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Nutritive evaluation of some Acacia tree leaves

from Kenya

S.A. Abdulrazak

a,b,*

, T. Fujihara

a

, J.K. Ondiek

b

, E.R. érskov

c aLaboratory of Animal Science, Shimane University, Matsue-shi-690-8504, Shimane, Japan

bDepartment of Animal Science, Egerton University, P.O. Box 536, Njoro, Kenya cRowett Research Institute, Bucksburn Road, Aberdeen AB2 9SB, Scotland, UK

Received 16 August 1999; received in revised form 6 December 1999; accepted 3 March 2000

Abstract

A study was conducted to evaluate the nutritive potential value of six species of acacia tree leaves: Acacia brevispica, nubica, tortilis, seyal, nilotica, and mellifera from Kenya. A wide variability in chemical composition, polyphenolics and gas production and in situ dry matter (DM) degradability was recorded. Crude protein (CP) content ranged from 134 to 213 g/kg DM. The content of neutral detergent ®bre (NDF) and acid detergent ®bre (ADF) ranged from 154 to 308 and from 114 to 251 g/kg DM, respectively, and was signi®cantly (p<0.05) different among the species.

A. nubica had the lowest ®bre, and polyphenolics concentration and the highest potential gas production and DM degradability. Mineral concentrations varied among species. All were relatively poor in phosphorus, moderate in calcium, magnesium and sulphur and rich in most microelements. Iron and selenium ranged from 132 to 459 and 13 to >100 mg/g (p<0.05), respectively. The rate of gas production was highest inA. nubica(0.1165 hÿ1) and lowest in

A. brevispica(0.0295 hÿ1). A

similar trend was observed with in situ DM degradability. A strong relationship between the cell-wall fraction and gas production after 12, 24, 48, 72 and 96 was established. A weak and negative correlation was recorded between total extractable phenolics (TEPH), total extractable tannins (TET) and total condensed tannins (TCT) with gas production.

The ranking order of the acacia species on the basis of their potential degradability was A. nubica>A. tortilis>A. mellifera>A. brevispica>A. seyal>A. nilotica. It is concluded that based on the moderate to high CP values and the degradation characteristics, these species have potential as livestock fodder.#2000 Elsevier Science B.V. All rights reserved.

Keywords:Acacia; In situ degradability; Gas production; Nutritive value 85 (2000) 89±98

*Corresponding author. Tel.:‡81-852-32-6584; fax:‡81-852-32-6537. E-mail address: abdul@life.shimane-u.ac.jp (S.A. Abdulrazak)

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1. Introduction

The use of browse species as fodder for ruminant is increasingly becoming important in many parts of the tropics. Generally, tree fodder is richer in crude protein (CP), minerals and digestible nutrients than grasses (Devendra, 1990; Topps, 1992). The use of tree legume fodder as supplement has improved intake, digestibility and animal performance (Norton, 1994; Abdulrazak et al., 1996). In Kenya, there is limited information on the nutritive value of tree shrubs fed to livestock (Abdulrazak, 1995). Moreover, studies on native tree species are limited than those of the introduced tree species like Leucaena, Gliricidia, Calliandra and Sesbania. The recent infestation of Leucaena leucocephalaby the pestHeteropsylla cubana(Reynolds and Bimbuzi, 1993) and the low palatability ofGliricidia sepium(Abdulrazak, 1995)suggests the importance of screening other browses for further use in farming system. Acacia trees dominate in many parts of the arid and semi arid areas of Sub-Saharan Africa, and have multiple uses. They provide food, medicine, fodder aside from being resistant to diseases and the harsh climatic conditions (Le Houerou, 1980). The presence of phenolic compounds in acacia species has a negative affect on their nutritional value and also on their intake by livestock (Degen et al., 1998). Tannins have been attributed to be one of the major causes of their limited use as livestock fodder (Makkar, 1993). Generally, tannins in fodder tree are known to have a negative effect on intake and digestibility (Kumar and D'Mello, 1995). Studies on some acacias have shown them to have either a positive (Ben Salem et al., 1999) or a negative effect (Degen et al., 1998) on animal performance. This variable effect could be attributed to the type of species, season and nutritive value. In vitro gas production (Siaw et al., 1993; Khazaal and érskov, 1994) and in sacco rumen degradability (Kibon and érskov, 1993; Apori et al., 1998) has been used to assess the nutritive value of browse species. These rapid and less expensive methods have been used to screen feed resources before making them available to livestock (Larbi et al., 1998). The objective of this study was to assess the potential nutritive value of some selected species of acacia from Kenya based on their chemical composition, polyphenolic concentration, in vitro gas production and in sacco degradability.

