Yujing Zhu · Guiping Hu · Bo Liu · Xuefang Zheng · Jianfu Zhang · Huaan Xie
Using phospholipid fatty acid technique to analysis the rhizosphere
specific microbial community of seven hybrid rice cultivars
Y. Zhu · G. Hu · B. Liu () · X. Zheng
Agricultural Biological Resource Research Institute, Fujian Academy of Agricultural Sciences, Fuzhou
350003, e-mail: laeptb@163.com
J. Zhang
Rice Research Institute, Fujian Academy of Agricultural Sciences, Fuzhou, 350018
H. Xie
Subcenter of Fuzhou, National Center of Rice Improvement, Fujian Agricultural Academy of Sciences,
Fuzhou, 350018
Abstract To analyze the intrinsic relationship between rhizosphere microbial community structure and
variety of rice, the microbial community structures in rhizosphere of different hybrid rice cultivars
were determined with phospholipid fatty acids (PLFA) analysis. Three series of hybrid rice cultivars in
China
were
tested
in
the
experiment,
IIyouming86
(II-32A/Minghui86),
IIyouhang1hao
(II-32A/Hang1hao) and IIyouhang2hao (II-32A/Hang2hao) with II-32A as female parent, XinyouHK02
(XinA/HK02) and YiyouHK02 (YXA/HK02) with HK02 as male parent, Chuanyou167
(ChuanxiangA/MR167) and 44you167 (Hunan44A/MR167) with MR167 as male parent. The results
showed that 40 PLFA biomarks were detected in all, The PCA of the PLFA composition showed that
the first two principal components PC1 and PC2 account for 69.62% and 17.82% of the variation.
Bacteria PLFAs were more abundant than fungi and actinomycetes PLFAs in paddy soil of the hybrid
rice tested. Both sulfate-reduсing and methane-oxidizing bacteria PLFAs were found to exist in the
hybrid rice rhizosphere. It was observed that microbial biomass revealed as PLFAs amount had positive
correlation with the rice grain number per spike (R2=0.801**), seed setting rate (R2=0.845**) and yield
(R2=0.909**), and had negative correlation with the rice plant height (R2=-0.969**). Based on the
characteristics of PLFAs and the biological traits of rice, the results of cluster analysis suggested that
microbial community structure and activity in rhizosphere were associated with genetic background of
the rice cultivar.
Key words Rice · Rhizosphere Microorganism · Phospholipid Fatty Acid · Diversity
Introduction
The rhizosphere is centered around the root, and is best defined by the biotic response to the
influence of the root. The spatial limits of the rhizosphere are determined by the soil biotic community
under the direct or indirect influence of plant roots. The composition of this biotic community is
dependent on plant species, root architecture, plant carbon allocation, soil physical and chemical
properties, microbial population diversity, among a host of other factors. The productivity of soil
system was known to depend greatly upon the structure and functions of soil microbial communities,
which regulated and influenced many ecosystem processes such as nutrient transformation, litter
decomposition, soil structure and plant health (Garbeva et al. 2004; Wang et al. 2007). Rhizosphere
microorganisms have positive or negative effects on plant growth and morphology by affecting the
plant hormone balance, plant enzymatic activity, nutrient availability and toxicity, and competition
with other plants. Rhizosphere microorganisms have positive or negative effects on plant growth and
morphology by affecting the plant hormone balance, plant enzymatic activity, nutrient availability and
toxicity, and competition with other plants (El-Shatnawi and Makhadmeh 2001).
Soil microbial
biomass was considered to act both as the agent of biochemical changes in soil and a repository of
plant nutrients in agricultural ecosystems (Zhang and Wang 2005; Zhang et al. 2007b).
