| Litter is a principal resource for improving forest quality.In order to investigate the ecological function(standing crop,water holding capacity and nutrients return)and spatial heterogeneity of litter nutrients and affecting factors,four 1-hm2 permanent plots of natural spruce-fir mixed forest were established for litter collection and stand structure survey before the peak of falling(late August)in Jingouling Forest Farm,Wangqing County,Jilin Province,northeastern China.A total of 800 litter samples in semi-decomposed(F)and complete decomposed(H)horizons were collected using an equidistant grid point sampling method to determine the ecological function indices,and spatial variation of litter nutrients concentration,return and use efficiency were analyzed using descriptive statistical analysis,semi-variogram analysis,spatial interpolation and correlation analysis.The results were showed as follows:1)The average standing crop of litter in the four plots was 29.10 t/hm2 in total,19.50 t/hm2 and 9.50 t/hm2 in the F and H horizons,respectively.The standing crop of litter in the F horizon was significantly higher than that in the H horizon(P<0.05),accounting for 55.57-72.72%of the total.The average water holding capacity(moisture content)of litter in the four plots was 16.39 t/hm2 in total and the average water holding rate was 236.37%.Litter in the H horizon had significantly higher water holding capacity and rate than that in the F horizon.The water holding capacity and rate were 5.56 t/hm2 and 64.08%in the F horizon,and 10.83 t/hm2 and 172.3%in the H horizon,respectively.2)Concentration,return and use efficiency of litter organic carbon(C),total nitrogen(N)and total phosphorus(P)in the F horizon were 421.68,18.86 and 1.26 g/kg,8.16,0.36 and 0.02 t/hm2,2.46,55.94 and 841.74,respectively,and they were 350.78,17.80 and 2.68 g/kg,3.22,0.17 and 0.03 t/hm2,3.09,58,10 and 408.15 in the H horizon.Litter C and N concentrations decreased with the increase of decomposition degree,and P use efficiency was greater than N and C.Therefore,P may be the limiting factor of plant growth in natural spruce-fir mixed forest.3)The coefficient of variation of litter nutrients(C,N and P)concentration,return and use efficiency in the F and H horizons varied in the four plots with a range of 10.94%?65.63%,indicative of a moderate variation,and the degree of variation was in the order of nutrient return>nutrient use efficiency>nutrient concentration in a specific plot.The spatial variation degree of litter C and P in the H horizon was larger than that in the F horizon.Litter nutrients concentration showed higher spatial autocorrelation,primarily resulting from the structure factors.The fractal dimension of litter C and P concentrations in the H horizon was lower than that in the F horizon.This indicated that the F horizon had a more complex spatial pattern,whereas litter N exhibited a better structure and stronger spatial dependence in the F horizon.4)Litter nutrients concentration,return and use efficiency in the four plots showed strip and patch gradient distribution except for those with the nugget-to-sill values in the F or H horizon larger than 75%,indicating that their spatial heterogeneity was mainly caused by random effect,and thus not suitable for interpolation method.Litter nutrients concentration and use efficiency had similar spatial distribution pattern but with an opposite change trend.However,the change rule of nutrients return was not so obvious as nutrients concentration and use efficiency.5)Litter nutrients return in the F and H horizons had a very significant positive correlation with the standing crop of litter(P<0.01).The water holding capacity was significantly and positively correlated with litter nutrients concentration(P<0.05),but had a significantly negative correlation with litter nutrients return and use efficiency.The effects of water holding capacity on litter C and N was more significant than P,and more significant effects were found in the H horizon than F horizon.In addition,litter nutrients concentration,return and use efficiency were significantly correlated with other litter nutrient indices and stoichiometric ratios6)Litter nutrients concentration,return and use efficiency were correlated with stand characteristics(i.e.,species number,stem number,biodiversity indices,proportion of conifer species and stems).The influence of species number and biodiversity indices on litter nutrient characteristics was more significant in the F horizon,while the effect of proportion of conifer species and stems on litter nutrient characteristics was more obvious in the H horizon.However,C was more weakly correlated with stand characteristics compared to P and N. |
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