Research article

Ecology Journal
ISSN (Print): 2708-6356, ISSN (Online): 2708-6364, Website: journal.esbangladesh.org
Ecol. J. (2021) 3 (2) : 143-150

BUCKWHEAT GROWTH AND PHYSIOLOGY AS AFFECTED BY SOWINGIMMEDIATELY AFTER BURNING UNDER DROUGHT CONDITION
Rino Nishida1 and Tomohiro Kondo2*
1

Faculty of Regional Innovation, University of Miyazaki, Miyazaki, Japan. 2 Graduate School of Agriculture, Kyoto University, Kyoto, Japan.

Corresponding e-mail: kondo.tomohiro.0z@kyoto-u.ac.jp
Received: 14 November 2021, Revised: 26 November 2021, Accepted: 15 December 2021

ABSTRACT
Shifting cultivation with sowing buckwheat seed immediately after burning, when the ash on the soil is still hot, iswidely practiced in Kyushu mountains, Japan. This study was conducted to investigate the beneﬁt of seed sowing
immediately after burning under well-irrigated and drought conditions on buckwheat. The seeds were heat-treated
and allowed to grow under well-irrigated and drought condition. Plant height and leaf number of the plants, andphysiological parameters were measured. Under drought stress condition, stomatal conductance and photosynthetic
rate of the buckwheat plants with heat treatment were increased compared to those of the plants without heat
treatment, though those under well-irrigated or light drought stress conditions were not changed. The plant withheat treatment to seed opened its stomata and maintained a high photosynthetic rate even under drought stresscondition. Heat treatment to seed did not change plant height and leaf number noticeably. Therefore, in shifting
cultivation, where buckwheat is often exposed to drought stress, seed sowing immediately after burning might beeﬀective in maintaining plant growth.
Keywords: Cross protection, drought stress, heat stress, photosynthetic rate, slash and burn cultivation, stomatal
conductanceIntroduction
The area of shifting cultivation in Kyushu mountains,
Japan, was about 2,500 ha in 1950’s, and after that the area
decreased rapidly (Sasaki, 1970). In Kyushu mountains,crop rotation and/or mix cropping of buckwheat(Fagopyrum esculentum), Japanese millet (Echinochloa
esculenta), foxtail millet (Setaria italica), adzuki bean
(Vigna angularis), soybean (Glycine max) and rice bean
(V. umbellata) was commonly practiced (Kondo and Koga
2021), and this type of shifting cultivation was reported
to widely practiced from tropical forest at mainland ofSoutheast Asia to temperate forest of East Asia (Sasaki1988). At Shiiba Village, Miyazaki Prefecture, locatedat the northern part of Kyushu mountains, the shifting
cultivation is still practiced. In that Village buckwheat is
cultivated as the ﬁrst crop after burning in early August.
Buckwheat seeds are sown immediately after burning,when the ash on the soil is still hot. In a preliminary survey,
we observed that the surface temperature of the ash was
50-60 °C on August 3, 2019 when the buckwheat seeds
were sown. This cultivation method was found widelypracticed in Kyushu mountains, though in the Southeast
Asia this method is not considered a standard practice.

From our observations, interviews, and old proverbs(Matsuoka 1977), it was revealed that sowing buckwheat
immediately after burning, when the ash on the soil was
still hot, had been widely practiced in Kyusyu mountains.
The farmers in Shiiba Village informed that buckwheat
growth was enhanced due to applying high temperature
to seed by sowing immediately after burning, butheat treatment to the buckwheat seed did not improve
growth under well irrigated condition in our preliminary
experiment (data not shown). Since buckwheat grownin shifting cultivation is often exposed to drought
stress, we hypothesized that under drought condition
the plant growth may be increased due to exposure ofseed to high temperature. Therefore, we initiated thisstudy to evaluate the eﬀect of heat treatment to seeds
on the growth performance of buckwheat under drought
condition.

Materials and Methods
The eﬀects of heat treatment to buckwheat seed onplant growth and physiology were examined in threeexperiments under diﬀerent climatic conditions.

Buckwheat sown immediately after burning

Research article

Experiment 1

days. The fourth to sixth leaves from the top were used forthese measurements. Plant height and leaf number were
measured on July 10, 17, and 24. On July 27 dry weight of
the above-ground part was measured.

