Molecular Plant Breeding 2024, Vol.15, No.1, 34-41 http://genbreedpublisher.com/index.php/mpb 38 Liu (2023) conducted a study on the effect of biodegradable film covering on soil microbial C and N content, and found that covering biodegradable film treatment can significantly increase soil microbial carbon, which is 26.5% higher than that of PE film treatment, but the difference between microbial nitrogen and that of covering PE film treatment is not significant, and the microbial carbon and nitrogen of the soil are significantly higher in the film-covering than in the bare-ground non-film treatment (Table 1). However, there was no significant difference in soil urease, cellulase, β-glucosidase, and acid phosphatase activities when covering biodegradable film compared with covering PE mulch. Wu Si's experiment also confirmed that soil microbiomass carbon was significantly higher under biodegradable mulch treatment than PE mulch treatment, but there was no significant difference in soil microbiomass nitrogen. Table 1 Effects of different treatments on soil microbial carbon and nitrogen (Adopted from Liu, 2023) Treatment Soil microbial carbon (mg/kg) Soil microbial nitrogen (mg/kg) 1 (107.1±4.2) c (11.8±6.1) c 2 (129.4±6.9) b (13.2±5.8) b 3 (130.8±6.7) b (15.5±7.2) ab 4 (155.7±7.4) a (16.7±4.5) a Note: Treatment groups 1, 2, 3 and 4 were without mulching, covered with ordinary PE mulch, standard PE mulch, and PBAT+PLA fully biodegradable film, respectively; different lowercase letters after the numbers in the same column indicate significant differences (p<0.05) 3.2 Soil respiration intensity Soil respiration intensity is commonly used to measure the total soil microbial activity. Li et al. (2022) studied the effects of biodegradable mulch on soil microbial abundance, activity and community structure, and the results showed that the soil respiration rate of biodegradable mulch treatment was higher than the trend of uncoated mulch and PE mulch cover treatments, which may be due to the fact that the biodegradable mulch started to break up in the middle of the crop growth period, and the residue was decomposed by the microorganisms in the soil intoH2Oand CO2, which enhanced the intensity of soil respiration, indicating that biodegradable mulch took into account the characteristics of ordinary PE mulch for heat preservation and moisture retention, and compared with ordinary PE mulch, covering biodegradable mulch had a tendency to increase microbial activity, which might have a promotion effect on soil microbial activity under long-term covering. 3.3 Soil microbial community structure Lu et al. (2023) demonstrated that the soil microbial community structure, species abundance, soil enzyme activity and tomato plant growth at different mulching sites could be improved by covering PBAT/PLA humic acid biodegradable mulch (FZS) compared with PE mulch, and that the mulching of PBAT/PLA humic acid biodegradable mulch (FZS) could help to increase the microbial activity of soil fungi Ascomycota and bacteria Verrucomicrobiota and Bacteroidota species abundance; soil sucrase activity and tomato stem thickness were significantly higher with PBAT/PLA humic acid biodegradable mulch (FZS) than with PE mulch. Bandopadhyay et al. (2020) demonstrated that several bacterial and fungal organisms were found to be in higher abundance in sandy loam soils compared to PE mulch, and the bacteria were categorized and found to be mainly divided into Methylobacterium, Arthrobacter, and Sphingomonas. This suggests that microorganisms of these genera may be the corresponding degrading colonies. The reduced bacterial set in degradable mulch compared to PE mulch is in line with the experimental prediction that PE, with its non-biodegradable and more hydrophobic surface, may accommodate a wider range of microorganisms without obvious selection. In summary, in addition to the same premise of heat preservation and moisturization as ordinary PE mulch, degradable mulch will promote the increase of soil microbial amount carbon content, soil respiration intensity, and will indirectly screen out some colonies that are favorable to their own degradation thus changing the community structure of microorganisms in the soil. The above experiments can also prove that biodegradable mulch can meet the needs of crop growth and development, promote its rapid growth, improve yield, and there is no significant difference in yield with ordinary PE mulch.
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