摘" " 要:【目的】云南會澤地區為我國四季草莓主產區,主要采取多年一栽模式,即一次定植連續多年收獲,后期產量逐年下降,多年生產后重新定植連作障礙問題十分嚴重。解析草莓多年一栽生產模式下的產量下降原因,能夠為該模式提質升級和可持續發展提供理論基礎。【方法】在盛果期對不同生產年份土壤取樣,檢測土壤有機質含量、pH、電導率以及主要礦質養分含量并比較分析;提取土壤微生物DNA,通過高通量測序分析細菌和真菌群落結構和功能變化,并與土壤理化性狀進行相關性分析。【結果】多年一栽模式下,土壤pH平均每年下降0.87,土壤電導率(EC)每年上升60.40%,第四年土壤有機質含量下降超過59%。微生物群落多樣性逐年降低,第4年土壤微生物Chao1指數下降41.8%,真菌多樣性下降52.5%;N循環相關細菌的相對豐度降低,大多數C循環與N循環細菌豐度與土壤有機質含量呈正相關,而與土壤EC呈負相關。同時,隨著收獲年限增加,FUNGuild分析顯示病原菌和腐生菌相對豐度呈增加趨勢,其中鐮孢菌屬為最主要病原菌,同時有益菌如共生真菌和叢枝菌根真菌相對豐度顯著降低。【結論】會澤地區特殊的栽培模式導致土壤酸化、土壤鹽漬化、有機質虧缺、土壤微生物群落結構失衡,從而導致土壤退化和草莓減產。
關鍵詞:草莓;多年一栽模式;產量下降;土壤退化
中圖分類號:S668.4 文獻標志碼:A 文章編號:1009-9980(2025)02-0376-15
Exploration of the reasons for yield decline in the perennial harvesting model of strawberries in Huize county of Yunnan province
LI Shuangtao1, SUN Rui 1#, WAN Hong2#, WEI Yongqing1, WU Ruishuang1, DONG Jing1, CHANG Linlin1, WEI Lingzhi1, TAO Pang2, XIONG Rong1, ZHONG Chuanfei1, GAO Yongshun1, ZHANG Hongli1, ZHANG Yuntao1, WANG Guixia1*, SUN Jian1*
(1Institute of Forestry and Pomology, Beijing Academy of Forestry and Pomology Sciences/Key Laboratory of Biology and Genetic Improvement of Horticultural Crops (North China), Ministry of Agriculture and Rural Affairs/Beijing Engineering Research Center for Strawberry/Beijing Engineering Research Center for Deciduous Fruit Trees/Key Laboratory of Urban Agriculture (North China), Ministry of Agriculture and Rural Affairs, Beijing 100093, China; 2Horticultural Research Institute, Yunnan Academy of Agricultural Sciences, Kunming 650205, Yunnan, China)
Abstract: 【Objective】 Strawberries (Fragaria × ananassa Duch.) are typically planted annually with annual disinfection treatments to suppress pests and diseases. In contrast, strawberries are cultivated perennially in Huize, Yunnan, China, fruits can be harvested for 3-5 years after planting. This strategy results in low carbon emissions and significantly reduces the labor input and the cost of nursery supplies, chemical fumigants, and plastic film. Under this cultivation system the yield and profits of strawberry decreases from the third year after planting, and the production becomes unprofitable in the fifth year. Soil degradation is suspected to be the reason for the inability to sustain stable production. This study aimed to survey the factors affecting the soil degradation in perennial cultivation (PC) area. 【Methods】 We examined the soil nutrient traits and the microbial structure of four strawberry fields following perennial cultivation in this area, the SOM (Soil organic matter) content, pH, and key mineral nutrient contents of the strawberry (N, P, K, Ca, Mg, Cu, Zn, and Mo) were assessed. The soil microbial community was analyzed by high-throughput amplicon sequencing based on Illumina MiSeq PE300 platform. The soil microbial functions were predicted to determine the effects of PC on soil microbial communities. The microbial function focusing on C-cycling and N-cycling processes were assessed to determine the soil productivity tendency. 