Applicability of the generalized wind profile model over mountainous forests.

The analytical equation based on Monin-Obukhov (M-O) similarity theory (i.e., wind profile equation) has been adopted since 1970s for using in the prediction of wind vertical profile over flat terrains, which is mature and accurate. However, its applicability over complex terrains remains unknown. This applicability signifies the accuracy of the estimations of aerodynamic parameters for the boundary layer of non-flat terrain, such as zero-displacement height (d) and aerodynamic roughness length (z0), which will determine the accuracy of frequency correction and source area analysis in calculating carbon, water, and trace gas fluxes based on vorticity covariance method. Therefore, the validation of wind profile model in non-flat terrain is the first step to test whether the flux model needs improvement. We measured three-dimensional wind speed data by using the Ker Towers (three towers in a watershed) at Qingyuan Forest CERN in the Mountainous Region of east Liaoning Province, and compared them with data from Panjin Agricultural Station in the Liaohe Plain, to evaluate the applicability of a generalized wind profile model based on the Monin-Obukhov similarity theory on non-flat terrain. The results showed that the generalized wind profile model could not predict wind speeds accurately of three flux towers separately located in different sites, indicating that wind profile model was not suitable for predicting wind speeds in complex terrains. In the leaf-off and leaf-on periods, the coefficient of determination (R2) between observed and predicted wind speeds ranged from 0.12 to 0.30. Compared to measured values, the standard error of the predicted wind speeds was high up to 2 m·s-1. The predicted wind speeds were high as twice as field-measured wind speed, indicating substantial overestimation. Nevertheless, this model correctly predicted wind speeds in flat agricultural landscape in Panjin Agricultural Station. The R2 between observed wind speeds and predicted wind speed ranged from 0.90 to 0.93. The standard error between observed and predicted values was only 0.5 m·s-1. Results of the F-test showed that the root-mean-square error of the observed and predicted wind speeds in each secondary forest complex terrain was much greater than that in flat agricultural landscape. Terrain was the primary factor affecting the applicability of wind profile model, followed by seasonality (leaf or leafless canopy). The wind profile model was not applicable to the boundary-layer flows over forest canopies in complex terrains, because the d was underestimated or both the d and z0 were underestimated, resulting in inaccurate estimation of aerodynamic height.

First report of Lasiodiplodia pseudotheobromae causing soft rot of plum in China.

