| Phosphorus (P) and its forms has a great influence on photosynthetic capacity and productivity of plant communities. Plant P uptake and cycling mechanisms is species-specific characteristics, and the minor difference in P uptake and cybetween tree species may modify the cycle of P in plant communites and its effectiveness. Subtropical region is one of regions with higher biodiversity in forest ecosystems while with relatively lower available phosphorus content in soils. This study discussed the response of photosynthesis on P forms and tree species diversity, using four tree species seedlings common in central subtropical region, and evaluated possible interactions in absorption of P and possible complementary effect in absorption of P.The study was a greenhouse pot experiment with application of inorganic P fertilizer (inorganic P), litter (organic P), top soils (organic P) and subsoils (inorganic P) representing4forms of phosphorus as substrate pretreatment. The4common species in central subtropical China, Castanea henryi (Ch), Lithocarpus glaber (Lg), Quercus fabri (Qf) and Liquidambar formosana (Lf) combinated species as monoculture (1M),2-species mixture(2M),4-species-mixture(4M), and summed12combinations representing the level of species diversity with4replicates. Seedlings, cultured from seeds in early April in pots of4forms of phosphorus substrate were irrigated with P-free nutrient solution and lasted for seven months through the growing season. The photosynthetic parameters of net photosynthetic rate (ANet), light response curves were measured with Licor-6400starting in mid-September. The final harvest of the seedlings was at the end of the growing season, conducted in November,2012. The seedlings were collected in separate paper bags for each pot according to different organs. For each pot, leaves of the same species individuals were mixed into one bag to increase the amount of material available for laboratory analysis of N and P. The main results showed that:(1) ANet of seedlings was pronounced different with varying P forms at the significant level of0.001. Except the Lf, it ranked as Topsoil (4.90μmol·m-2s-1)> Subsoil (4.49μmol·m-2s-1)> Litter (4.47μmol·m-2s-1)> Fertilizer (3.99μmol·m-2S-1).(2) The characteristic parameters of light response curves were pronounced different with P forms at the significant level of0.05. The maximum net photosynthetic rate (Amax) of four seedlings ranked as Topsoil> Subsoil, Litter> Fertilizer. With exception of Lg, apparent quantum efficiency (Φ) and dark respiration rate (Rday) of Ch, Qf and Lf seedlings were significantly increased with litter and topsoil treatments to some extent, increasing light saturation point (LSP) while reducing its light compensation point (LCP).(3) ANet of seedlings was significant increased with increasing tree species diversity at the significant level of0.001and was in the order as1M (4.09μmol·m-2s-1)<2M (4.43μmol·m-2s-1)<4M (4.59μmol·m-2s-1).(4) P concentrations in leaves were significantly different from treatments at the level of0.001.In General, leaf P concentration performed as Fertilizer (1583.87mg·kg-1)> Litter (579.52mg·kg-1)> Topsoil (374.14mg·kg-1)>Subsoil (367.57mg·kg-1).(5) P concentration in leaves of seedlings was not significantly influenced by tree species diversity (p=0.411).General performance was as2M (704.41±42.31m.g·kg-1)<1M (727.52±81.24mg·kg-1)<4M (751.74±56.57mg·kg-1).(6) Complementary utilization of P was recorded with2M and4M in treatments of fertilizer, subsoil and litter, with exception of the topsoil treatment. And complementary utilization of P by4M was significant different from1M and2M in the Litter treatment, indicating effects complementary utilization of P was relation to tree species diversity and more significant in soil organic P form. |
PDF Full Text Request