師志冰，周 勇，李 夏，任安芝，高玉葆

(南開(kāi)大學(xué)生命科學(xué)學(xué)院，天津 300071)

CO2濃度升高條件下內(nèi)生真菌感染對(duì)宿主植物的生理生態(tài)影響

師志冰，周 勇，李 夏，任安芝*，高玉葆

(南開(kāi)大學(xué)生命科學(xué)學(xué)院，天津 300071)

以內(nèi)蒙古草原常見(jiàn)伴生種、感染內(nèi)生真菌的天然禾草羽茅為研究對(duì)象，通過(guò)比較不同CO2濃度和不同養(yǎng)分供應(yīng)條件下，帶內(nèi)生真菌和不帶菌植物在種子發(fā)芽和幼苗生長(zhǎng)等方面的差異，探討帶內(nèi)生真菌的天然禾草對(duì)CO2濃度增加的響應(yīng)。結(jié)果表明：CO2濃度增加對(duì)帶菌種子發(fā)芽率和發(fā)芽速度均無(wú)顯著影響，但CO2濃度增加顯著降低了不帶菌種子的發(fā)芽率和發(fā)芽速度，即CO2濃度升高加大了帶菌和不帶菌種子發(fā)芽率之間的差異；內(nèi)生真菌感染顯著提高了宿主植物的最大凈光合速率和水分利用效率；羽茅的營(yíng)養(yǎng)生長(zhǎng)受CO2濃度和養(yǎng)分供應(yīng)的交互影響，高CO2濃度對(duì)生長(zhǎng)的促進(jìn)作用只出現(xiàn)在充足養(yǎng)分供應(yīng)條件下；CO2濃度升高和內(nèi)生真菌感染對(duì)植物根系形態(tài)有顯著的交互作用，在正常CO2濃度下，帶菌植株根徑gt;1.05 mm的根系比例顯著高于不帶菌植株，隨著CO2濃度的升高，帶菌植株上述根徑根系所占比例無(wú)顯著變化而不帶菌植株所占比例顯著升高，CO2濃度升高導(dǎo)致帶菌和不帶菌不同根徑根系分配之間的差異縮小。

CO2濃度升高；羽茅；種子發(fā)芽；根系形態(tài)

產(chǎn)業(yè)革命以來(lái)，由于人類(lèi)大量消耗石油化工燃料和對(duì)土地的不合理開(kāi)發(fā)利用，使得大氣CO2濃度逐步升高，從1958到2011年的50多年間，大氣CO2濃度已由280增加到391 μmol/mol，若以目前的每年增加 2 μmol/mol計(jì), 預(yù)計(jì)到2067年，全球大氣CO2濃度將超過(guò)500 μmol/mol[1- 2]。由于CO2是植物光合作用的重要原料，所以大氣中CO2濃度的升高，必將影響到植物光合產(chǎn)物的形成以及光合產(chǎn)物在植物及其共生的微生物之間的分配[3], 從而影響到植物和根瘤菌[4]、菌根真菌[5]以及內(nèi)生真菌[6- 7]等之間的相互作用。

