Abstract
This study aimed to evaluate changes in abundance, structure, and enzyme activity of the soil microbiome in response to 4 years of mulching using either black polyethylene plastic film (PM) or wheat straw (SM). Soil samples (depth 0–5 and 5–10 cm) were collected from conventional strawberry plots, in two samplings: 1 week prior (S1) and 7 weeks after straw application (S2). Selected soil properties were monitored in each system and the abundance and structure of microbial communities were characterized via phospholipid fatty acid (PLFA) analysis. The investigation of soil microbial functions included activities of the enzymes chitinase, leucine aminopeptidase, and acid phosphatase, as well as function genes involved in nitrogen transformation. Each mulch system resulted in distinct physicochemical properties. In particular, a pH value higher by one-unit under PM (7.6 ± 0.3) compared to SM (6.5 ± 0.3) was observed. Values for SOC, DOC, and total-N were 15%, 22%, and 16% higher in PM than in SM. The microbial biomass (total PLFAs) was 1.5-fold higher in SM compared to PM. The abundance of soil fungi (F) and bacteria (B) increased by 37% and 44% after straw incorporation compared to PM (S2). In particular, Gram-negative bacteria (gr–) increased by twofold in SM. Consequently, wider F:B and gr+:gr– ratios were observed in PM. According to the shifts in microbial abundance, the activity of the enzyme chitinase was lower by 27% in PM, while the activity of the acid phosphatase increased by 32%. Denitrification genes were not affected by the mulching systems. In conclusion, the abundance and structure of the investigated microbial groups and the enzyme activities were strongly influenced by the mulching system. In detail, effects on microbiota were primarily attributed to the altered soil pH and probably the input of degradable organic matter with straw mulching in SM. This resulted in higher abundance of soil microorganisms in SM, although measures within this cultivation system such as fungicide application may have exerted adverse effects on the microbiota.
Highlights
The high productivity of strawberry crops in Europe relies on the adoption of cultivation systems improving productivity and extending the harvest seasons [1]
We expect that higher pesticide loads may reach the soil in SM compared to plastic film (PM), due to the number of fungicides used in SM and the absence of the mechanical plastic barrier impeding the infiltration of fungicides into the soil [17,18]
Soil pH values were on average 1 pH unit higher (p < 0.001) in PM (7.6 ± 0.3) compared to SM (6.5 ± 0.3). This was not confirmed by Inorganic carbon (IC) contents that were largely similar in soils under both mulching systems
Summary
The high productivity of strawberry crops in Europe relies on the adoption of cultivation systems improving productivity and extending the harvest seasons [1]. Plastic mulches are used for a period of approximately two consecutive years in strawberry cultivation [3], combined with specific fertilization, pesticide management, and irrigation regimes. The extent of such management practices depends on environmental and geographic conditions, and the type of cultivation, adapted to the requirements of the field to optimize crop performance and economic benefits [7]. Shifts in microbial communities were observed by means of N-cycle functional groups: film mulching resulted in a significantly lower abundance of narG and nirS genes compared to no mulch [13] This effect reversed in the presence of increased fertilization. A comparison between systems and studies is difficult due to the heterogeneity generated by the climatic and geographic conditions; type of soil; modalities of cultivation; as well as the combination with highly diverse use of fertilizers, irrigation regimes, and pesticides
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