Environmental Engineering Reference
In-Depth Information
area is important since it provides physical protection and contributes organic matter that
enhances soil water holding capacity (WHC) and soil fertility characteristics (Wang et al.,
2012; Zhang et al., 2013; Zhang et al., 2013).
Glycine soja , or wild soybean(previously G. ussuriensis ) is an annual plant in
the legume family. It is the wild ancestor of soybean, an important crop. Phragmites australis
is one of the most important, widespread and constructive wetland plant species over the
YRD. There were about 2,600 ha of P. australis wetland in the YRD. It provides staging,
wintering and breeding sites for birds and may directly benefit from ecological restoration
engineering for wetlands (Wu et al., 2009). P. australis adapts to this area very well and is a
dominant species. The reed shows considerable morphological variations among populations
of different salinity.
Glycine soja , Phragmites australis and Cynanchum chinensis are three dominant plant
species adapted to the saline-alkaline habitat in YRD region, however, less information is
known about their photosynthetic characteristics. This work was carried out to investigate the
diurnal variation in photosynthesis of G. soja , P. australis and C. chinensis grown under
identical saline soil conditions, considering their relationship with the variation of key
environmental factors.
M ATERIALS AND M ETHODS
Site Description
This study was conducted in the Yellow River estuary, located in the Nature Reserve of
the Yellow River Delta (37ᄚ35'-38ᄚ12' N, 118ᄚ33'-119° 20' E) in Dongying City, Shandong
Province, China. The nature reserve has a typical continental monsoon climate with
distinctive seasons; summer is warm and rainy while winter is cold. The annual average
temperature is 12.1°C, the frost-free period is 196 days, and the effective accumulative
temperature is about 4300°C. Annual evaporation is 1962 mm and annual precipitation is
551.6 mm, with about 70% of precipitation occurring between June and August. The soils in
the study area are dominated by intrazonal tidal soil and salt soil.
Gas-Exchange and Environmental Measurements
Gas-exchange measurements were conducted in August 2010, aiming to evaluate such
physiological traits in a range of environmental conditions. Net photosynthesis rate ( P N ),
transpiration rate ( E ), stomatal conductance ( g s ) and intercellular CO 2 concentration ( C i ) were
determined simultaneously on fully-expanded leaves of each species using a portable open-
flow gas exchange system Li-6400 (LI-COR Biosciences, Lincoln, USA). The respective
results were expressed as μmol (CO 2 ) m -2 s -1 , mol (H 2 O) m -2 s -1 , and μmol (CO 2 ) mol -1 .
Measurements were taken at 7:00, 9:00, 11:00, 13:00, 15:00 and 17:00 on sunny days in
August 2010. Measurements were repeated three times for each leaf, for three leaves per
plant, and the averages were recorded. Photosynthetic active radiation (PAR), air temperature
( T a ), relative humidity (RH), air CO 2 concentration ( C a ), and vapor pressure deficit (VPD)
were determined concurrently. The water use efficiency (WUE) was calculated as the ratio of
P N / E .
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