大量的研究表明CO2濃度升高能夠提高菌根真菌的侵染率，增強(qiáng)菌根真菌對(duì)宿主植物的有益影響[8- 11]。與菌根真菌類(lèi)似，內(nèi)生真菌也是在植物中廣泛存在的一類(lèi)真菌，只是多生活在植物的地上部分[12]，據(jù)估計(jì)，大約三分之二的冷季型禾草中有與之共生的內(nèi)生真菌[13]，但就已報(bào)道的研究工作來(lái)看，大量的研究集中在兩個(gè)有重要經(jīng)濟(jì)意義的植物種即高羊茅(FestucaarundinaceaSchreb.)和黑麥草(LoliumperenneL.)上面，二者分別與內(nèi)生真菌Neotyphodiumcoenophialum和N.lolii構(gòu)成共生關(guān)系。內(nèi)生真菌與高羊茅和黑麥草等人工禾草的互惠共生關(guān)系已被大量的實(shí)驗(yàn)證據(jù)所證實(shí)，具體表現(xiàn)在一方面植物為內(nèi)生真菌提供光合產(chǎn)物；另一方面內(nèi)生真菌的代謝物能刺激植物的生長(zhǎng)發(fā)育[14]，提高宿主植物對(duì)生物脅迫和非生物脅迫的抵抗能力，其中的生物脅迫主要包括食草動(dòng)物[15]和食草昆蟲(chóng)[16]的取食、線蟲(chóng)[17]和其它真菌[18]的危害以及其它植物的競(jìng)爭(zhēng)[19]等；非生物脅迫包括干旱[20]、低養(yǎng)分[21]和高溫[22]等。由于內(nèi)生真菌依靠宿主植物獲得碳源，而對(duì)于多數(shù)C3植物而言，CO2濃度是其光合作用的限制因子，因此大氣CO2濃度的增加將會(huì)通過(guò)提高植物的光合能力并增加對(duì)共生真菌的光合產(chǎn)物供給，從而對(duì)禾草-內(nèi)生真菌的相互作用產(chǎn)生影響[6, 23]，研究感染內(nèi)生真菌的天然禾草對(duì)CO2濃度升高的響應(yīng)不僅有助于預(yù)測(cè)全球氣候變化條件下帶菌植物的競(jìng)爭(zhēng)力，而且有助于預(yù)測(cè)帶菌植物所在草原群落的發(fā)展和演替方向，為實(shí)現(xiàn)草原的可持續(xù)利用提供實(shí)驗(yàn)數(shù)據(jù)。

1 材料與方法

1.1 種子的采集

羽茅(Achnatherumsibiricum(L.) Keng)是禾本科芨芨草屬的一種多年生草本植物，在內(nèi)蒙古的各類(lèi)草場(chǎng)中較為常見(jiàn)，具有很高的內(nèi)生真菌侵染率(86%—100%)[24]，共生的內(nèi)生真菌為Neotyphodium屬內(nèi)生真菌[25]，種子于2012年采集自中國(guó)農(nóng)業(yè)科學(xué)院呼倫貝爾草原生態(tài)系統(tǒng)國(guó)家野外實(shí)驗(yàn)站，種子采集樣地位于119.40°E，49.06°N，海拔629 m，年降雨量367 mm，年均溫-2.0 ℃，土壤為暗栗鈣土，植被為草甸草原。對(duì)采回的種子進(jìn)行內(nèi)生真菌的檢測(cè)，發(fā)現(xiàn)帶菌率為100%，種子于4 ℃冰箱中保存。

1.2 羽茅帶菌(E+)和不帶菌(E-)種群的構(gòu)建

帶菌的種子由野外采集，存放于4 ℃冰箱中備用，不帶菌的種子則通過(guò)將野外采集的種子置于60 ℃溫箱中處理30 d后獲得，前期的研究表明，60 ℃高溫處理羽茅種子30 d能完全殺滅種子中的內(nèi)生真菌，同時(shí)高溫處理對(duì)種子發(fā)芽率、發(fā)芽勢(shì)和發(fā)芽指數(shù)均無(wú)顯著影響[26]。選取帶菌和不帶菌的、飽滿成熟的種子分別播種于裝滿蛭石的塑料花盆中，置于溫室中培養(yǎng)，待幼苗生長(zhǎng)1個(gè)月后，每盆分別選取3株長(zhǎng)勢(shì)良好的分蘗進(jìn)行內(nèi)生真菌的檢測(cè)，檢測(cè)方法參考Latch等的苯胺蘭染色法[27]。檢測(cè)結(jié)果顯示一直在4 ℃冰箱存放的種子所獲得的植株的帶菌率為100%，高溫處理過(guò)的種子所獲得的植株帶菌率為0。此時(shí)，進(jìn)行間苗，保證每盆有8棵健壯的幼苗，備用。

1.3 種子發(fā)芽實(shí)驗(yàn)

