Elsevier

Pedobiologia

Volume 77, November 2019, 150575
Pedobiologia

Shifts and recovery of soil microbial communities in a 40-year field trial under mineral fertilization

https://doi.org/10.1016/j.pedobi.2019.150575Get rights and content

Highlights

  • We examined the impact of 40-y mineral fertilization on soil microbial communities.

  • Fertilization affected the functioning and composition of microbial communities.

  • Enzyme activities were accompanied by changes in microbial community composition.

  • Soil bacteria are more resilient to mineral fertilization disturbances than fungi.

Abstract

Inorganic fertilizers have been reported to have effects on both microbial activities and soil microbial community structure. However, the published results are often contradictory. To overcome short-term fluctuations in microbial parameters it is necessary to study their changes over the long term. We investigated the impact of a 40-y inorganic fertilization of a grassland field on selected soil microbial enzymatic activities and on the composition of bacterial and fungal communities, assessed by terminal restriction fragment length polymorphism (T-RFLP). The following fertilizer treatments were compared: C (control, no fertilization), PK (phosphorus and potassium) fertilizer, 80N (lower nitrogen plus PK fertilizer) and 160 N (higher nitrogen plus PK fertilizer). The field trial also included a NF treatment where fertilization with high nitrogen doses was terminated after 20 y, and the subsequent 20 y were under a non-fertilization regime. Except for arylsulfatase, addition of PK was not sufficient intervention to influence enzyme activities. On the contrary, we observed a significant increase in cellobiosidase, phosphomonoesterase, and β-glucosidase activity in soils fertilized with N, although there was no difference in the enzyme activities between the 80N and 160N treatments. The activities of these enzymes in soils under NF treatment returned to the values of the control soils. Decreased activity of arylsulfatase was detected in treatments with fertilization compared to the control treatment. The shifts in the enzyme activities were accompanied by changes in the composition of whole bacterial and fungal communities, which was also affected by the long-term fertilization. Community composition in fertilized soils clearly differed from the control soils. Contrary to bacteria, 20 y following the cessation of fertilization in the NF treatment was not enough time for complete recovery of the fungal community to that observed in the control treatment. Our findings suggested that soil bacteria are more resilient to chemical fertilization disturbances than fungi.

Introduction

The application of fertilizers into soil is primarily used to increase nutrient availability to growing plants and therefore to raise the yield of the subsequent harvest; nevertheless, it can also affect soil microorganisms (Marschner et al., 2003). Soil microorganisms have long been recognized for their indispensable role in decomposition of organic residues, cycling of nutrients and production of crops (Shen et al., 2010).

Among the most ecologically relevant microbial parameters sensitive to changes in soil management (including fertilization) are microbial enzymatic activities, mainly due to their narrow relationship with the biological status of soil and relatively easy assessment (Moscatelli et al., 2018). Microbial enzymatic activities have been successfully used for assessment of the impact of both mineral and organic fertilizers on the microbial status of different soil types in various climatic regions (Debosz et al., 1999; Marinari et al., 2000; Pajares et al., 2009; Reardon and Wuest, 2016; Tamilselvi et al., 2015).

Inorganic fertilizers have been reported to have effects on both microbial activities and soil microbial community structure (Böhme et al., 2005; Chen et al., 2014b; Ding et al., 2016; Marschner et al., 2003; Pan et al., 2014). In a literature review by Allison and Martiny (2008), 84% of 38 studies reported that microbial community composition is sensitive to N/P/K fertilization. However, the results are often contradictory, and both stimulating and suppressing effects of fertilizers on activity and composition of microbial communities can be observed. In general, microbial communities are dynamic systems, able to change rapidly in response to a disturbance such as an addition of fertilizer.

