TITLE:
Interaction of Carbon Dioxide Enrichment and Soil Moisture on Photosynthesis, Transpiration, and Water Use Efficiency of Soybean
AUTHORS:
Madegowda Madhu, Jerry L. Hatfield
KEYWORDS:
Elevated Carbon Dioxide, Evaporation, Interactions, Photosynthetic Rate, Soil Moisture, Soybean, Water Use Efficiency
JOURNAL NAME:
Agricultural Sciences,
Vol.5 No.5,
April
9,
2014
ABSTRACT: Soybean (Glycine max (L.) Merrill) is one of
the most important oil and protein sources in the world. Interactive effect of elevated
carbon dioxide (CO2) and soil water availability potentially impact future
food security of the world under climate change. A rhizotron growth chamber experiment
was conducted to study soil moisture interactions with elevated CO2 on
gaseous exchange parameters of soybean under two CO2 concentrations (380
and 800 μmol·mol－1) with three soil moisture levels. Elevated CO2 decreased photosynthetic rate (11.1% and 10.8%), stomatal conductance (40.5% and
36.0%), intercellular CO2 concentration (16.68% and 12.28%), relative
intercellular CO2 concentration (17.4% and 11.2%), and transpiration
rate (43.6% and 39%) at 42 and 47 DAP. This down-regulation of photosynthesis was
probably caused by low leaf nitrogen content and decrease in uptake of nutrients
due to decrease in stomatal conductance and transpiration rate. Water use efficiency
(WUE) increased under elevated CO2 because increase in total dry weight
of plant was greater than that of water use under high CO2 conditions.
Plants under normal and high soil moisture levels had significantly higher photosynthetic
rate (7% to 16%) favored by optimum soil moisture content and high specific water
content of soybean plants. Total dry matter production was significantly high when
plants grown under elevated CO2 with normal (74.3% to 137.3%) soil moisture
level. Photosynthetic rate was significantly and positively correlated with leaf
conductance and intercellular CO2 concentration but WUE was significantly
negatively correlated with leaf conductance, intercellular CO2 concentration
and transpiration rate. However, the effect of high CO2 on plants depends
on availability of nutrients and soil moisture for positive feedback from CO2 enrichment.