2. Material and methods

2.1. Source of acacia samples

Leaves and petioles from six species of acacias, Acacia brevispica, nubica, tortilis, seyal, nilotica and mellifera were harvested from Chemeron site, Egerton station in Marigat area, Baringo district, Rift valley of Kenya. The area is located at an altitude of 1066 m above sea level. The mean annual rainfall and temperature is 700 mm and 24.08C, respectively. The selection of the tree species was based on herdsmen knowledge of the tree forages preferred by small ruminants. Forages were harvested at the end of rainy season from at least 12 individual trees or shrubs of each species, then pooled and oven-dried at 608C for 48 h before being shipped to Matsue, Japan for later analysis.

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2.2. Chemical analysis

Dry matter (DM), ash and nitrogen (N) content were measured according to (AOAC, 1990). Crude protein (CP) was calculated by multiplying N6.25. Neutral detergent ®bre (NDF), acid detergent ®bre (ADF) and acid detergent lignin (ADL) were determined according to Van Soest et al. (1991). Mineral concentration was determined by digesting samples in HNO3/HClO4and by using inductively coupled plasma spectroscopy (ICP) to

detect the elements Ca, Mg, P, S, Mn, Mo, Zn, Co, Cu and Fe (Varma, 1991). A ¯uorometric detection method using 2,3-diamononaphthalene derivative was used for the determination of Se (Watkinson, 1966).

2.3. Phenolics compounds

The extraction of phenolics was done using 70% aqueous acetone. The tubes containing samples were centrifuged at 48C for 20 min at about 2400 rpm and the supernatant was stored for analysis. Total extractable phenols (TEPH) were determined according to Julkunen-Titto (1985). A 0.05 ml aliquot and various amounts (0±0.1) of a tannic acid (0.5 mg/ml; dissolving 25 mg tannic acid in 50 ml of distilled water) standard solution was made up to 1.0 ml with distilled water. Then, 0.5 ml of Folin Ciocalteu reagent (1 N) was added and all tubes which were subsequently vortexed, followed by addition of 2.5 ml Na2CO3(20%) and vortexing all the tubes again. After 35 min,

the absorbance at 725 nm was read using an UV-1200 Spectrophotometer. The concentration of TEPH was calculated using the regression equation of the standard. Total extractable tannins (TET) were estimated indirectly after being absorbed to insoluble polyvinylypolyrrolidone (PVP). The mixture was then centrifuged at 2400 rpm for 10 min and the supernatant was used to determine the total remaining phenols. Concentration of TET was calculated by subtracting the TEPH remaining after PVP treatment from TEPH. The total condensed tannins (TCT) were measured using the method of Porter et al. (1986).

2.4. In situ degradability study

To determine the in sacco degradation characteristics of the samples, 4 g of dry sample milled through a 2.5 mm screen was weighed in nylon bags (140 mm75 mm, pore size 40±60 um). The bags were incubated in the rumen of three cannulated sheep. The animals were offered timothy hay ad libitum plus 200 g DM of concentrate twice a day at 08.00 and 17.00 h. Animals had free excess to water and mineral/vitamin licks. Nylon bags were withdrawn at 4, 8, 16, 24, 48, 72 and 96 h after insertion. The 0 h measurement was obtained by soaking the two bags of each sample in warm water (378C) for 1 h. The 0 h and incubated bags were then washed with cold water for 15 min in a washing machine and dried for 48 h at 608C. The DM degradation data were ®tted to the exponential equationpˆa‡b(1ÿeÿct

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arepresents zero intercept; ED denotes effective degradability, calculated at an out¯ow rate of 0.05 hÿ1

.

