Relationships Between Soil Microbial Diversity And Geochemical Elements In Typical Agricultural Products Bases In Shandong Province, China

Soil microbes comprise much of the earth's biodiversity and have a critical role in biogeochemistry cycles (BGC) as well as ecosystem functioning. By their competition, coordination and nutrient cycling driven, they have important effects on soil nutrient status, crop health, ecosystem stability, and overall crop productivity. In recent years, the study of soil microbial diversity has been the hotspot of microbial ecology. Many factors affect soil microbial communities. In previous work, the effects on microbial community have received much attention in soil type, organic matter, moisture, specific nutrient elements, and some toxic heavy metal elements on soil microbial community. However, until now, the application of geochemical data to study geochemical environments associated with soil microbial diversity has not been reported. It is well-known that geochemistry is the critical components of ecosystems. The element circulation in the biosphere will have an impact on crop growth, human health, ecosystem stability. Therefore, combining with mult-purpose geochemical investigation, a better understanding of soil geochemistry and microbial diversity not only has an important academic research meaning, but also is necessary for the development of more efficient, sustainable eco-agriculture system.In this study, the relationships between soil microbial diversity and geochemical elements were investigated in Yutai high quality rice base and Shouguang vegetable base, which are two of typical agricultural products bases in Shouguang province, China. The samplings were synchronized with "1: 250,000 multipurpose geochemical survey in the lower reach of the Yellow River", and the multipurpose geochemical mapping data were used in microbial diversity study for the first time. On the one hand, the soil geochemistry was investigated through a group of 28 chemical elements, such as pH, C(org), As, B, Cd, Co, Cr, Cu, F, Hg, Mn, Mo, Ni, P, Pb, V, Zn, Se, N, S, SiO₂, Al₂O₃, Fe₂O₃, MgO, CaO, Na₂O and K₂O. On the other hand, the soil microbial diversity was studied by three microbiological measurements, including traditional culture method, BIOLOG system and fatty acid methyl esters (FAME) analysis. The number of various physiological groups of microorganisms was studied by traditional culture method, the functional diversity on sole carbon source utilization (SCSU) was evaluated by the BIOLOG-ECO system, and the structural diversity was evaluated by FAME analysis. Finally, the multipurpose geochemical mapping data were used to resolve the relationships between soil microbial diversity and geochemistry.The study of soil geochemical elements showed that the useful elements of N, P, K, B, Mo, Mn, Se, Fe were enriched in Yutai high quality rice base soil. However, because of the man-made effects from much sewage pollution, pesticide application and fertilization, some heavy and toxic elements, such as As, Cd, Hg, Pb were obviously enriched in surface soil in Yutai. In the submergenic paddy soil (SPS), the higher content of S and the lower value of pH showed that it was apt to be acidification. In Shouguang vegetable base soil, the useful elements were enriched, and the polluted heavy metal elements were small. It was beneficial for the growth of green and non-polluted vegetable. The contents of P, N and S were obviously higher in plastic-greenhouse soil than in field soil. The differences in soil geochemistry among different plastic-greenhouses were larger than those among different field lands. The contents of geochemical elements were distinct in different layer in soil profile. The contents of N and P were decreased with increasing depth, but the content of F was increased. The contents of some heavy and toxic elements, such as Cd, Cr, Cu, Ni, Zn and As, were apt to be enriched in deeper soil layers.To various physiological groups of microorganisms, the results showed that the amounts and proportions of various physiological groups of microorganisms were different in Yutai surface soil. In the eight physiological groups of microorganisms, the numbers of culturable bacteria were dominate, the actinomyces and ammonifying bacteria took second place, and the cellulose-degrading bacteria were the least. The number of actinomyces in fluvo-aquic soil (FAS) was obviously greater than in SPS. In Shouguang surface soil, the numbers of culturable bacteri, actinomyces, nitrogen-fixing bacteria and ammonifying. Not only the total microbial amounts, but also the each kind of physiological group amounts were all higher in plastic-greenhouse than in fieldlands. The numbers and proportions of various physiological groups of microorganisms changed with depth. The amounts of most soil microbes were decreased with increasing depth.To the functional diversity on BIOLOG sole carbon source utilization patterns, in Yutai surface soil, the average values of substrates richness (S), average well color development (AWCD), Shannon's diversity index (H') and evenness index (S_E) were 21.18±3.76, 0.66±0.20, 3.04±0.15 and 1.01±0.04, respectively. In Yutai FAS soils, the values of substrates richness and AWCD were obviously higher than in SPS. In Shouguang surface soil, the average values S, AWCD, H' and S_E were 20.84±5.19, 0.72±0.27, 3.00±0.21, 1.04±0.22, respectively. The soil microbial communities had distinct carbon source substrate utilization patterns under different farmlands in Shouguang. The separation of different land use samples on principal component analysis (PCA) revealed that the open-field samples clustered in one section of the plot