Mapping Chinese annual gross primary productivity with eddy covariance measurements and machine learning.

Annual gross primary productivity (AGPP) is the basis for grain production and terrestrial carbon sequestration. Mapping regional AGPP from site measurements provides methodological support for analysing AGPP spatiotemporal variations thereby ensures regional food security and mitigates climate change. Based on 641 site-year eddy covariance measuring AGPP from China, we built an AGPP mapping scheme based on its formation and selected the optimal mapping way, which was conducted through analysing the predicting performances of divergent mapping tools, variable combinations, and mapping approaches in predicting observed AGPP variations. The reasonability of the selected optimal scheme was confirmed by assessing the consistency between its generating AGPP and previous products in spatiotemporal variations and total amount. Random forest regression tree explained 85 % of observed AGPP variations, outperforming other machine learning algorithms and classical statistical methods. Variable combinations containing climate, soil, and biological factors showed superior performance to other variable combinations. Mapping AGPP through predicting AGPP per leaf area (PAGPP) explained 86 % of AGPP variations, which was superior to other approaches. The optimal scheme was thus using a random forest regression tree, combining climate, soil, and biological variables, and predicting PAGPP. The optimal scheme generating AGPP of Chinese terrestrial ecosystems decreased from southeast to northwest, which was highly consistent with previous products. The interannual trend and interannual variation of our generating AGPP showed a decreasing trend from east to west and from southeast to northwest, respectively, which was consistent with data-oriented products. The mean total amount of generated AGPP was 7.03 ± 0.45 PgC yr-1 falling into the range of previous works. Considering the consistency between the generated AGPP and previous products, our optimal mapping way was suitable for mapping AGPP from site measurements. Our results provided a methodological support for mapping regional AGPP and other fluxes.

Eddy covariance-based differences in net ecosystem productivity values and spatial patterns between naturally regenerating forests and planted forests in China.

Net ecosystem productivity (NEP), the difference between gross primary productivity (GPP) and ecosystem respiration (ER), is the basis of forest carbon sinks. Revealing NEP differences between naturally regenerating forests (NF) and planted forests (PF) can benefit for making carbon neutrality strategies. Based on 35 eddy covariance measurements in China, we analyzed NEP differences in values and spatial patterns between NF and PF. The results showed that NF had slightly lower NEP than PF, resulting from the high stand age (SA) and soil fertilizer, while their differences were not significant (p > 0.05). The increasing latitude decreased mean annual air temperature thus decreased GPP both in NF and PF. However, the higher SA and soil fertilizer in NF made most GPP release as ER thus induced no significant NEP spatial variation, while lower SA and soil fertilizer in PF made NEP spatially couple with GPP thus showed a decreasing latitudinal pattern. Therefore, stand characteristics determined the differences in NEP values but indirectly affected the differences in NEP spatial variations through altering GPP allocation. The decreasing latitudinal pattern of NEP in PF indicates a higher sequestration capacity in the PF of South China. Our results provide a basis for improving the forest carbon sequestration.

Effects of ecosystem types on the spatial variations in annual gross primary productivity over terrestrial ecosystems of China.

Annual gross primary productivity (AGPP) serves as the basis for forming biomass and carbon sinks. Analysing the effects of ecosystem types on AGPP spatial variations would be beneficial for clarifying the spatial variability in AGPP, which would serve ecological management practices such as ensuring regional food security. Based on published eddy covariance measurements in China, we collected AGPP data from 128 ecosystems and analysed the effects of ecosystem types on the spatial variations in AGPP to reveal the AGPP spatial variability and its influencing factors over terrestrial ecosystems of China. The results showed that AGPP significantly differed among ecosystem types and vegetation regions, with the lowest AGPP appearing in grasslands, while different ecosystem types had comparable AGPP within the same vegetation region. The AGPP of all ecosystem types showed a decreasing latitudinal trend but slight longitudinal and altitudinal trends. Mean annual air temperature (MAT) and mean annual precipitation (MAP) were found to affect the spatial variations in AGPP over most ecosystem types, while other factors played little role. The mean annual leaf area index (LAI) and the maximum leaf area index (MLAI) were also found to affect the spatial variations in AGPP over most ecosystem types. Factors influencing the AGPP spatial variations differed among ecosystem types, but all included climatic and biotic factors. Therefore, climate inducing spatial distribution of ecosystem types and the non-zonal water supply made AGPP values and factors affecting the spatial variations in AGPP differ among ecosystem types, while different ecosystem types within the same vegetation region had comparable AGPP values. The spatial variation in AGPP over terrestrial ecosystems of China resulted from the integrated effects of climatic and biotic factors. Our study provided data support for improving the understanding of global AGPP spatial variability.

