Abstract
Ecosystem water use efficiency (WUE) and carbon use efficiency (CUE), as two of the most important ecological indicators of an ecosystem, represent the carbon assimilation rate of unit water consumption and the capacity of transferring carbon from the atmosphere to potential carbon sinks. Revealing WUE and CUE changes and their impact factors is vital for regional carbon-water interactions and carbon budget assessment. Climate affects carbon and water processes differently. Compared to WUE, the variations in CUE in response to climate factors and human activity remain inadequately understood. In this study, ecosystem-level WUE and CUE variations in the Songnen Plain (SNP), Northeast China, during 2001–2015, were investigated using Moderate Resolution Imaging Spectroradiometer (MODIS) satellite data. The relationships between WUE, CUE, main climate factors, and human impacts were explored. The results showed that ecosystem WUE and CUE have fluctuated over time, with regional average values of 1.319 gC·kg−1H2O and 0.516, respectively. Deciduous broad-leaved forests had the highest average WUE but the lowest CUE. The multiyear average CUE of grassland ranked in first place, while the lowest WUE indicated that a lesser capacity of net productivity was generated by the use of limited water supply. WUE and CUE showed a downward trend in most areas of the SNP, indicating that the carbon sequestration capacity of the terrestrial ecosystem became weaker in the past 15 years. Annual precipitation and relative humidity had positive influences on WUE and CUE in more than 60% of the study area. The total annual sunshine duration and annual average temperature negatively affected WUE and CUE in most areas. Human activities had a positive effect on ecosystem WUE changes in the SNP but might inhibit CUE variations. Our findings aid in understanding the biological regulation mechanisms of carbon-water cycle coupling and provide a scientific basis for formulating sustainable regional development strategies and guiding water and land resources management.
Highlights
Water use efficiency (WUE) is defined as the carbon assimilation rate of unit water consumption [1], which links the photosynthetic production of ecosystems to evapotranspiration and reflects ecosystem carbon and water cycles and their interactions
Ecosystemlevel WUE and Carbon use efficiency (CUE) variations in the Songnen Plain (SNP), Northeast China, during 2001–2015, were investigated using Moderate Resolution Imaging Spectroradiometer (MODIS) satellite data. e relationships between WUE, CUE, main climate factors, and human impacts were explored. e results showed that ecosystem WUE and CUE have fluctuated over time, with regional average values of 1.319 gC·kg−1H2O and 0.516, respectively
Deciduous broad-leaved forests had the highest average WUE but the lowest CUE. e multiyear average CUE of grassland ranked in first place, while the lowest WUE indicated that a lesser capacity of net productivity was generated by the use of limited water supply
Summary
Water use efficiency (WUE) is defined as the carbon assimilation rate of unit water consumption [1], which links the photosynthetic production of ecosystems to evapotranspiration and reflects ecosystem carbon and water cycles and their interactions. Carbon use efficiency (CUE) is the ratio of net primary productivity (NPP) to gross primary productivity (GPP), which indicates ecosystem capacity to transfer atmospheric CO2 into biomass and carbon sequestration. Because WUE and CUE are related to the processes of ecosystem evapotranspiration and photosynthesis, they are regarded as the important indicators for characterizing the carbon-water coupling of ecosystems. E quantitative analysis of spatial-temporal changes of WUE and CUE and their influencing factors will aid in better understanding the effects of future climate change on the water and carbon processes of ecosystems [2]. The lack of continuous ground observations may hinder the long-term analysis of the dynamics of vegetation development, satellite remote sensing provides useful information for investigating large-scale and longterm variabilities of ecosystem WUE and CUE. In 1999, Bastiaanssen analyzed crop WUE in India based on estimates of crop yields and evaporation (ET) using remote
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