The study was to determine the long-term effects of subtropical monoculture and rotational cropping systems and fertilization on soil enzyme activities and soil C, N, and P levels. Cropping systems included continuous...The study was to determine the long-term effects of subtropical monoculture and rotational cropping systems and fertilization on soil enzyme activities and soil C, N, and P levels. Cropping systems included continuous sorghum(Sorghum bicolor L.), cotton(Gossypium hirsutum L.), corn(Zea mays L.), and cotton/sorghum rotations after 26 years of treatment imposition. Soil under continuous sorghum and continuous corn had 15% and 11%, respectively, greater C concentrations than soil under continuous cotton.Organic C was 10% higher at 0–7.5 cm than at 7.5–15 cm. Total N followed similar trends with soil depth as organic C. Continuous sorghum had 19% higher total N than other crop species and rotations. With fertilization, continuous cotton had the highest total P at 0–7.5 cm and sorghum had the highest at 7.5–15 cm. Soil total P was 14% higher at 0–7.5 than at 7.5–15 cm, and fertilization increased 15% total P compared to unfertilized soil. Arylsulfatase, alkaline phosphatase, and β-d-glucosidase activity were the highest for sorghum and the lowest for cotton. Rotation increased enzyme activities compared to continuous cotton but not for continuous sorghum. Of all crop species and rotations, continuous cotton generally showed the lowest levels of organic matter and enzyme activities after 26 years. Fertilization significantly increased the yields for all cropping systems, but rotation had no significant effect on either sorghum or cotton lint yield compared to each crop grown in monoculture. Long-term cropping did not increase soil organic matter levels beyond short-term gains, indicating the difficulty in promoting C sequestration in subtropical soils.展开更多
The occurrence of nitri?cation in some acidic forest soils is still a subject of debate.Identi?cation of main nitri?cation pathways in acidic forest soils is still largely unknown.Acidic yellow soil(Oxisol) samples we...The occurrence of nitri?cation in some acidic forest soils is still a subject of debate.Identi?cation of main nitri?cation pathways in acidic forest soils is still largely unknown.Acidic yellow soil(Oxisol) samples were selected to test whether nitri?cation can occur or not in acidic subtropical pine forest ecosystems.Relative contributions of autotrophs and heterotrophs to nitri?cation were studied by adding selective nitri?cation inhibitor nitrapyrin.Soil NH^+_4-N concentrations decreased,but NO^-_3-N concentrations increased signi?cantly for the no-nitrapyrin control during the ?rst week of incubation,indicating that nitri?cation did occur in the acidic subtropical soil.The calculated net nitri?cation rate was 0.49 mg N kg^(-1)d^(-1)for the no-nitrapyrin control during the ?rst week of incubation.Nitrapyrin amendment resulted in a signi?cant reduction of NO^-_3-N concentration.Autotrophic nitri?cation rate averaged0.28 mg N kg^(-1)d^(-1)and the heterotrophic nitri?cation rate was 0.21 mg N kg^(-1)d^(-1)in the ?rst week.Ammonia-oxidizing bacteria(AOB) abundance increased slightly during incubation,but nitrapyrin amendment signi?cantly decreased AOB amo A gene copy numbers by about 80%.However,the ammonia-oxidizing archaea(AOA) abundance showed signi?cant increases only in the last 2weeks of incubation and it was also decreased by nitrapyrin amendment.Our results indicated that nitri?cation did occur in the present acidic subtropical pine forest soil,and autotrophic nitri?cation was the main nitri?cation pathway.Both AOA and AOB were the active biotic agents responsible for autotrophic nitri?cation in the acidic subtropical pine forest soil.展开更多
Background:Evaluation of carbon(C),nitrogen(N),and phosphorus(P)ratios in aquatic and terrestrial ecosystems can advance our understanding of biological processes,nutrient cycling,and the fate of organic matter(OM)in ...Background:Evaluation of carbon(C),nitrogen(N),and phosphorus(P)ratios in aquatic and terrestrial ecosystems can advance our understanding of biological processes,nutrient cycling,and the fate of organic matter(OM)in these ecosystems.Eutrophication of aquatic ecosystems can change the accumulation and decomposition of OM which can alter biogeochemical cycling and alter the base of the aquatic food web.This study investigated nutrient stoichiometry within and among wetland ecosystem compartments(i.e.,water column,flocculent,soil,and aboveground vegetation biomass)of two subtropical treatment wetlands with distinct vegetation communities.Two