2.5. In vitro gas production

Samples were incubated in vitro with rumen ¯uid in calibrated glass syringes following the procedure of Menke and Steingass (1988). Rumen liquor was obtained from three sheep fed on timothy hay and concentrate. Air-dried and ground (1.0 mm) samples of about 2005 mg were weighed in duplicate into calibrated glass syringes of 100 ml. The piston was then lubricated with pure oil to ease movement and to prevent escape of gas. The syringes were pre-warmed (398C) for 1 h, before the addition of 301.0 ml of rumen-buffer mixture into each syringe. The syringes were incubated in a water bath maintained at 390.18C, and were gently shaken every hour during the ®rst 8 h of incubation. Readings were recorded before incubation (0 h) and 3, 6, 12, 24, 48, 72 and 96 h after incubation. The mean gas volume readings were ®tted to the exponential equationpˆa‡b(1ÿeÿct

) (érskov and McDonald, 1979), wherepis the gas production at timet;a‡bare the potential gas production andcdenotes the rate of gas production.

2.6. Statistical analysis

Analysis of variance (ANOVA) was carried out on chemical composition, phenolics, cell wall parameters, in sacco degradability and in vitro gas production with species as the main factor using a general linear model (GLM) of Statistica for windows (Statistica, 1993). Signi®cance between means was tested using the least signi®cant difference (LSD). A simple correlation analysis was used to establish the relationship between polyphenolics concentration and in vitro gas production and DM degradability.

3. Results and discussion

The chemical composition of the acacia species is presented in Table 1. The CP ranged from 134 to 213 g/kg DM and was lowest inA. seyal. The NDF and ADF content were lowest in A. nubica and highest in A. nilotica. A. seyal had the highest lignin concentration (121 g/kg DM) andA. nubicathe lowest (51 g/kg DM). For all the samples the ADF fraction was a large proportion of the NDF, which indicate high content of cellulose and lignin and low levels of hemicellulose. The nitrogen bound to ®bre varied between 164±335 and 86±250 g/kg N for NDF and ADF, respectively, with lower concentration inA. nubica. The TEPH and TCT concentration ranged between 56±512 and 0.2±28.4 mg/g DM, respectively, and were lowest (p<0.05) inA. nubicaand highest inA. seyal.A. Brevispicahad the lowest TET, which was only different (p<0.05) fromA. seyal. The chemical composition was consistent with what has been reported in other work with acacia (Tanner et al., 1990; Sawe et al., 1998). The proportion of NDF-N and ADF-N was higher in acacia species than inSesbania sesbanandL. leucocephala(Bonsi et al., 1994). But comparable to that inAcacia cyanophylla(Ben Salem et al., 1997). A difference in the ratio of leaf to petioles in edible samples used for analysis could be

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partly responsible. Higher values of cell wall fractions in forage have been attributed to woody twigs included during the analysis (Topps, 1992).

The mineral concentration of acacia species is presented in Table 2. Except for phosphorus there were signi®cant (p<0.05) differences among the species.A. nubicawas exceptionally high in magnesium (4.0 g/kg DM), sulphur (5.3 g/kg DM) and iron (459 mg/kg DM). Selenium concentration varied greatly from 12.5 inA. seyal to more than 100 mg/kg in A. nubica and A. tortilis. Information about minerals in browse species, particularly about microelement is very limited. However, the values obtained in this study were consistent with the wide range of data reported (Topps, 1992; Norton, 1994) and those ofAcacia rigidulaandAcacia farnesiana(Ramirez and Ledezma-Torres, 1997). The high manganese and iron concentration in this study is comparable to some samples ofL. leucocephala(D'Mello and Fraser, 1981), with a concentration of 60 and 407 mg/kg of manganese and iron, respectively. The copper levels in our study were higher than those of acacia pods (Sawe et al., 1998). The use of pods instead of leaves in their study, site and variety difference may have caused the differences (Le Houerou, 1980). Low values of phosphorus were similar to those ofAcacia aneura (Ahn et al., Table 1

