Shady Slopes Research Articles

Watershed scale patterns and controlling factors of ecosystem respiration and methane fluxes in a Tibetan alpine grassland

Ecosystem respiration (Re) and methane (CH4) fluxes are two important soil-atmosphere carbon exchange processes that have been well documented at the local scale. However, the spatial patterns and controlling factors of these processes remain unclear in the Tibetan alpine permafrost region at the watershed scale. We conducted a two-year field monitoring study of Re and CH4 fluxes at three altitudinal positions on shady and sunny slopes in a Tibetan alpine grassland to determine the spatial variability in the two processes and to identify their underlying mechanisms. The microbial factor had a controlling effect on Re spatial variability in alpine grassland watersheds. The lower soil temperature and soil organic matter content at the upper slope positions on the shady slopes inhibited Re because they reduced the soil microbial activity. We found that the alpine grassland to be a net sink of atmospheric CH4, and the average CH4 flux rates exhibited large spatial variance ranging from −1.60 to −10.48 µg CH4 m−2 h−1 within the watersheds. The spatial variability in soil volumetric water content explained 76% of the variation in CH4 fluxes within the watersheds. We suggest that the influence of permafrost on hydrologic conditions may increase the spatial variability of soil moisture (measured as soil volumetric water content and water-filled pore space) in alpine grassland watersheds, and generally form poorly drained landscape at the lower slope position where Re and CH4 uptake are inhibited. Our results highlight the indirect effects of terrain and permafrost on Re and CH4 fluxes through their effects on biophysiochemical factors. We recommend that the spatial variability in Re and CH4 fluxes at the watershed scale of Tibetan alpine grassland should be given more attention in earth system models, especially the variability of CH4 fluxes with altitudinal position.

Responses of aggregates and associated soil available phosphorus, and soil organic matter in different slope aspects, to seasonal freeze–thaw cycles in Northeast China

Freeze-thaw is an important factor that affects soil aggregate size and integrity in mid-high latitudes or mountainous regions, which in turn impacts soil erosion. However, there are limited studies on the responses of aggregates and associated soil available phosphorus (AP), as well as soil organic matter (SOM) in different slope aspects to seasonal freeze–thaw cycles (FTCs). In this regard, soil samples at different depths (0–5 [D5], 5–10 [D10], 10–15 [D15], and 15–20 cm [D20]) were collected from sunny (SW) and shady (NE) slopes in Meihekou, Northeastern China. Temporal changes in aggregate size distribution, AP (extracted with 0.5 mol L−1 NaHCO3), and SOM of SW and NE were analyzed during one FTCs season (from October 2017 to March 2018). Seasonal FTCs significantly (p < 0.05) influenced aggregate size distribution and associated AP content. The results indicated that although there were similar patterns of change in soil aggregate size distribution over time between SW and NE, NE was more sensitive to seasonal FTCs than SW. The greatest reduction and increment rates were observed in aggregates sized > 5 mm and < 0.25 mm, respectively, at D5 in both SW (reduction rate = 44.9%, increment rate = 63.1%) and NE (reduction rate = 73.3%, increment rate = 76.3%). The mean weight diameters were significantly (p < 0.05) decreased by 0–22.6% in SW and 13.4–43.7% in NE at different soil depths after the seasonal FTCs. Good linear function relationships were observed between the proportion of aggregate fractions and associated AP content for aggregate sizes < 0.25 mm (r2 = 0.38**), 1–2 mm (r2 = 0.32**), and 2–5 mm (r2 = 0.42**) in SW and for > 0.25 mm (r2 = 0.68**), 0.25–1 mm (r2 = 0.38**), 1–2 mm (r2 = 0.52**), and 2–5 mm (r2 = 0.64**) in NE during the seasonal FTCs. The associated AP content showed positive correlations with the proportion of aggregates sized <0.25 mm and 0.25–1 mm and negative correlations with the proportion of aggregates sized 1–2 mm, 2–5 mm, and >5 mm in both SW and NE. The SOM was less sensitive to seasonal FTCs. After the seasonal freeze–thaw period, only the SOM content of partial aggregate sizes decreased significantly (p < 0.05) in NE, whereas there were no such significant changes in SW. Our results demonstrated that slope aspect is a key driver of the different responses of aggregates and associated AP and SOM content during the seasonal FTCs and that slope information could be useful for exploring soil erosion and nutrient loss in freeze–thaw agricultural ecosystems.

Vegetation carrying capacity based on soil water on typical slopes in the Diediegou small watershed of Liupan Mountains, northwestern China.

