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.

[Effects of simulated acid rain on soil N2O emission from typical forest in subtropical sou-thern China.] / æ¨¡æ‹Ÿé ¸é›¨å¯¹å—äºšçƒ­å¸¦å ¸åž‹æ£®æž—åœŸå£¤N2O排放的影响.

Based on a long-term simulated acid rain experiment, soil N2O emission fluxes were measured using static chambers and the gas chromatography method in a coniferous and broadleaved mixed forest and a monsoon evergreen broadleaved forest in southern China. During the five-year observation periods (2014-2018), soil N2O emission fluxes in the two forests showed obvious seasonal variation. The soil N2O emission fluxes in wet season were significantly higher than that in dry season, with a large annual variation. Due to the decreases of precipitation, soil N2O emission fluxes of the two forests in 2017 and 2018 were generally low. Soil N2O emission flux was positively correlated with soil temperature and soil moisture. In the monsoon evergreen broadleaved forest, soil N2O emission flux in the control plot was 12.6 µg N2O·m-2·h-1. Soil N2O emission fluxes under the pH 3.5 and pH 3.0 treatments increased by 42.9% and 61.1%, respectively. Soil N2O emission was significantly increased under simulated acid rain in the monsoon evergreen broadleaved forest. Acid rain promoted soil N2O emission in the coniferous and broadleaved mixed forest, but without significant difference among the treatments. Under the scenario of increasing acid rain, soil N2O emission fluxes in typical subtropical southern China forests would increase, and the magnitude of such increase was different among forest types.

Comparison of axial length and anterior chamber depth obtained by A scan ultrasonography and IOL Master in different axial length groups / 国际眼科杂志(Guoji Yanke Zazhi)

AIM:To evaluate the repeatability of axial length (AL) and anterior chamber depth (ACD) obtained by A scan ultrasonography, and to compare AL and ACD obtained by A scan with those obtained by IOL Master.METHODS:Two hundred and fifty-seven cataract eyes of 170 patients were included.IOL Master and A scan were performed for each eye.Five measurements of IOL Master and 3 measurements of A scan were obtained.All the tested eyes were divided into 5 groups according to AL obtained by A scan:Group A (2129mm, 21 eyes).Cronbach's Alpha coefficient and intraclass correlation coefficient (ICC) were applied to evaluate the repeatability of AL and ACD obtained by A scan.Paired t test and Pearson correlation coefficient were used to analyze the differences and correlations of AL and ACD obtained by the 2 devices, respectively.Bland-Altman plots were presented to analyze the agreements of AL and ACD obtained by the 2 devices.RESULTS:All the Cronbach's Alpha and ICCs of AL and ACD values were more than 0.98.The differences of AL values between A scan and IOL Master were-0.11±0.08mm in Group A,-0.15±0.10mm in Group B,-0.19±0.15 mm in Group C,-0.29±0.16mm in Group D and-0.45±0.29mm in Group E, respectively (all P0.89, all P<0.01).CONCLUSION:The AL and ACD values in cataract eyes obtained by A scan were repeatable.The AL and ACD values obtained by A scan were smaller than those obtained by IOL Master.With the increase of AL values, the differences of AL values between A scan and IOL Master increased.

[Accumulation of soil organic carbon and total nitrogen in Pinus yunnanensis forests at different age stages].

Taking three Pinus yunnanensis forests at different ages (19, 28 and 45 a) in Panxian County of Guizhou Province as test objects, we investigated vertical distributions and accumulation rates of soil organic carbon (SOC) and total nitrogen (TN), as well as their relationships with soil bulk density. For the three forests at different age stages, SOC and TN changed consistently along the soil profile, declining with the soil depth. Both SOC and TN storage increased with the forest age. The SOC and TN storage amounts were 96.24, 121.65 and 148.13 t x hm(-2), and 10.76, 12.96 and 13.08 t x hm(-2) for the forest stands with 19 a, 28 a and 45 a, respectively. SOC had a significant positive correlation with soil TN, while both of them had a significant negative relationship with the soil bulk density. The accumulation rates of both SOC and TN storage at different growth periods were different, and the rate in the period from age 19 to 28 was higher than in the period from age 28 to 45.

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.

