Grassland type-dependent spatiotemporal characteristics of productivity in Inner Mongolia and its response to climate factors

Abstract

Grassland located in the arid and semi-arid ecosystems has an evident ecological fragility and is easily vulnerable to climatic variations. Although several studies have shown the close relationship between net primary production (NPP) and seasonal or annual climate changes, it is currently unclear that whether such response in semi-arid regions is associated with grassland types that have different physiological characteristics, especially in the grassland ecosystem of Inner Mongolia that spans meadow-typical-desert steppe. This study used NPP estimated by Carnegie–Ames Stanford Approach (CASA) model, and focused on grassland type-dependent spatiotemporal changes of NPP and its response to climate factors on annual and seasonal scales. The results showed that the NPP simulated by the CASA model was in good agreement with the ground-observed NPP (R2 = 0.62, P < 0.001), and the RMSE value was 22.91 gC ∙ m−2. From 2001 to 2018, grassland NPP increased marginally with the increment of 0.89gC ∙ m−2 ∙ yr−1, the average NPP was 341.55gC ∙ m−2 ∙ yr−1, and there was a gradual decline from northeast to southwest. On the annual scale, grassland NPP had the strongest positive correlation with precipitation, followed by solar radiation and a negative correlation with temperature. On the seasonal scale, precipitation still had the greatest impact on NPP. In spring, grassland and solar radiation were positively correlated, but in summer and autumn, there was no significant correlation. In autumn, grassland had a positive correlation with temperature, while in spring and summer, there showed a negative correlation. For different grassland types, precipitation was the most important factor that influencing temperate typical steppe and temperate salted meadow in spring and summer, while solar radiation had the strongest effect on temperate desert steppe and temperate meadow. Temperate meadow steppe and temperate swamp meadow were most affected by precipitation in spring, while they were most affected by solar radiation in summer.