Abstract:

Phosphorus (P) is one of the key elements that affecting plant growth, and below-ground foraging plasticity of fine roots is an important way for plants to improve the absorption of soil P. Under natural environmental conditions, heterogeneous or patchy distributions of soil nutrients have been well documented, especially for relatively immobile nutrients such as P. It is unclear how plants adjust the plastic responses of different below-ground foraging traits to nutrient patches, and the prediction of plastic responses of specific fine root traits to below-ground foraging traits is more uncertain. In this paper, the influencing factors of plant below-ground foraging were summarized, and the plastic responses of fine roots (morphology, architecture, proliferation, chemistry, and physiology) and mycorrhizal fungi to P-rich patches were expounded. The differences of below-ground foraging traits and plastic responses between arbuscular mycorrhizal and ectomycorrhizal tree species were analyzed from the aspects of fungal colonization mode, root morphology structure and nutrient acquisition strategies. Based on the carbon cost hypothesis of below-ground foraging, it was considered that morphological plasticity and physiological plasticity of fine roots were the results of resource competition in many cases. The proliferation plasticity of fungal mycelia seemed to be more economically significant for plants, but when both root and mycorrhizal fungi were present in nutrient patches, root proliferation was more responsive than fungal response. The prediction of nutrient foraging plasticity by fine root traits was also discussed, and it was pointed out that fine root diameter was a good predictor of changes in below-ground foraging traits. Finally, focusing on the shortcomings of the current research on the below-ground foraging plasticity of plants, the future research directions were proposed from the aspects of below-ground foraging foraging plasticity framework, below-ground foraging mechanism, prediction of fine root traits on the plasticity of plant nutrient acquisition, and the relationship between fine root foraging plasticity and defense plasticity, which would be helpful to understand the strategies of plant below-ground P acquisition and its adaptation mechanisms to environmental changes.

Key words: below-ground foraging trait, phosphorus-rich patch, plasticity response, arbuscular mycorrhiza, ectomycorrhiza