Nitrogen deposition and greenhouse gas emissions from grasslands: uncertainties and future directions

Gomez‐Casanovas, Nuria; Hudiburg, T. W.; Bernacchi, Carl J.; Parton, William J.; DeLucia, Evan H.

doi:10.1111/gcb.13187

Cited by 52 publications

(21 citation statements)

References 69 publications

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“…Both pastures were net sources of CH 4 , and although fluxes were highly variable among years, emissions were within the range reported for temperate flooded and subtropical grasslands (range from À0.2 to 5 g C-CH 4 Ám À2 Áyr À1 ; Gomez-Casanovas et al 2016), and grazed and ungrazed temperate and subtropical pastures (range from À0.3 to 16 g C-CH 4 Ám À2 Áyr À1 ; Couwenberg et al 2010, Dengel et al 2011, Teh et al 2011, Baldocchi et al 2012, Chamberlain et al 2015, 2016. In both pastures, increased net CH 4 emissions in 2013 compared with 2014 and 2015 was likely explained by a wetter wet season (Figs.…”

Section: Discussionsupporting

confidence: 69%

Grazing alters net ecosystem C fluxes and the global warming potential of a subtropical pasture

Gomez‐Casanovas

DeLucia

Bernacchi

et al. 2018

Ecological Applications

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The impact of grazing on C fluxes from pastures in subtropical and tropical regions and on the environment is uncertain, although these systems account for a substantial portion of global C storage. We investigated how cattle grazing influences net ecosystem CO and CH exchange in subtropical pastures using the eddy covariance technique. Measurements were made over several wet-dry seasonal cycles in a grazed pasture, and in an adjacent pasture during the first three years of grazer exclusion. Grazing increased soil wetness but did not affect soil temperature. By removing aboveground biomass, grazing decreased ecosystem respiration (R ) and gross primary productivity (GPP). As the decrease in R was larger than the reduction in GPP, grazing consistently increased the net CO sink strength of subtropical pastures (55, 219 and 187 more C/m in 2013, 2014, and 2015). Enteric ruminant fermentation and increased soil wetness due to grazers, increased total net ecosystem CH emissions in grazed relative to ungrazed pasture (27-80%). Unlike temperate, arid, and semiarid pastures, where differences in CH emissions between grazed and ungrazed pastures are mainly driven by enteric ruminant fermentation, our results showed that the effect of grazing on soil CH emissions can be greater than CH produced by cattle. Thus, our results suggest that the interactions between grazers and soil hydrology affecting soil CH emissions play an important role in determining the environmental impacts of this management practice in a subtropical pasture. Although grazing increased total net ecosystem CH emissions and removed aboveground biomass, it increased the net storage of C and decreased the global warming potential associated with C fluxes of pasture by increasing its net CO sink strength.

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Section: Discussionsupporting

confidence: 69%

Grazing alters net ecosystem C fluxes and the global warming potential of a subtropical pasture

Gomez‐Casanovas

DeLucia

Bernacchi

et al. 2018

Ecological Applications

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“…The role of the CO 2 flux for the GHG budget can become even more pronounced in grasslands, as such ecosystems are often limited by soil N availability, and N addition during fertilization increases the CO 2 sink more than the N 2 O and CH 4 sources (Gomez-Casanovas, Hudiburg, Bernacchi, Parton, & DeLucia, 2016). The role of the CO 2 flux for the GHG budget can become even more pronounced in grasslands, as such ecosystems are often limited by soil N availability, and N addition during fertilization increases the CO 2 sink more than the N 2 O and CH 4 sources (Gomez-Casanovas, Hudiburg, Bernacchi, Parton, & DeLucia, 2016).…”

