Soil and plant components ecological stoichiometry in four steppe communities in the Loess Plateau of China

Grazing exclusion and vegetation restoration practices are the major ecosystem restoration measures that can address ecosystem degradation due to overgrazing and intensive farming in the Loess Plateau in northwest China. We examined plant tissue (root, litter, and living biomass) nutrients of the four most dominant steppe species (Artemisia gmelinii (AR), Thymus mongolicus (TH), Stipa bungeana (ST), and Agropyron cristatum (AG)), and their ecological stoichiometry characteristics. Our results indicated that vegetation types had significant effects on soil nutrients and soil ecological stoichiometry characteristics. TH soils had the highest concentrations of total C, total N and total P, and AR soils had the lowest concentrations of total C and total N. TH species had the greatest effects on improving soil nutrients. The concentrations of total N and total P differed with different plant tissues (P < 0.01). Living biomass had higher total N and total P than roots and litter in terms of the exit of nutrient resorption efficiency. However, total C remained in a narrow range for the different tissues. To determine which tissue of the different steppe species was more suitable in terms of plant nutrition limitations, we used N:P ratios in different tissues to estimate the nutrition limitation for the plant growth based on previous studies. Living biomass N:P ratios were significantly correlated with root N:P ratios (1)< 0.001), reflecting that underlying physiological processes are coordinated among plant tissues. We concluded that TH had the greatest effects on improving soil nutrients after grazing exclusion. Root N:P ratios could also be used to indicate the nutrition limitation for steppe species. (C) 2016 Elsevier B.V. All rights reserved.