【Results】 Our results indicated that PC resulted in significant soil acidification, salinization, and organic matter deficiency. The average soil pH was 5.58±0.67 in the first year and decreased to 4.35±0.53, 3.57±0.28, and 2.98±0.04 in the second, third, and fourth years, respectively. The average SOM content was 0.66%±0.14% in the first year and 0.27%±0.03% in the fourth year (a 25.6% decrease per year). The average soil EC was 328.5±113.3 in the first year and 923.7±158 in the fourth year (a 41.1% increase per year). The Ca content showed a generally decreasing trend at most sites, and the lowest Ca content was found in the fourth harvesting year of JC1 (Jiache Town 1, 0.878 g·kg-1, 74.4% lower than that in the first harvesting year). PC also significantly affected the soil microbial community. The Chao1 richness, Shannon, and ACE indices of the bacterial communities in the soils differed significantly among the harvesting years. The Chao1 richness decreased significantly by 13.6% from the first to the second harvesting year, 38.2% to the third harvesting year, and 41.8% to the fourth harvesting year. The greatest decline in the Chao1 richness index was observed in the fourth harvesting year of JC1 (52.2%) and the third harvesting year of JC2 (Jiache Town 2, 52.5%). The Chao1 richness and ACE indices for fungal diversity differed among the harvesting years at all sites except for XJ (Xinjie Street). The ACE index decreased by 28.7% from the first to the second year of DB (Daibu Town), 25.0% from the first to the second year of JC2, and 31.7% from the second to the third year of JC1. The fungal diversity of XJ was lower than those at the other three sites. The average ACE index of the XJ samples was 578.7, which was 37.2% lower than that of DB, 25.5% lower than that of JC1, and 33.2% lower than that of JC2. The relationship between the microbial community and environmental variables was analyzed by RDA. The RDA1 (34.33%) and RDA2 (21.96 %) explained 56.29% of the total variation in bacterial community structure. For fungi, the RDA1 (26.21%) and RDA2 (12.98 %) explained 39.19% of the total variation. The SOM, pH, and EC were the dominant contributors to the variation of bacterial community, accounting for 59.8%, 58.9%, and 51.8%, respectively. The soil EC and SOM were the most important contributors to the variation of fungal community, accounting for 83.3% and 82.7%, respectively. FAPROTAX was utilized to determine the functional effects of PC on the bacterial community. The relative abundance of N-cycling processes related bacteria showed a decreasing trend. The correlation analysis showed that most C-cycling and N-cycling processes were significantly positively correlated with the SOM content and negatively correlated with the EC, whereas most C-cycling processes was significantly positively correlated with pH. The FUNGuild analysis showed a significantly decreasing trend for that relative abundance of symbiotroph fungi and arbuscular mycorrhizal fungi (AMF), and the relative abundance of Fusarium, the main pathotroph of strawberry, showed a significantly increasing trend. 【Conclusion】 The PC of strawberries resulted in significant soil acidification, salinization, SOM deficiency, and shaped microbial community structures. Of both bacteria and fungi, the community diversity decreased by year, while symbiotroph fungi and AMF showed a significantly decreasing trend in the PC. The soil microbial function prediction suggested that PC reduced the N cycles related bacterial functions, while most C-cycling and N-cycling processes were positively correlated with the SOM, and negatively correlated with the EC. The PC of strawberries showed a significant negative impact not only on soil physicochemical properties but also on microbial community and function. Thus, for this perennial cultivation strategy of strawberries, maintaining soil physicochemical properties and soil microbial structure and function would be the key problem to solve for sustainable development.
