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Protective forests are the ecological barriers of oases in arid sand areas and can effectively prevent and control wind and sand hazards. The structural characteristics of individual trees, as the basic unit of protective forests, are the key factors affecting the protective benefits. With the typical leafless tree species of Ulan Buh Desert oasis, i.e. , Populus alba var. pyramidalis , Populus nigra var. thevestina , and Populus popularis , as the research objects, and by using the ground-based LiDAR and through computational fluid dynamics (CFD), we fully explored the structural characteristics of individual trees and their surrounding aerodynamic characteristics on the basis of real 3D models. We further established the relationship between structural parameters of individual trees and wind field index. The results showed that combining AdQSM and MeshLab to build tree models had high accuracy. The wind field around the individual trees could be roughly divided into six regions, including the attenuation zone of the windward side of the plant, the acceleration zone at the top of the plant, the eddy zone, the calm zone, the transition zone, and the recovery zone of leeward side of the plant. The pressure field around individual trees showed a gradual change of high pressure on the windward side to low pressure on the leeward side. Horizontally, in the range of 20% to 50% reduction in relative wind speed, the effective protection distances were 0.21H-1.51H, 0.20H-0.91H, and 0.25H-1.64H (H was the corresponding tree height) for P. alba var. pyramidalis , P. nigra var. thevestina , and P. popularis , corresponding to effective protection areas of 18-294, 15-227, and 18-261 m 2 , respectively. The maximum wind speed decay rate in the vertical direction was at 0.3H height for P. alba var. pyramidalis and P. popularis , and was reflected at 0.5H height for P. nigra var. thevestina . The correlation and stepwise regression analysis of the single tree structure parameters with the wind field indicators clearly indicated that optical porosity and volume porosity dominated the protection effect. Among the wind field factors, the best regression models related to the porous coefficient were screened for three factors, including diameter at breast height, tree surface area, and optical porosity. The regression variables screened for effective protection distance and effective protection area differed among the classes.

We examined the growth decline and health status of farmland protective forest belt ( Populus alba var . pyramidalis and Populus simonii shelterbelts) in Ulanbuh Desert Oasis by using airborne hyperspectral and ground-based LiDAR to collect the hyperspectral images and point cloud data of the whole forest belt respectively. Through correlation analysis and stepwise regression analysis, we constructed the evaluation model of the decline degree of farmland protection forest with the spectral differential value, vegetation index, and forest structure parameters as independent variables and the tree canopy dead branch index of the field survey as dependent variables. We further tested the accuracy of the model. The results showed that the evaluation accuracy of the decline degree of P. alba var. pyramidalis and P. simonii by LiDAR method was better than that by hyperspectral method, and that the evaluation accuracy of the combined LiDAR and hyperspectral method was the highest. Using the LiDAR method, hyperspectral method, the combined method, the optimal model of P. alba var. pyramidalis was all light gradient boosting machine model, with the overall classification accuracy being 0.75, 0.68, 0.80, and Kappa coefficient being 0.58, 0.43, 0.66, respectively. The optimal model of P. simonii was random forest model, random forest model, and multilayer perceptron model, with the overall classification accuracy being 0.76, 0.62, 0.81, and Kappa coefficient being 0.60, 0.34, 0.71, respectively. This research method could accurately check and monitor the decline of plantations.

To quantitatively evaluate the effects of drought on vegetation productivity in the Qinling-Daba Mountains, we analyzed the temporal and spatial characteristics of gross primary productivity (GPP) and drought, identified the fluctuation of negative GPP extremes under different vegetation types, and quantified the drought vulnerability and drought risk of GPP from 2001 to 2020 with MODIS GPP products and standardized precipitation evapotranspiration index (SPEI). The results showed that the annual GPP from 2001 to 2020 had an increasing trend in 98.0% of areas in the Qinling-Daba Mountains. The GPP of all vegetation types except wetlands increased significantly. SPEI decreased in 23.8% of area in the Qinling-Daba Mountains from 2001 to 2020. The number of negative GPP extremes had no significant trend, but abnormal GPP fluctuations had intensified, especially in the cultivated land. After 2011, the proportion of concurrent negative GPP extreme and drought had decreased for all vegetation types, but the spatial and temporal range of drought in these negative GPP extremes showed an expanding trend. Compared with the pattern during 2001-2010, the proportion of area with positive drought vulnerability and drought risk increased by 104.1% and 6.7% after 2011, indicating that the area with drought-induced GPP decline had expanded. Among all the vegetation types, drought caused the largest decrease of GPP in wetlands. The results revealed that drought led to an aggravation of GPP fluctuations and increased frequency of GPP extremes in the Qinling-Daba Mountains from 2001 to 2020, which resulted in GPP decline with different magnitudes in most vegetation types.

