In this paper,we prove that L(K_(x,y))(λ),theλ-fold line graph of the complete bipartite graph Ka,y,has a C_(6)-decomposition if and only if ry≥6,λxy(c+y-2)=0(mod 12)and(x+y)=0(mod 2),where x,y are nonnegative int...In this paper,we prove that L(K_(x,y))(λ),theλ-fold line graph of the complete bipartite graph Ka,y,has a C_(6)-decomposition if and only if ry≥6,λxy(c+y-2)=0(mod 12)and(x+y)=0(mod 2),where x,y are nonnegative integers and(x,y)≠(2,4)or(2,5).展开更多
Climatic changes in the onset of spring in northern China associated with changes in the annual cycle and with a recent warming trend were quantified using a recently developed adaptive data analysis tool, the Ensembl...Climatic changes in the onset of spring in northern China associated with changes in the annual cycle and with a recent warming trend were quantified using a recently developed adaptive data analysis tool, the Ensemble Empirical Mode Decomposition. The study was based on a homogenized daily surface air temperature （SAT） dataset for the period 1955–2003. The annual cycle here is referred to as a refined modulated annual cycle （MAC）. The results show that spring at Beijing has arrived significantly earlier by about 2.98 d （10 yr）-1, of which about 1.85 d （10 yr）-1 is due to changes in the annual cycle and 1.13 d （10 yr）-1 due to the long-term warming trend. Variations in the MAC component explain about 92.5% of the total variance in the Beijing daily SAT series and could cause as much as a 20-day shift in the onset of spring from one year to another. The onset of spring has been advancing all over northern China, but more significant in the east than in the west part of the region. These differences are somehow unexplainable by the zonal pattern of the warming trend over the whole region, but can be explained by opposite changes in the spring phase of the MAC, i.e. advancing in the east while delaying in the west. In the east of northern China, the change in the spring phase of MAC explains 40%–60% of the spring onset trend and is attributable to a weakening Asian winter monsoon. The average sea level pressure in Siberia （55°–80°N, 50°–110°E）, an index of the strength of the winter monsoon, could serve as a potential short-term predictor for the onset of spring in the east of northern China.展开更多
The traditional anomaly （TA） reference frame and its corresponding anomaly for a given data span changes with the extension of data length. In this study, the modulated annual cycle （MAC）, instead of the widely us...The traditional anomaly （TA） reference frame and its corresponding anomaly for a given data span changes with the extension of data length. In this study, the modulated annual cycle （MAC）, instead of the widely used climatological mean annual cycle, is used as an alternative reference frame for computing climate anomalies to study the multi-timescale variability of surface air temperature （SAT） in China based on homogenized daily data from 1952 to 2004. The Ensemble Empirical Mode Decomposition （EEMD） method is used to separate daily SAT into a high frequency component, a MAC component, an interannual component, and a decadal-to-trend component. The results show that the EEMD method can reflect historical events reasonably well, indicating its adaptive and temporally local characteristics. It is shown that MAC is a temporally local reference frame and will not be altered over a particular time span by an exten-sion of data length, thereby making it easier for physical interpretation. In the MAC reference frame, the low frequency component is found more suitable for studying the interannual to longer timescale variability （ILV） than a 13-month window running mean, which does not exclude the annual cycle. It is also better than other traditional versions （annual or summer or winter mean） of ILV, which contains a portion of the annual cycle. The analysis reveals that the variability of the annual cycle could be as large as the magnitude of interannual variability. The possible physical causes of different timescale variability of SAT in China are further discussed.展开更多
The increasing degree of plant invasion is an expanding problem that affects the functioning and composition of forest ecosystems with increasing anthropogenic activities, particularly soil nitrogen (N) cycles. Numero...The increasing degree of plant invasion is an expanding problem that affects the functioning and composition of forest ecosystems with increasing anthropogenic activities, particularly soil nitrogen (N) cycles. Numerous studies have revealed that one of the main factors for successful plant invasion is that plants could pose significant effects on soil N cycles via direct and/or indirect ways, such as changes in soil microbial communities, litter decomposition rates, and/or soil physicochemical properties. We thereby summarize the ecological effects of invasive plants on soil N cycles, including the aforementioned changes, to understand the mechanism of successful invasion. We also discuss the needs for further research on the relationship between invasive plants and soil N cycles.展开更多