Key words: Strawberry; Perennial harvesting; Yield decline; Soil degradation
草莓是世界各地廣泛種植的漿果,我國已經是世界第一草莓生產大國,大部分地區為冬春季生產。自2012年以來,我國四季草莓生產迅速發展,目前面積已達6700 hm2,有效填補了夏季草莓鮮果供給缺口。云南省會澤縣是我國四季草莓主產區,產量全國占比超過70% [1],該區1月平均氣溫在4.6 ℃左右,既能夠保障草莓自然越冬又能夠打破植株休眠,從而實現多年結果。該地區四季草莓生產主要采用多年一栽模式,一次定植后可以收獲3~7 a(年),顯著減少了勞動力投入和生產苗用量,是一種低成本和相對低碳的生產模式。草莓是連作障礙現象最明顯的果樹,在普遍的一年一栽制生產模式下,主要表現為成活率下降、長勢不整齊、結果期推遲、產量低、品質下降和病害多發等現象。在不消毒的情況下,草莓重茬死苗問題嚴重,部分重茬栽培地死苗在70%以上,3~4次補苗仍難以補齊,嚴重影響經濟效益[2]。發達國家草莓生產長期以化學熏蒸處理重茬土[3],主要使用溴化甲烷和氯化苦等熏蒸劑,但該方法也將大多數微生物殺死,對致病微生物不具有選擇性,同時降低有益微生物水平。目前我國一年一栽制草莓生產中,普遍采用夏季高溫期悶棚配合使用石灰氮[4]。在云南會澤地區的多年一栽制生產模式下,從第3年開始普遍出現草莓產量下降、病害多發問題,拉秧后重新定植出現嚴重的死苗等連作障礙問題。由于該地區多采用秋冬季收獲期結束后整地、次年早春定植的生產模式,不具備高溫悶棚作業的條件,因此解析該地區草莓生產土壤的退化機制對優化栽培措施、減緩重茬危害十分必要。
筆者在會澤縣選取4個取樣點,對多年一栽制草莓生產園土壤的有機質(soil organic matter,SOM)含量、土壤電導率(electrical conductivity,EC)、pH和礦質養分(N、P、K、Ca、Fe、Mn、Mg、Cu、Zn和Mo)含量進行了檢測。基于Illumina MiSeq PE300平臺,通過高通量擴增子測序分析土壤微生物群落、預測土壤微生物功能,以確定多年一栽制草莓生產對土壤微生物群落結構和碳循環、氮循環過程微生物功能的影響,綜合解析土壤生產力退化的原因,以期為該地區草莓優質高產提供理論依據。
1 材料和方法
1.1 試驗地概況
試驗地點位于云南省會澤縣,屬典型的溫帶高原季風氣候,年平均晴日225 d,年日照2100 h,年平均氣溫12.7 ℃,年均降雨量54億m3。其中待補鎮海拔2600 m、駕車鄉海拔2400~2460 m,新街街道海拔2260 m。
1.2 材料
采樣園區土壤均為紅壤土,前茬作物均為玉米;種植草莓品種均為蒙特瑞,草莓生產在南北向鋼架大拱棚設施進行避雨栽培,首次定植每666.7 m2加入發酵農家肥4~5 t,按照壟高55 cm、上部壟面寬度35 cm、基部壟面寬度45 cm的梯形高壟起壟。3月中旬雙行定植,90 000~97 500 株·hm2,采用滴灌進行肥水一體化管理,肥料以化肥為主,每公頃每年使用20-20-20 NPK硫酸鉀型水溶平衡肥0.75~1.2 t,高鉀型水溶平衡肥0.9~1.2 t。每年果品生產至11月結束,然后去除棚膜,植株自然越冬后去除老葉,進行病蟲害管理和植株修整,進入下一年度生產管理。
1.3 試驗設計