Reversible Photochromic Coordination Polymer by Phototriggered Subtle Molecular Conformation Variations.

Photochromic materials are constructed with molecules accompanied by structural change after triggering by light, which are of great importance and necessity for various applications. However, because of space-confinement effects, molecule stacking of these photoresponsive chromophores within coordination polymers (CPs) always results in an efficiency decrement and a response delay, and this phenomenon will lead to a poor photochromic property. Herein, a CP (named CIT-E) with a 3-fold-interpenetrating network structure, which was prepared with (Z)-1,2-diphenyl-1,2-bis[4-(pyridin-3-ylmethoxy)phenyl]ethene (1Z) and a CuI cluster, showed fast reversible photochromic behavior. Under UV-light illumination, the color of CIT-Z changed from pale yellow to reddish brown. With the illumination of green light, the polymer could return to its initial color within 10 s. To reveal the mechanism of reversible photochromic behavior of CIT-Z, single-crystal structures of each color state were fully studied, and other scientific study methods were also used, such as time-dependent density functional theory calculation and control experiments. It was found that, with light illumination, this behavior of CIT-Z was the result of a ligand-to-metal charge-transfer process, and this process was triggered by subtle molecular conformation variation of tetraphenylethylene. It should be noted that CIT-Z has high thermal and chemical stability, which are excellent advantages as smart photoresponsive materials. As a proof of concept, a uniform thin film with such a fascinating photochromic property allows applications in invisible anticounterfeiting and dynamic optical data storage. Overall, the present study opens up a new avenue toward reversible photochromic materials.

Thinking on large-scale terrestrial ecosystem management and its theoretical fundament and practice.

Ecosystem management at large scales is one of the core solutions to solve current global challenges of environmental and resources problem, mitigate climate change, govern ecosystems and environments regionally and achieve sustainable development. It is also a hotspot in the research and practice of conservation of global natural resources and ecosystems. Based on recalling and synthesizing of several large international actions on ecosystem management in the past two decades, this article rethought the concept of ecosystem management and its application from the perspective of discipline development of ecosystem management, theoretical fundaments and practices. The content included three parts: firstly, we reviewed the development of the scientific concept and practice of ecosystem management, discussed the connotations of the concept and redefined it, and summarized the practice of ecosystem management and its contribution to the development of the discipline. Secondly, we clarified the scientific and technological mission and basic tasks of ecosystem management, organized the discipline system of ecosystem management and its main research fields, summarized fundamental theories and the knowledge system of the science of ecosystem management, and clarified critical steps of ecosystem management actions, basic elements of management plans and management approaches. Finally, we proposed new trends of scientific research and the discipline development of ecosystem management, discussed the important spatial scales and its objects system of the scientific research on ecosystem management, proposed the cutting-edge scientific questions of global ecosystem management, integrative ecology thought and macro ecosystem approach. This review aimed at providing references for the scientific research and discipline deve-lopment of ecosystem management in China.

Discussion on the theoretical basis and technical system of large-scale terrestrial ecosystem science research.