Aims Soil water is the main limiting factor for vegetation,and it mainly comes from pre-cipitation in the Diediegou small watershed in the Liupan Mountains,northwestern China,where the structure of slope vegetation is usually closely related with the amount of precipitation. Our objectives were to develop a method for estimating vegetation carrying capacity (VCC) on sites based on water balance and to evaluate variation of VCC along typical slopes,for guiding the restoration and manage-ment of vegetation on similar slopes. Methods We established nine plots along two typical slopes of natural grassland and larch (Larix principis-rupprechti) plantation,measured leaf area index (LAI) every 15 days and continuously moni-tored all water fluxes and soil water dynamics. After analyzing plot water balance,we determined the relationships among evapotranspiration (ET),LAI and precipitation to estimate VCC based on growing season precipitation and calculated the variation of VCC along slopes.Important findings Our mathematical models for determining VCC (expressed as the maximal LAI) based on precipitation amount (P,mm) in growing season (April–October) were LAItree=exp ((0.773 1×P–186.12)/146.46) for the larch stand on the shady slope and LAIgrass=exp ((0.511 2× P–345.93)/227.89) for the grassland on the sunny slope. The VCC of larch stands on the shady slope in-creased from upper slope (1.45) to middle slope (4.83) and then stabilized between 3.0 and 3.3. For grassland on the sunny slope,VCC increased from upper slope (0.37) to middle slope (0.46) and then stabilized between 0.41 and 0.47. Measured values of LAI were close to those of simulated VCC,sup-porting the rationality of our method and the result. Using LAI as an index expressing VCC,which is mainly determined by soil water in dryland regions,is a new method for calculating VCC for slopes where precipitation water is redistributed in the forms of runoff and interflow.

Influence of Slope Direction on the Soil Seed Bank and Seedling Regeneration of Castanopsis hystrix Seed Rain

Objective: To investigate the impact of different slope directions on the quantity and quality of the soil seed bank and seedling germination process of Castanopsis hystrix plantations. Method: Fixed sample plots in forest stands of Castanopsis hystrix were established on different slope directions (sunny slope, semi-sunny slope, semi-shady slope, and shady slope). The characteristics of the forest stand were investigated, and per-wood scaling was carried out. The temporal dynamics of the seed rain and seed bank were quantified using seed rain collectors and by collecting soil samples from different depths. The quantity and quality of the seeds were determined, and the vigor of mature seeds was measured throughout the study. Results: (1) The diffusion of Castanopsis hystrix seed rain started in mid-September, reached its peak from late October to early November, and ended in mid-December. (2) The dissemination process, occurrence time, and composition of the seed rain varied between the different slope directions. The seed rain intensity on the semi-sunny slope was the highest (572.75 ± 9.50 grains∙m−2), followed by the sunny slope (515.60 ± 10.28 grains∙m−2), the semi-shady slope (382.13 ± 12.11 grains∙m−2), and finally the shady slope (208.00 ± 11.35 grains∙m−2). The seed rain on the sunny slope diffused earliest and lasted the longest, while the seed rain on the shady slope diffused latest and lasted the shortest time. Seed vigor and the proportion of mature seeds within the seed rain were greatest on the semi-sunny slope, followed by the sunny slope, semi-shady slope, and the shady slope. (3) From the end of the seed rain to August of the following year, the amount of total reserves of the soil seed banks was highest on the semi-sunny slope, followed by the sunny slope then the semi-shady slope, and it was the lowest on the shady slope. The amount of mature, immature, gnawed seeds and seed vigor of the soil seed bank in various slope directions showed a decreasing trend with time. The seeds of the seed bank in all slope directions were mainly distributed in the litter layer, followed by the 0–2 cm humus layer, and only a few seeds were present in the 2–5 cm soil layer. (4) The seedling density of Castanopsis hystrix differed significantly on the different slope directions. The semi-sunny slope had the most seedlings, followed by the sunny slope, semi-shady slope, and the shady slope. Conclusions: The environmental conditions of the semi-sunny slope were found to be most suitable for the seed germination and seedling growth of Castanopsis hystrix, and more conducive to the regeneration and restoration of its population.