選擇待補鎮(DB)、駕車鄉1(JC1)、駕車鄉2(JC2)、新街街道(XJ)的4個草莓園區不同連作年限的土壤進行試驗。待補鎮園區取種植1~4 a(年)土壤(DB Year 1,DB Year 2,DB Year 3,DB Year 4),駕車鄉園區分別取種植1~4 a土壤(JC1 Year 1,JC1 Year 2,JC1 Year 3,JC1 Year 4)及1~3 a土壤(JC2 Year 1,JC2 Year 2,JC2 Year 3),新街街道園區取種植1~3 a土壤(XJ Year 1,XJ Year 2,XJ Year 3)。
1.4 測定指標樣品采集及測定方法
取樣均在7月盛果期進行,在每個園區采集不同收獲年份的土壤樣品,在南北方向相鄰的兩株草莓中間點以土鉆取樣,隨機選擇6個采樣點進行混合取樣作為1份樣品,每個園區單個收獲年份采樣3份,取樣深度0~20 cm。土壤樣品過2 mm篩后冷藏保存運輸至實驗室用于進一步分析。樣品分為兩部分,分別用于土壤DNA提取和化學性質分析。園區草莓單位面積年產量為4月底至11月底累計值。
土壤樣品陰干后進行土壤電導率、pH和N、P、K、Ca、Fe、Mn、Mg、Cu、Zn、Mo等礦質養分含量測定,使用改進的凱氏定氮法(Kjeldahl方法)和中國國家標準系統(HJ 717—2014)測量總N含量[5]。使用電感耦合等離子體(inductively coupled plasma,ICP)光譜法和中國國家標準系統(HJ 803)分析P、K、Ca、Fe、Mn、Mg、Cu、Zn和Mo等其他元素的含量[6]。
1.5 土壤微生物結構分析
使用E.Z.N.A.?土壤DNA試劑盒(Omega Bio-tek,美國)從42個樣品中提取總DNA。使用NanoDrop? Lite Plus分光光度計(Thermo Scientific Inc.,美國)和1.0%瓊脂糖凝膠電泳確定DNA的質量和濃度。使用引物對338F(ACTCCTACGGGAGGCAGCAG)和806R(GGACTACHVGGGTWTCTAAT)擴增細菌16S rRNA V3-V4區,使用ITS1-1F(CTTGGTCATTTAGAGGAAGTAA)和ITS2R(GCTGCGTTCTTCATCGATGC)擴增真菌ITS1區。PCR(Polymerase Chain Reaction,聚合酶鏈式反應)反應體系和擴增循環條件參照前人研究工作[7]。
PCR產物以2%瓊脂糖凝膠提取和純化,使用GenEluteTM凝膠提取試劑盒(Sigma-Aldrich Co.,美國);使用NanoDrop? Lite Plus分光光度計(Thermo Scientific Inc.,美國)定量。將純化的擴增子以等摩爾量混合,并按照Majorbio Bio-Pharm Technology Co. Ltd.(上海,中國)使用的標準方法在Illumina MiSeq PE300平臺上測序。
獲得的原始數據通過質控、過濾、去重,利用UPARSE 7.1根據97%的序列相似性水平將優化序列聚類成OTUs(operational taxonomic units)[8]。使用RDP 2.2進行OTU的分類學信息分析[9],并與16S rRNA基因數據庫(silva138/16s_bacteria)或ITS數據庫(unite8.0/its_fungi)進行比對,以0.7作為置信度閾值。使用HMMER、EPA-NG和Gapp對OTU代表性序列對齊和比較。使用BugBase預測細菌群落的表型功能,并使用FAPROTAX(Functional Annotation of Prokaryotic Taxa)預測細菌群落的功能變化[10]。使用FUNGuild預測真菌群落功能[11]。
1.6 數據分析
