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The terrestrial ecosystem carbon cycle,an important component of the global carbon cycle,has significant impacts on the composition of atmospheric greenhouse gases(GHGs) and global climate change.Quantitative analysis,which provides knowledge of the terrestrial ecosystem carbon cycle,is not only a prerequisite for accurately predicting regional and global climate;it also provides a scientific basis from which governments can develop programs in response to global change.The major goal of this study is to quantify the carbon cycle of the Larix chinensis forest at Taibai Mountain,Shaanxi,China,which experienced significant climate change during the time period from 1958 to 2008.Process-based models are useful tools for predicting changes to the long-term ecosystem carbon cycle that is influenced by climate change.We quantitatively investigated the carbon cycle of the modeled area by using a process-based model,LPJ-GUESS,using climatic data from the Mountain Microclimate Simulation Model(MTCLIM) and CO2 concentration data to drive the model.Net primary productivity(NPP),biomass and net ecosystem carbon exchange(NEE) are the major outputs of the LPJ-GUESS model we used in this study.The NPP and biomass of L.chinensis and Abies fargesii were large in the L.chinensis forest,and both NPP and biomass of L.chinensis were larger than A.fargesii.The average NPP of L.chinensis and A.fargesii during 1958 and 2008 were 0.38 kgC · m-2 · a-1 and 0.25 kgC · m-2 · a-1,respectively.The sum of the two species′ NPP accounted for 86% of the biomass in L.chinensis forest.The average biomass of L.chinensis and A.fargesii during 1958 and 2008 were 2.91 kgC/m2 and 2.02 kgC/m2,respectively.The sum of the two species′ biomass was 94 percent of the NPP in L.chinensis forest.A.fargesii occupied the lower slope of the L.chinensis forest because of its altitudinal limitation,and the upper elevation forest was pure L.chinensis forest.Both L.chinensis and A.fargesii had larger NPP on the northern slope of Taibai Mountain than on the southern slope.Both slopes experienced increasing NPP of the two species over time,and the increase of the northern slope was smaller than the southern slope,so the difference of the L.chinensis forest′s NPP between the northern and southern slope was decreasing over the 51-year study period.Biomass of L.chinensis experienced inter-annual fluctuations during the 1958—2008 study period and increased alternatively between the northern and southern slope.The mean biomass on the southern slope between 1958 and 2008(2.94 kgC/m2) was greater than the northern slope(2.89 kgC/m2).Biomass of A.fargesii,which always occupied a larger part on the northern slope during the 51-year study period,had fewer inter-annual fluctuations compared with L.chinensis.The modeled value of NEE,whose average was-0.023 kgC · m-2 · a-1,showed that L.chinensis forest has been a carbon sink over the 51 years studied.There was no significant difference in average NEE between the northern and southern slope.Both slopes showed increasing carbon sink functioning,with an annual increase of 0.91 gC · m-2 · a-1 on the southern slope and 0.42 gC · m-2 · a-1 on the northern slope.This long-term simulation of the L.chinensis forest driven by climatic data and CO2 concentration was only a preliminary quantitative study of the carbon cycle dynamics.Additional field observations and manipulative experiments are needed to reveal the relationships between climate change and the ecosystem carbon cycle.

The major environmental risks associated with petroleum extraction(e.g.oil spills and leaks) are well known.There is a lot of information on the impacts of petroleum exploration on benthic communities in foreign studies.In this study,we probed the effects of petroleum exploration on macro-invertebrate assemblages,which are important components of benthic communities in this wetland ecosystem.The object of the investigation was to provide scientific data to guide the management,ecological restoration,conservation of biodiversity,and sustainable development of aquatic ecosystems.Physicochemical variables were measured at 34 sites in the Yellow River Delta wetland,Dongying,China,in October 2009,and benthic macro-invertebrate assemblages were collected using a D-frame net and a Peterson grab.The water body in the study area was oligohaline,its salinity ranging between 0.05 and 5 ppt.A total of 84 macro-invertebrate taxa,belonging to 70 genera,41 families,12 orders,6 classes,and 3 phyla,were collected.Insecta comprised 52.4% of all benthic invertebrate taxa,of which Odonata and Diptera accounted for 23% and 24%,respectively.The structure and diversity of macro-invertebrate assemblages were expressed using the Shannon-Wiener index,the Margalef index and the dominance index.Water quality was assessed by the Shannon-Wiener index and the biotic index.The dominant species at most of the sites were either Chironomus spp.or Glyptotendipes spp.with overall dominance indices of 0.0315 and 0.0522,respectively.Pearson correlation analysis showed that the Shannon-Wiener index was negatively correlated with total nitrogen(TN)(r=-0.446,P=0.02) but was not correlated with any of the other physicochemical variables measured.The biotic index was not correlated with any of the physicochemical variables.The numbers of molluscan taxa were negatively correlated with salinity(r=-0.422,P=0.028) and positively correlated with pH(r=0.435,P=0.023).Likewise,the percentages of individual Mollusca at the sites were negatively correlated with salinity(r=-0.395,P=0.041) and positively correlated with pH(r=0.565,P=0.002).The numbers of oligochaete taxa were significantly positively correlated with TN(r=0.524,P=0.005).The petroleum content of the water was not correlated with any of the biological indices and was not considered to be a major stressor.Canonical correspondence ordination analysis(CCA) showed that TN,pH,and salinity were the major contributors to the macro-invertebrate community structure,with 12.18% of species variation explained by these three variables.The substrate and hydrophytes also had effects on the structure of the macro-invertebrate communities.Cluster analysis and MDS ordination of sampling sites showed that all sites could be divided into 11 separate groups at the similarity level of 30%.Oligochaeta and Mollusca were the two main taxa responsive to environmental variables.The bio-assessment indicated that the Shannon-Wiener diversity index was a better indicator of water quality than the biotic index.Bio-assessment using the Shannon-Wiener index showed that the water quality of the Yihong River tributary,the Guangli River upstream,the Tiao River upstream,and the Dongzhang reservoir were clean,that nine sites were slightly polluted,and that the remaining sites were moderately to heavily polluted.We proposed that a comprehensive evaluation of water quality should ideally combine the Shannon-Wiener index,the biotic index,and physicochemical measurements.Additionally,other evaluation methods could be developed based on the biological indices for this region,taking into account the special characteristics of this native ecological environment.