The effects of nitrogen(N)deposition on forest soil organic carbon(SOC)are largely unclear,likely due to the divergent responses of particulate(POC)and mineral-associated carbon(MAOC).Conventional understory inorganic...The effects of nitrogen(N)deposition on forest soil organic carbon(SOC)are largely unclear,likely due to the divergent responses of particulate(POC)and mineral-associated carbon(MAOC).Conventional understory inorganic N(UIN)additions neglect canopy processes and the impacts of organic N,potentially misevaluating N deposition effects.This study was conducted in a long-term N addition experiment established in a Moso bamboo forest,which included six treatments combining canopy and understory N additions with organic(urea glycine)and inorganic(NH_(4)NO_(3))forms at a rate of 50 kg N·ha^(-1)·yr^(-1).Litterbags were installed for a two-year decomposition experiment and collected at quarterly intervals,together with concurrent soil sampling under litterbags at 0–10 cm depth.We aimed to examine the effects of canopy vs.understory N addition and organic vs.inorganic N form on soil POC and MAOC concentrations.Our results showed that canopy N additions significantly reduced POC(ased POC-15.9%)but did not affect MAOC(P>0.05).Conversely,understory N additions significantly incre(30.9%)and decreased MAOC(and fungal diversity(FuD),-28.9%).Canopy N additions decreased POC by enhancing peroxidase activity while understory N additions promoted POC by inhibiting litter decomposition.Additionally,understory N addition-induced soil acidification decreased soil Ca^(2+)concentration,microbial carbon use efficiency,and bacterial necromass C,as well as the release of litter water-soluble compounds,thereby inhibiting MAOC.Moreover,nitrogen forms(organic vs.inorganic)had no effect on SOC fractions.Our findings underscore that canopy and understory N addition approaches differentially regulate SOC fractions by altering litter decomposition–microbial–mineral interactions,and the understory approach may overestimate soil POC gain and MAOC loss driven by atmospheric N deposition.展开更多
Global grasslands can sequester soil organic carbon(SOC)while maintaining ecosystem function,thereby mitigating climate change.SOC consists of components with varying stability and turnover rates,such as particulate o...Global grasslands can sequester soil organic carbon(SOC)while maintaining ecosystem function,thereby mitigating climate change.SOC consists of components with varying stability and turnover rates,such as particulate organic carbon(POC)and mineral-associated organic carbon(MAOC).While these components have been extensively studied in the surface layer(0-30 cm),their distribution and controls in deeper layers remain poorly understood.This study combined precise measurements of POC and MAOC across seven sequential depth layers down to 2 m at 17 Inner Mongolian grassland sites with a global dataset to elucidate their vertical distribution patterns and underlying controls.Results showed that POC generally dominated MAOC in Inner Mongolian grassland soils,albeit with regional variations in this dominance.Interestingly,the proportion of MAOC to total SOC(MAOC:(MAOC+POC)),indicating SOC stability,increased with depth in the upper 0-50 cm but decreased below 50 cm,suggesting that environmental factors at depth may constrain POC decomposition and MAOC formation.POC accumulation was positively influenced by the mean annual precipitation in the top 30 cm and negatively affected by soil pH down to 50 cm.Contrastingly,MAOC was coregulated by the clay and silt content(CS)and aluminum(Al)oxide in surface soils(0-30 cm),whereas Al oxide dominated from 30 to 100 cm.Notably,MAOC:(MAOC+POC)correlated significantly with CS across all depths,underscoring the persistent role of physical protection mechanisms in deeper layers.These findings highlight depthspecific accumulation patterns and controls of POC and MAOC in the Inner Mongolian grasslands,indicating that optimizing SOC sequestration under changing climate and management scenarios requires depth-specific strategies that target both shortterm POC enhancement and long-term MAOC stabilization.展开更多
