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The Effect of Seasonal Variations, Covariations with Minerals and Forage Value on Itchgrass’ Foliar Silicification from Sudanian Benin

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Silica (SiO 2) in forage grasses has been found in reducing cell-wall digestibility. This study investigates whether: (i) the seasonal variability affects the silica and minerals accumulation and forage values of leaves of R. cochinchinensis and (ii) silica concentration is correlated with minerals and fodder value. In an itchgrass population selected in the W Biosphere Reserve, leaves were collected on 90 marked plants from May to October 2003 and 2004, at 15 days intervals except May, June and October. Some 300 g of fresh blades from the 3 rd most recently expanded leaves were oven dried and analyzed for dry mass, SiO 2, ash, N, Na, Ca, P, K, and Mg. Digestible Nitrogen Matter (DNM) and Fodder Energetic Value (FEV) were calculated using the Demarquilly formula. Apart from SiO 2, ash and forage value, data were log-transformed to restore homoscedasticity before statistical analyses. SiO 2 ranges from 5.69 % to 9.95 %, i.e. varying 1.4 fold between May and October, reaching 1.75 fold at mid-September. SiO 2 is positively related to Ca but negatively to K, P, N, DNM and FEV. The negative correlations suggest that SiO 2 concentration in R. cochinchinensis could be reduced with a significant increase in energy and accumulation of important nutrients such as N, P and K. Therefore, leaf silicification and nutritive value relationship should be conclusive in the case of itchgrass.
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AUTHOR'S PROOF JrnlID 12633 ArtID 9355 Proof#1 - 15/09/2015
UNCORRECTED PROOF
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DOI 10.1007/s12633-015-9355-y
ORIGINAL PAPER
1
The Effect of Seasonal Variations, Covariations
with Minerals and Forage Value on Itchgrass’
Foliar Silicification from Sudanian Benin
2
3
4
Valentin Missiakˆ
o Kindomihou1,2,5 ·Brice Sinsin1·Roland A Y Holou2·
Karimou J-M Ambouta3·Wolf Gruber4·S´
ebastien Adjolohoun5·
Marcel Houinato1·Jacques Herbauts4·Jean Lejoly6·Pierre Meerts4
5
6
7
Received: 23 January 2015 / Accepted: 1 September 20158
© Springer Science+Business Media Dordrecht 20159
Abstract Silica (SiO2)in forage grasses has been found
Q1
10
in reducing cell-wall digestibility. This study investigates11
whether: (i) the seasonal variability affects the silica and12
minerals accumulation and forage values of leaves of R.13
cochinchinensis and (ii) silica concentration is correlated14
with minerals and fodder value. In an Itchgrass population15
selected in the W Biosphere Reserve, leaves were collected16
on 90 marked plants from May to October 2003 and 2004, at17
15 days intervals except May, June and October. Some 300
Q2
18
g of fresh blades from the 3rd most recently expanded leaves19
were oven dried and analyzed for dry mass, SiO2,ash,20
N, Na, Ca, P, K, Mg. Digestible Nitrogen Matter (DNM)
Valentin Missiakˆ
o Kindomihou
kindomihou@gmail.com
1Laboratory of Applied Ecology, Department of Natural
Resources Management, Faculty of Agronomic Sciences
(FSA), University of Abomey-Calavi (UAC), 03 BP 1974,
Cotonou, Benin
2DiasporaEngager, Augusta, GA, USA
3Department of Soil Sciences, Faculty of Agronomy,
University Abdou Moumouni, Niamey, Niger
4Laboratoryof Plant Ecology and Biogeochemistry,
Department of Organisms Biology, Faculty of Sciences, Free
University of Brussels, La Plaine Campus, CP244, Triomphe
Boulevard, 1050 Brussels, Belgium
5Department of Animal Production, FSA, UAC, 01 BP 526,
Cotonou, Benin
6Herbarium and Library of African Botany (BRLU), Free
University of Brussels, Solbosch Campus, CP169, Avenue
F.D. Roosevelt 50, 1050, Brussels, Belgium
and Fodder Energetic Value (FEV) were calculated using 21
Demarquilly formula. Apart from SiO2, Ash and forage 22
value, data were log-transformed to restore homoscedastic- 23
ity before Statistical analyses. SiO2ranges from 5.69 % 24
to 9.95 %, i.e. varying 1.4 fold between May and Octo- 25
ber, reaching 1.75 fold at mid-September. SiO2positively 26
related to Ca but negatively to K, P, N, DNM and FEV. The 27
negative correlations suggest that SiO2concentration in R. 28
cochinchinensis could be reduced with a significant increase 29
in energy and accumulation of important nutrients such as 30
N, P and K. Therefore, leaf silicification and nutritive value 31
relationship should be conclusive in the case of Itchgrass. 32
Keywords Rottboellia cochinchinensis ·Silicification ·33
Minerals ·Seasonal variations ·Forage value ·34
Covariations ·Sudanian Benin 35
1 Introduction 36
Plant silicification has recently received increasing atten- 37
tion, especially where economy is agriculture dependent. 38
Grasses can have high silica content (1–13 %) [1]which,is 39
taken up as monosilicic acid and deposited in the cell walls 40
