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.