Char amendment is an option to lower climatic impact of agricultural soils.However,their effect can vary depending on char and soil properties,vegetation type and their interactions.Nutrient poor and acidic soils of b...Char amendment is an option to lower climatic impact of agricultural soils.However,their effect can vary depending on char and soil properties,vegetation type and their interactions.Nutrient poor and acidic soils of boreal region could benefit from char amendment.We conducted a three-month long mesocosm study representing a typical boreal forage-legume grassland to understand the effects of char application on greenhouse gas(GHG)emissions,soil organic carbon(SOC)pools and biomass yield.We examined biochar and hydrochar for changes in soil properties,gross nitrogen transformation rates,SOC and its fractions,biomass yield and all three major GHG fluxes.We assessed our results from two different perspectives;one,when chars were added at a uniform rate with fertilizer nitrogen(N)following the farmer’s practice and two,when chars were added based on the char C amount without fertilizer N.We show that only N_(2)O emissions(not CO_(2)and CH_(4))were affected when chars were added at a uniform rate with fertilizer N.Biochar increased N_(2)O emissions significantly compared to control whereas hydrochar restricted N_(2)O relative to control and lowered significantly compared to biochar treatments.Biochar with N amendment significantly increased gross NO_(3)−production(gross nitrification)and N_(2)O emissions,indicating a linkage between increased nitrifier activity and N_(2)O emissions.Hydrochar with N amendment showed lower gross nitrification rates and N_(2)O emissions,indicating a reduced nitrifier activity and N_(2)O emissions compared to biochar.Interestingly,hydrochar without N amendment showed lowest N_(2)O emissions with few N_(2)O uptake events and similar gross NO_(3)−consumption and production rates,hinting an enhanced soil N_(2)O reduction/sink mechanism,especially with actively photosynthesizing vegetation.Both chars increased soil particulate organic C(POC)significantly mainly owing to both chars themselves being carbon.The mineral associated organic C(MAOC)remained unaltered.Interestingly,we found significantly lower soil MAOC per unit of char C with biochar than with hydochar amendment,especially when endpoint soil MAOC was compared with initial soil MAOC.Our results suggest that destabilization of MAOC increased more with biochar than with hydrochar,especially with N fertilization and in the presence of actively photosynthesizing vegetation.This was further supported by a significantly greater rise in microbial biomass carbon with hydrochar than with biochar amendment.The total biomass yield remained unaffected.However,biochar with the applied N reduced the timothy grass yield compared to control,implying a reduced uptake of applied N by timothy.Our results shed light on the complex interactions among chars,soil,vegetation and N management.Therefore,future studies should focus on assessing the char amendment impacts including both plant and soil and at the whole agricultural field scale.Chars manufactured from diverse feedstocks need to be investigated for their impacts in diverse agricultural ecosystems,paving the way for their large-scale use.展开更多
文摘The effects of nitrogen(N)deposition on forest soil organic carbon(SOC)are largely unclear,likely due to the divergent responses of particulate(POC)and mineral-associated carbon(MAOC).Conventional understory inorganic N(UIN)additions neglect canopy processes and the impacts of organic N,potentially misevaluating N deposition effects.This study was conducted in a long-term N addition experiment established in a Moso bamboo forest,which included six treatments combining canopy and understory N additions with organic(urea glycine)and inorganic(NH_(4)NO_(3))forms at a rate of 50 kg N·ha^(-1)·yr^(-1).Litterbags were installed for a two-year decomposition experiment and collected at quarterly intervals,together with concurrent soil sampling under litterbags at 0–10 cm depth.We aimed to examine the effects of canopy vs.understory N addition and organic vs.inorganic N form on soil POC and MAOC concentrations.Our results showed that canopy N additions significantly reduced POC(ased POC-15.9%)but did not affect MAOC(P>0.05).Conversely,understory N additions significantly incre(30.9%)and decreased MAOC(and fungal diversity(FuD),-28.9%).Canopy N additions decreased POC by enhancing peroxidase activity while understory N additions promoted POC by inhibiting litter decomposition.Additionally,understory N addition-induced soil acidification decreased soil Ca^(2+)concentration,microbial carbon use efficiency,and bacterial necromass C,as well as the release of litter water-soluble compounds,thereby inhibiting MAOC.Moreover,nitrogen forms(organic vs.inorganic)had no effect on SOC fractions.Our findings underscore that canopy and understory N addition approaches differentially regulate SOC fractions by altering litter decomposition–microbial–mineral interactions,and the understory approach may overestimate soil POC gain and MAOC loss driven by atmospheric N deposition.
