Environmental Engineering Reference
In-Depth Information
response curves derived from the leaves were substantially affected by different species.
C. chinensis
showed highest apparent quantum efficiency (AQE), followed by
P.
australis
and
G. soja
, while apparent dark respiration (
R
d
),
convexity (
k
), light saturation
point (LSP) and maximum gross CO
2
assimilation rate
(
P
max
) of
G. soja
were higher than
P. australis
and
C. chinensis
. The irradiance response curve of
P
N
and WUE of different
plant species followed the same order:
G. soja
>
C. chinensis
>
P. australis
. They were both
higher than most of other species. It was concluded that plant species adapting to the
saline-alkaline habitat showed higher photosynthesis. In addition,
G. soja
is also effective
to improve saline-alkaline soil quality.
Keywords:
Photosynthesis, diurnal variation, Glycine soja, Phragmites australis, Cynanchum
chinensis
I
NTRODUCTION
Photosynthesis is the only natural conversion mechanism of photon energy into chemical
energy and it is responsible for 90-95% of the plant biomass accumulation (Gomez et al.,
2005). Approximately 40% of a plant's dry mass consists of carbon, fixed in photosynthesis.
Net photosynthetic rate (
P
N
) in plant leaves is often influenced by environment factors such
as irradiance, temperature, and water supply, and also by leaf age, leaf position, and
developmental stage (Ephrath et al., 2012; Lideman et al., 2013; Zhang et al., 2005). Plant
photosynthetic rate can be calculated using single leaf net photosynthetic rate (
P
N
), responses
to photosynthetically active radiation (PAR) and air temperature (
T
a
), leaf area index (LAI),
radiation interception, and transmission and distribution through the canopy depending on
crop architecture (Liu et al., 2012; Yan et al., 2013). Photosynthesis is an essential process for
developing the simulation models that enable estimates of plant growth and productivity.
Higher photosynthetic rates reflect the potential of a species to accumulate more biomass
(Naumann et al., 2010). The Yellow River Delta (YRD) is the fastest growing delta and the
most active land-ocean interacting region among the large river deltas in the world (Wang et
al., 2012), because the Yellow River brings great quantities of muddy sand into the Bohai
Sea. YRD located at Bohai sea gulf, is one of the three biggest deltas in China. Total land
area covering 12000 km
2
, with averagely 0.5 hm
2
per capita, and arable land is 0.19 hm
2
per
capita in the region. The YRD regarded as the ‗‗Golden Triangle'' due to its great
exploitation potential and development of the YRD gets more and more attention. With less
rainfall the mineral content in underground water was higher. These conditions caused soil
salinization and alkalization. Therefore land degradation is a typical problem in the field.
Through analysis of land use-cover change and driving force in YRD, it could be concluded
that these natural factors such as more evaporation, less rainfall, poorer fresh water limited
land use. Soils salinization easily occurred. Meanwhile, the variety of Yellow River
hydrology and human disturbances of land environment are also important driving factors
(Xing & Zhang 2006).
In this zone, vegetation destruction, caused by adverse environmental and extreme
climate conditions together with inappropriate human activities, has led to serious soil
erosion, a reduction in soil fertility and general environmental deterioration. A key factor in
the degradation of these soils is the loss of plant cover, allowing increased erosion and
