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RESEARCH ARTICLE

Effects of nitrogen addition on soil oxidisable organic carbon fractions in the rhizospheric and bulk soils of Chinese pines in north-western China

Hongfei Liu A , Sha Xue A B , Guoliang Wang A B and Guobin Liu C
+ Author Affiliations
- Author Affiliations

A College of Forestry, State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Northwest A&F University, Yangling 712100, Shaanxi, P. R. China.

B Institute of Soil and Water Conservation, Chinese Academy of Sciences and Ministry of Water Resources, Yangling 712100, Shaaxi, P. R. China.

C Corresponding author. Email: gbliu@ms.iswc.ac.cn

Soil Research 56(2) 192-203 https://doi.org/10.1071/SR16358
Submitted: 21 December 2016  Accepted: 21 August 2017   Published: 2 November 2017

Abstract

Increased atmospheric nitrogen (N) deposition caused by human activities has potentially important effects on ecosystem carbon (C) dynamics and different effects on C fractions with different stabilities and chemical compositions. A better understanding of the responses of different C fractions to N addition is vital for maintaining soil quality and protecting vegetation. In order to investigate the differential effects of N addition on total soil organic carbon (SOC) and four SOC fractions with increasing degrees of oxidisability in Pinus tabuliformis rhizospheric and bulk soils, a 6-year pot experiment was performed testing the effects of the addition of N at rates of 2.8, 5.6, 11.2, 22.4 and 44.8 g m–2 year–1 compared with a control (CK) group (no N addition). Addition of N addition had significant (P < 0.05) effects on SOC fractions of very labile C (C1) and recalcitrant C (C4), but negligible effects on total SOC (TOC) and SOC fractions of labile C (C2) and less labile C (C3). The C1 content and ratio of C1 to TOC in rhizospheres decreased following the addition of low levels (N2.8–N5.6) of N, but increased after the addition of high levels (N11.2–N44.8) of N, with minimum values obtained after the addition of 11.2 N g m–2 year–1. Low rates (N2.8–N5.6) of N addition considerably increased C4 and the ratio of C4 to TOC in the rhizosphere, whereas addition of high rates (N11.2–N44.8) of N decreased these parameters. The responses of C1 and C4 in the bulk soil to N addition were opposite. The SOC fraction was significantly higher in the rhizosphere than in the bulk soil, indicating large rhizospheric effects. However, increased N addition weakened these effects. These findings suggest that low rates (N2.8–N5.6) of N addition stabilise SOC against chemical and biological degradation, whereas increased rates of N addition increase the lability of SOC in the bulk soil. Thus, the rhizosphere plays a vital role in soil carbon stability and sequestration in response to N addition.

Additional keywords: Pinus tabuliformis, rhizosphere, nitrogen deposition, carbon stabilization.


References

Ai C, Liang G, Sun J, Wang X, Zhou W (2012a) Responses of extracellular enzyme activities and microbial community in both the rhizosphere and bulk soil to long-term fertilization practices in a fluvo-aquic soil. Geoderma 173–174, 330–338.
Responses of extracellular enzyme activities and microbial community in both the rhizosphere and bulk soil to long-term fertilization practices in a fluvo-aquic soil.Crossref | GoogleScholarGoogle Scholar |

Andersson P, Berggren D, Johnsson L (2001) 30 years of N fertilisation in a forest ecosystem – the fate of added N and effects on N fluxes. Water, Air, and Soil Pollution 130, 637–642.
30 years of N fertilisation in a forest ecosystem – the fate of added N and effects on N fluxes.Crossref | GoogleScholarGoogle Scholar |

Averill C, Turner BL, Finzi AC (2014) Mycorrhiza-mediated competition between plants and decomposers drives soil carbon storage. Nature 505, 543–545.
Mycorrhiza-mediated competition between plants and decomposers drives soil carbon storage.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC2cXhtFOls70%3D&md5=4b605f96a441e59639ee15771c3e2203CAS |

Blair GJ, Lefroy RDB, Lise L (1995) Soil carbon fractions based on their degree of oxidation, and the development of a carbon management index for agricultural systems. Australian Journal of Agricultural Research 46, 1459–1466.
Soil carbon fractions based on their degree of oxidation, and the development of a carbon management index for agricultural systems.Crossref | GoogleScholarGoogle Scholar |

