Adaptation of Rice to the Nordic Climate Yields Potential for Rice Cultivation at Most Northerly Site and the Organic Production of Low-Arsenic and High-Protein Rice

Abstract

There is an urgent demand for low-arsenic rice in the global market, particularly for consumption by small children. Soils in Uppsala, Sweden, contain low concentrations of arsenic (As). We hypothesize that if certain japonica paddy rice varieties can adapt to the cold climate and long day length in Uppsala and produce normal grains, such a variety could be used for organic production of low-arsenic rice for safe rice consumption. A japonica paddy rice variety, "Heijing 5," can be cultivated in Uppsala, Sweden, after several years' adaptation, provided that the rice plants are kept under a simple plastic cover when the temperature is below 10°C. Uppsala-adapted "Heijing 5" has a low concentration of 0.1 mg per kg and high protein content of 12.6% per dry weight in brown rice grain, meaning that it thus complies with all dietary requirements determined by the EU and other countries for small children. The high protein content is particularly good for small children in terms of nutrition. Theoretically, Uppsala-adapted "Heijing 5" can produce a yield of around 5100 kg per ha, and it has a potential for organic production. In addition, we speculate that cultivation of paddy rice can remove nitrogen and phosphorus from Swedish river water and reduce nutrient loads to the Baltic Sea and associated algae blooms.

Keywords: Baltic Sea; Uppsala rice cultivation; high-protein rice; infant food; low-arsenic rice; rice for cold climate.

FIGURE 1

A Chinese paddy rice variety “Heijing 5” (japonica) adapted to the Uppsala climate and produced normal panicles with fully-filled grains. (A) “Heijing 5” paddy in Uppsala. (B) “Heijing 5” panicles in a paddy in Uppsala. (C) Harvested rice plants from: (left) a greenhouse in Uppsala, (center) a paddy covered with a simple and easily openable polytunnel when the temperature was below 10°C, and (right) a paddy without a cover. (D) Harvested panicles from: (top row) a greenhouse in Uppsala (middle row), a paddy covered with plastic when the temperature was below 10°C, and (bottom row) a paddy without a cover. Bars = 10 cm in (C,D).

FIGURE 2

(A–J) Phenotypical traits of “Heijing 5” plants cultivated in Uppsala in (left) a greenhouse control, (center) a paddy block covered with a polytunnel shed when air temperature was below 10°C, and (right) an uncovered paddy block control. One-way ANOVA was used (Error bars show s.d.). ^∗∗P < 0.01 is shown for significant differences between controls and paddy.

FIGURE 3

Concentration or content of metals, proteins, starch, amylose, and oil in paddy rice cultivars grown in China and Sweden. (A,B) Raw rice caryopses of a purchased Chinese cultivar “Daohuaxiang” (japonica) cultivated in (left) Minyi and (center) Longfengshan in Wuchang City, China, and (right) “Heijing 5” cultivated in Uppsala. (C) Concentration of arsenic (As), mercury (Hg), and cadmium (Cd), and (D) Content of proteins in the corresponding raw rice grains. (E) Content of starch and amylose. (F) Content of oil or triacylglycerol (TAG). Upper panel in (F) is a Thin Layer Chromatogram (TLC). Bars = 6 mm in (A,B). One-way ANOVA was used (Error bars show s.d.). ^∗∗P < 0.01 is shown for significant differences between “Daohuaxiang” and “Heijing 5.”

FIGURE 4

Concentration of As in rice tissues aboveground and paddy soil/water mixture. (A) Rice plants of “Nipponbare” and “Heijing 5” in an Uppsala paddy plot. (B) Harvested rice tissues aboveground of “Nipponbare” and “Heijing 5” from a paddy plot. (C) As concentration in rice tissues aboveground of “Nipponbare” and “Heijing 5” and As concentration in Uppsala paddy soil/water mixture. One-way ANOVA was used (Error bars show s.d.). ^∗∗P < 0.01 is shown for significant differences between “Nipponbare” and “Heijing 5.”