Determination of leaf carbon isotope discrimination in C4 plants under variable N and water supply.
Understanding the mechanisms underlying variations in carbon isotope discrimination (Δ) in C4 plants is critical for predicting the C3/C4 ratio in C3/C4 mixed grassland. The value of Δ is determined by bundle sheath leakiness (Ф) and the ratio of intercellular to ambient CO2concentration (Ci/Ca). Leaf nitrogen concentration (Nleaf) is considered a driver of Δ in C4 plants. However, little is known about how Nleafaffects Ф and Ci/Ca, and subsequently Δ. Here leaf carbon isotope composition, Nleaf, Ф, and leaf gas exchange were measured in Cleistogenes squarrosa, a dominant C4 species in the Inner Mongolia grassland. Δ remained relatively stable under variable N and water supply. Higher N supply and lower water supply increased Nleaf, stimulated photosynthesis and further decreased Ci/Ca. High N supply increased Ф, which responded weakly to water supply. Nleafexerted similar effects on Ci/Caand on Ф in the field and pot experiments. Pooling all the data, Nleafexplained 73% of the variation in Ci/Ca. Overall, both Ф and Ci/Cadetermined Δ; however, the contribution of Ф was stronger. Nleafinfluenced Δ primarily though Ci/Ca, rather than Ф. Ф should be considered in estimating Δ of C4 endmember.
Key Laboratory of Ecosystem Observation and Modeling, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing, 100101, China. yangh@igsnrr.ac.cn.
Hao
H
Yang
National Hulunber Grassland Ecosystem Observation and Research Station, Institute of Agricultural Resources and Regional Planning, Chinese Academy of Agricultural Sciences, Beijing, 100081, China.
Qiang
Q
Yu
Key Laboratory of Ecosystem Observation and Modeling, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing, 100101, China.
Wen-Ping
WP
Sheng
Key Laboratory of Ecosystem Observation and Modeling, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing, 100101, China.
Sheng-Gong
SG
Li
Key Laboratory of Ecosystem Observation and Modeling, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing, 100101, China.
Jing
J
Tian
D002247:Carbon Isotopes / Q000378:metabolism*; D009584:Nitrogen / Q000008:administration & dosage / Q000378:metabolism*; D010788:Photosynthesis; D018515:Plant Leaves / Q000737:chemistry / Q000378:metabolism*; D006109:Poaceae; D014867:Water / Q000378:metabolism*
D002247:Carbon Isotopes; D014867:Water; D009584:Nitrogen