Effects of biochar on mycorrhizal colonization and the uptake of nitrogen and phosphorus in poplar trees
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SubjectMass balance; Nitrogen use efficiency; Biochar ash; Arbuscular mycorrhizal fungi; Biochar; AGR/13
In recent years the term “biochar”, has become popular in the context of carbon sequestration. Nowadays it is being exploited as a soil amendment. It is the solid product obtained from thermochemical conversion of biomass in the absence or with limited air heated to above 250°C, a process known as pyrolysis. While there are several terms used in materials related to biochar, the terms used and investigated in this thesis are pyrochar and hydrochar. Pyrochar is usually associated to chars obtained from pyrolysis and gasification processes; instead, hydrochar is obtained as the product of hydrothermal carbonization or liquefaction and is distinct from pyrochar due to its production process and properties. Two experiments were conducted to investigate the effects of two types of char (pyrochar and hydrochar) which are referred in this thesis as AGT and HTC respectively, into the potential impacts of char on poplars. Specifically, a 2-year pot experiment was set up with the following broad based objectives: (i) to evaluate if biochar can be a soil amendment, (ii) to quantify the fraction of char-derived N absorbed by the plant, (iii) to examine the allocation of nitrogen (N), phosphorus (P) and biomass over the two-year growth, (iv) to evaluate the effect of chars on AMF colonization and (v) if arbuscular mycorrhizal fungi (AMF) influence the uptake of N and P and growth in poplars. A second short-term pot experiment was undertaken to understand the interfaces between native biochar P and soil, biochar and soil-P, and the two pools of P with each other. The purpose was to support biochar products developed for better P delivery and/or recycling of P in soil–plant systems. Given that time is an important dimension in these interactions, as well as the morphological character of biochar and soil, local pH status, and mycorrhizal activity, two experiments were conducted to examine: (i) the effect of proximity to particle surface of P release using a naturally P-rich biochar and (ii) the delivery of P to poplar cuttings from specific P-enriched particles. The main findings from the main experiment demonstrated both pyrochar and hydrochar to have significantly influenced the first year biomass production and the biomass allocation pattern over the two-year study period. Regarding the fraction of char-derived N, the hydrochar proved to be an important short-term direct source of N, while pyrochar did not contribute directly to the nutrition of the plant except to a negligible extent. Availability of P was short-lived and became less bioavailable with time. Regarding AMF colonization, both chars affected AMF colonization positively. HTC-treated poplars showed a higher colonization compared with AGT-treated poplars. However, the presence of AMF did not affect the uptake of N and P positively. The results from the second short-term experiment demonstrated that P gets locked up in smaller particle sizes (0.12-0.063 mm) also known as “chash” particles and was more bioavailable to the poplar cutting in the first 103 days of growth.
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