Plum (Prunus salicina) is one of the most important fruit tree species worldwide (Valderrama-Soto et al. 2021). In June 2023, the postharvest soft rot symptoms were observed on plum fruits in several fruit markets of Guiyang city, Guizhou province, China. The disease incidence in these markets ranged from 20 to 25% with 70% disease severity. Plum fruits showed rotting, which was characterized by water soaked fruit tissue, softening and presence of whitish mycelia four days post inoculation. In severe conditions, whole fruits become rotted and were covered with white fungal mycelia. Small sections (5 × 3 mm) from 6 diseased plum fruits were surface sterilized by using 75% ethanol for 30 s followed by 0.1% mercuric chloride solution for 5 min, rinsed three times with ddH2O, and then transferred onto potato dextrose agar (PDA) and incubated at 25 ± 2°C for three days. Three pure cultures (GUCC23-0001 to GUCC23-0003) were obtained by transferring a single hyphal tip to new PDA plates. Colonies of these isolates were grayish-white initially, gradually turning to whitish brown with fluffy aerial mycelia and uneven edges and finally turned to a dark gray colony after five days of inoculation. The pseudoparaphyses were hyaline, cylindrical, aseptate, and rounded at apex. Conidia were ellipsoidal, hyaline, unicellular, and 24.2 to 28.6 × 12.3 to 15.5 µm in size (n = 30) (Fig. S1), which were similar to the morphology of Lasiodiplodia pseudotheobromae (Alves et al. 2008). Furthermore, fungal DNA was extracted from fresh mycelia of PDA after seven days by using fungus genomic DNA extraction kit (Biomiga, USA). Partial DNA sequences from four loci including internal transcribed spacer (ITS), translation elongation factor 1-alpha (tef1), beta-tubulin (tub2), and polymerase II second largest subunit (rpb2) were amplified with ITS1 and ITS4 (White et al. 1990), EF1-688F and EF1-1251R (Alves et al. 2008), Bt2a and Bt2b (Glass and Donaldson 1995), and RPB2-LasF and RPB2-LasR, respectively (Cruywagen et al. 2017). GenBank accession numbers are OR361680, OR361681, OR361682 for ITS, OR423394, OR423395, OR423396 for tef1, OR423397, OR423398, OR423399 for tub2, and OR423391, OR423392, OR423393 for rpb2, and gene sequencing showed 99.6 to 100% identity with ex-type strain of L. pseudotheobromae (CBS 116459). Phylogenetic analysis also placed our isolates in a highly supported clade with the reference isolate of L. pseudotheobromae (Fig. S2). Another experiment was designed to confirm the pathogenicity test for additional confirmation. Five mm mycelial plugs of L. pseudotheobromae from a three day old culture on PDA were placed on five surface-sterilized and non-wounded plum fruits for 12 hours and incubated at 25°C ± 2°C for four days. Sterilized fungus free PDA plugs were used as a negative control. Mycelial plugs were removed after 12 hours following which whole fruits were incubated in plastic boxes at 25°C ± 2°C. The experiment was repeated twice. The pathogenicity was evaluated under control conditions in laboratory (relative humidity, 70 ± 5% and temperature 25 ± 5˚C). Plum fruits showed rotting, which was characterized by water soaked fruit tissue, softening and presence of whitish mycelia four days post inoculation. These symptoms and signs were similar to the initially observed symptoms on plums in the markets. No disease symptoms were observed on the control fruits. The re-isolated fungus obtained from inoculated plum fruits was very similar to those isolated from diseased samples in morphology, fulfilling Koch's postulates. To the best of our knowledge, this is the first report of L. pseudotheobromae causing postharvest fruit rot of plum in China. In 2022, the total planting area of plum was 1946.5 thousand hectares, which produces approximately 6626300 tons of plum (Food and Agriculture Organization of the United Nations, 2022). Based on the disease incidence and severity reported in the current study, soft rot of plum may be responsible for nearly 35% of yield losses under severe. Therefore, our study laid a theoretical foundation for the prevention and control of this post-harvest disease of plum.

[Temporal variation and influencing factors of albedo in a deciduous broad-leaved forest]. / è½å¶é˜”å¶æž—åç §çŽ‡çš„æ—¶é—´å˜åŒ–ä¸Žå½±å“å› ç´ .

In situ measurement of albedo is important for estimating ecosystem energy budget and its remote sensing application. However, the measurement method of albedo on sloping land is limited and the difference in temporal variation in albedo between visible and near-infrared bands remains unclear. Taking a deciduous broad-leaved forest at the Maoershan Forest Ecological Station in Northeast China as an example, we explored the temporal variation and influencing factors of albedo for three bands: incident and reflected solar radiation (SR, 300-2800 nm), photosynthetically active radiation (PAR, 400-700 nm), and near infrared radiation (NIR, 700-2800 nm). The temporal difference in albedo measurements between the two installation methods of radiometers was analyzed. The results showed that, in sunny days, the diurnal variation in SR and NIR albedo had an asymmetric U-shaped curve around the local noon, while PAR increased from sunrise to sunset. In cloudy days, the albedo decreased sharply and then tended to be stable. The measurement with parallel sensors to the slope increased the daily mean value of albedo, but reduced the daily asymmetry of SR and NIR. For the whole growing season, the maximum albedos of SR, NIR and PAR in horizontal measurement were 0.16, 0.27 and 0.11, respectively, and the minimums were 0.07, 0.11 and 0.03, respectively. Albedo in the SR and NIR wavebands increased first and then decreased (the peak value was in July), while PAR showed a contrasting pattern. SR albedo was mainly controlled by NIR rather than PAR. The contribution of the influencing factors was ranked in the order of normalized difference vegetation index (61.7%-78.5%, representing leaf area index) > solar altitude angle (15.4%-36.9%) > clearness index (0.4%-36.9%).

[Fine root biomass, production, and turnover rate in a temperate deciduous broadleaved forest in the Maoer Mountain, China]. / å¸½å„¿å±±æ¸©å¸¦è½å¶é˜”å¶æž—ç»†æ ¹ç”Ÿç‰©é‡ã€ç”Ÿäº§åŠ›å’Œå‘¨è½¬çŽ‡.