The problem of decomposing a complete 3-uniform hypergraph into Hamilton cycles was introduced by Bailey and Stevens using a generalization of Hamiltonian chain to uniform hypergraphs by Katona and Kierstead. Decompos...The problem of decomposing a complete 3-uniform hypergraph into Hamilton cycles was introduced by Bailey and Stevens using a generalization of Hamiltonian chain to uniform hypergraphs by Katona and Kierstead. Decomposing the complete 3-uniform hypergraphs Kn（3） into k-cycles （3 ≤ k 〈 n） was then considered by Meszka and Rosa. This study investigates this problem using a difference pattern of combinatorics and shows that Kn·5m（3） can be decomposed into 5-cycles for n ∈ {5, 7, 10, 11, 16, 17, 20, 22, 26} using computer programming.展开更多
Mountainous areas exhibit highly variable decomposition rates as a result of strong local differences in climate and vegetation type. This paper describes the effect of these factors on two major determinants of the l...Mountainous areas exhibit highly variable decomposition rates as a result of strong local differences in climate and vegetation type. This paper describes the effect of these factors on two major determinants of the local carbon cycle: litter decomposition and carbon stabilization. In order to adequately reflect local heterogeneity, we have sampled 12 typical plant communities of the Russian Caucasus. In order to minimize confounding effects and encourage comparative studies, we have adapted the widely used tea bag index(TBI) that is typically used in areas with low decomposition. By incubating standardized tea litter for a year, we investigated whether(1) initial litter decomposition rate(k) is negatively correlated with litter stabilization(S) and(2) whether k or S exhibit correlations with altitude and other environmental conditions. Our results show that S and k are not correlated. Altitude, p H, and water content significantly influenced the stabilization factor S, while soil-freezing had no influence. In contrast, none of these factors predicted the decomposition rate k. Based on our data, we argue that collection of decomposition rates alone, as is now common practice, is not sufficient to understand carbon input to soils and can potentially lead to misleading results. Our data on community-specific decomposition and stabilization rates further constrain estimates of litter accumulation in subalpine communities and the potential effects of climate change.展开更多
The decomposition of plant litter is a key process of litter decomposition to global climate warming in plateau in the flows of energy and nutrients in ecosystems. However, the response wetlands remains largely unknow...The decomposition of plant litter is a key process of litter decomposition to global climate warming in plateau in the flows of energy and nutrients in ecosystems. However, the response wetlands remains largely unknown. In this study, we conducted a one-year litter decomposition experiment along an elevation gradient from 1891 m to 3260 m on the Yurman Plateau of Southwest China, using different litter types to determine the influences of climate change, litter quality and microenvironment on the decomposition rate. The results showed that the average decomposition rate （K） increased from 0.608 to 1.152, and the temperature sensitivity of litter mass losses was approximately 4.98%/℃ along the declining elevation gradient. Based on a correlation analysis, N concentrations and C ： N ratios in the litter were the best predictors of the decomposition rate, with significantly positive and negative correlations, respectively. Additionally, the cumulative effects of decomposition were clearly observed in the mixtures of Scirpus tabernaemontani and Zizania caduciflora. Moreover, the litter decomposition rate in the water was higher than that in the sediment, especially in high-elevation areas where the microenvironment was significantly affected by temperature. These results suggest that future climate warming will have significant impacts on plateau wetlands, which have important fimctions in biogeochemical cycling in cold highland ecosystems.展开更多
