No abstract

PurposePhosphorus (P) is a limiting nutrient in many managed forests. To further understand the risks and benefits of biochar as a sustainable P source in forest management, an improved mechanistic understanding of its interactions in root systems is required.MethodsA rhizobox experiment was conducted to observe root response of P. sylvestris (Scots pine) seedlings to different biochars in comparison to triple superphosphate (TSP) fertilizer as a P source. Three types of wood-derived biochar were compared: biochar from mixed softwood pellets (“Reference biochar”); from the vascular cambium zone of Picea sitchensis (Sitka spruce) (“VCZ biochar”) and from mixed softwood pellets infused with TSP (“Processed biochar”). These alternative types of biochar presented a range of available P from low to high. The activity of roots in the rhizoboxes was monitored and analyzed using spatial GIS software.ResultsThe total length of P. sylvestris roots did not significantly differ between treatments. However, roots showed strong preference for soil proximal to VCZ biochar and strong avoidance to TSP fertilizer. There was a milder avoidance effect for Processed biochar. Different preferences were mainly explained by available P: roots favored a moderate, sustained P source and avoided sources of high available P. The avoidance effect can be attributed partially to a considerable drop in soil pH around TSP fertilizer. ConclusionThe concentration and duration of P availability affects the root response of P. sylvestris to sources of P. In P-deficient conditions, the development of P. sylvestris roots can be markedly improved by introducing biochar with a certain native P content.