Despite the sensitivity of microbial parameters to soil management, they are naturally highly variable with regard to different soil types and various physico-chemical soil properties. Field experiments that are managed for a relatively long time (decades) are then a very effective tool for drawing plausible conclusions about the manipulated parameter, because the other variables remain unchanged. Moreover, long-term field trials, if appropriately arranged, might represent a great opportunity to survey the recovery of microbial communities, whether in terms of their structure or activity, if the manipulation (fertilization) is terminated. As proposed by Stevens (2016), recovery from an environmental perturbation can sometimes be difficult to define, because reversion to a pre-existing state often fails to consider natural developments within the system (e.g. succession). This means that in a permanently changing environment it is not always realistic to expect an individual site to return to a previous state. However, in replicated long-term trials with experimental controls, recovery can be advantageously considered as convergence with control plots (Stevens, 2016). Although, much of work has been done in the field of spontaneous recovery of plant diversity after cessation of fertilization in grasslands (e.g. Královec et al., 2009; Pallett et al., 2016), there are only a very limited number of studies involving terminated inorganic fertilization that are focused on microbial recovery (Chen et al., 2014a; Griffiths et al., 2012; Malý et al., 2009). In general, research on microbial communities after cessation of environmental disturbance is needed to provide a missing insight into their ecological resilience and recovery rate.

The present investigation was undertaken (1) to assess the impact of long-term inorganic fertilization of grassland field on soil microbial enzymatic activities and on the composition of soil bacterial and fungal communities, and (2) to analyze possible relationships between microbial community composition and activity. The investigation was carried out in soils of field trial in the Czech Republic, fertilized since 1969. In a previous study situated in the same long-term field fertilization trial (Malý et al., 2009), it was shown that permanent application of mineral fertilizers increased the proportion of r-strategists in soil. However, it was not clear whether the changes in the r/K strategy were linked to changes in the composition of microbial communities or caused by transition between the r/K physiological states. Here we hypothesize that long-term application of mineral fertilizers leads to changes in the functioning of microbial communities, assessed as the activity of extracellular enzymes, and that these changes are coupled with shifts in soil bacterial and fungal community composition. Furthermore, although it is likely in general that repeated additions of fertilizers impact the microbial communities to some degree, it is unknown whether the fertilization produces lasting effects, particularly after the plots return to a non-fertilization regime, and whether the microbial communities are ecologically resilient. Fortunately, the long-term field trial includes a treatment where application of fertilization was stopped after 20 y of fertilization, with the subsequent two decades under a non-fertilization regime. With this treatment, we have a rare opportunity to raise and test the hypothesis that the changes in microbial parameters caused by permanent inorganic fertilizer inputs persist beyond the cessation of the fertilization and can be apparent even 20 y afterward.

Section snippets

Experimental field

Soils for the study were sampled from a long-term experiment focused on surveying the effects of fertilization on the production and quality of fodder, as well as on soil quality. The experimental site is located at Závišín near Mariánské Lázně, Czech Republic (49°58′39′′N, 12°45′14′′E, altitude 750 m above sea level) and was established in 1969. The soil is a sandy loam classified as Haplic Cambisol (Dystric) (IUSS Working Group WRB, 2006). Soil characteristics, annual temperature,

Soil chemical properties and plant aboveground biomass

Long-term fertilization of grassland soil led to changes in plant aboveground biomass and almost all assessed soil chemical properties, which is shown in Table 1. Soil reaction (pHKCl) and the content of Ca were significantly higher in plots fertilized with N (80N and 160N). The increased values of pHKCl and Ca content reflect the fact that ammonium sulphate used as fertilizer in 80N and 160N plots also contained some limestone. In the case of NF plots, terminated fertilization led to the

Conclusion

We demonstrated that 40-y mineral fertilization of grassland soil had a significant effect on soil microbial communities in terms of both function and community composition. Fertilization altered the activity of selected extracellular enzymes; however, PK inputs alone, without N, did not represent a sufficient impact. Moreover, the shifts in enzyme activities were accompanied by changes in the composition of whole bacterial and fungal communities, implying a linkage between microbial community

Funding

The research was funded by the Ministry of Agriculture of the Czech Republic.

Declaration of competing interest

None.

Acknowledgements

The current owner of the study land is a private farmer Mr. Ivan Kožíšek. Thanks to his rare understanding, it is possible to maintain the field trial and to continue with monitoring of long-term fertilization.

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