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Influence of Elevated CO2 Concentration and Nitrogen Source on Photosynthetic Traits in the Invasive Species Eupatorium adenophorum (Asteraceae)

CO2浓度升高和不同氮源对紫茎泽兰生长及光合特性的影响



全 文 :CO2浓度升高和不同氮源对紫茎泽兰生长及光合特性的影响

欧阳芬1ꎬ2ꎬ 郑国伟1∗∗ꎬ 李唯奇1ꎬ3∗∗
(1 中国科学院昆明植物研究所中国西南野生生物种质资源库ꎬ 云南 昆明  650201ꎻ
2 中国科学院大学ꎬ 北京  100049ꎻ 3 红河学院生物系ꎬ 云南 蒙自  661100)
摘要: 大气 CO2浓度升高和植物入侵是全世界面临的两大重要问题ꎮ CO2浓度升高促进植物的光合作用ꎬ
但在某些植物中ꎬ 这种促进作用出现在短期高浓度 CO2下ꎬ 而在长期高浓度 CO2处理下消失 (称为 CO2驯
化)ꎬ 被认为源于高浓度 CO2对光呼吸和 NO3
-同化的抑制ꎮ 通过比较研究不同形式氮源 (全氮、 硝态氮)
和短期 (8 days)、 长期 (40 days) CO2浓度升高处理对入侵植物紫茎泽兰生理特征的影响ꎬ 结果表明在全
氮供应下ꎬ 短期和长期 CO2浓度升高均促进了紫茎泽兰的光合ꎻ 氨态氮缺失情况下ꎬ 长期 CO2浓度升高促
进紫茎泽兰的光合ꎬ 而短期 CO2浓度升高对紫茎泽兰的光合没有促进作用ꎻ 缺 NH4
+下ꎬ 短期高浓度 CO2
提高了叶片叶绿素含量ꎬ 长期 CO2升高又使其回复到正常 CO2下的较低水平ꎮ 这些结果表明紫茎泽兰并不
会对长期的 CO2升高产生驯化ꎬ 即长期 CO2升高会促进紫茎泽兰的光合作用ꎬ 而且这一促进作用不受土壤
中缺 NH4
+的影响ꎮ 鉴于培养介质中缺 NH4
+会导致一些植物产生 “CO2驯化”ꎬ 未来 CO2浓度升高情况下ꎬ
在缺 NH4
+的土壤中ꎬ 紫茎泽兰的竞争力可能会更强ꎮ
关键词: CO2浓度升高ꎻ 紫茎泽兰ꎻ 入侵植物ꎻ 光合驯化ꎻ NO3
-吸收
中图分类号: Q 945            文献标识码: A              文章编号: 2095-0845(2014)05-611-11
Influence of Elevated CO2 Concentration and Nitrogen Source
on Photosynthetic Traits in the Invasive Species
Eupatorium adenophorum (Asteraceae)
OUYANG Fen1ꎬ2ꎬ ZHENG Guo ̄Wei1∗∗ꎬ LI Wei ̄Qi1ꎬ3∗∗
(1 Germplasm Bank of Wild Species in Southwest Chinaꎬ Kunming Institute of Botanyꎬ Chinese Academy of Sciencesꎬ
Kunming 650201ꎬ Chinaꎻ 2 University of Chinese Academy of Sciencesꎬ Beijing 100049ꎬ Chinaꎻ
3 Biology Departmentꎬ Honghe Universityꎬ Mengzi 661100ꎬ China)
Abstract: Increases in the concentration of atmospheric CO2 and plant invasion are two important problems that face
humans worldwide. In some plantsꎬ exposure to a short ̄term elevated concentration of CO2 (SE [CO2]) promotes
photosynthesisꎬ but the promotion of elevated [CO2] (E [CO2]) to photosynthesis might disappear after long ̄term
treatment (so ̄called “CO2 acclimation”)ꎻ this might result from the associated inhibition of nitrate assimilation. The
present study investigated the physiological effects of short ̄term (8 days) and long ̄term (40 days) exposure to E
[CO2] when these were combined with different forms of inorganic N ( full Nꎻ nitrate (NO3
-) ̄N) in the invasive
species Eupatorium adenophorum. Exposure to E [CO2] increased the biomass of E􀆰 adenophorumꎬ regardless of the
duration of exposure to E [CO2] and the type of inorganic N that was supplied. E [CO2] could promote the photo ̄
synthesis of E􀆰 adenophorum seedlings fertilised with non ̄depleted Hoagland solutions (full N). For plants fertilised
植 物 分 类 与 资 源 学 报  2014ꎬ 36 (5): 611~621
Plant Diversity and Resources                                    DOI: 10.7677 / ynzwyj201413243

∗∗
Funding: NSFC (31070262)ꎬ West Light Foundation of the Chinese Academy of Sciences (CAS)ꎬ Germplasm Bank of Wild Species
Author for correspondence: E ̄mail: weiqili@mail􀆰 kib􀆰 ac􀆰 cnꎻ gwzheng@mail􀆰 kib􀆰 ac􀆰 cn
Received date: 2013-12-24ꎬ Accepted date: 2014-03-25
作者简介: 欧阳芬 (1989-) 女ꎬ 硕士研究生ꎬ 主要从事植物逆境分子生理研究ꎮ E ̄mail: ouyangfen@mail􀆰 kib􀆰 ac􀆰 cn
with NH4
+  ̄depleted Hoagland solution (NO3
-  ̄N)ꎬ LE [CO2] treatment promoted the photosynthesis of E􀆰 adenop ̄
horumꎬ but the promotion of photosynthesis by E [CO2] disappeared under SE [CO2] conditions. Photosynthetic
pigments contents were determined to estimate potential changes in the photosynthetic capacity of E􀆰 adenophorum.