Bowden RD, Davidson E, Savage K, Arabia C, Steudler P (2004) Chronic nitrogen additions reduce total soil respiration and microbial respiration in temperate forest soils at the Harvard Forest. Forest Ecology and Management 196, 43–56.
Chronic nitrogen additions reduce total soil respiration and microbial respiration in temperate forest soils at the Harvard Forest.Crossref | GoogleScholarGoogle Scholar |

Bremner JM, Mulvaney CS (1982) Nitrogen-total. Agronomy monograph 9. In ‘Methods of soil analysis, part 2, chemical and microbial properties’. (Eds AL Page, RH Miller, DR Keeney) pp. 595–624. (Agronomy Society of America: Madison, WI)

Britton AJ, Helliwell RC, Fisher JM, Gibbs S (2008) Interactive effects of nitrogen deposition and fire on plant and soil chemistry in an alpine heathland. Environmental Pollution 156, 409–416.
Interactive effects of nitrogen deposition and fire on plant and soil chemistry in an alpine heathland.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD1cXht12rtLnI&md5=21a4eac2fafeab41d080cfeaab863aeeCAS |

Butler JL, Williams MA, Bottomley PJ, Myrold DD (2003) Microbial community dynamics associated with rhizosphere carbon flow. Applied and Environmental Microbiology 69, 6793–6800.
Microbial community dynamics associated with rhizosphere carbon flow.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD3sXptVyktbw%3D&md5=ba0eee851257738153bbde1f50566724CAS |

Carrillo Y, Pendall E, Dijkstra FA, Morgan JA, Newcomb JM (2011) Response of soil organic matter pools to elevated CO2 and warming in a semi-arid grassland. Plant and Soil 347, 339–350.
Response of soil organic matter pools to elevated CO2 and warming in a semi-arid grassland.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC3MXhtFyjsbnL&md5=40b85c771277b284e0f22357eef2d40aCAS |

Chan KY, Bowman A, Oates A (2001) Oxidizible organic carbon fractions and soil quality changes in an Oxic Paleustalf under different pasture leys. Soil Science 166, 61–67.
Oxidizible organic carbon fractions and soil quality changes in an Oxic Paleustalf under different pasture leys.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD3MXjt1OitLw%3D&md5=3fc6b3b0b7fc2f5240200879ab7be255CAS |

Chen MC, Wang MK, Chiu CY, Huang PM, King HB (2001) Determination of low molecular weight dicarboxylic acids and organic functional groups in rhizosphere and bulk soils of Tsuga and Yushania in a temperate rain forest. Plant and Soil 231, 37–44.
Determination of low molecular weight dicarboxylic acids and organic functional groups in rhizosphere and bulk soils of Tsuga and Yushania in a temperate rain forest.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD3MXjvVSjtLw%3D&md5=86421d3f20ab3f82e5de2a1c1da0e008CAS |

Chen X, Li Y, Mo J, Otieno D, Tenhunen J, Yan J, Liu J, Zhang D (2012a) Effects of nitrogen deposition on soil organic carbon fractions in the subtropical forest ecosystems of S China. Journal of Plant Nutrition and Soil Science 175, 947–953.
Effects of nitrogen deposition on soil organic carbon fractions in the subtropical forest ecosystems of S China.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC38XhtVyktLjI&md5=e2ad2c00a6dcaf57262f6727cf0e6eaaCAS |

Chen X, Liu J, Deng Q, Yan J, Zhang D (2012b) Effects of elevated CO2 and nitrogen addition on soil organic carbon fractions in a subtropical forest. Plant and Soil 357, 25–34.
Effects of elevated CO2 and nitrogen addition on soil organic carbon fractions in a subtropical forest.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC38XhtVegt7jI&md5=d6e65ec367e06649a12f4ce79334addbCAS |

Cheng WX, Johnson DW, Fu SL (2003) Rhizosphere effects on decomposition: controls of plant species, phenology, and fertilization. Soil Science Society of America Journal 67, 1418–1427.
Rhizosphere effects on decomposition: controls of plant species, phenology, and fertilization.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD3sXnsVGluro%3D&md5=70c4a1d627022c82a0e5ab9cc0ff248bCAS |

