Assessing the Integrative Impact of Climate Change Factors On Soil Cation Nutrients.

Assessing the Integrative Impact of Climate Change Factors on Soil Cation Nutrients

Shuijin Hu¹, Lei Cheng¹, Jianguo Zhu², Fitzgerald L. Booker³, Kent O. Burkey³

¹ Department of Plant Pathology, North Carolina State University, Raleigh, NC 27695

² Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China

³ USDA-ARS Plant Science Research Unit and and Department of Crop Science, North Carolina State University Raleigh, NC 27607

Nutrient availability for plants is a major determinant of ecosystem productivity and critically affects plant responses to the increasing CO₂ in the atmosphere and the potential of ecosystem C sequestration. Crop yields are predicted to increase under future CO₂ scenarios assuming that N availability can be maintained through fertilization. However, this prediction essentially ignores limitations caused by other nutrients, particularly essential cation nutrients that are often deficient in many agroecosystems. Crop harvest constantly removes nutrients from agroecosystems, and because of their short life cycle, crop plants have to largely rely on labile nutrient pools (e.g., exchangeable cations). Increasing evidence has shown that climate change components (e.g., elevated CO₂, O₃ and reactive N inputs) can significantly alter rhizosphere processes through modifying root and microbial growth. The resulting changes in rhizosphere physiochemical environments may affect the valence state, displacement, and/or bioavailability of nutrient cations. However, the magnitude, directions and long-term implications of climate change effects on soil cations largely remain un-explored and the underlying mechanisms have not carefully been examined. We examined how climate change factors (elevated CO₂ and O₃) affect soil cation dynamics and availability for plants in rice paddies in China, and soybean and wheat fields in USA. While free air CO₂ enrichment (FACE) was used to manipulate CO₂ concentration in the rice-wheat systems, open-top facility is used to control CO₂ and O₃ in a soybean-wheat system. Elevated CO₂ in general increased Ca and Mg, but reduced K in solutions both in rice paddies and dryland soils. Corresponding to CO₂-stimulation of Ca, Mg and K availability in soil solutions, plant biomass K, Ca and Mg increased. CO₂-enhancement of cations in soil solutions positively correlated with root activities, indicating a major role of biological processes in CO₂-stimulation of cation release from soil. These results suggest that over the long term, atmospheric CO₂ enrichment may facilitate Ca and Mg losses from soil. The underlying mechanisms governing the CO₂-enhancement of soil Ca and Mg, and potential impacts on soil fertility will be discussed.