全 文 ：Effect of Mirabilis jalapa (Linn.) Growth on
Microbial Community in Bioremediation of
Petroleum-contaminated Saline-alkali Soil
Yu CEN1,2, Yujie LI3, Haihua JIAO2, Xiaohui WANG1*, Zhihui BAI2*
1. School of Environmental Science and Engineering, Hebei University of Science and Technology, Shijiazhuang 050018, China;
2. Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China;
3. Environmental Protection Bureau of Shijiazhuang City, Shijiazhuang 050021, China
Supported by Strategic Priority Research Program of the Chinese Academy of
Sciences (XDB15010404); National High Technology Research and Development
Program of China (863 program) (2013AA06A205); National Key Technology R&D
Program of China (2014 BAD14B01).
*Corresponding author. E-mail: zhbai@rcees.ac.cn; www_xxx_hhh@sina.com
Received: November 26, 2015 Accepted: March 19, 2016A
Agricultural Science & Technology, 2016, 17(5): 1223-1230
Copyright訫 2016, Information Institute of HAAS. All rights reserved Resources and Environment
S oil microorganisms are oftenlikened to the convertor of soilnutrient cycling, purifier of pol-
lutants and regulator of the stability of
ecological system, and play an impor-
tant role in sustaining the stability of
ecological system, and restoring and
reconstructing the damaged ecological
system. It was reported that there
were more than 70 genera, including
more than 200 species of microorgan-
isms capable of degrading hydrocar-
bon pollutants[1]. In addition, there were
many studies [2, 3] indicating that the gr-
owth of plants could increase the den-
sity of rhizosphere soil microorgan-
isms, resulting in enhanced degrada-
tion effect of microorganisms on pollu-
tants, and the microbial community
structure in rhizosphere soil and its
degradation function were influenced
by the type of corresponding plant.
Mirabilis jalapa Linn. in Mirabilis
Linn. of Nyctaginaceae is an annual
herbaceous plant [4]. It has good eco-
logical adaptability, fast growth and
stronger tolerance to bad environ -
ments, for instance, good chlorine
Abstract Microbial biomass and species in the rhizosphere soil of Mirabilis jalapa
(Linn.) (the saline-alkali soil contaminated by total petroleum hydrocarbon (TPH))
were studied with the technology of phospholipid fatty acids (PLFAs) analysis, to ex-
plore the effects of Mirabilis jalapa (Linn.) growth on the structure characteristics of
microbial communities and degradation of TPH in the petroleum-contaminated saline-
alkali soil. The result showed that compared with the CK soil without Mirabilis jalapa
(Linn.), the kind change rates of PLFAs were 71.4%, 69.2% and 33.3% in spring,
summer and autumn, respectively, and the degradation of TPH increased by 47.6%,
28.3%, and 18.9% in the rhizosphere soil in spring, summer and autumn, respec-
tively. Correlation analysis was used to determine the correlation between the
degradation of TPH and the soil microbial communities: 77.8% of the microbial
PLFAs showed positive correlation (the correlation coefficient r﹥0) with the degra-
dation of TPH, and 55.6% of the PLFAs had high positive correlation with the
degradation of TPH with a correlation coefficient r≥0.8. In addition, the relative
contents of SAT and MONO had high correlation with the degradation of TPH in
the CK soil, and the correlation coefficients were 0.92 and 0.60, respectively; but in
the rhizosphere soil, 42.1% of the PLFAs had positive correlation with it, and only
21.1% had high positive correlation with the degradation of TPH, the relative con-
tents of TBSAT, MONO and CYCLO had moderate or low positive correlation with
the degradation of TPH, and the correlation coefficients were 0.56, 0.50 and 0.07
respectively. It was shown that the growth of mirabilis jalapa (Linn.) highly affected
the microbial community structure and TPH degradation speed in the rhizosphere
soil, providing a theoretical basis for the research on phytoremediation of petroleum-
contaminated saline-alkali soil.
Key words Petroleum-contaminated saline-alkali soil; Petroleum hydrocarbon; Micro-
bial community; Phospholipid fatty acids (PLFAs); Mirabilis jalapa Linn.
