Aim Anthropogenic additions of nitrogen (N) are expected to drive terrestrial ecosystems toward greater phosphorus (P) limitation. However, a comprehensive understanding of how an ecosystem's P cycle responds to external N inputs remains elusive, making model predictions of the anthropogenic P limitation and its impacts largely uncertain. Location Global. Time period 1986‐2015. Major taxa studied Terrestrial ecosystems. Methods We conducted a meta‐analysis including 288 independent study sites from 192 articles to evaluate global patterns and controls of 10 variables associated with ecosystem P cycling under N addition. Results Overall, N addition increased biomass in plants (+34%) and litter (+15%) as well as plant P content (+17%), while decreasing P concentrations in plants and litter (−8% and −11%, respectively). N addition did not change soil labile P or microbial P, but enhanced phosphatase activity (+24%). The effects of N addition on the litter P pool and soil total P remained unclear due to significant publication biases. The response of P cycling to N addition in tropical forests was different from that in other ecosystem types. N addition did not change plant biomass or phosphatase activity in tropical forests but significantly reduced plant P and soil labile P concentrations. The shift in plant P concentration under N addition was negatively correlated with the N application rate or total N load. N‐induced change in soil labile P was strongly regulated by soil pH value at the control sites, with a significant decrease of 14% only in acidic soils (pH < 5.5). Main conclusions Our results suggest that as anthropogenic N enhancement continues in the future it could induce P limitation in terrestrial ecosystems while accelerating P cycling, particularly in tropical forests. A quantitative framework generated on the basis of this meta‐analysis is useful for our understanding of ecosystem P cycling with N addition, and for incorporating the anthropogenic P limitation into ecosystem models used to analyse effects of future climate change.

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Abstract. Increases in observed atmospheric concentrations of the long-lived greenhouse gas nitrous oxide (N 2 O) have been well documented. However, information on eventrelated instantaneous emissions during fertilizer applications is lacking. With the development of fast-response N 2 O analyzers, the eddy covariance (EC) technique can be used to gather instantaneous measurements of N 2 O concentrations to quantify the exchange of nitrogen between the soil and atmosphere. The objectives of this study were to evaluate the performance of a new EC system, to measure the N 2 O flux with the system, and finally to examine relationships of the N 2 O flux with soil temperature, soil moisture, precipitation, and fertilization events. An EC system was assembled with a sonic anemometer and a fast-response N 2 O analyzer (quantum cascade laser spectrometer) and applied in a cornfield in Nolensville, Tennessee during the 2012 corn growing season (4 April-8 August). Fertilizer amounts totaling 217 kg N ha −1 were applied to the experimental site. Results showed that this N 2 O EC system provided reliable N 2 O flux measurements. The cumulative emitted N 2 O amount for the entire growing season was 6.87 kg N 2 O-N ha −1 . Seasonal fluxes were highly dependent on soil moisture rather than soil temperature. This study was one of the few experiments that continuously measured instantaneous, high-frequency N 2 O emissions in crop fields over a growing season of more than 100 days.

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problems. Cotton seedlings are generally weak and conservation tillage can result in poor seedling establish-The development of conservation tillage systems for cotton (Gosment and poor crop growth due to soil compaction, sypium hirsutum L.), capable of reducing soil erosion and improving resulting in static or reduced cotton yields (Delaney, soil quality while increasing yields and profits, remains a challenge in the southeastern USA. Poor emergence and growth, delayed maturity,

Quantification of soil carbon (C) cycling as influenced by management practices is needed for C sequestration and soil quality improvement. We evaluated the 10-yr effects of tillage, cropping system, and N source on crop residue and soil C fractions at 0- to 20-cm depth in Decatur silt loam (clayey, kaolinitic, thermic, Typic Paleudults) in northern Alabama, USA. Treatments were incomplete factorial combinations of three tillage practices (no-till [NT], mulch till [MT], and conventional till [CT]), two cropping systems (cotton [Gossypium hirsutum L.]-cotton-corn [Zea mays L.] and rye [Secale cereale L.]/cotton-rye/cotton-corn), and two N fertilization sources and rates (0 and 100 kg N ha(-1) from NH(4)NO(3) and 100 and 200 kg N ha(-1) from poultry litter). Carbon fractions were soil organic C (SOC), particulate organic C (POC), microbial biomass C (MBC), and potential C mineralization (PCM). Crop residue varied among treatments and years and total residue from 1997 to 2005 was greater in rye/cotton-rye/cotton-corn than in cotton-cotton-corn and greater with NH(4)NO(3) than with poultry litter at 100 kg N ha(-1). The SOC content at 0 to 20 cm after 10 yr was greater with poultry litter than with NH(4)NO(3) in NT and CT, resulting in a C sequestration rate of 510 kg C ha(-1) yr(-1) with poultry litter compared with -120 to 147 kg C ha(-1) yr(-1) with NH(4)NO(3). Poultry litter also increased PCM and MBC compared with NH(4)NO(3). Cropping increased SOC, POC, and PCM compared with fallow in NT. Long-term poultry litter application or continuous cropping increased soil C storage and microbial biomass and activity compared with inorganic N fertilization or fallow, indicating that these management practices can sequester C, offset atmospheric CO(2) levels, and improve soil and environmental quality.