Establishment of mixed plantations of Pinus sylvestris var.mongolica and Populus×xiaozhuanica may not be appropriate:evidence from litter decomposition

Aims Mongolian pine(Pinus sylvestris var.mongolica)and Xiaozhuan poplar(Populus×xiaozhuanica)are two predominant afforestation tree species in the semi-arid sandy lands of northeast china,which are characterized by poor soil nutrients.Plant litter decomposition plays a critical role in regulating nutrient cycling in terrestrial ecosystems.Admixture of broadleaf litter to conifer litter is expected to improve litter decomposition and soil fertility,and thus productivity.However,the effects on the decomposition of litter mixture of the above two tree species are not well understood.therefore,it is essential to assess the decomposition performance of litter mixture with the aim of improving forest nutrient management and the establishment of mixed plantation.Appropriate forest manage-ment practice is critical for the sustainability of site productivity in plantation forests.Methods We conducted a field litterbag decomposition transplant experi-ment for single pine litter,single poplar litter and their mixture in a pine stand,a poplar stand and an adjacent grassland for 16 months in the Keerqin Sandy Lands,northeast china.Important Findings After 16 months of incubation,there remained significantly more litter mass of pine(73.8%)than of poplar(67.2%).the mass remaining was positively correlated with litter carbon(c):nitrogen(N),c:phosphorus(P)and lignin:N ratios,and negatively with litter N and P concentrations,which suggests that initial litter chemical properties were an important factor affecting litter decay.Generally,net N and P immobilizations were observed during decomposition.this indicates that litter decomposition in this area was N-limited as N was progressively immobilized,and then tended to induce P limitation.thus,we strongly recommend prohibiting litter harvesting by local residents to maintain soil fertility in this nutrient-poor area.Our results do not support the home-field advantage hypothesis,as illustrated by the fact that,in most cases,mass loss of litter from native habitat was comparable to that in transplanted habitats during decomposition.Furthermore,a dominant additive effect was detected,indicating that the establishment of mixed plantation may not be appropriate for these two species.