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1. Tree diversity increases decadal forest soil carbon and nitrogen accrual

   https://doi.org/10.1038/s41586-023-05941-9  

   Chen, Xinli; Taylor, Anthony R; Reich, Peter B; Hisano, Masumi; Chen, Han_Y H; Chang, Scott X (June 2023, Nature)

   Increasing soil carbon and nitrogen storage can help mitigate climate change and sustain soil fertility1,2. A large number of biodiversity-manipulation experiments collectively suggest that high plant diversity increases soil carbon and nitrogen stocks3,4. It remains debated, however, whether such conclusions hold in natural ecosystems5-12. Here we analyse Canada's National Forest Inventory (NFI) database with the help of structural equation modelling (SEM) to explore the relationship between tree diversity and soil carbon and nitrogen accumulation in natural forests. We find that greater tree diversity is associated with higher soil carbon and nitrogen accumulation, validating inferences from biodiversity-manipulation experiments. Specifically, on a decadal scale, increasing species evenness from its minimum to maximum value increases soil carbon and nitrogen in the organic horizon by 30% and 42%, whereas increasing functional diversity enhances soil carbon and nitrogen in the mineral horizon by 32% and 50%, respectively. Our results highlight that conserving and promoting functionally diverse forests could promote soil carbon and nitrogen storage, enhancing both carbon sink capacity and soil nitrogen fertility. 

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2. Nitrogen increases early‐stage and slows late‐stage decomposition across diverse grasslands

   https://doi.org/10.1111/1365-2745.13878  

   Gill, Allison L.; Adler, Peter B.; Borer, Elizabeth T.; Buyarski, Christopher R.; Cleland, Elsa E.; D'Antonio, Carla M.; Davies, Kendi F.; Gruner, Daniel S.; Harpole, W. Stanley; Hofmockel, Kirsten S.; et al (June 2022, Journal of Ecology)
3. Tropospheric Nitrogen Dioxide Increases Past Pre-Pandemic Levels Due to Economic Reopening in India

   https://doi.org/10.3389/fenvs.2022.962891  

   Liu, Qian; Srirenganathanmalarvizhi, Anusha; Howell, Katherine; Yang, Chaowei (July 2022, Frontiers in Environmental Science)

   This paper analyzes the spatiotemporal patterns of nitrogen dioxide (NO2) tropospheric vertical column densities (TVCDs) before and during the second wave of COVID-19 in India. The results indicate that the NO2 columns increase significantly in the reopening period before the second wave (Mar. 1 ∼ Apr. 20) in 2021, which exceed the levels of the same period in 2019. The relative difference from the mean of 2010–2019 is 18.76% higher in 2021 than that of 2019, during the reopening. The paper identifies Odisha, Madhya Pradesh, Chhattisgarh, Jharkhand and West Bengal as the five states with the largest increases in relative difference from 2019 to 2021, which are 33.81%, 29.83%, 23.86%, 30.01%, and 25.48% respectively. As illustrated by trends in the indices of industrial production (IIP), these unexpected increases in tropospheric NO2 can be attributed to reopening as well as elevated production across various sectors including electricity, manufacturing and mining. Analysis of NO2 TVCD levels alongside IIPs indicate a marked increase in industrial activity during the reopening period in 2021 than in the same time period in 2019. After the beginning of the second wave of COVID-19 (Apr. 21 ∼ Jun. 21), India re-implemented lockdown policies to mitigate the spread of the pandemic. During this period, the relative difference of total NO2 columns declined in India as well as in most individual study regions, when compared to 2019, due to the pandemic mitigation policies. The relative declines are as follows: 6.43% for the whole country and 14.25%, 22.88%, 4.57% and 7.89% for Odisha, Madhya Pradesh, Chhattisgarh and Jharkhan, respectively, which contain large industrial clusters. The change in relative difference in West Bengal from 2019 to 2021 is not significant during the re-lockdown period with a 0.04% increase. As with the first wave, these decreases in NO2 TVCD mainly due to the mitigation policies during the second wave. 

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4. Plant–microbial competition for nitrogen increases microbial activities and carbon loss in invaded soils

   https://doi.org/10.1007/s00442-017-3861-0  

   Craig, Matthew E.; Fraterrigo, Jennifer M. (July 2017, Oecologia)
5. Arbuscular mycorrhizal diversity increases across a plant productivity gradient driven by soil nitrogen availability

   https://doi.org/10.1002/pei3.70002  

   McPherson, Morgan_R; Zak, Donald_R; Ibáñez, Inés; Upchurch, Rima_A; Argiroff, William_A (August 2024, Plant-Environment Interactions)

   Abstract Arbuscular mycorrhizal fungi (AMF) are widespread obligate symbionts of plants. This dynamic symbiosis plays a large role in successful plant performance, given that AMF help to ameliorate plant responses to abiotic and biotic stressors. Although the importance of this symbiosis is clear, less is known about what may be driving this symbiosis, the plant's need for nutrients or the excess of plant photosynthate being transferred to the AMF, information critical to assess the functionality of this relationship. Characterizing the AMF community along a natural plant productivity gradient is a first step in understanding how this symbiosis may vary across the landscape. We surveyed the AMF community diversity at 12 sites along a plant productivity gradient driven by soil nitrogen availability. We found that AMF diversity in soil environmental DNA significantly increased along with the growth of the host plantsAcerrubrumandA. saccharum., a widespread tree genus. These increases also coincided with a natural soil inorganic N availability gradient. We hypothesize photosynthate from the increased tree growth is being allocated to the belowground AMF community, leading to an increase in diversity. These findings contribute to understanding this complex symbiosis through the lens of AMF turnover and suggest that a more diverse AMF community is associated with increased host–plant performance. 

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