Fine roots play an important role in energy flow and substance cycling in forests. How-ever, the estimates of biomass, production and turnover of fine roots remain large uncertainties, and the mechanism underlying local-scale spatial variation in fine roots is still unclear. In a temperate secondary forest in the Maoer Mountain in Northeast China, we investigated the vertical distribution of fine root biomass and necromass at the 0-100 cm profile and the dynamics, production and turnover rate of fine root in 0-20 cm soil layer. The sequential coring (including the Decision Matrix and the Maximum-Minimum formula) and the ingrowth core (3 cm diameter and 5 cm diameter) were compared in estimating production and turnover rate of fine roots. Forest stand variables that might affect fine roots were also explored. The results showed that 76.8% of fine root biomass and 62.9% of necromass concentrated in the 0-20 cm soil layer, and that both decreased exponentially with increa-sing soil depth. The seasonal variation in both fine root biomass and necromass was not significant in 0-20 cm soil layer, which might be related to the negligible snowfall in winter and the extremely high precipitation in summer. There was no significant difference in the results of the estimated fine root production between two diameter ingrowth cores. After log-transformed, fine root production and turnover rate estimated by the Decision Matrix, the Maximum-Minimum formula and ingrowth cores were significantly different among methods. With the increases of soil nutrient concentrations, fine root biomass/fine root necromass ratio significantly increased, fine root necromass significantly decreased, whereas fine root biomass, productivity, and turnover rate were not related to soil nutrient. There was a significant positive correlation between fine root production and aboveground woody biomass increment in the previous-year but not current-year.

[Carbon budget estimation based on different methods of CO2 storage flux in forest ecosystems]. / CO2储存通量估算方法对森林生态系统碳收支估测的影响.

Accurate measurement of CO2 storage flux (Fs) in forest ecosystems is of great significance for estimating ecosystem carbon budget by eddy covariance (EC). The errors in the estimation of ecosystem carbon budget caused by different methods for calculating Fs has yet not been comprehensively assessed. Using data from an open-path EC system and an eight-level CO2/H2O profile system (AP100, Campbell Scientific Inc., USA) in a broadleaved deciduous forest at the Maoer-shan in 2018, we evaluated the methodological effect of Fs[2-min mean profile (P2 min), 30-min mean profile (P30 min) and 30-min mean EC single point (Ps)] on the estimation of net ecosystem exchange (NEE), ecosystem respiration (Re), and gross primary productivity (GPP). The results showed that the impact of Fs methods on forest carbon flux generally increased with the increases of time scale, indicating that gap-filling of flux data would further amplify the impacts of Fs estimation methods. At the annual scale, NEE based on P2 min and Ps methods were 36.3% and 29.4% lower than that based on P30 min, while Re based on P2 min was higher than that based on P30 min and Ps by 8.7%. The GPP based on P2 min was 5.4% higher, while that based on Ps was 2.1% lower than that based on P30 min. The traditional P30 min ignored the instantaneous changes in CO2 concentration, Ps missed the changes of CO2 concentration within canopy, and thus both underestimated the actual Re. The approximately instantaneous profile (2-min mean profile) had higher temporal and spatial resolution and could more accurately estimate forest carbon budget with non-flat terrain and complex canopy structure. Our findings had great implications for solving the underestimation of forest Re and GPP as well as the overestimation of net carbon sink on complex conditions with the EC method.

[Functions and applications of Multi-Tower Platform of Qingyuan Forest Ecosystem Research Station of Chinese Academy of Sciences]. / ä¸­å›½ç§‘å­¦é™¢æ¸ åŽŸæ£®æž—ç”Ÿæ€ç³»ç»Ÿè§‚æµ‹ç ”ç©¶ç«™å¡”ç¾¤å¹³å°çš„åŠŸèƒ½å’Œåº”ç”¨.

