Activity of phosphatases in technosols afforested with N-fixing and non-N-fixing tree species

Tree species capable of forming symbiosis with N-fixing bacteria planted on reclaimed wastelands may increase not only their N content but also increase availability of P. The aim of our study was to compare the effect of rhizobial and actinorhizal N-fixing tree species and non-N-fixing species on the activity of phosphatases in various technosols. Soil samples were taken under black locust (Robinia pseudoaccaccia), black alder (Alnus glutinosa), silver birch (Betula pendula) and Scots pine (Pinus sylvestris) from two depths (0-5 cm and 5 – 20 cm) of technosols developing from different parent materials (Quaternary sands, fly ashes after lignite combustion,  acid and alkaline Tertiary clays). The samples were measured for the activities of acid and alkaline phosphatase, inorganic pyrophosphatase, microbial biomass (C_mic), texture, as well as contents of organic C (C_org), total N (N_t) and total P (P_t). Activities of acid (Pho_Aci), alkaline (Pho_Alk), total phosphatase (Pho_Sum) and inorganic pyrophosphatase (Pyro_Pho) were expressed per soil dry mass and per unit of C_mic (specific enzyme activities - Pho_Aci_SP, Pho_Alk_SP and Pho_Sum_SP for acid, alkaline and total phosphatase, respectively, Pyro_Pho_SP for pyrophosphatase). The soils under black locust exhibited higher Pho_Aci activity and higher specific activities of all enzymes (Pho_Aci_SP, Pho_Alk_SP,, Pho_Sum_SP and Pyro_Pho_SP) than the soils under both non-N-fixing trees. For alder  Pho_Aci activity was significantly higher only when compared to pine. However, the values of Pho_Aci_SP and Pho_Sum_SP were higher under alder than under both non-N-fixing trees. There were no differences in the activities or specific activities of measured enzymes between the soils under pine and birch. Our results indicated that rhizobial black locust stimulated activity of soil enzymes involved in P cycling much stronger than non-N-fixing tree species. This effect of black locust was consistent in technosols developing from various parent materials. The effect of actinorhizal black alder was less pronounced, but also evident.  The results of our study indicated that both N-fixing trees stimulated activity of enzymes involved in P cycling stronger than the non-fixing trees. Thus, the N-fixing trees may alleviate P deficiency in technosols as they stimulate development of phosphatase releasing microorganisms and increase P availability.

The study was financed by The National Science Centre, Poland, grant No. 2018/31/B/ST10/01626.