Abstract
The net ecosystem productivity (NEP) of drainage basins plays an important role in maintaining the carbon balance of those ecosystems. In this study, the modified CASA (Carnegie Ames Stanford Approach) model and a soil microbial respiration model were used to estimate net primary productivity (NPP) and NEP of the Yellow River Basin’s (YRB) vegetation in the terrestrial ecosystem (excluding rivers, floodplain lakes and other freshwater ecosystems) from 1982 to 2015. After analyzing the spatiotemporal variations in the NEP using slope analysis, the coefficient of variation, and the Hurst exponent, precipitation was identified as the main factor limiting vegetation growth in the YRB. Hence, precipitation was treated as the control variable and a second-order partial correlation method was used to determine the correlation between diurnal asymmetric warming and the YRB’s NEP. The results indicate that: (i) diurnal asymmetric warming occurred in the YRB from 1982 to 2015, with nighttime warming (Tmin) being 1.50 times that of daytime warming (Tmax). There is a significant correlation between variations in NPP and diurnal warming; (ii) the YRB’s NEP are characterized by upward fluctuations in terms of temporal variations, large differences between the various vegetation types, high values in the western and southeastern regions but low values in the northern region in terms of spatial distribution, overall relative stability in the YRB’s vegetation cover, and changes in the same direction being more dominant than those in the opposite direction (although the former is not sustained); and (iii) positive correlations between the NEP and nighttime and daytime warming are approximately 48.37% and 67.51% for the YRB, respectively, with variations in nighttime temperatures having more extensive impacts on vegetation cover.
Highlights
The Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) concluded that mean global surface temperatures have risen by approximately 0.85 ◦C in the past century [1], and that sustained increases in atmospheric CO2 concentration is the main cause of global climate change [2,3,4]
The net primary productivity (NPP) directly reflects the production capacity of vegetation communities under natural environmental conditions [15,16,17], but is a major factor for the determination of carbon sources/sinks and the regulation of ecological processes [18,19,20] and a global study on carbon storage in forest ecosystems initiated by the International Biological Program (IBP) [21] in the 1960s marked the beginning of studies on net ecosystem productivity (NEP)
It indicates that the temperature increased faster in nighttime than in daytime in the Yellow River basin
Summary
The Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) concluded that mean global surface temperatures have risen by approximately 0.85 ◦C in the past century [1], and that sustained increases in atmospheric CO2 concentration is the main cause of global climate change [2,3,4]. Terrestrial ecosystems form an important component of the global carbon cycle [10] and comprise the main platform through which atmospheric CO2 enters the terrestrial zone [11]. Vegetation forms the bulk of terrestrial ecosystems, plays an important bridging role in the global carbon cycle [12], and is able to effectively regulate the global carbon balance and mitigate increases in atmospheric greenhouse gases. In the context of global climate change, the net primary productivity (NPP) of vegetation is an important part of the biogeochemical carbon cycle [13,14]. The NPP directly reflects the production capacity of vegetation communities under natural environmental conditions [15,16,17], but is a major factor for the determination of carbon sources/sinks and the regulation of ecological processes [18,19,20] and a global study on carbon storage in forest ecosystems initiated by the International Biological Program (IBP) [21] in the 1960s marked the beginning of studies on net ecosystem productivity (NEP)
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