The relationship between the structure and function of forest ecosystems is the main intere-sts in the research area of forest ecology and management. However, over complex terrains in particular, these studies had been challenged as uneasy tasks due to the limitations in the forest survey and measurement techniques and other supporting technologies. Chinese Academy of Sciences (CAS) funded "Multi-Tower LiDAR/ECFlux Platform for Monitoring the Structure and Function of Secondary Forest Ecosystems" (Multi-Tower Platform, MTP) as a field station network corner-stone research infrastructure project, which was completed by Qingyuan Forest CERN (Chinese Ecosystem Research Network). In a distinctively-bounded and monitored-outlet watershed, the MTP was integrated by light detection and ranging (LiDAR) scanners, eddy covariance (EC) flux instrument systems, whole- and sub-watershed hydrology station network, long-term forest plot arrays, and live data center. Using LiDAR scanning, the MTP can get cloud data for holographic information on canopy structure. The EC-flux instrument system and hydrology station network along with forest plot arrays could ensure the reliability of water and carbon observations over this complex terrain, which allows to verify the studies on flux measurement technologies and methods, as well as to understand the processes of ecohydrology and CO2 exchange between forest ecosystem and the atmosphere. Further, we can also assess the primary ecosystem services, including water conservation and carbon sequestration. All the data from "tower-station" were streamed through wireless network, which would facilitate data monitoring, management, and sharing. There are three tasks of MTP team: 1) defining innovative methods and descriptors to quantify three-dimensional forest structure; 2) developing theories and techniques to measure CO2/H2O fluxes and other trace gases over complex terrains; 3) understanding the relationship between structure and function of forest ecosystems, providing information and rationales for forest management practices to assure broad and sustainable benefits from forests.

[Diurnal variation and light response of net ecosystem carbon exchange in a temperate broadleaved deciduous forest at Maoershan, Northeast China]. / å¸½å„¿å±±æ¸©å¸¦è½å¶é˜”å¶æž—å‡€ç”Ÿæ€ç³»ç»Ÿç¢³äº¤æ¢çš„æ—¥å˜åŒ–åŠå ‰å“åº”ç‰¹å¾.

Photosynthetically active radiation (PAR) is a key environmental factor affecting the change of net ecosystem exchange (NEE) during the daytime. However, the coordinate system of PAR measured by horizontal radiometers over sloping terrain does not match that of NEE after tilt-corrected of the ultrasonic anemometer. Using the temperate deciduous broad-leaved forest at the Maoershan site with an average slope of 9° and a azimuth of 296° as a case, we investigated the diurnal variations in NEE and its driving factors in the growing season (May to September) of 2016. We assessed the differences in estimating light response parameters and the explanations of NEE by other environmental factors between the PAR measured by horizontal and slope-parallel radiometers. The results showed that the diurnal change of NEE in each month of the growing season presented a morning-afternoon asymmetrically unimodal curve: the value was negative (net carbon absorption) about 2.5 h after sunrise, reached the peak around 12:00, then approached zero again at two hours before sunset. The daily net uptake maximized in July and minimized in May. During the whole growing season, the time-lag and difference in the PAR measured by the horizontal versus slope-parallel radiometers led to that the PAR values measured by the horizontal radiometer increased photosynthetic quantum yield (α) and daytime respiration rate (Rd) by 13.3% and 11.5%, respectively, and decreased the maximum photosynthetic efficiency (Amax) by 7.7%. The light response curves of NEE were asymmetrical in the morning and afternoon, with Rd and Amax in the afternoon being greater than that in the morning. Weather conditions affected light response parameters: on cloudy days, Amax was higher than that in sunny days, the α and Rd were lower versus those in sunny days for most conditions. However, the monthly Amax and Rd were generally higher for horizontally measured PAR than for slope-parallelly measured PAR, especially for Amax in the cloudy afternoon. The radiometer-orientation affected the explanation of daytime NEE by air temperature (Ta) and vapor pressure deficit (VPD). The correlation of NEE residual based on the slope-parallel radiometer with Ta and VPD (r ranged: 0.013 to 0.197, 0.098 to 0.224) was tighter than that based on the horizontal radiometer (r ranged: 0.082 to 0.219, 0.162 to 0.282) when the negative correlations with Ta for September was excluded. Our results indicated that the measurements of PAR on the inclined terrains could cause errors in the environmental interpretations of NEE. Such findings had implications for the radiometric measurement of mountain vegetation and the reasonable interpretation of carbon exchange in terrestrial ecosystems.

[Effects of detritus removal on soil carbon, nitrogen and phosphorus stoichiometry and related factors in a temperate deciduous forest in the Maoershan Mountain, China.] / æ¤ç‰©æ®‹ä½“åŽ»é™¤å¯¹å¸½å„¿å±±æ¸©å¸¦è½å¶æž—åœŸå£¤ç¢³ã€æ°®ã€ç£·åŒ–å­¦è®¡é‡ç‰¹å¾åŠå ¶ç›¸å ³å› å­çš„å½±å“.