of leaves, especially on the leaf perimeter [2]. Plant silica 41
content is greatly influenced by soil type, water uptake and 42
grass species. There can be over a 4-fold range in silica con- 43
tent in grass simply due to soil type. Clay soils have much 44
more available soluble silica than other soil types. 45
Silicon plays important roles in plants. Its physiologi- 46
cal benefits included nutrient uptake [3], photosynthesis and 47
solar tracking [4]. The management benefits included alu- 48
minium (Al) tolerance and heavy metal toxicities control 49
[3], diseases and pests’ resistance, and minimising lodging 50
[5]. However, the excess uptake of Si by grasses provides 51
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a higher mechanical resistance to degradation [6]. It also52
affected the quality of plant fibres [6,7]. Silica is mostly53
deposited in organs through high transpiration [8,9].54
Leaf silica deposits may result from evaporation, because55
silica content increases where transpiration is high [10,11].56
Silica (Si) is the largest mineral component of perennial57
grasses. Grasses containing high levels of silica react to58
variation in precipitation.59
Several studies had already showed that fodder species60
differ in silica content and this may affect their palatability61
and digestibility [10,12,13]. Silica may reduce livestock62
preference or palatability for certain plants [14]. Silicon63
may also reduce digestibility of fodder grass species [8] by:64
(i) acting as a varnish on the plant cell wall and reducing65
access to rumen microflora; (ii) complexing trace elements66
like Zn and reducing their availability to rumen microflora;67
or (iii) complexing enzymes that are integrally involved in68
rumen metabolism [12,15]. Other reports indicated that a69
water soluble form of Si inhibits activities of some digestive70
enzymes, but the insoluble form is chemically inert [14].71
Since tropical grass species were found to be highly sili-72
cified [11,16], how to reduce leaf silica concentration to73
improve their palatability, digestibility and nutrient value74
for animal high productivity become questionable. There is75
a wide variation in the constituents of plant species grown76
under various conditions and particularly in the case of pas-77
ture grasses grown on tropical ferric Acrisols. Investigations78
had focused the Itchgrass, an annual grass, which is widely79
dominant in sudano-sahelian savanna [17,18].80
In tropics, the harvesting of straw in the dry season81
replaced the hay and fodder conservation [19]andR.82
cochinchinensis is one of the preferred species [20]. This83
grass species ecology, germination and control management84
strategies are well documented [2124]. Indeed, Itchgrass is85
present in more than 30 warm-climate countries of Africa,86
America, Asia and Oceania. It thrives in moist, perme-87
able heavy-textured soils. Itchgrass as a weed is particularly88
troublesome in crops [25]. This plant species is an erect89
grass of 285 cm high, showing one single axis with reduced90
basal branching, no shelf of tillers and dotted distribution91
of ground cover [16]. Its adventitious roots with lower92
nodes are as stilt. It is very well known and encountered in93
good economy water stations. It grows along roadsides and94
densely in some well-drained stations [26].95
While it is feared by farmers because of its difficult96
control and progress [2730], however, R. cochinchinensis97
largely contribute to grassland biomass production for feed-98
ing herbivores in West African tropical grasslands including99
the northern Benin as its maximum biomass in the studied100
area is 1018 ±678 g DM ha1[16,18]. The species and101
a complex of other grass and broadleaved plants are rou-102
tinely grazed by herbivores [16,31] and its fruits are used
in feeding poultry [32]. At maturity, the stem is robust which 103
decreases its appetite for cattle. It is consumed between May 104
and November [16]. R. cochinchinensis is found to be a 105
useful fodder grass when young and suitable for ensiling. 106
When tall, its stiff hairs cause irritation and unpalatability 107
[33]. Tanzanian farmers rank it third behind Pennisetum pur- 108
pureum and Megathyrsus maximus for growth, milk yield 109
and general animal health. It can be mixed with other 110
grasses to feed cattle, which results in a higher dry matter 111
intake [34]. In Pakistan, Itchgrass was not found nutritive 112
enough for animal requirements and supplementation was 113
recommended [35]. In Samoa, wilting Itchgrass gave better 114
results than hay as dry season forage for goats and resulted 115
in higher voluntary dry matter intake, energy intake, and 116
crude protein digestibility [36]. The species is highly and 117
diversely browsed by ruminants in northern Benin. But, 118
until now, very few data exists on the nutritional aspects at 119
the green stage. Moreover, SiO2accumulates with the plant 120