Cheng XL, Luo YQ, Su B, Wan SQ, Hui DF, Zhang QF (2011) Plant carbon substrate supply regulated soil nitrogen dynamics in a tallgrass prairie in the Great Plains, USA: results of a clipping and shading experiment. Journal of Plant Ecology 4, 228–235.
Plant carbon substrate supply regulated soil nitrogen dynamics in a tallgrass prairie in the Great Plains, USA: results of a clipping and shading experiment.Crossref | GoogleScholarGoogle Scholar |

Datta SP, Rattan RK, Chandra S (2010) Labile soil organic carbon, soil fertility, and crop productivity as influenced by manure and mineral fertilizers in the tropics. Journal of Plant Nutrition and Soil Science 173, 715–726.
Labile soil organic carbon, soil fertility, and crop productivity as influenced by manure and mineral fertilizers in the tropics.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC3cXhsVSqsbjK&md5=ec7ad052ee6dfeb910ff5eb4133ca81cCAS |

DeForest JL, Zak DR, Pregitzer KS, Burton AJ (2004) Atmospheric nitrate deposition, microbial community composition, and enzyme activity in northern hardwood forests. Soil Science Society of America Journal 68, 132–138.
Atmospheric nitrate deposition, microbial community composition, and enzyme activity in northern hardwood forests.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD2cXmsFaltg%3D%3D&md5=ebcb97a962bbebeedf37a571fd517a35CAS |

Dennis PG, Miller AJ, Hirsch PR (2010) Are root exudates more important than other sources of rhizodeposits in structuring rhizosphere bacterial communities? FEMS Microbiology Ecology 72, 313–327.
Are root exudates more important than other sources of rhizodeposits in structuring rhizosphere bacterial communities?Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC3cXmslKmurg%3D&md5=5878529072da8e5156224ccafa38c99aCAS |

Dijkstra FA, Carrillo Y, Pendall E, Morgan JA (2013) Rhizosphere priming: a nutrient perspective. Frontiers in Microbiology 4, 216
Rhizosphere priming: a nutrient perspective.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC3sXhtlGju7fM&md5=0c95146c79fcd902c9297ac93c2ffcc0CAS |

Emmett BA, Reynolds B, Silgram M, Sparks TH, Woods C (1998) The consequences of chronic nitrogen additions on N cycling and soilwater chemistry in a Sitka spruce stand, North Wales. Forest Ecology and Management 101, 165–175.
The consequences of chronic nitrogen additions on N cycling and soilwater chemistry in a Sitka spruce stand, North Wales.Crossref | GoogleScholarGoogle Scholar |

Fang YT, Yoh M, Koba K, Zhu W, Takebayashi Y, Xiao Y, Lei C, Mo J, Zhang W, Lu X (2011) Nitrogen deposition and forest nitrogen cycling along an urban–rural transect in southern China. Global Change Biology 17, 872–885.
Nitrogen deposition and forest nitrogen cycling along an urban–rural transect in southern China.Crossref | GoogleScholarGoogle Scholar |

Fenn ME, Poth MA, Aber JD, Baron JS, Bormann BT, Johnson DW, Lemly AD, McNulty SG, Ryan DF, Stottlemyer R (1998) Nitrogen excess in North American ecosystems: predisposing factors, ecosystem responses, and management strategies. Ecological Applications 8, 706–733.
Nitrogen excess in North American ecosystems: predisposing factors, ecosystem responses, and management strategies.Crossref | GoogleScholarGoogle Scholar |

Fenn ME, Baron JS, Allen EB, Rueth HM, Nydick KR, Geiser L, Bowman WD, Sickman JO, Meixner T, Johnson DW, Neitlich P (2003) Ecological effects of nitrogen deposition in the western United States. Bioscience 53, 404–420.
Ecological effects of nitrogen deposition in the western United States.Crossref | GoogleScholarGoogle Scholar |

Fontaine S, Henault C, Aamor A, Bdioui N, Bloor JMG, Maire V, Mary B, Revaillot S, Maron PA (2011) Fungi mediate long term sequestration of carbon and nitrogen in soil through their priming effect. Soil Biology & Biochemistry 43, 86–96.
Fungi mediate long term sequestration of carbon and nitrogen in soil through their priming effect.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC3cXhsVGrs7rO&md5=c152ccccc09e41b642ddd2ad2430fcedCAS |

