Plant–plant nitrogen transfer is prevalent in a semi‐arid shrubland and affects the foliar N content of recipient plants

Abstract In agroecosystems, it is well known that nitrogen (N) can be transferred below‐ground among plants, especially between legumes and forage crops. However, we still lack a deep mechanistic understanding of this ecological process and its implications in plant communities, especially in semi‐arid environments where soil N availability depends on sporadic pulses of precipitation. This study comprehensively (i) assesses the prevalence of below‐ground N transfer among the dominant species in a semi‐arid scrubland community, (ii) examines the temporal dynamics and environmental influences on this transfer and (iii) assesses the impact of N transfer on the nutritional condition of the receiver plants (i.e. foliar N content). We quantified plant–plant 15 N transfer between 126 pairs of plants through field experiments in which donors were 15 N‐labelled through foliar absorption, and the increment in foliar δ 15 N of their neighbour plants (i.e. receiver) was periodically registered over two reproductive periods (14 months, 953 foliar samples). We selected pairs of plants of the nine most dominant species in the community (55 donors and 126 receivers). The donors were 15 N‐labelled at the beginning of the growing period (May) in the first reproduction period. Over the second, four more labelling pulses were applied. Below‐ground N transfer was prevalent among all plant species. A 72% of the plants showed evidence of 15 N transfer following the first pulse of 15 N labelling. The magnitude of the transfer progressively increased across labelling pulses, with increments in foliar δ 15 N values ranging from 0.82‰ to 12.35‰. N transfer to receiver plants started in less than a week and reached the maximum δ 15 N values approximately 60 days after labelling, getting back to pre‐labelling values after 120 days. In donor plants, 15 N enrichment lasted 170 days. Interestingly, multiple pulses of δ 15 N showed an effect on the nutritional condition of the receiver, increasing its total foliar N content over a year. Plant–plant N transfer is a common ecological process taking place in this plant community and its effects on plant nutritional condition suggest that it can be a relevant mechanism shaping plant co‐existence in N‐poor environments. Read the free Plain Language Summary for this article on the Journal blog.