age and high SiO2concentrations were generally associated 121
with sclerophylly (i.e. a high proportion of vascular tissue 122
and sclerenchyma, and a low specific leaf area (SLA) and 123
relative water content [1]. However, the functional signifi- 124
cance of the differences in SiO2content within the growth 125
period has been still little studied. 126
Variations in SiO2concentrations in relation to other leaf 127
traits were recently analysed in Andropogon gayanus var. 128
bisquamulatus, Elymandra androphila, Hyparrhenia sub- 129
plumosa,Panicum maximum C1and Panicum maximum. As 130
results, silica was correlated negatively with carbon and pos- 131
itively with relative water content, nitrogen, soluble ash and 132
specific leaf area [37]. Furthermore, leaf traits differed with 133
rainfall and species from drier sites showed lower SLA and 134
higher N, as a response to stronger average irradiance in arid 135
habitats [38]. But, there has been no attempt yet now to cor- 136
relate variation in SiO2concentration with variation in the 137
nutritional value of the leaves of grasses. 138
In this work, we investigated: (i) the seasonal variabil- 139
ity in silica and minerals concentrations and forage values 140
of leaves of R. cochinchinensis throughout its growth sea- 141
son; and (ii) leaf silica concentration covariations with other 142
minerals and fodder value. 143
2 Material and Methods 144
2.1 Study Area 145
The study was conducted in the W Biosphere Reserve in 146
Benin (WBR), 1126’-1226’N and 217’-305’E (Fig. 1). 147
It covers 6,102 km2representing 56.32 % of the trans- 148
boundary Biosphere reserve shared by Benin, Niger 149
and Burkina-Faso. There is trade wind from April to
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Fig. 1 The study area in northern Benin
November in south-west direction and Harmattan from150
November to March in north-east direction. This generates151
very low air humidity and environmental dry conditions.152
Minimum temperature decreases by 17 C during the period153
of Harmattan in which the air dryness is the highest and the154
relative humidity is lower than 30 %. Climate is sudanian155
and characterized by a rainy season and a dry season. Rainy156
season occurs from May to October with average annual157
rainfall from 900 to 1100 mm [39]. Monthly mean tempera-158
ture ranges from 25 Cto35C and the relative moisture is159
the highest in August (81 %) while the lowest in February160
(26 %). Relative irradiance averages 2950 hours [39]and161
determines the environmental water balance. Annual ear-162
lier rains provide soil humidification followed by the humid163
period and the period of establishment of the active herba-164
ceous vegetation. At the end of the rainy season, soil still165
remains relatively humid and some herbaceous species may166
still use available water for a maximum growth.167
Agriculture, cattle breeding and hunting are the most168
important socio-economic activities which highly threat the169
landscapes conservation of the WBR [40]. The human den-170
sity is about 18.2 inhabitants/km2and the most dominant
ethnic groups are Batonou (32.6 %), Peul (22.1 %) and 171
Dendi (18.2 %) [41]. The geological substratum rock is 172
composed of quartzite, basilar rock, micaschist, schist, gran- 173
ite, gneiss and sandstone. Mineral, ferruginous and gley 174
soils occur [19]. The main vegetation type encountered was 175
shrubby and grass savannah and dry forest. 176
2.2 Materials and Samplings 177
ARottboellia cochinchinensis pasture was sampled in the 178
protected area at the establishment of the earlier native 179
pasture in 25th march 2003. Plants that are showed good 180
shape were sampled among the species population in the W 181
national Park (235’10”E; 1220’38”N). Leaves were col- 182
lected on various 90 plants sampled among the grassland, 183
i.e. in 90 small plots of 1 m2. Standardized leaves were 184
marked on the same internodes on each plant stem. Blades 185
were collected from the 3rd most recently expanded leaves 186
from May to October at 15 days intervals except May, June 187
and October. The leaves were washed to remove dust and 188
stored in envelopes, sun dried for three days, oven dried 189
for 2 days and used for mineral analyses. Ninety samples 190
were harvested (i.e. 3 plants ×5 months ×2 treatments 191
×3 replicates). Soil and subsoil samples were taken for 192
hydrogen-ion determinations at the time the grass samples 193
were collected. But no analyses were yet made and available 194
for these samples. These collections were repeated from 195
May to October 2004 on the same site. 196
2.3 Measurement of Leaf Traits 197
Sections were cut 6 cm above the ground and weighed. For 198
each plot of 1 m2, fresh material harvested at each date of 199
cuttings has been registered (FM). A sample of about 300 200
g of fresh material has been taken on each plot, weighed in 201
fresh (FM) and in dry (DM) after 48 hours oven dried at 202
