Leaching of inorganic and organic phosphorus and nitrogen in contrasting beech forest soils – seasonal patterns and effects of fertilization

[摘要] Leaching is one major pathway of phosphorus (P) andnitrogen (N) losses from forest ecosystems. Using a full factorial N×P fertilization and irrigation experiment, we investigated theleaching of dissolved organic and inorganic P (DOP and DIP) and N (DON andDIN) from organic layers (litter, Oe / Oa horizons) and mineral A horizons attwo European beech sites of contrasting P status. Leachates showed the highestDIP and DIN concentrations in summer and lowest in winter, while dissolvedorganic forms remained rather constant throughout seasons. During the dryand hot summer of 2018, DOC:DOP and DOC:DON ratios in leachates wereparticularly narrow, suggesting a release of microbial P due to cell lysisby drying and rewetting. This effect was stronger at the low-P site. Theestimated annual mean fluxes from the Oe / Oa horizons in the non-fertilizedtreatment were 60 and 30  mg m - 2 yr - 1 for dissolved total P and 730and 650  mg m - 2 yr - 1 for dissolved total N at the high-P and thelow-P site, respectively. Fluxes of P were highest in the organic layers anddecreased towards the A horizon likely due to sorption by minerals.Fertilization effects were additive at the high-P but antagonistic at thelow-P site: at the high-P site, fertilization with + N, + P, and + N + P increased total P fluxes from the Oe / Oa horizon by + 33 %, + 51 %, and + 75 %, while the respective increases were + 198 %, + 156 %, and + 10 %at the low-P site. The positive N effect on DIP leaching possibly resultsfrom a removed N limitation of phosphatase activity at the low-P site.Fluxes of DOP remained unaffected by fertilization. Fluxes of DIN and DONfrom the Oe / Oa horizons increased upon +N and +N+P but not upon +Pfertilization. In conclusion, the estimated P fluxes from the A horizonswere comparable in magnitude to reported atmospheric P inputs, suggestingthat these systems do not deplete in P due to leaching. However, aparticularly high sensitivity of DIP leaching to hotter and drier conditionssuggests accelerated P losses under the expected more extreme future climateconditions. Increases in P leaching due to fertilization anddrying–rewetting were higher in the low-P system, implying that the low-Psystem is more susceptible to environmental future changes.

[学科分类] 大气科学