Impact Of Elevated Temperature And Drought On N₂O Emissions And The Related Microorganisms

Climate change is perhaps the biggest challenge that the human race has ever faced throughout the history of humanity.It is projected that as climate change progresses,it is likely to lead to more extreme weather patterns,including heat waves,heavy precipitation,more frequent storms or severe droughts.However,the impact of climate change on nutrient cycling,including nitrogen?N?cycling in managed agricultural soils and natural forest soils is largely unknown.The changed climate may affect the community structures of N-related soil microorganisms and consequently influence N₂O emissions from soil,which,in turn,may lead to increased or decreased concentrations of N₂O in the atmosphere and thus have a feedback on climate change.Furthermore,with increased awareness of the importance of climate change,several useful measures have been taken to control climate change processes.However,the legacy effect of historical climate change on N cycling and cascading effects on N₂O emissions is rarely studied.Thus,we used greenhouses to simulate warmer and drier climate conditions and used molecular biology methods,such as qPCR and high-throughput sequencing,to study the impact of simulated climate change and their legacy effect on N₂O emissions and related microorganisms?AOA,AOB,nirS-,nirK-and nosZ-type denitrifiers and fungi?vegetable and forest soils in the field study.The effect of temperature or soil moisture content alone on N₂O emissions and related microorganisms were also studied under controlled laboratory conditions.Knowledge from these studies will help us to better predict future N₂O emissions under a changing climate and develop strategies to improve agricultural management to minimize climate change impacts.Our results showed that:?1?The combined effect of warmer and drier conditions on N₂O emissions and related microorganis ms depended on different soil conditions.Simulated climate change significantly increased N₂O emssions in the vegetable soil,but had no significant effect on N₂O emissions in the forest soil.In the fertilized vegetable soil,AOB communities were better adapted to the simulated climate change than AO A,but were less adapted to the acidic forest soil.NirK-type denitrifers were well adapted to the simulated climate change in the vegetable soil,while their abundances?both nirK and nirS?significantly decreased in the forest soil under the simulated warmer and drier climatic conditions.?2?The legacy effect of warmer and drier conditions decreased N₂O emissions in the vegetable soil,but increased N₂O emissions in the forest soil,and the legacy effect on microorganisms was short-lived.The legacy effect significantly increased the abundance of AOB in both the urea and manure treated vegetable soils,but only increased the abundance of AO A in the manure treated vegetable soil.The legacy effect of simulated climate change significantly increased the abundance of both AOB and AOA in the urea treated forest soil.The legacy effect of simulated climate change on all functional denitrifier communities?nirS-,nirK-and nosZ-type denitrifiers?was short lived and disappeared as soon as the simulated climatic conditions were removed.?3?High temperature increased N₂O emissions from non-biological processes but decreased N₂O emissions from biological processes,and fungal nirK was a major contributor of N₂O emissions under high temperature conditions.In the vegetable soil,increased temperature significantly increased N₂O emissions in both the urea treated and manure treated soils.But in the forest soil,increased temperature significantly increased N₂O emissions in the urea treated soil,but decreased N₂O emissions in the manure treated soil The abundance of AOA in the manure treated vegetable soil significantly increased with increasing temperature,and AOA probably dominated the ammonia oxidation under 40°C temperature in the vegetable soil.The abundance of both AOA and AOB significantly decreased with increasing temperature in the acidic forest soil.For denitrifiers,the nirS-type denitrifiers were well adaped to the high temperature conditions in the manure-treated vegetable soil,while the abundance of all the functional denitrifying bacteria?nirS-,nirK-and nosZ-type denitrifiers?were significantly decreased under the high temperature conditions?for example,40??in the acidic forest soil.However,the community of fimgal nirK was well adapted to the high temperature conditios in the manure-treated acidic forest soils,and was probably a major contributor of N₂O emissions under high temperature conditions.?4?The drought conditions?40%F.C.?significantly decreased N2o emissions in both the vegetable and forest soils,and AOA and fungal hirK were well adapted to the drought conditions In the manure-treated vegetable and forest soils.The drought conditiorns significantly increased the abundance of AOA community in the manure-treated vegetable soil,but significantly decreased the abundance of AOA in both the manure-and urea-treated forest soils.AOB only grew under the 100%water holding capacity?F.C.?conditions in both the vegetable and forest soils.For denitrifiers,not only the present soil moisture content,but also the previous soil moisture content affected the abund:ance of nirS in the manure-treated vegetable soil.Drought conditions decreased the abundance of all the functional denitrifying bacteria?nirS-,nirK-and nosZ-type denitrifiers?,but had no significant effect on the abundance of fimgal nirK gene,indicating that fungal nirK were well adapted to the drought conditions and might be a major contributor to N₂O emissions in the drought-affected acidic forest soil.