本實(shí)驗(yàn)為兩因素實(shí)驗(yàn)，因素一為CO2濃度，包括400 μmol/mol (C-)和800 μmol/mol (C+)兩個(gè)水平；因素二為內(nèi)生真菌感染狀態(tài)，包括帶菌(E+)和不帶菌(E-)，每個(gè)處理5個(gè)重復(fù)。實(shí)驗(yàn)開(kāi)始時(shí)，分別在每個(gè)培養(yǎng)皿中均勻擺放浸泡好的種子50枚，將培養(yǎng)皿分別放入不同CO2濃度的智能人工培養(yǎng)箱中，兩個(gè)培養(yǎng)箱除CO2濃度不同外，其余的實(shí)驗(yàn)參數(shù)均完全相同，即溫度25 ℃，濕度60%。種子開(kāi)始發(fā)芽后，每天觀察并記錄發(fā)芽種子數(shù)目，直至連續(xù)兩天無(wú)種子萌發(fā)為止，共歷時(shí)14 d，計(jì)算種子發(fā)芽率及發(fā)芽速度指數(shù)。種子發(fā)芽率及發(fā)芽速度指數(shù)計(jì)算公式[28]如下：

發(fā)芽率=(發(fā)芽種子數(shù)/供試種子數(shù))×100%

發(fā)芽速度指數(shù)=(N1/1)+(N2-N1)/2 +(N3-N2)/3+…+(Nn-Nn-1)/n

式中，N為第1天、第2天…第n天的發(fā)芽種子數(shù)目。

1.4 幼苗生長(zhǎng)實(shí)驗(yàn)

本實(shí)驗(yàn)為三因素實(shí)驗(yàn)，因素一為CO2濃度，包括400 μmol/mol (C-)和800 μmol/mol (C+)兩個(gè)濃度；因素二為養(yǎng)分處理：包括充足養(yǎng)分供應(yīng)(N+P+)、缺氮(N-P+)和缺磷(N+P-)3個(gè)水平；因素三為內(nèi)生真菌感染狀態(tài)，包括帶菌(E+)和不帶菌(E-)，每個(gè)處理5個(gè)重復(fù)。將花盆分別放入不同CO2濃度的培養(yǎng)箱中，兩個(gè)培養(yǎng)箱的其它參數(shù)為：溫度25 ℃，濕度50%，光強(qiáng)40%，光照12 h。養(yǎng)分處理通過(guò)澆灌Hoagland營(yíng)養(yǎng)液控制，充足養(yǎng)分供應(yīng)組澆完全營(yíng)養(yǎng)液；缺氮處理組使用CaCl2和KCl分別替代Hoagland營(yíng)養(yǎng)液中的Ca(NO3)2和KNO3，缺磷處理組使用KCl代替KH2PO4，每周定期澆營(yíng)養(yǎng)液1次，期間保證水分充足供應(yīng)。實(shí)驗(yàn)期間每周隨機(jī)調(diào)換培養(yǎng)箱內(nèi)花盆的位置，以使花盆位置對(duì)實(shí)驗(yàn)的影響效應(yīng)最小。

1.5 各項(xiàng)指標(biāo)的測(cè)定

在幼苗進(jìn)入智能人工培養(yǎng)箱之前，測(cè)量每盆的總分蘗數(shù)、葉片數(shù)、株高，分析其差異性，結(jié)果發(fā)現(xiàn)這些指標(biāo)在帶菌和不帶菌植株之間均無(wú)顯著差異。在人工培養(yǎng)箱培養(yǎng)6周后，用LI-6400便攜式光合作用測(cè)定儀(LI-COR，Lincoln，USA)測(cè)定植株的最大凈光合速率、氣孔導(dǎo)度和蒸騰速率，測(cè)定時(shí)選取植株剛剛完全伸展開(kāi)的葉片，光強(qiáng)由LI-6400-02BLED紅藍(lán)光源自動(dòng)控制到1200 μmol·m-2·s-1，葉片水分利用效率由光合速率/蒸騰速率計(jì)算獲得[29]，收獲前統(tǒng)計(jì)每盆中的葉片數(shù)、分蘗數(shù)和株高。在收獲時(shí)，將地上部分和地下部分分開(kāi)，取一定量的根系，洗凈后放入裝有蒸餾水的無(wú)色透明塑料盤(pán)中，用EPSON 1680掃描儀(Epson，Long Beach，USA)以400 dpi分辨率掃描獲取根系圖像，并以WinRHIZO軟件分析得到相關(guān)數(shù)據(jù)。將地上部和地下部烘干稱重，計(jì)算生物量和根冠比。所得數(shù)據(jù)采用SPSS 19.0軟件進(jìn)行統(tǒng)計(jì)處理。

