The physiological processes and mechanisms for superior water productivity of a popular ground cover rice production system

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Ground cover rice production systems (GCRPS) have been shown to both save water and increase yields compared to traditional paddy rice production systems (TPRPS). Physiological processes and mechanisms explaining the superiority of a popular GCRPS were investigated in a series of hydroponic, soil column and field experiments. Soil water, temperature and nitrogen, leaf gas exchange, plant water and nitrogen, growth and yield, transpiration, and water productivity were analyzed. Compared to TPRPS, plant available soil inorganic nitrogen was generally improved under GCRPS due to a combination of higher soil temperature and less nitrogen loss through non-physiological water consumption, especially during the early growing season. Consequently, more nitrogen was absorbed by plants under GCRPS except serious drought conditions, accompanied by higher nitrogen contents in plant tissues. Preferable specific leaf nitrogen might lead to higher leaf photosynthetic rate under optimal water conditions and less decrease relative to leaf transpiration rate under water stress. Therefore, rice under GCRPS grew faster with much more biomass and grain yield while transpiration consumption was limited in spite of the fact that the number of tillers and therefore leaf area were increased relative to TPRPS, resulting in superior water productivity. Compared to TPRPS, the root system under GCRPS was limited, but it could absorb enough water and nutrients (especially nitrogen) to support a relatively large canopy even when under water stress, which might be attributed to its higher nitrogen content and thus stronger activity.