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放牧是草地的主要利用方式之一,主要通过牲畜的采食、践踏、卧息和排泄粪便等方式对地表植被、土壤养分以及土壤微生物产生影响[1]。土壤微生物在有机质的分解、养分循环与转化等方面具有重要作用[2],其数量和群落功能多样性能够在一定程度上指示土壤质量及其可持续利用性[3]。研究放牧与土壤微生物的关系,有助于揭示过度放牧导致草场沙漠化的机制。根际是植物、土壤、微生物之间进行物质和能量交换的关键区域,是植物和土壤相互作用的重要界面,诸多学者对植物根际与非根际土壤的养分、微生物数量及群落组成的差异性开展了大量的研究[4-7]。邱权等[8]综合比较了4种人工灌木丛根际和非根际土壤的特性,发现土壤酶活性和微生物数量呈现出根际高于非根际;对宁夏宁南山区猪毛蒿Artemisia scoparia,百里香Thymus mongolicus等9种典型植物[9]和内蒙古羊草Leymus chinensis,大针茅Stipa grandis和冷蒿Artemisia frigida等典型植物[10]进行研究,表明大多数植物的根际土壤微生物数量、活性及多样性等均高于非根际土壤,是由于植物物种差异所引起。冷蒿是菊科Compositae蒿属Artemisia植物,多年生小半灌木,是退化草场的典型植物,具有强烈的耐牧生存能力,高强度放牧干扰后仍能够生长繁殖并维持一定的生产力,这与其自身的生物学特性[11]及根系代谢产物[12]对土壤微环境的调控密切相关。目前,关于放牧干扰对冷蒿根际土壤微生物群落多样性影响的研究尚未报道。本研究拟采用微生物传统培养法和Biolog-ECO板技术,对不同放牧强度下冷蒿根际土壤化学性质、微生物数量及其群落功能多样性进行研究,分析冷蒿根际土壤微生物数量及代谢功能多样性对放牧干扰的响应,探讨冷蒿耐牧性与土壤微生物群落多样性之间的关系,为揭示冷蒿成为草场退化阻击者提供土壤生态学方面的理论依据。
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由表 1可知:放牧对2种土壤中的有机质、全磷、碱解氮、速效钾和pH值具有极显著影响,对全氮和全钾具有显著影响。放牧特别是重度放牧后,NRS土壤中各养分质量分数均显著增加,pH值显著下降;ARS土壤中有机质和其他养分质量分数均显著增加,重度放牧后,有机质、全氮、全磷、碱解氮、速效磷和速效钾与对照相比分别增加20.0%,29.1%,17.7%,13.0%,3.4%和6.7%,但pH值显著降低,重度放牧后呈弱碱性;相同放牧处理下ARS土壤各养分质量分数均显著高于NRS土壤,pH值明显低于NRS土壤。
表 1 不同放牧强度下土壤化学性质
Table 1. Soil chemical properties under different grazing intensity
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不同放牧强度下2类土壤中微生物的总量、主要类群数量差异显著(图 1),微生物总量以LG-ARS和ck-ARS最高,分别为24.6×106个(cfu)·g-1和20.4×106个(cfu)·g-1,显著高于其他处理组。三大类异养微生物数量在各土壤微生物组成中均以细菌类群占绝对优势,但细菌、真菌、放线菌间的组成比例差异较大,其中细菌占微生物总数88%~95%,放线菌其次,占微生物总数的3%~12%,真菌最少。放牧后NRS土壤中细菌、真菌数量显著下降,而ARS土壤中真菌数量增加显著,且显著高于NRS,细菌数量在轻度放牧后显著增加,重度放牧后下降。
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图 2为土壤微生物群落代谢活性(AWCD)随培养时间的变化曲线:在培养初始的24 h内土壤微生物活性较低,24 h后AWCD值快速增长,168 h时各处理的AWCD值均达到最大,利用碳源能力的顺序为LG-ARS>ck-ARS>ck-NRS>LG-NRS>HG-ARS>HG-NRS,平均值分别为0.999,0.918,0.861,0.769,0.695,0.310;相同牧压下ARS土壤微生物的AWCD值均显著高于NRS,对照、轻度和重度放牧后AWCD值分别是NRS的1.07倍、1.30倍和2.24倍。
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放牧强度不同,土壤微生物对不同种类碳源利用强度存在显著差异(表 2);冷蒿根际土壤中,轻度放牧可增加微生物对不同种类碳源的利用能力,碳源代谢的优势群落与对照相同,依次为糖类>氨基酸>羧酸>聚合物>胺类>酚酸代谢群落,土壤微生物群落结构稳定;重度放牧后,微生物对各类碳源的利用率显著下降,优势群落发生改变;冷蒿非根际土壤中,放牧强度增强,土壤微生物对不同种类碳源利用率变化较大,未显示一定的规律性,土壤微生物群落功能多样性变化很大,不稳定。
表 2 不同放牧强度下土壤微生物群落对6类碳源的利用(96 h)
Table 2. Effect of soil microbial on the ability to utilize six types carbon source under different grazing intensity (96 h)
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随放牧强度的增加,冷蒿根际和非根际土壤微生物的4种指数均显著降低(表 3)。Shannon指数和碳源利用丰富度指数表明放牧降低微生物群落功能多样性,减少碳源的利用数目,而冷蒿根际土壤微生物种类多且较均匀,利用的碳源数量较多;冷蒿根际土壤的Simpson指数显著高于非冷蒿根际,表明冷蒿能够显著提高优势菌的数量,削弱放牧对常见微生物物种的不良影响;LG-ARS和HG-ARS的McIntosh指数显著高于LG-NRS和HG-NRS,说明LG-ARS和HG-ARS的土壤微生物种类更为丰富,碳源利用程度较高;重度放牧后McIntosh指数最低,表明过度放牧会降低土壤微生物种类丰富度和碳源利用程度。
表 3 不同放牧强度下土壤微生物群落功能多样性指数比较(96 h)
Table 3. Functional diversity indices for soil microbial community under different grazing intensity (96 h)
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运用SPSS软件对培养96 h测定的AWCD数据进行主成分分析,得到2个与土壤微生物利用碳源多样性相关的主成分,累计贡献率达到69.3%。其中第1主成分(PC1)的方差贡献率为52.1%,权重最大,第2主成分(PC2)贡献率为17.2%。因其他主成分贡献率较小,因此只用PC1和PC2得分作图来表征微生物群落碳源代谢特征(图 3)。由图 3可知:不同处理在PC轴上出现明显的分布差异,HG-ARS位于PC1负方向,得分系数为-0.308,其他处理均位于PC1正方向,得分系数为0.160~1.030;HG-NRS位于PC2负方向,得分系数为-0.357,其他处理位于PC2正方向,得分系数范围为0.300~0.950。可见,提取的2个主成分基本上能够区分不同放牧强度ARS和NRS土壤类别的微生物群落功能多样性。另外,将主成分PC1和PC2的得分系数与31种单一碳源做相关性分析,其中与PC1相关的碳源有16种,其中11个呈负相关,主要是糖类、羧酸类和聚合物,肝糖与PC1显著负相关;5个呈正相关,主要是氨基酸类和胺类。与PC2相关的碳源有17种,其中15种呈正相关,主要是糖类和羧酸类碳源,L-苯丙氨酸与其相关性显著。可见羧酸类和氨基酸类碳源在主成分分离中具有主要贡献作用。