For plants fertilised with non ̄depleted Hoagland solutionꎬ there were no significant differences in chlorophyll among
the three [CO2] treatmentsꎬ but the treatment of SE [CO2] increased the levels of chlorophyll in leaves. The ap ̄
parent promotion of biomass accumulation and photosynthesis at LE [CO2] without a decrease in chlorophyll indi ̄
cates that E􀆰 adenophorum might not acclimate to long ̄term exposure to E [CO2]. NH4
+ depletion did not affect the
capacity of LE [CO2] to promote the photosynthesis of E􀆰 adenophorum. Thusꎬ considering some plants fertilised
with NO3
- acclimating to LE [CO2]ꎬ E􀆰 adenophorum might be more competitive in areas where the soils are rela ̄
tively poor in NH4
+ as levels of atmospheric CO2 continue to rise.
Key words: Elevated CO2ꎻ E􀆰 adenophorumꎻ Invasive plantsꎻ Photosynthesis acclimationꎻ NO3
- assimilation
  Atmospheric concentrations of CO2([CO2]) have
increased by more than 0􀆰 01% ( from 0􀆰 027% to
0􀆰 0379%) since the beginning of the industrial rev ̄
olutionꎬ and are predicted to rise to 0􀆰 073% or even
0􀆰 102% by the end of the century (Solomon et al.ꎬ
2007). Besides being a major greenhouse gas that
causes global warmingꎬ CO2 is also the main source
of carbon for photosynthesis. Elevated [ CO2 ] ( E
[CO2]) will have a complicated influence on plant
physiology and growthꎬ as well as species distribu ̄
tions (Smith et al.ꎬ 2013ꎻ Kooij and Kokꎬ 1996).
E [CO2] affects plant growth and development
by changing patterns of photosynthetic carbon assim ̄
ilation (Reddy et al.ꎬ 2010)ꎬ water ̄use efficiency
(Jackson et al.ꎬ 1994) and flowering time through
impacting the rate of leaf production ( Song et al.ꎬ
2009). E [CO2] can also delay the senescence of
C3 plants (Curtis et al.ꎬ 1989). Whereas short ̄time
exposure to E [ CO2 ] in controlled experimental
conditions increases CO2 assimilation ratesꎬ pro ̄
longed exposure often results in “acclimation”ꎬ with
either no variation or a decrease of photosynthesisꎻ
this has been observed in Arabidopsisꎬ wheatꎬ toma ̄
toꎬ maize and alpine grassland (Bloom et al.ꎬ 2002ꎻ
Cousins and Bloomꎬ 2003ꎻ Searles and Bloomꎬ
2003ꎻ Korner et al.ꎬ 1997). The availability of N
affects this plant response to E [CO2]. Fertilisation
of wheat with nitrate (NO3
- ) was less efficient in
stimulating growth under elevated [CO2] conditions
than fertilisation with ammonium (NH4
+) (Bloom et
al.ꎬ 2002). Moreoverꎬ E [CO2] inhibited NO3
- as ̄
similation in wheat and Arabidopsisꎻ this might play
an important role in the decline of photosynthesis
and growth of C3 plants after prolonged exposure to
high CO2 ( Bloom et al.ꎬ 2010). N is one of the
mineral elements for which plants have the highest
demand (Epstein and Bloomꎬ 2004). Climate change
has contributed to increased levels of N deposition
in recent decades (IPCCꎬ 2007). Elevated N depo ̄
sition reduces species diversity (Stevens et al.ꎬ 2004).
Nonethelessꎬ elevated CO2 can ameliorate the nega ̄
tive effects of N enrichment on species richness
(Reichꎬ 2009). In terms of inorganic N in soilꎬ NO3

and NH4
+ are the primary sources for terrestrial plants.
The extent to which plants use NO3
- versus NH4
+ as
N sources varies among species. For instanceꎬ re ̄
gardless of prior N provisionꎬ NH4
+ uptake in seed ̄
lings of Scots pine (Pinus sylvestris) and European
larch ( Larix decidua) was consistently higher than
that of NO3
- (Bowler and Pressꎬ 1996). Howeverꎬ
Vaccinium arboreum can assimilate NO3
- efficiently
and tolerate an environment where NO3
- is the pre ̄
dominant form of N (Darnell and Hissꎬ 2006). This
introduces the fundamental question of whether E
[CO2] could inhibit NO3
- assimilation in plants that
preferred NO3
-ꎬ and thus enable “CO2 acclimation”.