A detritus-removal experiment was conducted in a temperate deciduous broad-leaved forest in 2007 at the Maoershan Ecological Station in Northeast China, including two treatments: Litterfall removal (NL), root removal (NR). Soil water content, bulk density and the concentrations of soil C, N and P were measured in 2016. The results showed that the C concentration at the surface soil layer (0-10 cm) was reduced by 15.6% and 10.7% for the NL and NR treatments, respectively, while the weighted-mean soil C concentration in 0-30 cm depth was reduced by 7.9% and 4.6%, respectively. The N concentration of the surface layer in the NL treatment decreased by 10.2%, whereas the surface-soil P concentration in the NR treatment increased by 6.6%, resulting in reduced C:P and N:P for both treatments. The standardized major axis regressions showed that the regression slopes between the C, N and P at each layer of 0-30 cm soil depth differed significantly among the treatments. The intercepts of the regressions between soil C concentration and bulk density or soil water content had significant differences among the treatments. The results suggested that detritus-removal caused a coordinated variation in soil C, N and P stoichiometry and physical properties. Therefore, we recommend taking the effect on soil ecological stoichiometry into account in future detritus-removal experiments.

[Application of near-surface remote sensing in monitoring the dynamics of forest canopy phenology.] / è¿‘åœ°é¥æ„Ÿåœ¨æ£®æž—å† å±‚ç‰©å€™åŠ¨æ€ç›‘æµ‹ä¸­çš„åº”ç”¨.

Near-surface remote sensing is an important technique for in-situ monitoring of forest phenology and a robust tool for scaling of the phenology with a high temporal resolution and mode-rate spatial coverage. Here, we first reviewed the methods of near-surface remote sensing with three major optical sensors (i.e., radiometer, spectrometer, and digital camera) for monitoring forest phenology. Second, we analyzed sources of uncertainties from distinguishing the phenophases by using the data obtained at the Maoershan flux site in the temperate forest. We found that the error was mainly attributed to the extracting method. Third, we analyzed the linkage of near-surface remote sensing with other methods and its intrinsic problems. Finally, we proposed four priorities in the research of this field: 1) linking optical (or canopy structural) phenology with functional phenology (physiological and ecological processes); 2) integrating the regional networks of canopy phenology for global networking observation and data sharing of canopy phenology; 3) integrating multi-source and multi-scale phenological data with the help of near-surface remote sensing; 4) developing phenology models based on near-surface remote sensing in order to improve the phenology simulation in the dynamic global vegetation models.

[Spatial variation in diurnal courses of stem temperature of Betula platyphylla and Fraxinus mandshurica and its influencing factors]. / ç™½æ¡¦å’Œæ°´æ›²æŸ³æ ‘å¹²æ¸©åº¦æ—¥å˜åŒ–çš„ç©ºé—´å˜å¼‚åŠå ¶å½±å“å› å­.

Plant temperature is an important parameter for estimating energy balance and vegetation respiration of forest ecosystem. To examine spatial variation in diurnal courses of stem temperatures (Ts) and its influencing factors, we measured the Ts with copper constantan thermocouples at different depths, heights and azimuths within the stems of two broadleaved tree species with contrasting bark and wood properties, Betula platyphylla and Fraxinus mandshurica. The results showed that the monthly mean diurnal courses of the Ts largely followed that of air temperature with a 'sinusoi dal' pattern, but the Ts lagged behind the air temperature by 0 h at the stem surface to 4 h at 6 cm depth. The daily maximal values and ranges of the diurnal course of Ts decreased gradually with increasing measuring depth across the stem and decreasing measuring height along the stem. The circumferential variation in Ts was marginal, with slightly higher daily maximal values in the south and west directions during the daytime of the dormant season. Differences in thermal properties (i.e. , specific heat capacity and thermal conductivity) of both bark and wood tissue between the two species contributed to the inter specific variations in the radial variation in Ts through influencing the heat exchange between the stem surface and ambient air as well as heat diffusion within the stem. The higher reflectance of the bark of B. platyphylla decreased the influence of solar radiation on Ts. The stepwise regression showed that the diurnal courses of Ts could be well predicted by the environmental factors (R2 > 0.85) with an order of influence ranking as air temperature > water vapor pressure > net radiation > wind speed. It is necessary to take the radial, vertical and inter specific varia-tions in Ts into account when estimating biomass heat storage and stem CO2 efflux.