Frey SD, Knorr M, Parrent JL, Simpson RT (2004) Chronic nitrogen enrichment affects the structure and function of the soil microbial community in temperate hardwood and pine forests. Forest Ecology and Management 196, 159–171.
Chronic nitrogen enrichment affects the structure and function of the soil microbial community in temperate hardwood and pine forests.Crossref | GoogleScholarGoogle Scholar |

Galloway JN, Dentener FJ, Capone DG, Boyer EW, Howarth RW, Seitzinger SP, Asner GP, Cleveland CC, Green PA, Holland EA, Karl DM, Michaels AF, Porter JH, Townsend AR, Vöosmarty CJ (2004) Nitrogen cycles: past, present, and future. Biogeochemistry 70, 153–226.
Nitrogen cycles: past, present, and future.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD2MXpsFShtw%3D%3D&md5=b93c31d62000a8dfda1cd4a63577c7a3CAS |

Galloway JN, Townsend AR, Erisman JW, Bekunda M, Cai ZC, Freney JR, Martinelli LA, Seitzinger SP, Sutton MA (2008) Transformation of the nitrogen cycle: Recent trends, questions, and potential solutions. Science 320, 889–892.
Transformation of the nitrogen cycle: Recent trends, questions, and potential solutions.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD1cXlslygsbw%3D&md5=837e6d3057edd8d8622a187f811cd8feCAS |

Grayston SJ, Vaughan D, Jones D (1997) Rhizosphere carbon flow in trees, in comparison with annual plants: the importance of root exudation and its impact on microbial activity and nutrient availability. Applied Soil Ecology 5, 29–56.
Rhizosphere carbon flow in trees, in comparison with annual plants: the importance of root exudation and its impact on microbial activity and nutrient availability.Crossref | GoogleScholarGoogle Scholar |

Griffiths BS (1994) Microbial-feeding nematodes and protozoa in soil – their effects on microbial activity and nitrogen mineralization in decomposition hotspots and the rhizosphere. Plant and Soil 164, 25–33.
Microbial-feeding nematodes and protozoa in soil – their effects on microbial activity and nitrogen mineralization in decomposition hotspots and the rhizosphere.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK2MXitlyktLs%3D&md5=0106ef41eca38c71db42c46a6283c58fCAS |

Gruber N, Galloway JN (2008) An Earth-system perspective of the global nitrogen cycle. Nature 451, 293–296.
An Earth-system perspective of the global nitrogen cycle.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD1cXnt1Cqsg%3D%3D&md5=ce9f93155720c4cc4fe0ace00973d5b4CAS |

Hagedorn F, Kammer A, Schmidt MWI, Goodale CL (2012) Nitrogen addition alters mineralization dynamics of 13C-depleted leaf and twig litter and reduces leaching of older DOC from mineral soil. Global Change Biology 18, 1412–1427.
Nitrogen addition alters mineralization dynamics of 13C-depleted leaf and twig litter and reduces leaching of older DOC from mineral soil.Crossref | GoogleScholarGoogle Scholar |

Han XW, Tsunekawa A, Tsubo M, Li SQ (2011) Aboveground biomass response to increasing nitrogen deposition on grassland on the northern Loess Plateau of China. Acta Agriculturae Scandinavica, Section B – Soil & Plant Science 61, 112–121.
Aboveground biomass response to increasing nitrogen deposition on grassland on the northern Loess Plateau of China.Crossref | GoogleScholarGoogle Scholar |

Hinsinger P, Bengough AG, Vetterlein D, Young IM (2009) Rhizosphere: biophysics, biogeochemistry and ecological relevance. Plant and Soil 321, 117–152.
Rhizosphere: biophysics, biogeochemistry and ecological relevance.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD1MXos1enu78%3D&md5=6e537f757f77c3354222b437e2883e5bCAS |

Hobbie JE, Hobbie EA (2006) N-15 in symbiotic fungi and plants estimates nitrogen and carbon flux rates in Arctic tundra. Ecology 87, 816–822.
N-15 in symbiotic fungi and plants estimates nitrogen and carbon flux rates in Arctic tundra.Crossref | GoogleScholarGoogle Scholar |