Concentration of organic matter (OM), crude protein (CP), neutral detergent ®bre (NDF), acid detergent ®bre (ADF), acid detergent lignin (ADL), hemicellulose (HEM) (g/kg DM); nitrogen bound to NDF (NDF-N) and ADF (ADF-N) (g/kg N); total extractable phenolics (TEPH), total extractable tannins (TET) and condensed tannins (TCT) (mg/g DM) of acacia speciesa

OM CP NDF ADF ADL HEM NDF-N ADF-N TEPH TET TCT

A. brevispica 951 213 c 308 c 210 cd 114 cd 98 d 252 c 89a 59 a 32 a 1.1 a

A. nubica 882 213 c 154 a 114 a 51 a 40 a 164 a 86 a 56 a 39 a 0.2 a

A. tortilis 955 172 b 296 c 251 c 110 cd 45 ab 307 d 250 d 141 a 100 a 28 e

A. seyal 957 134 a 230 b 168 b 121 d 62 bc 189 ab 118 b 512 b 480 b 25 de

A. nilotica 940 172 b 312 c 217 c 99 bc 95 d 206 b 166 c 162 a 109 a 11 b

A. mellifera 930 194 c 269 bc 192 bc 77 b 78 cd 335 d 170 c 104 a 86 a 20 cd S.E.M.b 7.7 8.6 16.8 12.9 7.3 6.9 19.1 17.2 47.3 46.5 3.2

aMeans with different letters within a column are signi®cantly different (p<0.05). bS.E.M.: standard error of the means.

Table 2

Concentration of macro (g/kg DM) and micro (mg/kg DM) elements in acacia speciesa

Ca Mg P S Mn Mo Zn Co Cu Fe Se

A. brevispica 6.8 a 1.9 b 0.9 1.3 a 32 bcd 37 bcd 20 b 4.8 b 63 b 132 a 38.0 ab

A. nubica 11.2 d 4.0 d 0.8 5.3 b 29 bcd 42 bcd 16 a 4.7 b 52 b 459 bc >100 c

A. tortilis 7.9 b 1.4 a 0.8 1.0 a 27 abcd 16 a 13 a 3.1 a 44 ab 198 a >100 c

A. seyal 6.4 a 1.8 b 0.8 1.5 a 37 bcd 39 bcd 21 b 3.2 a 54 b 418 b 12.5 a

A. nilotica 8.9 c 1.7 b 1.3 1.6 a 25 abc 37 bcd 21 b 3.9 ab 66 b 212 a 97 c

A. mellifera 11.3 d 2.3 c 0.9 1.4 a 18 a 36 bc 14 a 3.2 a 28 a 216 ab 50 b S.E.M.b 0.59 0.26 0.07 0.50 2.07 2.62 1.11 0.25 13.34 83.01 10.8

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1989). Similarly, Topps (1992) reported low values of phosphorus for most of the tree legume forages. Calcium is closely related to phosphorus metabolism in the formation of bones and a Ca:P ratio of 2:1 is recommended. The Ca:P ratio in our study ranged from 7.1:1 to 12.6:1. Topps (1992) reported a much higher Ca:P ratio of 21.3:1, and indicated that the tree and shrubs were unlikely to be a well balanced source of minerals. Factors such as soil, climate, stage of maturity and season contribute to variations in the concentration of minerals in forages (Le Houerou, 1980; Topps, 1992; Spears, 1994).

Table 3 presents the gas production data. Signi®cant (p<0.05) differences among the species were recorded in gas production after 12, 24, 48, 72 and 96 h. The highest rate of gas production was recorded with A. nubica (0.1165 hÿ1

) and the lowest with A. brevispica(0.029). The potential gas production (a‡b) ranged between 34.2 and 41.5 ml. The calculated organic matter digestibility from gas production value at 24 h was subsequently highest inA. nubica(640 g/kg DM) and lowest inA. brevispica(480 g/kg DM). The gas production parameters were comparable with those reported for other multipurpose tree forages (Larbi et al., 1998). In their study, the rate of gas production of 18 edible forage samples of trees and shrubs was within a range of 0.0248±0.1256 hÿ1

. Among the acacia samples, the higher gas production rate inA. nubicacould be attributed to a relatively low cell-wall contents and TCT concentration. Apori et al. (1998) reported a higher rate of gas production with Ghanaian leaves containing a relatively low concentration of total condensed tannins.

