automatically adjusted the air temperature, were installed, so that the microclimate inside the chamber was similar to natural conditions. Secondly, the canopy chamber was made of acrylic material, which had a high light transmission rate. In this study, the photosynthetic characteristics and water use efficiency (WUE), and their relations with above-ground biomass yield under drought stress were examined. The objectives of this study were: (1) to study photosynthetic characteristics of sweet sorghum under different soil moisture conditions; (2) to elucidate the relationship between canopy and leaf photosynthetic characteristics; and (3) to determine soil moisture conditions, which optimize yield and WUE, thus providing some theoretical foundation for using marginal land effectively and developing production of sweet sorghum.
MATERIALS AND METHODS
Study site. The experiment was carried out in 2009 at the Linze Inland River Basin Research Station (39°21' N, 100°02' E, 1400 m a.s.l.). It is located in the oasis edge region of the northern part of Linze in the middle reach of Hexi Corridor in Gansu Province in northwest of China. It is a typical desert oasis and relies on the Heihe River. It has an arid desert climate, where the mean annual precipitation is 116.8 mm. The mean annual evaporation is 2390 mm, which is 20 times higher than the precipitation. The average daily temperature is 7.6°C with a total range from 39.1 to -27°C. The accumulated annual temperature of >10°C is around 3088°C, and the frost-free period is 165 days. The annual total number of sunlight hours is 3045. The drought, high temperatures, and strong wind are the main climate characteristics.
Plant material and experimental design. The seeds of sweet sorghum (Sorghum bicolor (Linn.) Moench) hybrid BJ0601 were sown on March 12, 2009 in 9 plots (4 x 4 m) and planted at 60 x 40 x 20 cm spacing (100050 plants per ha). The soil water content was 23.2% of field capacity, and the bulk density was
1.47 g/cm3. The seeds began to germinate on March 23. Sweet sorghum reached the flowering stage on August 19 and the soft dough stage on September 1. The crop was harvested on September 25, 2009.
The experiment design was a completely randomized sampling plot with three replications under three water levels (table 1). The experiment was started on May 23, 2009, which maintained the soil moisture at the main distributed range of sweet sorghum roots (0-60 cm) within three water levels (table 1). The soil moisture (0-20 cm, 20-40 cm, and 40-60 cm) was measured every two days by gravimetric determination, then the water requirement of each plot was calculated by to the differences between the designed soil moisture and measured soil moisture, and the required water was supplied in the next day, thus maintaining the soil moisture at the designed level. The amount of water added to each plot during the experimental period was 20, 10, and 6 m3 for normal water supply (NW), moderate drought stress (MD), and severe drought stress (SD), respectively.
The measurement principle and calculation. Canopy apparent photosynthesis of sweet sorghum was measured in an assimilation chamber ("Beijing Ecotek", China) with LI-8100 ("LI-COR", United States). The LI-8100 is a fully automated system dedicated to making measurements of soil CO2 flux. It uses IRGA to measure the change in CO2 and H2O concentrations in the chamber.
The length, width, and height of the assimilation chamber were all 50 cm. An acrylic material that allows for more than 95% light transmittance was used. The assimilation chamber was installed with two mixing fans to ensure that the gas in the chamber was thoroughly mixed. The temperature was monitored by two temperature sensors inside and outside the chamber. Temperature was controlled by the electronic cooling components in the chamber. The upper and lower edges of the chamber were sealed by strips to ensure gas tightness. A small cylinder attached to the roof and wall and driven by a small compressor controlled the opening and closing of the roof. The assimilation chamber was controlled by LI-8100. Once the measurement parameters were set up, the instrument was able to operate automatically.
The working principle of the canopy photosynthesis measurement system is described in Fig. 1. After the beginning of measurement, the gas in the assimilation chamber was mixed by the fans and passed through the air outlet into the IRGA of the LI-810
Для дальнейшего прочтения статьи необходимо приобрести полный текст. Статьи высылаются в формате PDF на указанную при оплате почту. Время доставки составляет менее 10 минут. Стоимость одной статьи — 150 рублей.