本研究中土壤的基本生物信息學分析是在Majorbio云平臺(https://cloud.majorbio.com)上進行的。從OTU信息中獲得稀釋曲線,使用Mothur v1.30.1計算α多樣性指數[12]。使用Vegan v2.5-3包進行主坐標分析(principal coordinate analysis,PCoA)和冗余分析(redundancy analysis,RDA)[13],以研究微生物群落相似性和對土壤物理化學性質的響應。
2 結果與分析
2.1 草莓多年一栽模式對土壤化學性質的影響
由圖1可以看出,所有測試園區的土壤pH和SOM含量從第一年到第四年呈現顯著下降趨勢,而土壤EC呈顯著上升趨勢。第一年土壤平均pH為5.58,在第二年、第三年和第四年分別下降到4.35、3.57和2.98。SOM含量在第一年為0.66%,在第四年為0.27%,平均每年下降0.13個百分點。土壤EC在第一年為328.5 μS·cm-1,在第四年為923.7 μS·cm-1,平均每年增加60.40%,以上結果表明多年生產導致土壤有機質含量降低、土壤酸化和鹽漬化。同時,大多數園區的Ca含量總體呈下降趨勢,最低的Ca含量出現在JC1第四年(0.878 g·kg-1,比第一年低74.4%)。
如圖2所示,與第一年相比,隨著草莓種植年限的延長,JC1土壤中總N和P含量先升后降再升,Fe和Cu含量先降后升,K和Zn含量先升后降;JC2土壤中N、P、Fe、Mn含量下降,Mg含量上升;DB土壤中N、P、K含量先降后升,Fe、Mg、Mn、Zn、Cu含量先升后降;XJ土壤中K含量上升,Fe、Mg、Mn、Zn、Cu、Mo含量下降。各取樣點土壤礦質含量變化趨勢各異可能是管理措施差異所致。
土壤化學性質參數的相關性分析表明,pH與SOM含量呈顯著正相關(R=0.502),EC與pH呈顯著負相關(R=-0.573);EC與SOM含量呈顯著負相關(R=-0.769)。總N含量(R=-0.428)和P含量(R=-0.583)與pH呈顯著負相關;Mg含量與pH呈顯著正相關(R=0.410)。K含量與EC呈顯著正相關(R=0.537);Fe含量(R=-0.512)、Cu含量(R=-0.441)、Zn含量(R=-0.484)和Mo含量(R=-0.521)與EC呈顯著負相關。
2.2 不同年份草莓栽培生產對土壤微生物多樣性的影響
原始數據經過濾后,獲得了3 317 973個細菌序列和2 558 395個真菌序列。在97%的相似性水平下,獲得了26 644個細菌OTUs和5264個真菌OTUs。細菌OTUs屬于47個門、160個綱、410個目、679個科和1470個屬。真菌OTUs屬于16個門、58個綱、134個目、319個科和727個屬。細菌群落的Chao1指數、Shannon指數和ACE(Abundance-based Coverage Estimator)指數在收獲年份之間顯著不同(圖3-A~C),Chao1指數第二年顯著下降了13.6%,第三年下降了38.2%,第四年下降了41.8%。在JC1的第四年和JC2的第三年,Chao1指數的最高降幅分別為52.2%和52.5%。在除XJ外的取樣點,真菌多樣性的Chao1指數和ACE指數在不同生產年份之間存在顯著差異。從第一年到第二年,DB取樣點的ACE指數顯著下降了28.7%,JC2顯著下降了25.0%,從第二年到第三年,JC1顯著下降了31.7%。XJ的真菌多樣性低于其他3個地點(圖3-D~F)。XJ樣本的平均ACE為578.7,比DB1低37.2%,比JC1低25.5%,比JC2低33.2%。
