Effects of Heavy Metals on Nitrogen in Soils of Different Ecosystems in the Karst Desertification of South China

Abstract

Nitrogen, as a crucial limiting nutrient in terrestrial ecosystems, plays a vital role in determining land quality. Heavy metals, as drivers of soil substance transformation, are important indicators for assessing ecosystem function. Currently, the relationship between soil nitrogen and heavy metals in karst desertification areas remains unclear. Therefore, this study focuses on the soil of grassland, forest, and agroforestry ecosystems in a karst desertification area to investigate the relationship between heavy metals and nitrogen distribution using ecological stoichiometry. The findings revealed the following: (i) Total nitrogen (TN) and available nitrogen (AN) exhibited the trend of agroforestry * > forest > grassland, while soil microbial biomass nitrogen (SMBN) showed the trend of forest * > grassland * >> agroforestry; (ii) Chromium (Cr), Ferrum (Fe), Niccolum (Ni), and Plumbum (Pb) showed the trend of agroforestry * > grassland > forest, while Cuprum (Cu) demonstrated the trend of agroforestry > grassland > forest, and Zincum (Zn) exhibited the trend of grassland > forest * >> agroforestry. The Nemerow comprehensive pollution index were 0.77 for grassland, 0.69 for forest, and 0.94 for agroforestry; (iii) The sensitivity of soil nitrogen and heavy metals ranked as grassland > agroforestry > forest. The research findings aim to provide a scientific reference for karst desertification control, ecological protection and restoration, and enhancement of ecosystem function.