Changes in above and belowground traits of a rhizome clonal plant explain its predominance under nitrogen addition

Abstract

Despite extensive studies documenting that changes in plant community structure in response to enhanced atmospheric nitrogen (N) deposition were driven by positive effects of N enrichment on rhizome clonal plants in grassland communities, few studies have specifically investigated the responses of rhizome clonal plants to N enrichment in terms of above-and below-ground plant traits. By monitoring above-ground and below-ground plant traits, we investigated long-term (13-year) effects of N addition (64 g m−2 yr.−1) on Leymus chinensis, a rhizome clonal plant, in temperate steppes of northern China. Nitrogen addition enhanced the relative above-ground biomass of L. chinensis from 0.6% (2004) to 75% (2016) in steppe communities. Nitrogen addition enhanced leaf N and chlorophyll concentrations, and specific leaf area, thus leading to a marked increase in photosynthetic rates. Nitrogen addition altered the patterns of carbon allocation, by enhancing the ratios of below-ground to above-ground biomass, while N addition reduced the ratios of rhizome to root biomass. Nitrogen addition modified morphological traits of absorptive fine roots (first two-order roots) by enhancing specific root length and reducing root tissue density and average root diameter. Nitrogen addition significantly shortened rhizome internodes and increased bud density of L. chinensis. Nitrogen addition enhanced L. chinensis resource-acquiring and vegetative reproduction capability, thereby leading to its predominance in the steppe communities.