Zhouqu County is located in the transition region from the Qinghai-Tibet Plateau to the Qinba Mountains, and is an important part of the ecological barrier in the upper stream of the Yangtze River. In this study, we used the Google Earth Engine cloud processing platform to perform inter-image optimal reconstruction of Landsat surface reflectance images from 1998-2019. We calculated four indicators of regional wet, green, dry, and hot. The component indicators were coupled by principal component analysis to construct remote sensing ecological index (RSEI) and to analyze the spatial and temporal variations of ecological environment quality in Zhouqu County. The results showed that the contribution of the four component indicators to the eigenvalues of the coupled RSEI were above 70%, with even distribution of the loadings, indicating that the RSEI integrated most of the features of the component indicators. From 1998 to 2019, the RSEI of Zhouqu County ranged from 0.55 to 0.63, showing an increasing trend with a growth rate of 0.04·(10 a) -1 , and the area of better grade increased by 425.56 km 2 . The area with altitude ≤2200 m was dominated by medium and lower ecological environment quality grade, while the area of better ecological environment quality grade area increased by 16.5%. The ecological and environmental quality of the region from 2200 to 3300 m was dominated by good grades, increasing to 71.3% in 2019, with the area of medium and below ecological and environmental quality grades decreasing year by year. The area with altitude ≥3300 m was dominated by the medium ecological quality grade. The medium and below ecological quality grades showed a "U" shape trend during the study period. The trend of ecological environment quality in Zhouqu County was becoming better, but with fluctuations. It is necessary to continuously strengthen the protection and management of ecological environment in order to guarantee the continuous improvement of ecological environment quality.

Variations of functional traits with leaf age reflect plant life history strategy and indicate allocation pattern and trade-off characteristics in the limiting resource. In this study, leaves with different ages of Taxus wallichiana var. chinensis saplings were taken as experimental materials. Fourteen leaf functional traits of leaves at three differebt ages were measured in order to reveal changes of the saplings' ecological strategies with leaf aging. The results showed that one-year-old leaves had significantly higher specific leaf area than two- and three-year-old lea-ves, while three-year-old leaves had significantly greater leaf thickness, leaf area, volume, fresh weight and dry weight than leaves at other ages. In addition, one-year-old leaves had significantly greater nitrogen content (N), phosphorus content (P) and N:P than two- and three-year-old leaves, but lower C:N than three-old-year leaves. The slope of allometric relationship between leaf water content and dry weight, leaf thickness and leaf area of one-year-old leaves, leaf thickness and leaf area of three-year-old leaves were all significantly lower than 1.0. Two-year-old leaves showed significantly allometric relationships between many leaf traits, with slope being not equal to 1.0. In conclusion, one-year-old leaves of T. wallichiana var . chinensis saplings tended to have higher photosynthetic capacity, two-year-old leaves had stronger dry matter accumulation, and three-year-old leaves would construct defense system. The coordination and complementation of functional traits among leaves with different ages might have great significance for maintaining individual homeostasis and survival.

The distribution characteristics of exogenous carbon (C) in the C fractions of biocrusts-covered soil are critical for understanding the geochemical cycling of C with biocrusts in drylands. A 13 C pulse labeling experiment was conducted for moss-dominated biocrusts-covered soil and bare soil on the Loess Plateau of China with semiarid climate, with the content of 13 C in different C fractions being continuously measured to determine the biocrust effects on the distribution of exogenous C in each C fraction. Our results showed that, 1) the 13 C abundance of each C fraction in the biocrusts-covered soil was steadily changed with time, due to the relatively low rate of nutrient cycling in the biocrusts-covered soil and also to the relatively low biomass of moss in the biocrusts-covered soil as compared with vascular plants. 2) The 13 C content of each C fraction in the biocrusts-covered soil was significantly higher than that in the bare soil. Specifically, the 13 C content of total organic C (TOC), microbial biomass C (MBC), and dissolved organic C (DOC) in the biocrusts-covered soil was 0.258, 0.078, and 0.004 mg·kg -1 , respectively, which was 3.1, 18.5, and 2.6 times higher than that in the bare soil. Moreover, the 13 C content in the moss of the biocrusts-covered soil was 1.45 mg·kg -1 . 3) The presence of biocrusts changed the distribution characteristics of each C fraction, with the newly assimilated C being mainly distributed in active organic C and biological components of the biocrusts-covered soil. In the biocrusts-covered soil, the 13 C distribution in MBC (30.6%) was higher than that in DOC (1.7%), and the 13 C distribution in the C of moss was 20.3%. 4) The transferred amount and storage capacity of MB 13 C in the biocrusts-covered soil were 15.7 and 19.5 times of that in the bare soil, respectively. The turnover rate of MB 13 C in the biocrusts-covered soil and bare soil was 2.94 and 3.30 times per month, respectively, implying that the turnover time of MB 13 C in the biocrusts-covered soil was 1.1 times longer than that in the bare soil. In conclusion, biocrusts could greatly change the distribution characteristics of each C fraction and increase C turnover rate, highlighting its important roles in C cycling in dryland ecosystems.