[Assessing the surface heating effect of the open-path analyzer of an eddy covariance system with fine-wire thermocouples]. / åˆ©ç”¨ç»†ä¸çƒ­ç”µå¶è¯„ä¼°æ¶¡åº¦ç›¸å ³ç³»ç»Ÿå¼€è·¯åˆ†æžä»ªè¡¨é¢åŠ çƒ­æ•ˆåº”.

The open-path CO2/H2O analyzer that is currently widely used in the eddy covariance (EC) system possesses a surface heating effect, which may influence the accuracy of the eddy-flux measurements. Taking the open-path EC system in the temperate deciduous forest of the Maoershan Ecosystem Research Station as a case, we assessed the heating effect of the open-path CO2/H2O ana-lyzer (Li-7500) with fine-wire thermocouples and tested the applicability of Burba's equations. The results indicated that between April 23 and May 28 in 2016, the daytime air temperature in the mid-optical-path of the Li-7500 was on average 0.2 ℃ higher than the ambient air temperature, while the nocturnal temperature was almost equal, with the peak of the heating often occurring in the morning transition period and at noon or in the early afternoon. The diurnal variation in the heating effect on the sensible heat flux (HS,HE) estimated from the simple linear-fitting models in the fourth method by Burba (BurbaLF) was overall a rectangle-like wave, whereas that from the multiple regression models (BurbaMR) showed a weak mono-peak shape. Compared with direct mea-surements (K079) with the K-type fine-wire thermocouples (with a 0.079 mm diameter of single bare wire) and the HS,HE modeled with two fine-wire thermocouples (K079Model), the estimated HS,HE with the BurbaLF and BurbaMR varied little in the daytime with a lower but wider daytime-peak (20 W·m-2), a sharp transition between daytime and nighttime, and a typical nocturnal va-lue of ＜ 5 W·m-2. The peak values of HS,HE estimated from the K079 and K079Model could be higher than 40 W·m-2, and the values at night fluctuated around zero. The sensible heat flux in the optical-path of the Li-7500 was increased by 13.6% during the daytime. The value of the daytime heating effect on the CO2 turbulent flux (Fc,HC) estimated from the K079 and K079Model was averaged about 0.5 mg CO2·m-2·s-1, twice of the value estimated previously. Compared with the direct measurements, the Burba equations underestimated the Fc,HC around the noon due to the inadequate HS,HE, but overestimated the Fc,HC in the morning, the late afternoon and the night because of over-corrections of HS,HE, resulting in an overall overestimate of Fc,HC. These findings validated that both K079 and K079Model methods can be used to estimate the Fc,HC.

[Changes in stoichiometry of soil carbon, nitrogen and phosphorus in the early stage of temperate forest succession in Maoershan, Northeast China]. / 帽儿山温带森林演替初期土壤碳、氮、磷计量特征的变化.

A soil displacement experiment was established in the Maoershan Forest Ecosystem Research Station in 2004, replacing the cropland soil of the 0-30 cm depth with the eluvial horizon soil (A treatment), the sediment horizon soil (B treatment) and the parent material horizon soil (weathered sand, C treatment) of an adjacent temperate broadleaved stand. The three treatments simulated the secondary successions from forest clear-cutting, bare soil without seed bank, and primary succession, respectively. Changes in soil carbon, nitrogen, phosphorus and their stoichiometry were examined in 2014. The results indicated that during the ten-year succession, the contents of soil C, N and P changed insignificantly in the A treatment. The contents of soil C and N decreased by 34.7% and 38.6% in the B treatment, but increased by 63.4% and 198.4% in the C treatment, respectively. The slope of the log-transformed N-C relationships decreased significantly during the succession, while the slope of the log-transformed P-N relationships increased significantly. After 10-year's succession, only the C:N decreased by 44.5%, and the N:P increased by 283.6% in the C treatment, with no significant changes for others. The contents of C, N and P were significantly correlated with the root biomass and necromass, suggesting that the succession might change the soil elements and their stoichiometric relationships through modifying organic matter inputs.

