The ecological consequences of precipitation change and increased atmospheric nitrogen(N)deposition have profound impacts on ecosystem CO2 exchange in grassland ecosystems.Water and N can largely influence grassland p...The ecological consequences of precipitation change and increased atmospheric nitrogen(N)deposition have profound impacts on ecosystem CO2 exchange in grassland ecosystems.Water and N can largely influence grassland productivity,community composition and ecosystem functions.However,the influences of water and N addition on the ecosystem CO2 exchange of alpine grassland ecosystems remain unclear.A field manipulative experiment with water and N additions was conducted in an alpine meadow on the Tibetan Plateau over 4 years with contrasting precipitation patterns.There were four treatments:control(Ctrl),N addition(N),water addition(W)and N and water addition(NW),each replicated three times.N addition,but not water addition,increased gross ecosystem productivity(GEP),plant biomass,community cover and community-weighted mean height.The responses of ecosystem CO2 exchange to water and N addition varied between the wet and dry years.Water addition had a positive effect on net ecosystem carbon exchange(NEE)due to a larger increase in GEP than in ecosystem respiration(ER)only in the dry year.On the contrary,N addition significantly enhanced ecosystem CO2 exchange only in the wet year.The increased GEP in N addition was attributed to the larger increase in NEE than ER.Moreover,N addition stimulated NEE mainly through increasing the cover of dominant species.Our observations highlight the important roles of precipitation and dominant species in regulating ecosystem CO2 exchange response to global environmental change in alpine grasslands.展开更多
In this work,we propose the possible assignment of the newly observed X(2239),as well asη(2225),as a molecular state from the interaction of a baryonΛand an antibaryonΛ.With the help of effective Lagrangians,theΛ...In this work,we propose the possible assignment of the newly observed X(2239),as well asη(2225),as a molecular state from the interaction of a baryonΛand an antibaryonΛ.With the help of effective Lagrangians,theΛΛinteraction is described within the one-boson-exchange model withη,η′,ω,ϕ,andσexchanges considered.After inserting the potential kernel into the quasipotential Bethe-Salpeter equation,the bound states from theΛΛinteraction can be studied by searching for the pole of the scattering amplitude.Two loosely bound states with spin parities I^(G)(J^(PC))=0^(+)(0^(−+))and 0^(−)(1^(−−))appear near the threshold with almost the same parameter.The 0^(−)(1^(−−))state can be assigned to X(2239)observed at BESⅢ,which is very close to theΛΛthreshold.The scalar mesonη(2225)can be interpreted as a 0^(+)(0^(−+))state from theΛΛinteraction.The annihilation effect is also discussed through a coupled-channel calculation plus a phenomenological optical potential.It provides large widths to two bound states produced from theΛΛinteraction.The mass of the 1^(−)state is slightly larger than the mass of the 0^(−)state after including the annihilation effect,which is consistent with our assignment of these two states as X(2239)andη(2225),respectively.The results suggest that further investigation is required to understand the structures near theΛΛthreshold,such as X(2239),η(2225),and X(2175).展开更多
基金supported by the Outstanding Youth Scientist Program of NSFC(41725003)National Key Research&Development Program of China(2017YFA0604802)+2 种基金the National Natural Science Foundation of China(41991234,42077422)the National Key Research&Development Program of China(2016YFC0501802)the Strategic Priority Research Program of Chinese Academy of Sciences(XDA20050102).
文摘The ecological consequences of precipitation change and increased atmospheric nitrogen(N)deposition have profound impacts on ecosystem CO2 exchange in grassland ecosystems.Water and N can largely influence grassland productivity,community composition and ecosystem functions.However,the influences of water and N addition on the ecosystem CO2 exchange of alpine grassland ecosystems remain unclear.A field manipulative experiment with water and N additions was conducted in an alpine meadow on the Tibetan Plateau over 4 years with contrasting precipitation patterns.There were four treatments:control(Ctrl),N addition(N),water addition(W)and N and water addition(NW),each replicated three times.N addition,but not water addition,increased gross ecosystem productivity(GEP),plant biomass,community cover and community-weighted mean height.The responses of ecosystem CO2 exchange to water and N addition varied between the wet and dry years.Water addition had a positive effect on net ecosystem carbon exchange(NEE)due to a larger increase in GEP than in ecosystem respiration(ER)only in the dry year.On the contrary,N addition significantly enhanced ecosystem CO2 exchange only in the wet year.The increased GEP in N addition was attributed to the larger increase in NEE than ER.Moreover,N addition stimulated NEE mainly through increasing the cover of dominant species.Our observations highlight the important roles of precipitation and dominant species in regulating ecosystem CO2 exchange response to global environmental change in alpine grasslands.
基金Supported by the National Natural Science Foundation of China(11675228,11775050,61871124)the Fundamental Research Funds for the Central Universities,the national defense Pre-Research foundation of China,by State Key Laboratory of Acoustics,Chinese Academy of Sciences(SKLA201604)Science and Technology on Sonar Laboratory,the Stable Supporting Fund of Acoustic Science and Technology Laboratory。
文摘In this work,we propose the possible assignment of the newly observed X(2239),as well asη(2225),as a molecular state from the interaction of a baryonΛand an antibaryonΛ.With the help of effective Lagrangians,theΛΛinteraction is described within the one-boson-exchange model withη,η′,ω,ϕ,andσexchanges considered.After inserting the potential kernel into the quasipotential Bethe-Salpeter equation,the bound states from theΛΛinteraction can be studied by searching for the pole of the scattering amplitude.Two loosely bound states with spin parities I^(G)(J^(PC))=0^(+)(0^(−+))and 0^(−)(1^(−−))appear near the threshold with almost the same parameter.The 0^(−)(1^(−−))state can be assigned to X(2239)observed at BESⅢ,which is very close to theΛΛthreshold.The scalar mesonη(2225)can be interpreted as a 0^(+)(0^(−+))state from theΛΛinteraction.The annihilation effect is also discussed through a coupled-channel calculation plus a phenomenological optical potential.It provides large widths to two bound states produced from theΛΛinteraction.The mass of the 1^(−)state is slightly larger than the mass of the 0^(−)state after including the annihilation effect,which is consistent with our assignment of these two states as X(2239)andη(2225),respectively.The results suggest that further investigation is required to understand the structures near theΛΛthreshold,such as X(2239),η(2225),and X(2175).