The dry matter degradation characteristics of acacia species are presented in Table 4. A signi®cant (p<0.05) difference in DM disappearance after 8, 16, 24, 48, 72 and 96 h was recorded. The soluble fraction varied from 146 to 505 g/kg DM. The rate of degradation ranged between 0.021 and 0.1115 hÿ1

. The potential and effective degradability varied signi®cantly (p<0.05) from 642 to 880 g/kg DM and from 324 to 747 g/kg DM, respectively. The rate of degradation forA. mellifera,A. brevispicaandA. nubicaagreed with values reported for other browse species (Abdulrazak et al., 1996; Larbi et al., 1998). Table 3

Gas production (ml/200 mg DM) after 12, 24, 48, 72, 96 h and gas production characteristics in acacia speciesa

12 24 48 72 96 a b c a‡b ‡

S.E.M.d 7.33 6.59 5.39 4.30 4.03 5.23 7.93 0.03473 3.50 0.71 64.2

aMeans with different letters within a column are signi®cantly different (p<0.05);a,b,care constants in the equation

(érskov and McDonald, 1979).

ME: metabolizable energy estimated from equation; ME (MJ/kg DM)ˆ14.78ÿ0.0147 ADF (Menke and Steingass, 1988).

c‡‡

OMD24: organic matter digestibility calculated from the equation; OMD (g/kg DM)ˆ185.3‡9.239 gas production‡0.540 crude protein (Menke and Steingass, 1988).

dS.E.M.: standard error of the means.

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A. tortilis,A. seyalandA. niloticahad a low rate of degradation, consistent with the value of 0.0254 hÿ1

for coppice leaves of Calliandra calothyrus, reported by Salawu et al. (1999). The range in potential degradability is similar to that ofC. calothyrus (Salawu et al., 1999),L. leucocephala(Abdulrazak et al., 1996) and other browse species (Tolera et al., 1997). On the basis of their potential degradability the species could be ranked as A. nubica>A. tortilis>A. mellifera>A. brevispica>A. seyal>A. nilotica. A positive relation between in situ parameters, voluntary feed and digestibility have been reported (Kibon and érskov, 1993) suggesting that the acacia species used in this study, exceptA. seyal andA. niloticahave a good potential for small ruminant feeding in Kenya. However, it is important to note that other factors such as the phenolics concentrations, seasonal variability and agronomic characteristics will contribute to the selection of the browses to be incorporated in the farming system.

Table 5 presents the correlation between the polyphenolics, cell-wall parameters and CP in acacia species. The concentration of TEPH, TET and TCT were strongly correlated. Table 4

In situ rumen dry matter (g/kg) disappearance and degradation characteristics of the acacia speciesa

16 24 48 72 96 A B c(hÿ1) A‡B ED (kˆ0.05

A. brevispica 431 b 497 b 643 b 688 bc 698 b 267 b 455 b 0.0410 b 721 bc 423 b

A. nubica 824 e 846 d 871 d 882 e 880 d 505 e 375 a 0.1115 d 880 e 747 d A. tortilis 301 a 388 a 559 a 644 ab 690 b 146 a 652 c 0.0210 a 795 cd 324 a

A. seyal 393 a 423 ab 554 a 567 a 615 a 274 c 384 a 0.0225 ab 658 ab 396 b

A. nilotica 334 ab 431 ab 530 a 589 a 609 a 225 b 417 a 0.0295 ab 642 a 346 a

A. mellifera 620 d 660 c 752 c 769 d 763 c 381 d 387 a 0.0635 c 768 cd 583 c S.E.M.b 55.9 49.4 37.4 33.4 28.1 34.7 29.6 0.00971 25.3 44.8

aAis the water-soluble fraction,Bthe insoluble but fermentable fraction;cdenotes the degradation rate ofB, A‡Bare the potential degradability, ED represents the effective degradability calculated for an out¯ow rate of 0.05 hÿ1; means with different letters within a column are signi®cantly different (p<0.05).

bS.E.M.: standard error of the means.