Buckwheat, local variety in Shiiba Villege, was used
for the experiment 1. On June 12, 2020 the seeds were
subjected to a heat treatment as described below. A
stainless tray ﬁlled with quartz sand was placed in anoven at 70 °C. Then, the stainless tray was ﬂoated in awater bath set at 60 °C. The seeds were placed on thequartz sand for 90 minutes. The surface temperature of thequartz sand ranged from 56 to 62 °C. The seeds without
heat treatment were used as the control. Replication ofeach treatment was 8. On June 15, the seeds germinatedindoors beforehand were sown in 1/5000-a Wagner potsin the greenhouse at the University of Miyazaki (131.4°E, 31.8 °N). Soil collected from the shifting cultivationﬁeld at Shiiba Village used for the experiment following
the methods of Kondo and Koga (2021). Magnesium limeof 2.5 g and 2 g of chemical fertilizer (N:P:K=8:8:8) wereapplied per pot.

Experiment 2
The same buckwheat variety as in the experiment 1 wasused for the experiment 2. On August 7, 2020 the seeds
were subjected to a heat treatment using the same method
as of the experiment 1. Replication of each treatment
was 15. On August 10, the seeds, germinated indoors
beforehand, were sown in 1/5000-a Wagner pots in thegreenhouse at the University of Miyazaki. Soil collectedfrom the experimental ﬁeld in the University of Miyazaki
was used. Magnesium lime of 2.5 g and 2 g of chemicalfertilizer (N:P:K=8:8:8) was applied per pot.
During the experiment 2, the amount of irrigation was
reduced compared to the experiment 1. From August 10
to 31, 110 mL of water was applied twice a day on sunnydays and once a day on cloudy and rainy days. From
September 1 to 24, 55 mL of water was applied once a
day on sunny and cloudy days and no water was applied inrainy days. Soil water content, air temperature, and PAR
were measured, and soil water potential was calculated
during the experiment using the same method as in theexperiment 1.

The plant was irrigated appropriately for not to be
subjected to a drought stress from June 15 to July 21. From
July 22 to 24, all the plants were subjected to a drought
stress. On July 21 water was applied until water came out
through the bottom of the pots at 9:00. For exposing to
the stress, on July 22, 55 mL of water was applied at 9:00
and 12:00. On July 23, 55 mL of water was applied at
9:30. On July 24, no water was applied. After July 25,
suﬃcient water was applied. Soil water content (v/v), airtemperature, and photosynthetic active radiation (PAR)were measured once every 30 min during the experimentusing a soil moisture sensor, a thermometer, and a PAR
photon ﬂux sensor (EC-5, VP-4, and QSO-S respectively;
METER Group, Inc., USA). These data were recorded
on a data logger (EM50, METER Group, Inc., USA).
Using the data of the soil moisture sensor and a soil water
potential sensor (TERSO-21, METER Group, Inc., USA),the relationship between water content (v/v) and water
potential of the soil was determined, and then the soil
water potential was calculated.

Photosynthetic rate was measured at 13:00 on September
9 using a photosynthetic rate measurement device(MIC-100, Masa International Co., Ltd., Japan). The
measurement conditions were as follows: PAR 1200μmol/m2/s, stabilization time 3 sec, measurement
started when CO2 concentration was stable at 400 ppm,
and measurement CO2 span was 10 ppm. The stomatal
conductance was measured at 15:00 on September 9 and
SPAD value was measured on September 12 using thesame devices as in the experiment 1. The fourth to sixthleaf from the top was used for these measurements. Plant
height and leaf number were measured on August 21, 28,
September 5, 13, and 24. On September 24, dry weight ofabove-ground part was measured.

Stomatal conductance was measured at 6:00, 9:00,
12:00, 15:00, and 18:00 on July 21 and 23 using a leaf
porometer (SC-1, METER Group, Inc., USA). The
maximum quantum eﬃciency of photosystem II (Fv/Fm)
was measured at 20:00 on the same days, using a portablechlorophyll ﬂuorometer (OS-30P, Opti-Sciences, Inc.,
USA). Relative leaf chlorophyll content (SPAD value)
was also measured using a chlorophyll-meter (SPAD502, Konica Minolta Sensing, Inc., Japan) on the same

Experiment 3
The same buckwheat variety as in the experiment 1 wasused for the experiment 3. On July 6, 2021 the seeds were
subjected to a heat treatment using the same method as
the experiment 1. Replication of each treatment was 7. On
July 9, the seeds, germinated indoors beforehand, were144

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Research article

Statistical analysis

sown in 1/5000-a Wagner pots in the greenhouse at the
Kyoto University (135.8 °E, 35.0 °N). Soil mixed withweathered granite soil and bark compost at a ratio of 1:1
by volume was used. Magnesium lime of 2.5 g and 2 gof chemical fertilizer (N:P:K=8:8:8) were applied per pot.

The data, except for those of stomatal conductance inthe experiment 1 and 3, were analyzed using t-test. The
data of stomatal conductance in the experiment 1 and3 were analyzed by a two-way ANOVA (treatment ×
measurement time). The signiﬁcance level was adjudged
at p < 0.05.

