Response of soil biological properties and bacterial diversity to different levels of nitrogen application in sugarcane fields

Field experiments were performed in early March 2019 at the farm of the Sugarcane Research Institute, Guangxi Academy of Agricultural Sciences. Four concentrations of nitrogen application were employed as follows: that is, urea applications 964, 482, 96, 0 kg ha− 1, respectively. And 300 kg ha− 1 calcium, magnesium, and phosphorus were likewise applied in 4 different treatments. The results showed that the soil microbial biomass carbon and phosphorus were altered significantly by non- and low-nitrogen input. Moreover, the indexes of soil bacterial richness and diversity in the sugarcane field could be significantly improved, even by low nitrogen input. At the genus level, norank_f__SC-I-84, Mycobacterium, norank_f__Micropepsaceae, norank_f__norank_o__Saccharimonadales, norank_f__norank_o__Subgroup_2 and norank_f__Acetobacteraceae were the unique dominant bacteria in the soil with the high nitrogen input treatment. norank_f__JG30-KF-CM45 and Jatrophihabitans were the unique dominant genera in the moderate nitrogen input treatment. norank_f__norank_o__norank_c__Subgroup_6, HSB_OF53-F07, Streptomyces, norank_f__67 − 14, norank_f__norank_o__SBR1031 and norank_f__norank_o__norank_c__KD4-96 were the unique dominant genera in the low nitrogen input treatment. In contrast, FCPS473, Actinospica, 1921-2, Sinomonas, and norank_f__Ktedonobacteraceae were the unique dominant genera in CK (no nitrogen application treatment). It suggested that low nitrogen input was the most significant effect on the soil microbial biomass carbon and phosphorus in the sugarcane field. Moreover, low nitrogen input also can improve the diversity and richness of sugarcane soil bacteria. The dominant bacterial genera of low nitrogen input and the other treatments were different for the compositions of dominant bacteria, and the largest abundance difference of dominant bacterial genera was norank_f__norank_o__norank_c__Subgroup_6. However, whether low nitrogen stress can improve the yield and quality of sugarcane warrants further research.

Riverine nitrogen supply to the global ocean and its limited impact on global marine primary production: a feedback study using an Earth system model

A common notion is that negative feedbacks stabilize the natural marine nitrogen inventory. Recent modeling studies have shown, however, some potential for localized positive feedbacks leading to substantial nitrogen losses in regions where nitrogen fixation and denitrification occur in proximity to each other. Here we include dissolved nitrogen from river discharge in a global 3-D ocean biogeochemistry model and study the effects on near-coastal and remote-open-ocean biogeochemistry. We find that at a steady state the biogeochemical feedbacks in the marine nitrogen cycle, nitrogen input from biological N2 fixation, and nitrogen loss via denitrification mostly compensate for the imposed yearly addition of 22.8 to 45.6 Tg of riverine nitrogen and limit the impact on global marine productivity to < 2 %. Global experiments that regionally isolate river nutrient input show that the sign and strength of the feedbacks depend on the location of the river discharge and the oxygen status of the receiving marine environment. Marine productivity generally increases in proximity to the nitrogen input, but we also find a decline in productivity in the modeled Bay of Bengal and near the mouth of the Amazon River. While most of the changes are located in shelf and near-coastal oceans, nitrogen supply from the rivers can impact the open ocean, due to feedbacks or knock-on effects.

Rhizosphere-Associated Microbiomes of Rice (Oryza sativa L.) Under the Effect of Increased Nitrogen Fertilization

Crops assemble and rely on rhizosphere-associated microbiomes for plant nutrition, which is crucial to their productivity. Historically, excessive nitrogen fertilization did not result in continuously increasing yields but rather caused environmental issues. A comprehensive understanding should be developed regarding the ways in which crops shape rhizosphere-associated microbiomes under conditions of increased nitrogen fertilization. In this study, we applied 16S and 18S ribosomal RNA gene profiling to characterize bacterial and fungal communities in bulk and rhizosphere soil of rice subjected to three levels of nitrogen fertilization for 5 years. Soil biochemical properties were characterized, and carbon-, nitrogen-, and phosphorus-related soil enzyme activities were investigated, by assays. Increasing nitrogen fertilization led to a decreasing trend in the variation of microbial community structures and demonstrated a more definite influence on fungal rather than bacterial community compositions and functions. Changes in the level of nitrogen fertilization significantly affected chemical properties such as soil pH, nutrient content, and microbial biomass levels in both rhizosphere and bulk soil. Soil enzyme activity levels varied substantially across nitrogen fertilization intensities and correlated more with the fungal than with the bacterial community. Our results indicated that increased nitrogen input drives alterations in the structures and functions of microbial communities, properties of soil carbon, nitrogen, and phosphorus, as well as enzyme activities. These results provide novel insights into the associations among increased nitrogen input, changes in biochemical properties, and shifts in microbial communities in the rhizosphere of agriculturally intensive ecosystems.

