Mitigation of N_(2)O emissions in water-saving paddy fields:Evaluating organic fertilizer substitution and microbial mechanisms

Water-saving irrigation strategies can successfully alleviate methane emissions from rice fields,but significantly stimulate nitrous oxide(N_(2)O)emissions because of variations in soil oxygen level and redox potential.However,the relationship linking soil N_(2)O emissions to nitrogen functional genes during various fertilization treatments in water-saving paddy fields has rarely been investigated.Furthermore,the mitigation potential of organic fertilizer substitution on N_(2)O emissions and the microbial mechanism in rice fields must be further elucidated.Our study examined how soil N_(2)O emissions were affected by related functional microorganisms(ammonia-oxidizing archaea(AOA),ammonia-oxidizing bacteria(AOB),nirS,nirK and nosZ)to various fertilization treatments in a rice field in southeast China over two years.In this study,three fertilization regimes were applied to rice cultivation:a no nitrogen(N)(Control),an inorganic N(Ni),and an inorganic N with partial N substitution with organic manure(N_(i)+N_(o)).Over two rice-growing seasons,cumulative N_(2)O emissions averaged 0.47,4.62 and 4.08 kg ha^(−1)for the Control,Ni and N_(i)+N_(o)treatments,respectively.In comparison to the Ni treatment,the N_(i)+N_(o)fertilization regime considerably reduced soil N_(2)O emissions by 11.6%while maintaining rice yield,with a lower N_(2)O emission factor(EF)from fertilizer N of 0.95%.Nitrogen fertilization considerably raised the AOB,nirS,nirK and nosZ gene abundances,in comparison to the Control treatment.Moreover,the substitution of organic manure for inorganic N fertilizer significantly decreased AOB and nirS gene abundances and increased nosZ gene abundance.The AOB responded to N fertilization more sensitively than the AOA.Total N_(2)O emissions significantly correlated positively with AOB and nirS gene abundances while having a negative correlation with nosZ gene abundance and the nosZ/nirS ratio across N-fertilized plots.In summary,we conclude that organic manure substitution for inorganic N fertilizer decreased soil N_(2)O emissions primarily by changing the soil NO_(3)^(−)-N,pH and DOC levels,thus inhibiting the activities of ammonia oxidation in nitrification and nitrite reduction in denitrification,and strengthening N_(2)O reduction in denitrification from water-saving rice paddies.

Mode-insensitive and mode-selective optical switch based on asymmetric Y-junctions and MMI couplers

Driven by the large volume demands of data in transmission systems,the number of spatial modes supported by mode-division multiplexing(MDM)systems is being increased to take full advantage of the parallelism of the signals in different spatial modes.As a key element for photonic integrated circuits,the multimode waveguide optical switch(MWOS)is playing an important role for data exchange and signal switching.However,the function of the traditional MWOS is simple,which could only implement the mode-insensitive or mode-selective switching function;it is also difficult to scale to accommodate more spatial modes because of the limitation of the device structure.Therefore,it is still challenging to realize a multifunctional and scalable MWOS that could support multiple modes with low power consumption and high flexibility.Here,we propose and experimentally demonstrate a multifunctional MWOS based on asymmetric Y-junctions and multimode interference(MMI)couplers fabricated on a polymer waveguide platform.Both mode-insensitive and mode-selective switching functions can be achieved via selectively heating different electrode heaters.The fabricated device with the total length of∼0.8 cmshows an insertion loss of less than 12.1 dB,and an extinction ratio of larger than 8.4 dB with a power consumption of∼32 mW for both mode-insensitive and mode-selective switching functions,at 1550 nm wavelength.The proposed MWOS can also be scaled to accommodate more spatial modes flexibly and easily,which can serve as an important building block for MDM systems.