細菌群落在門水平上的優勢物種組成相似,變形菌門(Proteobacteria)、放線菌門(Actinobacteriota)和綠彎菌門(Chloroflexi)在所有土壤樣本中占61.1%~76.7%,其他門細菌在第三年到第四年呈現下降趨勢。與第一年相比,酸桿菌門(Acidobacteriota)在JC1的第四年下降到48.5%,芽單胞菌門(Gemmatimonadota)在JC2的第三年下降到20.2%,黏菌門(Myxococcota)和疣微菌門(Verrucomicrobiota)在JC1的第四年分別下降到4.3%和5.45%。值得注意的是,在DB和JC1,從第一年到第四年,厚壁菌門(Firmicutes)的比例分別增加了125.9%和181.1%(圖4-A)。在所有土壤樣本中,子囊菌門(Ascomycota)是門水平上的優勢真菌,平均為71.1%。與第一年相比,被孢霉門(Mortierellomycota)在JC1從30.0%下降到第四年的5.8%。壺菌門(Chytridiomycota)在3~4年的收獲期間呈現下降趨勢,在不同地點與第一年相比分別下降了24.4%和63.3%(圖4-B)。
2.3 土壤化學性質與微生物群落結構的關聯分析
通過RDA(圖5-A、B)分析了微生物群落與環境變量之間的關系。RDA1和RDA2解釋了細菌群落結構總變異的56.29%。對于真菌群落結構,RDA1和RDA2解釋了總變異的39.19%。SOM、土壤pH和土壤EC是細菌群落變異的主要貢獻者,分別占59.8%、58.9%和51.8%。土壤EC和SOM是真菌群落變異的最重要貢獻者,分別占83.3%和82.7%。
基于Spearman相關性分析,圖5-C、D顯示了土壤性質與相對微生物豐度(屬水平前50)之間的關系。結果表明,細菌屬中芽單胞菌屬(Gemmatimonas,R=0.78)、嗜酸棲熱菌屬(Acidothermus,R=-0.74)和慢生根瘤菌屬(Bradyrhizobium,R=0.71)與SOM含量呈顯著相關。鞘氨醇單胞菌屬(Sphingomonas,R=0.89)、Granulicella(R=-0.83)、Chujaibacter(R=-0.81)和Conexibacter(R=-0.76)與pH呈顯著相關。Chujaibacter(R=0.66)和Gemmatimonas(R=-0.64)與EC顯著相關。Conexibacter(R=-0.81)、硝化螺旋菌屬(Nitrospira,R=0.74)、Gaiella(R=0.72)和鞘氨醇單胞菌屬(Sphingomonas,R=0.71)與Ca含量呈顯著相關。對于真菌屬,青霉屬(Penicillium,R=0.74)、被孢霉屬(Mortierella,R=-0.70)和木霉屬(Trichoderma,R=0.69)與EC呈顯著相關。青霉屬(Penicillium,R=-0.86)、螺旋聚孢霉屬(Clonostachys,R=0.71)和木霉屬(Trichoderma,R=-0.70)與SOM含量呈顯著相關。
2.4 草莓4年栽培生產對土壤微生物群落功能的影響
2.4.1 多年生產對細菌群落功能的影響 利用BugBase預測細菌群落的表型功能,結果表明從第一年到第四年,厭氧菌、兼性厭氧菌、革蘭氏陰性菌和形成生物膜的細菌相對豐度呈現下降趨勢;潛在致病菌、逆境耐受菌等相對豐度呈現上升的趨勢(圖6-A)。
利用FAPROTAX分析多年生產對細菌群落功能的潛在影響,結果表明,與C循環相關的細菌,如化學異養菌、好氧化學異養菌和纖維素分解菌的相對豐度呈現顯著提高的趨勢,而與芳香化合物降解、光養、光異養、烴降解和幾丁質分解相關的細菌相對豐度呈現下降趨勢(圖6-B);與N循環相關的細菌,如硝酸鹽還原菌、亞硝酸鹽氨化菌和硝酸鹽氨化菌的相對豐度呈現提高趨勢,而與脲酶、固氮、反硝化、亞硝酸鹽反硝化和一氧化二氮反硝化相關的細菌相對豐度呈現下降趨勢(圖6-C)。相關性分析表明,大多數C循環和N循環細菌相對豐度與SOM含量呈顯著正相關,與EC呈負相關,并且大多數C循環過程細菌相對豐度與pH呈顯著正相關(圖6-D~E)。