Table 5

Correlation coef®cient (r) of the relationship between the concentration of phenolic compounds, crude protein and cell-wall component of the acacia species

Yvariable Correlation coefficient with

TEPH TET CT ADF ADL HEM CP

TEPH 0.97** 0.70**

TET 0.79**

CT

NDF 0.58 0.49 0.42 0.92** 0.92* 0.69** ÿ0.51

ADF 0.67* 0.61 0.67* 0.91** 0.34 ÿ0.65*

ADL 0.42 0.29 0.67 0.51 ÿ0.39

HEM 0.80** 0.80** 0.88** ÿ0.01

CP ÿ0.90** ÿ0.89** ÿ0.71*

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The TEPH and TCT were strongly correlated with hemicellulose and ADF but not with NDF. The CP was negatively related with the cell-wall fractions especially with the ADF and the polyphenolics compounds. The relation between cell-wall parameters and phenolics contrasts with those of Khazaal and érskov (1994) and Tolera et al. (1997), but is comparable to those of Reed (1986) reporting a positive relationship between the insoluble proanthocyanidins and ®bre fraction. Reed (1986) concluded that tannins and other phenolics interfere with the detergent system of analysis.

Concentrations of TEPH, TET, TCT and cell-wall fractions were negatively correlated with gas production data (Table 6). Particularly, NDF and ADF, correlated strongly (p<0.01), with gas production characteristics, ranging fromrˆÿ0.73 (with ADF) at 24 h to rˆÿ0.90 (with NDF) at 96 h. However, a poor relationship was recorded between polyphenolics compounds and the gas production data. These ®ndings were consistent with other studies (Khazaal and érskov, 1994; Tolera et al., 1997; Larbi et al., 1998). Khazaal and érskov (1994) and Tolera et al. (1997) reported a signi®cant correlation between the TCT and the gas production, which contrast our results. Similarly, Larbi et al. (1998) reporting a weak relationship between proanthocyanidins and gas production data of 18 multipurpose trees during the wet and dry season in west Africa. A possible reason could be the differences in nature of tannins between the browse species (Jackson et al., 1996).

The results have shown that the CP content of acacia forages was suf®ciently high to warrant consideration of their use as protein supplement to low quality diets. The potential nutritive value of the acacia species was comparable to other browses and that the species were rich in most minerals. Among the species, Acacia nilotica and Acacia seyal showed less promising potential than the rest. However, more work especially on animal responses, is needed to af®rm the nutritional characteristics reported in this study.

Table 6

Correlation coef®cient (r) of the relationship between the concentration of phenolic compounds, ®bre components and gas production (ml/200mg/DM) from the acacia species after 12, 24, 48, 72 or 96 h incubation

Correlation coefficient with

TEPH TET CT NDF ADF ADL HEM

Gas production after

H12 ÿ0.46 ÿ0.43 ÿ0.37 ÿ0.90** ÿ0.80** ÿ0.79** ÿ0.78**

H24 ÿ0.34 ÿ0.30 ÿ0.27 ÿ0.90** ÿ0.73** ÿ0.76* ÿ0.80*

H48 ÿ0.30 ÿ0.22 ÿ0.11 ÿ0.88** ÿ0.69** ÿ0.79* ÿ0.84*

H72 ÿ0.32 ÿ0.21 ÿ0.15 ÿ0.85** ÿ0.73** ÿ0.84** ÿ0.67*

H96 ÿ0.39 ÿ0.30 ÿ0.26 ÿ0.90** ÿ0.79** ÿ0.85** ÿ0.67* Gas production characteristics

b ÿ0.46 ÿ0.39 ÿ0.41 ÿ0.97** ÿ0.91** ÿ0.92** ÿ0.64*

c ÿ0.40 ÿ0.37 ÿ0.37 ÿ0.91** ÿ0.77** ÿ0.76* ÿ0.75*

a‡b ÿ0.45 ÿ0.33 ÿ0.23 ÿ0.80** ÿ0.76** ÿ0.81** ÿ0.52

*Level of signi®cancep<0.05. **Level of signi®cancep<0.01.

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Acknowledgements

Research grant from International Foundation for Science (IFS), Sweden through IFS grant No. B2728 is gratefully acknowledged. Abdulrazak, S.A. also received the Japan Society for Promotion of Science (JSPS) fellowship.

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