Ecological stoichiometry of plant-soil-enzyme interactions drives secondary plant succession in the abandoned grasslands of Loess Plateau, China

Abstract

Ecological stoichiometry is the study of the interaction and balance of multiple chemical elements in ecological processes. However, how ecological stoichiometric interactions among plants, soils, and enzymes in the rhizosphere affect secondary plant succession is largely unknown. In this study, we collected the dominant and main companion species Artemisia capillaris, A. sacrorum, and Stipa bungeana, along a secondary succession chronosequence (7, 12, 17, 22, and 32-year) following a cropland abandonment in the Loess Plateau, China. We measured the carbon (C), nitrogen (N) and phosphorus (P) concentrations of plant shoots and roots, as well as the concentrations of C, N, P, available N (aN), available P (aP), and the activity of one C-acquiring enzyme (β-glucosidase (BG)), two N-acquiring enzymes (N-acetylglucosaminidase (NAG), leucineaminopeptidase (LAP)), and one P-acquiring enzyme (alkaline phosphatase (AP)) found in the rhizospheric soil to explore the C:N:P stoichiometry that drives secondary plant succession. The C:P and N:P ratios in the shoots of dominant plant species significantly decreased to a minimum value at the 22-year site and then increased with plant secondary succession. Compared with the 7-year site, the rhizosphere soil C:P and N:P ratios, and enzyme N:P ratios (ln(NAG + LAP):ln(AP)) increased 103.6%, 72.0%, and 221.3%, respectively, but enzyme C:N ratios (ln(BG):ln(NAG + LAP)) decreased 48.2% in the dominant plant species at the 32-year site. Principal component analysis indicated that the stoichiometry characteristics of the plant-soil-enzyme continuum differed for each plant species and succession stage. Stoichiometric homeostasis indices for the plant species indicated a relatively strong homeostasis, while redundancy analysis revealed that the variations in soil BG, NAG, and AP activity and enzyme C:N ratio had significant effects on the stoichiometries and nutrient concentrations of the plant tissues. The results indicated that rhizosphere stoichiometry is a powerful tool for evaluating plant-soil interactions in terrestrial ecosystems and that the variation in rhizospheric soil enzyme activity driving the secondary succession of plants.