Analysis of Mediterranean Vegetation Fuel Type Changes Using Multitemporal LiDAR

Increasing fire size and severity over the last few decades requires new techniques to accurately assess canopy fuel conditions and change over larger areas. This article presents an analysis on vegetation changes by mapping fuel types (FT) based on conditional rules according to the Prometheus classification system, which typifies the vertical profile of vegetation cover for fuel management and ecological purposes. Using multi-temporal LiDAR from the open-access Spanish national surveying program, we selected a 400 ha area of interest, which was surveyed in 2010 and 2016 with scan densities of 0.5 and 2 pulses·m−2, respectively. FTs were determined from the distribution of LiDAR heights over an area, using grids with a cell size of 20 × 20 m. To validate the classification method, we used a stratified random sampling without replacement of 15 cells per FT and made an independent visual assessment of FT. The overall accuracy obtained was 81.26% with a Kappa coefficient of 0.73. In addition, the relationships among different stand structures and ecological factors such as topographic aspect and forest vegetation cover types were analyzed. Our classification algorithm revealed that stands lacking understory vegetation usually appeared in shady slopes, which were mainly covered by beech stands, whereas sunny areas were preferentially covered by oak stands, where the understory reached greater height thanks to more light availability. Our analysis on FT changes during that 6 year time span revealed potentially hazardous transitions from cleared forests towards a vertical continuum of canopy fuels, where wildfire events would potentially reach tree crowns, especially in oak forests and southern slopes with higher sun exposure for lower fuel moistures and increased flammability. Accurate methods to characterize forest canopy fuels and change over time can help direct forest management activities to priority areas with greater fire hazard. Multi-date canopy fuel information indicated that while some forest types experienced a growth of the shrub layer, others presented an understory decrease. On the other hand, loss of understory was more frequently detected in beech stands; thus, those forests place lower risk of wildfire spread. Our approach was developed using low-density and publicly available datasets and was based on direct canopy fuel measurements from multi-return LiDAR data that can be accurately translated and mapped according to standard fuel type categories that are familiar to land managers.

Allometric scaling relationships of Larix potaninii subsp. chinensis traits across topographical gradients

The variation of phenotypic traits with environmental gradient can reveal the plant adapting strategies and predict reactions to future climate changes. However, it remains elusive, especially for alpine timberline tree species. To quantify the variation and explore the patterns of twig, leaf, stoma traits, and determine the scaling relationships along the topographic gradients, 576 current-year branches of Larix potaninii ssp. chinensis were collected and scaling relationships were analyzed. The results showed that the twig, leaf and stoma traits varied nonlinearly along altitudinal gradients (2900–3500 m) in both sunny and shady slopes, with a reversal point at about 3250 m, at which the optimum growth of twig length (78.53 mm), twig cross-sectional area (3.35 mm2), internode length (13.14 mm), leaf length (19.30 mm), specific leaf area (0.01 mm2mg−1), stomatal length (47.05 µm) and density (160.20 mm−2). In addition, the values of leafing intensity, leaf number and stomatal density on sunny slope, 1.52 mm−3, 88.79 and 160.20 mm−2 respectively, were higher than that on shady slope. Moreover, the relationships between leaf-twig traits were significantly correlative, and the leaf area-twig cross-sectional area and leaf intensity-leaf area scaling relationships were allometric (slope ≠ 1 or slope ≠ −1) and showed common slope with different y-intercept across altitudes and slope aspects (P < 0.01). Overall, the scaling relationships of different traits across topographical gradients were governed by functional coordination. The twig-size-leaf-size always maintains the balance between geometric dimension and mass in a certain growth rate. The inverse proportion in leaf size and number revealed its maximizing limited resource use efficiency.

Spatial distribution characteristics of reconstructed soil bulk density of opencast coal-mine in the loess area of China

Controlling and adjusting the reconstructed soil bulk density (RSBD) in an artificially disturbed ecosystem is one of the main challenges in land reclamation. Exploring the spatial distribution of RSBD is the best starting point to analyze and improve reclamation technology. This study quantifies the spatial distribution pattern and variation of RSBD on reclaimed land in the loess area of China using geostatistical spatial interpolation and multiple regression analysis. Topography (platform, slope, and slope aspects), vegetation cover, soil particle size distribution, and soil erosion were found to affect the spatial variability of the RSBD. The boundary between the sunny slope and shady slope was considered to be the dividing line for the RSBD, which was generally distributed in stripes and patches. The RSBD was higher on the sunny slope than on the shady slope at 0–10 cm, while the opposite was observed at 20–40 cm. However, the RSBD at the depths of 40–60 cm increased from west to east, and the direction of the strong spatial variability also gradually changed from “ Southwest ↔ Northeast ” to “ West ↔ East ”. The unary quadratic regression equations accurately represent the variation laws of RSBD at different soil depths under different topography and vegetation cover (R2 > 0.90). Measures that utilize engineering and vegetation to improve the RSBD should be adjusted according to the specific landscape and topography. This study provides a theoretical basis for the improvement of the RSBD and the optimization of land reclamation technology used in opencast coal-mine dumps in the loess area.

