四个典型温带树种不同根序细根分解速率及其主要影响因素

Decomposition of different root branch orders and its dominant controlling factors in four temperate tree species

细根分解是森林生态系统土壤碳和养分的主要输入途径,但目前人们对于影响细根分解的主要因素和细根分解模式的了解仍然很少。该研究采用根序划分等级方法,将红松(Pinus koraiensis)、落叶松(Larix gmelinii)、水曲柳(Fraxinus mandschurica)和白桦(Betula platyphylla)细根组分前四级根划分为两个等级:一级和二级根混合为低级根,三级和四级根混合为高级根。利用埋袋法对东北地区4个树种不同根序细根进行连续4年的分解实验,并对其分解速率以及影响因素进行研究。结果显示,红松低级根和高级根分解系数分别为0.342和0.461,落叶松依次分别为0.304和0.436,水曲柳分别为0.450和0.555,白桦为0.441和0.579。4个树种均显示低级根分解速率较慢,而高级根分解速率较快。实验表明,根系分解系数与酸不溶性物质(AUF)和非结构性碳水化合物(TNC)均具有显著相关性。出现上述结果的主要原因是低级根含有较多的AUF,很难被分解,以及含有较少的TNC,为分解者提供能量较少。

Aims Fine root decomposition is the major pathway of carbon and nutrient input to the soil in forest ecosystems. However, the patterns and controlling factors of the decomposition of these roots, especially the finest roots, are poorly understood. Methods Using a root branch-order classification, we separated the first four orders of fine root systems of Pinus koraiensis, Larix gmelinii, Fraxinus mandschurica and Betula platyphylla into two classes: first- and second- order roots combined into lower-order; third- and fourth-order roots combined into higher-order. We conducted a four-year field litterbag study on decomposition of these four root orders of four temperate tree species in northeast China. Important findings The results showed that the lower-order and higher-order roots had a decomposition rate constant of 0.342 and 0.461 for Pinus koraiensis, 0.304 and 0.436 for Larix gmelinii, 0.450 and 0.555 for Fraxinus mandschurica, and 0.441 and 0.579 for Betula platyphylla, respectively. We observed slower decay rates in lower-order than in higher-order roots in all four studied tree species. The root decay constants (k) was significantly correlated with both acid-unhydrolyzable fraction (AUF) and total non-structural carbohydrate (TNC). We concluded that slow decomposition of lower-order roots was mainly driven by their high AUF and low TNC concentrations.