Sampling Strategy Of Fine Roots In A Subtropical Evergreen Broad-leaved Forest Based On Minirhizotrons And Soil Coring Method

Fine roots,commonly defined as roots<2 mm in diameter,play an important role in nutrient cycle and energy flow in forest ecosystems.In belowground ecology,accurate estimate of fine root turnover has always been one of the hot and difficult problems.To determine a reasonable sampling strategy is the premise of fine root turnover study.In this thesis,by using soil coring and minirhizotrons,96 soil cores and minirhizotrons were taken randomly in a subtropical evergreen broad-leaved forest located at Sanming,Fujian province.In order to provide guidance for forest root sampling,we studied the spatial heterogeneity and diameter distribution of fine root biomass and fine root morphological characteristics.We also estimated the sample sizes required for getting various fine root variables.The results showed that:(1)Under a large number of samples,the Shapiro-Wilk test showed that,only fine root biomass density of 0-1 mm for soil core sampling method conformed to the normal distribution,and all others did not conform to the normal distribution.(2)Tree fine roots are highly spatially heterogeneous in subtropical evergreen broad-leaved forest.All the root variables of different soil depths and different diameter classes showed moderate to great variability.For the same root variable,the coefficient of variation(CV)observed by minirhizotrons was greater than soil coring method.(3)The distribution patterns of root length,surface area and volume along with the change of root diameter were different:for roots with smaller diameter,their length and surface area account for the vast majority of the total root length and total root surface area,while their volume accounts for only a small part of the total root volume.(4)The fine root population observed by minirhizotrons and soil coring method were inconsistent.Compared with the soil coring method,the roots observed by minirhizotrons were small in diameter.(5)The results from Monte Carlo method showed that,by using minirhizotrons,55 samples can meet the requirement for determination of fine root length density(at 90%confidence level and 80%estimated precision);While by using soil coring method,collecting 45 and 55 cores respectively can meet the requirements for determination of fine root biomass density and fine root length density(at 90%confidence level and 90%estimated precision).By comparison,the sample sizes used in most of the previous root studies were seriously inadequate.In order to improve the accuracy of fine root observation,rhizotrons or minirhizotrons with bigger image dimensions should be applied,and increasing sampling size is an urgent need for fine root study in the future.These results provided a scientific basis for optimizing sampling size and sampling strategy in subtropical evergreen broad-leaved forest and are therefore helpful to belowground studies.