Nitrogen addition shifts fine root nutrient-acquisition strategies differently in ectomycorrhizal and arbuscular mycorrhizal plantations: A case study of Pinus massoniana and Cunninghamia lanceolata

Abstract

Aims

Tree species associated with ectomycorrhizal (ECM) and arbuscular mycorrhiza (AM) exhibit distinct strategies for nutrient acquisition. However, the effects of varying nitrogen (N) additions on the nutrient-acquisition strategies of fine roots in ECM and AM species have not been fully elucidated.

Methods

We investigated fine root traits, mycorrhizal colonization rates, and rhizosphere enzyme activity in Pinus massoniana (ECM) and Cunninghamia lanceolata (AM) plantations at 16-year-old under five levels of N addition (0, 25, 50, 100 and 200 kg N ha⁻¹ yr⁻¹).

Results

The fine root biomass of Pinus massoniana (ECM) initially increased and then declined with increasing N additions, whereas that of Cunninghamia lanceolata (AM) exhibited a continuous increase. The specific root length (SRL) and root area (SRA) of P. massoniana did not significantly change with increasing levels of N, while those in C. lanceolata increased initially and then decreased. For both species, the mycorrhizal colonization rate decreased as the level of N addition increased. Furthermore, rhizosphere extracellular enzyme activity in P. massoniana increased at high N levels, while that in C. lanceolata increased at low N levels.

Conclusions

With increasing N addition, the fine roots of C. lanceolata shifted from prioritizing nutrient exploration efficiency (via SRL) to nutrient exploration quantity (via biomass), while the fine roots of P. massoniana initially relied on fine root biomass and mycorrhizal associations, eventually transitioning to exploration efficiency and a decoupling from mycorrhiza. Our findings enhance understanding of plant-soil interactions and provide insightful information for forest management under N deposition.