Rice (Oryza sativa L.) was the largest crop in terms of planted area and yield in China. The
continuing reduction of cultivated land area and the serious lack of water resource during the past three
decades appealed to develop and extend super rice varieties or hybrids with wide adaptation and super
high yielding potential (Chen et al. 2007). Numerous researches had given an account of the
relationship between soil fertility and microbial biomass in rice field ecosystems (Zhang et al. 2007b;
Brookes et al. 2008). Most of the studies on microbial community structure were focused on polluted
soil, soil management practices, nutrient cycling and ecology, and various habitats of irrigated rice
system (Zhang et al. 2007a; Kong et al. 2008). However, there were quite few studies on the soil
microbial biomass of different hybrid rice cultivars. The composition and amount of microorganisms
presented in the rhizospheres of different rice cultivars might differ due to variations in the quantity
and quality of compounds exuded by the different plants. Recent methodological advanced such as
analysis of DNA and the phospholipid fatty acids (PLFAs) as well as cultivation on Biolog
Gram-negative (GN)-plates allowed us to obtain more detailed information on soil microbial activities
and community structure (Zhang et al. 2007b). Polar lipids in soil microbes were primarily
phospholipids. Thus determination of PLFAs could provide a quantitative measurement of microbial
biomass and information on community structure composition of microorganism with specific PLFAs
markers (Mubyana-John et al. 2007). The present study compared the microbial community structures
in rhizosphere of seven hybrid rice cultivars, in which three of them were from a same female parent
and four from two male parents, by measuring their PLFAs compositions. Furthermore, the inherent
correlation between the community structure and the cultivar characteristics were evaluated, such as
the rice growth ability and the genetic relationship. Our findings are helpful to our further
understanding of hybrid rice cultivation and varietal improvement in China.
Material and methods
Field experiment
The trials were conducted at the No.3 field of Rice Experimental Station, Rice Research Institute,
Fujian Academy of Agricultural Sciences, Shaxian, Fujian, China. Shaxian (26°24’N, 117°48’E, 119 m
above sea level) is in the Subtropical Zone and continental monsoon area with the average annual
temperature about 15.6°C-19.6°C and a frost-free period of 270-300 days. The annual precipitation is
about 1,661.9 mm with above 50% in May and June. The field area was 2,001 m2 with 2 m protection
rows around and the experiment was carried out from May to September, 2008. Three series of hybrid
rice cultivars were used in this experiments, IIyouming86 (II-32A/Minghui86), IIyouhang1hao
(II-32A/Hang1hao) and IIyouhang2hao (II-32A/Hang2hao) with II-32A as female parent, XinyouHK02
(XinA/HK02) and YiyouHK02 (YXA/HK02) with HK02 as male parent, Chuanyou167
(ChuanxiangA/MR167) and 44you167 (Hunan44A/MR167) with MR167 as male parent.
The rice seeds were sown on sowing 16th May under dry condition in greenhouse, and the
seedlings were transplanted at 26th June. Plot size was 3.6 m2 with row length of 4 m, plant-to-plant of
13 cm and row-to-row spacing of 30 cm in each plot. The plants were singly cultivated. The
experiment was set up in a randomized block design with three replications. Seven rice cultivars had
total 21 plots. Standard cultivation practices as commonly performed in the area were followed in all
experimental plots. For variety evaluation, early-maturing rice varieties were harvested on 25th
September, while the middle-maturing varieties at 22nd October, late-maturing varieties on 8
November. Ten plants at the center of each plot were selected and the agronomic parameters were
recorded, including grain number per spike, seed setting rate (%), plant height (cm) and paddy yield
(kg/666 m2).
Soil sampling
For PLFAs analysis, sampling was conducted on 27th July at rice booting stage by root-shaking
method. After the plant with root was dug out, the soil combining loose on the root were removed by
shaking. And then the soil tight attached on the root within 0-4 mm was brushed as rhizosphere soil
sample. Five plants were sampled by quincunx-sampling method in each plot. The soil samples of each
plot were mixed and transported by plastic bag to the laboratory at the same day. Each rice cultivar had
three replications. The rhizosphere samples were air-dried at room temperature till the soil moisture
was in the range of 25-30%. Afterwards, the samples were filtered with 2 mm sieve and then
maintained at -80°C until phospholipid extraction.