Large-scale terrestrial ecosystem science research becomes an important research field with the promotion of meeting the scientific demand of biodiversity conservation, global climate change mitigation, regional eco-environment governance, and social sustainable development. It is developing rapidly under the guidance of China's ecological civilization construction strategy. Here, we systematically discussed the missions, theoretical foundation and methodology of large-scale terrestrial ecosystem science research and proposed a new theoretical foundation, conceptual system and logical framework for macroecosystem science research on the basis of macrosystem ecology theory. It elaborated the discipline connotation and application of the macroecosystem science to 1) deve-lop the conceptual network of ecosystem science based on the systematic characteristics of ecosystems; 2) develop the theoretical system of ecosystem state change analysis based on the ecosystem integrity and emergence characteristics; 3) develop the theoretical system of integrated research for ecosystem structure-process-function-service cascade relationship based on the attributes and state of ecosystems. We also discussed the methodology and technical system of regional and continental macroecosystem science research, and highlighted the urgency to construct a new generation of continental ecosystem observation and research network, and to develop the network observation-network experiment-numerical simulation-knowledge fusion four-in-one infrastructures.

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Ecology is not only a branch of biology, but also an important part of environmental science and earth system science. The results of ecological studies can be directly applied in biodiversity conservation of plant, animal and microbe, biological resource utilization and biological industry management, and other fields. The concept of ecosystem extends classic ecology or basic ecology research to a new stage of ecosystem ecology or ecosystem science, which has laid a theoretical foundation for the scientific research of ecological environment at the global and continental scales, and has promoted the integration of biology, geography, and environmental science, and cross disciplinary of the natural sciences, humanities, and social economic sciences. During the integration processes, together with constantly absorbing nutrition from different disciplines, researches of eco-logy put forward a lot of scientific concepts or theories, and have been applied and developed in the relevant scientific research, formed contemporary ecology and ecosystem science system centered on the cognition of ecosystem, resource environment, and the mutual feedback relation with human society. We comprehensively discussed the scientific concept, basic theory, and discipline system of contemporary ecology from the origin and development of ecological thought, the scientific connotation, and extension of ecological concept, etc., and tried to sort out, investigate, and analyze the scientific connotation, discipline category and discipline system of contemporary ecology, put forward the branch discipline system classification scheme of basic ecology and applied ecology, with the aim to provide references for perfecting and reconstructing the discipline system of contemporary ecology.

[Regulation effects of temperate broadleaved Korean pine forest on temperature and humidity in Changbai Mountain, China.] / 长白山温带阔叶红松林对温湿环境的调节效应.

Forests can improve climate and regulate micro-environment. The study of forest micro-climate is of great significance to reveal forest ecosystem function and evaluate the benefits of forest ecological environment. With broadleaved Korean pine forest in Changbai Mountain as test material, the diurnal and seasonal variations of the mean, maximum and minimum temperature, relative humidity and surface soil temperature were analyzed based on the meteorological data of flux tower in the forest and nearby meteorological station in the open land from 2003 to 2014. The results showed that air temperature and relative humidity in the forest showed a unimodal U-shaped diurnal pattern, respectively. The diurnal range was 2.31 ℃ and 8.3% lower than that of the open land. The diurnal surface soil temperature tended to be a constant, indicating an alleviating effects of broadleaved Korean pine forest on the diurnal variation of temperature and moisture. The cooling effect was mainly observed in summer, while the warming effect was significant in winter. The air and soil temperatures in forest in summer were 1.30 and 3.91 ℃ lower than those in the open land, and were 2.06 and 5.44 ℃ higher than those in the open land in winter. Forest regulated the maximum and minimum temperatures significantly. On the season scale, the maximum air and soil temperature in forest decreased by 1.80 and 5.45 ℃ in summer, while the minimum air and soil temperature increased by 3.69 and 7.92 ℃ in winter. On the annual scale, the maximum air and soil temperature in forest were 1.60 and 4.99 ℃ lower than those in the open land, and the minimum air and soil temperature were 1.12 and 8.82 ℃ higher than those in the open land, respectively. The regulating effects of forests on soil temperature was stronger than that on air temperature. Forests mainly warmed the air and soil temperature at cold condition.

