Modeling rhizosphere carbon and nitrogen cycling in Eucalyptus plantation soil

Abstract

Abstract. Vigorous Eucalyptus plantations produce 105 to 10 6 km ha -1 of fine roots that probably increase carbon (C) and nitrogen (N) cycling in rhizosphere soil. However, the quantitative importance of rhizosphere priming is still unknown for most ecosystems, for instance Eucalyptus plantations. Therefore, the objective of this work was to propose and evaluate a mechanistic model for predicting rhizospheric C and N cycling in Eucalyptus plantations. The potential importance of the priming effect was estimated for a typical Eucalyptus plantation in Brazil. The process-based model (ForPRAN -Forest 15 plantation rhizospheric available nitrogen) predicts the change in rhizosphere C and N cycling resulting from root growth and consists of two modules: (1) fine root growth, and (2) C and N rhizosphere cycling. The model describes a series of soil biological processes: root growth, rhizodeposition, microbial uptake, enzymatic synthesis, depolymerization of soil organic matter, respiration, mineralization, immobilization, microbial death, microbial emigration and immigration, SOM formation.Model performance was satisfactory quantitatively and qualitatively when compared to observed data in the literature. The 20 input variables that most influenced N gain by rhizospheric mineralization were (in order of decreasing importance): root diameter > rhizosphere thickness > soil temperature > clay content. The priming effect in a typical Eucalyptus plantation producing 42 m³/ha/year of wood, with assumed losses of 40 % of the total N mineralized, was estimated to be 24.6 % of plantation N demand (shoot + roots + litter). The rhizosphere cycling model should be considered for adaptation to other forestry and agricultural production models where the inclusion of such processes offer the potential for improved model 25 performance.

What regulates the rhizodeposition of winter oilseed rape during growth?

“…However, this decomposition may increase the availability of nutrients such as nitrogen and may be one of the most important rhizosphere effects in the context of plant nutrition (Finzi et al 2015). This assumption is also supported by model simulations showing that rhizosphere processes could be an important supplement to soil derived N (Valadares et al 2018).…”