PLFA analysis
The phospholipid fatty acids extraction procedure employs a mild alkaline methanolysis method
developed by Dr. Rhae Drijber, University of Nebraska, Lincoln, NE (Drijber, 1998, personal
communication). The particular steps were as follow. In the first step, 15 ml of 0.2 M KOH in methanol
were added to a 50-ml Teflon-lined, screw-cap glass centrifuge tube containing 3 g of soil. The
contents of the tubes were mixed and incubated at 37°C for 1 h, during which ester-linked fatty acids
were released and methylated. Samples were vortexed every 10 min during the incubation period. In
the second step, 3 ml of 1.0 M acetic acid were added to neutralize the pH of the tube contents. PLFAs
were partitioned into an organic phase by adding 10 ml of hexane followed by centrifugation at
2000 r min-1 for 15 min. and then the hexane was transferred to a clean glass test tube and
evaporated under a stream of N2. Finally, PLFAs were dissolved in 0.5 ml 1:1 hexane:methyl-tert
butyl ether and transferred to a GC via and kept at 4°C until analysis.
All samples were analyzed on automated Sherlock® Microbial Identification System (MIDI,
Newark, DE, USA). The system is based on GC-FID platform employing HP 6890 Series GC with
equivalent column ULTRA 2 (25 m × 0.2 mm × 0.33 μm) operated under default conditions. The
shorthand nomenclature common in biochemistry and fully supported by the Sherlock® & MIDI
was used for identification of the fatty acids in the form as <number of carbon atoms>:<number of
double bonds> ω <position of double bonds from methyl end of molecule>. Prefixes i, a and cy
are used for iso-, anteiso and cyclopropyl- fatty acids. Hydroxy groups are indicated by ‘OH’.
10Me denotes a methyl group on the 10th carbon from carboxylic end of molecule. Methyl
nonadecanonate (C19:0) was used as the internal standard and the PLFAs were expressed as
equivalent peak responses to the internal standard. The total microbial biomass was expressed as
µg PLFAs g-1 dry weight soil.
PLFAs that correspond to carbon chain lengths of 12-20 carbons are generally associated
with microorganisms. PLFAs used as markers for microorganism were list in Table 1.
Table 1 PLFAs used as markers for microorganism
microorganism
PLFAs maker
reference
bacteria
i15:0, a15:0, 15:0, 16:0, 16:1ω5, 16:1ω9, i17:0,
Hill et al., 2000; Bossio et al., 1998
a17:0, 17:0, 18:1ω7t, 18:1ω5, i19:0, a19:0
Fungal
18:1ω9, 18:2ω6, 18:3ω6, 18:3ω3
Myers et al., 2001; Vestal & White., 1989
Actinomycetic
10Me 17:0, 10Me 18:0
Turpeinen et al., 2004
Gram-positive bacteria
i14:0, i15:0, a15:0, i16:0, i17:0, a17:0
O’Leary and Wilkinson., 1988; Wander et al.,
Gram-negative bacteria
cy17:0,
1995; Zelles et al., 1995; Sundh et al., 1997
cy19:0,
16:1ω9c,
18:1ω9c,
15:1ω4c,
18:1ω7c, 17:1ω9c, 12:0, 14:0, 12:0 2OH, 12:0 3OH
Ratledge and Wilkinson, 1988; Wander et al.,
1995; Zelles et al., 1995; Sundh et al., 1997；han
xuemei 2003
Mycorrhizal
16:1ω5, cis16:1ω5, 18:2ω6, cis18:2ω6, 18:2ω9
Balser et al., 2005; Belen Hinojosa et al., 2005
Sulfate-reducing bacteria
10Me16:0, i17:1ω7, 17:1ω6
Hill et al., 2000
Methane-oxidizing bacteria
16:1ω8c, 16:1ω8t, 16:1ω5c, 18:1ω8c, 18:1ω8t,
Hill et al., 2000
18:1ω6c
Protozoa
20:2ω6,9,c, 20:3ω6,9,12c, 20:4ω6,9,12,15c
White et al., 1996
Statistical analysis
All the statistical analysis was performed using software SPSS version 17, Chicago, Ill. Analysis of
variance (ANOVA) was performed by using Fisher’s least significant difference comparison of means
(LSD). Principal component analysis (PCA) were completed using the content of individual fatty acid
methyl esters. The cluster analysis was carried out by using the seven rice cultivars as samples, the
detected fatty acids as indexes. The correlation analysis was completed using the PLFAs’ content and
the plant characteristics (grain number per spike, seed setting rate, paddy yield and plant height) of rice.