紫茉莉修复石油污染盐碱土壤
过程中的微生物群落响应
岑浴 1,2，李玉洁 3，焦海华 2，王晓辉 1*，白志辉 2*
（1.河北科技大学环境科学与工程学院，河北
石家庄 050018；2.中国科学院生态环境研究中
心，北京 100085；3.石家庄市环保局，河北石家
庄 050021）
摘 要 以石油污染盐碱土壤为研究对象，利
用磷脂脂肪酸(PLFAs)活性微生物标记法，分析
紫茉莉 (Mirabilis jalapa Linn.)根际土壤微生物
群落结构的动态变化，探讨紫茉莉生长对根际
土壤微生物与石油烃（TPH）降解的影响。 结果
表明， 供试土壤中， 先后出现了 24 种微生物
PLFAs，包括标识细菌的饱和脂肪酸 （SAT）、标
识革兰氏阳性菌（G+）的末端支链型饱和脂肪酸
（TBSAT）、标识革兰氏阴性菌（G-）的单不饱和
脂肪酸（MONO）和环丙脂肪酸（CYCLO）、标识
真菌的多不饱和脂肪酸(PUFA)和标识放线菌的
中间型支链型饱和脂肪酸 （MBSAT）等六大类
型。 与未种紫茉莉土壤（CK）相比，根际土壤微
生物 PLFAs 种类变异率在春、夏、秋季分别为
71.4%、69.2%和 33.3%；TPH 降解率在春、夏、秋
季分别提高了 47.6%、28.3%、18.9%。 相关性分
析表明， 石油烃的降解在 CK 土壤中与 77.8%
的 PLFAs 具有正相关关系 (r＞0)，55.6%的种类
具有高度正相关性 (r≥0.8)， 其中， 与 SAT 和
MONO 类群的相对含量正相关，相关系数分别
为 0.92、0.60； 根际土壤中仅与 42.1%的 PLFAs
正相关，21.1%的种类高度正相关， 与 TBSAT、
MONO 和 CYCLO 类群的相对含量正相关 ，相
关系数分别为 0.56、0.50、0.07。说明紫茉莉生长
对根际土壤微生物群落结构及 TPH 降解速率
均具有较大影响，且随生长季节的不同而有很
大差异。
关键词 石油污染盐碱土壤；石油烃；微生物群
落；磷脂脂肪酸；紫茉莉
基金项目 中国科学院战略性先导科技专项课
题 (XDB15010404)； 国 家 863 计 划 课 题
(2013AA06A205)；国家科技支撑计划课题(2014
BAD14B01)。
作者简介 岑浴 (1991- ),女 ,湖北黄冈人 ，硕
士研究生 ， 从事环境污染生物修复技术研
究 ，E-mail：happycenyu@163.com。 *通讯作者，
E-mail：zhbai@rcees.ac.cn; www_xxx_hhh@sina.
com。
收稿日期 2015-11-26
修回日期 2016-03-19
DOI:10.16175/j.cnki.1009-4229.2016.05.041
Agricultural Science & Technology 2016
resistance [5], high salt tolerance [6] and
high Cd enrichment capacity [7]. In re-
cent years, there have been many re-
ports about the application of Mirabilis
jalapa Linn. in the remediation of
heavy metal-contaminated soil [8-9], wh-
ile the studies on the application in the
remediation of petroleum-contaminat-
ed saline-alkali soil were still few.
The phospholipid fatty acids
(PLFAs) analysis is a modern bio-
chemical method developed on the
basis of the specificity of microbial
PLFAs, and it has been widely ap-
plied in the discussion of diversity of
soil microbial community structure [10].
In this study, the PLFAs analysis
method was applied to analyze the ef-
fect of Mirabilis jalapa growth on the
micro-ecological environment of
petroleum-contaminated saline-alkali
soil and to reveal the effect of the
change in soil microorganisms on the
degradation of total TPH (TPH), so as
to provide a theoretical foundation for
the research on the bioremediation
technique for petroleum-contaminated
saline-alkali soil and the development
and utilization of plant resources.
Materials and Methods
Experimental design and soil sam-
ple collection
The experimental soil is typical
saline-alkali soil collected from oil field.
The soil conditions included: a TPH
content of (6.3±0.3) g/kg, a total car-
bon content of (3.5±0.5) g/kg, a total
nitrogen content of (0.5±0.2) g/kg, an
available phosphorus content of
(26.9±0.6) g/kg, an available potassi-
um content of (8.2 ±0.3) g/kg, a pH
value of 8.8±0.7, and an electric con-
ductivity (EC) of 1 387 μs/cm. The ex-
periment adopted the way of potted
Mirabilis jalapa, for which the pots had
a specification of 20 cm × 25 cm, and
there were 30 pots, 10 of which formed
a control group (CK) without Mirabilis
jalapa. Seedlings with 1-2 true leaves
were transplanted according to 2
plants in one pot. During the whole ex-
periment period, the experiment
adopted natural illumination, a tem-
perature at 15 -38 ℃ and a humidity
kept at 50%-60%. Forty soil samples
were collected once in the middle ten
days of each month with a hole
puncher around the root zones of
Mirabilis jalapa (0-20 cm), these rhi-
zosphere soil samples (2 samples/pot)
were mixed into one sample after the
removal of impurities such as stones
and animal and plant residual bodies.
