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硒是人体所必需的一种营养元素,能参与人体谷胱甘肽过氧化酶等多种硒蛋白的合成,辅助调节体内的抗氧化系统 [1 − 2]. 人体中缺少硒会引发诸如克山病、大骨病及阿尔兹海默症等疾病[3 − 6]. 硒的摄入主要是通过食用含硒的农作物,相关农作物将土壤中的无机硒转化为高生物利用度的硒蛋白,使其能被人类或动物吸收. 据报道中国面临缺硒风险的人就有约7000万[7 − 8]. 为降低缺硒给人群带来的风险,人们开始开展富硒农业,现形成了以陕西安康、湖北恩施为典型区域,涵盖陕西、广西等地的富硒农产品开发格局[9]. 在天然富硒区域种植农作物是生产富硒食品的主要方式,近年来在非富硒区域通过人工施用硒肥来提高农产品中硒含量的生产方式迅猛发展,但硒肥的大量施用很可能导致环境中硒含量过高从而对生态环境和人体造成威胁. 土壤中的硒蓄积于农作物中,通过摄食进入人体. 每天摄入超过400 μg的硒即可导致脱发、肝坏死、脑水肿和神经毒性[10].
土壤微生物在土壤系统的新陈代谢中发挥重要作用,不仅促进土壤碳循环和能量循环,还能改善土壤结构[11],在土壤系统中占有重要地位. 通过研究硒对微生物的影响,可以掌握硒对土壤生态系统最基础与最直接的作用. 前人的研究表明低浓度的硒能改变微生物群落结构,从而改善土壤环境. 1.0 mg·kg−1硒与甲壳素结合,可以减少土壤磷淋失[12]. 硒浓度为0.40—2.83 mg·kg−1时能增加土壤细菌群落和真菌群落的多样性[13],5.0 mg·kg−1硒能增加土壤中氮代谢和碳水化合物代谢[14]. 而当硒浓度过高,则对微生物群落产生威胁. 当硒浓度达20 mg·kg−1时,土壤细菌和真菌数量降低[15]. 前人关于硒对土壤微生物影响的研究中,控制实验设计的浓度组一般较少,而原位硒对微生物的研究又大多是直接将硒含量划分为高硒和低硒两部分来研究,因此需要探究硒浓度梯度变化对土壤微生物群落的影响.
PLFA方法是一种常用的测定土壤微生物组成并定量的方法[16 − 17],其原理是通过测定磷脂脂肪酸来表征微生物类别. 磷脂是构成生物膜所需磷脂双分子层的主要成分. 微生物死亡后,磷脂会被迅速分解,因此PLFA方法是鉴定土壤中活微生物的重要方法[18 − 19]. 相较于耗时费力的平板微生物分离法、Biolog微平板法和价格高昂且结果不确定性较高的16S rRNA方法,PLFA方法更加经济、快捷、准确.
本研究选取典型富硒农业发展区土壤,探讨了土壤理化性质、原位硒含量、土壤微生物丰度与群落结构的相关性. 同时为排除土壤理化性质的干扰,进行室内控制变量实验. 参考野外原位硒含量设计室内控制实验中硒的浓度梯度,并探讨控制变量下更广跨度硒含量对土壤微生物菌群短期(2 d)和长期(21 d)的影响. 本研究结合野外原位硒和实验室外源硒对微生物的影响,相关实验结果可以为富硒农业可持续绿色发展提供有力参考.
土壤原位硒及外源硒处理下土壤微生物群落特征分析
Characteristics of soil microbial communities treated with orthotopic and exogenous selenium
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摘要: 本研究采用野外原位硒研究和实验室外源硒控制实验结合的方法,利用磷脂脂肪酸(phospholipid fatty acid,PLFA)法表征土壤微生物组成并对其定量,探究土壤硒对微生物群落特征的影响的定量关系. 结果表明,土壤微生物总量、革兰氏阳性菌和革兰氏阴性菌的量均与原位硒含量(范围0.101—4.563 mg·kg−1)呈显著正相关,同时其与土壤总氮和总有机碳呈极显著正相关. 室内外源硒控制实验中,在短期培养(培养2 d)时,随着外源硒浓度的增大,除真菌响应不显著,细菌、革兰氏阳性菌和革兰氏阴性菌含量均呈现先升高后降低的趋势. 当硒含量为2.28 mg·kg−1时,对革兰氏阴性菌生长繁殖的促进作用最强,对细菌、革兰氏阳性菌促进作用最强的硒含量为4.57 mg·kg−1. 外源添加硒实验的结果同野外原位硒与土壤微生物相关性的分析结果一致. 当硒含量达22.8 mg·kg−1时,短期(2 d)会促进细菌增长,但长期(21 d)下则表现为显著抑制. 当硒含量为32.0 mg·kg−1时,不论是短期培养(2 d)还是长期培养(21 d),对细菌、革兰氏阳性菌和革兰氏阴性菌生长表现出显著抑制作用. 本研究表明硒含量在一定范围可以促进土壤微生物繁殖,而过量的硒则会抑制微生物的生长,该结果可为富硒农业的可持续绿色发展提供科学依据.Abstract: This study adopted a combination of the field in situ selenium research and laboratory exogenous selenium control experiments to investigate the quantitative relationship between soil selenium and microbial community characteristics. A phospholipid fatty acid (PLFA) method was used to characterize and quantify the composition of soil microorganisms. The results showed that the total amount of soil microorganisms, Gram-positive bacteria, and Gram-negative bacteria was significantly positively correlated with the in situ selenium content (range 0.101—4.563 mg·kg−1) and was also significantly positively correlated with the total nitrogen and total organic carbon in the soil. In the lab exogenous selenium control experiment in the short-term culture (cultured for 2 d), with the increase of exogenous selenium concentration, except that the response of fungi was not significant, the content of bacteria, Gram-positive bacteria and Gram-negative bacteria all showed a trend of first increasing and then decreasing. When the selenium content was 2.28 mg·kg−1, the promotion effect on the