Dynamics of soil metallic nutrients across a 6000-km temperature transect in China

Global warming has exerted profound effects on terrestrial ecosystems. Soil metallic nutrients, an integrated part of soil nutrient fertility, play a significant role in the maintenance of ecosystem functions. However, how soil metallic nutrients respond to global warming remains poorly understood. Spatial observations across a temperature gradient provide a solid evidence in clarifying the long-term responses of soil metallic nutrients to global warming. But due to the collinearity between temperature and precipitation in the geographical patterns, the influence of temperature on soil metallic nutrients might be interfered by the precipitation effect. To minimize the precipitation effect, this study conducted a soil sampling over broad geographical scale along the 400 mm isohyet in China, which extends about 6000 km. Variations in soil potassium (K), calcium (Ca), magnesium (Mg) and iron (Fe) concentrations across the temperature transect were investigated. These four elements all increased until mean annual temperature (MAT) increased to about 2 °C and then decreased with increasing MAT. Temperature, soil property and vegetation type were responsible for the changes of soil metallic nutrients at MAT below 2 °C; altitude, soil property, vegetation type and soil parent material were dominant influential factors of soil metallic nutrients at MAT above 2 °C. Temperature exerted an indirect influence on soil metallic nutrients through its effects on soil property, vegetation type, rock weathering, microbial decomposition and plant growth. It could be expected based on our results that the effects of global warming on soil K, Ca, Mg and Fe might depend on local MAT. Different regions with different climates should adopt different strategies to cope with the effect of global warming on soil metallic nutrients so that ecosystems maintain stable.