Hobbie SE, Eddy WC, Buyarski CR, Adair EC, Ogdahl ML, Weisenhorn P (2012) Response of decomposing litter and its microbial community to multiple forms of nitrogen enrichment. Ecological Monographs 82, 389–405.
Response of decomposing litter and its microbial community to multiple forms of nitrogen enrichment.Crossref | GoogleScholarGoogle Scholar |

Janzen H (1987) Soil organic matter characteristics after long-term cropping to various spring wheat rotations. Canadian Journal of Soil Science 67, 845–856.
Soil organic matter characteristics after long-term cropping to various spring wheat rotations.Crossref | GoogleScholarGoogle Scholar |

Jiang XY, Cao LX, Zhang RD (2014) Changes of labile and recalcitrant carbon pools under nitrogen addition in a city lawn soil. Journal of Soils and Sediments 14, 515–524.
Changes of labile and recalcitrant carbon pools under nitrogen addition in a city lawn soil.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC3sXhvFeit7fK&md5=edd5273c2012ea674f7a75256a4a8a3eCAS |

Jones DL, Nguyen C, Finlay RD (2009) Carbon flow in the rhizosphere: carbon trading at the soil–root interface. Plant and Soil 321, 5–33.
Carbon flow in the rhizosphere: carbon trading at the soil–root interface.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD1MXos1enu7c%3D&md5=51c8999456d646e2f5a2dae617868afbCAS |

Kuzyakov Y, Biryukova OV, Kuznetzova TV, Molter K, Kandeler E, Stahr K (2002) Carbon partitioning in plant and soil, carbon dioxide fluxes and enzyme activities as affected by cutting ryegrass. Biology and Fertility of Soils 35, 348–358.
Carbon partitioning in plant and soil, carbon dioxide fluxes and enzyme activities as affected by cutting ryegrass.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD38Xks1SrtLs%3D&md5=6432240d0a6617dbf34ff03d11a1a8adCAS |

Laungani R, Knops JMH (2012) Microbial immobilization drives nitrogen cycling differences among plant species. Oikos 121, 1840–1848.
Microbial immobilization drives nitrogen cycling differences among plant species.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC3sXkvFeisQ%3D%3D&md5=5dda15e02ac7357df883d57889a2e995CAS |

Liljeroth E, Kuikman P, Vanveen JA (1994) Carbon translocation to the rhizosphere of maize and wheat and influence on the turnover of native soil organic-matter at different soil-nitrogen levels. Plant and Soil 161, 233–240.
Carbon translocation to the rhizosphere of maize and wheat and influence on the turnover of native soil organic-matter at different soil-nitrogen levels.Crossref | GoogleScholarGoogle Scholar |

Liu LL, Greaver TL (2010) A global perspective on belowground carbon dynamics under nitrogen enrichment. Ecology Letters 13, 819–828.
A global perspective on belowground carbon dynamics under nitrogen enrichment.Crossref | GoogleScholarGoogle Scholar |

Lovett GM, Arthur MA, Weathers KC, Fitzhugh RD, Templer PH (2013) Nitrogen addition increases carbon storage in soils, but not in trees, in an eastern US deciduous forest. Ecosystems 16, 980–1001.
Nitrogen addition increases carbon storage in soils, but not in trees, in an eastern US deciduous forest.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC3sXhtlWru7bN&md5=79de1b45056bd3b428c327fe6ddb2371CAS |

Lu XK, Mo JM, Gilliam FS, Zhou GY, Fang YT (2010) Effects of experimental nitrogen additions on plant diversity in an old-growth tropical forest. Global Change Biology 16, 2688–2700.
Effects of experimental nitrogen additions on plant diversity in an old-growth tropical forest.Crossref | GoogleScholarGoogle Scholar |

Lv F, Xue S, Wang G, Zhang C (2017) Nitrogen addition shifts the microbial community in the rhizosphere of Pinus tabuliformis in northwestern China. PLoS One 12, e0172382
Nitrogen addition shifts the microbial community in the rhizosphere of Pinus tabuliformis in northwestern China.Crossref | GoogleScholarGoogle Scholar |