[Experience of LU Zhi-zheng to apply tenuifolia].

Professor LU Zhi-zheng, one of the first traditional Chinese medicine masters, is good at using tenuifoliain clinical practice, which often brings unexpected surprises. Lu said, tenuifolia is a mild herbal medicine with the nature of upward dispersion and outward penetration but not dryness. Tenuifolia has the following functions: making people conscious, relieving sore throat, diverging incubated diseases, regulating functional activities of qi, sending up Yang, dispelling wind evil and eliminating dampness, and activating collaterals to relieve pain. When well used, it will not only enhance the effect of monarch drug, but also restrict the impetuosity nature in a prescription, achieving better efficacy.

Spatial patterns and climate drivers of carbon fluxes in terrestrial ecosystems of China.

Understanding the dynamics and underlying mechanism of carbon exchange between terrestrial ecosystems and the atmosphere is one of the key issues in global change research. In this study, we quantified the carbon fluxes in different terrestrial ecosystems in China, and analyzed their spatial variation and environmental drivers based on the long-term observation data of ChinaFLUX sites and the published data from other flux sites in China. The results indicate that gross ecosystem productivity (GEP), ecosystem respiration (ER), and net ecosystem productivity (NEP) of terrestrial ecosystems in China showed a significantly latitudinal pattern, declining linearly with the increase of latitude. However, GEP, ER, and NEP did not present a clear longitudinal pattern. The carbon sink functional areas of terrestrial ecosystems in China were mainly located in the subtropical and temperate forests, coastal wetlands in eastern China, the temperate meadow steppe in the northeast China, and the alpine meadow in eastern edge of Qinghai-Tibetan Plateau. The forest ecosystems had stronger carbon sink than grassland ecosystems. The spatial patterns of GEP and ER in China were mainly determined by mean annual precipitation (MAP) and mean annual temperature (MAT), whereas the spatial variation in NEP was largely explained by MAT. The combined effects of MAT and MAP explained 79%, 62%, and 66% of the spatial variations in GEP, ER, and NEP, respectively. The GEP, ER, and NEP in different ecosystems in China exhibited 'positive coupling correlation' in their spatial patterns. Both ER and NEP were significantly correlated with GEP, with 68% of the per-unit GEP contributed to ER and 29% to NEP. MAT and MAP affected the spatial patterns of ER and NEP mainly by their direct effects on the spatial pattern of GEP.

[Characteristics of evapotranspiration in an alpine shrub meadow in Haibei, Qinghai of Northwest China].

Evapotranspiration (ET) is an important component of hydrological cycle of terrestrial ecosystem. To study the seasonal and interannual ET variation patterns of typical ecosystems is essential to better understand the water cycle process and to provide reference for the rational utilization of water resources. By using eddy covariance method, this paper studied the seasonal and interannual variation characteristics of ET and water budget in an alpine shrub meadow ecosystem in Haibei of Qinghai from 2003 to 2011. There was an obvious seasonal variation of ET in the study area in 2003-2011, with the maximum (4.4-5.7 mm x d(-1)) in the vigorous growth season (July-August) and the minimum (0.09 +/- 0.04 mm x d(-1)) in January or December. The annual ET varied greatly among the nine consecutive years, being 451.3 mm in 2010 and 681.3 mm in 2007. More than 70% of the annual ET occurred in the growth season from May to September. The average ratio of annual ET to annual precipitation was 1.06 +/- 0.17, indicating that the water budget of this ecosystem was nearly balanced at year scale, and almost all the precipitation was released into atmosphere by ET.

Handwritten Chinese text recognition by integrating multiple contexts.

