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<p>Soil acidification has increasingly become a critical issue for sustainable production due to the excessive nitrogen (N) fertilization in agricultural systems. Application of N fertilizers and the consequent nitrification yield protons (H<sup>+</sup>), which strongly and irreversibly accelerate dissolution of soil inorganic carbon (SIC) e.g., CaCO<sub>3</sub>, leading to CO<sub>2</sub> release in the atmosphere. Here, <sup>14</sup>C-labeled CaCO<sub>3</sub> was added to calcareous soil (0.75% CaCO<sub>3</sub>) to investigate the effects of chicken manure, urea, NH<sub>4</sub>NO<sub>3, </sub>KNO<sub>3 </sub>and<sub> </sub>(NH<sub>4</sub>)<sub>2</sub>SO<sub>4</sub> on soil acidification and to estimate the SIC contribution to CO<sub>2</sub> emission. 250 mL gas-tight jars were filled with a cropland soil (pH = 7.2), homogenously mixed with 1.3% Ca<sup>14</sup>CO<sub>3</sub> powder (<sup>14</sup>C activity = 11.3 kBq pot<sup>-1</sup>). Following fertilization in rates of 0.1, 0.15, 0.25 g N kg<sup>-1</sup> soil, NaOH was applied to trap the emitted CO<sub>2</sub> and to determine <sup>14</sup>C activity. CaCO<sub>3</sub> addition increased soil pH values by 0.17-0.43 units. Addition of ammonium-based fertilizers ((NH<sub>4</sub>)<sub>2</sub>SO<sub>4</sub>, NH<sub>4</sub>NO<sub>3</sub>) strongly decreased pH up to 0.3 units. All fertilizers increased CO<sub>2</sub> emission (5.1%-180%) compared to the unfertilized soil after 44 days of incubation except KNO<sub>3</sub>. SIC-originated CO<sub>2</sub> due to fertilization was ranged from 2.9 to 160 mg C kg<sup>-1</sup> (1.1% to 48% of total emitted CO<sub>2</sub>). Manure and urea had lowest impacts on SIC-driven CO<sub>2</sub> during the first 5 days (2.9-34 mg C kg<sup>-1</sup>) irrespective of the application rate. Thereafter, the effects of fertilizers on SIC-originated CO<sub>2</sub> increased in the order: urea < manure < KNO<sub>3</sub> < NH<sub>4</sub>NO<sub>3</sub> < (NH<sub>4</sub>)<sub>2</sub>SO<sub>4</sub>. As nitrification of (NH<sub>4</sub>)<sub>2</sub>SO<sub>4</sub> yields in 4 mol H<sup>+</sup>, which neutralizes 2 mol carbonates, it initially caused the highest SIC-originated CO<sub>2</sub><sub> </sub>until 9 days. Urea and NH<sub>4</sub>NO<sub>3</sub> release by nitrification 2 mol H<sup>+ </sup>per mole of fertilizer, but urea initially hydrolyses to NH<sub>4</sub>OH, which increases soil pH. So, urea addition had the minimum SIC loss as CO<sub>2</sub><sub> </sub>in the first 5 days, but starting from 16<sup>th</sup> day, CO<sub>2</sub> emission sharply increased and reached to highest values among the fertilizers. Manure increased SIC-originated CO<sub>2</sub> emission from 23<sup>rd</sup> day of incubation. Gradual and incomplete mineralization of organic N of chicken manure duration 44 days explains the smallest released CO<sub>2</sub> from CaCO<sub>3</sub> and slowest acidification in the first 16 days. Furthermore, Ca<sup>2+</sup> and Mg<sup>2+</sup> in manure may be precipitated as carbonates, which decrease the SIC share in the emitted CO<sub>2</sub>. Generally, the higher the applied fertilizer amounts, the larger was the proportion of CO<sub>2</sub> released from SIC. Both the fertilizer chemistry and the application rate played significant roles in dissolution of carbonates. Summarizing, the correct selection of the type and amount of fertilizers based on soil properties and plant demand is necessary to decrease SIC-originated CO<sub>2</sub> emission to mitigate global warming, and also save various ecosystem services such as organic matter stability and increase C sequestration.</p>

<p>Terrestrial ecosystems play a significant role in global warming by regulating CO<sub>2</sub> concentration in the atmosphere. A comprehensive understanding of carbon (C) sources and stocks in soils, as well as the driving mechanisms, are critical to reducing CO<sub>2</sub> emission from soil and thus mitigating climate change. To date, most studies have solely focused on processes involving soil organic C (SOC), but few studies have addressed the potential contribution of soil inorganic C (SIC) mostly CaCO<sub>3</sub> pool to ecosystem C fluxes. SIC can potentially be a regulator of atmospheric CO<sub>2</sub>. However, so far the effects of plant species (i.e. variations in nitrogen (N) demand and N use efficiency (NUE)) as well as soil temperature on SIC-derived CO<sub>2</sub> are unclear. We hypothesized that 1) relatively less SIC-derived CO<sub>2</sub> is expected from soils covered under plant species with lower N demand and higher NUE. We conducted a 4-month field experiment from June to October 2021 at the research station of the University of Göttingen in Deppoldshausen (51.58<sup>o</sup>N, 9.97<sup>o</sup>E) with ca. 6% CaCO<sub>3</sub> equivalent in the topsoil. We analyzed the effects of two plant species 1) wheat (high N demand and low NUE), 2) legume (low N demand and high NUE) and two N fertilization (urea) levels, 1) low (50 kg N ha<sup>-1</sup>), 2) high (200 kg N ha<sup>-1</sup>) on CO<sub>2</sub> emission out of SIC. Each treatment had four replicate plots (1×1 m<sup>2</sup>), and at least a 0.5 m gap was established between plots. We measured CO<sub>2</sub> fluxes weekly by using the static chamber method. The δ<sup>13</sup>C natural abundance was used to determine the contribution of SIC and SOC in the emitted CO<sub>2</sub>. The total CO<sub>2</sub> emission and its δ<sup>13</sup>C signature increased with soil temperature, indicating that the portion (%) of SIC-derived CO<sub>2</sub> was stimulated by temperature (<sup>o</sup>C) (slope = 0.33). The portion of SIC-derived CO<sub>2</sub> stimulated by temperature increased faster under wheat than under legume (slope = 0.36 vs. 0.26), especially under high N treatment (slope = 0.65 vs. 0.54). The portion of SIC-derived CO<sub>2</sub> under wheat (13.0%) was higher than that under legume (11.3%). Moreover, the portion of SIC-derived CO<sub>2</sub> was 1.2% higher under wheat than under legume at high N fertilization level, whereas it was increased to 2.2% under low N fertilization. This indicates a significant role of plant species with different N demand and NUE on dynamics of SIC pool and its contribution in CO<sub>2</sub> emission from soil. The rate of SIC-derived CO<sub>2</sub> was comparable between wheat and legume under high N fertilization, but it was 1.6 times higher under wheat than that under legume at low N fertilization. The contribution of SIC-derived C to the atmosphere was ~63.7 g C m<sup>-2</sup> yr<sup>-1</sup> under legume with low N demand vs. ~82.1 g C m<sup>-2</sup> yr<sup>-1</sup> under wheat with high N demand. In this regard, the impacts of plant species and their N demand and NUE are important controlling factors determining the dynamics of the SIC pool in agroecosystems.</p>