120
B. Yan et al.
Microplastics regulate marine macrobenthos bioactivity and maintain geochemical cycles. Microbenthos mainly consist of bacteria, cyanobacteria, diatoms, flagellates, amoebas, and ciliates. Microbenthos mainly live in the upper sediments (0–
2 mm), and are the main source of many sediment eaters, including, Pratt et al. [102].
Their functions include the decomposition of organic detrital, primary production,
and the transfer of substances and energy between trophic levels. It is an important part of the benthic micro-food network and functions as a dispensable role in
the benthic ecosystem. Although marine benthos is the main producer, it also relies
on organic nitrogen transported to the sediment surface. Marine benthos are a major
source of unstable organic matter in soft sediments [103], and studies have suggested
that the nitrogen cycle can be affected by both changes in the quality and quantity of
organic matter [104]. Marine benthos, therefore, which lives in the sediment-water
interface, is also involved in the regulation of nutrients and nitrogen fixation[96].
The net NH 4
+ flux is also related to the feeding, biological activity, and excretion
of marine organisms such as Liliana [105], which exists on the surface of sediments
and lives by ingestion of marine benthos. The presence of Liliana can increase the
efflux of NH 4
+ , nevertheless, when the quantity of Liliana is reduced or its functional
effect is impaired, it will lead to the decrease of efflux of NH4
+ and will inhibit the
denitrification process [105, 106]. You et al. reported that the increase of polyethylene
terephthalate could affect the physiological reaction of Iliana, and the choice of
feeding particles, feeding rate, or physiological activity [107]. Moreover, changes
in Liliana’ s activities would affect the primary production and nitrogen cycle in
sediments [107]. In a sub-nitrogen environment, marine benthos tends to retain and
compete for limited nitrogen in the ocean, thereby suppressing the anti-nitrification
reaction and resulting in a decrease in denitrification rates.
Microplastics may also interact with benthic organisms to influence denitrification. Huang et al. found that the existence of microplastics or chironomids could
promote the process of denitrification and ammoxidation [108]. However, microplastics have a negative effect on benthic invertebrates, causing physiological toxicity.
When microplastics and benthic invertebrates coexist, especially when microplastics
are exposed at a high concentration and under the positive regulation of Chironomus,
the negative nitrogen removal function caused by physiological toxicity will be offset
by the positive regulation of Chironomes.
Microplastics not only have a negative effect on the abundance of microbial
communities, but also have a positive effect. Studies have shown that microplastics in the sedimentary environment can be used as the organic matter matrix in the
microbial environment [96], so as to promote the growth of microorganisms in the
sediments and provide a material basis for the development of benthic organisms.
Therefore, the interaction between microplastics and benthos is complex.
Currently, the study involves the effect of microplastics and benthic organisms on
the nitrogen cycle is still limited. Therefore, it is of great importance to investigate
the nitrogen cycle and its mechanism under the joint action of microplastics and
benthic organisms.
B. Yan et al.
Microplastics regulate marine macrobenthos bioactivity and maintain geochemical cycles. Microbenthos mainly consist of bacteria, cyanobacteria, diatoms, flagellates, amoebas, and ciliates. Microbenthos mainly live in the upper sediments (0–
2 mm), and are the main source of many sediment eaters, including, Pratt et al. [102].
Their functions include the decomposition of organic detrital, primary production,
and the transfer of substances and energy between trophic levels. It is an important part of the benthic micro-food network and functions as a dispensable role in
the benthic ecosystem. Although marine benthos is the main producer, it also relies
on organic nitrogen transported to the sediment surface. Marine benthos are a major
source of unstable organic matter in soft sediments [103], and studies have suggested
that the nitrogen cycle can be affected by both changes in the quality and quantity of
organic matter [104]. Marine benthos, therefore, which lives in the sediment-water
interface, is also involved in the regulation of nutrients and nitrogen fixation[96].
The net NH 4
+ flux is also related to the feeding, biological activity, and excretion
of marine organisms such as Liliana [105], which exists on the surface of sediments
and lives by ingestion of marine benthos. The presence of Liliana can increase the
efflux of NH 4
+ , nevertheless, when the quantity of Liliana is reduced or its functional
effect is impaired, it will lead to the decrease of efflux of NH4
+ and will inhibit the
denitrification process [105, 106]. You et al. reported that the increase of polyethylene
terephthalate could affect the physiological reaction of Iliana, and the choice of
feeding particles, feeding rate, or physiological activity [107]. Moreover, changes
in Liliana’ s activities would affect the primary production and nitrogen cycle in
sediments [107]. In a sub-nitrogen environment, marine benthos tends to retain and
compete for limited nitrogen in the ocean, thereby suppressing the anti-nitrification
reaction and resulting in a decrease in denitrification rates.
Microplastics may also interact with benthic organisms to influence denitrification. Huang et al. found that the existence of microplastics or chironomids could
promote the process of denitrification and ammoxidation [108]. However, microplastics have a negative effect on benthic invertebrates, causing physiological toxicity.
When microplastics and benthic invertebrates coexist, especially when microplastics
are exposed at a high concentration and under the positive regulation of Chironomus,
the negative nitrogen removal function caused by physiological toxicity will be offset
by the positive regulation of Chironomes.
Microplastics not only have a negative effect on the abundance of microbial
communities, but also have a positive effect. Studies have shown that microplastics in the sedimentary environment can be used as the organic matter matrix in the
microbial environment [96], so as to promote the growth of microorganisms in the
sediments and provide a material basis for the development of benthic organisms.
Therefore, the interaction between microplastics and benthos is complex.
Currently, the study involves the effect of microplastics and benthic organisms on
the nitrogen cycle is still limited. Therefore, it is of great importance to investigate
the nitrogen cycle and its mechanism under the joint action of microplastics and
benthic organisms.