Results
The biological characteristics of seven hybrid rice cultivars
The field experiment showed that Seed setting rate of IIyou series was higher significantly than that of HK02
series, the lowest seed setting rate was you167 series. The quality of Grain number per spike and yield was the
same as seed setting rate. Howerer, the plant height of you167 series was highest, and than was than of HK02
series , the shortest was than of IIyou series.
Table 1 The biological characteristics of seven hybrid rice cultivars
Biological characteristics
Hybrid rice
Grain number per spike
133.17cd
Seed setting rate
79.96bc
Yield
533.39a
Plant height
123a
IIyouhang1hao
141.03bcd
75.23c
526.72a
125a
IIyouhang2hao
163.14abc
72.72c
520.17a
122a
XinyouHK02
128.22d
70.48c
516.55a
130a
YiyouHK02
125.50d
72.71c
504.30a
125a
Chuanyou167
172.78ab
92.70ab
573.96a
112a
44you167
180.71a
94.88a
596.56a
110a
IIyouming86
*The data in the table represented means, different letters in a column indicated significant difference among rice cultivars（LSD，
P<0.05）
PLFAs detected in rhizosphere of the hybrid rice
The rhizosphere of each hybrid rice cultivar contained various PLFAs composed of saturated,
unsaturated, methyl-branched and cyclopropane fatty acids (Table 2). Forty PLFAs with chain lengths
ranging from C12 to C20 were identified, including the PLFA biomarks of i14:0, a14:0, 15:0 2OH,
15:0 3OH, i15:0 and a15:0 indicative of aerobic bacteria, i17:0, and a17:0 indicative of G+ bacteria,
i15:0 3OH, 16:1ω9с, 16:1 ISO G, i16:0, a16:0, 17:1ω8с, i17:0 3OH, сy17:0, i18:0 and i18:1 H
indicative of G- bacteria, 10Me17:0 indicative of actinomycetes, 18:1ω9с and 18:3ω6с(6,9,12)
indicative of fungi and 20:4ω6,9,12,15с indicative of protozoa. Twenty-six PLFAs existed in all the
rice soil samples such as 14:0, i14:0 and 10Me17:0, whereas the other 14 PLFAs presented only in part
of the samples such as 14:1 ω5с, 15:0 2OH and i15:0 3OH. Therefore, there are two types of
distributing patterns were found for the PLFAs detected in the rice rhizosphere, namely, complete
distribution and incomplete distribution.
Table 2
PLFAs*
12:0
14:0
14:1ω5с
i14:0
a14:0
15:0 2OH
15:0 3OH
15:1 ISO G
i15:0
PLFAs detected in rhizosphere of seven hybrid rice cultivars
Contents of PLFAs in rhizosphere of hybrid rice (µg g-1)
Ⅱyouming86
34.10c
82.80c
0.00c
31.63c
30.25c
25.65a
57.46b
211.03a
241.94ba
Ⅱyouhang1hao
46.83b
100.18bc
0.00c
42.36bc
60.77b
0.00b
61.91b
29.80c
298.14a
Ⅱyouhang2hao
54.02b
121.68b
0.00c
54.15b
59.99b
0.00b
71.35b
32.05c
306.80a
XinyouHK02 YiyouHK02
26.71c
35.39c
96.37bc
116.04b
26.77b
0.00c
40.33bc
46.40bc
59.60b
67.85b
0.00b
0.00b
51.70b
0.00c
32.45c
38.95c
236.47c
302.35a
Chuanyou167
46.82b
107.82bc
0.00c
46.03bc
49.27bc
0.00b
48.48b
0.00d
282.18ab
44you167
119.67a
412.03a
90.39a
153.74a
274.40a
0.00b
