幼龄柠条细根的空间分布和季节动态

以晋西北黄土高原区5年生柠条(Caragana korshinskii)人工林为研究对象,应用Minirhizotron技术,分别在距茎干水平距离0 cm和50 cm处设点(以下简称为0 cm位点和50 cm位点),对林地0—100 cm土层深度范围内的柠条细根进行了观测。以2009年生长季(4—10月)的细根根长密度(RLD,mm/cm2)和表面积密度(RAD,mm2/cm2)数据为基础,结合同期环境因子(气温、降雨量、土壤温度和土壤含水量等)数据,对0 cm和50 cm两个位点的细根动态特点进行了比较研究。结果表明:(1)两个水平位点的细根垂直分布和季节变化趋势均具有一定差异,主要差异是0 cm位点0—60 cm各土层的RLD均大于50 cm位点,前者各测定期的RLD(RAD)均大于后者。因此,0 cm位点的细根分布量(4.04 mm/cm2和4.67 mm2/cm2)显著大于50 cm位点(3.07 mm/cm2和2.99 mm2/cm2)。(2)就整体(两个位点平均值)而言,RLD(RAD)的垂直分布以40—50cm土层最大,以60—70cm土层最小。RLD(RAD)的季节变化具有由小变大再变小的趋势。年生长季幼龄柠条细根的RLD和RAD总平均值分别为3.55 mm/cm2和3.83 mm2/cm2。(3)就0 cm位点、50 cm位点或整个林地而言,细根RLD的季节变化与气温和土壤温度的季节变化均具有显著正相关性。以上结果表明,幼龄柠条细根的水平分布具有"近主根"特点;RLD的季节变化与温度因子的季节变化具有高度一致性。

The spatial distribution and seasonal dynamics of fine roots in a young Caragana korshinskii plantation

It is important and significant to know the spatial distribution pattern of fine roots for understanding the utilization status of the available resources belowground. The objective of this study was to investigate the fine root dynamics of Caragana korshinskii Kom, a shrub species widely planted to control soil erosion and land desertification in the semiarid area of China, in a 5-year-old plantation in the Loess Plateau area of Northwest Shanxi, China. Using the minirhizotron technique. The minirhizotron tubes were installed at two horizontal distances (0 cm and 50 cm) from the plant stems in the top 100-cm of soil. Based on the data sampled in the growing season (from April to September) of 2009, we analyzed the spatial-temporal patterns of fine root length density (RLD, mm/cm²) and fine root surface area density (RAD, mm²/cm²) in the plantation, and explored the relationships of RLD and RAD with the environment factors such as air temperature, soil temperature, rainfall and soil water content. The results showed that (1) there were certain differences in both vertical distribution patterns and seasonal change trends of fine roots between the two horizontal sites, and the obvious difference was that the values of RLD in the upper 0-60cm soil layers at the 0cm horizontal site were greater than those at the 50 cm horizontal site, and that the values of RLD (RAD) measured in every month for the former were larger than those for the latter. Therefore the RLD and RAD for the former (4.04 mm/cm² and 4.67 mm²/cm²) were significantly larger than those for the latter (3.07 mm/cm² and 2.99 mm²/cm²). (2) As a whole (for the average of two horizontal sites), the maximum value of RLD (RAD) appeared in 40-50 cm soil layer while the minimum value in 60-70 cm soil layer in the 100 cm soil profile. The RLD (RAD) showed a common seasonal trend with the peak value in the middle period of growing season. The total averages of RLD and RAD of fine roots in the growing season were 3.55 mm/cm² and 3.83 mm²/cm², respectively. (3) For 0 cm horizontal site, 50 cm horizontal site or the average of two horizontal sites (i.e. the plantation), the seasonal change course of RLD was significantly and positively related with air temperature and soil temperature, respectively. The above results showed that the horizontal distribution of the fine roots of young Caragana korshinskii was characterized by appearing mainly around the taproots, and the seasonal change trend of RLD was highly consistent with the change of temperature factor. Although the correlation coefficients between the seasonal change courses of RLD (RAD) and water indices (rainfall and soil water content) were not significant, this did not imply that fine root growth was not affected by water factor. Further research is required on the mechanisms of fine root dynamics in the annual growing season because of the internal and external controls of fine root growth.