Distance-dependent, species-specific effects of legumes on nitrogen utilization by companion non-legumes in the Gurbantunggut desert, Northern China

Abstract

Legumes, as an important biological nitrogen (N) fixation resource, could effectively supplement N inputs to terrestrial ecosystems, especially in N-poor desert ecosystems. However, there is limited research on the N utilization strategies of different plant life forms coexisting under the “fertilizer island effect” created by leguminous shrubs. The study aims to explore the N acquisition patterns of herbaceous plants adjacent to Eremosparton songoricum (Litv.) Vassilcz. in the Gurbantungut Desert of northern China. In this study, the 15N isotope labeling method was used to track the N acquisition of the companion plants Ceratocarpus arenarius L. and Centaurea pulchella Ledeb. within 0–10 cm (D1), 30–40 cm (D2), 60–70 cm (D3), and 90–100 cm (D4) from a dominant legume species E. songoricum. The results showed that: (1) The “N acquisition” by herbaceous plants near leguminous shrubs showed distinct effects related to distance, with a preference for N-NH4+ (contribution rate: 25.42 % ∼ 58.94 %) at a closer distance from the shrub, and a preference for N-NO3−(contribution rate: 17.17 %–54.65 %) at a farther distance. (2) There was niche separation in the acquisition of organic N by the associated species of different life forms, in which the 15N-Glycine recovery and absorption rate of Cer. arenarius decreased with the increase of distance level (D1 > D2 > D3 > D4). However, Cen. pulchella had the maximum 15N-Glycine recovery at D4 (90–100 cm) (D1 < D2 < D3 < D4). (3) By analyzing the key driving factors that influence the N form preferences of non-leguminous plants associated with leguminous shrubs, it was found that the biomass of the 2 species tended to increase with increasing distance levels, and the preference for N forms changed from ammonium N to nitrate N. However, increased distance had a positive effect on the acquisition of N-Glycine and N-NO3−, whereas it negatively impacted the uptake of N-NH4+. These findings revealed that in N-poor desert ecosystems, herbaceous plants near leguminous shrubs adjusted their N preferences based on distance to optimize N uptake and facilitate niche coexistence. This study provides data that support a deeper understanding of the mechanisms of species coexistence and ecological stability assessments among diverse plant species in desert environments.