65 C. The dry matter content in the sample was calculated 203
by the ratio DM/FM. Harvested dry matter is the product of 204
FM by % DM. 205
Silica (SiO2), nitrogen (N) and soluble ashes (SA) 206
concentrations were analyzed in samples. Nitrogen was 207
analyzed by the Kjeldahl method. Silica was analyzed 208
gravimetrically by dry ashing. Samples were oven-dried 209
for 48 h at 105 C and ground with a mill (Retsch ZM 210
100, Germany). The samples were ashed in crucibles at 211
550 C in a muffle furnace (Lenton LCO4-1.06 Eurotherm 212
2416CG temperature/programmer; multi-program version 213
2416P8, Brussels, Belgium) for about 12 hours. Ashes were 214
weighted (total ashes) and dissolved in hydrochloric acid 215
(36–38 %) on a sand bath at 100 C for 2 h, and filtered 216
with ash-free filters (Schleicher and Sch¨
ull ashless, 5892,90 217
mm diameter). Filters were ignited in the muffle furnace for
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Table 1 Seasonal change in foliar dry matter content, mineral concentrations and nutritional value of Rottboellia cochinchinensis from sudanian
Benin during 2003 and 2004
t1.3
Dates DM SiO2Ash K Mg Ca P N Na Forage DNM
t1.4
(%) (%DM) (%DM) (%DM) (%DM) (%DM) (%DM) (%DM) (ppm) Energy (g kg1DM)
t1.5
(100 kg1DM)
t1.6
End May 20.30 5.69 13.93 3.96 0.28 0.15 0.28 1.42 122.67 98.53 46.70
t1.7
±±±±±±±±±± ± t1.8
2.05a 0.63a 1.51ab 0.50e 0.05b 0.02a 0.04b 0.10d 12.06c 3.41c 4.20d
t1.9
End June 23.60 8.56 15.00 3.09 0.20 0.26 0.32 1.05 130.00 87.75 25.78
t1.10
±±±±±±±±±± ± t1.11
1.70ab 0.10b 2.00b 0.50d 0.05ab 0.03bc 0.02b 0.04abc 13.01c 8.00c 3.00b
t1.12
Middle 27.43 9.35 15.59 2.96 0.44 0.22 0.27 1.02 256.67 72.45 23.73
t1.13
July ±±±±±±±±±± ± t1.14
1.85bc 0.34b 2.18bc 0.25d 0.05c 0.03ab 0.05b 0.06abc 25.17d 3.00b 3.00b
t1.15
End July 29.33 9.06 16.00 2.71 0.26 0.24 0.27 0.96 62.83 50.50 20.33
t1.16
±±±±±±±±±± ± t1.17
1.90cd 0.90b 2.00bc 0.20cd 0.04ab 0.03b 0.06b 0.03ab 7.37a 3.00a 2.14b
t1.18
Middle 30.73 9.15 15.00 2.01 0.22 0.26 0.25 1.19 64.83 65.20 33.63
t1.19
August ±±±±±±±±±± ± t1.20
4.45cd 0.64b 1.20b 0.20ab 0.03ab 0.05b 0.04b 0.11c 6.43a 6.00b 2.03c
t1.21
End 33.47 9.69 15.00 2.34 0.15 0.32 0.32 1.02 75.00 61.20 24.02
t1.22
August ±±±±±±±±±± ± t1.23
1.86de 1.00b 3.00b 0.20bc 0.04a 0.04c 0.03b 0.10abc 7.21ab 9.00b 3.00b
t1.24
Middle 36.07 9.95 13.00 1.36 0.16 0.21 0.25 1.02 53.00 62.50 25.55
t1.25
September ±±±±±±±±±± ± t1.26
3.04e 0.94b 2.00a 0.12a 0.04a 0.02b 0.04b 0.06bc 4.36a 6.00ab 2.01b
t1.27
End 40.40 9.58 15.00 1.41 0.16 0.21 0.24 1.02 92.17 75.17 23.76
t1.28
September ±±±±±±±±±± ± t1.29
1.80f 1.10b 3.00b 0.12a 0.02a 0.03ab 0.03b 0.09abc 5.13b 4.93b 2.00b
t1.30
End 44.27 8.04 12.00 1.56 0.22 0.22 0.15 0.84 117.33 94.13 13.55
t1.31
October ±±±±±±±±±± ± t1.32
1.16f 0.81b 2.00a 0.20a 0.04a 0.03ab 0.02a 0.08a 9.29c 5.95c 1.02a
M±SD (means plus and minus standard deviations); letters corresponded to post hoc groups at 5 % t1.33
12 hours. The residue (i.e. silica) was weighted and soluble
Q3
218
ashes were calculated as (total ashes – silica). Soluble ashes219
and silica concentrations were expressed on an organic mat-220
ter basis as follows: ODM =DM-SiO2(1); %SA =100221
×(TA-SiO2)/ODM (2); %SiO2=100×SiO2/ODM (3);222
DM=dry mass, ODM=Organic Dry Mass; TA =Tota l223
Ashes.224
Ninety samples of blades were analyzed for silica and225
soluble ashes, Na, K, Ca and Mg were analyzed in filtered226
solutions by Inductively Coupled Plasma Atomic Emission227
Spectrometry ICP-AES (Varian Vista MPX). Percentage228
based on dry mass was calculated for each parameter. Fod-229
der value traits i.e. Digestible Nitrogen Matter (DNM)230
and Fodder Energetic value (FEV) were calculated using 231
Demarquilly formula, i.e. DNM =[(%N ×6.25) – 4.5] (4). 232
2.4 Data Analysis 233
Data were examined with Dixon test to detect outliers [42]. 234
Chemical concentrations were compared to standards of 235
Epstein & Bloom [43]. Statistical analyses were performed 236
with STATISTICA 7.1 software (StatSoft Inc. 2005). Most 237
data (except SiO2and SA), were log-transformed before 238
analysis to restore homoscedasticity, i.e. N, P, K, Na, Ca, 239
and Mg. ANOVAs were performed on the whole chemical 240
and nutritional traits (N, P, K, Mg, Na, Ca, FEV, DNM, Ash, 241
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and SiO2). One-way ANOVAs with the date of cutting mim-242
icking the growth period as main factor were performed to243
test differences between date’s treatments. No transforma-244
tion was performed for nutritional traits, i.e. FEV, DNM.245
Relationships between SiO2and the other traits (Ca, Mg, K,246
Na, DNM and FEV) were also assessed by means of Pearson247
correlation coefficients at 5 %. As there are no significant248
differences between the results obtained with materials col-249
lected from the same site in 2003 and 2004, only results250
from 2004 were shown in the present study as no significant251
difference was found among years.252