growth and reproduction of Gram-negative bacteria was the strongest. The selenium content had the strongest promotion effect on bacteria when Gram-positive bacteria was 4.57 mg·kg−1. The results of the exogenous selenium addition experiment were consistent with the analysis results of the correlation between field in situ selenium and soil microorganisms. When the selenium content reached 22.8 mg·kg−1, short-term culture (2 d) would promote the growth of bacteria, but long-term culture (21 d) showed significant inhibition. When the selenium content was 32.0 mg·kg−1, both short-term culture (2 d) and long-term culture (21 d) showed significant inhibition on the growth of bacteria, Gram-positive bacteria, and Gram-negative bacteria. This study shows that selenium content in a certain range can promote the reproduction of soil microorganisms, while excessive selenium will inhibit the growth of microorganisms, which can provide the scientific basis for the sustainable green development of selenium-rich agriculture.
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Key words:
- selenium /
- soil /
- microbial community /
- phospholipid fatty acids.
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表 1 野外土壤硒含量及理化性质
Table 1. Selenium content and physical and chemical properties of wild soil
样点
Sampling site硒量/(mg·kg−1)
Se content总氮/( g·kg−1)
Total nitrogen总有机碳/( g·kg−1)
Total organic carbon含水率/%
Moisture contentpH 1 0.101 0.77 9.05 6.71 4.27 2 0.157 1.02 9.40 7.83 6.54 3 0.206 0.99 10.63 4.90 5.79 4 0.207 1.84 16.59 7.01 5.48 5 0.214 0.73 7.10 9.09 7.36 6 0.227 0.87 10.08 4.45 4.91 7 0.298 0.97 10.49 4.43 6.60 8 0.299 1.51 16.76 13.05 6.92 9 0.300 1.52 17.40 2.29 7.47 10 0.319 0.89 9.26 8.03 7.08 11 0.330 1.96 19.46 13.75 6.84 12 0.336 2.05 26.02 14.71 6.86 13 0.360 1.09 12.10 13.37 6.84 14 0.360 1.15 12.01 10.34 7.05 15 0.430 1.40 16.54 9.38 6.04 16 0.468 1.21 13.09 13.83 6.94 17 0.531 1.44 18.19 6.81 7.30 18 0.544 1.60 17.99 18.30 6.50 19 0.657 1.63 27.04 15.23 7.43 20 1.064 1.38 25.71 7.08 6.86 21 1.153 4.28 98.36 4.60 7.55 22 4.563 2.00 53.99 4.70 7.32 表 2 野外土壤微生物各菌群磷脂脂肪酸含量
Table 2. The content of microbial phospholipid fatty acid under the wild soil
样点
Sampling
point总PLFA/
(nmol·g−1)
Total细菌PLFA/
( nmol·g−1)
Bacte ria真菌PLFA/
( nmol·g−1)
Fungi革兰氏阳性菌PLFA/
( nmol·g−1)
Gram-positive bacterium革兰氏阴性菌PLFA/
( nmol·g−1)
Gram-negative bacterium1 29.59 27.61 1.99 0.00 7.79 2 39.32 37.97 1.35 2.69 15.54 3 78.13 78.13 0.00 15.69 39.45 4 72.55 69.14 3.41 24.70 15.54 5 42.20 42.20 0.00 0.00 13.58 6 41.22 33.06 8.16 3.15 4.58 7 37.60 36.76 0.00 3.59 16.41 8 42.32 41.33 0.99 0.85 15.78 9 40.13 38.91 1.22 3.30 15.81 10 38.59 38.59 0.00 0.00 14.88 11 76.56 72.48 4.09 22.41 22.66 12 46.82 46.82 0.00 3.92 19.94 13 40.97 39.07 1.27 5.63 11.61 14 38.09 35.95 1.05 3.31 16.78 15 58.32 58.32 0.00 10.70 19.12 16 43.52 42.20 0.00 7.50 10.55 17 104.11 91.80 12.31 27.49 30.57 18 44.43 44.43 0.00 3.76 16.63 19 59.47 59.47 0.00 7.63 23.11 20 42.27 40.04 1.39 3.70 14.97 21 150.56 140.90 9.67 22.35 65.89 22 62.25 60.56 1.69 14.02 25.14 -
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