Eupatorium adenophorumꎬ a notorious weed that
causes major economic losses worldwideꎬ was first
introduced into Yunnan Province in Southwest China
in the 1940sꎬ and is now spreading into Northern
and Eastern China ( Sang et al.ꎬ 2010). The suc ̄
216                                  植 物 分 类 与 资 源 学 报                            第 36卷
cessful invasion of E􀆰 adenophorum can be attributed
to its remarkable plasticity to adapt to different envi ̄
ronments through flexible regulation of its seed ger ̄
minationꎬ photosynthesisꎬ respirationꎬ and capacity
to secrete the phytotoxin o ̄coumaric acid to compete
with its neighbours (Li and Fengꎬ 2009ꎻ Niu et al.ꎬ
2011ꎻ Zheng et al.ꎬ 2012). Besides this allelopathic
strategy to deter competitorsꎬ E􀆰 adenophorum can
also alter the micro ̄environment of ground soil to en ̄
hance its suitability for growthꎻ indeedꎬ the soil con ̄
tent of NO3
- was nearly double that of NH4
+ in a
habitat that had been invaded extensive by E􀆰 aden ̄
ophorum (Li et al.ꎬ 2009). Lei et al. (2012) also
found that synergistic interactions of E [CO2] and
N deposition might exacerbate invasion by E􀆰 aden ̄
ophorum. Howeverꎬ little is known about the effects
of different forms of inorganic N on the response of
E􀆰 adenophorum plants to high CO2 .
The rising atmospheric level of the greenhouse
gas CO2 and biological invasions are two major
threats to biodiversity worldwide. Accordinglyꎬ in ̄
vestigation of the performance of invasive plants un ̄
der conditions of E [CO2] is of great importance if
plant invasiveness is to be controlled. In the present
studyꎬ we investigated the effects of long ̄term (40
days) and short ̄term ( 8 days ) CO2 enrichment
(0􀆰 076%) on the physiological performance of inva ̄
sive E􀆰 adenophorum when these were combined with
the supply of different forms of N (full Nꎻ NO3
-  ̄N).
Two questions were addressed: (1) In terms of its
photosynthesisꎬ does E􀆰 adenophorum acclimate to E
[CO2] after long ̄term treatment? (2) What is the
influence of different forms of N on the response of
E􀆰 adenophorum to E [CO2]?
1  Materials and methods
1􀆰 1  Plant material
Seeds of E􀆰 adenophorum were collected from
the Botanic Garden of Kunming Institute of Botanyꎬ
Chinese Academy of Sciencesꎬ Kunmingꎬ Yunnan
Provinceꎬ in 2008. All seeds were sterilized with
ethanol (70%) for 2 min and sodium hypochlorite
(5%) for 2 minꎬ and then rinsed three times with
sterile distilled water. Surface ̄sterilized seeds were
kept at 4 ℃ for two days before germinating the
seeds and growing the seedlings on 1 / 2 MS (Mu ̄
rashige and Skoogꎬ 1962) medium that contained
0􀆰 3% gellan gum (G1910ꎻ Sigma ̄Aldrich) for four
weeks. Four ̄week ̄old seedlings were grown in 1 / 4
Hoagland solution for hydroponic culture as de ̄
scribed by Tocquinet et al. (2003). The conditions
in the growth chamber were 22 / 18 ℃ꎬ a 12 / 12 h
light / dark cycleꎬ with a relative humidity (RH) of
65% and photosynthetic photon flux density (PPFD)
of 120 μmol m-2s-1 .
1􀆰 2  Experiment design
The environmental conditions to which E􀆰 aden ̄
ophorum was exposed involved combinations of three
CO2 treatments and two kinds of nitrogen nutrients.
Seeds were germinated and grown for 4 weeks. Four ̄
week ̄old seedlings were subjected to various concen ̄
trations of CO2 and nitrogen nutrientsꎬ which were
provided in different combinations. All treatments
were performed in two closed ̄top chambers (E ̄sheng
Tech. Co.ꎬ Beijingꎬ China). The CO2 was supplied
as compressed CO2 gasꎬ with the CO2 concentration
controlled automatically with a computer ̄controlled
CO2 supply system (LT / ACR ̄ePLCꎬ E ̄Sheng Tech.
Co.ꎬ Beijingꎬ China). The humidity and tempera ̄
ture in the chamber were also controlled by the com ̄
puter. The concentrations of ambient and elevated
CO2 provided were 0􀆰 038% and 0􀆰 076% CO2ꎬ re ̄
spectively. For long ̄term CO2 treatmentsꎬ seedling
growth occurred under ambient (0􀆰 038%) and ele ̄
vated (0􀆰 076%) CO2 conditionsꎬ indicated by the
letter codes LA (long ̄term ambient) and LE (long ̄
term elevated )ꎬ respectively. For short ̄term E
[CO2] treatmentꎬ 32 ̄day ̄old hydroponic seedlings
grown with ambient CO2 concentration were trans ̄
ferred to elevated CO2 conditions and grown for eight
daysꎻ this was indicated by the letter code SE
( short ̄term elevated ). Treatments with different
forms of nitrogen nutrients included Hoagland solu ̄
tion ( full N) and NH4
+  ̄depleted solution (NO3
-  ̄
3165期      OUYANG Fen et al.: Influence of Elevated CO2 Concentration and Nitrogen Source on Photosynthetic 􀆺     
N). In the solution in which NH4
+ was depletedꎬ the
NH4
+ was replaced by Na+ . For exampleꎬ NH4NO3
was replaced by NaNO3ꎬ at the same molar concen ̄
tration. Nutrient solution was replaced twice during
the growing season. Every treatment combination in ̄
volved 12 replicatesꎬ and each experiment was re ̄
peated three times.