2.4.2" " 四年生產對真菌群落潛在功能的影響" " FUNGuild分析顯示,病原菌和腐生菌相對豐度整體上呈提高趨勢(圖7-A、B),而共生菌相對豐度整體上呈下降趨勢(圖7-C)。在JC1,腐生菌相對豐度從第一年的23.23%顯著提高到第四年的51.10%,共生菌相對豐度從第一年的42.31%顯著下降到第四年的9.88%,叢枝菌根真菌(Arbuscular mycorrhizal fungi,AMF)從第一年的0.24%顯著下降到第四年的0%(圖7-D)。值得注意的是,在XJ,病原菌從第一年的21.25%提高到第三年的43.20%(圖7-A)。
2.5 不同年份產量與土壤化學指標和微生物指標的相關性
產量分析表明,JC1、JC2、DB試驗園區產量呈先上升后下降趨勢,XJ試驗園區產量隨著種植年限增加逐漸降低,且各試驗地點均出現從第三年開始產量下降的趨勢(表1)。相關性分析表明,產量與Ca、Mn、Zn和有機質含量及pH呈正相關,與P含量和EC呈負相關,與N和K含量相關性不顯著;以產量為變量進行的偏最小二乘回歸分析顯示,VIP值大于1的自變量分別為EC(1.738)、pH(1.577)、有機質含量(1.359)、鈣含量(1.206)、鋅含量(1.203),多年一栽模式草莓產量下降的主要原因是鹽分升高、土壤酸化、有機質虧缺和鈣、鋅等中量元素虧缺。
以產量為變量,真菌屬豐度為自變量進行的偏最小二乘回歸分析(表2)顯示,對產量影響權重最高的真菌為鐮孢菌屬Fusarium,該分析結果與田間觀察到的尖孢鐮刀菌枯萎病一致,說明導致產量下降的主要病原菌為鐮孢菌屬真菌。值得注意的是,其他常見真菌病害如炭疽病病原菌Colletotrichum、紅葉病病原菌Pestalotiopsis、黃萎病病原菌Verticillium在各年份差異并不顯著。
3 討 論
3.1 草莓多年一栽模式對土壤理化性質的影響
本研究發現,草莓多年一栽模式導致土壤pH和SOM含量呈現逐年下降趨勢,而土壤EC呈現上升趨勢;有機質含量平均每年下降0.13個百分點,導致土壤碳虧缺。前人研究表明,長期耕作系統中土壤有機碳普遍下降,需要施用有機肥料來維持土壤生產力[14],果園的地面覆蓋管理對土壤碳代謝有顯著影響,長期施用生物有機肥料和果園生草能夠顯著提高SOM含量,改變土壤微生物群落結構,并提高土壤生產力[15-16]。在定植前施足有機肥或通過滴灌補充有機態肥料是補充土壤有機質的重要手段。本研究中該生產模式中以化肥投入為主、有機肥投入不足,但是田間觀察葉片形態未有明顯的缺素表現;在植株方面,每年進行植株整理、保留1~3個分蘗,分蘗會重新發出根系,因此整體存活植株的生長勢差異不明顯,從不同年份礦質養分含量對比可以發現,除有機質以外,其他主要養分含量均在合理區間。
在本研究中觀察到了明顯的土壤酸化和鹽漬化現象。土壤pH在第四年下降到2.98。土壤酸化降低了磷的生物有效性,并增加了作物被鐮刀菌感染的風險[17]。前人研究表明,N肥的過度使用對區域土壤酸化有顯著作用,在25年的常規施肥后觀察到的土壤pH下降2.2[18]。值得注意的是,本研究中每年pH下降0.87。此外,土壤EC每年上升60.40%,SOM含量每年減少0.13個百分點,表明在多年一栽模式草莓生產中,土壤酸化、鹽漬化、有機質含量下降是土壤退化的主要特征。
3.2 土壤微生物多樣性變化
