[Analysis of Temporal and Spatial Carbon Stock Changes and Driving Mechanism in Xinjiang Region by Coupled PLUS-InVEST-Geodector Model].

Based on the goal of "dual-carbon" strategy, it is important to explore the impacts of land use change on carbon stock and the drivers of spatial differentiation of carbon stock in Xinjiang. Here, we predicted the land use types in Xinjiang in 2035 under different scenarios and analyzed the impacts of land use on carbon stock, which is of great theoretical and practical importance for policy formulation, land use structure adjustment, and carbon neutrality target achievement in Xinjiang. The coupled PLUS-InVEST-Geodector model was used to explore the spatial and temporal patterns of carbon stock change under the scenarios of rapid development, natural change, arable land protection, and ecological protection in Xinjiang in 2035 and to quantitatively reveal the attribution of influences on the changes in carbon stock from the perspectives of land use change and the combination of nature-socioeconomic-accessibility. The results showed that： ① From 1990 to 2020, the area of arable land and construction land in Xinjiang increased, and in terms of the transfer direction, it was mainly shifted from unutilized land to grassland. ② On the time scale, the carbon stock in Xinjiang showed the fluctuation of "decrease-increase-decrease," with an overall increasing trend. The transfer of unutilized land to grassland was the main reason for the increase in carbon stock； on the spatial scale, the carbon stock in the Altai Mountains in the north, the Tianshan Mountains in the middle, and the Kunlun Mountains in the south was higher, whereas the carbon stock in the Tarim Basin and the Junggar Basin was lower. ③ In 2035, the carbon stock of the natural development and rapid development scenarios decreased by 27.24 Tg and 71.17 Tg compared with 2020, respectively, and the ecological protection and arable land protection scenarios increased by 492.55 Tg and 46.67 Tg. The ecological protection scenario could significantly increase the carbon stock of the Xinjiang Region compared with that in the other scenarios, and the distribution pattern of the carbon stock in the four scenarios was more or less the same as that in 2020. In addition to land transformation, soil erosion intensity was the main driver of spatial differentiation of carbon stocks in Xinjiang （q value of 0.3501）, followed by net primary productivity of vegetation. The results of multifactor interactions showed that the spatial differentiation of carbon stocks in Xinjiang was the result of the joint action of multiple factors. All the factors had a synergistic enhancement under the interactions. The interaction between soil erosion intensity and the net primary productivity of vegetation was the main driver of the spatial differentiation of carbon stocks in Xinjiang.

How has carbon storage changed in the Yili-Tianshan region over the past three decades and into the future? What has driven it to change?

Predicting future land use changes and assessing carbon storage remain challenging. Nowadays, how nature and socioeconomics drive changes in carbon storage is a hot topic in research. In this study, through the projection of land use type and the integration of the PLUS, Integrated Valuation of Ecosystem Services and Trade-offs (InVEST), and Geodetector models, we constructed a framework for assessing carbon storage in different land use scenarios. Utilizing this framework, it is possible to project land use change and estimate carbon storage based on different development scenarios. We applied the framework to the Yili Tianshan region and identified the main driving forces for carbon storage change. Further, we estimated the carbon storage in the Yili Tianshan region in 2035 under four scenarios (RE, NE, EP, and CLP). The results showed the following: 1) Between 1990 and 2020, there was an increase in the forest area and water bodies in the Yili-Tianshan region, mainly from bare land. 2) As shown on the time scale, carbon storage increases in the Yili-Tianshan region with a W-shaped fluctuation by converting grasslands and bare land into forests. On a spatial scale, the carbon storage was lower in the center and higher on both sides in the Yili-Tianshan region. 3) In 2035- RE, 2035-ND, and 2035-EP scenarios, the carbon storage was increased by 4.30 Tg, 6.67 Tg, and 12.08 Tg; in the 2035-CLP scenario, it was decreased by 14.63 Tg. The Yili-Tianshan region experienced a notable rise in carbon storage under the 2035-EP scenario compared to the other three scenarios. 4) Soil type played a significant role in the spatial differentiation of carbon storage in Yili-Tianshan (q value 0.5958), followed by population density (0.5394). The changes in carbon storage in the Yili-Tianshan region are the result of synergistic effects of multiple factors, in which the soil type∩soil erosion intensity are the most important. This research could provide a reference method for improving regional carbon storage.