1􀆰 3  Gas exchange measurements
Gas exchange measurements were carried out in
situ using a portable gas analysis systemꎬ LI ̄COR
6400 (LI ̄CORꎬ USA)ꎬ equipped with a 6 cm2 LED
chamber ( LI ̄6400 ̄02B). Measurements were per ̄
formed after 5-10 min of stabilization at light ̄satura ̄
ting PPFD of 900 μmol m-2 s-1ꎬ ambient humidity
(55%-65%) and gaseous flow rate of 300 μmol s-1
through the gas exchange chamber. Photosynthetic
responses to intercellular CO2 concentration ( Ci )
were determined on new fully expanded leaves ( the
third leaf from the top) of three individuals per
treatment. CO2 concentration was controlled using an
LI ̄6400 CO2 injector system (LI ̄6400 ̄01). Light ̄
saturated A ̄Ci curves started with an ambient CO2
concentration of 0􀆰 038%ꎬ followed by decreases to
0􀆰 03%ꎬ 0􀆰 02%ꎬ 0􀆰 01%ꎬ 0􀆰 005% and 0ꎬ and then
increases to 0􀆰 005%ꎬ 0􀆰 01%ꎬ 0􀆰 015%ꎬ 0􀆰 02%ꎬ
0􀆰 03%ꎬ 0􀆰 04%ꎬ 0􀆰 05%ꎬ 0􀆰 06%ꎬ 0􀆰 08%ꎬ 0􀆰 1%ꎬ
0􀆰 12%ꎬ 0􀆰 14%ꎬ 0􀆰 16% and 0􀆰 2%. Leaves were
allowed to equilibrate for at least 3 min at each step
before logging data. Water use efficiency (WUE)
was estimated as follows: WUE = net photosynthesis
rates to transpiration rates ratio (Pn / Tr).
1􀆰 4   Seedling biomass and photosynthetic pig ̄
ment content
Seedlings were divided into roots and aerial
parts and dried for three days in an oven at 70 ℃
before their dry weights were measured. Chlorophyll
contents were measured as described by Porra et al.
(1989). Brieflyꎬ after assessment of the photosyn ̄
thetic rateꎬ half of the leaf was cut and immersed in
8 mL of Nꎬ N ̄dimethylformamide at 4 ℃ overnight.
The absorbance of the supernatant was detected at
647ꎬ 664 and 480 nm. Thenꎬ the glass tubes that
contained the leaf were oven ̄dried for three days at
70 ℃ and the sample dry weights were measured.
The photosynthetic pigment concentrations were cal ̄
culated using the following equations: total micro ̄
grams of chlorophyll a per litre = [12􀆰 00×(A664)]
-[3􀆰 11×(A647)]ꎻ total micrograms of chlorophyll
b per litre = [20􀆰 78×(A647)] -[4􀆰 88×(A664)]ꎻ
and total micrograms of carotenoid per litre ={[1000
×(A480)]-[1􀆰 12×Ca]-[34􀆰 07×Cb]} / 245. Lev ̄
els of photosynthetic pigments were then determined
according to the volume of extraction buffer and the
dry weight of the sample.
1􀆰 5  Determination of NO3
- content
The content of inorganic NO3
- was determined
as described by Cataldo et al. (1975)ꎬ with minor
modifications. Each frozen leaf sample was ground in
the liquid nitrogen. The ground samples were sus ̄
pended in 1􀆰 5 mL of deionised water and the mixture
was centrifuged at 18 000 × g for 15 min. Thenꎬ 0􀆰 4
mL of salicylic acid (5%) was added to 0􀆰 1 mL of
supernatantꎬ and the solution was incubated at room
temperature for 20 minꎻ subsequentlyꎬ 9􀆰 5 mL of 2
mol􀅰L-1 NaOH was added to raise the pH to above
12. Samples were then cooled to room temperature
and absorbance at 410 nm was determined. Similar ̄
lyꎬ 0􀆰 1 mL of standards containing 1 - 60 μg of
NO3
-  ̄N were mixedꎬ measured as mentioned above
and analysed with each set of samples. After the de ̄
termination of NO3
- levelsꎬ the microcentrifuge tubes
with the pelleted sample were oven ̄dried for three
days at 70 ℃ꎬ and the sample dry weights were
measured. Levels of NO3
- were determined by con ̄
sidering the volume of extraction buffer and the dry
weight of the sample.
2  Results and discussion
2􀆰 1  Elevated [CO2] enhances the growth of
E􀆰 adenophorum
We studied the influence of different nitrogen
nutrients on the response of E􀆰 adenophorum to E
[CO2]. Plants grown in hydroponic solutions where
NO3
- was the sole inorganic N source did not show a
416                                  植 物 分 类 与 资 源 学 报                            第 36卷
significant phenotypic difference in terms of response
to [ CO2 ] changes compared with the seedlings
grown in non ̄depleted Hoagland solution. Our subse ̄
quent studies investigated the influence of NH4
+ de ̄
pletion on the response of E􀆰 adenophorum to E
[CO2]. Regardless of whether plants were grown in
non ̄depleted Hoagland solutions or NH4
+  ̄depleted
Hoagland solutionsꎬ LE [CO2] always promoted a
substantial increase in E􀆰 adenophorum biomass. The
changes in biomass resulted from changes in the ae ̄
rial parts of the plantsꎻ the root weight did not show
a major difference between each treatment (Fig􀆰 1A).
