中亚热带杉木人工林细根生物量空间变异与取样数量估算

林木细根生物量具有一定的空间异质性,因此采用合理的细根取样策略对精确估算细根生物量十分重要。通过在福建省三明杉木人工林林内采用土钻法随机选取100个取样点,分析不同细根类型(杉木、林下植被、总细根)生物量的空间变异特征,并对细根生物量所需的取样数量进行估计。结果表明:不同细根类型单位面积生物量随径级(0—1、1—2 mm)及土层深度的增加变异增大,所需的取样数量也相应增加。Shapiro-Wilk检验表明,仅0—2 mm杉木细根和总细根单位面积生物量符合正态分布,其余各个细根类型不同径级不同土层单位面积生物量均不符合正态分布,均呈明显的右偏分布。蒙特卡罗统计模拟分析表明:在置信水平为95%、精度为80%的条件下,直径为0—1 mm、1—2 mm和0—2 mm的细根,杉木采集95、96、32个样品可以满足测定单位面积生物量的需要,林下植被分别采集98、98、63个样品可以满足测定单位面积生物量的需要,而总细根分别采集93、93、18个样品可以满足测定单位面积生物量的需要。

Spatial heterogeneity of fine roots and appropriate sampling methods in a subtropical Chinese fir plantation

Because of its high level of spatial heterogeneity, the fine root biomass of forest ecosystems can be accurately estimated only by adopting an appropriate sampling strategy. In this study, 100 soil cores each 1 m in length were taken from randomly distributed locations in a Chinese fir plantation at Sanming, in Fujian Province. Then, the soil cores were each divided into ten 10 cm sections. The cores were then washed with tap water, after which the roots were removed and separated into two diameter classes (0-1 mm and 1-2 mm). Dead roots and large living roots were discarded. In order to design a sampling strategy suitable for the study of fine roots in forest ecosystems, we examined the spatial heterogeneity of the distribution of fine roots of different types (Chinese fir, undergrowth vegetation, and total fine roots). The minimum sample sizes required to estimate fine root biomass were also calculated. The coefficient of variation (CV) and the required sampling sizes for different types of fine root biomass all increased with increasing diameter class (0-1 vs. 1-2 mm). As soil depth increased, the fine root biomass per unit ground area decreased in both diameter classes, and their respective CVs and required sampling sizes increased accordingly. With the exception of the 1-2 mm fine roots of undergrowth vegetation, which had a CV of 120% for biomass per unit ground area, all fine roots from different diameter classes and different root types had CVs of biomass per unit ground area consistently between 40%-90%. Meanwhile, the biomass per unit ground area of 0-2 mm roots of different types was characterized by medium variations. With the exception of 0-1 mm fine-roots in 0-20 cm and 50-60 cm soil depth, which exhibited medium variations in biomass per unit ground area, all fine roots of different diameter classes and different root types were characterized by high levels of variation. The total fine roots (0-2 mm) exhibited high levels of variation in biomass per unit ground area at all soil depths, except for the 0-10 cm and 10-20 cm depths, where there were medium variations. The Shapiro-Wilk test showed that, among different diameter classes and root types, only the biomass per unit ground area of the 0-2 mm fine roots of Chinese fir and the total fine roots were normally distributed; the roots of other diameter classes, soil depths, and types conformed to a noticeably right-skewed distribution. The minimum sampling sizes were estimated using the Monte Carlo simulation, at a confidence leve1 of 95% and with a precision level of 80%. To determine the biomass per unit ground area of 0-1 mm, 1-2 mm, and 0-2 mm roots, 95, 96, and 32 cores were needed for Chinese fir roots, 98, 98, and 63 cores were needed for understory roots, and 93, 93, and 18 cores for the overall roots. To estimate biomass per unit ground area for roots from the top soil layer to the lowest soil layer (at 10 cm intervals), 39, 63, 117, 97, 119, 94, 613, 318, 478, and 532 cores, respectively, were required for the 0-1 mm fine roots, 97, 168, 207, 302, 219, 333, 769, 598, 722, and 3168 cores, respectively, were required for the 1-2 mm fine roots, and 38, 59, 103, 125, 120, 123, 382, 262, 432, and 628 cores, respectively, were required for the 0-2 mm fine roots.