Canopy‐scale relationships between stomatal conductance and photosynthesis in irrigated rice

Abstract

Modeling stomatal behavior is critical in research on land-atmosphere interactions and climate change. The most common model uses an existing relationship between photosynthesis and stomatal conductance. However, its parameters have been determined using infrequent and leaf-scale gas-exchange measurements and may not be representative of the whole canopy in time and space. In this study, we used a top-down approach based on a double-source canopy model and eddy flux measurements throughout the growing season. Using this approach, we quantified the canopy-scale relationship between gross photosynthesis and stomatal conductance for 3 years and their relationships with leaf nitrogen content throughout each growing season above a paddy rice canopy in Japan. The canopy-averaged stomatal conductance (gsc ) increased with increasing gross photosynthesis per unit green leaf area (Ag ), as was the case with leaf-scale measurements, and 41-90% of its variation was explained by variations in Ag adjusted to account for the leaf-to-air vapor-pressure deficit and CO2 concentration using the Leuning model. The slope (m) in this model (gsc versus the adjusted Ag ) was almost constant within a 15-day period, but changed seasonally. The m values determined using an ensemble dataset for two mid-growing-season 15-day periods were 30.8 (SE = 0.5), 29.9 (SE = 0.7), and 29.9 (SE = 0.6) in 2004, 2005, and 2006, respectively; the overall mid-season value was 30.3 and did not greatly differ among the 3 years. However, m appeared to be higher during the early and late growing seasons. The ontogenic changes in leaf nitrogen content strongly affected Ag and thus gsc . In addition, we have discussed the agronomic impacts of the interactions between leaf nitrogen content and gsc . Despite limitations in the observations and modeling, our canopy-scale results emphasize the importance of continuous, season-long estimates of stomatal model parameters for crops using top-down approaches.

The Impact of Sunlight Conditions on the Consistency of Vegetation Indices in Croplands—Effective Usage of Vegetation Indices from Continuous Ground-Based Spectral Measurements

“…The details of each site are shown in Table 1. All three sites belong to AsiaFlux (http://asiaflux.net/), where fluxes of CO2, sensible heat, and latent heat, in addition to basic micrometeorological and physiological data have been collected since 1999 at the rice site, 2007 at the maize site, and 2004 at the grass site [28][29][30]. …”

Hysteresis loops between canopy conductance of grapevines and meteorological variables in an oasis ecosystem

“…Canopy conductance (g c ) plays a key role in gas and energy exchanges across vegetated surfaces via their direct controls on CO 2 uptake and water losses (Alfieri et al, 2008;Berry et al, 2010;Damour et al, 2010;Ono et al, 2013). Therefore, studying the responses of g c to the environmental variables is essential to understand the relationships between the plant physiological and environmental processes (Daly et al, 2004;Kumar et al, 2011;Ghimire et al, 2014).…”

Estimation of methane emission from rice paddy soils in Japan using the diagnostic ecosystem model

“…The reason is that satellite observation can detect lower solar radiation due to longer hovering of the Baiu front during growing season e.g., Saigusa et al, 2008;Sasai et al, 2011Sasai et al, , 2012 . Since the photosynthesis and biomass production of rice plants are inhibited under the lower radiation Resurreccion et al, 2001;Sasai et al, 2012;Ono et al, 2013 , the carbon substrates of the methane production were decreased by lower litter and root exudation Sass et al, 1991;Lu et al, 2002 . The year's event of 2003 ensures a consistent understanding to the methane estimation over Japan.…”