微生物對農業可持續發展至關重要,因為其在養分轉化、運輸和SOM降解中起著關鍵作用[19]。試驗結果表明,多年一栽模式顯著影響了土壤微生物群落結構。Chao’指數、Shannon指數和ACE指數反映了細菌和真菌微生物多樣性的逐年下降。環境因素對土壤細菌和真菌群落的影響不同,對于細菌群落結構,SOM、pH和EC是變異的主要貢獻者,分別占59.8%、58.9%和51.8%。另一方面,對于真菌群落,土壤EC和SOM是主要的變異貢獻者,分別占83.3%和82.7%。這一發現與先前的研究結果一致,土壤酸化、礦物和氮肥施用是影響土壤微生物群落和功能的主要因素[20],土壤鹽漬化指標,如pH和EC對細菌群落結構有顯著影響[21]。
在屬水平上,青霉菌屬(Penicillium)和木霉屬(Trichoderma)與EC呈顯著正相關,與SOM含量呈顯著負相關,這兩個屬的豐度在多年生產中增加。木霉屬是一種絲狀真菌屬,以其他真菌為食,作為植物生長促進菌影響植物對非生物和生物脅迫的響應[22]。青霉菌屬是一種環境中常見的真菌屬,許多青霉菌屬真菌增強了根對養分(如可溶性P)的吸收[23],并在鹽脅迫下產生植物激素,如赤霉素[24]。在連續種植黃瓜的根際土壤中,青霉屬與農藝性狀顯著相關[25]。一些青霉屬真菌顯示出對某些病原體的天然拮抗活性,青霉屬種能有效控制由交鏈孢霉屬(Alternaria sp.)和鐮刀菌屬(Fusarium sp.)真菌引起的香蕉腐爛病[26]。值得注意的是,田間觀察顯示鐮刀菌引起的枯萎病是草莓多年連作導致田間死苗的常見原因。本試驗結果表明,青霉屬、木霉屬等微生物群體對保護植物免受土壤病原體侵害以及緩解土壤酸化和鹽漬化引起的脅迫至關重要。未來研究中應關注第四年或更長年份田間正常生產的植株根際微生物組成和植物生理特征,并嘗試從中分離和純化培養促生菌,如木霉屬和青霉屬微生物,從而開發新型菌劑用于生產。
3.3 土壤微生物功能變化
革蘭氏陰性菌依賴于從植物中獲得的簡單C化合物[27]。在本研究中,革蘭氏陽性菌與革蘭氏陰性菌的比例增加表明有機土壤中相對C可用性下降和生態系統生產力下降,這與每年SOM含量下降的現象一致。病原菌和腐生菌比例的增加以及共生菌比例的下降與病害加重和產量下降的現象一致。此外,隨著收獲年份的增加,叢枝菌根真菌(AMF)的豐度顯著下降,AMF能夠促進植物生長和產量提高,特別是在鹽脅迫等非生物脅迫下[28-29]。AMF比例的下降表明隨著年份增加,草莓生長的土壤微生物環境惡化。
4 結 論
在本試驗條件下,發現多年一栽模式草莓生產產量呈現下降趨勢,產量與Ca、Mn、Zn、有機質含量及pH呈正相關,與P含量和EC呈負相關,與N和K含量相關性不顯著;多年一栽模式草莓產量下降的主要原因是鹽分升高、土壤酸化、有機質虧缺和鈣、鋅等中量元素虧缺,因此在施肥過程中應增加對有機質與鈣、鋅等中量元素的補充。同時產量下降與土壤微生態的惡化相關,具體表現為土壤微生物群落多樣性降低、病原菌水平提高、與N循環相關的功能弱化、AMF比例下降等,其中鐮孢菌屬真菌是導致產量下降的核心病原菌因素。
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收稿日期:2024-09-04 接受日期:2024-11-11
基金項目:現代農業產業技術體系(CARS-24-A-14);北京農林科學院科技創新能力建設專項基金(KJCX20230118)
作者簡介:李雙桃,女,助理研究員,博士,主要從事草莓非生物脅迫響應機制研究。E-mail:lishuangtao90@163.com。#為共同第一作者。
*通信作者Author for correspondence. E-mail:sjroad@126.com;E-mail:wgxia1972@163.com