Effects of artificial nitrogen addition and reduction in precipitation on soil CO₂ and CH₄ effluxes and composition of the microbial biomass in a temperate forest

Abstract

To understand the effects of artificially increased atmospheric nitrogen (N) and decreased precipitation on the soil microbial community and soil CO2 and CH4 efflux, a two‐factorial field experiment was carried out with the following treatments: (a) control, (b) N addition (+50 kg N ha−1 year−1), (c) decreased precipitation (−30% of throughfall) and (d) combined N addition and decreased precipitation (+50 kg N ha−1 year−1, −30% of throughfall). The N addition and decreased precipitation treatments had a positive effect on mean CO2 efflux (2.61 μmol CO2 m−2 s−1 for control, 4.26 μmol CO2 m−2 s−1 for N addition, 3.62 μmol CO2 m−2 s−1 for reduction in precipitation) and mean rates of CH4 uptake (0.00088 μmol CH4 m−2 s−1 for control, 0.00154 μmol CH4 m−2 s−1 for N addition, 0.00151 μmol m−2 s−1 for reduction in precipitation) during the growing season. The combined N addition and reduction in precipitation also led to increased soil CO2 efflux and CH4 uptake, but the combined response was weaker than the response to single variable treatments (3.10 μmol CO2 m−2 s−1 and 0.00130 μmol CH4 m−2 s−1 interaction), indicating antagonistic effects of the combined treatment. At the seasonal scale, changes in soil CO2 and CH4 efflux were complex, especially in the spring freezing and thawing period, during which pulses of CO2 efflux and CH4 uptake occurred. Decreased precipitation altered the composition of the bacterial community in the winter and growing seasons, and composition of the microbial community also showed a seasonal change. However, changes in microbial community structure under N addition, precipitation reduction and their interaction might be important factors leading to an increase or decrease in soil carbon efflux. Highlights How global changes (N addition and decreased precipitation) affect soil C flux. Seasonal effects of global changes on soil C flux were analysed quantitatively. Decreased precipitation and N‐addition increased soil CO2 flux and decreased soil CH4 flux. Global changes regulate soil C flux by altering soil water, microbial and nutrient status.

Stimulated or Inhibited Response of Methane Flux to Nitrogen Addition Depends on Nitrogen Levels

“…Soil water content was suggested to be a determining factor affecting CH 4 consumption in upland soil (Luo et al., 2012; Zheng et al., 2016), indicating a unimodal response of CH 4 flux to soil water content with peak CH 4 uptake under optimal soil moisture conditions. The favorable soil water content was found to be from 10% to 40% of grassland and forest soils (Borken et al., 2006; Chen et al., 2011; Murguia‐Flores et al., 2018; Yan et al., 2019), which was similar to our finding of ∼20%–30%. The limited diffusion of CH 4 from the atmosphere into soil associated with excessive moisture could induce a decrease in CH 4 consumption by MOB; however, under low soil water conditions, MOB could be depressed, which could also induce decreased CH 4 oxidation.…”

Short Legacy Effects of Growing Season Nitrogen Addition and Reduced Precipitation alter Soil Respiration during Nongrowing Season

“…We added or removed one collar of the same size for each height adjustment and sealed the gaps between collars with water-and air-proof tape. Detailed information of adjusting soil collars in the nongrowing season has been described by Yan et al (2019c) [25]. Rs and Rh were measured between 10:00 am and 12:00 am (Beijing time) and each measurement was repeated three times for each collar to produce a mean value.…”

Soil carbon flux research in the Asian region: Review and future perspectives

“…These findings were consistent with those of most previous studies Schindlbacher et al, 2012;Deng et al, 2017 . However, in a tropical forest located in the Dinghushan Biosphere Reserve, southern China, an increase in the frequency of precipitation had stimulated R s due to enhanced leached dissolved organic C production Deng et al, 2018 . In contrast, in a temperate forest located in the Changbai Mountains Natural Reserve, northeast China, reduced precipitation significantly increased R s due to changes in the bacterial community Yan et al, 2019a . These contradictory findings may be attributed to differences in soil texture, moisture regime, and microbial community composition among the different ecosystems.…”

“…Forest management practices such as thinning Son et al, 2004;Tian et al, 2009;Pang et al, 2013;Teramoto et al, 2019;Wang et al, 2019b;Zhao et al, 2019a, clear-cutting Kim, 2008Bai et al, 2020 , andN addition Liu et al, 2016a;Wang et al, 2019d;Yan et al, 2019a;Wang et al, 2020b may affect C sequestration, storage, and flux over time Peng et al, 2008;Bai et al, 2020 . Thinning, defined as the partial removal of trees from a plantation, is the most common silvicultural practice for sustainable forest management. Thinning changes the micro-climatic conditions and soil properties, such as soil temperature and moisture, organic matter and nutrient content, pH, conductivity, and microbial activity, ultimately impacting on R s Tian et al, 2009;Teramoto et al, 2019 .…”

“…This needs to be implemented alongside considerations to the global warming potential of N 2 O emissions and rice yields Wassmann et al, 2000a;Wang et al, 2012;Tirol-Padre et al, 2018 . External N deposition, originating mainly from fossil-fuel burning and artificial fertiliser applications, have been widely reported to enhance plant and soil microbial respiration by directly altering soil N availability and indirectly altering physiochemical properties Zhou et al, 2014;Peng et al, 2017;Yan et al, 2019a . In many areas in the Asian region, N deposition is expected to continue to increase Zhao et al, 2009 . Artificial N addition was found to increase R s in a temperate forest Yan et al, 2019a andmeadow grasslands Zhang et al, 2014;Zhu et al, 2015;Fang et al, 2017;Wang et al, 2020b . Moreover, a 12-year long-term N enrichment treatment decreased R s , and was also observed to produce soil acidification in grasslands Chen et al, 2016.…”