Repeatability and accuracy of corneal parameters measured by RTVue Fourier-domain optical coherence topography / 中华实验眼科杂志

Background Corneal parameters (such as curvature,thickness,etc) are essential to the diagnosis of corneal related diseases,contact lenses fitting and corneal refractive surgery.Objective The aim of this study was to assess the repeatability and accuracy of corneal parameters obtained by RTVue Fourier-domain optical coherence topography (FD-OCT).Methods In this prospective study,77 eyes of 43 subjects with the refraction from-1.25 D to-10.00 D and astigmatism ＜2 D were enrolled in keratorefractive surgery center,Eye Hospital of Wenzhou Medical College.The anterior and posterior corneal curvature in 3 mm central zone (Ranterior and Rposterior),the ratio of posterior and anterior curvature (Rposterior/Ranterior),corneal central thickness (CCT),total corneal power(Knet),the simulated corneal power (Sim K),the anterior and posterior corneal power (Kanterior,Kposterior)were measured by FD-OCT.Corneal power (Km) was obtained by Topolyzer topography based on Placido ring.Three consecutive scans were acquired in every tested eye.Repeatability of FD-OCT measurement was assessed using the coefficient of variation CV),Cronbach Alpha and intra-class correlation coefficient (ICC).Repeated measure ANOVA was used to analyze the differences among SimK,Knet and Km.Pearson correlation analysis was used to analysis the correlation between SimK and K Knet and Km,SimK and Km.The agreement between Sim K and K Knet and Km,SimK and Km was assessed by Bland-Altman plots analysis.All the subjects understood the purpose of this investigation and written informed consent was obtained prior to the medical examination.Results The Ranterior,Rposterior,Rposterior/Ranterior,Kanterior,Kposterior,Sim K,Knet and CCT were (7.691 ±0.302) mm,(6.532±0.276) mm,0.849±0.014,(48.97±1.92)D,(-6.13±0.26)D,(43.95±1.72) D,(42.95±1.68) D and (545.20± 35.04) μm,respectively.The CV of all parameters was less than 1％.The Cronbach Alpha and ICC were both more than 0.9 except 0.802(ICC)of the Rposterior/Ranterior.SimK was (0.27±0.34) D higher than Km,and Knet was (0.73±0.37) D lower than Km.SimK was (1.01 ±0.11) D higher than K and all the differences showed a statistical significance (P＜0.001).There were close positive correlations between SimK and Km,Knet and Km,SimK and Knet(all r ≥ 0.976,P＜0.001).The Bland-Altman analysis showed a poor agreement between SimK and Km,Knet and Km,SimK and Knet.Conclusions The RTVue FD-OCT measuring corneal curvature and CCT performes good repeatability.The Sim K obtained by RTVue FD-OCT is slightly greater than that obtained by corneal topography,and the Rposterior/Ranterior obtained by RTVue FD-OCT is slightly lower than that from Gullstrand model eye.These results offer a basis for establishing a more accurate standardized model eye.

[Radiometers performance attenuation and data correction in long-term observation of total radiation and photosynthetically active radiation in typical forest ecosystems in China].

Based on the total radiation and photosynthetically active radiation (PAR) observations with net radiometer (CNR1) and quantum sensor (Li-190SB) in 4 ChinaFLUX forest sites (Changbaishan, Qianyanzhou, Dinghushan, and Xishuangbanna) in 2003-2008, this paper analyzed the uncertainties and the radiometers performance changes in long-term and continuous field observation. The results showed that the 98% accuracy of the total radiation measured with CNR1 (Q(cNR1)) could satisfy the technical criterion for the sites except Xishuangbanna where the Q(CNR1) was averagely about 7% lower than Q(CM11), the radiation measured with high accuracy pyranometer CM11. For most sites, though the temperature had definite effects on the performance of CNR1, the effects were still within the allowable range of the accuracy of the instrument. Besides temperature, the seasonal fog often occurred in tropical rain forests in Xishuangbanna also had effects on the performance of CNR1. Based on the long-term variations of PAR, especially its ratio to total radiation in the 4 sites, it was found that quantum sensor (Li-190SB) had obvious performance attenuation, with the mean annual attenuation rate being about 4%. To correct the observation error caused by Li-190SB, an attempt was made to give a post-correction of the PAR observations, which could basically eliminate the quantum sensor's performance attenuation due to long-term field measurement.