Fig. 1 Classification of plant nutrient-acquisition strategies.

Fig. 2 Morphology of plant nutrient-acquisition strategies. A, Hyphae of the arbuscular mycorrhizal fungus Glomus caledonium growing into soil from a host root of Trifolium repens (Fabaceae). Photo by Iver Jakobsen; reprinted with permission of Springer-Verlag (Olsson et al., 2002). B, A seedling of Pinus sylvestris (Pinaceae) growing in a microcosm in association with the ectomycorrhizal fungus Suillus bovinus. The fungal mycelium can be seen spreading in the soil in the microcosm (arrowhead) and proliferating locally to form well-defined dense patches (arrows). Reprinted with permission of Elsevier B.V. (Lambers et al., 2008). C, Ericoid mycorrhizal root of Woollsia pungens, showing epidermal cells colonized by coils of an ericoid mycorrhizal fungus (stained blue, arrowed). Reprinted with permission of Elsevier B.V. (Lambers et al., 2008). D, Nodules of Astragalus mahoshanicus (Fabaceae). E, Cluster roots of Banksia grandis (Proteaceae). Photo by ZHONG Hong-Tao. F, Sand-binding roots of Actinocephalus cabralensis (Ericaulaceae)(Oliveira et al., 2015). G, Dauciform roots of Tetraria species (Cyperaceae). Reprinted with permission of Elsevier B.V. (Lambers et al., 2008). H, Vellozioid roots of Barbacenia tomentosa (Velloziaceae) collected in field (Abrahão et al., 2020). EMF, ericoid mycorrhizal fungus; RE, root epidermis; RVS, root vascular system.

Fig. 3 Temporal changes in plant nutrient-acquisition strategies (NASs) with increasing soil age. AM, arbuscular mycorrhiza; CR, cluster roots; DR, dauciform roots; ECM, ectomycorrhiza; FR, fine roots; N fixation, nitrogen fixation; OM, orchid mycorrhiza; Ptase, phosphatases; SR, sand-banding roots; VR, vellozioid roots. The change in intensity of the background color represents abundance in diversity of NASs. The width of irregular polygons on the top of the figure represents the general trend of three classes of NASs with soil age. The size of cycles represents the relative importance of a particular NAS in plant acquiring nutrients in different stages of pedogenesis. The dotted circle of FR indicates that more evidence is needed to support the role of the fine root strategy in plant acquiring nutrients. The change in intensity of color in soil nitrogen (N) and phosphorus (P) pool rectangles represents variation in total N and P availability, respectively, with soil age.

Fig. 4 Conceptual scheme showing effects of plant nutrient-acquisition strategies (NASs) on vegetation primary succession and coexistence and diversity of species. The change in intensity of color in soil nitrogen (N) and phosphorus (P) pool rectangle represents variations in total N and P pool with soil age, respectively. In the first stage of pedogenesis, plant NASs contribute to the establishment of pioneer community through facilitation. For example, N fixation and carboxylate-releasing strategies improve soil available nutrient pools and thus facilitate the settlement, growth and reproduction of subsequent species. In the early-intermediate stage, there are adequate soil available nutrients, NASs contribute to the competitiveness of plant species. Species with more effective NASs may have advantages in competition. And thus this will result in species turnover and promote succession. In the late stage, soil available nutrients are low or impoverished, especially for P, plant have to develop diverse NASs to acquire limited nutrients. The relationships between these NASs are mainly complementary. Diverse and complementary NASs have important impacts on the coexistence and diversity in the late stage of pedogenesis, although we still do not know the exact contribution to them. In addition, as proposed by Lambers et al. (2018), the different abilities against pathogens of plant species with different NASs also contribute the coexistence of plant species at this stage.