[Seasonal variation of water utilization sources and responses to precipitation in the dominant species of broad-leaved and needle-leaved mixed forests in Mount Lushan, China]. / 庐山针阔混交林优势种水分利用来源季节变化及对降水的响应.

Elucidating the seasonal patterns of water sources for dominant species in the sub-tropical humid mountainous forest, analyzing the eco-hydrological complementarity and competition mechanisms among coexisting species, investigating the responses of plant water utilization to precipitation, could provide a theoretical basis for vegetation restoration and management. Based on the stable hydrogen and oxygen isotope technique, we analyzed the δ2H and δ18O characteristics of precipitation, xylem water from Pinus massoniana and Quercus variabilis, and soil water from 0-100 cm depth in Mount Lushan, China. The MixSIAR model, Levins index, and PS index were used to calculate the relative contribution rate of each water source, the hydrological niche breadth, and niche overlap of P. massoniana and Q. variabilis. The results showed that, in the wet season (March to July), P. massoniana primarily utilized soil water from the 0-20 cm and 20-40 cm depths, while Q. variabilis primarily utilized that from the 20-40 cm and 40-60 cm depths. During the dry season (August to September), P. massoniana and Q. variabilis utilized 40-60 cm and 60-80 cm of soil water, respectively, resulting in an increase in the depth of water absorption. In the early growing season (March to April) and the late growing season (September), there was a high hydrological niche overlap between P. massoniana and Q. variabilis, resulting in intensitive water competition. In the middle of the growing season (May to August), the water source was adequately allocated, and the hydrolo-gical niche was segregated to meet the high transpiration demand. Q. variabilis primarily utilized soil water from a depth of 60-80 cm and 60-80 cm before a precipitation event, and from a depth of 0-20 cm and 20-40 cm after the event. In contrast, P. massoniana primarily utilized soil water from a depth of 0-20 cm and 20-40 cm both before and after a precipitation event. In conclusion, water utilization patterns of P. massoniana and Q. variabilis exhibited a seasonal trend, with shallow water uptake during the rainy season and deep water uptake during the dry season. These species are capable of efficiently allocating water resources during the peak growth season, and their root systems actively respond to change in soil moisture level. They have strong adaptability to extreme precipitation events and exhibit remarkable water conservation capabilities.

[Ecological Environment Assessment and Driving Mechanism Analysis of Nagqu and Amdo Sections of Qinghai-Xizang Highway Based on Improved Remote Sensing Ecological Index].

The ecological environment along the Qinghai-Xizang highway is an important part of the construction of the ecological civilization in the Xizang region, and current research generally suffers from difficulties in data acquisition, low timeliness, and failure to consider the unique "alpine saline" environmental conditions in the study area due to the unique geographical environment of the Qinghai-Xizang plateau. Based on the GEE platform and the unique geographical environment of the study area, the remote sensing ecological index (RSEI) was improved, and a new saline remote sensing ecological index (SRSEI) applicable to the alpine saline region was constructed by using principal component analysis as an ecological environment quality evaluation index. The spatial distribution pattern and temporal variation trend of ecological environment quality along the Qinghai-Xizang Highway Nagqu-Amdo section were analyzed at multiple spatial and temporal scales using the ArcGIS 10.3 platform and geographic probes, and the driving mechanisms of eight control factors, including natural and human-made, on the spatial and temporal changes in SRSEI were investigated. The results showed that:① compared with RSEI, SRSEI was more sensitive to vegetation and had a stronger discriminatory ability in areas with sparse vegetation and severe salinization, which is suitable for ecological quality evaluation in alpine saline areas. ② The spatial scale of ecological environment quality in the study area had obvious geographical differentiation, and the areas with poor ecological quality were mainly concentrated in the northern Amdo County, whereas the areas with excellent and good quality grades were mainly distributed in the central-western and southeastern Nagqu areas. On the temporal scale, the ecological environment of the study area as a whole showed an improvement trend over 32 years, and the vegetation cover in the central-western and southeastern areas increased significantly, which had a strong improvement effect on the ecological environment. The improvement area was 1 425.98 km2, accounting for 99.82%. The mean value of SRSEI was 0.49, with an overall fluctuating upward trend and an average increase of 0.015 7 a-1. ③ The land use pattern was the most driving influence factor in the change of ecological environment quality in the study area, with an average q value of 0.157 6 over multiple years, and the influence of environmental factors was low. The multi-factor interaction results showed that the ecological environment in the study area was the result of multiple factors acting together, all factors had synergistic enhancement under the interaction, the influence of human factors was gradually increasing, and the interaction of the net primary productivity (NPP) of vegetation and land use pattern was the main interactive control factor of ecological environment quality in the study area. This study can provide a theoretical basis for ecological environmental protection and sustainable development along the Nagqu to Amdo section.