Plant height was substantially promoted under LE
[CO2]ꎬ but not SE [CO2] (Fig􀆰 1B). The lengths
of roots of E􀆰 adenophorum grown under all treat ̄
ments had no significant difference (Fig􀆰 1C). The
specific leaf area (SLW) was greater in LE [CO2] ̄
than in either LA [ CO2 ] ̄ or SE [ CO2 ] ̄treated
plants. The different N sources tested did not influ ̄
ence the response of SLW to E [CO2] (Fig􀆰 1D).
There was also no significant difference in ratio of
root to shoot dry weight in E􀆰 adenophorum among all
treatments ( Fig􀆰 1E). These results might indicate
that E􀆰 adenophorum can use NO3
- as the sole inor ̄
ganic N sourceꎬ and that E [CO2] greatly acceler ̄
ated the growth of the plants.
2􀆰 2  Interactions of elevated CO2 concentration
and nitrogen source on photosynthesis of E􀆰 aden ̄
ophorum
LE [CO2] greatly enhanced the net photosyn ̄
thesis rates ( Pn) of E􀆰 adenophorumꎬ and the N
forms in cultured solutions did not influence this en ̄
hancement. Howeverꎬ under SE [CO2] conditionsꎬ
this enhancement occurred in seedlings grown in
non ̄depleted Hoagland solutionꎬ but not in NH4
+  ̄
depleted Hoagland solution (Fig􀆰 2A). LE [CO2]
did not influence the stomatal conductance ( gs) of
E􀆰 adenophorum under either of the N treatments
tested. NH4
+ depletion promoted the closure of sto ̄
mata in LA ̄treated plantsꎬ which was indicated by
Fig􀆰 1  Differences in growth and morphological characteristics of E􀆰 adenophorum grown under conditions of long ̄term ambient CO2 con ̄
centration (LA)ꎬ short ̄term elevated CO2 concentration (SE) and long ̄term elevated CO2 concentration (LE) when plants were ferti ̄
lised using Hoagland solution (Hoagland) and NH4 +  ̄depleted solution (NH4 + depletion) . A. plant weightꎻ B. plant heightꎻ C. root
lengthꎻ D. SLW (specific leaf weight)ꎻ E. ratio of root to shoot dry weight. Different letters indicate significant differences (P<0􀆰 05)
among treatments according to one ̄way ANOVA. Values of plant weightꎬ SLW and the ratio of root to shoot dry weight are means ± SD of
four replicatesꎻ values of plant height and root length are means ± SD of seven replicatesꎻ all experiments were repeated three times
5165期      OUYANG Fen et al.: Influence of Elevated CO2 Concentration and Nitrogen Source on Photosynthetic 􀆺     
Fig􀆰 2  Differences in gas exchange in E􀆰 adenophorum grown under conditions of long ̄term ambient CO2 concentration (LA)ꎬ short ̄term
elevated CO2 concentration (SE) and long ̄term elevated CO2 concentration (LE) when fertilised with Hoagland solution (Hoagland) and
NH4 +  ̄depleted solution (NH4 + depletion) . A. Pn (net photosynthesis rates measured at growth ambient CO2 concentration and saturated
light intensity)ꎻ B. gs (stomatal conductance)ꎻ C. Ci ( intercellular CO2concentration)ꎻ D. Ci / Ca ( ratio of intercellular to air CO2 con ̄
centration)ꎻ E. Trmmol ( transpiration rate)ꎻ F. WUE (water use efficiency) . Different letters indicate significant differences (P<0􀆰 05)
among treatments according to one ̄way ANOVA. Values are means ± SD of four replicatesꎻ the experiments were repeated three times
the decline of gs. SE [CO2] treatment greatly re ̄
duced gs (Fig􀆰 2B). The intercellular CO2 concen ̄
tration ( Ci)ꎬ which was measured at each of the
CO2 concentrations testedꎬ was lower after the SE
than after the LE treatmentꎬ and NH4
+ depletion did
not influence this response (Fig􀆰 2C). The ratio of
intercellular CO2 concentration to air CO2 concentra ̄
tion (Ci / Ca) was not influenced by SE and NH4

depletionꎻ howeverꎬ plants under LE treatment
maintained a higher Ci / Ca than plants subjected to
SE [CO2] (Fig􀆰 2D). Trends of changes of transpi ̄
ration rate (Trmmol) were the same as those for gs
(Fig􀆰 2E ). SE [ CO2 ] ̄treated seedlings had the
highest WUEꎬ which was independent of the type of
nitrogen supplyꎬ and there was no significant differ ̄
ence in WUE between LA ̄ and LE ̄treated plants
fertilised with NH4
+  ̄depleted solution (Fig􀆰 2F).
