The relationship between leaf and ecosystem CO2 exchanges in a maize field
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The relationship between leaf photosynthetic rate (A) in a vegetation canopy and the net ecosystem CO2 exchange (NEE) over an entire ecosystem is not well understood. The aim of the present study is to assess the coordinated changes in NEE derived with eddy covariance, A measured in leaf cuvette, and their associations in a rainfed maize field. The light response-curves were estimated for the carbon assimilation rate at both the leaf and ecosystem scales. NEE and A synchronically changed throughout the day and were greater around noon and persisted longer during rapid growth periods. The leaf A had a similar pattern of daytime changes in the top, middle, and bottom leaves. Only severe leaf ageing led to a significant decline in the maximum efficiency of photosystem II (PSII) photochemistry. The greater maximum NEE was associated with a higher ecosystem quantum yield. NEE was positively and significantly correlated with the leaf A averaged based on the vertical distribution of leaf area. The finding highlights the feasibility of assessing NEE by leaf CO2 exchange because of most of experimental data obtained with leaf cuvette methods; and also implies that simultaneously enhancing leaf photosynthetic rate, electron transport rate, net carbon assimilation at whole ecosystem might play a critical role for the enhancement of crop productivity.
KeywordsEddy covariance Leaf photosynthetic rate Canopy Net CO2 ecosystem exchange Photosynthetic quantum yield Photosystem II photochemistry Upscaling
We are greatly indebted to Shi Chunqiao, Yang Yang, Liu Jingli, Wang Yunlong for their work during the experiment.
National Natural Science Foundation of China (41330531), and China Special Fund for Meteorological Research in the Public Interest (GYHY201506001-3; GYHY201506019).
Compliance with ethical standards
Conflict of interest
All authors declare that they have no conflict of interest.
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