The Variations of Satellite-Based Ecosystem Water Use and Carbon Use Efficiency and Their Linkages with Climate and Human Drivers in the Songnen Plain, China

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, ecosystemlevel WUE and 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 −1 H 2 O 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. 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. e 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.

Spatio-Temporal Variations of Carbon Use Efficiency in Natural Terrestrial Ecosystems and the Relationship with Climatic Factors in the Songnen Plain, China

“…We compared the CUE calculated by the same model of different ecosystems at the annual scale from other reported studies (Table 4). The order of annual CUE of different ecosystems in SNP was as follows: GRA (0.567) > WET (0.542) > MF (0.480) > DBF (0.479) [19]. Tang et al [3] found the largest CUE for WET on a global scale.…”

“…The trend analysis method was used to analyze trend in seasonal CUE changes for the period 2001-2015. The outputs of the trend analysis are the maps of regression slope values, expressed by the following formula [19]:…”

“…The CUE of ecosystem describes the relationship between photosynthesis and respiration, which is an important indicator of the ability of plants to transfer carbon [16]. As one of the key controlling factors of ecosystem carbon storage, CUE is defined as follows [19]:…”

“…Concerns for the aggravation of desertification have led to many measures and management actions for ecological and environmental protection. The trend of desertification and exacerbation has gradually slowed down [19]. Previous studies have mostly focused on the land cover/use change and effects of agricultural activities on environment [20].…”

Nitrogen Deposition Enhances the Positive Contribution of CO2 Fertilization to China’s Carbon and Water Use Efficiencies

“…Besides ND and CO 2 (Figure S2), various other factors also have profound effects on CUE and WUE at different temporal and spatial scales. The temperature and precipitation factors also showed an upward trend; rising air temperature decreased the CUE ratio, and increased precipitation led to an increase in the CUE ratio [52][53][54][55][56][57][58][59]. In environmental conditions, temperature, precipitation, solar radiation, etc, are all key climate-change factors that affect the WUE of ecosystems [60].…”