Speculation for quantifying increased C4 plants under future climate conditions: Inner Mongolia, China case study

Alternating conditions from cold to warm periods since the Late Glacial provided a significant contrast for future hydroclimatic variation, as did the corresponding variation in vegetation. To predict the potential variability in C-3/C-4 biomass under future warmer climatic conditions, we determined the current spatiotemporal distribution of C-3 and C-4 vegetation by estimating the variability of delta C-13(org) values in 125 topsoil samples and investigating the geological period variability of C-4 plants growing in Inner Mongolia, China. We examined the factors contributing to the growth of C-4 plants and the variability in C-4 plants for each 1 degrees C increase in temperature during recent and geological times. The results revealed that the relative abundance of C-4 plants in Inner Mongolia shows an increasing trend from the northwest to the southeast. The biomass of C-4 plants was found to be positively correlated with temperature, although weakly correlated with precipitation, thereby indicating that temperature is the primary climatic factor determining the growth of C-4 plants in this region. Furthermore, we found that in response to each 1 degrees C increase in temperature, there would be an approximate 2.1% increase in the spatiotemporal variation of present-day C-4 plant biomass in Inner Mongolia, whereas during the geological period, there was a corresponding increase of 10.7%. Comparatively, the spatiotemporal variation in present-day C-4 biomass on the Chinese Loess Plateau has undergone a 4.0% increase in response to each 1 degrees C increase in temperature, whereas 6.0% and 7.5% increases in the geological period were estimated based on core samples taken from the Lantian and Xingyang sections, respectively. Interestingly, for each 1 degrees C increase in temperature during the current growth month of C-4 plants, there is a 6.6% increase in C-4 biomass, which is essentially consistent with the results obtained for the geological period results (i.e., 6.0% and 7.5% for the Lantian and Xingyang sections, respectively). The findings of this study reveal a distinct contrast in the variation of C-4 plants during recent and geological periods, thereby enabling us to quantitatively estimate the potential changes in C-4 vegetation in response to projected climate conditions.