Effect on functional diversity of Artemisia frigida rhizosphere soil microbial community with grazing
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摘要: 为揭示放牧扰动对内蒙古典型草原植物冷蒿Artemisia frigida根际土壤微生物的影响,运用平板计数法和Biolog-ECO板技术,对不同放牧强度[对照(ck),轻度放牧(LG),重度放牧(HG)]下冷蒿根际(ARS)和非根际(NRS)土壤微生物群落特征及其功能多样性进行了研究。结果表明:不同放牧强度下冷蒿根际土壤微生物数量均显著高于非根际土壤(P < 0.05),土壤微生物均以细菌占优势。Biolog分析显示,土壤微生物群落代谢活性(AWCD)随培养时间延长而逐渐增加,不同放牧强度处理后AWCD值差异显著(P < 0.05),大小顺序依次为LG-ARS > ck-ARS > ck-NRS > LG-NRS > HG-ARS > HG-NRS。土壤微生物群落Shannon指数、Simpson指数、McIntosh指数和丰富度指数的总体趋势为ck-ARS和LG-ARS最高,ck-NRS,LG-NRS和HG-ARS次之,HG-NRS最低。不同放牧强度的土壤微生物对不同碳源利用强度存在较大差异(P < 0.05),其中LG-ARS利用率最高,HG-NRS利用率最低,糖类和氨基酸类碳源是各放牧强度下土壤微生物的主要碳源。聚合物类和氨基酸类碳源在主成分分离中发挥了主要贡献作用。总之,放牧处理能够降低土壤微生物群落多样性,但冷蒿根际微生物种群密度和群落多样性均高于非根际,说明冷蒿生长能够提高土壤微生物群落功能多样性,削弱放牧干扰;冷蒿根际丰富的土壤微生物有利于改善土壤微生态,进而促进冷蒿生长,使它们成为草场退化的阻击者。Abstract: To understand the response mechanism of soil microbial biomass in the rhizosphere soil of Artemisia frigida, we measured the functional diversity of Artemisia frigida rhizosphere (ARS) and non-rhizosphere soil (NRS) microbial community under three levels (no, light and heavy) of manipulative grazing conditions using the Biolog EcoPlate analysis. Results showed that with different grazing intensities, the soil microbial population of ARS was significantly greater than NRS (P < 0.05) with bacteria playing a dominant role in all soil microbial species accounting for 88%-97%. The average well color development (AWCD), directly reflecting microbial activity and functional diversity, increased over time; whereas, AWCD for the two soil types significantly changed (P < 0.05) along with increased grazing intensity such that:LG-ARS > ck-ARS > ck-NRS > LG-NRS > HG-ARS > HG-NRS. The Simpson, Shannon-Wiener, richness, and McIntosh indexes of ck-ARS were all higher (P < 0.05) than HG-NRS, and for ARS, population density and diversity of microbial communities were higher (P < 0.05) than NRS. The PCA was used to obtain two principal components related to soil microbial biomass utilization and that explained separately 52.1% (PC1) and 17.2% (PC2). The carbon carboxylic and amino acid play a major role in the separation of principal components. Thus, A. frigida growth could increase diversity of the soil microbial community, weaken grazing disturbances, improve the soil micro-ecology, and prevent degradation of the grasslands.
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Key words:
- botany /
- Biolog-ECO plate /
- microbial community functional diversity /
- grazing /
- Artemisia frigida /
- soil microorganism
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表 1 不同放牧强度下土壤化学性质
Table 1. Soil chemical properties under different grazing intensity
表 2 不同放牧强度下土壤微生物群落对6类碳源的利用(96 h)
Table 2. Effect of soil microbial on the ability to utilize six types carbon source under different grazing intensity (96 h)
表 3 不同放牧强度下土壤微生物群落功能多样性指数比较(96 h)
Table 3. Functional diversity indices for soil microbial community under different grazing intensity (96 h)
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https://zlxb.zafu.edu.cn/article/doi/10.11833/j.issn.2095-0756.2017.01.013