This paper presents an effective approach for the offline recognition of unconstrained handwritten Chinese texts. Under the general integrated segmentation-and-recognition framework with character oversegmentation, we investigate three important issues: candidate path evaluation, path search, and parameter estimation. For path evaluation, we combine multiple contexts (character recognition scores, geometric and linguistic contexts) from the Bayesian decision view, and convert the classifier outputs to posterior probabilities via confidence transformation. In path search, we use a refined beam search algorithm to improve the search efficiency and, meanwhile, use a candidate character augmentation strategy to improve the recognition accuracy. The combining weights of the path evaluation function are optimized by supervised learning using a Maximum Character Accuracy criterion. We evaluated the recognition performance on a Chinese handwriting database CASIA-HWDB, which contains nearly four million character samples of 7,356 classes and 5,091 pages of unconstrained handwritten texts. The experimental results show that confidence transformation and combining multiple contexts improve the text line recognition performance significantly. On a test set of 1,015 handwritten pages, the proposed approach achieved character-level accurate rate of 90.75 percent and correct rate of 91.39 percent, which are superior by far to the best results reported in the literature.

Spatio-temporal variability of soil respiration of forest ecosystems in China: influencing factors and evaluation model.

Understanding the influencing factors of the spatio-temporal variability of soil respiration (R (s)) across different ecosystems as well as the evaluation model of R (s) is critical to the accurate prediction of future changes in carbon exchange between ecosystems and the atmosphere. R (s) data from 50 different forest ecosystems in China were summarized and the influences of environmental variables on the spatio-temporal variability of R (s) were analyzed. The results showed that both the mean annual air temperature and precipitation were weakly correlated with annual R (s), but strongly with soil carbon turnover rate. R (s) at a reference temperature of 0°C was only significantly and positively correlated with soil organic carbon (SOC) density at a depth of 20 cm. We tested a global-scale R (s) model which predicted monthly mean R (s) (R (s,monthly)) from air temperature and precipitation. Both the original model and the reparameterized model poorly explained the monthly variability of R (s) and failed to capture the inter-site variability of R (s). However, the residual of R (s,monthly) was strongly correlated with SOC density. Thus, a modified empirical model (TPS model) was proposed, which included SOC density as an additional predictor of R (s). The TPS model explained monthly and inter-site variability of R (s) for 56% and 25%, respectively. Moreover, the simulated annual R (s) of TPS model was significantly correlated with the measured value. The TPS model driven by three variables easy to be obtained provides a new tool for R (s) prediction, although a site-specific calibration is needed for using at a different region.

Modeling the water use efficiency of soybean and maize plants under environmental stresses: application of a synthetic model of photosynthesis-transpiration based on stomatal behavior.

Understanding the variability of plant WUE and its control mechanism can promote the comprehension to the coupling relationship of water and carbon cycle in terrestrial ecosystem, which is the foundation for developing water-carbon coupling cycle model. In this paper, we made clear the differences of net assimilation rate, transpiration rate, and WUE between the two species by comparing the experiment data of soybean (Glycine max Merr.) and maize (Zea mays L.) plants under water and soil nutrient stresses. WUE of maize was about two and a half times more than that of soybean in the same weather conditions. Enhancement of water stresses led to the marked decrease of Am and Em of two species, but water stresses of some degree could improve WUE, and this effect was more obvious for soybean. WUE of the two species changed with psiL in a second-order curve relation, and the WUE at high fertilization was higher than that at low fertilization, this effect was especially obvious for maize. Moreover, according to the synthetic model of photosynthesis-transpiration based on stomatal behavior (SMPTSB) presented by Yu et al. (2001), the WUE model and its applicability were discussed with the data measured in this experiment. The WUE estimated by means of the model accorded well with the measured values. However, this model underestimated the WUE for maize slightly, thus further improvement on the original model was made in this study. Finally, by discussing some physiological factors controlling Am and WUE, we made clear the physiological explanation for differences of the relative contributions of stomata- and mesophyll processes to control of Am and WUE, and the applicability of WUE model between the two species. Because the requirement to stomatal conductance by unit change of net assimilation rate is different, the responses of opening-closing activity of stomata to environmental stresses are different between the two species. To obtain the same level of net assimilation rate, soybean has to open its stomata more widely to keep small stomatal resistance, as compared with maize.