Nitrogen deposition suppresses soil respiration by reducing global belowground activity.

Soil respiration (Rs) indicates below-ground biological activities. Previous studies have suggested that higher nitrogen (N) deposition due to human activities exerts an increasingly negative effect on Rs. However, the mechanisms underlying this negative effect remain highly uncertain on a global scale. Using a global dataset of 262 N addition experiments, here we show the overall N addition effects on Rs changed from positive to negative with increasing N addition rate and duration. By constructing a structural equation model (SEM) that explained 41 % variation in the responses of Rs to N addition, we revealed that Rs under increasing N addition was simultaneously associated with decreases in soil pH, root biomass and microbial biomass, with the strongest influence by root biomass. Decreasing soil pH had cascading effects on root and microbial biomass, while N-addition-induced root biomass reduction further manifested a decrease in microbial biomass. Across global variations in the environment, lower background soil pH amplified the negative impacts of N addition on root and microbial biomass, which consequently exhilarated the negative impact of high N on Rs. Our results highlight that predicting the response of belowground biological activities to global changes is complex with the essence of integrative understanding for the multivariate pathways through soil physical properties, plants and microorganisms.

Pregnancy outcomes and disease phenotype of hypertensive disorders of pregnancy in singleton pregnancies after in vitro fertilization: a retrospective analysis of 1130 cases.

BACKGROUND: Although in vitro fertilization (IVF) can increase the incidence of hypertensive disorders of pregnancy (HDP), the pregnancy outcomes and disease phenotype of HDP in singleton pregnancies conceived via IVF remain unclear. METHODS: This retrospective cohort study enrolled 1130 singleton pregnancies with HDP from 2016 to 2020. According to the mode of conception, they were allocated into IVF (n = 102) and natural conception (NC) groups (n = 1028). All IVF pregnancies were subdivided into frozen embryo transfer (FET) group (n = 42) and fresh embryo transfer (ET) group (n = 60). Demographic data, pregnancy outcomes and disease phenotypes of HDP among the groups were compared. The risk factors for severe preeclampsia (PE) and early-onset PE were analyzed. RESULTS: The incidences of early-onset PE (P<0.001), severe PE (P = 0.016), cesarean section (P<0.001) and preterm births (P = 0.003) in the IVF-HDP group were significantly higher than those in the NC-HDP group, and gestational age at diagnosis of HDP (P = 0.027) and gestational age at delivery (P = 0.004) were earlier and birthweight of the neonates (P = 0.033) were lower in the IVF group. In singleton pregnancies with HDP, IVF was associated with increased risks for both severe PE and early-onset PE (aOR 1.945, 95% CI 1.256, 3.014; and aOR 2.373, 95% CI 1.537, 3.663, respectively), as well as FET, family history of preeclampsia, intrahepatic cholestasis of pregnancy, gestational hypothyroidism and multiparity were associated with increased risks of severe PE and early-onset PE. CONCLUSIONS: In singleton pregnancies with HDP, IVF was associated with an increased incidence of the disease phenotype (severe or early-onset PE), as well as an increased incidence of pregnancy outcomes related to severe PE and early-onset PE.

Mapping global soil acidification under N deposition.

Soil pH is critically important in regulating soil nutrients and thus influencing the biodiversity and ecosystem functions of terrestrial ecosystems. Despite the ongoing threat of nitrogen (N) pollution especially in the fast-developing regions, it remains unclear how increasing N deposition affects soil pH across global terrestrial ecosystems. By conducting a global meta-analysis with paired observations of soil pH under N addition and control from 634 studies spanning major types of terrestrial ecosystems, we show that soil acidification increases rapidly with N addition amount and is most severe in neutral-pH soils. Grassland soil pH decreases most strongly under high N addition while wetlands are the least acidified. By extrapolating these relationships to global mapping, we reveal that atmospheric N deposition leads to a global average soil pH decline of -0.16 in the past 40 years and regions encompassing Eastern United States, Southern Brazil, Europe, and South and East Asia are the hotspots of soil acidification under N deposition. Our results highlight that anthropogenically amplified atmospheric N deposition has profoundly altered global soil pH and chemistry. They suggest that atmospheric N deposition is a major threat to global terrestrial biodiversity and ecosystem functions.