Biogeochemical feedback processes between soil organic carbon (SOC) in high-latitude organic soils and climate change is of great concern for projecting future climate. More accurate models of the SOC stock and its dy...Biogeochemical feedback processes between soil organic carbon (SOC) in high-latitude organic soils and climate change is of great concern for projecting future climate. More accurate models of the SOC stock and its dynamics in organic soil are of increasing importance. As a first step toward creating a soil model that accurately represents SOC dynamics, we have created the Physical and Biogeochemical Soil Dynamics Model (PB-SDM) that couples a land surface model with a SOC dynamics model to simulate the feedback cycle of SOC accumulation and thermal hydrological dynamics of high-latitude soils. The model successfully simulated soil temperatures for observed data from a boreal forest near Fairbanks, and 2000 year simulations indicated that the effect of the feedback cycle of SOC accumulation on soil thickness would result in a significant differences in the amount of SOC.展开更多
Let be a family of subgraphs of a graph G. An L-decomposition of G is an edge-disjoint decomposition of G into positive integer copies of H<sub>i</sub>, where . Let C<sub>k</sub>, P<sub>k...Let be a family of subgraphs of a graph G. An L-decomposition of G is an edge-disjoint decomposition of G into positive integer copies of H<sub>i</sub>, where . Let C<sub>k</sub>, P<sub>k</sub> and S<sub>k</sub> denote a cycle, a path and a star with k edges, respectively. For an integer , we prove that a balanced complete bipartite multigraph has a -decomposition if and only if k is even, and .展开更多
A k-cycle system of order v with index A, denoted by CS（v, k, λ）, is a collection A of k-cycles （blocks） of Kv such that each edge in Kv appears in exactly λ blocks of A. A large set of CS（v, k, λ）s is a part...A k-cycle system of order v with index A, denoted by CS（v, k, λ）, is a collection A of k-cycles （blocks） of Kv such that each edge in Kv appears in exactly λ blocks of A. A large set of CS（v, k, λ）s is a partition of the set of all k-cycles of Kv into CS（v, k, λ）s, and is denoted by LCS（v, k, λ）. A （v - 1）-cycle in K, is called almost Hamilton. The completion of the existence problem for LCS（v, v- 1,λ） depends only on one case： all v ≥ 4 for λ=2. In this paper, it is shown that there exists an LCS（v,v - 1,2） for all v ≡ 2 （mod 4）, v ≥ 6.展开更多
枯落物分解是影响湿地生态系统物质循环和全球气候变化的关键过程之一.为了全面了解湿地枯落物分解的发展趋势和研究热点,使用Web of Science(WOS)数据库,通过文献计量学软件CiteSpace,对相关内容进行可视化分析.同时,梳理湿地枯落物分...枯落物分解是影响湿地生态系统物质循环和全球气候变化的关键过程之一.为了全面了解湿地枯落物分解的发展趋势和研究热点,使用Web of Science(WOS)数据库,通过文献计量学软件CiteSpace,对相关内容进行可视化分析.同时,梳理湿地枯落物分解的研究进展;归纳湿地枯落物的分解过程、影响机制和研究方法;提出相关领域的研究展望.结果显示:湿地枯落物研究分为缓慢-平稳-快速增长3个阶段,研究核心内容包括植物群落多样性、微生物驱动机制、枯落物性质、全球气候变化、碳循环等.同时,枯落物分解主要受到生物和非生物因素的影响,其中土壤微生物及相关酶活性是影响枯落物分解的初始限制性因子;研究方法以室内培养法及野外分解袋法为主.综上,现在湿地枯落物分解研究仍处于快速发展阶段,尽管从植物、土壤和微生物各因素上进行了较多探讨,但受限于以往研究手段,科学界对枯落物分解的影响机制,特别是各因素间的相互作用机制还缺乏系统了解.因此,未来研究亟需提出新的枯落物分解研究方法,重点关注植物-土壤-微生物间复杂的相互作用关系,为湿地枯落物研究乃至土壤碳循环研究提供重要理论支撑.展开更多
文摘In this paper,we prove that L(K_(x,y))(λ),theλ-fold line graph of the complete bipartite graph Ka,y,has a C_(6)-decomposition if and only if ry≥6,λxy(c+y-2)=0(mod 12)and(x+y)=0(mod 2),where x,y are nonnegative integers and(x,y)≠(2,4)or(2,5).
基金sponsored by the National Basic Research Program of China(Grant Nos. 2011CB952000, 2006CB400504)the Na-tional Natural Science Foundation of China (Grant No.41005039)+1 种基金Wu was sponsored by the National Science Foundation of USA (ATM-0917743)Yan was sponsored by the National Basic Research Program of China(Grant No. 2009CB421401)
文摘Climatic changes in the onset of spring in northern China associated with changes in the annual cycle and with a recent warming trend were quantified using a recently developed adaptive data analysis tool, the Ensemble Empirical Mode Decomposition. The study was based on a homogenized daily surface air temperature （SAT） dataset for the period 1955–2003. The annual cycle here is referred to as a refined modulated annual cycle （MAC）. The results show that spring at Beijing has arrived significantly earlier by about 2.98 d （10 yr）-1, of which about 1.85 d （10 yr）-1 is due to changes in the annual cycle and 1.13 d （10 yr）-1 due to the long-term warming trend. Variations in the MAC component explain about 92.5% of the total variance in the Beijing daily SAT series and could cause as much as a 20-day shift in the onset of spring from one year to another. The onset of spring has been advancing all over northern China, but more significant in the east than in the west part of the region. These differences are somehow unexplainable by the zonal pattern of the warming trend over the whole region, but can be explained by opposite changes in the spring phase of the MAC, i.e. advancing in the east while delaying in the west. In the east of northern China, the change in the spring phase of MAC explains 40%–60% of the spring onset trend and is attributable to a weakening Asian winter monsoon. The average sea level pressure in Siberia （55°–80°N, 50°–110°E）, an index of the strength of the winter monsoon, could serve as a potential short-term predictor for the onset of spring in the east of northern China.