[Enrichment Characteristics, Source Apportionment, and Risk Assessment of Heavy Metals in the Industrial and Mining Area of Northern Guangdong Province].

In order to understand the heavy metal pollution of the industrial and mining area in northern Guangdong Province, topsoil samples (0-20 cm) from 209 sites in study area were collected, and the concentrations of As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn were analyzed. The source and distribution characteristics of Cd, Cr, Hg, Ni, Pb, As, Cu, and Zn in soil samples were analyzed using the geographic information system (GIS) and principal component analysis (PCA), and the geo-accumulation index and potential ecological hazard index were used to evaluate their pollution status and ecological risk. The results showed that:① Except Ni, all seven heavy metal elements exceeded the national soil background value but were below the pollution risk screening value. The soil environment as a whole was relatively clean. ② The spatial distribution of heavy metals in soil differed. The contents of As and Pb showed northwest-southeast zonal distribution. The contents of Cd, Cu, Hg, and Zn generally decreased from the middle to the surrounding, which was consistent with the industrial and mining enterprise locations. However, the spatial distribution of Cr and Ni had no direct relationship with the location of pollution sources such as industrial enterprises. ③ The eight heavy metals could be identified as three principal components (PCs). PC1 (Cd, Cu, Pb, and Zn) was mainly affected by human activities such as lead-zinc deposit dressing, traffic emissions, and agricultural production. However, PC2 (Cr and Ni) was a natural source, mainly affected by soil parent material. In addition, PC3 (As and Hg) was mainly affected by industrial activities such as non-ferrous metal smelting and thermal power generation. ④ According to the geo-accumulation index method, the risk degree of the eight heavy metals was:Cd>As>Zn>Hg>Pb>Cu>Cr=Ni. The contents of Cr and Ni in soil were at a no-risk level; the contents of As, Cu, Hg, Pb, and Zn were at a low-risk level; and the content of Cd was at a high-risk level. Most potential ecological hazards for single elements in the study area were at a mild risk level. In contrast, a small proportion of the surface soils in areas of intense industrial activity were subject to substantial levels of heavy metal stress and require further attention.

[Effects of CO2 concentration and soil water content on short-term water-use efficiency at whole-plant level]. / CO2浓度和土壤含水量对植物个体尺度短期水分利用效率的影响.