Lynch JM, Whipps JM (1990) Substrate flow in the rhizosphere. Plant and Soil 129, 1–10.
Substrate flow in the rhizosphere.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK3MXotVCjtQ%3D%3D&md5=88db0b75095a479cbbab022cc40ef41cCAS |

Mack MC, Schuur EAG, Bret-Harte MS, Shaver GR, Chapin FS (2004) Ecosystem carbon storage in arctic tundra reduced by long-term nutrient fertilization. Nature 431, 440–443.
Ecosystem carbon storage in arctic tundra reduced by long-term nutrient fertilization.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD2cXnslelsro%3D&md5=ae49f30eb8838522ce2d809d852a2fd1CAS |

Maia SMF, Xavier FAS, Oliveira TS, Mendonça ES, Araújo Filho JA (2007) Organic carbon pools in a Luvisol under agroforestry and conventional farming systems in the semi-arid region of Ceará, Brazil. Agroforestry Systems 71, 127–138.
Organic carbon pools in a Luvisol under agroforestry and conventional farming systems in the semi-arid region of Ceará, Brazil.Crossref | GoogleScholarGoogle Scholar |

Nadelhoffer KJ, Downs MR, Fry B (1999) Sinks for N-15-enriched additions to an oak forest and a red pine plantation. Ecological Applications 9, 72–86.
Sinks for N-15-enriched additions to an oak forest and a red pine plantation.Crossref | GoogleScholarGoogle Scholar |

Neff JC, Townsend AR, Gleixner G, Lehman SJ, Turnbull J, Bowman WD (2002) Variable effects of nitrogen additions on the stability and turnover of soil carbon. Nature 419, 915–917.
Variable effects of nitrogen additions on the stability and turnover of soil carbon.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD38Xot1Klurw%3D&md5=001dcddd3e1075e036f99626017f8b7eCAS |

Nelson DW, Sommers LE, Sparks D, Page A, Helmke P, Loeppert R, Soltanpour P, Tabatabai M, Johnston C, Sumner M (1996) Total carbon, organic carbon, and organic matter. Methods of soil analysis Part 3 (Eds Nelson DW and Sommers LE)-chemical methods: 961-1010 (Soil Science Society of America and American Society of Agronomy: Madison, WI).

Ochoa-Hueso R, Stevens CJ, Ortiz-Llorente MJ, Manrique E (2013) Soil chemistry and fertility alterations in response to N application in a semiarid Mediterranean shrubland. The Science of the Total Environment 452–453, 78–86.
Soil chemistry and fertility alterations in response to N application in a semiarid Mediterranean shrubland.Crossref | GoogleScholarGoogle Scholar |

Phillips RP, Fahey TJ (2008) The influence of soil fertility on rhizosphere effects in northern hardwood forest soils. Soil Science Society of America Journal 72, 453–461.
The influence of soil fertility on rhizosphere effects in northern hardwood forest soils.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD1cXjsFynsbs%3D&md5=b7626eab27f045f61955c5e76f16553aCAS |

Phoenix GK, Emmett BA, Britton AJ, Caporn SJM, Dise NB, Helliwell R, Jones L, Leake JR, Leith ID, Sheppard LJ, Sowerby A, Pilkington MG, Rowe EC, Ashmore MR, Power SA (2012) Impacts of atmospheric nitrogen deposition: responses of multiple plant and soil parameters across contrasting ecosystems in long-term field experiments. Global Change Biology 18, 1197–1215.
Impacts of atmospheric nitrogen deposition: responses of multiple plant and soil parameters across contrasting ecosystems in long-term field experiments.Crossref | GoogleScholarGoogle Scholar |

Puglisi E, Fragoulis G, Del Re AAM, Spaccini R, Piccolo A, Gigliotti G, Said-Pullicino D, Trevisan M (2008) Carbon deposition in soil rhizosphere following amendments with compost and its soluble fractions, as evaluated by combined soil–plant rhizobox and reporter gene systems. Chemosphere 73, 1292–1299.
Carbon deposition in soil rhizosphere following amendments with compost and its soluble fractions, as evaluated by combined soil–plant rhizobox and reporter gene systems.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD1cXhtlSgsL%2FI&md5=140ed8e2e58b6511c60e2c4b20ae697bCAS |