Monitoring of Wheat Powdery Mildew under Different Nitrogen Input Levels Using Hyperspectral Remote Sensing

Both wheat powdery mildew severities and nitrogen input levels can lead to changes in spectral reflectance, but they have been rarely studied simultaneously for their effect on spectral reflectance. To determine the effects and influences of different nitrogen input levels on monitoring wheat powdery mildew and estimating yield by near-ground hyperspectral remote sensing, Canopy hyperspectral reflectance data acquired at Feekes growth stage (GS) 10.5.3, 10.5.4, and 11.1 were used to monitor wheat powdery mildew and estimate grain yield under different nitrogen input levels during the 2016–2017, 2017–2018, 2018–2019 and 2019–2020 seasons. The relationships of powdery mildew and grain yield with vegetation indices (VIs) derived from spectral reflectance data across the visible (VIS) and near-infrared (NIR) regions of the spectrum were studied. The relationships of canopy spectral reflectance or first derivative spectral reflectance with powdery mildew did not differ under different nitrogen input levels. However, the dynamics of VIs differed in their sensitivities to nitrogen input levels, disease severity, grain yield, The area of the red edge peak (Σdr680–760 nm) was a better overall predictor for both disease severity and grain yield through linear regression models. The slope parameter estimates did not differ between the two nitrogen input levels at each GSs. Hyperspectral indices can be used to monitor wheat powdery mildew and estimate grain yield under different nitrogen input levels, but such models are dependent on GS and year, further research is needed to consider how to incorporate the growth stage and year-to-year variation into future applications.

Response of Soil Biological Properties and Bacterial Diversity to Different Levels of Nitrogen Application in Sugarcane Fields

Field experiments were performed in early March 2019 at the farm of the Sugarcane Research Institute, Guangxi Academy of Agricultural Sciences. Four concentrations of nitrogen application were employed as follows: that is, urea applications 964, 482, 96, 0 kg ha− 1, respectively. And 300 kg ha− 1 calcium, magnesium, and phosphorus were likewise applied in 4 different treatments. The results showed that the soil microbial biomass carbon and phosphorus were altered significantly by non- and low-nitrogen input. Moreover, the indexes of soil bacterial richness and diversity in the sugarcane field could be significantly improved, even by low nitrogen input. At the genus level, norank_f__SC-I-84, Mycobacterium, norank_f__Micropepsaceae, norank_f__norank_o__Saccharimonadales, norank_f__norank_o__Subgroup_2 and norank_f__Acetobacteraceae were the unique dominant bacteria in the soil with the high nitrogen input treatment. norank_f__JG30-KF-CM45 and Jatrophihabitans were the unique dominant genera in the moderate nitrogen input treatment. norank_f__norank_o__norank_c__Subgroup_6, HSB_OF53-F07, Streptomyces, norank_f__67 − 14, norank_f__norank_o__SBR1031 and norank_f__norank_o__norank_c__KD4-96 were the unique dominant genera in the low nitrogen input treatment. In contrast, FCPS473, Actinospica, 1921-2, Sinomonas, and norank_f__Ktedonobacteraceae were the unique dominant genera in CK (no nitrogen application treatment). It suggested that low nitrogen input was the most significant effect on the soil microbial biomass carbon and phosphorus in the sugarcane field. Moreover, low nitrogen input also can improve the diversity and richness of sugarcane soil bacteria. The dominant bacterial genera of low nitrogen input and the other treatments were different for the compositions of dominant bacteria, and the largest abundance difference of dominant bacterial genera was norank_f__norank_o__norank_c__Subgroup_6. However, whether low nitrogen stress can improve the yield and quality of sugarcane warrants further research.