Divergent responses of root traits of nitrogen-fixing and non-nitrogen fixing seedlings to phosphorus addition in Southern China

Background and aimsPhosphorus (P) limitation is common for plant growth and seedling regeneration in highly weathered soil of southern China. The responses of plant growth to various P supply are well conducted. However, the responses of different root orders of different functional tree seedlings to various soil P availability is still unclear.MethodsA field-based manipulative experiment was carried out to investigate the responses of different orders of roots of Ormosia pinnata (N-fixing), Michelia macclurei (non-N-fixing), and Schima superba (non-N-fixing) seedlings to P addition in southern China.Results(1) P addition mainly changed the morphological traits of the 3rd order root of tree seedlings. N-fixing seedling tended to invest more resource in acquisition traits such as specific root length (SRL) rather than non-N-fixing species. (2) The contents of N and P in 3rd roots of non-N-fixing tree seedlings was greatly affected by external P addition, but only the P content in 1st order root was affected. P addition only increased the 3rd order root N:P ratio of N-fixing species. (3) P addition increased soluble sugar content while reduced starch contents in 2nd and 3rd order roots and greatly changed the distribution pattern of non-structural carbohydrates (NSC) of N-fixing seedling.ConclusionsN-fixing seedling is relatively more adaptable to the environment of exogenous P addition and have stronger ability to use soil P. The physiological shapes of different functional seedlings such as root N and P contents and NSC contents to various P availability was divergent, which was tightly related to the root hierarchy of seedlings in southern China.