Read DJ, Perez-Moreno J (2003) Mycorrhizas and nutrient cycling in ecosystems – a journey towards relevance? New Phytologist 157, 475–492.
Mycorrhizas and nutrient cycling in ecosystems – a journey towards relevance?Crossref | GoogleScholarGoogle Scholar |

Reay DS, Dentener F, Smith P, Grace J, Feely RA (2008) Global nitrogen deposition and carbon sinks. Nature Geoscience 1, 430–437.
Global nitrogen deposition and carbon sinks.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD1cXnvFCgsLs%3D&md5=2feb4a3776db295fc95662769ebf3e29CAS |

Reid JP, Adair EC, Hobbie SE, Reich PB (2012) Biodiversity, nitrogen deposition, and CO2 affect grassland soil carbon cycling but not storage. Ecosystems 15, 580–590.
Biodiversity, nitrogen deposition, and CO2 affect grassland soil carbon cycling but not storage.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC38XmvFGrsLg%3D&md5=83cdb48f0b4cdb45871c4621caa3e401CAS |

Reynolds B, Wilson EJ, Emmett BA (1998) Evaluating critical loads of nutrient nitrogen and acidity for terrestrial systems using ecosystem-scale experiments (NITREX). Forest Ecology and Management 101, 81–94.
Evaluating critical loads of nutrient nitrogen and acidity for terrestrial systems using ecosystem-scale experiments (NITREX).Crossref | GoogleScholarGoogle Scholar |

Rodriguez A, Lovett GM, Weathers KC, Arthur MA, Templer PH, Goodale CL, Christenson LM (2014) Lability of C in temperate forest soils: assessing the role of nitrogen addition and tree species composition. Soil Biology & Biochemistry 77, 129–140.
Lability of C in temperate forest soils: assessing the role of nitrogen addition and tree species composition.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC2cXht12ntLzI&md5=8d9f98c6658b78e5c2f65a2c85760232CAS |

Schlesinger WH (2009) On the fate of anthropogenic nitrogen. Proceedings of the National Academy of Sciences of the United States of America 106, 203–208.
On the fate of anthropogenic nitrogen.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD1MXltF2lsw%3D%3D&md5=7bfab95eac8d4daff895e1ea08598a2bCAS |

Sherrod L, Peterson G, Westfall D, Ahuja L (2005) Soil organic carbon pools after 12 years in no-till dryland agroecosystems. Soil Science Society of America Journal 69, 1600–1608.
Soil organic carbon pools after 12 years in no-till dryland agroecosystems.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD2MXhtVWis7bO&md5=823fca018b6207ea09bc977661f5a566CAS |

Song CC, Liu DY, Song YY, Mao R (2013) Effect of nitrogen addition on soil organic carbon in freshwater marsh of northeast China. Environmental Earth Sciences 70, 1653–1659.
Effect of nitrogen addition on soil organic carbon in freshwater marsh of northeast China.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC3sXhsFentbzE&md5=35bfa057dd3d7b13886617d3cc426f87CAS |

Treseder KK (2008) Nitrogen additions and microbial biomass: a meta-analysis of ecosystem studies. Ecology Letters 11, 1111–1120.
Nitrogen additions and microbial biomass: a meta-analysis of ecosystem studies.Crossref | GoogleScholarGoogle Scholar |

Vitousek PM, Howarth RW (1991) Nitrogen limitation on land and in the sea: how can it occur? Biogeochemistry 13, 87–115.
Nitrogen limitation on land and in the sea: how can it occur?Crossref | GoogleScholarGoogle Scholar |

Vitousek P, Matson P (1991) ‘Gradient analysis of ecosystems.’ (Springer: New York, NY)

Vitousek PM, Aber JD, Howarth RW, Likens GE, Matson PA, Schindler DW, Schlesinger WH, Tilman D (1997) Human alteration of the global nitrogen cycle: sources and consequences. Ecological Applications 7, 737–750.

Waldrop MP, Zak DR, Sinsabaugh RL, Gallo M, Lauber C (2004) Nitrogen deposition modifies soil carbon storage through changes in microbial enzymatic activity. Ecological Applications 14, 1172–1177.
Nitrogen deposition modifies soil carbon storage through changes in microbial enzymatic activity.Crossref | GoogleScholarGoogle Scholar |

Walkley A, Black I (1934) An examination of the Degtjareff method for determining soil organic matter, and a proposed modification of the chromic acid titration method. Soil Science 37, 29–38.