2 結(jié)果與分析

2.1 種子萌發(fā)

所有種子均在第3天開(kāi)始發(fā)芽，直至第12天后發(fā)芽數(shù)量不再增加。隨著CO2濃度的增加，帶菌和不帶菌種子的發(fā)芽率和發(fā)芽速度的變化不同(圖1)，表現(xiàn)在正常CO2濃度下，帶菌種子的發(fā)芽率和發(fā)芽速度均顯著高于不帶菌種子；而在高濃度CO2處理下，與正常CO2濃度相比，帶菌種子的發(fā)芽率和發(fā)芽速度無(wú)顯著變化，而不帶菌種子的發(fā)芽率和發(fā)芽速度均顯著下降，即CO2濃度增加使得帶菌和不帶菌種子的發(fā)芽率和發(fā)芽速度之間的差異變得更大。

圖1 不同CO2濃度下內(nèi)生真菌感染對(duì)羽茅種子發(fā)芽率和發(fā)芽速度的影響Fig.1 Effects of endophyte infection on seed germination rate and germination speed of Achnatherum sibiricum under different CO2 concentrations字母不相同表示差異顯著(Plt;0.05)

2.2 幼苗生長(zhǎng)

羽茅的營(yíng)養(yǎng)生長(zhǎng)受CO2濃度和養(yǎng)分供應(yīng)的交互影響(表1，圖2)。在正常CO2濃度下，羽茅的葉片數(shù)和地上部分生物量均以充足養(yǎng)分供應(yīng)組最優(yōu)，缺氮組最差，缺磷組居中；在高濃度CO2處理下，羽茅的生長(zhǎng)狀況與養(yǎng)分供應(yīng)的關(guān)系雖然與正常CO2處理組相似，但與正常CO2處理組相比，充足養(yǎng)分供應(yīng)顯著促進(jìn)了羽茅的營(yíng)養(yǎng)生長(zhǎng)，而缺氮和缺磷組羽茅的生長(zhǎng)并沒(méi)有隨CO2濃度的提高而增加。內(nèi)生真菌感染顯著提高了宿主植物的最大凈光合速率和水分利用效率(圖3)，且內(nèi)生真菌對(duì)宿主植物的這一有益作用不受CO2濃度和養(yǎng)分供應(yīng)的影響。

表1不同CO2濃度和養(yǎng)分處理下內(nèi)生真菌感染對(duì)羽茅影響的三因素方差分析

Table1Three-wayANOVAforgrowthcharactersofendophyte-infected(E+)orendophyte-free(E-)AchnatherumsibiricumundervariousconditionsofCO2andnutrientsavailability

葉片數(shù)Leafnumber分蘗數(shù)Tillernumber株高Height地上干重Shootdryweight地下干重Rootdryweight總干重Totaldryweight根冠比Root∶shoot凈光合速率Netphotosyntheticrate氣孔導(dǎo)度Stomatalconductance蒸騰速率Evaporationrate水分利用效率WateruseefficiencyCO2(C)***NS**NS******NS**養(yǎng)分(N)****************NSNS**內(nèi)生真菌(E)NSNSNSNSNSNSNS**NSNS**C×N*NSNS**NS*NSNSNSNSNSC×ENSNSNSNSNSNSNSNSNSNSNSN×ENSNSNSNSNSNSNSNSNSNSNSC×N×ENSNSNSNSNSNSNSNSNSNSNS