The preferences of plants for different forms of
inorganic N vary among speciesꎬ and may be related
to environmental factors (Peuke and Tischnerꎬ 1991ꎻ
Bledsoe and Zasoskiꎬ 1983). Wheat and tea can
grow in media in which NH4
+ is the sole inorganic N
source (Bloomꎬ 2009ꎻ Yang et al.ꎬ 2013)ꎬ whereas
Juglans sigillata grew poorly in such culture media
owing to cell membrane damage caused by excessive
accumulation of NH4
+ ( Fan et al.ꎬ 2013 ). The
mechanism of CO2 acclimation might be that E [CO2]
decreases the rate of photorespiration and inhibits
the assimilation of NO3
- into NH4
+ . In wheat and Ar ̄
abidopsis plantsꎬ the phenomenon of CO2 acclimation
arise due to the inhibition of N assimilation upon
long ̄term treatment with NO3
- (Bloom et al.ꎬ 2010).
Interestinglyꎬ for E􀆰 adenophorumꎬ E [CO2] did not
induce photosynthesis acclimation when provided
with non ̄depleted Hoagland solutions. The acclima ̄
tion of E􀆰 adenophorum in terms of its photosynthesis
did not occur in LE [CO2] ̄treated plants in the ab ̄
sence of NH4
+ . This differs from the findings for
wheat and Arabidopsis (Bloom et al.ꎬ 2010). Short ̄
term [CO2] elevation can greatly promote stomatal
closure in E􀆰 adenophorum and the subsequent de ̄
cline of Ciꎬ which might explain photosynthesis ̄re ̄
lated acclimation after SE [CO2] and NH4
+  ̄deple ̄
ted treatment. The ability of NH4
+ depletion to inhi ̄
616                                  植 物 分 类 与 资 源 学 报                            第 36卷
bit the promotion of photosynthesis by SE [ CO2 ]
might also be attributable to the inhibition of NO3

assimilationꎬ as reported for wheat and Arabidopsis
(Bloom et al.ꎬ 2010). The considerable plasticity of
E􀆰 adenophorum might have enabled it to adapt to
the conditions of NH4
+ depletion by maintaining a
high rate of photosynthesis.
Plants can maintain relatively constant Ci / Ca
values by adjusting stomatal anatomy and chloroplast
biochemistry (Frans et al.ꎬ 2013). NH4
+ depletion
has no influence on the Ci / Ca ratio. The value of
Ci / Ca in SE [ CO2 ] ̄treated plants was similar to
that of LA [CO2 ] ̄treated plantsꎻ howeverꎬ plants
subjected to long ̄term [CO2] elevation maintained a
higher Ci / Ca value. This indicated that only long ̄
term (40 days) E [CO2] adaptation can enable
E􀆰 adenophorum to adjust its stomata and chloroplasts
in order to adapt to E [CO2]. The lower stomatal
conductance of plants after NH4
+ depletion observed
for the other nitrogen forms studied might be accoun ̄
ted for by the ability of NH4
+ to promote high meso ̄
phyll conductance ( Guo et al.ꎬ 2002ꎻ Raab and
Terryꎬ 1994). CO2 enrichment might promote WUE
by decreasing both stomatal conductance and the rate
of leaf transpiration (Conley et al.ꎬ 2001ꎻ Wullschl ̄
egerꎬ 2002). Thereforeꎬ invasive species with high ̄
er WUE induced by high CO2 concentration grew
faster than native species in water ̄limited ecosystems
(Blumenthal et al.ꎬ 2013). Howeverꎬ CO2 enrich ̄
ment promoted WUE of E􀆰 adenophorum only under
SE [CO2]ꎬ mainly as a consequence of the marked
decrease of gs after short ̄term E [CO2] exposure.
Howeverꎬ LE [CO2 ] ̄treated plants might have a ̄
dapted to the conditions of CO2 enrichment: they
could maintain high levels of Pn and gsꎬ which pos ̄
sibly contributed to the relatively low level of WUE.
2􀆰 3  Interactions of elevated CO2 concentration
and nitrogen source on A / Ci response curves of
E􀆰 adenophorum
    A / Ci response curves were used to detect pho ̄
tosynthetic acclimation to CO2 enrichment in indivi ̄
dual E􀆰 adenophorum leaves ( Fig􀆰 3 ). For plants
grown in NH4
+ ̄depleted Hoagland solutionꎬ the A / Ci
response curves under LE [CO2] were no different
from those of plants under LA [ CO2 ] treatment.
The initial slope of the A / Ci response curve of plants
under SE [CO2] treatment was 0􀆰 284 ± 0􀆰 0056ꎬ
which was 42% lower (P<0􀆰 05) than that of leaves
under long ̄term CO2 treatment ( including LA and
LE [CO2 ] treatments). There were no significant
differences among the three CO2 treatments in the
upper portion of the A / Ci response curves. For plants
Fig􀆰 3  Differences in A ̄Ci curves determined for E􀆰 adenophorum grown under conditions of long ̄term ambient CO2 concentration
(LA)ꎬ short ̄term elevated CO2 concentration (SE) and long ̄term elevated CO2 concentration (LE) when fertilised with Hoagland
solution (Hoagland) and NH4 +  ̄depleted solution (NH4 + depletion) . A. Light ̄saturated A ̄Ci curves of E􀆰 adenophorum under non ̄
depleted Hoagland solutionsꎻ B. Light ̄saturated A ̄Ci curves of E􀆰 adenophorum under NH4 +  ̄depleted Hoagland solutions. Values are
means ± SD of three replicatesꎻ the experiments were repeated three times
7165期      OUYANG Fen et al.: Influence of Elevated CO2 Concentration and Nitrogen Source on Photosynthetic 􀆺     
grown in non ̄depleted Hoagland solutionꎬ there was
almost complete overlap in the A / Ci response curves
for the three CO2 treatments.