The plant was irrigated appropriately not to be subjected
to a drought stress from July 9 to August 6. From August
7 to 11, all the plants were subjected to a drought stress as
described below. On August 7, 55mL of water was applied
at 12:00. After that no water was applied. Soil watercontent, air temperature, and PAR were measured, andsoil water potential was calculated during the experimentusing the same method as in the experiment 1.

Results
Experiment 1
Until July 21, soil water potential was higher than -6.8
kPa and ranged from -55 to -80 kPa on July 23 (Figure1). Maximum and minimum temperature during themeasuring time were 41 °C and 25 °C on July 21 and 38°C and 23 °C on July 23. Maximum PARs were 1256 and1091 μmol/m2/s on July 21 and 23, respectively.

Photosynthetic rate was measured on August 6 and 11,
from 10:00 to 12:00 using the same device as in theexperiment 2. The measurement conditions were thesame as in the experiment 2. On August 6 and 11, thestomatal conductance was measured at 6:00, 9:00, 12:00,
15:00 and 18:00, and SPAD value was measured using
the same devices as in the experiment 1. On the same days
Fv/Fm was measured at 20:00 using the same device asin the experiment 1. Plant height and leaf number were
measured on August 1, 6, and 11. On August 13, dryweights of above-ground part and root were measured.

Interaction between measurement time and heat treatment
for stomatal conductance on July 21 and 23 was notobserved. On July 21, stomatal conductance under wellirrigated condition was not aﬀected by heat treatment(Figure 2). On July 23, stomatal conductance underdrought stress condition was increased by heat treatment.

Figure 1. Air temperature, PAR and soil water potential on July 21 (A) and 23 (B) in the experiment 1.

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Figure 2. Eﬀect of heat treatment to buckwheat seed on stomatal conductance under well-irrigated (A) and drought stress (B) conditions.
Bars indicate standard errors (n=8).

Fv/Fm and SPAD value on July 21 and 23 were not aﬀectedby heat treatment (Table 1). Heat treatment did not aﬀectplant height during the experiment (Figure 3). On July 24,
leaf number was decreased by heat treatment. Dry weightof above-ground part was not aﬀected by heat treatment.

leaf number during the experiment 2 (Figure 6).
Experiment 3
Until August 6, soil water potential was higher than -1.0
kPa, and that on August 11 ranged from -55 to -75 kPa(Figure 7). On August 6 and 11 temperatures ranged from25 to 35 °C and 21 to 33 °C and maximum PARs were 923
and 648 μmol/m2/s during the measuring time.

Experiment 2
Soil water potential decreased gradually from August 28
to lower than -300 kPa (Figure 4). Increase of soil water
potential to more than -1.0 kPa on September 7 was due
to rainfall from the typhoon that removed the plastic ﬁlmof the greenhouse. Then again, the soil water potential
decreased to lower than -500 kPa. On September 9, during
the measuring time, soil water potential ranged from -65
to -75 kPa, air temperature was about 30 °C and maximum
PAR was 835 μmol/m2/s (Figure 5).

Interaction between measurement time and heat treatment
for stomatal conductance was not observed, and stomatal
conductance was not aﬀected by heat treatment with andwithout drought stress (Figure 8). Photosynthetic rate, Fv/
Fm, and SPAD value were not aﬀected by heat treatment(Table 3). Dry weight of above-ground part, root, and sumof them were not aﬀected by heat treatment. Root/shootratio was not aﬀected by heat treatment. Heat treatment
did not aﬀect plant height and leaf number during theexperiment 3 (Figure 9).

Under drought stress, photosynthetic rate in heat treatment
plant was about 30 % higher than that in control plant,
though stomatal conductance was not aﬀected by heat
treatment (Table 2). SPAD value on September 12 was
not aﬀected by the heat treatment. Dry weight of aboveground part of the plants was not aﬀected by the heat
treatment. Heat treatment did not aﬀect plant height andDiscussion
By heat treatment to seed, stomatal conductance wasincreased in the experiment 1 and photosynthetic rate wasincreased in the experiment 2. Photosynthetic rate also

Table 1. Eﬀects of heat treatment to buckwheat seed on Fv/Fm and SPAD value under irrigated and drought conditions anddry weight of above-ground part
Fv/Fm

SPAD value

Irrigation(July 21)

Drought(July 23)

Irrigation(July 21)

Drought(July 23)

Dry weight ofabove-ground part(g)Control

0.80

0.80

41.2

43.5

41.8

Heat treatment

0.80

.081

40.2

44.8

42.1

ns

ns

ns

ns

ns

NS indicates not signiﬁcant by t=test (n=8).