3Results253
3.1 Dry Mass Production254
The leaf dry mass production ranged from 20.3 to 44.27 %255
depending on the growth season with the highest value at the256
End October and the lowest at the End-May (Table 1). The257
general one way ANOVA showed a significant effect of the258
growing season on the dry mass production (F8,18 =31.37;259
P<0.000001; CV=24.2). The oldest leaves of Rottboellia260
cochinchinensis produced 118 % leaf dry mass more than261
the earliest.262
3.2 Silica Concentration263
The value of the leaves SiO2concentration of Rottboellia264
cochinchinensis ranging other the growing period are given265
in the Table 1. The leaves are rich in SiO2(>0.1 %DM),266
as SiO2concentration ranged from 5.69 % to 9.95 %,267
depending on the growth period. There was a highly sig-268
nificant growth period effect (Table 2). End of May gener-269
ally showed lower values (<6 %), whereas from July to270
September showed much higher values (>8%)(Table1).271
Silica concentration varied 1.4 fold between the earliest and272
the latest growth periods, i.e. End-May and End-October273
respectively, reaching 1.75 fold at the Middle-September274
and there was a strong correlation among the harvest 275
dates during the growth period (Table 2;F
8,18 =8.43; 276
p<0.000095; CV =16.12 %). 277
3.3 Other Leaf Traits 278
As for silica, there was a highly significant season effect 279
in all other R. cochinchinensis leaf traits except for ash 280
(Table 2). This was most large for K, N and Na concentra- 281
tions and for nutritional traits. 282
Table 1of the mineral concentrations of R. cochinchi- 283
nensis during the growth period indicate that these leaves 284
are: (a) rich in Na (>10 ppm DM) and K (>1%DM); 285
(b) poor in Ca (<0.5 %DM) and N (<1.5 %DM); (c) rich 286
in Mg (>0.2 %DM) except leaves that are harvested 287
from the End-August to End-September; (d) rich in P (>288
0.2 %DM) except the leaves that are harvested at the 289
End-October. 290
Compared to other periods, the End-May gener- 291
ally showed higher values of N (1.42±0.10 %DM), K 292
(3.96±0.5 %DM), Mg (0.28±0.10 %DM), FEV (98.53±293
3.41g/100kgDM) and DNM (46.70±4.20 g.kg1DM). End- 294
October showed lower values of ash (12±2 %DM), N 295
(0.84±0.08 %DM), P (0.15±0.02 %), DNM (13.55±1.02 296
g.kg1DM) (Table 1). The leaves at the highest silica value 297
(9.95±0.94 %DM) showed the lowest Na (53±4.36 ppm 298
DM), K (1.36±0.12 %DM) and Mg (0.16±0.04 %DM) in 299
the Middle September. 300
3.4 Silica Concentrations Relationship with Other Traits 301
Table 3shows Pearson coefficients of correlation between 302
silica and the other parameters. Across the whole data 303
set, silica concentrations are correlated positively with Ca 304
and dry mass, but negatively with N, K, FEV and DNM 305
(Table 3). 306
SiO2negatively correlated respectively with N concen- 307
trations (Fig. 2), K (Fig. 3), FEV (Fig. 4) and DNM (Fig. 5). 308
The general negative trend is due to the leaves which were 309
Table 2 One way ANOVA of the effect of the growth season on mineral and forage value traits of Rottboellia cochinchinensis;F
8,18 value and
significance at 5 % threshold
t2.1
t2.2
t2.3 Source of df DM SiO2Ash K Mg Ca P N Na Energy DNM
t2.4 variation
t2.5 Growth season 8, 18 31.37 8.43 1.05 28.01 14.38 6.39 5.12 12.23 87.74 23.41 37.18
t2.6 Probability – 1069.5 1050.43 1062. 1065.5 1040.002 7. 106106106106
t2.7 Significance ***** **** ns ***** **** *** ** **** ***** ***** *****
t2.8 CV 24.18 16.12 15.10 37.09 40.03 22.33 22.34 15.79 56.52 22.11 34.81
CV: coefficient of variation; CV=SD/Means; **:p<0.01; ***: P<0.001; ****: P<0.0001; *****: P<0.00001; ns: non-significant
t2.9
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Table 3 Covariations Q4
between Minerals and forage value of leaves of Rottboellia cochinchinensis
t3.1
t3.2 DM SiO2Ash K Mg Ca P N Na FE NDM
t3.3 DM 1
t3.4 SiO20.45 1
t3.5 *
t3.6 Ash 0.30 0.32 1
t3.7 ns ns
t3.8 K0.86 0.57 0.26 1
t3.9 *** ** ns
t3.10 Mg 39 0.15 0.16 0.43 1
t3.11 *ns ns *
t3.12 Ca 0.17 0.38 0.06 0.18 0.34 1
t3.13 ns *ns ns ns
t3.14 P0.68 0.07 0.44 0.44 0.03 0.14 1
t3.15 *** ns **ns ns
t3.16 N0.63 0.50 0.04 0.58 0.14 0.25 0.26 1
t3.17 *** ** ns ** ns ns ns
t3.18 Na 0.28 0.15 0.07 0.42 0.80 0.19 0.02 0.03 1
t3.19 ns ns ns * *** ns ns ns
t3.20 FE -0.12 0.69 0.24 0.32 0.11 045 0.26 0.22 0.37 1
t3.21 ns *** ns ns ns * ns ns ns
t3.22 NDM 0.69 0.55 0.14 0.56 0.09 039 0.34 0.88 0.01 0.28 1
t3.23 *** ** ns ** ns *ns *** ns ns
Data in bold: Significant correlation i.e. Coefficient of correlation and probability of significance
t3.24
harvested in September and August and showed the highest310
SiO2concentration (>9.5 %) with the lower N (<1.30 %),311
K(<1.80 %) and FEV (<90/100kg DM), and the opposite312
DM (%)
SiO2
(%DM)
4.5
5.5
6.5
7.5
8.5
9.5
10.5
11.5
16 20 24 28 32 36 40 44 48
Fig. 2 Relationships between foliar concentrations in SiO2 (%DM)
and Dry mass (%); Where R =0.45; p <0.05; N =30 (5 months.
