Above- and below-ground resource acquisition strategies determine plant species responses to nitrogen enrichment

Background and Aims: Knowledge of plant resource acquisition strategies is crucial for understanding the mechanisms mediating the responses of ecosystems to external nitrogen (N) input. However, few studies have considered the joint effects of above-ground (light) and below-ground (nutrient) resource acquisition strategies in regulating plant species responses to N enrichment. Here, we quantified the effects of light and non-N nutrient acquisition capacities on species relative abundance in the case of extra N input. Methods: Based on an N-manipulation experiment in a Tibetan alpine steppe, we determined the responses of species relative abundances and light and nutrient acquisition capacities to N enrichment for two species with different resource acquisition strategies (the taller Stipa purpurea, which is colonized by arbuscular mycorrhizal fungi, and the shorter Carex stenophylloides, which has cluster roots). Structural equation models were developed to explore the relative effects of light and nutrient acquisition on species relative abundance along the N addition gradient. Key Results: We found that the relative abundance of taller S. purpurea increased with the improved light acquisition along the N addition gradient. In contrast, the shorter C. stenophylloides, with cluster roots, excelled in acquiring phosphorus (P) so as to elevate its leaf P concentration under N enrichment by producing large amounts of carboxylate exudates that mobilized moderately labile and recalcitrant soil P forms. The increased leaf P concentration of C. stenophylloides enhanced its light use efficiency and promoted its relative abundance even in the shade of taller competitors. Conclusions: Our findings highlight that the combined effects of above-ground (light) and below-ground (nutrient) resources rather than light alone (the prevailing perspective) determine the responses of grassland community structure to N enrichment.

Automated summary

The study revealed that under extra nitrogen input, plant species relative abundance is influenced by both light and non-nitrogen nutrient acquisition capacities. Taller Stipa purpurea increases in relative abundance by improving light acquisition, while shorter Carex stenophylloides excels in phosphorus acquisition to elevate its relative abundance under nitrogen enrichment.