Whittinghill KA, Currie WS, Zak DR, Burton AJ, Pregitzer KS (2012) Anthropogenic N deposition increases soil C storage by decreasing the extent of litter decay: analysis of field observations with an ecosystem model. Ecosystems 15, 450–461.
Anthropogenic N deposition increases soil C storage by decreasing the extent of litter decay: analysis of field observations with an ecosystem model.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC38XkvVWrtLw%3D&md5=07ea6ae6f0ebef30678445bca2b93342CAS |

Yang XM, Kay BD (2001) Impacts of tillage practices on total, loose- and occluded-particulate, and humified organic carbon fractions in soils within a field in southern Ontario. Canadian Journal of Soil Science 81, 149–156.
Impacts of tillage practices on total, loose- and occluded-particulate, and humified organic carbon fractions in soils within a field in southern Ontario.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD3MXlvVGqsr4%3D&md5=15953aa19961cb0fffecd26e09518849CAS |

Yang Y, Guo J, Chen G, Yin Y, Gao R, Lin C (2009) Effects of forest conversion on soil labile organic carbon fractions and aggregate stability in subtropical China. Plant and Soil 323, 153–162.
Effects of forest conversion on soil labile organic carbon fractions and aggregate stability in subtropical China.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD1MXht1CmtLrK&md5=69a8d02fcff9678efcbe058902f70aeeCAS |

Yeomans J, Bremner JM (1988) A rapid and precise method for routine determination of organic carbon in soil 1. Communications in Soil Science and Plant Analysis 19, 1467–1476.
A rapid and precise method for routine determination of organic carbon in soil 1.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaL1cXlt1Oru7w%3D&md5=f4e48b08799944b8cda2d352f1414048CAS |

Zak DR, Holmes WE, Burton AJ, Pregitzer KS, Talhelm AF (2008) Simulated atmospheric NO3 – deposition increases soil organic matter by slowing decomposition. Ecological Applications 18, 2016–2027.
Simulated atmospheric NO3 deposition increases soil organic matter by slowing decomposition.Crossref | GoogleScholarGoogle Scholar |

Zeng DH, Li LJ, Fahey TJ, Yu ZY, Fan ZP, Chen FS (2010) Effects of nitrogen addition on vegetation and ecosystem carbon in a semi-arid grassland. Biogeochemistry 98, 185–193.
Effects of nitrogen addition on vegetation and ecosystem carbon in a semi-arid grassland.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC3cXksFCqurs%3D&md5=21e60b80d053615487904c047e1f7347CAS |

Zhang WD, Wang SL (2012) Effects of NH4 + and NO3 – on litter and soil organic carbon decomposition in a Chinese fir plantation forest in South China. Soil Biology & Biochemistry 47, 116–122.
Effects of NH4 + and NO3 on litter and soil organic carbon decomposition in a Chinese fir plantation forest in South China.Crossref | GoogleScholarGoogle Scholar |

Zhang DQ, Hui DF, Luo YQ, Zhou GY (2008) Rates of litter decomposition in terrestrial ecosystems: global patterns and controlling factors. Journal of Plant Ecology 1, 85–93.
Rates of litter decomposition in terrestrial ecosystems: global patterns and controlling factors.Crossref | GoogleScholarGoogle Scholar |

Zhu B, Gutknecht JLM, Herman DJ, Keck DC, Firestone MK, Cheng W (2014) Rhizosphere priming effects on soil carbon and nitrogen mineralization. Soil Biology & Biochemistry 76, 183–192.
Rhizosphere priming effects on soil carbon and nitrogen mineralization.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC2cXhtVCisb7F&md5=83fd5fd85ef67a243751694593f333d1CAS |

Zoysa AKN, Loganathan P, Hedley MJ (1999) Phosphorus utilisation efficiency and depletion of phosphate fractions in the rhizosphere of three tea (Camellia sinensis L.) clones. Nutrient Cycling in Agroecosystems 53, 189–201.
Phosphorus utilisation efficiency and depletion of phosphate fractions in the rhizosphere of three tea (Camellia sinensis L.) clones.Crossref | GoogleScholarGoogle Scholar |