*，**分別表示Plt;0.05，0.01，NS表示差異不顯著

圖2 不同CO2濃度和養(yǎng)分處理對(duì)羽茅葉片數(shù)和地上生物量的影響Fig.2 Effects of CO2 and nutrients availability on leaf number and shoot biomass of Achnatherum sibiricum*表示差異顯著(Plt;0.05)

圖3 內(nèi)生真菌感染對(duì)羽茅葉片最大凈光合速率和水分利用效率的影響Fig.3 Effects of endophyte infection on maximum net photosynthetic rate and water use efficiency of Achnatherum sibiricum*表示差異顯著(Plt;0.05)

2.3 根系形態(tài)

根系表面積的大小與植物吸收能力密切相關(guān)，CO2濃度增加和充足的養(yǎng)分供應(yīng)都顯著增加了羽茅的根系表面積，而內(nèi)生真菌感染對(duì)這一參數(shù)無(wú)顯著影響(圖4)。為了明確粗細(xì)不同的各級(jí)根系對(duì)表面積變化的貢獻(xiàn)，本文按照根徑大小將根系劃分為如下3類(lèi)：即根徑 lt;0.45 mm、0.45—1.05 mm、gt;1.05 mm，計(jì)算了各根徑下根系長(zhǎng)度的百分比，結(jié)果發(fā)現(xiàn)(表2，圖5)，前兩個(gè)級(jí)別根系的比例只受到養(yǎng)分供應(yīng)的顯著影響，而后一個(gè)級(jí)別根系的比例除與養(yǎng)分供應(yīng)有關(guān)外，也與CO2濃度和內(nèi)生真菌狀態(tài)有關(guān)，在正常CO2濃度下，帶菌植株根徑gt;1.05 mm根系的比例顯著高于不帶菌植株，隨著CO2濃度的升高，帶菌植株根徑gt;1.05 mm根系所占比例無(wú)顯著變化而不帶菌植株該級(jí)別根系所占比例顯著升高，即CO2濃度升高導(dǎo)致帶菌和不帶菌不同根徑根系分配之間的差異縮小。

圖4 不同二氧化碳濃度、養(yǎng)分處理和內(nèi)生真菌感染狀態(tài)對(duì)羽茅根系表面積的影響Fig.4 Effects of CO2 concentration, nutrients availability and endophyte infection on root surface area of Achnatherum sibiricum字母不相同表示差異顯著(Plt;0.05)

Table2Three-wayANOVAforrootmorphologyofendophyte-infected(E+)orendophyte-free(E-)AchnatherumsibiricumundervariousconditionsofCO2andnutrientsavailability

總長(zhǎng)度Totallength總表面積Totalarea平均直徑Averagediameterlt;0.45mm0.45—1.05mmgt;1.05mmCO2(C)NS*NSNSNSNS養(yǎng)分(N)***********內(nèi)生真菌(E)NSNSNSNSNS**C×NNSNSNSNSNSNSC×ENSNSNSNSNS*N×ENSNSNSNSNSNSC×N×ENSNSNSNSNS**

圖5 不同CO2濃度下內(nèi)生真菌感染對(duì)羽茅根徑gt;1.05 mm根系比例的影響Fig.5 Effects of endophyte infection on the proportion of root length with a diameter of gt;1.05 mm of Achnatherum sibiricum under different CO2 concentrations*表示差異顯著(Plt;0.05)