A required amount of soil sample was
obtained by quartering, filled in a
sealed bag and transported into the
laboratory. The soil sample was stored
in a refrigerators at -20℃, and micro-
bial PLFAs and TPH content were an-
alyzed as soon as possible. The anal-
ysis of PLFAs used fresh soil, while
the TPH analysis used dry soil ob-
tained by freeze drying, grinding and
sieving with a 100 mesh metal sieve.
The samples collected from March to
May were recorded as the spring sam-
ples, the samples collected from June
to August were recorded as the sum-
mer samples, and the samples collect-
ed from September to November were
recorded as the autumn samples.
Determination of soil physical and
chemical properties and petroleum
hydrocarbon content
The contents of total carbon and
total nitrogen in soil were determined
with an elemental analyzer (Vario Toc,
Germany); the pH value of amixture at a
water-soil ratio of 5:1 was determined
with a pHmeter (pHs-3C); electric con-
ductivity was determined with a con-
ductivitymeter (DDS-11A); and thecon-
tent of available phosphorous was de-
termined by the molybdenum-antimony
anti-spectrophotometric method[11]. The
content of total TPH in soil was deter-
mined according to the method by
Riser-Roberts[12].
Determination of soil microbial
PLFAs
The extraction of PLFAs was
performed by the method according
to Bligh and Dyer [13] with nonane-de-
canoic acid with the internal standard,
and the content of soil microbial
PLFAs was determined by GC-MS.
Qualitative analysis was performed ac-
cording to the method of automatically
searching an MS library with a com-
puter; and quantitative analysis was
performed by peak area normalization
method of total ion current, and calcu-
lating the content of each kind of fatty
acid methyl ester according to the ratio
of peak area of fatty acid/peak area of
internal standard (c19:0).
Nomenclature of PLFAs
PLFAs were named according to
the “ω” system with a general molecu-
lar formula as (i/a/me/ cy)X:YωZ(c/t),
among which the prefix “i”/“a”/ “me”
represented the position of a methyl
branch. Specifically, “i” represented
that the methyl branch was located on
the second carbon from the end of the
molecular chain; “a” represented that
the methyl branch was located on the
third carbon from the end of the
molecular chain; “me” represented
that the methyl branch was located on
the carbon in the middle of the fatty
acid molecular chain, and as to the
figure before it, for instance, “10 me”
represented that the methyl group was
on the tenth carbon from the initial end;
“cy” represented the cyclopropyl in
the molecule; X referred to the number
of the carbon atoms in the fatty acid; Y
represented the number of the double
bond in the molecule; ω referred to the
double bond; Z was the position of the
double bond (the number of carbon
atoms from the carbon atom at the end
of the molecule); and the suffix “c” or
“t” represented the cis-or trans-from of
the molecule[14-16].
Data analysis
The calculation formula of the
kind change rate of PLFAs : kind
change rate of PLFAs (% ) =
Number of different PLFAs
Number of all PLFAs ; the de-
termination result of PLFAs was ana-
lyzed by NEST5.0 fingerprinting
database; and SPSS17.0 was used for
the processing and analysis of related
data.
Results and Analysis
Finger-print of soil microbial PLFAs
The extracted soil microbial
PLFAs samples were analyzed by GC-
MS. Taking the chromatogram (Fig. 1)
of the soil microbial PLFAs extracted
from the autumn rhizosphere soil of
Mirabilis jalapa as an example, the
vertical coordinates represented the
peak value of various PLFAs, and the
horizontal coordinates represented the
time when the characteristic peaks ap-
peared.
The Finger-print information was
converted into data form (Table 1).
The PLFAs could be divided into 6
types according to molecular struc-
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Agricultural Science & Technology2016
Fig. 1 Chromatogram of micorbial phospholipid fatty acids in the rhizosphere soil of
Mirabilis jalapa in autumn
1, 3 and 5 represent the soil samples of the CK group without Mirabilis jalapa in spring,
summer and autumn, respectively, and 2, 4 and 6 represent the rhizosphere soil samples
of Mirabilis jalapa in spring, summer and autumn, respectively.