Nitrogen (N) labeled with 15 N was evenly added into plots of moss-dominated biological soil crusts (BSCs) and bare soil on the Chinese Loess Plateau. After that, the surface BSCs and bare soil samples were continuously collected within 1-30 days. The 15 N content of each N fraction in soil, microorganisms, and mosses was measured for each sample. The effects of BSCs on soil N fate and cycling was determined through analyzing the differences in the distribution of 15 N fractions between the BSCs and bare soil. Our results showed that: 1) The 15 N content of total N (TN), microbial biomass N (MBN), and dissolved organic N (DON) in the BSCs was 2.9, 17.5, and 9.0 times higher than that in the bare soil, respectively. The 15 N content of moss plants in the BSCs was 4.73 mg kg -1 . 2) The residual rate of 15 N in the BSCs and bare soil was 13.0% and 3.3%, respectively, indicating that the N fixing and holding ability of BSCs was four times higher than that of bare soil. The percentage of each 15 N fraction in T 15 N in the BSCs was in the order of MBN (54.3%)>moss plant N (22.5%)>DON (6.2%), while that in the bare soil was in the order of MBN (11.5%)>DON (2.6%). Over all, microorganisms and mosses in the BSCs had 65.3% higher capacity of N fixation as compared with the bare soil. 3) The transferred amount and storage capacity of MB 15 N in the BSCs were 17.2 and 20.5 times higher than that in the bare soil, respectively. Accordingly, the turnover rate of MB 15 N in the BSCs and bare soil was 5.8 and 7.2 times per month, respectively, with the turnover time of MB 15 N in the BSCs being 1.2 times longer than that in bare soil. In conclusion, BSCs fix and hold more N than bare soil and change the distribution of each N fraction, implying that BSCs play a critical role in N cycling in dryland ecosystems.

Qinghai-Tibet Plateau wetland, an important component of terrestrial ecosystem, plays an essential role in global carbon cycling. To understand the variation of organic carbon storage in vegetation-soil system during vegetation degradation in the Gahai wetland we examined aboveground litter, root biomass and soil organic carbon content in different degradation stages (CK: no degradation, SD: light degradation, MD: moderate degradation, HD: heavy degradation). The results showed that except for HD, carbon storage of aboveground biomass was 99.58-205.64 g·m -2 and that of root biomass (0-40 cm) was 56.96-754.37 g·m -2 . The carbon stocks of aboveground and roots decreased significantly with degradation. Soil bulk density increased first and then decreased with degradation. Soil bulk density of each layer under degraded wetland was greater than that of the control. The carbon storage of litter was 17.29-35.69 g·m -2 , which was significantly higher in CK than in MD and HD. The carbon storage in the soil (0-40 cm) was 7265.06-9604.30 g·m -2 , with the order of MD＞CK＞SD＞HD. The carbon storage in CK and MD as significantly higher than that in SD and HD. The total carbon storage in the vegetation-soil system was 7265.06-10389.94 g·m -2 under different degradation stages. The largest was in CK, followed by MD, SD, and HD. Organic carbon was mostly stored in soil, which accounted for over 90% of the storage. Moderate interference might benefit carbon sequestration of the alpine wetland ecosystems.