Effects of slope aspect on altitudinal pattern of soil C:N:P stoichiometry in alpine forest of Tibet

Knowledge of altitudinal patterns in soil C, N and P distribution is important for understanding biogeochemical processes in mountainous forests, yet the influence of slope aspects on soil stoichiometry has been largely neglected in previous studies. In this paper, a total number of 150 topsoil samples at four altitudes (3700, 3900, 4100, 4380 m a.s.l.) on sunny and shady slopes of Sygera mountains in the Southeastern Tibet were collected. Soil C, N and P contents, and pH, were measured. Soil temperature, moisture and richness of plant species were investigated at each sampling site. The results showed that: 1) in sunny slope, soil C, N and P concentrations increased with the increase in altitude, whereas soil C:N, C:P, and N:P decreased along the altitudinal gradient on s. Soil moisture was the main regulator of soil nutrition and stoichiometric ratios. 2) In shady slope, soil C and N contents had no significant difference along the altitudinal gradient except the higher values at low altitude, whereas soil P increased first and then decreased. Soil C:N increased with the increase in altitude, whereas C:P and N:P decreased first and then increased. Soil temperature and species richness were the main factors influencing soil nutrition and stoichiometric ratios. 3) Decoupling of soil C:N:P stoichiometry was observed in shady slope owing to changes in soil pH and temperature. 4) The rich contents of soil C and P were observed at two slopes along the altitudinal gradient, and high capacity of N supply existed at the topsoil in shady slope. These results suggested that slope aspect plays an important role in shaping the altitudinal pattern of soil C:N:P stoichiometry in mountainous forests.

Analysis of vegetation spatial distribution characteristics in Northwest China’s arid desert area

It is of great significance to study the characteristics of vegetation distribution in desert area for restoring vegetation, stabilizing ecosystem and ecological restoration in mining area. Taking the small watershed in Northwest China’s arid desert area where the typical open-pit coal mine is located as the study area, using GF-2 (Gaofen-2 satellite) images, calculating the NDVI (Normalized Difference Vegetation Index) results of the study area, extracting NDVI&gt;0 as the vegetation cover area and combing with DEM (Digital Elevation Model), we analyse the relationship between vegetation distribution and slope aspect and water flow path. We conclude that in the natural state, the proportion of vegetation distribution on semi-sunny slope and shady slope in the study area is 74.8%, the proportion of sunny slope in the total area of the study area is 33.1%, and the proportion of vegetation distribution on this slope is only 11.9%, indicating that semi-sunny slope and shady slope are more suitable for growth in the study area. In the upper reaches of the basin, which is less affected by human activities, natural vegetation is distributed in strips along the flow path; In the mining area, which is obviously affected by human activities, the vegetation distribution characteristics change significantly with vegetation mainly distributed in the office area and being artificial greening.

Relationship between soil organic carbon density and topography in three-dimensional space in a small watershed of loess hilly region in China

In order to display the three-dimensional spatial distribution of soil organic carbon density (SOCD) and analyze the relationship between SOCD and topography, this study took 290 soil samples at the depth of 0 to 100 cm in the Nangou watershed in the loess hilly region of China, simulated the spatial distribution of SOCD by the three-dimensional inverse distance weighting method, and compared the SOCD of several soil sections of different slope shapes and different slope aspects when the land use were all forests. The results showed that the SOCD tended to decrease with increasing soil depth; the mean varied from 0.52 kg m–2 (60 to 100 cm) to 1.03 kg m–2 (0 to 10 cm), and there was obvious stratification in the vertical direction. The variation coefficients of the SOCD were between 23.43% (60 to 100 cm) and 41.15% (10 to 20 cm), which were relatively close in the topsoil of the depth of 0 to 30 cm and gradually decreased with soil depth. The SOCD in the watershed was higher in the northeast, followed by the southwest and lower in the middle. The three-dimensional spatial distribution of the SOCD contained more information, and its prediction accuracy was higher than that of the corresponding two-dimensional method. In slopes where the land use were all forests, the SOCD was ranked as concave slope > straight slope > convex slope and shady slope > sunny slope, and its complexity was ranked as concave slope > convex slope > straight slope and shady slope > sunny slope. Our results highlighted the carbon (C) sequestration ability of concave slopes on the shady side and provided scientific reference for the development of slope C sequestration policies in the loess hilly region of China.