flow-ways(FWs)within the network of Everglades Stormwater Treatment Areas in south Florida(USA)were selected for this study.We evaluated nutrient stoichiometry of these to understand biogeochemical cycling and controls of nutrient removal in a treatment wetland within an ecological stoichiometry context.Results:This study demonstrates that C,N,and P stoichiometry can be highly variable among ecosystem compartments and between FWs.Power law slopes of C,N,and P within surface water floc,soil,and vegetation were significantly different between and along FWs.Conclusions:Assessment of wetland nutrient stoichiometry between and within ecosystem compartments suggests unconstrained stoichiometry related to P that conforms with the notion of P limitation in the ecosystem.Differences in N:P ratios between floc and soil suggest different pathways of organic nutrient accumulation and retention between FWs.Surface nutrient stoichiometry was highly variable and decoupled(or close to decoupled as indicated by<25%explained variation between parameters),in particular with respect to P.We hypothesize that decoupling may be the imprint of variability in inflow nutrient stoichiometry.However,despite active biogeochemical cycles that could act to restore nutrient stoichiometry along the FW,there was little evidence that such balancing occurred,as the degree of stochiometric decoupling in the water column did change with distance downstream.This information is only the beginning of a larger journey to understand stoichiometric processes within wetland ecosystems and how they relate to ecosystem function.展开更多
Introduction:The Florida Everglades has undergone significant ecological change spanning the continuum of disturbance to restoration.While the restoration effort is not complete and the ecosystem continues to experien...Introduction:The Florida Everglades has undergone significant ecological change spanning the continuum of disturbance to restoration.While the restoration effort is not complete and the ecosystem continues to experience short duration perturbations,a better understanding of long-term C dynamics of the Everglades is needed to facilitate new restoration efforts.This study evaluated temporal trends of different aquatic carbon(C)pools of the northern Everglades Protection Area over a 20-year period to gauge historic C cycling patterns.Dissolved inorganic C(DIC),dissolved organic C(DOC),particulate organic C(POC),and surface water carbon dioxide(pCO2(aq))were investigated between May 1,1994 and April 30,2015.Results:Annual mean concentrations of DIC,DOC,POC,and pCO2(aq)significantly decreased through time or remained constant across the Water Conservation Areas(WCAs).Overall,the magnitude of the different C pools in the water column significantly differed between regions.Outgassing of CO2 was dynamic across the Everglades ranging from 420 to 2001 kg CO2 year−1.Overall,the historic trend in CO2 flux from the marsh declined across our study area while pCO2(aq)largely remained somewhat constant with the exception of Water Conservation Area 2 which experienced significant declines in pCO2(aq).Particulate OC concentrations were consistent between WCAs,but a significantly decreasing trend in annual POC concentrations was observed.Conclusions:Hydrologic condition and nutrient inputs significantly influenced the balance,speciation,and flux of C pools across WCAs suggesting a subsidy-stress response in C dynamics relative to landscape scale responses in nutrient availability.The interplay between nutrient inputs and hydrologic condition exert a driving force on the balance between DIC and DOC production via the metabolism of organic matter which forms the base of the aquatic food web.Along the restoration trajectory as water quality and hydrology continues to improve,it is expected that C pools will respond accordingly.展开更多
Soil redox is a critical environmental factor shaping the microbial community structure and ultimately alters the nutrient cycling.However,the response of soil microbial community structure to prolonged or repeated re...Soil redox is a critical environmental factor shaping the microbial community structure and ultimately alters the nutrient cycling.However,the response of soil microbial community structure to prolonged or repeated redox fluctuations is not yet clear.To study the dynamic effects of prolonged redox disturbances to the soil microbial community structure,soil samples experiencing 8,5 and 0 alternating oxic-anoxic cycles within approximately 6 months each year were collected and the microbial community structure were evaluated using phospholipid fatty acid analysis(PLFA)profiles.Prolonged