基金supported by the National Natural Science Foundation of China(Grant Nos.42375116&32241036)。
文摘Global grasslands can sequester soil organic carbon(SOC)while maintaining ecosystem function,thereby mitigating climate change.SOC consists of components with varying stability and turnover rates,such as particulate organic carbon(POC)and mineral-associated organic carbon(MAOC).While these components have been extensively studied in the surface layer(0-30 cm),their distribution and controls in deeper layers remain poorly understood.This study combined precise measurements of POC and MAOC across seven sequential depth layers down to 2 m at 17 Inner Mongolian grassland sites with a global dataset to elucidate their vertical distribution patterns and underlying controls.Results showed that POC generally dominated MAOC in Inner Mongolian grassland soils,albeit with regional variations in this dominance.Interestingly,the proportion of MAOC to total SOC(MAOC:(MAOC+POC)),indicating SOC stability,increased with depth in the upper 0-50 cm but decreased below 50 cm,suggesting that environmental factors at depth may constrain POC decomposition and MAOC formation.POC accumulation was positively influenced by the mean annual precipitation in the top 30 cm and negatively affected by soil pH down to 50 cm.Contrastingly,MAOC was coregulated by the clay and silt content(CS)and aluminum(Al)oxide in surface soils(0-30 cm),whereas Al oxide dominated from 30 to 100 cm.Notably,MAOC:(MAOC+POC)correlated significantly with CS across all depths,underscoring the persistent role of physical protection mechanisms in deeper layers.These findings highlight depthspecific accumulation patterns and controls of POC and MAOC in the Inner Mongolian grasslands,indicating that optimizing SOC sequestration under changing climate and management scenarios requires depth-specific strategies that target both shortterm POC enhancement and long-term MAOC stabilization.
基金supported by Finnish Ministry of Agriculture and Forestry and Walter Ahlstrom Foundation(Woodpro:Grant No:VN/17097/2022)the Research Council of Finland through project,“Mechanism of nitrous oxide(N_(2)O)uptake in different cropping systems in different climate zones(ENSINK,Grant No.334422).
文摘Char amendment is an option to lower climatic impact of agricultural soils.However,their effect can vary depending on char and soil properties,vegetation type and their interactions.Nutrient poor and acidic soils of boreal region could benefit from char amendment.We conducted a three-month long mesocosm study representing a typical boreal forage-legume grassland to understand the effects of char application on greenhouse gas(GHG)emissions,soil organic carbon(SOC)pools and biomass yield.We examined biochar and hydrochar for changes in soil properties,gross nitrogen transformation rates,SOC and its fractions,biomass yield and all three major GHG fluxes.We assessed our results from two different perspectives;one,when chars were added at a uniform rate with fertilizer nitrogen(N)following the farmer’s practice and two,when chars were added based on the char C amount without fertilizer N.We show that only N_(2)O emissions(not CO_(2)and CH_(4))were affected when chars were added at a uniform rate with fertilizer N.Biochar increased N_(2)O emissions significantly compared to control whereas hydrochar restricted N_(2)O relative to control and lowered significantly compared to biochar treatments.Biochar with N amendment significantly increased gross NO_(3)−production(gross nitrification)and N_(2)O emissions,indicating a linkage between increased nitrifier activity and N_(2)O emissions.Hydrochar with N amendment showed lower gross nitrification rates and N_(2)O emissions,indicating a reduced nitrifier activity and N_(2)O emissions compared to biochar.Interestingly,hydrochar without N amendment showed lowest N_(2)O emissions with few N_(2)O uptake events and similar gross NO_(3)−consumption and production rates,hinting an enhanced soil N_(2)O reduction/sink mechanism,especially with actively photosynthesizing vegetation.Both chars increased soil particulate organic C(POC)significantly mainly owing to both chars themselves being carbon.The mineral associated organic C(MAOC)remained unaltered.Interestingly,we found significantly lower soil MAOC per unit of char C with biochar than with hydochar amendment,especially when endpoint soil MAOC was compared with initial soil MAOC.Our results suggest that destabilization of MAOC increased more with biochar than with hydrochar,especially with N fertilization and in the presence of actively photosynthesizing vegetation.This was further supported by a significantly greater rise in microbial biomass carbon with hydrochar than with biochar amendment.The total biomass yield remained unaffected.However,biochar with the applied N reduced the timothy grass yield compared to control,implying a reduced uptake of applied N by timothy.Our results shed light on the complex interactions among chars,soil,vegetation and N management.Therefore,future studies should focus on assessing the char amendment impacts including both plant and soil and at the whole agricultural field scale.Chars manufactured from diverse feedstocks need to be investigated for their impacts in diverse agricultural ecosystems,paving the way for their large-scale use.