×2 treatments ×3 replicates); Symbols: *: end October; :end
September;: middle September; : end August;: middle August; :
end July; : middle July; : end June; O: end May
trend with the leaves from End May which showed lower 313
values of SiO2(<6.5 %) and higher values of N (>1.30 %) 314
and K (>1.8 %). 315
K(%DM)
SiO2
(%DM)
4.5
5.5
6.5
7.5
8.5
9.5
10.5
11.5
1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
Fig. 3 Relationships between foliar concentrations in SiO2 (%DM)
and Potassium concentrations (%DM); Where R =−0.57; p <0.01;
N=30 (5 months. ×2 treatments ×3 replicates); Symbols: *: end
October; : end September; : middle September; : end August; :
middle August; :endJuly;: middle July; : end June; O: end May
AUTHOR'S PROOF JrnlID 12633 ArtID 9355 Proof#1 - 15/09/2015
UNCORRECTED PROOF
Silicon
CA (%DM)
SiO2
(%DM)
4.5
5.5
6.5
7.5
8.5
9.5
10.5
11.5
0.10 0.14 0.18 0.22 0.26 0.30 0.34 0.38
Fig. 4 Relationships between foliar concentrations in SiO2 (%DM)
and Calcium (%DM); Where R =0.38; p <0.05; N =30 (5 months. ×
2 treatments ×3 replicates); Symbols: *: end October; : end Septem-
ber; : middle September; : end August; : middle August; :end
July; : middle July; : end June; O: end May
Figures 2and 4respectively show the positive cor-316
relation between SiO2concentration and dry mass and317
Ca. Generally, the positive trend is mostly due to the leaves318
which are harvested at the End May and show lower val-319
ues for SiO2, dry mass (<21 %), Ca (<0.20 %DM), and320
those which are harvested in August and September with321
highest values (respectively >9.50 %DM, and 0.32 %DM).322
The pattern was not consistent for FEV and DNM. In fact,323
FEV and DNM values in the leaves of R. cochinchinensis324
N (%DM)
SiO2
(%DM)
4.5
5.5
6.5
7.5
8.5
9.5
10.5
11.5
0.7
0.8
0.9
1.0
1.1
1.2
1.4
1.5
1.6
Fig. 5 Relationships between foliar concentrations in SiO2 (%DM)
and Nitrogen (%DM); Where R =−0.50; p <0.05; N =30 (5 months.
×2 treatments ×3 replicates); Symbols: *: end October; :end
September; : middle September; : end August; : middle August;
:endJuly;: middle July; : end June; O: end May
FEV (g kg-1DM)
SiO2
(%DM)
4.5
5.5
6.5
7.5
8.5
9.5
10.5
11.5
40 50 60 70 80 90 100 110
Fig. 6 Relationships between foliar SiO2 (%DM) and Forage ener-
getic value (g kg-1DM); Where R =−0.69; p <0.001; N = 30 (5
months. ×2 treatments ×3 replicates); Symbols: *: end October;
: end September; : middle September; : end August; : middle
August; :endJuly;: middle July; : end June; O: end May
varied significantly within the growth period (Tables 1,2). 325
While, both traits highlighted the highest values at the End- 326
May, FEV showed the highest values at the End October 327
and DNM at the End-May. SiO2showed strong negative 328
correlation with FEV and DNM (Fig. 67). It appeared that 329
the leaves that are harvested at the Middle May generally 330
showed higher values of N (>1.30 %), K (>1.80 %), FEV 331
(>90/100kg DM) and DNM (>40 g.kg1DM). At the 332
End-October, they showed lower values of N (<0.85 %), P 333
DNM (100 g kg-1DM)
SiO2
(%DM)
4.5
5.5
6.5
7.5
8.5
9.5
10.5
11.5
5 1525354555
Fig. 7 Relationships between foliar SiO2 (%DM) and Digestible
Nitrogen Matter (100 g kg-1DM). Where R =−0.55; p <0.01; N =
30 (5 months. ×2 treatments ×3 replicates); Symbols: *: end Octo-
ber; : end September;: middle September; : end August; : middle
August; :endJuly;: middle July; : end June; O: end May
AUTHOR'S PROOF JrnlID 12633 ArtID 9355 Proof#1 - 15/09/2015
UNCORRECTED PROOF
Silicon
(<0.20 %), DNM (<15 g.kg1DM) and higher values of334
dry mass (>40 %), FEV (>90/100kgDM) and Na (>110335
ppm).336
4 Discussion337
4.1 Effect of Season on Foliar Silica Accumulation338
Our results confirm that silica concentration often increases339
with growth season. There have been relatively few tests of340
the response of silica content to phenology. Takahashi &341
Miyake [44] and Sinsin [16] are often found as field demon-342
strating the character of silica increase with the growing343
season. However, among the species they examined only344
Eustachys paspaloides and Andropogon schirensis showed345
enhanced silica accumulation with the growth period. Most346
other authors found lower concentrations of silica in plant347
leaves grown in the season [4547,49].348
We found concentrations depending on phenological349
stage. Phenological stage is well known to influence sil-350
ica accumulation [48]. The higher leaf SiO2content of R.351
cochinchinensisis consistent with the hypothesis that sil-352
ica concentration increases with the plant’ age [10,15]. Our353
study indicates that R. cochinchinensis’ increased its SiO2
354
concentrations from May to September. Increasing SiO2
355
concentration with age has already been reported [4951].356
Our study examines other leaf parameters. Interestingly,357
growing season affected other leaf traits. A recurring pattern358
was the production of leaves with lower nitrogen concen-359
tration. Why silica concentration could increase in those360
leaves?361
It was observed that on the poorer pastures, the plants362
were characterized by their high content of silica [16].363
We have also found the phosphorus and nitrogen contents364
of Itchgrass relatively high, which suggests that this plant365
requires a relatively high fertility level for its successful366
growth. R. cochinchinensis is higher in phosphorus, nitrogen367
and silica than Loxodera ledermannii [52]. These data sug-368
gest that L. ledermannii will tolerate a lower fertility level369
than will Itchgrass. This is consistent with the findings that370
Itchgrass is a weed species for food crops such as maize and371
cassava [2730], which required important investments for372
high productivities in tropics. However, the ash and nitrogen373
contents did not change significantly from May to August.374
But these decreased in Middle-September and End-October375
which should be a good measure of the relative tolerance of376
this plant to various soil fertility levels.377
Higher nutritional quality and lower silica content were378
found as a pattern in grass from heavily grazed sites [53,54].379
Increased silica accumulation might be a protective mecha-380
nism in leaves that would otherwise be palatable. Alterna-381
tively, enhanced silica accumulation might be an inevitable382
response. It is well known that silica accumulation is corre- 383