3 討論

關(guān)于CO2濃度增加對(duì)種子發(fā)芽時(shí)間和發(fā)芽率影響的報(bào)道存在明顯的差異，有的報(bào)道為無(wú)直接聯(lián)系[30]，有的報(bào)道為有明顯的促進(jìn)作用[31]。內(nèi)生真菌是靠宿主的種子進(jìn)行傳播的，關(guān)于內(nèi)生真菌感染對(duì)宿主種子發(fā)芽率的影響，Clay[32]發(fā)現(xiàn)，帶菌的黑麥草和高羊茅種子，其發(fā)芽率均比相應(yīng)不帶菌種子高10%左右，在對(duì)黑麥草的研究中也發(fā)現(xiàn)，內(nèi)生真菌感染顯著提高了宿主種子的發(fā)芽勢(shì)和發(fā)芽率[33]，而在天然禾草中，彭清青等[34]發(fā)現(xiàn)，內(nèi)生真菌感染只是提高了宿主植物的發(fā)芽勢(shì)，而對(duì)宿主植物的發(fā)芽率無(wú)顯著影響，本研究中雖然在兩種CO2濃度處理下，帶菌種子的發(fā)芽率和發(fā)芽速度均顯著高于不帶菌種子，然而，我們的不帶菌種子是通過(guò)高溫殺菌的方法獲得的，因此內(nèi)生真菌對(duì)宿主發(fā)芽的促進(jìn)作用還需進(jìn)一步證實(shí)。值得注意的是，帶菌和不帶菌種子對(duì)于CO2濃度增加的反應(yīng)不同，CO2濃度增加對(duì)帶菌種子發(fā)芽率和發(fā)芽速度均無(wú)顯著影響，但CO2濃度增加顯著降低了不帶菌種子的發(fā)芽率和發(fā)芽速度，即CO2濃度升高加大了帶菌和不帶菌種子發(fā)芽率之間的差異。

關(guān)于CO2濃度增加對(duì)內(nèi)生真菌-禾草相互作用影響的研究目前還很少，Compant等[35]報(bào)道CO2濃度增加會(huì)提高高羊茅的內(nèi)生真菌感染率，與之相對(duì)照，Marks和Clay[36]和Chen等[23]發(fā)現(xiàn)CO2濃度增加對(duì)禾草-內(nèi)生真菌共生體的影響不大，本研究中內(nèi)生真菌感染顯著提高了宿主植物的凈光合速率和水分利用效率，但內(nèi)生真菌的這一有益影響不受CO2濃度的影響。內(nèi)生真菌對(duì)根系形態(tài)的影響與CO2濃度有關(guān)，在正常CO2濃度下，帶菌植株根徑gt;1.05 mm根系的比例顯著高于不帶菌植株，隨著CO2濃度的升高，帶菌植株上述根徑根系所占比例無(wú)顯著變化而不帶菌植株所占比例顯著升高，CO2濃度升高導(dǎo)致帶菌和不帶菌植株不同根徑根系分配之間的差異縮小，在他人的研究中，Compant等[35]報(bào)道CO2濃度升高使得宿主體內(nèi)的生物堿濃度下降，Hunt等[6]發(fā)現(xiàn)帶菌和不帶菌植物體內(nèi)碳水化合物濃度的差異也隨著CO2濃度的增加而減小，即CO2濃度升高縮小了帶菌和不帶菌幼苗生長(zhǎng)和代謝物之間的差異。

與菌根真菌-植物共生體相比，內(nèi)生真菌-禾草共生體對(duì)CO2濃度增加較為不敏感[23]，Hunt等[6]發(fā)現(xiàn)與正常CO2濃度相比，不帶菌植株中的可溶性蛋白濃度在高濃度CO2下下降約40%，而帶菌植株的可溶性蛋白濃度隨CO2濃度增加無(wú)顯著變化，本研究中也發(fā)現(xiàn)隨著CO2濃度的升高，帶菌種子的發(fā)芽率和根系分配均無(wú)顯著變化，而不帶菌植株的上述指標(biāo)均發(fā)生了顯著變化，內(nèi)生真菌感染有可能弱化CO2濃度增加對(duì)宿主植物的影響。當(dāng)然，本文只在種子發(fā)芽和幼苗生長(zhǎng)方面研究了感染內(nèi)生真菌的植物對(duì)CO2濃度增加的相應(yīng)，要闡明感染內(nèi)生真菌的植物對(duì)CO2濃度增加的綜合反應(yīng)及其反應(yīng)機(jī)制，還需要大量的研究工作。

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Physio-ecologicaleffectsofendophyteinfectiononthehostgrasswithelevatedCO2