Uncovering the variations of short-term water-use efficiency (WUEp) at whole-plant level in response to CO2 concentration (Ca) and soil water content (SWC) can improve the understanding of plant survival strategies under climate change. In this study, Platycladus orientalis saplings were cultured in simulated climate chambers.There were totally 15 treatments, including Ca of 400 (C400), 600 (C600) and 800 (C800) µmol·mol-1 and SWC of 35%-45% field water holding capacity (FC), 50%-60%FC, 60%-70%FC, 70%-80%FC and 95%-100%FC. The WUEp was measured by mini-lysimeters, weighting method, and static assimilation chamber. The results showed that both daytime (0.12-1.87 mol·h-1) and nighttime transpiration rates (0.01-0.16 mol·h-1) at whole-plant level reached the maximum at C400×70%-80%FC, while the whole-plant daytime net photosynthetic rate (2.12-22.10 mmol·h-1) reached the maximum at C800×70%-80%FC. In contrast, nighttime respiration rate (0.84-4.41 mmol·h-1) increased with increasing SWC, but decreased with increasing of Ca, reaching the maximum at C400×95%-100%FC. For WUEp (5.37-24.35 mmol·mol-1), it reached the maximum at C800×50%-60%FC, indicating that plants could use less water and fixed more carbon by adjusting adaptation strategies under high Ca and drought conditions. In addition, leaf instantaneous water-use efficiency was a good predictor of WUEP when the canopy structure was similar.

Soil water stress overrides the benefit of water-use efficiency from rising CO2 and temperature in a cold semi-arid poplar plantation.

The counteractive effect of atmospheric CO2 (ca ) enrichment and drought stress on tree growth results in great uncertainty in the growth patterns of forest plantations in cold semi-arid regions. We analysed tree ring chronologies and carbon isotopes in Populus simonii plantations in cold semi-arid areas in northern China over the past four decades. We hypothesized that the hydraulic stress from drought would override the stimulating effect of increasing ca and temperature (T) on stem growth (basal area increment [BAI]). We found the stimulating effect of rising ca and T on the growth, indicated by continuous increase of intrinsic water-use efficiency in all stands and a positive correlation between T and BAI. However, these effects failed to alleviate the negative impacts of drought on tree growth. Concurrent acceleration of BAI reversed during the intensive drought episodes. Water stress resulted from inaccessibility of roots to deep soil water rather than from lack of precipitation, suggested by the decoupling of BAI from precipitation and vapour pressure deficit. Local soil water limitation might also cause greater stomatal regulation in declining trees, indicated by lower intercellular CO2 concentration. Thus, site-specific soil moisture conditions growth sensitivity to global warming resulting in site-specific decline episodes in drought-prone areas.

[Erosion process of loess slope and influencing factors in the loess hilly-gully region, China]. / é»„åœŸä¸˜é™µæ²Ÿå£‘åŒºé»„åœŸå¡é¢ä¾µèš€è¿‡ç¨‹åŠå ¶å½±å“å› ç´ .

Rainfall intensity, slope length, and slope gradient are the important factors affecting runoff and sediment yield. In order to quantitatively analyze the effects of rainfall intensity, slope length, and slope gradient on the erosion process of Ansai loess slope in loess hilly and gully region, we analyzed the variation of runoff and sediment yield on Ansai loess with two slope lengths (5, 10 m), three slopes (5°, 10°, 15°) and two rainfall intensities (60, 90 mm·h-1) in an indoor simulated rainfall experiment. The results showed that the initial runoff generation time decreased with the increases of slope length, though the overall change was not significant. The initial runoff generation time decreased with the increases of rainfall intensity. Compared with the intensity of 60 mm·h-1, the initial runoff generation time decreased by 5.7-18 min under the intensity of 90 mm·h-1. Among them, the runoff initiation time on the slope of 10° was the fastest. With the duration of rainfall, runoff yield rate increased rapidly at first, and then gradually fluctuated around a certain value. The sediment yield rate increased rapidly in a short period of time at the initial stage of runoff generation, and then decreased after reaching the maximum, and being gradua-lly stable. The rates of runoff and sediment yield increased with the increases of slope length and rainfall intensity, but the law of change with slope was not obvious. With the increases of rainfall intensity, slope length and gradient, the total sediment yield increased accordingly. Under the rainfall intensity of 90 mm·h-1, the slope surface with the length of 10 m and slope of 15° generated rill, leading to the highest total erosion amount (11885.66 g). Under the rainfall intensity of 60 mm·h-1, the erosion amount per unit area decreased with the increases of slope length, and there was a critical erosion slope length in 5-10 m slope section. Slope length, slope and rainfall intensity all played a promoting role in runoff process. Rainfall intensity, slope length, and their interaction contributed more to runoff yield rate and total erosion amount. Rainfall intensity contributed the most to runoff yield rate, with a contribution rate of 49.8%. The contribution rate of slope length to the total erosion was the largest, which reached 37.8%.

