Plant nutrient-acquisition strategies contribute to species replacement during primary succession

1. Plant nutrient-acquisition strategies (NAS) linking soil nutrients to plant growth are considered crucial to species replacement during primary succession. However, empirical evidence from field studies remains scarce. 2. We examined the replacement of Hippophae tibetana (Elaeagnaceae) by Populus purdomii (Salicaceae) during the first three stages (S1-S3) of succession along the Hailuogou postglacial chronosequence in southwest China. We investigated changes in the scavenging, mining and N-2-fixing strategies of the two species with varying soil nutrient levels and evaluated how these NAS influenced plant performance with succession. 3. Bioavailable nitrogen and phosphorus concentrations increased significantly from near detection limits at the S1 stage to 60 and 41 mg kg(-1) at the S3 stage, respectively. Despite this, H. tibetana maintained mining and N-2-fixing strategies, as indicated by rhizothamnia, cluster roots and lower pH, and higher carboxylate concentration and acid phosphatase activities in soil surrounding roots compared with those around P. purdomii at all sites. Conversely, P. purdomii relied on scavenging strategies, evidenced by higher ectomycorrhizal colonization and specific root length, smaller root diameter and more negative leaf delta C-13 than those of H. tibetana. Leaf nitrogen and phosphorus concentration, along with the relative abundance of H. tibetana, were significantly higher than those of P. purdomii at S1, but this reversed at S3. Linear mixed models indicated that mining and N-2-fixing strategies were positively correlated with nutrient concentrations at low soil nutrient levels, while scavenging strategies can enhance leaf nutrients at relatively high soil nutrient levels. Linear regression models showed that leaf nitrogen and phosphorus accounted for 13% and 31% of variation in relative abundance, respectively. The residuals of these models were further reduced by 35% and 39% when accounting for the combined effects of mining and N-2-fixing strategies. Results from incubation experiments, functional gene abundance and enzymatic activities showed that microbial nitrogen mineralization and phosphorus solubilization were similar in the rhizosphere of both species. 4. Synthesis. Distinct investments and changing efficiency of plant nutrient-acquisition strategies (NAS) in response to soil nutrient availability are key drivers of species turnover during primary succession. These findings underscore the importance of belowground plant NAS mechanisms in shaping aboveground community dynamics during early pedogenesis.