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[MIS11-05] Why is Rawanbuki large?
Keywords:Rawanbuki, stream water quality, Agricultural crops
1. Introduction
Rawanbuki, a variety of the Japanese butterbur Akitabuki (Petasites japonicus subsp. giganteus), is grown naturally along the Rawan and Moashoro Rivers, Hokkaido. Most Rawanbuki plants reach 2–3 m in height and 10 cm in diameter in two months, and these are much larger than those grown along other nearby rivers. However, the reason that Rawanbuki plants are extremely large remains unknown.
It is hypothesized that nutrients exported from upland areas stimulate the growth rates of Rawanbuki, resulting in them being extremely large. To test this hypothesis, three experiments were conducted: 1) an analysis of the stream water quality, 2) an evaluation of the growth and environmental conditions of Rawanbuki, including soil nutrients, and 3) a manipulation experiment to test fertilization effects on the growth of butterburs.
2. Methods
1) Stream water quality
Synoptic stream water sampling was conducted. The sampling was conducted every 1–3 months from August 2015 to July 2016. The samples were analyzed for electric conductivity (EC), major ions (Cl-, NO3-, SO42-, Na+, NH4+, K+, Mg2+, and Ca2+), and soluble reactive phosphorus (SRP).
2) Growth and environmental conditions of Rawanbuki
The growth of Rawanbuki and soil physicochemical properties were evaluated at three sites along the Rawan River (R1, R2, and R3) and at three sites along the tributary of the Toshibetsu River (T1, T2, and T3) as control sites. At each site, butterburs were harvested in these plots on June 2016 when most butterburs were fully grown. Stem height, stem diameter, leaf width, and the mass of the leaves and stems were measured. Soil physicochemical properties, such as water content, temperature, pH (H2O), EC, inorganic N pool, net N mineralization/nitrification rate, and available P pool, were also measured.
3) Manipulation experiment
Four different treatment plots [control (C), nutrient (N), water (W), and nutrient + water (N + W)] were established. Treatments were conducted for a growing period. After the treatments, all butterburs were harvested, and their stem height, stem diameter, leaf width, and the mass of the leaves and stems were measured.
3. Results and discussion
1) Stream water quality
Solute concentrations, including nitrate, soluble reactive phosphorus, and minerals, in the Rawan and Moashoro Rivers were much higher than those in the neighboring rivers (Toshibetsu and Ashoro Rivers). The underlying geology in the Rawan and Moashoro Rivers is very different from that in the Toshibetsu and Ashoro Rivers, and this geology can characterize the stream water quality in the Rawan River.
2) Growth and environmental conditions of Rawanbuki
Rawanbuki plants grown along the Rawan River is much larger than those along the Toshibetsu River. The high level of soil nutrients and water along the Rawan River may cause the extremely large Rawanbuki plants. Nutrient-rich conditions in the Rawan River likely result from upland stream water inflow.
3) Manipulation experiment
Manipulation experiment confirms the hypothesis that additional nutrients enhance the size of butterburs. Stem height and stem diameter were significantly greater for the nutrient-addition plots (N and N+W) than for the control (C) and water-addition plot (W).
4. Conclusion
The extremely large butterburs are caused by a large amount of nutrients exported from upland areas. These results are the first demonstration of the role of stream water nutrients in enlarging agricultural crops.
Suggested Reading
Chiwa, M. et al. Nutrients exported from upland stream water enlarge perennial biomass crops. Scientific Reports 11, 2200, doi:10.1038/s41598-021-81191-x (2021).
Rawanbuki, a variety of the Japanese butterbur Akitabuki (Petasites japonicus subsp. giganteus), is grown naturally along the Rawan and Moashoro Rivers, Hokkaido. Most Rawanbuki plants reach 2–3 m in height and 10 cm in diameter in two months, and these are much larger than those grown along other nearby rivers. However, the reason that Rawanbuki plants are extremely large remains unknown.
It is hypothesized that nutrients exported from upland areas stimulate the growth rates of Rawanbuki, resulting in them being extremely large. To test this hypothesis, three experiments were conducted: 1) an analysis of the stream water quality, 2) an evaluation of the growth and environmental conditions of Rawanbuki, including soil nutrients, and 3) a manipulation experiment to test fertilization effects on the growth of butterburs.
2. Methods
1) Stream water quality
Synoptic stream water sampling was conducted. The sampling was conducted every 1–3 months from August 2015 to July 2016. The samples were analyzed for electric conductivity (EC), major ions (Cl-, NO3-, SO42-, Na+, NH4+, K+, Mg2+, and Ca2+), and soluble reactive phosphorus (SRP).
2) Growth and environmental conditions of Rawanbuki
The growth of Rawanbuki and soil physicochemical properties were evaluated at three sites along the Rawan River (R1, R2, and R3) and at three sites along the tributary of the Toshibetsu River (T1, T2, and T3) as control sites. At each site, butterburs were harvested in these plots on June 2016 when most butterburs were fully grown. Stem height, stem diameter, leaf width, and the mass of the leaves and stems were measured. Soil physicochemical properties, such as water content, temperature, pH (H2O), EC, inorganic N pool, net N mineralization/nitrification rate, and available P pool, were also measured.
3) Manipulation experiment
Four different treatment plots [control (C), nutrient (N), water (W), and nutrient + water (N + W)] were established. Treatments were conducted for a growing period. After the treatments, all butterburs were harvested, and their stem height, stem diameter, leaf width, and the mass of the leaves and stems were measured.
3. Results and discussion
1) Stream water quality
Solute concentrations, including nitrate, soluble reactive phosphorus, and minerals, in the Rawan and Moashoro Rivers were much higher than those in the neighboring rivers (Toshibetsu and Ashoro Rivers). The underlying geology in the Rawan and Moashoro Rivers is very different from that in the Toshibetsu and Ashoro Rivers, and this geology can characterize the stream water quality in the Rawan River.
2) Growth and environmental conditions of Rawanbuki
Rawanbuki plants grown along the Rawan River is much larger than those along the Toshibetsu River. The high level of soil nutrients and water along the Rawan River may cause the extremely large Rawanbuki plants. Nutrient-rich conditions in the Rawan River likely result from upland stream water inflow.
3) Manipulation experiment
Manipulation experiment confirms the hypothesis that additional nutrients enhance the size of butterburs. Stem height and stem diameter were significantly greater for the nutrient-addition plots (N and N+W) than for the control (C) and water-addition plot (W).
4. Conclusion
The extremely large butterburs are caused by a large amount of nutrients exported from upland areas. These results are the first demonstration of the role of stream water nutrients in enlarging agricultural crops.
Suggested Reading
Chiwa, M. et al. Nutrients exported from upland stream water enlarge perennial biomass crops. Scientific Reports 11, 2200, doi:10.1038/s41598-021-81191-x (2021).