Considering that soil microbes mediate many key biogeochemical processes in carbon and nitrogen cycling, they are central to the overall ecosystem function (
Journal of Resources and Ecology, Volume. 11, Issue 3, 298(2020)
A Meta-analysis of the Effects of Organic and Inorganic Fertilizers on the Soil Microbial Community
In order to investigate the general tendency of soil microbial community responses to fertilizers, a meta-analysis approach was used to synthesise observations on the effects of inorganic and organic fertilizer addition (N: nitrogen; P: phosphorus; NP: nitrogen and phosphorus; PK: phosphorus and potassium; NPK: nitrogen, phosphorus and potassium; OF: organic fertilizer; OF+NPK: organic fertilizer plus NPK) on soil microbial communities. Among the various studies, PK, NPK, OF and OF+NPK addition increased total phospholipid fatty acid (PLFA) by 52.0%, 19.5%, 334.3% and 58.3%, respectively; while NP, OF and OF+NPK addition increased fungi by 5.6%, 21.0% and 8.2%, respectively. NP, NPK and OF addition increased bacteria by 6.4%, 9.8% and 13.3%, respectively; while NP and NPK addition increased actinomycetes by 7.0% and 14.8%, respectively. Addition of ammonium nitrate rather than urea decreased gram-negative bacteria (G -). N addition increased total PLFA、bacteria and actinomycetes in croplands, but decreased fungi and bacteria in forests, and the F/B ratio in grasslands. NPK addition increased total PLFA in forests but not in croplands. The N addition rate was positively correlated with the effects of N addition on gram-positive bacteria (G +) and G -. Therefore, different fertilizers appear to have different effects on the soil microbial community. Organic fertilizers can have a greater positive effect on the soil microbial community than inorganic fertilizers. The effects of fertilizers on the soil microbial community varied with ecosystem types. The effect of N addition on the soil microbial community was related to both the forms of nitrogen that were added and the nitrogen addition rate.
1 Introduction
Considering that soil microbes mediate many key biogeochemical processes in carbon and nitrogen cycling, they are central to the overall ecosystem function (
Field experiments have analysed the potential effects of inorganic and organic fertilizers on the soil microbial community. However, some issues still needed to be further resolved. First, there are inconsistent results reported in various studies. For example, several studies have demonstrated that long-term use of nitrogen fertilizer will adversely affect soil microbes (
Therefore, in this study, we compiled data from published studies related to the effects of fertilizers on the soil microbial community which were derived from PLFA measurements. The main objectives were to (1) examine the general quantitative effects of inorganic and organic fertilizers on 10 variables related to the soil microbial community; (2) determine whether environmental factors and/or vegetation types can affect the responses of the soil microbial community to fertilizers; and (3) determine whether the responses of the soil microbial community to fertilizers varied with the different forms of fertilizers that were tested.
2 Materials and methods
2.1 Data compilation
We sought papers and theses published prior to 2015 using the Web of Science and the China National Knowledge Infrastructure. The compiled database included measurements of soil total PLFA, fungi, bacteria, gram-positive bacteria (G+), gram-negative bacteria (G-), actinomycetes, the ratio of soil fungi to bacteria (F/B ratio) and the ratio of gram-positive to gram-negative bacteria (G+/G- ratio).
Similar to many meta-analyses (
Considering that temperature, precipitation and vegetation types are important environmental factors (
2.2 Statistical analyses
The METAWIN 2.1 software (Sinauer Associates Inc., Sunderland, MA, USA) (
where ${{\bar{X}}_{c}}$ and ${{\bar{X}}_{t}}$ are the mean values in the control and experimental treatments, respectively.
For each study, the inverse of the pooled variance (1/
where$S_{c}^{2}$and $S_{t}^{2}$ are the standard deviations of the control and experimental treatments, respectively; and ${{n}_{c}}$and${{n}_{t}}$are the sample sizes of the control and experimental treatments, respectively.
Therefore, the mean effect sizes ($\overline{\ln \text{ }R}$) for all observations were obtained,
where
We used a fixed effects model, which is the simplest data structure model for a meta-analysis, to test whether a treatment had a significant effect on each variable across all studies (
A fixed effects model with a grouping variable was used to compare the responses among vegetation types and forms of nitrogen fertilizers, which is analogous to ANOVA (
(
A random effects model with a continuous variable (【-逻*辑*与-】gt; 20 observations) was used to examine the relationships between the mean effect size of nitrogen addition and latitude, longitude, mean annual temperature, mean annual precipitation, nitrogen addition rate (kg N hm2 yr-1), nitrogen load (kg N hm2) and nitrogen addition duration (
For grouping and continuous models, the total heterogeneity (
3 Results
There were significant differences in the effects of fertilizers on total PLFA among the N(nitrogen), P(phosphorus), NP(nitrogen and phosphorus), PK(phosphorus and potassium), NPK(nitrogen, phosphorus and potassium), OF(organic fertilizer) and OF+NPK(organic fertilizer plus NPK) additions (
Figure 1.