薄毛海绵杜鹃结实和萌发特性随环境的变化

PDF HTML阅读 XML下载 导出引用 引用提醒 薄毛海绵杜鹃结实和萌发特性随环境的变化 DOI: 10.5846/stxb201905231062 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（31860123，31560153，31260147）；西藏农牧学院2016年生态学科建设项目 Variation of fruiting and germination characteristics of Rhododendron aganniphum var. schiaopeplum with environmental factors Author: Affiliation: Fund Project: The National Natural Science Foundation of China (31560123，31860153，31260147）、 2016 Ecological Discipline Construction Project of Tibet Agriculture and Husbandry University 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:选择青藏高原东南林线地区优势植物薄毛海绵杜鹃为对象，研究薄毛海绵杜鹃结实特性和萌发特性随海拔（4183-4673 m）、坡度、坡向等环境梯度的变化规律。对比了不同环境条件下薄毛海绵杜鹃果实的长、宽、重量、单果种子数、种子千粒重等结实特性；并测试了不同环境所产种子的萌发对温度和光照的响应。结果表明：（1）在高海拔低温胁迫环境下，薄毛海绵杜鹃的生殖投入加大，果实大且质量重，种子数量多但质量轻；（2）坡向是影响单果种子数量的主要环境因子，阴坡单果种子数显著大于阳坡，生活在阴坡的薄毛海绵杜鹃的繁衍能力更强；（3）较高和较低土壤湿度都会影响薄毛海绵杜鹃的种子质量，中等土壤湿度（28.3%-32.5%）薄毛海绵杜鹃种子萌发能力最强；（4）薄毛海绵杜鹃的种子是需光性种子，在黑暗条件下几乎不萌发；（5）在光照条件下，温度对种子萌发率和萌发速率有显著影响，高温（25/5℃）有助于提高萌发率并促使萌发进程显著提前。研究揭示了不同海拔薄毛海绵杜鹃结实和萌发特性与环境之间的关系，为薄毛海绵杜鹃的种质资源保护和气候变化背景下藏东南林线动态预测提供了基础资料。 Abstract:Fruiting and germination characteristics of the dominant plant species Rhododendron aganniphum var. schiaopeplum and their variation along the environmental gradients such as altitude (4183-4673 m), slope and aspect were studied at the alpine treeline ecotone on the southeastern Tibetan Plateau. The fruiting characteristics including fruit length, width, weight, seed number per capsule and 1000-seed weight of R. aganniphum var. schiaopeplum from different habitats were measured and compared, and the responses of seed germination to temperature and light were tested. The results showed that: (1) as cold-temperature stress increasing at higher altitude, the reproductive input of R. aganniphum var. schiaopeplum increased, with larger and heavier fruits, more seed number per capsule but smaller seeds than that from other environments; (2) slop aspect was the main factor affecting seed number per capsule with significantly larger seed number per fruit on the shady slope than that on the sunny slope, indicating a better reproductive ability on the shady slope; (3) seeds of the population in moderate soil moisture conditions (28.3%-32.5%) showed highest germination ability; (4) seeds of R. aganniphum var. schiaopeplum are photosensitive and cannot germinate in darkness; (5) in light conditions, germination percentage and rate are significantly affected by temperature, and the highest germination percentage and the most speedy germination showed at 25/5 ℃. This study investigated the relationship between fruiting and germination characteristics of R. aganniphum var. schiaopeplum and their habitat conditions, which provides basic data for the germplasm conservation and the dynamic prediction of the tree-line on the southeastern Tibetan Plateau in the context of climate change. 参考文献 相似文献 引证文献

Plant morphological and functional characteristics combined with elevation and aspect influence phytogenic mound parameters in a dry-hot valley

Isolated plants growing on steep slopes with erodible bedrock are usually associated with the formation of phytogenic mounds in semiarid and arid ecosystems. Identifying the plant characteristics that affect phytogenic mounds and predicting a plant community’s potential for erosion control are of great interest to workers seeking to improve the management of degraded ecosystems. We studied the phytogenic mounds of three dominant perennial grass species found between 1,400 and 1,700 m above sea level in Jiangjiagou Gully: <i>Heteropogon contortus, Eulaliopsis binata</i>, and <i>Eriophorum comosum</i>. Morphological and functional characteristics were measured for a total of 42 individuals from the three grass species on both sunny and shady slope aspects. Soil samples were collected from the mounds and from bare land 30 cm upslope from each mound to determine particle size distribution. Morphological and functional characteristics, as well as mound parameters, were summarized using principal component analysis (PCA). Pearson’s correlation analysis, linear regression analysis, and redundancy analysis were conducted to identify the relationships between plant characteristics and mound parameters. Then we used analysis of covariance to examine the combined effects of aspect and elevation and plant characteristics on mound parameters. We found that there are no differences in morphological characteristics, functional characteristics, or mound parameters between the three grass species, or soil particle size distribution between mounds and bare land. PCA shows that mound parameters are best correlated (positively) with interception length and total dry weight. Crown length in the direction of the slope and root width are also positively correlated with maximum height and maximum width but to a lesser extent. Plant morphological and functional characteristics can explain greater than 60% of the variance of all mound parameters except maximum length, with the greatest contributions from crown length and interception length. Aspect and elevation, combined with some plant characteristics, also affected mound parameters. Our study indicates that perennial grass species can accumulate sediment deposits during growth in a dry-hot valley. Our results provide useful information for evaluating the function of plants in erosion control and for identifying ways to improve the effectiveness of species in mound formation in dry-hot valley ecosystems.

