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Aims: Nitrogen (N) is not only a major regulator of productivity in terrestrial systems but can also be a pollutant. While the effects of fertilizer addition to soil N cycling processes and the associated soil microbial groups have been extensively studied, little attention has been paid to the interaction of fertilizer amendment and the intrinsic fertility of the soil. Methods: We conducted a filed study on the Chinese Loess Plateau with soils of two fertility levels (low fertility and high fertility), amended with or without synthetic fertilizer (N and phosphorus, NP). Soil samples were collected three times in a continuous winter wheat cropping system and analyzed for soil potential nitrification (PNA) and denitrification (DEA) rates, nitrifiers and denitrifiers. Results: Populations of ammonia-oxidizing archaea (AOA) and bacteria (AOB) and the resulting PNA were increased by the NP application regardless of intrinsic soil fertility. The NP application increased DEA by 15–228% in the low fertility soil, but decreased DEA by 18–46% in the high fertility soil. Soil denitrifiers also showed divergent responses to NP application in low and high fertility soils, i.e., the abundance of nirS-nitrite reducers increased in the low fertility soil, while nirS- and nirK-nitrite reducers were unchanged in the high fertility soil. The narG-nitrate reducers, AOB and AOA were more responsive to the NP application in the tillering stage (BBCH 25–26) than in other periods, whereas PNA, DEA and denitrifier gene abundance (nirS and nirK) varied more in the flowering stage (BBCH 65). Conclusions: Our results suggest that the responses of soil nitrification/nitrifiers and denitrification /denitrifiers to NP application varied with intrinsic soil fertility levels. The contrasting responses of nitrification and denitrification to NP application in high fertility soil indicate a decoupling of both processes. [ABSTRACT FROM AUTHOR]

Aims: Concerns over food security and global climate change require an improved understanding of how to achieve optimal crop yields whilst minimizing net greenhouse gas emissions from agriculture. In the semi-arid Loess Plateau region of China, as elsewhere, fertilizer nitrogen (N) inputs are necessary to increase yields and improve local food security. Methods: In a dryland annual cropping system, we evaluated the effects of N fertilizers on crop yield, its long-term impact on soil organic carbon (SOC) concentrations and stock sizes, and the distribution of carbon (C) within various aggregate-size fractions. A current version (RothC) of the Rothamsted model for the turnover of organic C in soil was used to simulate changes in SOC. Five N application rates [0 (N0), 45 (N45), 90 (N90), 135 (N135), and 180 (N180) kg N ha] were applied to plots for 25 years (1984-2009) on a loam soil (Cumulic Haplustoll) at the Changwu State Key Agro-Ecological Experimental Station, Shaanxi, China. Results: Crop yield varied with year, but increased over time in the fertilized plots. Average annual grain yields were 1.15, 2.46, 3.11, 3.49, and 3.55 Mg ha with the increasing N application rates, respectively. Long-term N fertilizer application increased significantly ( P = 0.041) SOC concentrations and stocks in the 0-20 cm horizon. Each kilogram of fertilizer N applied increased SOC by 0.51 kg in the top soil from 1984 to 2009. Using RothC, the calculated annual inputs of plant C (in roots, stubble, root exudates, etc.) to the soil were 0.61, 0.74, 0.78, 0.86, and 0.97 Mg C ha year in N0, N45, N90, N135 and N180 treatments, respectively. The modeled turnover time of SOC (excluding inert organic C) in the continuous wheat cropping system was 26 years. The SOC accumulation rate was calculated to be 40.0, 48.0, 68.0, and 100.0 kg C ha year for the N45, N90, N135 and N180 treatments over 25 years, respectively. As aboveground biomass was removed, the increases in SOC stocks with higher N application are attributed to increased inputs of root biomass and root exudates. Increasing N application rates significantly improved C concentrations in the macroaggregate fractions (>1 mm). Conclusions: Applying N fertilizer is a sustainable practice, especially in carbon sequestration and crop productivity, for the semiarid Loess Plateau region. [ABSTRACT FROM AUTHOR]

Aims: Crop rotation plays an important role in changing soil microbial communities, which is critical to maintaining soil multifunctionality. However, limited data exist on the long term impact of crop rotations on soil multifunctionality and its link with soil fungal community in drylands.In a dryland field experiment with 30-year legume- and non-legume-based winter wheat rotations and winter wheat-fallow system, we investigated the soil multifunctionality (via cycling and pools of soil carbon and nitrogen) and the overall community and functional groups of soil fungi. The links between soil multifunctionality and fungal communities were also explored.We found that long-term crop rotation increased soil multifunctionality index and that of carbon cycle. Crop rotation shifted soil fungal community composition, and reduced the proportion of putative pathotrophs. The overall fungal community was almost equally explained by soil and plant variables, while fungal functional groups (i.e., saprotrophs and pathotrophs) were more affected by soil variables. The indicator taxa in the non-legume-winter wheat rotation were distinctly different from those in the legume-based winter wheat rotation soils, indicating that the non-legume-winter wheat rotation selects different fungal taxa from the legume-based winter wheat