Quantifying differences in water and carbon cycling between paddy and rainfed rice (Oryza sativa L.) by flux partitioning

Abstract

Agricultural crops play an important role in the global carbon and water cycle. Global climate change scenarios predict enhanced water scarcity and altered precipitation pattern in many parts of the world. Hence, a mechanistic understanding of water fluxes, productivity and water use efficiency of cultivated crops is of major importance, i.e. to adapt management practices. We compared water and carbon fluxes of paddy and rainfed rice by canopy scale gas exchange measurements, crop growth, daily evapotranspiration, transpiration and carbon flux modeling. Throughout a monsoon rice growing season, soil evaporation in paddy rice contributed strongly to evapotranspiration (96.6% to 43.3% from initial growth to fully developed canopy and amounted to 57.9% of total water losses over the growing seasons. Evaporation of rainfed rice was significantly lower (by 65% on average) particularly before canopy closure. Water use efficiency (WUE) was significantly higher in rainfed rice both from an agronomic (WUEagro, i.e. grain yield per evapotranspiration) and ecosystem (WUEeco, i.e. gross primary production per evapotranspiration) perspective. However, our results also show that higher WUE in rainfed rice comes at the expense of higher respiration losses compared to paddy rice (26% higher on average). Hence, suggestions on water management depend on the regional water availability (i.e. Mediterranean vs. Monsoon climate) and the balance between higher respiratory losses versus a potential reduction in CH4 and other greenhouse gas emissions. Our results suggest that a shift from rainfed/unsaturated soil to waterlogged paddy conditions after closure of the rice canopy might be a good compromise towards a sustainable use of water while preserving grain yield, particularly for water-limited production areas.

Effects of water management and cultivar on carbon dynamics, plant productivity and biomass allocation in European rice systems

“…The rice paddies under both water management systems were net sinks of atmospheric C and did not differ significantly from each other in terms of NEE, GPP, RE or decomposition rates for the seasonal mean or during any of the key stages of plant growth measurement. Mean daily NEE in the CF rice paddy was −15.21 ± 0.95 g C m −2 d −1 (range:-38.87 to −0.61), and GPP 24.01 ± 1.20 g C m −2 d −1 (range: 51.07 to 4.97), affirming prior results of rice paddy studies using eddy covariance techniques in East Asia, India and the USA, where NEE estimates are between 5 and −39 and GPP between 5 and 50 g C m −2 day −1 (Alberto et al, 2009; Bhattacharyya et al, 2013; Miyata et al, 2005; Nay-Htoon et al, 2018; Saito et al, 2005; Swain et al, 2016). However, unlike in other studies where they reported a more positive NEE in intermittently flooded systems (Alberto et al, 2014; Liu et al, 2013; Miyata et al, 2000), mean daily NEE fluxes under AWD in this study were very similar to CF (−16.00 ± 1.00 g C m −2 d −1 (range: −38.39 to −0.70), and GPP 23.26 ± 1.27 g C m −2 d −1 (range: 56.46 to 4.02)), challenging our first hypothesis ( H1 ).…”

Variation between rice accessions in photosynthetic induction in flag leaves and underlying mechanisms

“…5 ). This is likely to be due to the shape and small size of rice stomata allowing fast responses ( McAusland et al , 2016 ), but also the evolutionary history of rice, which was domesticated from emergent aquatic progenitors and then bred in paddy conditions where water would not be limiting to the plant ( Nay-Htoon et al , 2018 ).…”

Variation in photosynthetic induction between rice accessions and its potential for improving productivity

“…Its wild ancestors were emergent aquatic plants, and most breeding programmes that target the improvement of lowland rice utilize flooded paddies, where water is not limiting. After millennia of cultivating rice in conditions with plentiful water, it is likely that rice is less conservative in its water usage, explaining the lower L S (Nay-Htoon et al, 2018).…”