投加石灰石和菱镁矿对酸化土壤上马尾松(Pinus massoniana)林的影响

Effect of limestone and magnesite applications on masson pine(Pinus massoniana) forest growing on acidified soil

为了确定酸化森林生态系统的修复效果,在重庆铁山坪的马尾松林内设立了6个10m×10m的样地,其中2个作为对照样地,另外4个分别在土壤表面施撒石灰石和菱镁矿粉末,各有2个重复。在处理前和处理1a后的生长季末各进行了一次植被观测,协方差分析和多重比较的结果显示投加修复剂对马尾松生长的影响已经初步显现,马尾松的胸径增量和针叶平均长度都有显著的增加,而针叶中Ca、Mg元素含量也表现出显著的差别。另外,立木更新的变化、细根生物量的增加和物种多度的变化也较明显,总体来说生态系统有恢复的趋势。土壤上层细根的增加较快,这与在土壤表面施撒修复剂,上层土壤的化学变化较显著是一致的。而两种修复剂对生态系统的影响也表现出明显的差异,相对而言,施撒菱镁矿的效果可能会更好。由于土壤修复的效果是长期的,其影响观测还将继续下去。

The effects of limestone and magnesite additions on masson pine （Pinus massoniana） forest growing on acidified soil were studied at Tieshanping, Chongqing in Southwest China. The site receives very high sulfur deposition （about 16g·m^-2 a^-1 measured in canopy throughfall） and severe forest defoliation and mortality are observed. The pH value of soil is in the range of 3.6-4.2, much lower than what considered optimal for masson pine （4.5- 6.0）. A field manipulation experiment was set up in 2003 in a planted 40 year old masson pine stand. 6 adjacent sample plots of 10 × 10 m2 were divided into two blocks of three plots each. Within each block, one plot was randomly assigned to one out of three treatments. The three treatments consisted of two different liming treatments （one-time addition of 30 kg limestone and 25 kg magnesite respectively on the soil surface in December 2003） and a reference treatment. The magnesite powder was much coarser than the limestone. To find the effect of such treatments, ecological investigation was first carried out in November 2003 and redone in November 2004, including the measurement of tree height and diameter at breast height （ DBH）, evaluation of crown color and crown density, collection of needles and fine roots, and analysis of ground vegetation. The comparison of the results before and after the treatments indicates that some ecological responses may be visible already after one year. The average increments of DBH in limestone and magnesite treated plots were 0.43 and 0.38 cm respectively, much higher than 0.27 em in reference plots （with the significance of p 〈 0.005）. The average needle density and biomass did not change significantly after liming （p 〉 0.05）, but the average needle length in the magnesite-treated plots was remarkably higher than that in reference plots （p 〈 0.005）. The biomass of fine roots in the upper 30era of the soil increased in all plots （including reference plots）, with larger increment in the treated ones. This indicates that liming may increase the root biomass production. The average increments of fine root biomass were 0.16, 0.32, and 0.67 kg/m3 in the upper 10 cm soil layer from the reference, limestone-treated, and magnesite-treated plots respectively, 0.20, 0.17, and 0.35 kg/m^3 in the middle 10 em layer, and - 0.07, 0.15, and 0.21 kg/m^3 in the lower 10 cm. Hence, the change of root biomass was more notable in upper layer of soil than lower. Although most studies in Europe indicated that there was no increase in tree growth in general as a result of liming, it seems that application of limestone and/or magnesite in this study could increase the growth of masson pine. The treatment also had effects on the biodiversity of ground vegetation, for instance decreased the abundance of oxyphilic species such as Miscanthus sinensis and Dicranopteris pedata quickly. The five 1 x 1 m2 quadrates in each limestone-treated plot lost on average three clusters of Miscanthus sinensis and five clusters of Dicranopteris pedata, and the magnesite-treated plots lost on average 10 and 18, respectively. Many seedlings were found in the treated plots, so were several dead saplings of oxyphilic plants such as Camellia sinensis. In contrast, very few seedlings and several dead saplings of Cunninghamia lanceolata and Quercu^fabri were found in the reference plots. In conclusion, the two treatments show different effects on the ecosystem. In addition to the DBH and average needle length of masson pine, the Ca and Mg content of needle in magnesite-treated plots was remarkably higher than that in limestone-treated plots. It seems that the addition of magnesite is more effective for increasing forest growth than limestone. It should also be noted that the Ca and Mg content of needle in limestone-treated plots was even lower than that in reference plots, which indicates that the addition of Ca only with large amount may cause deficiency of other nutrient elements such as Mg. Long term follow up of controlled liming experiments should be conducted before conclusions regarding large scale applications are drawn.