Absorptive roots and arbuscular mycorrhizal fungi (AMF) constitute two distinct pathways for plant nutrient acquisition, and play a key role in belowground carbon and nutrients cycling. However, whether and how soil nutrient availability can regulate the integrated structural patterns and growth consequences of roots and AMF remains unclear.To address this question, we analyzed the net primary production (NPP), trait plasticity of absorptive roots and AMF, as well as the intra-radical AMF community composition in response to four-year nitrogen (N) and phosphorus (P) additions in a Chinese fir (Cunninghamia lanceolata) plantation.
Results/Conclusions
We found strong relationships between AMF hyphal length and absorptive root production, but this relationship shifted with soil N and P availability. AMF hyphal length scaled isometrically with absorptive root production under the same P availability, whereas absorptive root production increased faster than AMF hyphal length with N addition. AMF hyphal length can explain ~40% variation in stem growth, as the coupling between AMF hyphal length and stem production was strong in nutrient-poor soils and weak in forest soils with nutrient additions. In addition, root tissue density decreased, and specific root length (SRL) increased with P addition, but remained unchanged under N addition.
Overall, as soil nutrient conditions improved, C. lanceolataallocated more carbon to stems, thus reducing carbon for mycorrhiza and roots. Such dynamics suggest key importance for multiple dimension responses in the structure of both AMF and roots. We argue that integrating allometry and trait plasticity in both roots and AMF can improve future predictions in the context of forest belowground process.