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Figure 3. Eﬀect of heat treatment to buckwheat seed on plant height (A) and leaf number (B). Bars indicate standard errors (n=8).

Figure 4. Soil water potential during the experiment 2.

Figure 5. Air temperature, PAR, and soil water potential on
September 9 in the experiment 2.
Table 2. Eﬀects of heat treatment to buckwheat seed on photosynthesis rate, stomatal conductance, SPAD value, and dry weightof above-ground part under drought condition
Photosynthetic rate(µmol/m2s)

Stomatal conductance(µmol/m2s)

SPAD value

Dry weight of above
ground part (g)Control

14.7

247.8

40.7

7.1

Heat treatment

19.3

350.9

42.3

7.5

*

ns

ns

ns

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Figure 6. Eﬀect of heat treatment of buckwheat seed on plant height (A) and leaf number (B). Bars indicate standard errors (n=15).

Figure 7. Air temperature, PAR, and spo; water potential on August 6 (A) and 11 (B) in the experiment 3.

Figure 8. Eﬀect of heat treatment to buckwheat seed on stomatal conductance under well-irrigated (A) and drought stress (B) conditions.
Bars indicate standard errors (n=7).

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Table 3. Eﬀects of heat treatment to buckwheat seed under irrigated and drought conditions on photosynthesis rate, Fv/Fm,
SPAD value, , dry weights and Root/Shoot ratio
Photosynthetic rate

Fv/Fm

SPAD value

Irrigation(Aug. 6)

Drought(Aug. 11)

Irrigation(Aug. 6)

Drought(Aug. 11)

Irrigation(Aug. 6)

Drought(Aug. 11)

Control

18.6

13.7

0.83

0.84

39.3

Heat treatment

19.5

15.6

0.83

0.84

39.2

ns

ns

ns

ns

ns

Dry weight (g)
Root

Root/
Shoot
ratio

5.94

1.60

0.27

5.76

1.74

0.31

ns

ns

ns

Sum

Aboveground part

44.7

7.54

46.7

7.50

ns

ns

Figure 9. Eﬀect of heat treatment of buckwheat seed on plant height (A) and leaf number (B). Bars indicate standard errors (n=7).

Under well-irrigated condition, heat treatment did notenhance stomatal conductance and photosynthetic rate.
Therefore, the positive eﬀect of heat treatment might beappeared under drought condition. However, stomatal
conductance and photosynthetic rate were not enhancedby the heat treatment in the experiment 3 even underdrought condition. Stomatal conductance of the control
plant during the day, 12:00 and 15:00, in the experiment
3 was higher than those at the experiment 1 and 2 (300350 mmol/m2/s in the experiment 3, 250 mmol/m2/s
in the experiment 2, and 200-230 mmol/m2/s in theexperiment 1). Thus, drought stress in the experiment 3
might have been lighter, though the soil water potential
in the experiment 3 was as low as those in the experiment
1 and 2. Cloudy weather on the measuring day inexperiment 3 might lessened the drought stress eﬀect on
the plant. Therefore, under severe drought stress, withlower stomatal conductance than 250 mmol/m2/s, heat
treatment might enhanced stomatal conductance andphotosynthetic rate.

might have increased in the experiment 1, due to highstomatal conductance, though we did not measure the rate.
Thus, buckwheat plants grown with heat stressed seeds
might have kept open its stomata and maintained highphotosynthetic rate even under drought condition. Sowing
immediately after burning, which has been practiced in
shifting cultivation in Kyushu mountains, may have theeﬀect of keeping growth even under drought condition,
while in the experiment 2 under long-term drought stress
buckwheat growth with heat treatment tended to be
increased though the diﬀerence was not signiﬁcant. The
reason for such increased of buckwheat growth underdrought condition could be due to cross-protection;
exposure of plants to moderate stress induces resistanceto other stress (Sabehat et al. 1998). Heat stress induced
tolerance to abiotic stresses, such as drought, salinity, andchilling stress with accumulation of heat-shock proteins,and changing in the synthesis of plant hormones andsignaling molecules (Hossain et al. 2018). In the present
study buckwheat also might have acquired drought stress
tolerance induced by cross-protection with heat stress.
Drought tolerance induced by cross-protection withsowing immediately after burning practiced in shifting
cultivation was not reported earlier, though there aremany reports about the beneﬁt of cross-protection on plant
growth (Sabehat et al. 1998, Hossain et al. 2018).

In conclusion, heat treatment to seed improved droughttolerance due to cross-protection. The unique methodsof shifting cultivation at Kyushu mountains, i.e. sowing
immediately after burning, might be eﬀective to enhancebuckwheat growth.
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