基金supported by Grant 2006CB400504 from the National Basic Research Program of ChinaGrant LCS-2006-03 fromthe Laboratory for Climate Studies, China MeteorologicalAdministration+1 种基金sponsored by the National Science Foundation of USA (ATM-0653136, ATM-0917743)sponsored by National Key Technologies R&D Pro-gram under Grant No. 2007BAC29B03
文摘The traditional anomaly （TA） reference frame and its corresponding anomaly for a given data span changes with the extension of data length. In this study, the modulated annual cycle （MAC）, instead of the widely used climatological mean annual cycle, is used as an alternative reference frame for computing climate anomalies to study the multi-timescale variability of surface air temperature （SAT） in China based on homogenized daily data from 1952 to 2004. The Ensemble Empirical Mode Decomposition （EEMD） method is used to separate daily SAT into a high frequency component, a MAC component, an interannual component, and a decadal-to-trend component. The results show that the EEMD method can reflect historical events reasonably well, indicating its adaptive and temporally local characteristics. It is shown that MAC is a temporally local reference frame and will not be altered over a particular time span by an exten-sion of data length, thereby making it easier for physical interpretation. In the MAC reference frame, the low frequency component is found more suitable for studying the interannual to longer timescale variability （ILV） than a 13-month window running mean, which does not exclude the annual cycle. It is also better than other traditional versions （annual or summer or winter mean） of ILV, which contains a portion of the annual cycle. The analysis reveals that the variability of the annual cycle could be as large as the magnitude of interannual variability. The possible physical causes of different timescale variability of SAT in China are further discussed.
文摘The increasing degree of plant invasion is an expanding problem that affects the functioning and composition of forest ecosystems with increasing anthropogenic activities, particularly soil nitrogen (N) cycles. Numerous studies have revealed that one of the main factors for successful plant invasion is that plants could pose significant effects on soil N cycles via direct and/or indirect ways, such as changes in soil microbial communities, litter decomposition rates, and/or soil physicochemical properties. We thereby summarize the ecological effects of invasive plants on soil N cycles, including the aforementioned changes, to understand the mechanism of successful invasion. We also discuss the needs for further research on the relationship between invasive plants and soil N cycles.
基金Supported by the National Natural Science Foundation of China(Grant No.11161032)
文摘The problem of decomposing a complete 3-uniform hypergraph into Hamilton cycles was introduced by Bailey and Stevens using a generalization of Hamiltonian chain to uniform hypergraphs by Katona and Kierstead. Decomposing the complete 3-uniform hypergraphs Kn（3） into k-cycles （3 ≤ k 〈 n） was then considered by Meszka and Rosa. This study investigates this problem using a difference pattern of combinatorics and shows that Kn·5m（3） can be decomposed into 5-cycles for n ∈ {5, 7, 10, 11, 16, 17, 20, 22, 26} using computer programming.
基金supported by Russian Science Foundation(RSF),grant№16-14-10208
文摘Mountainous areas exhibit highly variable decomposition rates as a result of strong local differences in climate and vegetation type. This paper describes the effect of these factors on two major determinants of the local carbon cycle: litter decomposition and carbon stabilization. In order to adequately reflect local heterogeneity, we have sampled 12 typical plant communities of the Russian Caucasus. In order to minimize confounding effects and encourage comparative studies, we have adapted the widely used tea bag index(TBI) that is typically used in areas with low decomposition. By incubating standardized tea litter for a year, we investigated whether(1) initial litter decomposition rate(k) is negatively correlated with litter stabilization(S) and(2) whether k or S exhibit correlations with altitude and other environmental conditions. Our results show that S and k are not correlated. Altitude, p H, and water content significantly influenced the stabilization factor S, while soil-freezing had no influence. In contrast, none of these factors predicted the decomposition rate k. Based on our data, we argue that collection of decomposition rates alone, as is now common practice, is not sufficient to understand carbon input to soils and can potentially lead to misleading results. Our data on community-specific decomposition and stabilization rates further constrain estimates of litter accumulation in subalpine communities and the potential effects of climate change.
