Influences of stand, soil and space factors on spatial heterogeneity of leaf area index in a spruce-fir valley forest in Xiao Hinggan Ling, China

YANG Huan-Ying, SONG Jian-Da, ZHOU Tao, JIN Guang-Ze, JIANG Feng, LIU Zhi-Li

Chin J Plant Ecol 2019, 43 (4): 342-351. DOI: 10.17521/cjpe.2018.0310

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AimsSpatial heterogeneity of leaf area index (LAI) is very important for exploring the growth and spatial distributions of plants, as well as response strategy of plants to climate changes. Many previous studies have shown that biotic and abiotic factors had significant influences on spatial heterogeneity of LAI. However, few studies have been conducted to show the relative contributions of different influencing factors to the total variations of LAI. Our aim was to quantify the relative contributions of stand, soil and space factors to the total spatial variations of LAI in a spruce-fir valley forest in northeast China.
MethodsWe relied on a 9.12 hm ² (380 m × 240 m) spruce-fir valley forest plot in Xiao Hinggan Ling, China, which was divided into 228 subplots (20 m × 20 m). First, we measured LAI for each subplot by using the LAI-2200 plant canopy analyzer and then analyzed the spatial heterogeneity of LAI using geo-statistic methods (semivariogram and Kriging interpolation). Second, we measured 28 stand factors and 10 soil factors for each subplot, and quantified space factors using principal coordinates of neighbor matrices (PCNM). Finally, we quantified the relative contributions of stand, soil and space factors to the total spatial variations of LAI using the variance partitioning method.
Important findings The results showed that strong spatial autocorrelations of LAI values within 37 m distances in the spruce-fir valley forest, and the LAI presented different spatial patterns along distinct directions. The stand, soil and space factors totally explained 50.4% of the total spatial variations of LAI in the forest plot. The space factors explained greater spatial variations of LAI in relative to stand and soil factors, and solely explained 25.5% of the total spatial variations. The density of middle tree group (5 cm < diameter at breast height ≤ 10 cm) and basal area of major tree groups (including Abies nephrolepis and Picea spp.) were both significantly and positively correlated with LAI; and soil mass moisture content was significantly and negatively correlated with LAI. These results generally suggest that the spatial autocorrelation is more important than stand factor and soil factor for determining spatial heterogeneity of LAI of the spruce-fir valley forest in Xiao Hinggan Ling, China.

在林分因子中, 中等树密度(p < 0.001)、主要树种BA (p < 0.001)和全部树阔针比(p < 0.05)显著影响LAI的变异, 分别解释了LAI变异的17%、5%和2%。对于土壤因子, 容重(p < 0.05)和质量含水率(p < 0.01)显著影响LAI, 分别解释了LAI变异的4%和2% (表2)。在谷地云冷杉林内, 5个显著因子均具有较大的变异, 变异系数范围39%-118% (表3)。3个林分因子均与LAI显著正相关, 而2个土壤因子均与LAI显著负相关, 但全部树阔针比和容重与LAI的相关性较弱(图6)。

在10个土壤因子中, 容重和质量含水率对谷地云冷杉林LAI的空间变异具有显著影响(图6)。土壤容重是指单位体积的土壤重量(g·cm-3), 其对土壤的物理结构和化学性质都有重要影响, 随着土壤容重的增大, 会使土壤变得硬实, 从而降低土壤透气性(郑纪勇等, 2004), 因此, 过大的土壤容重通常会抑制植物叶片生长(Oussible et al., 1992; Andrade et al., 1993), 进而造成LAI的减小。质量含水率与LAI显著负相关可能源于该区域的谷地云冷杉林具有湿度大、温度低、土壤含水率较高等特点, 且土壤具有岛状永冻层分布(李文华, 1980)。然而, 随着近年来全球气温的不断上升(丁一汇和孙颖, 2006), 使得多年永冻层融化, 急剧增加了该林分的土壤含水率(王庆贵, 2004), 但当含水率持续增大时, 很可能会影响植物根系的呼吸作用, 从而限制植物的生长, 进而造成LAI的减小, 这很可能也是造成谷地云冷杉林内大面积树木死亡的一个重要原因。