lated to transpiration [15,55]. Tropical leaves with a high 384
photosynthetic capacity may have higher transpiration rates, 385
thus increasing silica deposition rate. 386
4.2 Silica Correlations with Other Leaf Traits 387
Correlations between the various constituents of the species 388
are given in Table 3. In some cases, the response of other 389
traits is similar to that of silica. However, the results are 390
complex. Globally, there is a highly significant effect of 391
growth period on leaf chemical accumulation (Table 2). 392
SiO2was negatively correlated to K (RSiO2/K=−0.57; 393
P<0.01) and N (RSiO2/N=−0.50; P<0.01). The corre- 394
lation was positive with Ca (RSiO2/Ca =0.38; P<0.05) or 395
not significant with others. There is a high positive correla- 396
tion between K, Mg, P, N and Na. This might be expected 397
in case either of these is limiting factors in plant growth. P 398
and N are in the same family of elements. Generally, pat- 399
tern of foliar SiO2concentration is not clear throughout 400
the growth period. Increased SiO2accumulation during the 401
growth period might also result from interaction with uptake 402
of other minerals. The positive correlation between SiO2403
and Ca suggests that the pattern of R. cochinchinensis foliar 404
SiO2accumulation is identical to that of Ca. This is consis- 405
tent with previous results on tropical grass species [1]. SiO2406
and Ca might be synergistic in these leaves. The more sili- 407
cified leaves (harvested in September) show extreme values 408
for Ca in the season and the lowest N, P, Mg and K. The 409
low silicified leaves (i.e. harvested in May) hold the high- 410
est values of N, K, Mg, P and DNM and FEV early in the 411
season. These elements show strong decreasing concentra- 412
tions throughout the growth period, which might result from 413
mineral dilution in a higher biomass production. 414
Both Ca and SiO2passively accumulated in plant organs 415
having a high transpiration, and little mobile in the phloem. 416
Indeed, SiO2was in synergy with Ca in rice iron-stressed 417
conditions [56]. In contrast SiO2is antagonist to N, P, K, 418
and Mg. Van der Vorm [57] observed that high SiO2con- 419
tent in nutrients solutions exerted suppressive effects on the 420
contents of Ca and Mg in the leaves of rice and sugar- 421
cane. Clarifications are needed in the case of tropical grass 422
silicification. 423
Otherwise, K is necessary for the sap moving [5]. If SiO2424
is accumulated through transpiration stream [58], the plants 425
that are poor in K might show lower SiO2concentration. 426
K might be a functional regulator that reduces plant water 427
loss. We found high K values in leaves harvested in April 428
and August. This may imply that SiO2is either excluded 429
for preferential uptake of K. Indeed, SiO2and K antagonis- 430
tic and synergistic relationships have been documented [56]. 431
Moreover, more silicified leaves i.e. harvested in Septem- 432
ber, show extreme values for Ca and the lowest values in 433
AUTHOR'S PROOF JrnlID 12633 ArtID 9355 Proof#1 - 15/09/2015
UNCORRECTED PROOF
Silicon
N, P and K. The low silicified leaves i.e. harvested in May,434
showed the highest values of N, K, P and DNM early in435
the season. Negative correlation of SiO2with DNM and N436
suggests that silica might reduce the nutritional value of for-437
age. Further studies are needed to analyzing covariations438
between SiO2and structural and organic compounds and439
modeling tropical grass nutritional performances.440
Plant silica generally increased during the growth period,441
as well as Ca. The mechanism of the apparent response is442
not clear. The intensity of transpiratory stream could be an443
important determinant of the silica concentration during the444
growth season.445
Acknowledgments The field research was funded by the446
LEA/FSA/UAC. Laboratory analyses were funded by the447
“D´
epartement des Relations Internationales (DRI-Belgium)” and448
“Agence G´
en´
erale de Coop´
eration et D´
eveloppement de Belgique449
(AGCD-Belgium)” and the Laboratory of Plant Ecology and Biogeo-450
chemistry, Faculty of Sciences, Free University of Brussels, Belgium.451
Houessou Laurent, PhD Agronomy helped in pasture mapping.452
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... • Annual species grown in rainy season wither and die. Their reproduction requires mature seed, whose formation can be hindered by intense plant exploitation [7]. ...
... The most world widely grown are rice, maize, wheat, barley, and sorghum, respectively. Otherwise, about four pseudo-cereals are also worldwide recognized but not yet well scientifically supported: buckwheat (Fagopyrum esculentum, Polygonaceae), quinoa (Chenopodium quinoa, Chenopodiaceae), amaranth (Amaranthus spp., Adapted from [3,[6][7][8][10][11][12][13][14]. Table 1. ...
Article
Full-text available
We examined the effect of grazing exclosures in reducing the concentration of silica, the effect of experimental defoliation on silica accumulation, and the existence of genotypic variability in silica content in plants of Agrostis tenuis. Silica content of plants was higher in heavily grazed areas than within exclosures during the summer, but no significant differences in content were found in winter. Laboratory experiments indicated that there were significant differences among genotypes in their silica content. Some genotypes increased their silica content after clipping at intervals of 14 days but most of them reduced their silica content when clipped weekly. The existence of a significant genotype-clipping treatment interaction term showed that silica accumulation as a response to clipping varied among genotypes, and may provide the basis for microevolutionary changes in natural populations of A. tenuis. However, the possibility of silica acting as a defence was not supported when caterpillars of the graminivorous Lepidoptera, Pararge aegeria, fed on plants. The caterpillars fed more extensively on plants from grazed areas, which had a higher silica content. We conclude that there is some genetic variation in patterns of silica accumulation in plants of A. tenuis and that different grazing histories lead to differences in silica content of plants. Although the effect of silica concentration on large herbivores remains uncertain, herbivores can exert an effect on the silica content of the leaf blades of A. tenuis.