Understanding the responses of winter green manure February orchid (Orychophragmus violaceus) to different levels of nitrogen (N) supply in Northern China and determining the optimal soil N supply level to meet N demands of green manure production with high yield and efficiency, could provide a theoretical foundation and practice reference for maximizing ecological effects of green manure and optimizing N management for spring maize-green manure rotation system in intensive farmland in Northern China. We carried out a field experiment in a site which had received no fertilizer for many years. The aboveground biomass accumulation, N uptake of February orchid and soil residual inorganic N before green manure incorporation, as well as the N balance during the green manure growing season were determined under different levels of N supply. The results showed that N fertilizer application significantly increased the biomass and N uptake of February orchid under low soil inorganic N content (15 kg·hm -2 in 0-90 cm soil layer). At the application rate of 90 kg·hm -2 , the biomass (dry mass) and N uptake reached the maximum, being 2031 and 42 kg·hm -2 , respectively. The soil residual inorganic N amount rose with the increases of N fertilizer application before sowing, growing very rapidly once the application rate was over 60 kg·hm -2 . With the increases of N application rate, the calculated apparent N balance changed from deficit to surplus in the growing season of February orchid. The inputs and outputs of N reached a balance at the application rates of 60 to 90 kg·hm -2 . The relationships between February orchid biomass, N uptake, soil inorganic N before green manure incorporation, and soil N supply amount (0-90 cm preplant soil inorganic N content plus N application rate) could be fitted by the quadratic, linear plus plateau and exponential models respectively. Based on the simulation, we calculated the preplant soil N supply and soil residual inorganic N content before green manure incorporation would be 136 and 78 kg·hm -2 individually, as the biomass of February orchid reached the maximum (2010 kg·hm -2 ). While N uptake was at the highest level of 40 kg·hm -2 , the biomass of February orchid was 95% of the maximum biomass mentioned above (1919 kg·hm -2 ) and the soil residual inorganic N before green manure incorporation decreased to 57 kg·hm -2 whose corresponding minimum soil N supply amount was 105 kg·hm -2 . This value was quite near to the recommended soil residual inorganic N (100 kg·hm -2 ) after maize harvest under optimized N management in Nor-thern China. Taken together, our results showed that the level of soil N supply should be at approximately 100 to 105 kg·hm -2 in spring maize-winter green manure system for improving tradeoffs between agronomic and environmental impacts.

Metabolisms are fundamental processes of organisms. They are related to carbon and water cycling of a plant. The relationship between the metabolic rate and the body size of an organism has been a hot spot in ecological research. The typical WBE model with 3/4 power has been controversial. This study tested the applicability of WBE model and examined the change of metabolic exponents with the age class at branch scale in a typical plant, Salix psammophila in the southern edge of the Mu Us desert. The results showed that the estimated metabolic exponent based on the leaf biomass and total biomass was 0.97 for all branches of the S. psammophila. This was significantly greater than the constant power of 3/4 proposed by the WBE model. The branching radius exponent and branching length exponent were 2.67 and 3.83, respectively, being significantly greater than the constant values of 2.0 and 3.0, respectively. The ranges of branching radius exponents and branching length exponents among the age classes were 2.64-3.24 and 2.86-4.30, respectively. Meanwhile, the estimated values and calculated values of metabolic exponents ranged from 1.01-1.29 and 0.94-1.13, respectively. The values of all above were statistically indistinguishable among the six age classes. The common slopes among the six age classes for estimated values and calculated values of metabolic exponents, branching radius exponents and branching length exponents were 1.08, 1.00, 2.84 and 3.35, respectively. These values were significantly greater than the constant values. The changes of the intercept at the y-axis shifted negatively at the common slope of estimated metabolic exponents with significant elevation shift between groups, and the higher age class branches had the greater shift. These indicated that the age classes did not change the metabolic exponents, but changed the metabolic constant significantly. The older branches had lower metabolic activity than the younger branches.

A field experiment was conducted on fluvo-aquic soil in the North China Plain to study the effects of nitrogen application rate on soil nitrogen contents and enzyme activities in rhizosphere and non-rhizosphere of summer maize. The results showed that the soil enzyme activities under different nitrogen application rates showed similar seasonal patterns. In comparison to no nitrogen ferti-lizer treatment, all nitrogen application treatments significantly increased NO 3 - -N contents in rhizosphere and non-rhizosphere soils, NH 4 + -N content in rhizosphere soil and the activities of β-N-acetylglucosaminidase, β-glucosidase, β-xylosidase and Cellobiohyrolase. During the whole summer maize growing season, the NO 3 - -N content in non-rhizosphere soil was significantly higher than that in rhizosphere soil. The NH 4 + -N content in non-rhizosphere soil was also significantly higher than that in rhizosphere soil at filling stage but significantly lower at seedling and maturity stages. Furthermore, soil enzyme activities in rhizosphere soil were significantly higher than those in non-rhizosphere soil. Effect of nitrogen application on soil organic carbon content was not significant. Soil total nitrogen content increased significantly when the nitrogen application rate was 0-180 kg·hm -2 but decreased significantly when the rate was higher than 180 kg·hm -2 . Generally, a proper rate of nitrogen fertilizer application could significantly increase soil enzyme activities and total nitrogen content, and then improve soil biochemistry properties.