[Effects of coordinate rotations on eddy fluxes over a forest on a mountainous terrain in Northeast China.] / åæ ‡æ—‹è½¬å¯¹ä¸œåŒ—å±±åœ°æ£®æž—æ¶¡åŠ¨é€šé‡çš„å½±å“.

Coordinate rotation is an essential step in eddy covariance (EC) flux measurements particularly on complex terrains. Systematically assessing impacts of coordinate rotation methods can improve the accuracy in EC flux estimations. Taking the Maoershan flux tower in a temperate deci-duous forest on valley slopes as a case, we comprehensively examined the effects of various tilt-correction methods on sensible heat flux (H), latent heat flux (LE), CO2 fluxes (Fc), energy ba-lance, friction velocity (u*), and vertical velocity (w) using the standardized major axis method. Compared with the unrotated fluxes, the double rotation (DR), planar fit (PF), vertical velocity unbiased planar fit (NBPF), monthly planar fit (MPF), triple rotation (TR) and monthly sector-wist planar fit (MSWPF) changed the H by +1.5%, +3.8%, +3.1%, +3.3%, -1.3% and -7.1%, respectively. The NBPF and DR increased LE by 1.0% and 0.4%, respectively. The PF also increased LE by 0.671 W·m-2, and the MPF decreased LE by 0.4%, but increased the intercept by 0.747 W·m-2. In contrast, the MSWPF and TR decreased the LE by 4.5% and 15.1%, respectively. The coordinate rotation reduced the Fc by 6.0% (DR)-12.1% (TR). Among the studied methods, the PF increased the energy balance closure by about 2%, whereas the TR decreased it by about 6%. In the light of u* and w, the TR and NBPF were inappropriate for anemometer tilt correction. Considering the precision and practical application of EC measurements, we recommend the PF as the first choice for the Maoershan flux tower site, followed by the DR. These findings are useful for tilt correction of anemometer in EC flux observations over complex terrains.

[Monitoring temporal dynamics in leaf area index of the temperate broadleaved deciduous forest in Maoershan region, Northeast China with tower-based radiation measurements.] / 基于塔载辐射监测帽儿山落叶阔叶林.

Broadband vegetation indices (BVIs) derived from routine radiation measurements on eddy flux towers have the advantage of high temporal resolutions, and thus have the potential to obtain detailed information of dynamics in canopy leaf area index (LAI). Taking the temperate broadleaved deciduous forest around the Maoershan flux tower in Northeast China as a case, we investigated the controlling factors and smoothing method of four BVI time-series, i.e., broadband norma-lized difference vegetation index (NDVIB), broadband enhanced vegetation index (EVIB), the ratio of the near-infrared radiation reflectance to photosynthetically active radiation reflectance (SRNP), and the ratio of the shortwave radiation reflectance to photosynthetically active radiation reflectance (SRSP). We compared the seasonal courses of the BVIs with the LAI based on litterfall collection method. The values for each BVI were slightly different among the three calculation methods by Huemmrich, Wilson, and Jenkins, but showed similar seasonal patterns. The diurnal variations in BVIs were mainly influenced by the solar elevation and the angle between the solar elevation and slope, but the BVIs were relatively stable around 12:30. The noise of daily BVI time-series could be effectively smoothed by a threshold of clearness index (K). The seasonal courses of BVIs for each time of day around the noon had similar patterns, but their thresholds of K and the percen-tages of remaining data were different. Therefore, the daily values of BVIs might be optimized based on the smoothing and the proportion of remaining data. The NDVIB was closely correlated linearly with the LAI derived from the litterfall collection method, while the EVIB, SRNP, and SRSP had a logarithmic relationship with the LAI. The NDVIB had the advantage in tracking the seasonal dyna-mics in LAI and extrapolating LAI to a broader scale. Given that most eddy flux towers had equipped with energy balance measurements, a network of monitoring canopy LAI could be readily achieved if the reflectance of photosynthetically active radiation was measured synchronously.

[Error analysis of CO2 storage flux in a temperate deciduous broadleaved forest based on different scalar variables].

