Inorganic Nitrogen Addition Affects Soil Respiration and Belowground Organic Carbon Fraction for a Pinus tabuliformis Forest

Abstract

The capability of forest ecosystems to sequester carbon from the atmosphere largely depends on the interaction of soil organic matter and nitrogen, and thus, this process will be greatly influenced by nitrogen deposition under the future scenario of global change. To clarify this interaction, the current study explored the variations in soil carbon fraction and soil respiration with different levels of nitrogen deposition. NH4NO3 was added at concentrations of 0, 50, 100, 200, and 400 kg N ha−1 year−1 separately on twenty 100 m2 plots in a Pinus tabuliformis Carr forest in northern China. Soil samples were analyzed for their nutrient content and biophysical properties two years after nitrogen application, and the soil respiration rate was measured every month during the study period. Seasonal variation and nitrogen addition significantly affected soil respiration rate. On average, nitrogen addition significantly reduced the annual soil respiration rate by 23.74%. Fine root biomass significantly decreased by an average of 43.55% in nitrogen treatment plots compared to the control plot. However, the average proportions of autumn and winter soil respiration rates out of the annual cumulative soil respiration rate greatly increased from 23.57% and 11.04% to 25.90% and 12.18%, respectively. The soil microbial biomass carbon content in the control plot was 342.39 mg kg−1, 23.50% higher than the average value in nitrogen treatment plots. The soil dissolved organic carbon was reduced by 22.60%, on average, following nitrogen addition. Significant correlations were detected between fine root biomass and the annual cumulative soil respiration rate, soil microbial biomass carbon content, and soil dissolved organic carbon content. This demonstrates that nitrogen addition affects soil organic carbon transformation and carbon emission, mainly by depressing fine root production.

Nitrogen Addition Alleviates Microbial Nitrogen Limitations and Promotes Soil Respiration in a Subalpine Coniferous Forest

“…At present, a global meta-analysis showed that atmospheric N deposition negatively affects soil microbial growth, composition, function, and respiration across all terrestrial ecosystems; these negative effects increased with the N application rate and experimental duration [32]. However, the responses of soil respiration and microbial activities to N addition were inconsistent in previous studies [26], showing promotion [13,33,34], inhibition [16,35], and no effects [5,36]. The response of major microbial groups to N in terrestrial ecosystems was found to be mainly influenced by the duration and content of N inputs [17,37].…”

“…N addition effects on microbial biomass (G + , B, MBC and MBN) were likely the most potent drivers of soil respiration, according to the RDA and SEM results. Third, increasing N availability benefited plant growth by enhancing new soil organic matter input, thus leading to an increase in soil respiration [16,43,44].…”

“…Although many studies regarding the effects of atmospheric N deposition on microbial respiration and microbial community composition in terrestrial ecosystems have been conducted [7,[13][14][15][16][17], a clear understanding of microbial activity and microbial nutrient limitations in alpine regions remains elusive.…”

The Roles of Bacteria in Soil Organic Carbon Accumulation under Nitrogen Deposition in Stipa baicalensis Steppe

“…The critical N load is estimated to be between 8 and 10 g N m −2 year −1 [16]. Conversely, the SOC content was reduced following N addition in a Pinus tabuliformis forest [17] and Tibetan alpine meadow [18], especially in the 10-20 cm soil layer [19]. Research has found that N addition tends to enhance SOC mineralization [20].…”

Effects of long-term nitrogen addition on soil respiration and its components in a boreal forest

“…3), which was much higher than that of 1.05 μmol CO 2 m -2 s -1 in spruce forest, 0.96μmol CO 2 m -2 s -1 in Abies forest (Wang et al 2019a), and the mean value of Chinese coniferous forest (2.32 μmol CO 2 m -2 s -1 ) (Dai et al 2015). In all treatments, the Rs of Larix gmelinii forest showed positive responses to low N treatment, which was different from other results (Wang et al 2019b;Zhang et al 2019b;Yan et al 2020). Zhong et al (2016) considered that forest was less affected by human activities, and had a balanced soil N cycle.…”