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An understanding of the mineral nutrition of plants is of fundamental importance in both basic and applied plant sciences. The Second Edition of this book retains the aim of the first in presenting the principles of mineral nutrition in the light of current advances. This volume retains the structure of the first edition, being divided into two parts: Nutritional Physiology and Soil-Plant Relationships. In Part I, more emphasis has been placed on root-shoot interactions, stress physiology, water relations, and functions of micronutrients. In view of the worldwide increasing interest in plant-soil interactions, Part II has been considerably altered and extended, particularly on the effects of external and interal factors on root growth and chapter 15 on the root-soil interface. The second edition will be invaluable to both advanced students and researchers.
Article
As part of a study on seasonal variations in the chemical composition of pastures, Sl, AI, Fe, Zn, Cu, and Mn were determined in monthly samplings at 7 sites in the lower North Island. Total element determinations were made by X-ray fluorescence spectrometry on bulked grass, clover, and (at one site only) 'other species' separates of the pasture herbage. Soil contamination was estimated from the Al content of herbage and soil and was checked by Ti analysis of a limited number of samples, and plant analyses for Si, Zn, Cu, and Mn were corrected accordingly. Corrections for Al and Fe were not attempted because of the uncertainties involved. Results for the uncorrected (contaminated) samples showed means and ranges similar to those reported in previous work. Al and Fe levels in grass and clover separates, and Si in clover, showed similar trends closely paralleling estimated soil contamination levels, with maximum levels during the period of lowest dry matter (OM) production in late winter. Uncorrected Si levels in grass were high throughout the year but corrected values showed a tendency to peak in summer. Of the trace elements, Zn showed high levels in ‘other species’ (herbs) at the one site these were sampled, but grass and clover separates gave variable results with no clear seasonal trends. Low values appeared to be associated with sites or periods of high OM production. Cu levels showed even less seasonal variation, but levels in clover were consistently a little higher than in grass. Mn showed the greatest variability, seasonally and between sites. Similar seasonal trends in Mn levels were observed in grass and clover separates, suggesting a soil effect on plant uptake; Mn in grass, but not in clover, was negatively correlated with topsoil pH. In general, the herbage analyses showed no evidence of a deficiency of Zn, Cu, or Mn.
Article
Respected and known worldwide in the field for his research in plant nutrition, Dr. Horst Marschner authored two editions of Mineral Nutrition of Higher Plants. His research greatly advanced the understanding of rhizosphere processes and trace element uptake by plants and he published extensively in a variety of plant nutrition areas. While doing agricultural research in West Africa in 1996, Dr. Marschner contracted malaria and passed away, and until now this legacy title went unrevised. Despite the passage of time, it remains the definitive reference on plant mineral nutrition. Great progress has been made in the understanding of various aspects of plant nutrition and in recent years the view on the mode of action of mineral nutrients in plant metabolism and yield formation has shifted. Nutrients are not only viewed as constituents of plant compounds (constructing material), enzymes and electron transport chains but also as signals regulating plant metabolism via complex signal transduction networks. In these networks, phytohormones also play an important role. Principles of the mode of action of phytohormones and examples of the interaction of hormones and mineral nutrients on source and sink strength and yield formation are discussed in this edition. Phytohormones have a role as chemical messengers (internal signals) to coordinate development and responses to environmental stimuli at the whole plant level. These and many other molecular developments are covered in the long-awaited new edition. Esteemed plant nutrition expert and Horst Marschner's daughter, Dr. Petra Marschner, together with a team of key co-authors who worked with Horst Marschner on his research, now present a thoroughly updated and revised third edition of Marschner's Mineral Nutrition of Higher Plants, maintaining its value for plant nutritionists worldwide. A long-awaited revision of the standard reference on plant mineral nutrition Features full coverage and new discussions of the latest molecular advances Contains additional focus on agro-ecosystems as well as nutrition and quality.
Article
(1) The contents of water, crude protein, cell contents, cell wall, lignocellulose, hemicellulose, cellulose, lignin, silica, ash and nineteen elements, and their variation with season, soil type and grazing intensity, were examined in East African savanna grasses. (2) As the growing season progressed, there was a systematic decline in nutritional value at all sites, as indicated by fibre properties. However, fibre nutritional values were at all times higher in areas of high herbivore use intensity (HUI) than of low HUI. There were few differences in fibre properties between soil types. (3) In contrast, there were marked differences in element contents between samples from different soil types, and relatively less variation in element contents with time and HUI. Much of the between-site variation was due to different plant species compositions. (4) These contrasting patterns of variation resulted in poor correlations between fibre properties and element contents. (5) The data suggest that grazing animals can regulate plant nutritional properties by increasing soil nutrient levels and by changing species composition. Their activities may contribute to the development of localized areas of nutritional sufficiency in the absence of intrinsic soil differences.
Article
Evaluates the hypothesis that silicification of grass parts is a product of herbivore-mediated natural selection and that leaf silicification represents an inducible defense against herbivores, using Agropyron smithii and Schizachyrium scoparium.-from Authors