Fig. 2 PCA and factor analysis of soil PLFAs
Fig. 3 Change trend of biomass of acitive mi-
croorganisms in soil samples
tures. The first type was the saturated
fatty acid (SAT), such as c14:0, c15:0,
c16:0, c17:0 and c18:0 indentifying
bacteria [17]; the second type was the
saturated fatty acid with a methyl
branch at the end of molecule (TB-
SAT), such as i13:0, i15:0, i16:0, a14:0
and a16:0 indentifying gram positive
bacteria (G+)[18]; the third type was the
saturated fatty acid with a methyl
branch on the carbon in the middle of
molecule (MBSAT), such as 9Me14:0,
9Me16:0, and 10Me18:0 which was a
typical PLFA indentifying actino-
mycetes; the fourth type was the mo-
nounsaturated phospholipid fatty acid
(MONO), such as 16:1ω5, 16:1ω7t,
18:1ω7c, 18:1ω9c and 18:1ω9t identi-
fying gram negative bacteria (G -) [20];
the fifth group was the fatty acid with a
cyclopropyl (CYCLO), such as cy16:0
and cy18:0 indicating eutrophic envi-
ronment or pollution stress; and the
sixth type was the polyunsaturated
fatty acid (PUFA), such as 18:2ω6,9
which was a typical PLFA indentifying
fungi[21,22].
Changes in microbial community
structure in the rhizosphere soil of
Mirabilis jalapa
Kinds and distribution characteris-
tics of microbial PLFAs
As shown in Table 1 that, there
were 22 PLFAs detected in the soil in
total. Among them, 19 kinds were de-
tected during the whole growth period
of Mirabilis jalapa, and 17 kinds were
detected in the CK without plant.
Compared with the CK, the total kinds
in the rhizosphere soil of Mirabilis jala-
pa exhibited no significant increase,
but the composition of the microbial
PLFAs varied significantly according to
different growth seasons. Twelve
kinds of PLFAs were detected in the
rhizosphere soil of Mirabilis jalapa in
spring, 9 kinds were detected in sum-
mer, and 15 kinds were detected in
autumn; and there were 6, 8 and 16
kinds of microbial PLFAs in the soil of
the CK in the 3 seasons, respectively.
Compared with the CK, the kinds of
microbial PLFAs in the rhizosphere
soil increased by 50%, and there was
no obvious increase in summer and
autumn (P＞0.5), but the kind change
rates of PLFAs were 71.4% , 69.2%
and 33.3% in spring, summer and au-
tumn, respectively.
The dominant groups were TB-
SAT (58.0%) and MBSAT (21.4%) in
spring in the soil of the CK, and TB-
SAT (48.5%) and MONO (38.3%) in
the rhizosphere soil. It could be seen
that the first groups of both of the soils
were TBSAT, but the proportions were
different greatly. In summer, the typical
dominant groups were MONO (37.1%)
and TBSAT (32.4%) in the soil of the
CK, while the dominant groups in the
rhizosphere soil were SAT (45.9% )
and MBSAT (21.8% ). It was shown
that the first and second dominant
groups were both different in summer.
As to autumn, the dominant groups
were SAT (38.4% ) and MONO
(32.5%) in the soil of the CK, and TB-
SAT (37.4%) and MONO (30.0%) in
the rhizosphere soil. It was thus clear
that for the two different soils, the first
dominant groups in autumn were dif-
ferent. In comparison with the CK, the
CYCLO and CYCLO/MONO identify-
ing environment stress in the rhizo-
sphere soil were higher than those in
the CK group in the 3 seasons. The
ratios of fungi to bacteria in the rhizo-
sphere soil were higher than that in the
CK in spring and autumn. It was indi-
cated that the microbial community
structure in the rhizosphere soil was
greatly different from that in the CK.