The initial slope of the A / Ci response curve is
determined by the total ribulose ̄1ꎬ 5 ̄bisphosphate
carboxylase oxygenase (Rubisco) activity (Sharkeyꎬ
2012ꎻ Voncaemmerer and Farquharꎬ 1981). Given
the effect of Rubisco activity on the initial slope and
the decreased initial Rubisco activity in wheat flag
leaves under CO2 enrichment ( Sicher and Bunceꎬ
1997) suggest that the fact that NH4
+ depletion de ̄
creased the initial slope of the A / Ci response curve
of plants under SE [CO2] treatment might have re ̄
sulted from the decrease of Rubisco activity. Rubisco
activity is regulated in order to maintain a balance
with the capacity in RuBP regenerationꎬ and the a ̄
vailable products of photo ̄energy (ATPꎬ NADPH)
could determine the regeneration of RuBP (Sage et
al.ꎬ 1988)ꎬ and the photo ̄energy cost for ammoni ̄
um supply is 145% less than for nitrate supply (Ra ̄
venꎬ 1985). Assimilation of NO3
- in the leaf led to
consumption of a substantial proportion of products
of the electron transport chain of photosynthesis
(Bloom et al.ꎬ 1989 ). Thusꎬ some plants have
higher rates of both CO2 assimilation and RuBP re ̄
generation per leaf area when fertilised with NH4

rather than NO3
- (Florian et al.ꎬ 2013). Given the
higher rates of photosynthesis supported by NH4
+ re ̄
lative to NO3
-ꎬ the inhibition of the increase in pho ̄
tosynthesis induced by SE [CO2] and the decrease
of initial slope of the A / Ci response curve in E􀆰 aden ̄
ophorum fertilised with NO3
- as the only N source
suggest that the assimilation of NO3
- alone might
lead to the consumption of more products of photo ̄
energyꎻ the decreased available products of photo ̄
energy used for photosynthesis might eventually in ̄
hibit the activity of Rubisco and thus affect the ca ̄
pacity for photosynthesis.
2􀆰 4  Effects of elevated [CO2] on photosynthet ̄
ic pigment content
    Photosynthetic pigment contents were deter ̄
mined to estimate potential changes in the photosyn ̄
thetic capacity of E􀆰 adenophorum (Table 1). With
non ̄depleted Hoagland solutionsꎬ there were no sig ̄
nificant differences in the levels of chlorophyll and
carotenoids among the three CO2 treatments. In
plants under NH4
+  ̄depleted Hoagland solutionsꎬ the
contents of chlorophyll were lower than for those
grown in non ̄depleted Hoagland solutions under LA
and LE [CO2]. The plants grown under SE [CO2]
exhibited higher levels of chlorophyll aꎬ chlorophyll
b and carotenoids than those grown in ambient at ̄
mospheric CO2 conditions with NH4
+  ̄depleted Hoag ̄
land solution. The increases in the levels of chloro ̄
phyll a and chlorophyll bꎬ total chlorophyll and ca ̄
rotenoid levels in plant leaves were 31􀆰 8%ꎬ 37􀆰 0%ꎬ
25􀆰 0% and 30􀆰 4%ꎬ respectively. Howeverꎬ follow ̄
ing the LE [CO2] treatmentꎬ the levels of chloro ̄
phyll aꎬ bꎬ total chlorophyll and carotenoids of plants
decreased and were similar to those of plants grown
under ambient [CO2] with NH4
+ ̄depleted Hoagland
solution. Rong et al. (2010) asserted that NH4
+ can
Table 1  Difference in photosynthetic pigment content of E􀆰 adenophorum leaves under conditions of long ̄term ambient CO2 concentration (LA)ꎬ
short ̄term elevated CO2 concentration (SE) and long ̄term elevated CO2 concentration (LE) when fertilised with Hoagland solution
(Hoagland) and NH4 +  ̄depleted solution (NH4 + depletion) . Different letters indicate significant differences (P<0􀆰 05) among
treatments according to one ̄way ANOVA. Values are means ± SD of four replicatesꎻ the experiments were repeated three times
Photosynthetic pigment content of E􀆰 adenophorum under various nitrogen nutrient and [CO2] treatment
Hoagland
LA SE LE
NH4 + depletion
LA SE LE
Chlorophyl a (mg􀅰g-1 DW) 11􀆰 59±1􀆰 53ab 13􀆰 30±0􀆰 97a 12􀆰 09±2􀆰 32ab 9􀆰 33±1􀆰 37c 12􀆰 30±0􀆰 68ab 8􀆰 06±0􀆰 92c
Chlorophyl b (mg􀅰g-1 DW) 4􀆰 51±0􀆰 73ab 5􀆰 28±1􀆰 02a 4􀆰 41±0􀆰 81ab 3􀆰 51±0􀆰 72bc 4􀆰 81±0􀆰 18a 3􀆰 06±0􀆰 34c
Chlorophyl a+b (mg􀅰g-1 DW) 16􀆰 10±2􀆰 23a   18􀆰 59±1􀆰 97a 16􀆰 50±3􀆰 09a   12􀆰 84±2􀆰 09b 17􀆰 11±0􀆰 85a   11􀆰 11±1􀆰 23b  
Carotenoid (mg􀅰g-1 DW) 2􀆰 47±0􀆰 36ab 2􀆰 86±0􀆰 18a 2􀆰 67±0􀆰 53a 2􀆰 04±0􀆰 34b 2􀆰 66±0􀆰 17a 2􀆰 01±0􀆰 30b
816                                  植 物 分 类 与 资 源 学 报                            第 36卷
increase rates of chlorophyll synthesis in plants by
stimulating the accumulation of the precursors of
chlorophyllꎬ such as glutamate and 2 ̄oxoglutaric
acid. NH4
+ depletion might deduce levels of photo ̄
synthetic pigments in LA ̄ and LE [ CO2 ] ̄treated
plants. Howeverꎬ short ̄term E [CO2 ] could com ̄
pensate for the reduced pigment synthesis observed
in plants fertilised with NH4
+  ̄depleted Hoagland so ̄
lution. This increase of photosynthetic pigments also
suggests that E􀆰 adenophorum with NH4
+  ̄depleted
Hoagland solution needed more photo ̄energy to com ̄
plete NO3
- assimilation and promote photosynthesis
when grown under SE [CO2] than when grown with
non ̄depleted Hoagland solution.