[Quantitative separation of evapotranspiration components of Platycladus orientalis ecosystem based on multiple isotope models]. / åŸºäºŽå¤šç§åŒä½ç´ æ¨¡åž‹çš„ä¾§æŸæž—ç”Ÿæ€ç³»ç»Ÿè’¸æ•£ç»„åˆ†å®šé‡æ‹†åˆ†.

To fully understand the changes in the evapotranspiration components in forest ecosystem and their contribution to evapotranspiration at daily scale, we used the hypothesis theory of isotopic steady state and non-steady state combined with the water isotope analyzer system to quantitatively split and compare the evapotranspiration components of Platycladus orientalis ecosystem during the growing season. Results showed that the 18O of water from different sources during the four mea-surement days (August 5, 8, 10, 11, 2016) all showed surface soil water and oxygen isotope composition (δS) > branch water and oxygen isotope composition (δX) > atmospheric water vapor oxygen isotopes composition (δV), with obvious differences due to the isotope fractionation. Oxygen isotopes composition of soil evaporated water vapor (δE) was between -26.89‰ï½ž-59.68‰ at the daily scale, showing a pattern of first rising and then decreasing. The oxygen isotopic composition of evapotranspiration water vapor in forest ecosystem (δET) was between -15.99‰ï½ž-10.04‰. The oxygen isotopic composition of transpired water vapor under steady state(δT-ISS) was between -12.10‰ï½ž-9.51‰. The oxygen isotopic composition of transpired water vapor under non-steady state (δT-NSS) was between -13.02‰ï½ž-7.23‰. δET and δT-NSS had the same changing trend throughout the day at the daily scale, while the trend of δET, δT-ISS and δT-NSS was approximately the same during 11:00-17:00. In general, the contribution rate of plant transpiration to total evapotranspiration showed that FT-ISS was between 79.1%-98.7%, and FT-NSS was between 88.7%-93.7%. Our results suggested that water consumption through soil evaporation was far less than that of vegetation transpiration in the study area, and that vegetation transpiration dominated forest evapotranspiration.

Effects of thinning intensity on the understory water-holding capacity of Pinus sylvestris var. mongolica plantation in the Bashang area of north China.

The complex terrain and poor climatic conditions in Bashang area of Hebei Province result in water and soil loss and geological disasters, which pose a serious threat to ecological safety in North China. In order to improve local environmental quality, barren-resistant and fast-growing tree species such as Pinus sylvestris var. mongolica and Larix gmelinii are planted with large areas. However, unreasonable plantation density will lead to inefficient utilization of rainfall and intensify the conflict between forest and water. In this study, we analyzed the effects of five thinning intensities (0, 20%, 40%, 60%, 80%) of P. sylvestris var. mongolica plantation on herbs, litter, soil and overall water-holding capacity, with the aim to provide scientific basis for management of P. sylvestris var. mongolica. The results showed that water-holding rate of herb varied from 47.7% to 90.7%, and that the water-holding capacity of herb decreased with increasing thinning intensity. When the thinning intensity was less than 40%, water-holding capacity decreased slowly, and then decreased rapidly. With the increase of thinning intensity, natural water-holding rate and maximum water-holding rate of undecomposed layer and semi-decomposed layer decreased gradually, with the effective water-holding rate being 60%>40%>20%>80%>0, and the water-holding capacity of semi-decomposed layer being better than that of undecomposed layer. The water-holding capacity of soil decreased gradually with the increases of thinning intensity. Thinning intensity less than 40% promoted water holding capacity. Under different thinning intensities, the total water-holding rate of understory was 8.3%-14.3%, with an order of 20%>0>40%>60%>80%. In view of understory all layers and overall changes, the thinning intensity at 20% in the study area could effectively improve the understory water-holding capacity and achieve better ecological benefits.