| Nutrient resorption during leaf senescence and return to soil with litterfall are major nutrient processes in forested ecosystems,however,it is difficult to estimate both processes in natural forests with abundant species.This is because that the detailed seasonal dynamics of leaf-fall phenology and canopy nutrient concentration in temperate deciduous broad-leaved forests have not been comprehensively quantified,which brings great uncertainty to the accurate estimation of leaf nutrient return and leaf nutrient resorption efficiency（Nu RE）.Therefore,in this paper,nine plots of deciduous broad-leaved temperate forest in the Moershan of Northeast China were taken as an example,leaf-fall phenology and temporal shifts in nitrogen（N）,phosphorus（P）concentrations and N:P in leaf litter for 28 tree species were studied by high-frequency litter collection,and the errors in canopy nutrient return and resorption efficiency for 15 species and nine plots were quantified.The main results were as follows:（1）Mean annual total litterfall mass was 4898.7±172.9 kg hm-2 for the nine plots,of which leaf litterfall accounted for 75.6%at deciduous broad-leaved forest.The day of year（DOY）of start of leaf-fall,DOY of peak leaf-fall,and the length of leaf-fall period differed dramatically among the 28 tree species.The species could be roughly divided into three groups:early leaf-fall,intermediate leaf-fall and late leaf-fall.The ranges of species differences in DOY of start of leaf-fall reached 89 d.The length of leaf-fall period mainly depended on the start rather than the end of leaf-fall.（2）Concentrations of N and P in leaf litter usually declined during the summer and autumn seasons.N:P of leaf litter at ecosystem scale showed a significant decline trend,indicating that there were weak N limit in Maoershan.Nutrient concentration at the DOY of collected peak of leaf-fall lower than mass weighted average nutrient concentration.There was a significant negative correlation between the mass weighted average nutrient concentration of leaf litter and the start of leaf-fall,demonstrating that the earlier leaf litter was associated with larger ecosystem nutrient losses.Annual nutrient return of total canopy litterfall at the ecosystem level were 65.7±6.1 kg N ha-1 yr-1 and 4.7±0.8 kg P ha-1 yr-1 of which leaf litterfall accounted for 77.7 and75.6%,respectively.The N（NRE）and P（PRE）resorption efficiencies at the ecosystem level calculated based on the percentage of nutrient pool resorbed from canopy leaves were 49.8±3.9and 48.0±7.1%,respectively.（3）Calculating nutrient return with species-specific nutrient concentration at the DOY of peak leaf-fall underestimated N and P return by an average of 10.5 and 13.8%;In contrast,the corresponding errors in N and P return estimated using plot-specific nutrient concentration at the DOY of peak leaf-fall were–5.3 and–6.7%.In addition,NRE and PRE for major species based on nutrient concentration at the DOY of peak leaf-fall were overestimated by an average of 9.5and 11.6%,and those for nine plots by 11.1 and 16.8%;using plot-specific nutrient concentration at the DOY of peak leaf-fall lowered mean errors in NRE and PRE to 9.7 and 11.1%.The N and P return of leaf litter increased with increasing basal area of each species,and when the ecosystem level Nu RE were estimated by basal-area-weighted mean species-specific Nu RE for the whole season,NRE and PRE estimates were underestimated by 9.5%and 7.9%,respectively.The relative errors of nutrient return and NRE（but not PRE）were smaller when calculating by basal-area-weighted mean Nu RE before and after the DOY of peak leaf-fall.These results indicate that estimating canopy nutrient return and Nu RE using litterfall collected at the DOY of peak leaf-fall can lead to non-negligible errors,and species-specific combined litterfall collected at and slightly before the DOY of peak leaf-fall may be a better simplified scheme for estimating nutrient return and Nu RE at both species and ecosystem scales. |