Principal component analysis of
soil microbial PLFAs
Principal component analysis
(PCA) was performed on the soil mi-
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Agricultural Science & Technology 2016
Table1 Dynamic changes of PLFAs in soils during the growth period of Mirabilis jalapa
Number PLFAs
Spring//nmol/g Summer//nmol/g Autumn//nmol/g
CK Rhizospherer CK Rhizospherer CK Rhizospherer
1 c14:0 0 0 0 0 0.469 2.59
2 c15:0 0 0 0.603 0 0.371 0.525
3 c16:0 0.064 3 0.457 0 2.05 4.94 0
4 c17:0 0 0 0 0 0.533 0.469
5 c18:0 0 1.24 0 0.136 1.89 1.09
6 n16:0 0 0 0 0 0.400 0.423
7 i13:0 0 0.661 0 0 1.28 2.05
9 i15:0 0.237 5.81 4.12 0.0749 0.711 1.13
9 i16:0 0 0 0 0 0 0.322
10 a14:0 0 3.74 0 0.412 0 0.438
11 a16:0 0.250 1.46 1.29 0.350 1.17 5.45
12 i16:1ω5 0 0.275 0 0 0 0
13 16:1ω7t 0.093 6 5.34 0 0.341 3.55 2.98
14 18:1ω7c 0 0 0 0 2.25 0
15 18:1ω9c 0 3.79 2.63 0.185 1.48 4.55
16 18:1ω9t 0.015 3 0 3.58 0 0 0
17 18:2ω6,9 0 0.158 1.34 0 0.725 0.994
18 cy16:0 0 0 0.488 0.182 0 1.38
19 cy18:0 0 1.28 0 0 0 0
20 9me14:0 0 0.393 0 1.04 0.20 0
21 9me16:0 0.180 0 0 0 1.91 0
22 10me18:0 0 0 2.67 0 0.551 0.678
Total amount of phospholipid fatty
acids (∑PLFAs)//nmol/g 0.840 24.6 16.7 4.77 22.4 25.1
Kinds of phospholipid fatty acids 6 12 8 9 16 15
SAT//% 7.65 6.88 3.60 45.9 38.4 20.3
TBSAT//% 58.0 48.5 32.4 17.5 14.1 37.5
MONO//% 13.0 38.3 37.1 11.0 32.5 30.1
PUFA//% 0 0.642 8.02 0 3.23 3.97
CYCLO//% 0 5.20 2.92 3.81 0 5.49
MBSAT//% 21.4 1.60 16.0 21.8 11.9 2.71
CYCLO/MONO 0 0.135 0.0785 0.347 0 0.183
fungi/bacteria 0.024 0.208 1.26 0.0548 0.125 0.317
crobial PLFAs in different growth peri-
ods. The characteristic roots and vari-
ance contribution rates of the main
principal components of PLFAs were
extracted, the principal component 1
with the highest variance contribution
rate (PC1, 31.1% ) and the principal
component 2 (PC2, 23.2%) were used
for the analysis of microbial community
diversity.
As shown in Fig. 2, the PLFAs
with higher contribution rates to PC1
were mainly a14:0, a16:0, cy18:0,
cy16:0, 18:1ω9c, i16:1ω5, 16:1ω7t,
i15:0, i16:0, i13:0, c14:0, c18:0, c15:0
and 9me14:0, explaining 40.9% of the
variable; and the PLFAs with higher
contribution rates to PC2 were 18:1
ω9t, 18:1ω7c, 10me18:0, 9me16:0,
c16:0, c17:0 and n16:0, explaining
26.1% of the variable. The differences
in microbial community PLFAs be-
tween the CK and the rhizosphere soil
in spring were mainly showed on PC1,
such as cy18:0, cy16:0, a14:0, a16:0,
i16:0, i15:0 and 18:1ω9c; In summer
and autumn, the differences in micro-
bial community PLFAs between the
CK and the rhizosphere soil were
showed on both of PC1 and PC2. It
was indicated that the growth of
Mirabilis jalapa greatly affected the mi-
crobial community structure in its rhi-
zosphere soil.