355.54a
110.44b
0.00d
PLFAs*
i15:0 3OH
a15:0
16:0
16:0 N ALCOHOL
i16:0
a16:0
10Me16:0
16:1ω5с
16:1ω9с
16:1 2OH
16:1 ISO G
17:0
i17:0
i17:0 3OH
a17:0
17:1ω8с
cy17:0
10Me 17:0
18:0
18:1ω5с
18:1ω7с
18:1ω9с
18:3ω6с(6,9,12)
i18:0
i18:1 H
10Me18:0
11Me 18:1ω7с
cy19:0ω8с
20:0
20:1ω9с
20:4ω6,9,12,15с
Contents of PLFAs in rhizosphere of hybrid rice (µg g-1)
Ⅱyouming86
0.00b
153.50c
830.64b
42.52e
142.42b
309.14b
232.16b
149.62bc
30.71cd
61.76d
0.00c
43.26d
104.03b
0.00b
95.26c
139.04b
55.09bc
42.75c
179.34c
0.00c
559.92a
482.63c
81.55cd
0.00c
0.00b
141.08c
244.74a
221.33c
98.54cd
0.00b
85.39bc
Ⅱyouhang1hao
0.00b
215.53bc
967.73ab
61.10de
186.12b
104.83cd
251.58b
188.65b
36.27bcd
138.35b
0.00c
89.06b
122.68b
0.00b
130.30bc
36.71d
60.93bc
60.32b
221.75bc
0.00c
271.94cd
551.77b
92.88bcd
0.00c
0.00b
143.08bc
40.82cd
274.94c
114.26bc
34.12a
93.13b
Ⅱyouhang2hao
0.00b
212.20bc
1088.41a
129.53b
180.65b
95.03cd
286.98b
148.98bc
43.19bc
64.08d
38.37b
56.95cd
118.47b
0.00b
126.98bc
58.40c
74.38b
50.87bc
262.93b
0.00c
352.76b
673.05a
118.57b
0.00c
0.00b
187.88b
48.40c
248.08c
130.58b
0.00b
77.28bcd
XinyouHK02 YiyouHK02
0.00b
0.00b
190.77bc
248.69b
815.26b
336.72c
90.70c
81.51cd
143.66b
187.41b
98.43cd
143.21c
182.18b
243.29b
158.71bc
130.23c
27.14d
44.32b
37.85e
50.36de
0.00c
54.98a
44.70d
65.60c
86.03b
122.39b
0.00b
0.00b
114.34c
182.30b
30.51d
46.07cd
46.76c
69.00bc
38.38c
53.85bc
164.43c
220.81bc
0.00c
0.00c
228.82d
296.56bc
444.78c
457.36c
73.11d
112.69bc
0.00c
36.69b
0.00b
0.00b
97.52c
141.94bc
28.97d
51.77c
182.55c
238.23c
74.53d
75.54d
0.00b
0.00b
68.50cd
64.69d
Chuanyou167
0.00b
199.55bc
917.53b
90.10c
164.40b
86.74d
214.24b
138.46bc
41.02bc
90.88c
37.46b
74.09bc
103.69b
0.00b
115.08c
41.06cd
60.79bc
46.08bc
201.51bc
2465.77a
297.92bc
540.40b
109.04bc
29.44b
0.00b
112.08c
40.99cd
825.61b
90.70cd
0.00b
60.99d
44you167
166.18a
1043.14a
968.33ab
258.34a
782.76a
634.49a
1108.86a
660.11a
174.85a
260.83a
0.00c
243.56a
584.31a
161.92a
857.78a
214.20a
324.02a
236.09a
875.16a
1149.82b
0.00e
0.00d
420.61a
111.90a
106.65a
604.80a
116.44b
1062.93a
304.19a
0.00b
186.26a
*The data in the table represented means, different letters in a row indicated significant difference among soils of rice cultivars（LSD，
P<0.05）
Soil microbial community structure
The PCA of the PLFAs composition (Fig. 1) showed that the first two principal components PC1 and
PC2 account for 69.62% and 17.82% of the variation, respectively. PLFAs 16:0, 18:1ω7с, 18:1ω9с and
10Me16:0 were positively correlated with PC1. PLFAs a15:0, i16:0, a16:0, i17:0 3OH, i18:0 and i18:1
H were highly negatively correlated with PC1. PLFAs 15:0 2OH, i15:0 3OH, i17:0 3OH, i18:0 and
i18:1 H were highly positively correlated with PC2. PLFAs 12:0, 14:1ω5с, 15:0 2OH, i15:0, 16:1 ISO
G and 20:1ω9с were highly negatively correlated with PC2.