Section: Introductionmentioning

confidence: 99%

Greenhouse gas fluxes over managed grasslands in Central Europe

Hörtnagl

Barthel

Buchmann

et al. 2018

Global Change Biology

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Central European grasslands are characterized by a wide range of different management practices in close geographical proximity. Site-specific management strategies strongly affect the biosphere-atmosphere exchange of the three greenhouse gases (GHG) carbon dioxide (CO ), nitrous oxide (N O), and methane (CH ). The evaluation of environmental impacts at site level is challenging, because most in situ measurements focus on the quantification of CO exchange, while long-term N O and CH flux measurements at ecosystem scale remain scarce. Here, we synthesized ecosystem CO , N O, and CH fluxes from 14 managed grassland sites, quantified by eddy covariance or chamber techniques. We found that grasslands were on average a CO sink (-1,783 to -91 g CO m year ), but a N O source (18-638 g CO -eq. m year ), and either a CH sink or source (-9 to 488 g CO -eq. m year ). The net GHG balance (NGB) of nine sites where measurements of all three GHGs were available was found between -2,761 and -58 g CO -eq. m year , with N O and CH emissions offsetting concurrent CO uptake by on average 21 ± 6% across sites. The only positive NGB was found for one site during a restoration year with ploughing. The predictive power of soil parameters for N O and CH fluxes was generally low and varied considerably within years. However, after site-specific data normalization, we identified environmental conditions that indicated enhanced GHG source/sink activity ("sweet spots") and gave a good prediction of normalized overall fluxes across sites. The application of animal slurry to grasslands increased N O and CH emissions. The N O-N emission factor across sites was 1.8 ± 0.5%, but varied considerably at site level among the years (0.1%-8.6%). Although grassland management led to increased N O and CH emissions, the CO sink strength was generally the most dominant component of the annual GHG budget.

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“…Similarly, net ecosystem CO 2 exchange (NEE) and its components of gross ecosystem production (GEP) and ecosystem respiration (ER) may also respond nonlinearly to increasing N loading rates (Fleischer et al, 2013;Gomez-Casanovas et al, 2016;Tian et al, 2016). In the N-limited stage, low rates of N addition could stimulate ecosystem productivity (Aber et al, 1989), GEP (Fleischer et al, 2013;Gomez-Casanovas et al, 2016), and ER (Hasselquist et al, 2012;Zhu et al, 2016), while in the N saturation stage, high doses of N addition could have negative effects on GEP and ER (Treseder, 2008;Janssens et al, 2010;Maaroufi et al, 2015). The unbalanced responses of GEP and ER may lead to changes in NEE.…”

Section: Introductionmentioning

confidence: 99%

Initial shifts in nitrogen impact on ecosystem carbon fluxes in an alpine meadow: patterns and causes

et al. 2017

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Abstract. Increases in nitrogen (N) deposition can greatly stimulate ecosystem net carbon (C) sequestration through positive N-induced effects on plant productivity. However, how net ecosystem CO 2 exchange (NEE) and its components respond to different N addition rates remains unclear. Using an N addition gradient experiment (six levels: 0, 2, 4, 8, 16, 32 gN m −2 yr −1 ) in an alpine meadow on the Qinghai-Tibetan Plateau, we explored the responses of different ecosystem C fluxes to an N addition gradient and revealed mechanisms underlying the dynamic responses. Results showed that NEE, ecosystem respiration (ER), and gross ecosystem production (GEP) all increased linearly with N addition rates in the first year of treatment but shifted to N saturation responses in the second year with the highest NEE (−7.77 ± 0.48 µmol m −2 s −1 ) occurring under an N addition rate of 8 gN m −2 yr −1 . The saturation responses of NEE and GEP were caused by N-induced accumulation of standing litter, which limited light availability for plant growth under high N addition. The saturation response of ER was mainly due to an N-induced saturation response of aboveground plant respiration and decreasing soil microbial respiration along the N addition gradient, while decreases in soil microbial respiration under high N addition were caused by N-induced reductions in soil pH. We also found that various components of ER, including aboveground plant respiration, soil respiration, root respiration, and microbial respiration, responded differentially to the N addition gradient. These results reveal temporal dynamics of N impacts and the rapid shift in ecosystem C fluxes from N limitation to N saturation. Our findings bring evidence of short-term initial shifts in responses of ecosystem C fluxes to increases in N deposition, which should be considered when predicting long-term changes in ecosystem net C sequestration.

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Nitrogen deposition and greenhouse gas emissions from grasslands: uncertainties and future directions

Cited by 52 publications

References 69 publications

Grazing alters net ecosystem C fluxes and the global warming potential of a subtropical pasture

Grazing alters net ecosystem C fluxes and the global warming potential of a subtropical pasture

Greenhouse gas fluxes over managed grasslands in Central Europe

Initial shifts in nitrogen impact on ecosystem carbon fluxes in an alpine meadow: patterns and causes

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