Dynamic changes in soil microbial
biomass
The total biomass of active mi-
croorganisms in soil microbial com-
munities was calculated according to
all kinds of PLFAs; the biomass of
bacteria was calculated according to
the total amount of SAT, TBSAT,
MONO and CYCLO; the biomass of
fungi was calculated according to the
amount of PUFA; and the total
biomass of actinomycetes was calcu-
lated according to the amount of MB-
SAT, and the results showed that the
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Agricultural Science & Technology2016
Fig. 4 Changes in pH and EC in soil samples
Fig. 5 Changes in content of total petroleum
hydrocarbon (TPH) in soil during different
seasons
Fig. 6 Spearam corrleatrion coefficients bettween degradation of TPH and realtive contents
of characteristic PLFAs of soil microorganisms
Fig. 7 Spearam corrleatrion coefficients
bettween degradation of TPH and bimasses
of different microbial communities in soil
samples
total biomasses of active microorgan-
isms in the rhizosphere soil were 24.6,
4.77 and 25.1 nmol/g in spring, sum-
mer and autumn, respectively; and the
total biomasses in the soil of CK were
0.840, 16.7 and 22.3 nmol/g, respec-
tively. The biomasses of different mi-
crobial groups (Fig. 3) showed differ-
ent dynamic change trends in the rhi-
zosphere soil and the soil of CK. In the
rhizosphere soil, the condition of bac-
teria was spring (20.3 nmol/g)>autumn
(18.9 nmol/g)>summer (3.55 nmol/g);
the condition of fungi was autumn
(5.55 nmol/g)>spring (3.95 nmol/g)>
summer (0.185 nmol/g); and actino-
mycetes showed a condition of sum-
mer (1.04 nmol/g) >autumn (0.678
nmol/g)>spring (0.394 nmol/g). In the
CK soil, bacteria were in a condition of
autumn (17.6 nmol/g)>summer (6.51
nmol/g) >spring (0.65 nmol/g); fungi
showed a condition of summer (7.55
nmol/g)>autumn (2.21 nmol/g)>spring
(0.0153 nmol/g); and the condition of
actinomycetes was summer (2.67
nmol/g)>autumn (2.66 nmol/g)>spring
(0.180 nmol/g). In comparison with
CK, bacteria and fungi showed the
fluctuation trend of increasing in
spring, decreasing in summer, and in-
creasing in autumn again, and the acti-
nomycetes increased in spring and de-
creased in summer and autumn.
Changes in pH and electric con-
ductivity of the rhizosphere soil of
Mirabilis jalapa
The pH of the rhizosphere soil of
Mirabilis jalapa showed a non-signifi-
cant difference from the CK (P>0.05),
while the electric conductivity of the
rhizosphere soil was significantly lower
than the CK (P<0.05), as shown in Fig.
4.
Changes in the degradation rate of
the petroleum hydrocarbon in the
rhizosphere soil of Mirabilis jalapa
The growth of Mirabilis jalapa had
an obvious promoting effect on the
degradation of TPH, as shown in Fig.
5. In the soil of the CK, the total re-
moval rate of TPH was 28.3% ; and
specifically, the removal rates in
spring, summer and autumn were
9.6%, 10.2% and 11.6%, respectively.
In the rhizosphere soil of Mirabilis jala-
pa, the degradation speed of TPH was
improved remarkably (P<0.05), and the
total removal rate was 81.7%. The re-
moval rates in the 3 seasons were
57.2%, 38.5% and 30.6%, respectively.
Correlation analysis between soil
microorganisms and petroleum hy-
drocarbon degradation
Correlation analysis between
petroleum hydrocarbon degrada-
tion and characteristic PLFAs
Spearman correlation analysis
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Agricultural Science & Technology 2016
was performed between the relative
contents of the 22 characteristic soil
microbial PLFAs and the degradation
rate of TPH (Fig. 6). A correlation coef-
ficient r>0 indicates positive correlation
between the characteristic PLFAs and
TPH degradation; a correlation coeffi-
cient r<0 indicates negative correlation
between the characteristic PLFAs and
TPH degradation; in case of ｜r ｜≥0.8,
there is high correlation; as to the con-
dition of 0.6≤｜r｜<0.8, it is indicated that
the correlation is at a medium degree;
in case of 0.3≤｜r ｜<0.6, the correlation
is at a low degree; and under the con-
dition of ｜r ｜<0.3, there is hardly any
correlation. As shown in Fig. 6, the
degradation of TPH in the CK was in
positive correlation with 77.8% of the
PLFAs, and the PLFAs in high positive
correlation with the degradation of
TPH (｜r｜≥0.8) were c14:0, c16:0, c17:
0, c18:0, c15:0, n16:0, i13:0, 16:1ω7t,
18:1ω7c, 9me14:0 and 9me16:0; and
the PLFAs in positive correlation with
the degradation of TPH at medium and
low degrees (0.3 <|r |<0.8) included
c15:0, a16:0, 18:1ω9c and 18:2ω6,9.
In the rhizosphere soil, the degrada-
tion of TPH were in positive correlation
with 31.6% of the characteristic
PLFAs, which decreased by 46.1% in
comparison with the CK. The PLFAs in
positive correlation with the degrada-
tion of TPH were i15:0, a14:0, cy18:0,
i16:1ω5, 16:1ω7t and c18:0 with the
correlation coefficients of 0.89, 0.96,
0.96, 0.96, 0.67 and 0.35, respectively.
