Importance of overstorey attributes for understorey litter production and nutrient cycling in European forests

Background:In contrast with the negligible contribution of the forest understorey to the total aboveground phytobiomass of a forest,its share in annual litter production and nutrient cycling may be more important.Whether and how this functional role of the understorey differs across forest types and depends upon overstorey characteristics remains to be investigated.Methods:We sampled 209 plots of the FunDivEUROPE Exploratory Platform,a network of study plots covering local gradients of tree diversity spread over six contrasting forest types in Europe.To estimate the relative contribution of the understorey to carbon and nutrient cycling,we sampled non-lignified aboveground understorey biomass and overstorey leaf litterfall in all plots.Understorey samples were analysed for C,N and P concentrations,overstorey leaf litterfall for C and N concentrations.We additionally quantified a set of overstorey attributes,including species richness,proportion of evergreen species,light availability(representing crown density)and litter quality,and investigated whether they drive the understorey’s contribution to carbon and nutrient cycling.Results and conclusions:Overstorey litter production and nutrient stocks in litterfall clearly exceeded the contribution of the understorey for all forest types,and the share of the understorey was higher in forests at the extremes of the climatic gradient.In most of the investigated forest types,it was mainly light availability that determined the contribution of the understorey to yearly carbon and nutrient cycling.Overstorey species richness did not affect the contribution of the understorey to carbon and nutrient cycling in any of the investigated forest types.

A Preliminary Study on Cold Tolerance in Cinnamomum japonicum Sieb. at Different Ages

[ Objective] This study aimed to further expand the production and application of Cirmamomumjaponicum Sieb. and investigate the mechanism of cold resistance in evergreen broad-leaved tree species. [ Method] Using adult Cinnamonum campora as control, during the entire wintering period from October 2011 to March 2012, the wintering adaptability of C. japonicum leaves at different ages was observed; the electrolyte leakage was measured under indoor low-temperature treatment to calculate the semi-lethal temperature （LT50） by fitting Logistic equation, thus conducting dynamic analysis and comprehensive evaluation of the cold re- sistance in C. japonicum. [ Result] The results showed that the chilling injuries in leaves of different materials were aggravated with the decreasing temperature. According to the results of five times of dynamic observation on wintering adaptability, the cold resistance in different materials presented a decreasing order of adult C. japonicum medium-aged C. japonicum 〉 young C. japon/cum 〉 adult C. campora. The relationship between indoor low temperature and leaf injury rate showed an S-shaped curve. The significance test suggested relatively high fitting degree with Logistic equation. The semi-lethal temperature presented a V-shaped curve with the changing temperature and roached the minimum during late December to early February in the following year. The dynamic changes and minimum value of semi-lethal temperature indicated a consistent order of cold resistance in different materials to the results of wintering adaptability observation. Therefore, results of two analysis methods could be combined for cold resistance evaluation. [ Conclusion] This study laid the foundation for the introduction and populariza- tion of C. japonicum in northern gardens along the Yangtze River.

Root-order-associated variations in fine-root decomposition and their effects on soil in a subtropical evergreen forest

Background:Despite the importance of root decomposition in predicting ecosystem responses to future climate change,the effects of branch order on root decomposition and the feedback to soil still remains poorly understood.Here we separated root samples taken from two tree species(Castanopsis fargesii and Schima superba in subtropical forests along the coastal area in eastern China)into four-order classes(1st–2nd order,3rd order,4th order,and 5th order)and conducted a 540-day litterbag incubation experiment in laboratory to examine root mass loss,nutrient release,and the influence on soil during decomposition.Results:C.fargesii roots of 1st–2nd and 3rd order decayed more slowly than those of 4th and 5th order,but this pattern was not significant for S.superba.Of all the measured root traits,the decomposition rates correlated best with root C/N ratio,diameter and specific root length(SRL)based on the structural equation modeling.Both tree species and root order exhibited significantly effects on root initial traits.Overall,C.fargesii roots decay faster than S.superba,and this appears to be associated with root initial C quality and N concentration.In addition,root order positively affected root decomposition rates mainly through root diameter and SRL.However,no significant difference was found in C and N content between soils below the litterbag with different-order roots.Conclusions:Our findings suggest the effects of branch order on root decomposition are dependent on tree species.Moreover,root morphological properties might also be the controlling factor in root decay besides root chemistry fractions.Overall,the integrative effects should be considered to improve our understanding of the fate of fine-root litter and their contribution to soil C and N pool.

Seasonal characteristics and determinants of tree growth in a Chinese subtropical forest

Aims To quantify the seasonal differences in effects of leaf habit,species identity,initial diameter,neighborhood interaction and stand environment on tree absolute diameter growth rates in a subtropical forest in China.Methods We used man-made dendrometer bands to record radial increments of all trees with diameter at breast height(DBH)≥5 cm and height≥3 m within 25 comparative study plots(30×30 m for each)of the‘Biodiversity-Ecosystem Functioning Experiment China’(BEF-China)in the Gutianshan National Nature Reserve,Zhejiang Province,China.We measured stem circumferences twice a year from 2011 to 2014 to calculate absolute diameter growth rate of a warm and wet season(WWS,April to September)and a dry and cold season(DCS,October to the next March)for each individual tree:annual growth(GR_(year)),growth during the WWS(GR_(WWS))and growth during the DCS(GR_(DCS)).We firstly tested the differences in growth rates between different seasons using paired t-tests with Bonferroni correction.Then we applied linear mixed models to explore the effects of leaf habit,species identity,initial diameter,neighborhood interaction(indicated by richness,density and total basal area of all neighboring trees within a radius of 5 m around target trees),stand age and topography(elevation,slope and aspect)on tree growth rates of the two different seasons in three deciduous and 14 evergreen species.Important Findings GR_(year),GR_(WWS)and GR_(DCS)varied between 0.04-0.50 cm year^(−1)(mean=0.21),0.03-0.46 cm season^(−1)(mean=0.18)and 0.01-0.05 cm season^(−1)(mean=0.03)across the 17 species,respectively.GR_(WWS)was significantly higher than GR_(DCS)for all species.Growth rates of faster growing species tended to have larger absolute differences between the WWS and DCS.Tree growth rates of both seasons and of the year(GR_(year),GR_(WWS)and GR_(DCS))varied significantly among leaf habit and species,and increased allometrically with initial diameter,decreased with stand age,but were not significantly related to topography and neighborhood richness or density.GR_(WWS)decreased with neighborhood total basal area,while GR_(DCS)did not.In conclusion,species might the temporally complementary,contributing to plot growth at different times of the year.