rotation. Moreover, the changes in community composition of soil fungi, putative saprotrophs and pathotrophs were related to soil multifunctionality and that of carbon and nitrogen cycles.Our results highlight that long-term crop rotations shape the soil fungal communities; the changes in soil fungi and fungal functional groups have potential to improve soil multifunctionality in the crop rotation systems in drylands.Methods: Crop rotation plays an important role in changing soil microbial communities, which is critical to maintaining soil multifunctionality. However, limited data exist on the long term impact of crop rotations on soil multifunctionality and its link with soil fungal community in drylands.In a dryland field experiment with 30-year legume- and non-legume-based winter wheat rotations and winter wheat-fallow system, we investigated the soil multifunctionality (via cycling and pools of soil carbon and nitrogen) and the overall community and functional groups of soil fungi. The links between soil multifunctionality and fungal communities were also explored.We found that long-term crop rotation increased soil multifunctionality index and that of carbon cycle. Crop rotation shifted soil fungal community composition, and reduced the proportion of putative pathotrophs. The overall fungal community was almost equally explained by soil and plant variables, while fungal functional groups (i.e., saprotrophs and pathotrophs) were more affected by soil variables. The indicator taxa in the non-legume-winter wheat rotation were distinctly different from those in the legume-based winter wheat rotation soils, indicating that the non-legume-winter wheat rotation selects different fungal taxa from the legume-based winter wheat rotation. Moreover, the changes in community composition of soil fungi, putative saprotrophs and pathotrophs were related to soil multifunctionality and that of carbon and nitrogen cycles.Our results highlight that long-term crop rotations shape the soil fungal communities; the changes in soil fungi and fungal functional groups have potential to improve soil multifunctionality in the crop rotation systems in drylands.Results: Crop rotation plays an important role in changing soil microbial communities, which is critical to maintaining soil multifunctionality. However, limited data exist on the long term impact of crop rotations on soil multifunctionality and its link with soil fungal community in drylands.In a dryland field experiment with 30-year legume- and non-legume-based winter wheat rotations and winter wheat-fallow system, we investigated the soil multifunctionality (via cycling and pools of soil carbon and nitrogen) and the overall community and functional groups of soil fungi. The links between soil multifunctionality and fungal communities were also explored.We found that long-term crop rotation increased soil multifunctionality index and that of carbon cycle. Crop rotation shifted soil fungal community composition, and reduced the proportion of putative pathotrophs. The overall fungal community was almost equally explained by soil and plant variables, while fungal functional groups (i.e., saprotrophs and pathotrophs) were more affected by soil variables. The indicator taxa in the non-legume-winter wheat rotation were distinctly different from those in the legume-based winter wheat rotation soils, indicating that the non-legume-winter wheat rotation selects different fungal taxa from the legume-based winter wheat rotation. Moreover, the changes in community composition of soil fungi, putative saprotrophs and pathotrophs were related to soil multifunctionality and that of carbon and nitrogen cycles.Our results highlight that long-term crop rotations shape the soil fungal communities; the changes in soil fungi and fungal functional groups have potential to improve soil multifunctionality in the crop rotation systems in drylands.Conclusions: Crop rotation plays an important role in changing soil microbial communities, which is critical to maintaining soil multifunctionality. However, limited data exist on the long term impact of crop rotations on soil multifunctionality and its link with soil fungal community in drylands.In a dryland field experiment with 30-year legume- and non-legume-based winter wheat rotations and winter wheat-fallow system, we investigated the soil multifunctionality (via cycling and pools of soil carbon and nitrogen) and the overall community and functional groups of soil fungi. The links between soil multifunctionality and fungal communities were also explored.We found that long-term crop rotation increased soil multifunctionality index and that of carbon cycle. Crop rotation shifted soil fungal community composition, and reduced the proportion of putative pathotrophs. The overall fungal community was almost equally explained by soil and plant variables, while fungal functional groups (i.e., saprotrophs and pathotrophs) were more affected by soil variables. The indicator taxa in the non-legume-winter wheat rotation were distinctly different from those in the legume-based winter wheat rotation soils, indicating that the non-legume-winter wheat rotation selects different fungal taxa from the legume-based winter wheat rotation. Moreover, the changes in community composition of soil fungi, putative saprotrophs and pathotrophs were related to soil multifunctionality and that of carbon and nitrogen cycles.Our results highlight that long-term crop rotations shape the soil fungal communities; the changes in soil fungi and fungal functional groups have potential to improve soil multifunctionality in the crop rotation systems in drylands. [ABSTRACT FROM AUTHOR]