On the other hand , The microbial community structure expressed as the relative abundance of bacteria,
fungi and actinomycetes by PLFAs proportion is presented in Fig. 2. The results showed that PLFAs of
the three main kinds of microbe varied among different hybrid rice cultivars plots. In general, bacteria
were most predominant followed by fungi and actinomycetes as the second and third abundant
microorganism in the rice rhizosphere. Moreover, the sulfate-reduсing bacteria and methane-oxidizing
bacteria in rhizosphere of different rice cultivars were compared with 10Me16:0 and 16:1ω5с as
indicators respectively (Fig. 3). The sulfate reducers were more plentiful than methabitriphs in all the
treatments. The rhizosphere of MR167 series rice contained higher amounts of both of sulfate-reducing
and methane-oxidizing bacteria than HK02 and MR167 series.
Fig.1 Principal component analysis of individual PLFA
Fig.2
The microbial community structure in rhizosphere of seven hybrid rice cultivars by using 16:0,
18:1ω9с and 10Me l7:0 as measures of biomasses for bacteria, fungi and actinomycetes, respectively.
Fig.3 The specific microbe in rhizosphere of seven hybrid rice cultivars by using 10Me 16:0 and 16:1ω5с as
measures of biomasses for sulfate-reduсing bacteria and methane-oxidizing bacteria, respectively. Bar S represents
sulfate-reduсing bacteria and Bar M represents methane-oxidizing bacteria.
Relationship between soil microbial biomass and biological characteristics of rice cultivar
The statistic analysis showed that the seven tested hybrid rice cultivars could be clustered into two
groups at 3.68 of Lance-William distance (Fig. 4). The first group consisted of two subgroups: one
subgroup included the two rice cultivars of HK-02 series with characteristics of lowest PLFAs
biomasses (>5000 µg g-1), grain number per spike (<130), seed setting rate (<72.72%) and yields
(<520.00 kg) as well as highest plant height (>125 cm), and the other subgroups comprised the three
rice cultivars of II-32 series with characteristics of middle values of the PLFAs biomasses and the
biological characteristics mentioned above. The hybrid rice Chuanyou167 and 44you167 were involved
in the second group with characteristics of highest PLFAs biomasses (>7000 µg g-1), grain umber per
spike (>172), seed setting rate (>92%) and yields (>573 kg/666 m2) as well as lowest plant height
(<112 cm).
On the other hand, the amount of PLFAs biomasses in the rhizosphere of hybrid rice had positive
correlation with the rice grain number per spike (R2=0.801**), seed setting rate (R2=0.845**) and yield
(R2=0.909**), and had negative correlation with the rice plant height (R2=-0.969**). For example,
XinyouHK02 had grain number per spike, seed setting rate, yield and plant height as 128.22, 70.48%,
516.55 kg and 130 cm, while 44you167 had 180.71, 94.70%, 573.96 kg and 112 cm for the same
biological characteristics, respectively (Table 1).
Lance-William distance
Fig.4
Cluster analysis of seven hybrid rice cultivars by using unweighted pair-group mean average (UPGMA)
method
Discussion
Microbial communities include viruses, eubacteria, archaebacteria, fungi, protozoa, micrometazoa, and
algae (Vestal and White 1989). In nature, microbial communities play an important role in the
biosphere, primarily in recycling biologically important elements (Wieland et al. 2001). The use of
PLFAs analysis to assess microbial community composition has been used in rhizosphere, clinical
sediments and biofouling studies (Mubyana-John et al. 2007; Peng et al. 2007). Structure of bacterial
community inhabiting rice roots and the rhizosphere was highly heterogeneous (Lu et al 2006). We
found that the microbial community in rhizosphere of hybrid rice comprised bacteria, fungi,
antinomycetes and protozoa according to the 40 PLFA biomarks detected.
It is well known that soil microorganisms that colonize the rhizosphere assist plants in the uptake of
several vital nutrients, such as phosphorous, potassium and nitrogen, from the soil (Cocking 2003;
Ikeda et al. 2006). The rice field is a unique agro-ecosystem, where the field is maintained under
flooded conditions during most of the period of rice cultivation, and is left under drained conditions
during the off-crop season. The microorganisms were mainly anaerobic bacteria, such as
Sulfate-reducing bacteria. Owing to leakage of O2 and organic substances from roots, the rice roots and
the rhizosphere provide niches for diverse organisms performing various biogeochemical processes
(Peng et al. 2007). Kimura and Asakawa (2006) reported that rice soils were characterized by the
predominance of actinomycetes and Gram-positive bacteria in comparison with other habitats in central
Japan. Both fungi and actinomycetes played a major role in decomposition of organic residues high in
cellulose and lignin (Mubyana-John et al. 2007).
