Spatial–Temporal Correlations between Soil pH and NPP of Grassland Ecosystems in the Yellow River Source Area, China

• Published in: International Journal of Environmental Research and Public Health
• Main Authors: Xiaoning Zhang, Lili Nian, Xingyu Liu, Xiaodan Li, Samuel Adingo, Xuelu Liu, Quanxi Wang, Yingbo Yang, Miaomiao Zhang, Caihong Hui, Wenting Yu, Xinyu Zhang, Wenjun Ma, Yaoquan Zhang
• Format: Article in Journal/Newspaper
• Language: English
• Published: MDPI AG 2022
• Subjects: MODIS; time-lag effect; coupling relationship; contribution index; alpine area; Medicine; R; permafrost
• Online Access: https://doi.org/10.3390/ijerph19148852; https://doaj.org/article/0f094549fc354de8ad7ca8593f37388a

In recent years, ecological concerns such as vegetation destruction, permafrost deterioration, and river drying have been paid much more attention to on the Yellow River Basin in China. Soil pH is regarded to be the fundamental variable among soil properties for vegetation growth, while net primary productivity (NPP) is also an essential indicator to reflect the healthy growth of vegetation. Due to the limitation of on-site samples, the spatial–temporal variations in soil pH and NPP, as well as their intrinsic mechanisms, remain unknown, especially in the Yellow River source area, China. Therefore, it is imperative to investigate the coupling relationship between soil pH and NPP of the area. The study coupled MODIS reflectance data (MOD09A1) with on-site soil pH to estimate spatial–temporal variations in soil pH, explore the response of NPP to soil pH, and assess the extent to which they contribute to grassland ecosystems, thus helping to fill knowledge gaps. Results indicated that the surface spectral reflectance for seven bands could express the geographic pattern of soil pH by applying a multiple linear regression equation; NPP exhibited an increasing trend while soil pH was the contrary in summer from 2000 to 2021. In summer, NPP was negatively correlated with soil pH and there was a lag effect in the response of NPP to soil pH, revealing a correlation between temperate steppes > montane meadows > alpine meadows > swamps in different grassland ecosystems. In addition, contribution indices for temperate steppes and montane meadows were positive whereas they were negative for swamps and alpine meadows, which are apparent findings. The contribution index of montane and alpine meadows was greater than that of temperate steppes and swamps. The approach of the study can enable managers to easily identify and rehabilitate alkaline soil and provides an important reference and practical value for ecological restoration and sustainable development of grassland ecosystems in alpine regions.