redox disturbances had significant effects on soil physiochemical properties and soil microbial community structure.The relative abundance of straight chain saturated PLFAs,cyclopropyl,and terminal-and mid-branched chain saturated PLFAs increased due to prolonged redox disturbances,but there was a consistent decrease in linear monounsaturated PLFAs and polyunsaturated PLFAs in the fluctuating zone.Prolonged redox disturbances had a negative impact on the total PLFA content(a proxy for biomass).Both the fluctuating zone(8-cycle and 5-cycle plots)and the never flooded zone(0-cycle plots)were dominated by Gram-positive bacteria and a low content of fungi,actinomycetes and protozoa.The fungi and protozoa abundance decreased significantly with an increase in the occurrence of alternating flooding-dry events,suggesting that the prolonged redox disturbance leads to high stress on the fungi and protozoa populations.Moreover,total organic matter(TOC)and C:N ratio,environmental factors that can be influenced by recurring redox fluctuations,also influenced the microbial community structure.展开更多
文摘The study was to determine the long-term effects of subtropical monoculture and rotational cropping systems and fertilization on soil enzyme activities and soil C, N, and P levels. Cropping systems included continuous sorghum(Sorghum bicolor L.), cotton(Gossypium hirsutum L.), corn(Zea mays L.), and cotton/sorghum rotations after 26 years of treatment imposition. Soil under continuous sorghum and continuous corn had 15% and 11%, respectively, greater C concentrations than soil under continuous cotton.Organic C was 10% higher at 0–7.5 cm than at 7.5–15 cm. Total N followed similar trends with soil depth as organic C. Continuous sorghum had 19% higher total N than other crop species and rotations. With fertilization, continuous cotton had the highest total P at 0–7.5 cm and sorghum had the highest at 7.5–15 cm. Soil total P was 14% higher at 0–7.5 than at 7.5–15 cm, and fertilization increased 15% total P compared to unfertilized soil. Arylsulfatase, alkaline phosphatase, and β-d-glucosidase activity were the highest for sorghum and the lowest for cotton. Rotation increased enzyme activities compared to continuous cotton but not for continuous sorghum. Of all crop species and rotations, continuous cotton generally showed the lowest levels of organic matter and enzyme activities after 26 years. Fertilization significantly increased the yields for all cropping systems, but rotation had no significant effect on either sorghum or cotton lint yield compared to each crop grown in monoculture. Long-term cropping did not increase soil organic matter levels beyond short-term gains, indicating the difficulty in promoting C sequestration in subtropical soils.
基金financially supported by the National Natural Science Foundation of China(No.41271267)
文摘The occurrence of nitri?cation in some acidic forest soils is still a subject of debate.Identi?cation of main nitri?cation pathways in acidic forest soils is still largely unknown.Acidic yellow soil(Oxisol) samples were selected to test whether nitri?cation can occur or not in acidic subtropical pine forest ecosystems.Relative contributions of autotrophs and heterotrophs to nitri?cation were studied by adding selective nitri?cation inhibitor nitrapyrin.Soil NH^+_4-N concentrations decreased,but NO^-_3-N concentrations increased signi?cantly for the no-nitrapyrin control during the ?rst week of incubation,indicating that nitri?cation did occur in the acidic subtropical soil.The calculated net nitri?cation rate was 0.49 mg N kg^(-1)d^(-1)for the no-nitrapyrin control during the ?rst week of incubation.Nitrapyrin amendment resulted in a signi?cant reduction of NO^-_3-N concentration.Autotrophic nitri?cation rate averaged0.28 mg N kg^(-1)d^(-1)and the heterotrophic nitri?cation rate was 0.21 mg N kg^(-1)d^(-1)in the ?rst week.Ammonia-oxidizing bacteria(AOB) abundance increased slightly during incubation,but nitrapyrin amendment signi?cantly decreased AOB amo A gene copy numbers by about 80%.However,the ammonia-oxidizing archaea(AOA) abundance showed signi?cant increases only in the last 2weeks of incubation and it was also decreased by nitrapyrin amendment.Our results indicated that nitri?cation did occur in the present acidic subtropical pine forest soil,and autotrophic nitri?cation was the main nitri?cation pathway.Both AOA and AOB were the active biotic agents responsible for autotrophic nitri?cation in the acidic subtropical pine forest soil.
基金sample collection and analysis was provided by the South Florida Water Management District(Contract#4600003031).