Simulations of spatial patterns and species distributions in sandy land using unmanned aerial vehicle images

The spatial distribution of vegetation in sandy lands is closely related to micro-topography. Point pattern analysis of vegetation distribution from ground surveys and satellite images is a commonly used method but does not capture the influence of spatial heterogeneity at small scales. This study examined long-term ecological observation sites of elm (Ulmus pumila) sparse forest in the Otindag Sandy Land, China. Elevation models from unmanned aerial vehicles (UAVs) and ground survey data on vegetation structure from 3768 elms were used to classify the terrain of sampled sites using a decision tree classification. It combined terrain factors, including slope, aspect, and small-scale altitude differences. Plots were divided into five topographic types: sand flat (53%), sand lowland (17%), sunny slope (13%), shady slope (10%), and sandy ridges (7%). Elm densities varied from 141.7 trees hm−2 on shady slopes to 17.0 trees hm−2 on sand lowland. A 2D Poisson fitting method was applied to the diameter at breast height, crown width, and other vegetation growth characteristics to simulate and verify the distribution of elms in the plots. Multivariate analysis was undertaken to confirm the effect of topographic factors on variation of tree characteristics. The integrated terrain approach could better characterize the spatial distribution of sparse forests. This research demonstrated that UAVs were a useful tool to measure spatial heterogeneity of sand micro-topography. Simulations of the distribution of plant characteristics indicated that the terrain classification matched the spatial pattern analysis of elms in semi-arid regions. Simulation of vegetation distribution is a useful technique for analyzing arid regions. This study will assist with further research on ecological restoration and vegetation protection in semi-arid areas.

Interannual Variation of Transpiration and Its Modeling of a Larch Plantation in Semiarid Northwest China

Quantifying the variation of forest transpiration (T) is important not only for understanding the water and energy budget of forest ecosystems but also for the prediction, evaluation, and management of hydrological effects as well as many other ecosystem services of forests under the changes of climate, vegetation, and anthropological impacts. The accurate prediction of T, a key component of water used by forests, requires mechanism-based models describing the T response to environmental and canopy conditions. The daily T of a larch (Larix principis-rupprechtti) plantation was measured through monitoring the sap flow in the growing season (from May to September) of a dry year (2010), a normal year (2012), and a wet year (2014) at a shady slope in the semi-arid area of Liupan Mountains in northwest China. Meanwhile, the meteorological conditions, soil moisture, and forest canopy leaf area index (LAI) were monitored. To get a simple and easily applicable T model, the numerous influencing parameters were grouped into three factors: the atmospheric evapotranspiration demand indicated by the potential evapotranspiration (PET), the soil water supply ability indicated by the relative extractable soil water content (REW), and the vegetation transpiration capacity indicated by the forest canopy LAI. The T model was established as a continuous multiplication of the T response equations to individual factors, which were determined using the upper boundary lines of measured data. The effect of each factor on the T in a dry year (2010) or normal year (2012) was assessed by comparing the measured T in the baseline of the wet year (2014) and the model predicted T, which was calculated through inputting the actual data of the factor (i.e., PET) to be assessed in the dry or normal year and the measured data of other two factors (i.e., REW, LAI) in the baseline of the wet year. The results showed that the mean daily T was 0.92, 1.05, and 1.02 mm; and the maximum daily T was 1.78, 1.92, and 1.89 mm in 2010, 2012, and 2014, respectively. The T response follows a parabolic equation to PET, but a saturated exponential equation to REW and LAI. The T model parameters were calibrated using measured data in 2010 and 2012 (R2 = 0.89, Nash coefficient = 0.88) and validated using measured data in 2014 satisfactorily (R2 = 0.89, Nash coefficient = 0.79). It showed a T limitation in the dry year 2010 for all factors (18.5 mm by PET, 11.5 mm by REW, and 17.8 mm by LAI); while a promotion for PET (1.4 mm) and a limitation for REW (4.2 mm) and LAI (14.3 mm) in the normal year 2012. The daily T model established in this study can be helpful to assess the individual factor impact on T and improve the daily T prediction under changing environmental and canopy conditions.

Effects of tree species and topography on soil and microbial biomass stoichiometry in Funiu Mountain, China