The results indicated that the degra-
dation of TPH in the soil of the CK was
caused by the combined action of all
indigenous microorganisms, while the
degradation of TPH in the rhizosphere
soil were mainly due to the minority
characteristic microorganisms.
Correlation analysis between
degradation of petroleum hydro-
carbon and microbial biomass
Correlation analysis was per-
formed between the degradation of
TPH and the total biomasses of dif-
ferent microbial groups, and the result
was shown in Fig. 7. It could be seen
that the degradation of TPH in the soil
of the CK was in high positive correla-
tion with the bacterial biomass identi-
fied by SAT with a correlation coeffi-
cient r equal to 0.92, in medium posi-
tive correlation (r =0.60) with the G-
biomass indentified by MONO, and in
low positive correlation (r=0.19) with
the fungus biomass indentified by PU-
FA. In the rhizosphere soil, there were
only microbial groups in medium and
low positive correlation (0. ≤｜r ｜<0.8)
with the degradation of TPH, including
G+ (r=0.56) indentified by TBSAT and
G- (r=0.50) indentified by MONO.
Discussion
Effect of Mirabilis jalapa cultivation
on the microbial community struc-
ture in petroleum-contaminated
saline-alkali soil
In comparison with the CK, the
rhizosphere soil of Mirabilis jalapa
showed a kind change rate of micro-
bial PLFAs in the range of 33.3% -
71.4%, exceeding 60% in the vigorous
growth seasons, i.e., spring and sum-
mer. The microbial biomass in the rhi-
zosphere soil exhibited a fluctuation
change mode in the 3 growth seasons,
while the microbial biomass in the soil
of the CK showed a trend of gradually
increasing. Compared with the CK, the
microbial biomass in the rhizosphere
soil increased by 28 times in spring,
decreased by 71% in summer, and in-
creased by 11% in autumn. The ratio,
CYCLO/MONO increased in all of the
3 seasons, and especially in summer
by 77% . The ratio of CYCLO/MONO
always change with the stressing ef-
fect of environmental eutrophication
and pollution. The ratio, fungi/bacteria
characterizes the relative abundance
of the two groups in microbial commu-
nity[23]. The ratios of fungi to bacteria in
the rhizosphere soil were higher than
those in the CK group in spring and
autumn, while no PLFAs of fungi were
detected in summer; and for the soil of
the CK, no PLFAs of fungi were detect-
ed in spring. Fungi are susceptible to
the changes in environmental factor[24].
Therefore, the changes of fungi in dif-
ferent growth periods and in the mi-
crobial community of rhizosphere soil
are complicated.
Due to the root exudates of
Mirabilis jalapa with certain accumula-
tive allelopathy on rhizosphere mi-
croorganisms as well as the adaptabil-
ity of microorganisms to environment
changes, the secretion activity of roots
increases the content of organic mat-
ter in soil in the early growth stages of
Mirabilis jalapa, the kinds and
biomasses of the microbial communi-
ties in the rhizosphere soil change
greatly. The exudates accumulated in
rhizosphere soil increase gradually
with the growth period, the allelopathy
of the root exudates is enhanced, re-
sulting in the death of susceptible mi-
crobial groups and decrease in micro-
bial kinds and biomasses, which could
be reflected by the remarkable de-
crease in summer. Owing to the
adaptability of microorganisms to envi-
ronment[25], the kinds and biomasses of
soil microbial groups both increase in
autumn. There have been studies
deeming that the root exudates of
plants could provide nutrients for rhi-
zosphere microorganisms, and also
contained some components which
could serve as the signal molecules for
regulating the behaviors of rhizo-
sphere microorganisms, thereby af-
fecting the community structure and
function of microorganisms in rhizo-
sphere soil [26]. Zhao et al.[27] found that
the root exudates of Mirabilis jalapa
continuously changed the balance be-
tween supply and demand of soil nu-
trients, and affected the activities of
some metabolic enzymes, thereby af-
fecting the conversion of soil nutrients
and the microecological balance of
soil. Furthermore, due to the allelopa-
thy of the root exudates of Mirabilis
jalapa, the numbers of soil bacteria
and actinomycetes decreased re-
markably. Specifically. The exudates
at a medium concentration could facili-
tate the increase in the quantity of fun-
gi, and the exudates at low and high
concentrations could both result in the
decrease in the quantity of fungi. Liu et
al.[28] proved by the growth rate method
that the extract of Mirabilis jalapa could
inhibit the growht of Monilia cinerea.