2􀆰 5  Effects of elevated [CO2] on plant NO3

status
The content of inorganic NO3
- in E􀆰 adenophor ̄
um grown in non ̄depleted Hoagland solutions was
not affected by the various CO2 treatments. NH4
+ de ̄
pletion greatly reduced the level of inorganic NO3
- of
LA ̄ and LE [CO2] ̄treated plantsꎬ especially in the
latter group. Howeverꎬ the level of inorganic NO3

for SE [CO2] under NH4
+  ̄depleted conditions re ̄
mained highꎬ which is the same as the case of grow ̄
ing with non ̄depleted Hoagland solutions (Fig􀆰 4).
E [CO2] might not influence the absorption and as ̄
similation of NO3
- with solutions that contain NH4
+ .
Howeverꎬ compared with short ̄term E [CO2] treat ̄
mentꎬ NH4
+ depletion induced a marked decline in
the NO3
- content in LE [ CO2 ] ̄treated plants. A
higher exogenous NO3
- concentration could promote
the activity of nitrate reductase in maize leaves
(Wang et al.ꎬ 2009)ꎬ whereas a high concentration
of NH4
+ decreased nitrate reductase activity (Claus ̄
sen and Lenzꎬ 1999). Hoagland solutions depleted
of NH4
+ had relatively high levels of NO3
- compared
with non ̄depleted Hoagland solutions. The high con ̄
centration of NO3
- might increase nitrate reductase
activity in E􀆰 adenophorum and reduce the residual
concentration of NO3
- in leaves ( Fig􀆰 4). Whereas
SE [CO2] treatment might inhibit the promotion of
nitrate reductase activity induced by NH4
+ deple ̄
tionꎬ and LE [CO2] treatment eliminates this inhi ̄
bition in E􀆰 adenophorum.
Fig􀆰 4  Differences in NO3 - content of E􀆰 adenophorum leaves under
conditions of long ̄term ambient CO2 concentration (LA)ꎬ short ̄term
elevated CO2 concentration (SE) and long ̄term elevated CO2 concen ̄
tration (LE) when plants were fertilised with Hoagland solution (Ho ̄
agland) and NH4 +  ̄depleted solution (NH4 + depletion) . Different let ̄
ters indicate significant differences (P<0􀆰 05) among treatments ac ̄
cording to one ̄way ANOVA. Values are means ± SD of four replicatesꎻ
the experiments were repeated three times
3  Conclusion
This study of the invasive plant E􀆰 adenophorum
investigated the effect of various treatments that com ̄
bined an elevated [CO2] with different forms of in ̄
organic N. E [CO2] promoted the photosynthesis of
E􀆰 adenophorumꎬ regardless of the duration of treat ̄
ment with non ̄depleted Hoagland solution. Whereas
NH4
+ depletion could inhibit the promotion of E􀆰 aden ̄
ophorum photosynthesis by short ̄term E [ CO2 ].
The apparent ability of NO3
- at LE [CO2] to pro ̄
mote biomass accumulation and photosynthesis with ̄
out a decrease in chlorophyll indicates that E􀆰 aden ̄
ophorum might not acclimate to long ̄term exposure
to E [CO2]. Thusꎬ considering some plants ferti ̄
lised with NO3
- acclimating to LE [CO2]ꎬ E􀆰 aden ̄
ophorum might be more competitive in areas where
the soils are relatively poor in NH4
+ as levels of at ̄
mospheric CO2 continue to rise.
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兼具学术性、 技术性、 知识性、 信息性等特点ꎮ 据 «中国科技期刊引证报告» (核心版) 统计ꎬ «中国稻
米» 2013年的影响因子为 0􀆰 553ꎮ 2008年度还有一篇文章被评为中国百篇最具影响的国内文章ꎮ 适合我
国水稻产区各级技术人员及农业与粮食行政管理人员、 科研教学人员和稻农阅读ꎮ 本刊为双月刊ꎬ 标准
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1265期      OUYANG Fen et al.: Influence of Elevated CO2 Concentration and Nitrogen Source on Photosynthetic 􀆺