Contribution of mycorrhizal symbiosis and root strategy to red clover aboveground biomass under nitrogen addition and phosphorus distribution

Soil nutrients exhibit heterogeneity in their spatial distribution, presenting challenges to plant acquisition. Notably, phosphorus (P) heterogeneity is a characteristic feature of soil, necessitating the development of adaptive strategies by plants to cope with this phenomenon. To address this, fully crossed three-factor experiments were conducted using red clover within rhizoboxes. Positions of P in three conditions, included P even distribution (even P), P close distribution (close P), and P far distribution (far P). Concurrently, N addition was two amounts(0 and 20 mg kg^{- 1}), both with and without AMF inoculation. The findings indicated a decrease in aboveground biomass attributable to uneven P distribution, whereas N and AMF demonstrated the potential to affect aboveground biomass. In a structural equation model, AMF primarily increased aboveground biomass by enhancing nodule number and specific leaf area (SLA). In contrast, N addition improved aboveground biomass through increased nodule number or direct effects. Subsequently, a random forest model indicated that under the far P treatment, fine root length emerged as the primary factor affecting aboveground biomass, followed by thickest root length. Conversely, in the even P treatment, the thickest root length was of paramount importance. In summary, when confronted with uneven P distribution, clover plants adopted various root foraging strategies. AMF played a pivotal role in elevating nodule number, and SLA.