BackgroundSoil and microbial biomass stoichiometry plays an important role in understanding nutrient cycling in terrestrial ecosystems. However, studies on soil and microbial biomass stoichiometry in forests are rare. This study investigated the effect of tree species and topographic factors on the ecological stoichiometry of soil and soil microbial biomass.MethodsThree types of forest stands (Quercus variabilis, Larix principis-ruprechtii, and Cotinus coggygria Scop.) in the Beiru River basin of Funiu Mountain were analyzed in September 2018. Six slope positions (sunny bottom slope, sunny middle slope, sunny top slope, shady bottom slope, shady middle slope, and shady top slope) were selected, and the total number of sampling plots was 108. The stoichiometric indices of soil and microbial biomass were determined.ResultsAt a depth of 0–10 cm, the soil organic C contents in different stands followed the order of C. coggygria (27.7 ± 5.2 g/kg) > Q. variabilis (24.5 ± 4.9 g/kg) > L. principis-ruprechtii (20.8 ± 4.3 g/kg) (P < 0.05). The soil organic C contents at depths of 0–10 cm with different slope aspects and at different slope positions also showed significant differences (P < 0.05). The highest MBC content was observed at the slope bottom (1002 ± 157 mg/kg), whereas the lowest was observed at the slope top (641 ± 98.3 mg/kg). Redundancy analysis showed that the contribution of tree species to these differences was 57.1%, whereas that of topographical factors was 36.2%.ConclusionsTree species more significantly affected soil nutrients and microbial biomass C, N and P than did topographic factors.

Water use patterns differed notably with season and slope aspect for Caragana korshinskii on the Loess Plateau of China

Flexible water use patterns are of great importance for the survival of vegetation in dryland regions. Our study aimed to investigate the influences of season and slope aspect on the water use patterns of Caragana korshinskii on typical shady and sunny slopes on the Loess Plateau in China. We collected xylem water, soil water from the 0–200 cm soil layers, and precipitation in May, July, September and November 2018 and measured their hydrogen (δD) and oxygen (δ18O) isotope compositions. The root distribution of C. korshinskii in the 0–200 cm soil layer on both slopes was also investigated. The 0–20, 20–80, and 80–200 cm soil layers were identified as three potential water sources for C. korshinskii, and their proportional contributions to the plant water supply were calculated using a linear mixed model. The results showed that C. korshinskii on the sunny slope absorbed 89.3% of their water from the 0–20 cm soil layer in May but mainly utilized water from the 0–20 and 20–80 cm soil layers in both July and September, and the total contribution percentages of these layers were 84.5% and 89.2%, respectively. However, C. korshinskii on the shady slope extracted water evenly from all three soil layers in May. Thereafter, the plants absorbed water from the 20–80 and 80–200 cm soil layers in both July and September, and the total contribution percentages of these layers were 96.0% and 91.8%, respectively. In November, C. korshinskii absorbed 84.8% and 78.0% of their water from the 80–200 cm soil layer on the shady and sunny slopes, respectively. The generally shallower soil water use of C. korshinskii on the sunny slope than on the shady slope may be due to the larger fine-root (d < 2 mm) length density in the 0–80 cm soil layer on the sunny slope (1.12 ± 0.28 mm/cm3) than on the shady slope (0.57 ± 0.16 mm/mm3) (P < 0.05). This study indicates that C. korshinskii on both shady and sunny slopes seasonally switched their water sources from different soil water layers during the growing season. However, due to their reliance on soil water at the 0–20 cm depth, which is supplied by unstable rainfall, C. korshinskii on sunny slopes may be more vulnerable to future climatic warming and drying on the Loess Plateau. Our findings provide valuable information related to optimal water management in the afforested shrublands in this region.

Influence of dragon bamboo with different planting patterns on microbial community and physicochemical property of soil on sunny and shady slopes.

Dragon bamboo (Dendrocalamus giganteus) is a giant sympodial bamboo species widely distributed in Asia. However, it remains unclear how dragon bamboo and soil microbes interact to affect soil properties. In this study, we investigated the planting patterns (semi-natural and artificial) on different slopes (sunny and shady) to determine the effects on soil properties and microbial community. The results showed that the soil in which dragon bamboo was grown was acidic, with a pH value of ∼5. Also, the soil organic matter content, nitrogen hydrolysate concentration, total nitrogen, available potassium, and total potassium of the dragon bamboo semi-natural forest significantly improved, especially on the sunny slope. In contrast, the available phosphorus level was higher in the artificial bamboo forest, probably owing to the phosphate fertilizer application. The bacterial and fungal diversity and the bacterial abundance were all higher on the sunny slope of the semi-natural forest than those in the other samples. The microbial operational taxonomic units (OTUs) shared between the shady and sunny slopes accounted for 47.8-62.2%, but the core OTUs of all samples were only 24.4-30.4% of each sample, suggesting that the slope type had a significant effect on the microbial community. Some acidophilic microbes, such as Acidobacteria groups, Streptomyces and Mortierella, became dominant in dragon bamboo forest soil. A PICRUSt analysis of the bacterial functional groups revealed that post-translational modification, cell division, and coenzyme transport and metabolism were abundant in the semi-natural forest. However, some microorganisms with strong stress resistance might be activated in the artificial forest. Taken together, these results illustrated the influence of dragon bamboo growth on soil physicochemical property and microbial community, which might help understand the growth status of dragon bamboo under different planting patterns.