Using the measurement data from an 8-level vertical profile of CO2/H2 0 in a temperate deciduous broadleaved forest at the Maoershan Forest Ecosystem Research Station, Northeast China, this paper quantified the errors of CO2 storage flux (Fs ) calculated with three scalar variables, i. e. , CO2 density (rho c), molar fraction (cc), and molar mixing ratio relative to dry air (Xc). The dry air storage in the control volume of flux measurement was not a constant, and thus, the fluctuation of the dry air storage could cause the CO2 molecules transporting out of or into the control volume, i. e. , the variation of the dry air storage adjustment term (Fsd). During nighttime and day-night transition periods, the relative magnitude of Fsd to eddy flux was larger, and ignoring the Fsd could introduce errors in calculating the net CO2 exchange between the forest ecosystem and the atmosphere. Three error sources in the Fs calculation could be introduced from the atmospheric hydrothermal processes, i. e. , 1) air temperature fluctuation, which could cause the largest error, with one order of magnitude larger than that caused by atmospheric pressure (P) , 2) water vapor, its effect being larger than that of P in warm and moist summer but smaller in cold and dry winter, and 3) P, whose effect was generally smaller throughout the year. In estimating the effective CO2 storage (Fs_E) , the Fs value calculated with rho c, cc, and Xc was overestimated averagely by 8. 5%, suggested that in the calculation of Fs, adopting the Xc conservation to atmospheric hydrothermal processes could be more appropriate to minimize the potential errors.

[Spatial variation of non-structural carbohydrates in Betula platyphylla and Tilia amurensis stems].

Taking the two diffuse-porous tree species Betula platyphylla and Tilia amurensis in a temperate forest in Northeast China as test objects, this paper studied the spatial variation of the non-structural carbohydrates (NSC) concentrations in the stem xylem after leaf-fall. For the two tree species, the concentrations of total non-structural carbohydrate (TNC, soluble sugars plus starch) and soluble sugars in the stem xylem decreased gradually with the increasing depth from cambium to pith, whereas the starch concentration showed little radial variation. There was still a substantial amount of NSC in the inner wood close to pith. The concentrations of the NSC in the two species stems decreased gradually from the stump to the breast height, and then increased vertically. The maximum concentrations of the TNC, soluble sugars, and starch occurred at different heights, depending on the species and the TNC components. The ratio of sugar to starch showed a contrasting vertical trend for the two species, i. e., increasing from the stump to the top for B. platyphylla, but decreasing for T. amurensis. The estimation error of the stem NSC storage was mainly from the axial variation, and then, from the radial variation of NSC concentration. The TNC concentration (1.0% dry mass) in the stem of shade-intolerant species B. platyphylla was significantly lower than that (4.3% dry mass) of shade-tolerant species T. amurensis, which could be related to their different life-history strategies. Applying the sampling protocols considering the axial and radial variations of NSC could effectively reduce the potential uncertainty in estimating the NSC storage at tree or stand level.

[Soil nitrous oxide emission in four temperate forests in northeastern China].

Seasonal dynamics of N2O flux and its controlling factors for four representative temperate forests in northeastern China were examined with a static closed chamber-gas chromatograph technique. These forests were Korean pine (Pinus koraiensis) plantation, Dahurian larch (Larix gmelinii) plantation, Mongolian oak ( Quercus mongolica) forest and hardwood broadleaved forest (dominated by Fraxinus mandshurica, Juglans mandshurica, and Phellodendron amurense). The results showed that all ecosystems were overall atmospheric N2O source during the growing season. The N2O flux (microg x m(-2) x h(-1)) decreased in order of the hardwood broadleaved forest (21.0 +/- 4.9) > the pine plantation (17.6 +/- 4. 6) > the larch plantation (9.8 +/- 5.9) > the oak forest (1.6 +/- 12.6). Overall, there was no consistent seasonal pattern in N2O flux for the four ecosystems. The N2O flux was significantly positively correlated to soil gravimetric water content (0-10 cm depth) consistently for all ecosystems, but significantly negatively correlated to NO3(-)-N content for each ecosystem. However, the responses of N2O flux to soil temperature and NH4(+)-N differed among the ecosystems. The N2O fluxes for the coniferous plantations were positively correlated to NH4(+)-N, but not correlated to the soil temperature at 5 cm depth; while those for the broadleaved forests displayed an opposite trend. The soil water content was the dominator of soil N2O emission for the forests in 2007 perhaps resulting from relative drought in the year. Interactions of vegetation type, environmental factor, and nitrogen availability to soil N2O emission should be further studied in the future.