Wang [29] proved by an in-vitro experi-
ment that the protein components con-
tained in the roots of Mirabilis jalapa
had an inhibition effect on staphylo-
coccus aureus, Shigella dysenteriae
and Escherichia coli.
Correlation between soil microor-
ganism and degradation of
petroleum hydrocarbon
The results of this study showed
that the degradation rate of TPH in the
rhizosphere soil of Mirabilis jalapa
1228
Agricultural Science & Technology2016
greatly increased (P<0.05), and were
different with different growth periods;
and in comparison with the CK, the
degradation rate increased by 48% ,
28% and 19% in spring, summer and
autumn, respectively. There was high-
ly positive correlation (r≥0.8) between
the degradation of TPH and the 21%
microbial PLFAs in the rhizosphere
soil, which decreased by 42% com-
pared with the soil of the CK. The mi-
crobial groups in the rhizosphere soil
in positive correlation with the degra-
dation of TPH were mainly G+ indenti-
fied by TBSAT and G - indentified by
MONO, while the microbial groups in
the CK soil in positive correlation with
the degradation of TPH were mainly
bacteria indentified by SAT and PUFA
indentified by fungi. Joynt et al. [30]
found that with the G+ bacteria in rhi-
zospere soil increasing, the conversion
speed of organic pollutants in soil in-
creased remarkably. Liste et al. [31] re-
ported that in the soil cultivated with
plants, the removal rate of pyrene in-
creased by 34% in comparison with
the soil of the CK group; Sicilian et
al. [32] found that the amount of re-
moved TPH in the contaminated soil
planted with plants was two times of
that in the soil without plants by two
years of phytoremediation. With the
growth period of Mirabilis jalapa, the
decrease in the degradation rate of
TPH was mainly due to that: (1) the
growth of Mirabilis jalapa accelerates
the metabolism effect of soil microor-
ganisms on TPH, the degradation-
susceptible TPH components in soil
decrease, while the content of degra-
dation-resistant components in soil in-
creases relatively, thereby increasing
the difficulty of TPH degradation by
soil microorganisms; (2) the allelopa-
thy of root exudates is enhanced and
kills susceptible microbial groups or
decreases the growth and metabolism
activity of them; and (3) the respiration,
metabolism and secretion of roots af-
fect the microenvironment of soil, for
instance, the root exudates could im-
prove the content of organic matter in
soil, thereby decreasing the contents
of soil alkali-hydrolyzable nitrogen,
available phosphorus and potassium.
In addition, the metabolic activity of
root could improve the activity of soil
proteinase, thereby decreasing the
activities of soil urease, alkaline phos-
phatase and cellulase[33]. The changes
in the activities of various enzymes af-
fect the biological and chemical pro-
cesses such as assimilation or com-
plexation of plants and soil microor-
ganisms on organic matter or inorgan-
ic ions which change the pH and EC of
soil environment, thereby affecting the
metabolism of microorganisms. This
result accords with the change in mi-
crobial community structure in the rhi-
zosphere soil ofMirabilis jalapa.
It was reported that Mirabilis jala-
pa exhibited certain resistance to en-
vironment pollution [34-36], could absorb
heavy metal ions in soil and could
serve as a kind of plant for roil reme-
diation, while there were few studies
on the application of Mirabilis jalapa in
the remediation of petroleum-contami-
nated saline-alkali soil. Whether the
degradation of TPH is related to the
absorption, degradation and enrich-
ment effects of Mirabilis jalapa still
needs further study.
Conclusions
(1) The cultivation of Mirabilis
jalapa greatly affected microbial
species and biomasses in the rhizo-
sphere soil. Compared with the soil in
the CK, the microorganism kinds in-
dentified by the PLFAs in the 3 sea-
sons showed the change rates all over
30%; and the microbial biomass fluc-
tuated greatly in different seasons, and
specifically, it increased by 28 times in
spring, decreased by 71% in summer,
and increased by 11% in autumn.
(2) The cultivation of Mirabilis
jalapa could accelerate the degrada-
tion of TPH in the rhizosphere soil, and
there were significant differences be-
tween different seasons (P<0.05). The
degradation rate of TPH in the rhi-
zospere soil was 57% in spring, 38%
in summer, and 31% in autumn.
Compared with the CK, it was in-
creased by 48% in spring, 28% in
summer, and 19% in autumn.
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