respectively, but the plastic-greenhouse samples were scattered. The results clearly indicated that the variations in SSCU patterns in plastic-greenhouse soils under different management were more obvious than in open-field soils in Shouguang. The values of S, H', McIntosh' diversity index (U) and AWCD decreased with the increase of depth, but the Gini's evenness index (G), S_E and Mclntosh' evenness index (ME) increased. Although the microbial metabolic diversity was different at every depth, it could be classified into three main groupings by principal component analysis and cluster analysis.To the structural diversity on FAMEs patterns in Yutai, the microbial community structural diversity was distinct among different soil samples. The contents of Gram-positive bacteria (GP), Gram-negative bacteria (GN), fungi, Gram-positive /Gram-negative (GP/GN) and Bacteria/fungi were 21.6±9.8, 23.9±8.1, 22.7±9.2, 0.9±0.3 and 2.1±0.4μg FAMEs g^-1 dry soil, respectively. In all soil samples, the contents of bacteria were more than fungi. The total FAMEs in FAS soils were significantly higher than in SPS soils. The soil microbial structures based on FAMEs were various in different type soils in Yutai. In Shouguang, the microbial community structural diversity was distinct among different soil samples. The average contents of GP, GN, fungi, GP/GN and Bacteria/fungi were 8.44±3.31, 12.87±3.60, 15.29±7.07, 0.65±0.14 and 1.57±0.53μg FAMEs g^-1 dry soil, respectively. PCA of FAME data demonstrated distinctive soil fatty acid profiles among different farm lands. The samples collected from tomato plastic-house deviated obviously from the other vegetable fields. The contents of GP, GN and Fungi decreased with increasing depth in tendency. It indicated that the soil microbial biomass reduced because of the lack of nutriment with increasing depth.The results of soil microbial diversity comparing between Yutai and Shouguang showed that the amounts of culturable bacteria, actinomyces, ammonifying bacteria and cellulose-degrading bacteria in Yutai samples were obviously less than in Shouguang. There was no distinct difference in functional diversity index based on SCSU patterns, while there were significant variations in structural diversity index based on FAMEs profiles. The values of GP, GN, GP/GN and Bac/Fungi were obviously higher in Yutai soil than in Shouguang soil, but the total FAMEs marked fungi were significantly lower in Yutai than in Shouguang.The correlation analysis between soil geochemistry and microbial diversity showed that many microbial diversity index had significant correlations to geochemical elements (P < 0.05), and the different microbial parameters had the various correlations to geochemical elements. The amounts of culturable bacteria had very high negative correlations with Co, Mn, Ni and V (P < 0.01). The quantities of fungi had very high negative correlations with Co, Cr, Ni and V, but had very high positive correlations with P and SiO₂ (P < 0.01). The number of actinomyces had very high negative correlations with Co, Cr and Ni (P < 0.01). The amounts of nitrogen-fixing bacteria had very high negative correlations with Cr, Ni and V, but had very high positive correlations with SiO₂ (P < 0.01). The quantities of cellulose-degrading bacteria had very high negative correlations with Ni. The McIntosh' diversity index (U) based on BIOLOG had very high negative correlations with Co, Cr, Ni and V, but had very high positive correlations with SiO₂ (P < 0.01). The value of S_E had very high positive correlations with Cr (P < 0.01). The value AWCD had very high negative correlations with Co, Cr and Ni (P < 0.01). The FAME parameters including GP, GN, Fungi, GP+GN, Bac+Fungi, GP/GN and Bac/Fungi had significant correlations with most geochemical elements, and the different index had the various correlations.Because the microbial community characteristics, including species, amounts, physiological profiles, activities, and so on, change accordingly with environment, the microbial parameters may be used in environmental inspecting. In our study, the amounts of culturable bacteria, fungi, actinomyces, nitrogen-fixing bacteria and cellulose-degrading bacteria; the values of U and AWCD based on BIOLOG; the index of GP, GN, GP+GN, Bac+Fungi, GP/GN and Bac/Fungi had significant correlations with most of geochemical elements. They were expected to be the sensitive microbial indicator of geochemical environment. Our study indicated that the culturable bacteria were expected to be the indicator of Co, Mn, Ni and V, fungi and nitrogen-fixing bacteria to be the indicator of Co, Cr, Ni and V, actinomyces to be the indicator of Co, Cr and Ni, cellulose-degrading bacteria to be the indicator of Ni. The values of GP, GN, GP+GN, Bac+Fungi, GP/GN and Bac/Fungi were expected to be the indicator of As, Cr, Pb, Zn and Cu. The values of Bac/Fungi and fungi may be the indicator of Cr and Ni.In this research, the soil microbial diversity and its relationships with geochemical elements were studied in Yutai and Shouguang, which are two of the typical agricultural products bases in Shandong province, China. The results showed that the different areas had distinct soil microbial amounts, structures and functions. Even if in the same area, there were also variations in soil microbial diversity in different type soil or various farmlands. The microbial community diversity was different at different depths. Many microbial diversity indexes had significant correlations to geochemical elements, and the different microbial parameters had the various correlations to geochemical elements. Therefore, the soil microbial indexes were screened out as geochemical environments sensitive indicators.