基金Under the auspices of Special Projects of National Key Basic Research Program of China(No.2012CB426509)National Natural Science Foundation of China(No.40971285,31370497,31500409)Yunnan Innovation Talents of Science and Technology Plan of China(No.2012HC007)
文摘The decomposition of plant litter is a key process of litter decomposition to global climate warming in plateau in the flows of energy and nutrients in ecosystems. However, the response wetlands remains largely unknown. In this study, we conducted a one-year litter decomposition experiment along an elevation gradient from 1891 m to 3260 m on the Yurman Plateau of Southwest China, using different litter types to determine the influences of climate change, litter quality and microenvironment on the decomposition rate. The results showed that the average decomposition rate （K） increased from 0.608 to 1.152, and the temperature sensitivity of litter mass losses was approximately 4.98%/℃ along the declining elevation gradient. Based on a correlation analysis, N concentrations and C ： N ratios in the litter were the best predictors of the decomposition rate, with significantly positive and negative correlations, respectively. Additionally, the cumulative effects of decomposition were clearly observed in the mixtures of Scirpus tabernaemontani and Zizania caduciflora. Moreover, the litter decomposition rate in the water was higher than that in the sediment, especially in high-elevation areas where the microenvironment was significantly affected by temperature. These results suggest that future climate warming will have significant impacts on plateau wetlands, which have important fimctions in biogeochemical cycling in cold highland ecosystems.
文摘Biogeochemical feedback processes between soil organic carbon (SOC) in high-latitude organic soils and climate change is of great concern for projecting future climate. More accurate models of the SOC stock and its dynamics in organic soil are of increasing importance. As a first step toward creating a soil model that accurately represents SOC dynamics, we have created the Physical and Biogeochemical Soil Dynamics Model (PB-SDM) that couples a land surface model with a SOC dynamics model to simulate the feedback cycle of SOC accumulation and thermal hydrological dynamics of high-latitude soils. The model successfully simulated soil temperatures for observed data from a boreal forest near Fairbanks, and 2000 year simulations indicated that the effect of the feedback cycle of SOC accumulation on soil thickness would result in a significant differences in the amount of SOC.
文摘Let be a family of subgraphs of a graph G. An L-decomposition of G is an edge-disjoint decomposition of G into positive integer copies of H<sub>i</sub>, where . Let C<sub>k</sub>, P<sub>k</sub> and S<sub>k</sub> denote a cycle, a path and a star with k edges, respectively. For an integer , we prove that a balanced complete bipartite multigraph has a -decomposition if and only if k is even, and .
基金Supported in part by the National Natural Science Foundation of China(No.10901051,11201143)the Fundamental Research Funds for the Central Universities(No.2016MS66)the Co-construction Project of Bejing Municipal Commission of Education
文摘A k-cycle system of order v with index A, denoted by CS（v, k, λ）, is a collection A of k-cycles （blocks） of Kv such that each edge in Kv appears in exactly λ blocks of A. A large set of CS（v, k, λ）s is a partition of the set of all k-cycles of Kv into CS（v, k, λ）s, and is denoted by LCS（v, k, λ）. A （v - 1）-cycle in K, is called almost Hamilton. The completion of the existence problem for LCS（v, v- 1,λ） depends only on one case： all v ≥ 4 for λ=2. In this paper, it is shown that there exists an LCS（v,v - 1,2） for all v ≡ 2 （mod 4）, v ≥ 6.
文摘枯落物分解是影响湿地生态系统物质循环和全球气候变化的关键过程之一.为了全面了解湿地枯落物分解的发展趋势和研究热点,使用Web of Science(WOS)数据库,通过文献计量学软件CiteSpace,对相关内容进行可视化分析.同时,梳理湿地枯落物分解的研究进展;归纳湿地枯落物的分解过程、影响机制和研究方法;提出相关领域的研究展望.结果显示:湿地枯落物研究分为缓慢-平稳-快速增长3个阶段,研究核心内容包括植物群落多样性、微生物驱动机制、枯落物性质、全球气候变化、碳循环等.同时,枯落物分解主要受到生物和非生物因素的影响,其中土壤微生物及相关酶活性是影响枯落物分解的初始限制性因子;研究方法以室内培养法及野外分解袋法为主.综上,现在湿地枯落物分解研究仍处于快速发展阶段,尽管从植物、土壤和微生物各因素上进行了较多探讨,但受限于以往研究手段,科学界对枯落物分解的影响机制,特别是各因素间的相互作用机制还缺乏系统了解.因此,未来研究亟需提出新的枯落物分解研究方法,重点关注植物-土壤-微生物间复杂的相互作用关系,为湿地枯落物研究乃至土壤碳循环研究提供重要理论支撑.