文摘Background:Evaluation of carbon(C),nitrogen(N),and phosphorus(P)ratios in aquatic and terrestrial ecosystems can advance our understanding of biological processes,nutrient cycling,and the fate of organic matter(OM)in these ecosystems.Eutrophication of aquatic ecosystems can change the accumulation and decomposition of OM which can alter biogeochemical cycling and alter the base of the aquatic food web.This study investigated nutrient stoichiometry within and among wetland ecosystem compartments(i.e.,water column,flocculent,soil,and aboveground vegetation biomass)of two subtropical treatment wetlands with distinct vegetation communities.Two flow-ways(FWs)within the network of Everglades Stormwater Treatment Areas in south Florida(USA)were selected for this study.We evaluated nutrient stoichiometry of these to understand biogeochemical cycling and controls of nutrient removal in a treatment wetland within an ecological stoichiometry context.Results:This study demonstrates that C,N,and P stoichiometry can be highly variable among ecosystem compartments and between FWs.Power law slopes of C,N,and P within surface water floc,soil,and vegetation were significantly different between and along FWs.Conclusions:Assessment of wetland nutrient stoichiometry between and within ecosystem compartments suggests unconstrained stoichiometry related to P that conforms with the notion of P limitation in the ecosystem.Differences in N:P ratios between floc and soil suggest different pathways of organic nutrient accumulation and retention between FWs.Surface nutrient stoichiometry was highly variable and decoupled(or close to decoupled as indicated by<25%explained variation between parameters),in particular with respect to P.We hypothesize that decoupling may be the imprint of variability in inflow nutrient stoichiometry.However,despite active biogeochemical cycles that could act to restore nutrient stoichiometry along the FW,there was little evidence that such balancing occurred,as the degree of stochiometric decoupling in the water column did change with distance downstream.This information is only the beginning of a larger journey to understand stoichiometric processes within wetland ecosystems and how they relate to ecosystem function.
文摘Introduction:The Florida Everglades has undergone significant ecological change spanning the continuum of disturbance to restoration.While the restoration effort is not complete and the ecosystem continues to experience short duration perturbations,a better understanding of long-term C dynamics of the Everglades is needed to facilitate new restoration efforts.This study evaluated temporal trends of different aquatic carbon(C)pools of the northern Everglades Protection Area over a 20-year period to gauge historic C cycling patterns.Dissolved inorganic C(DIC),dissolved organic C(DOC),particulate organic C(POC),and surface water carbon dioxide(pCO2(aq))were investigated between May 1,1994 and April 30,2015.Results:Annual mean concentrations of DIC,DOC,POC,and pCO2(aq)significantly decreased through time or remained constant across the Water Conservation Areas(WCAs).Overall,the magnitude of the different C pools in the water column significantly differed between regions.Outgassing of CO2 was dynamic across the Everglades ranging from 420 to 2001 kg CO2 year−1.Overall,the historic trend in CO2 flux from the marsh declined across our study area while pCO2(aq)largely remained somewhat constant with the exception of Water Conservation Area 2 which experienced significant declines in pCO2(aq).Particulate OC concentrations were consistent between WCAs,but a significantly decreasing trend in annual POC concentrations was observed.Conclusions:Hydrologic condition and nutrient inputs significantly influenced the balance,speciation,and flux of C pools across WCAs suggesting a subsidy-stress response in C dynamics relative to landscape scale responses in nutrient availability.The interplay between nutrient inputs and hydrologic condition exert a driving force on the balance between DIC and DOC production via the metabolism of organic matter which forms the base of the aquatic food web.Along the restoration trajectory as water quality and hydrology continues to improve,it is expected that C pools will respond accordingly.
基金financed by the National Natural Science Foundation of China(Nos.41271267,41301315).
文摘Soil redox is a critical environmental factor shaping the microbial community structure and ultimately alters the nutrient cycling.However,the response of soil microbial community structure to prolonged or repeated redox fluctuations is not yet clear.To study the dynamic effects of prolonged redox disturbances to the soil microbial community structure,soil samples experiencing 8,5 and 0 alternating oxic-anoxic cycles within approximately 6 months each year were collected and the microbial community structure were evaluated using phospholipid fatty acid analysis(PLFA)profiles.Prolonged redox disturbances had significant effects on soil physiochemical properties and soil microbial community structure.The relative abundance of straight chain saturated PLFAs,cyclopropyl,and terminal-and mid-branched chain saturated PLFAs increased due to prolonged redox disturbances,but there was a consistent decrease in linear monounsaturated PLFAs and polyunsaturated PLFAs in the fluctuating zone.Prolonged redox disturbances had a negative impact on the total PLFA content(a proxy for biomass).Both the fluctuating zone(8-cycle and 5-cycle plots)and the never flooded zone(0-cycle plots)were dominated by Gram-positive bacteria and a low content of fungi,actinomycetes and protozoa.The fungi and protozoa abundance decreased significantly with an increase in the occurrence of alternating flooding-dry events,suggesting that the prolonged redox disturbance leads to high stress on the fungi and protozoa populations.Moreover,total organic matter(TOC)and C:N ratio,environmental factors that can be influenced by recurring redox fluctuations,also influenced the microbial community structure.