Despite their small volume, soil microorganisms were key players in the global cycling of organic
matter, reworking organic residues or mineralizing them to CO2, H2O, nitrogen, phosphorus, sulfur, and
other nutrients (Wieland et al. 2001). Lu et al. (2006) studied the structure and activity of bacterial
community inhabiting rice roots and the rhizosphere and suggested that cycling of iron and sulfur is
active in the rhizosphere. Gram-positive sulfate reducing bacteria have been reported as an important
group in rice field soil (Stubner and Meuser, 2000). Rice plants that were grown in flooded rice soil
microcosms were examined for their ability to exhibit sulfate reducing activity and Washed excised rice
roots showed sulfate reduction potential when incubated in anaerobic medium indicating the presence
of sulfate-reducing bacteria (Wind et al 1999). In rice field bulk and rhizosphere soil, the
Desulfobacteraceae were the predominant main group (Stephan 2004). We also found both
sulfate-reduсing bacteria and methane-oxidizing bacteria existed plentifully in the hybrid rice
rhizosphere.
High microbial biomass is generally considered beneficial to agricultural soils. Determination of
PLFAs can provide a quantitative measurement of microbial biomass. By using PLFAs technology, it
has been found that soil nutrient deficiency and unbalanced fertilization to rice crop had negative effect
on the diversity of the microbial community and total microbial biomass in the soil, which
consequently affected plant growth (Zhang and Wang 2005). Although the same fertilization process
was applied in all the treatments, the hybrid rice cultivars of MR167 series with higher rhizosphere
microbial biomass produced more rice yield than the II-32 and HK02 series. The results demonstrated
that the diversity and activity of microbial communities in the rhizosphere of irrigated rice soils
influence the soil fertility and nutrient use efficiency.
Bacterial communities in root-associated habitats responded with respect to density, composition and
activity to the abundance and great diversity of organic root exudates, eventually yielding plant
species-specific microfloras. Erika et al (2008) found Plant growth promoting rhizobacteria improve
growth and essential oil yield on biomass, and qualitative and quantitative composition of soil in
Origanum majorana L. Arab et al. (2001) used PLFAs method to determine the rhizosphere specific
microbial communities of two wheat cultivars, and the results notified the rhizosphere wheat cultivar
Bohouth-6 involved larger amount of Pseudomons spp. than cultivar Salamouni. Plant characteristics are
known to alter endophytic and rhizosphere microbial communities (Siciliano et al 1998).
Germida and
Siciliano (2004) found rhizosphere microbial communities associated with roots of various spring
wheat (Triticum spp.) cultivars of related lineage. Significant differences were also found between the
seven hybrid rice cultivars tested. Based on the characteristics of PLFAs biomarks and the biological
traits, the rice cultivars could be divided into there groups by cluster analysis, in accordance with their
parent origin. It might be presumed that the microbial community also reflected the genetic background
of hybrid rice, which provided useful information in the cultivation of the super rice. Maria et al (2005)
discovered the population dynamics, genotypic diversity and activity of naturally-occurring
2,4-diacetylphloroglucinol (DAPG)-producing Pseudomonas spp. of four plant species (wheat, sugar
beet, potato, lily) were different. Plant-growth-promoting rhizobacteria and kinetin as ways to promote
corn growth and yield in a short-growing-season area( Pan et al 1999). These PGPR were benefit for
agriculture production and largely applied
Rhizosphere bacteria influence plant growth through several mechanisms that Major beneficial
activities of soil bacteria include solubilization of minerals, fixation of nitrogen, production of
growth-promoting hormones and competitive suppression of pathogens (Gaskins et al 1985).
rhizobacterias of crops were required to create and develop beneficial microoganisicm communities for
creating yield enhancing associations with crops ( Sturz and Nowak 2000). Inhibition of root cell
energy metabolism is suggested to be responsible for potato yield reductions in short potato-rotation
soils.( Albert and Bob 1987)
Acknowledgements The present investigation was supported by the National High Technology
Research and Development Program ("863" Program) of China (2006AA100101 and 2006AA10A211).
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