In arid and semi-arid areas, plant physiological responses to water availability depend largely on the intensity and frequency of rain events. Knowledge on the responses of xerophytic plants to rain events is important for predicting the structure and functioning of dryland ecosystems under changing climate. The sap flow of Hedysarum scoparium in the Mu Us Sand Land was continuously measured during the growing season of 2012 and 2013. The objectives were to quantify the dynamics of sap flow under different weather conditions, and to examine the responses of sap flow to rain events of different sizes. The results showed that the daily sap flow rates of H. scoparium were lower on rainy days than on clear days. On clear days, the sap flow of H. scoparium showed a midday plateau, and was positively correlated with solar radiation and relative humidity. On rainy days, the sap flow fluctuated at low levels, and was positively correlated with solar radiation and air temperature. Rain events not only affected the sap flow on rainy days through variations in climatic factors (e.g., solar radiation and air temperature), but also affected post-rainfall sap flow velocities though changes in soil moisture. Small rain events (<20 mm) did not change the sap flow, whereas large rain events (>20 mm) significantly increased the sap flow on days following rainfall. Rain-wetted soil conditions not only resulted in higher sap flow velocities, but also enhanced the sensitivity of sap flow to solar radiation, vapor pressure deficit and air temperature.

A semi-static test of Pb exposure (0, 0.2, 0.8, and 1.6 mg L(-1)) was carried out to examine the Pb accumulation and elimination in different tissues of juvenile Chinese sturgeon (Acipenser sinensis). With increasing Pb concentration in water, the Pb concentration in juvenile A. sinensis tissues increased, showing a clear dose-response relationship. The Pb accumulation had a trend of being higher in bone (dorsalbone plate and cartilaginous bone) and muscle, followed by in stomach, intestine, and skin, and relatively low in liver, gill, and notochord. A 6-week duration test after Pb exposure showed that in low dose group (0.2 mg x L(-1)), the Pb concentration in all tissues had no significant differences to the control group, but in medium dose group (0.8 mg x L(-1)), the Pb concentration in most tissues except gill stomach, cartilaginous bone, and muscle was significantly higher than the control. In high dose group (1.6 mg x L(-1)), the Pb concentration in the tissues other than liver, intestine and skin was significantly higher than the control. Through the comparison of accumulation and elimination, it was found that after low- and medium dose exposure, the Pb concentration in skin, gill, and liver was higher than its accumulation, presuming that Pb was absorbed from gill, skin, and alimentary canal, and eliminated from gill and skin.

The growth and development of larval Amur sturgeon Acipenser schrenckii could be divided into two stages, i.e., pre-larval or free embryonic stage [from hatching (0 day of age and 10.17 +/- 0.63 mm of body length) to initial feeding (9 days of age and 18.93 +/- 0.74 mm of body length)], and post-larval stage [from initial feeding to juvenile stage (38 days of age and 41.89 +/- 5.09 mm of body length)]. During pre-larval stage, some organs related to feeling, feeding, breathing and swimming developed and differentiated rapidly; and during post-larval stage, dorsal, lateral and ventral scuta appeared, and the fish morphologically developed into juvenile. The growth characteristics of larval A. schrenckii presented allometric patterns, i.e., the growth inflexion points of eye diameter, mouth width, tail fin length, and pectoral fin length appeared in the ages of 2 days, 8-9 days, 10 days, and 11 days, respectively. Before the growth inflexion points, the organs grew fast; while after the growth inflexion points, the growth slowed down and approximately appeared isometric. The organs of larval A. schrenckii had the characteristics of congruous and rapid development. With the development of the organs related to feeling, feeding, breathing and swimming, larval A. schrenckii obtained the ability of escaping from predators and feeding, and consequently, its survival chance increased.