SHI Zhibing, ZHOU Yong, LI Xia, REN Anzhi*, GAO Yubao

CollegeofLifeSciences,NankaiUniversity,Tianjin300071,China

Carbon dioxide (CO2) enrichment in the atmosphere stimulates photosynthetic activity and growth of C3plants. This may in turn alter the availability of photosynthates for plant-associated microbes, modifying the symbiosis formed such as mycorrhizae and plant-endophyte complexes. Documents are accumulating to show that elevated CO2increases hyphal growth and root colonization by arbuscular mycorrhizal fungi (AMF). Similar to AMF, endophytes are also fungi that are widely associated with plants but they mostly exist in the shoots rather than the roots of plants. Up to now, however, few studies have focused on the responses of endophyte-infected plants to elevated CO2. In the present study, we examined how elevated CO2affects endophytes and their functions, usingAchnatherumsibiricum(L.) Keng as model species.A.sibiricumis a caespitose perennial grass, widely distributed in the Inner Mongolia steppe and usually highly infected byNeotyphodiumendophytes. Seeds ofA.sibiricumwere collected from natural population in Hailar in the Northeast part of China. Detection of endophytes using the aniline blue staining method showed that endophyte infection frequency of the Hailar population was almost 100%. To eliminate the endophyte, we heat-treated a subset of randomly chosen seeds in a convection drying oven for 30 d at 60 ℃. Two experiments were performed in two growth chambers, with ambient (C-) and elevated (C+) CO2, separately. In Experiment 1, germination rates of endophyte-infected (E+) and endophyte-free (E-) seeds were compared under two different CO2concentrations. In Experiment 2, vegetative growth of E+ and E- seedlings was compared. The design of this experiment was completely randomized and a 2×2×3 factorial, with CO2concentration (C+ vs. C-), infection status (E+ vs. E-) and nutrients availability (N+P+, N-P+, N+P-, i.e. N and P supply, N deficiency P supply, N supply P deficiency) as the variables. There were five replicates per treatment group. The results showed that both the germination rate and germination speed of E+ seeds were not affected by elevated CO2while those of E- seeds were significantly decreased by elevated CO2. That is to say, elevated CO2increased the germination rate difference between E+ and E- seeds. Endophyte infection significantly improved maximum net photosynthetic rate and water use efficiency of the host grass. The vegetative growth was significantly affected by the interaction of elevated CO2and nutrients availability, but was not affected by endophyte infection. The beneficial improvement of elevated CO2on vegetative growth ofA.sibiricumoccurred only under N+P+ conditions. With N or P deficiency, the beneficial effect of elevated CO2on the growth did not exist. The root morphological characters were affected by the interaction of elevated CO2and endophyte infection. In the ambient CO2treatment, the proportion of root length with a diameter of gt;1.05 mm was significantly higher in E+ than in E- plants. With elevated CO2, no significant difference was found in the proportion of the root length stated above between E+ and E- roots. Elevated CO2decreased the difference of root morphology between E+ and E- plants. When compared with plant-AMF associations, the present study suggested that the grass-endophyte association was less sensitive to CO2enrichment. It is suggested that more experiments are needed to fully examine the potential impacts of elevated CO2on plant-endophyte associations.

elevated CO2;Achnatherumsibiricum; seed germination; root morphology

國(guó)家自然科學(xué)基金資助項(xiàng)目(31270463); 國(guó)家基礎(chǔ)學(xué)科人才培養(yǎng)基金資助項(xiàng)目(J1103503)

2013- 06- 08;

2013- 07- 23

*通訊作者Corresponding author.E-mail: renanzhi@ nankai.edu.cn

10.5846/stxb201306081432

師志冰，周勇，李夏，任安芝，高玉葆.CO2濃度升高條件下內(nèi)生真菌感染對(duì)宿主植物的生理生態(tài)影響.生態(tài)學(xué)報(bào),2013,33(19):6135- 6141.

Shi Z B, Zhou Y, Li X, Ren A Z, Gao Y B.Physio-ecological effects of endophyte infection on the host grass with elevated CO2.Acta Ecologica Sinica,2013,33(19):6135- 6141.