The upper Yellow River Basin is an important ecological security barrier and a water conservation area in northwest China. The sustainability of its water yield services has generated much concern and debate. Spatial and temporal patterns of water yield factors are considered to be important scientific data. Therefore, the climate and land data of the upper Yellow River Basin in Maqu County are studied. Water yield for the period 1990–2020 was estimated using the water yield module in the InVEST model. Impacts and contribution weights of climate and land use/cover change on regional water yield were also quantified under 12 scenarios. The results indicate that (1) the average water yield in Maqu County has fluctuated and increased in the past 30 years. The increase in rainfall was more pronounced than the increase in potential evapotranspiration. Grassland areas continue to increase and unutilized land areas continue to decrease. (2) The average water yield for different types of land use during this period also varied. It showed grassland > unutilized land > forest > construction land > waterbody > cropland. (3) Climate change has a greater impact on water yield in Maqu County and further increases its contribution to regional water yield. The impact of land use/cover change was smaller and the contribution was smaller.
Environmental heterogeneity in temperature, moisture, and soil fertility caused by elevation gradients can affect the trade-offs in the survival strategies of tree species. There is uncertainty about the allocation of resources to different tissues of trees in response to the elevation gradient with respect to carbon (C), nitrogen (N), and phosphorus (P). Here, the C, N, and P content of leaves, branches, trunks, and thick and fine roots of Picea crassifolia (Qinghai spruce) and their stoichiometric changes across three different elevations were investigated in the Qilian Mountains. We found that N:P of Qinghai spruce was <14 in all tissues at most elevations, indicating that Qinghai spruce was more susceptible to N limitation. Meanwhile, the N content and N:P of Qinghai spruce each were significantly negatively correlated with temperature (p < 0.05), and its P content was lower at high elevation. The contribution of soil–climate interactions on the elevation gradient to each tissue type was 34.02% (leaves), 16.84% (branches), 67.78% (trunks), 34.74% (thick roots), and 49.84% (fine roots), indicating that interacting climate and soil factors on the elevation gradient predominately drove the C, N, and P content and stoichiometry variation in each tissue type of Qinghai spruce trees. The results of this study clarify that the elevation gradient regulates the elemental content and resource allocation in Qinghai spruce, providing basic data and an important timely reference for future forest management in the regions where coniferous trees grows. These findings also help improve our understanding of elevational patterns of forest ecosystem stoichiometry in arid and semiarid regions.
Background Understanding the stoichiometric characteristics and nutrient allocation strategies of dominant tree species in montane forest systems can provide a basis for decision-making in relation to montane system management. Therefore, according to precipitation and temperature gradients, we selected three typical areas in the Qilian Mountains on the eastern margin of the Qinghai-Tibet Plateau to analyse the spatial relations of plant-soil stoichiometric characteristics and nutrient allocation strategies of plant tissues for Qinghai spruce (Picea crassifolia) along different environmental gradients. Results 1) The plant and soil stoichiometric characteristics had similar spatial patterns. The C content of plants and soils tended to decrease with increasing latitude, and the N and P contents and the N:P ratio tended to increase with increasing latitude. 2) The stoichiometric characteristics of the plant tissues also interacted with each other and showed synergistic trade-offs. Nutrient allocation in the eastern section of the Qilian Mountains was similar to that in the western section, while more N and P in the plant stems were allocated to maintain plant growth in the relatively arid western Sect. 3) The nutrient allocation strategies in the plant tissues were mainly regulated by soil and climate. Conclusions Information on plant-soil stoichiometric characteristics along different gradients can help us better understand the nutrient patterns and dynamics of forest ecosystems under arid and semiarid conditions at a wide geographic scale from the perspective of plant nutrient partitioning.
Water resources are the material basis for human social development. They play an essential role in human production and life. They are vital for the healthy growth of ecosystem services. The quantitative assessment of the water conservation (WC) function is of great significance to the management of regional ecosystems and the construction of ecological civilization. Gannan is an influential water supply area in the upper Yellow River Basin. Understanding the current status and future changes of its WC function can provide scientific support for the stable use and sustainable development of water resources in the upper Yellow River Basin; its ecological status is highly important. The present study quantitatively assesses the WC function of Gannan based on the InVEST model. It aims to explore the regional ecological compensation mechanism, enhance regional ecological regulation capacity and increase water supply by studying the trend in changes in the WC function and the influence mechanism. The results show that: (1) The overall trend in WC capacity in Gannan increased during the period 2000–2020. (2) The spatial distribution of WC in Gannan varies from year to year, but there is some similarity, showing a high degree in the southwest and a low degree in the northeast. (3) Climatic factors are the dominant factors underlying the spatial and temporal distribution of WC in Gannan. (4) The important areas of WC are located in the southwest and southeast of Gannan.
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