There were significant differences in the effects of fertilizers on fungi (
Latitude, longitude, MAT, MAP, Nitrogen load, and Nitrogen duration were not correlated with fertilizers for soil PLFA, fungi, bacteria, G+, or G-. The nitrogen addition rate was positively correlated with fertilizers for gram-positive bacteria (G+), and gram-negative bacteria (G-) (
There were significant differences in the effects of fertilizers on G+ (
N addition increased total PLFA by 24.4% and actinomycetes by 5.8% in croplands, decreased fungi by 37.1% and G- by 16.4% in forests, and decreased the F/B ratio by 14.3% in grasslands (
Ammonium nitrate addition decreased G- by 16.9% (
Figure 2.
Figure 3.
Figure 4.
Figure 5.
Figure 6.
4 Discussion
Nitrogen addition did not affect soil total PLFA or fungi, which was in line with a previous meta-analysis (
In this study, organic fertilizer addition had stronger positive effects on soil total PLFA, fungi, bacteria and gram- negative bacteria than inorganic fertilizer addition. In contrast, NP and NPK additions had stronger positive effects on actinomycetes than organic fertilizer addition. These results demonstrated that organic and inorganic fertilizers may have different effects on the soil microbial community. Organic fertilizers may not only provide a greater diversity of substrates than inorganic fertilizers for microbial activity but they also directly introduce microorganisms which occur naturally in the organic fertilizers into the soil (
The different effects among OF, NPK and OF+NPK additions on soil total PLFA, fungi, bacteria and actinomycetes implied that inorganic fertilizer addition may dampen the positive effects of organic fertilizer addition on soil total PLFA, fungi and bacteria; while organic fertilizer addition may dampen the positive effect of inorganic fertilizer on actinomycetes. These results implied that there may be an antagonistic effect between organic and inorganic fertilizers on the soil microbial community.
Relationships between the effect sizes of nitrogen addition on microbial indicators (total PLFA, fungi, bacteria, actinomycetes, G+, G-, and F/B ratio), and experimental variables (latitude, longitude, MAT, MAP, nitrogen addition rate, nitrogen load, and nitrogen addition duration) based on a random effects model with a continuous variable meta- analysis.
Relationships between the effect sizes of nitrogen addition on microbial indicators (total PLFA, fungi, bacteria, actinomycetes, G+, G-, and F/B ratio), and experimental variables (latitude, longitude, MAT, MAP, nitrogen addition rate, nitrogen load, and nitrogen addition duration) based on a random effects model with a continuous variable meta- analysis.
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NPK addition had stronger effects on soil total PLFA, bacteria and actinomycetes than N, P and NP additions. PK addition had a stronger effect on soil total PLFA than N, P, NP and NPK additions. P addition increased the F/B ratio, while NPK addition decreased the F/B ratio. These results indicated that there may be interactive effects between N, P and K fertilizers on the soil microbial community, as different nitrogen, phosphorus, and potassium combinations produce different effects.
In our study, the effect of nitrogen addition on the soil microbial community varied among the different forms of nitrogen (
5 Conclusions
In summary, organic and inorganic fertilizers may have different effects on the soil microbial community. Inorganic fertilizer addition may dampen the positive effects of organic fertilizer addition on soil total PLFA, fungi and bacteria, so there may be an antagonism effect between organic and inorganic fertilizers on the soil microbial community. There may be interactive effects of N, P and K fertilizers on the soil microbial community. The effect of nitrogen addition on soil microbial community varied with the different forms of nitrogen that were applied. The effect of fertilization on soil microbial community varies among different ecosystems.
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Jiangwei WANG, Guangyu ZHANG, Chengqun YU. A Meta-analysis of the Effects of Organic and Inorganic Fertilizers on the Soil Microbial Community[J]. Journal of Resources and Ecology, 2020, 11(3): 298
Received: Dec. 12, 2019
Accepted: Feb. 8, 2020
Published Online: Apr. 23, 2021
The Author Email: YU Chengqun (yucq@igsnrr.ac.cn)