Spatial distribution characteristics of the soil thickness on different land use types in the Yimeng Mountain Area, China

A significant characteristic of the strata in the Yimeng Mountain area is the dual earth-rock structure. Soil thickness directly affects the habitat conditions and is closely related to the survival rate of vegetation. This study aims to reveal the spatial distribution characteristics and influencing factors of the soil thickness in a typical watershed in the Yimeng mountain area. In April 2019, 1816 soil thickness measurements were collected in the Yimeng Mountain area. The differences in the soil thickness, spatial distribution characteristics, and influencing factors of the different land use types were analysed using multivariate statistics and geostatistics. The results revealed the following conclusions. (1) There are significant differences in the soil thicknesses of the different land use types, i.e., farmland (42.63 cm) > forest land (39.26 cm) > grassland (20.35 cm). (2) The optimal semi-variogram model of soil thickness is an exponential model (R2 = 0.914). The ST in the study area has a medium spatial correlation. The high value areas of Populous simonii Carr. and slope farmland and the low value areas of Robinia pseudoacacia L. and grasslands exhibit spatial clustering. (3) The soil thickness varies significantly with land preparation measures, slope direction, and slope position. The high soil thickness values are mainly concentrated on the terrace preparation measures, the half shady slope, and the lower slope. These results provide a scientific basis for improving the survival rate of near-natural vegetation restoration in the Yimeng Mountain area in the earth-rocky mountainous areas of northern China.

Vegetation Growth Status and Topographic Effects in the Pisha Sandstone Area of China

Fractional vegetation coverage (FVC) plays an important role in monitoring vegetation growth status and evaluating restoration efforts in ecological environments. In this study, FVC was calculated using a binary pixel model and analyzed in the Pisha Sandstone area of China, using MODIS-EVI data from 2000 to 2019. Topographic effects were analyzed from elevation, slope and aspect using a terrain niche index model. The results were as follows. (1) From 2000 to 2019, FVC in the Pisha Sandstone area of China gradually increased at a mean rate of 0.0074/a, and the growth status of vegetation gradually improved. (2) The spatial distribution of FVC steadily decreased from southeast to northwest. FVC was the lowest in bare parts of the Pisha Sandstone area, whereas those in the sand- and soil-covered parts were the middle and highest, respectively. (3) With increasing elevation, the inferior coverage area and terrain niche index increased, and inferior coverage distribution changed from non-dominant to dominant. Meanwhile, the low, medium and high coverage areas decreased, and their distributions changed from dominance to non-dominance. (4) With increasing slope, distributions of the inferior, medium and high coverage areas changed from dominant to non-dominant, while the low coverage area had a dominant distribution. (5) Analyses of aspect effects revealed that the inferior coverage area was the dominant distribution in shady slopes but was non-dominant in semi-shady, semi-sunny and sunny slopes. The low, medium and high coverage areas were non-dominant in shady slopes, but dominant in semi-shady, semi-sunny and sunny slopes.

Dynamics and Drivers of the Alpine Timberline on Gongga Mountain of Tibetan Plateau-Adopted from the Otsu Method on Google Earth Engine

The alpine timberline, an ecosystem ecotone, indicates climatic change and is tending to shift toward higher altitudes because of an increase in global warming. However, spatiotemporal variations of the alpine timberline are not consistent on a global scale. The abundant and highest alpine timberline, located on the Tibetan Plateau, is less subject to human activity and disturbance. Although many studies have investigated the alpine timberline on the Tibetan Plateau, large-scale monitoring of spatial-temporal dynamics and driving mechanisms of the alpine timberline remain uncertain and inaccurate. Hence, the Gongga Mountain on the southeastern Tibetan Plateau was chosen as the study area because of the most complete natural altitudinal zonation. We used the Otsu method on Google Earth Engine to extract the alpine timberline from 1987–2019 based on the normalized difference vegetation index (NDVI). Then, the alpine timberline spatiotemporal patterns and the effect of topography on alpine timberline distribution were explored. Four hillsides on the western Gongga Mountain were selected to examine the hillside differences and drivers of the alpine timberline based on principal component analysis (PCA) and multiple linear regression (MLR). The results indicated that the elevation range of alpine timberline was 3203–4889 m, and the vegetation coverage increased significantly (p &lt; 0.01) near the alpine timberline ecotone on Gongga Mountain. Moreover, there was spatial heterogeneity in dynamics of alpine timberline, and some regions showed no regular trend in variations. The spatial pattern of the alpine timberline was generally high in the west, low in the east, and primarily distributed on 15–55° slopes. Besides, the drivers of the alpine timberline have the hillside differences, and the sunny and shady slopes possessed different driving factors. Thus, our results highlight the effects of topography and climate on the alpine timberline on different hillsides. These findings could provide a better approach to study the dynamics and formation of alpine timberlines.