不同水分供应对塔里木河下游土壤种子库种子萌发的影响

Effect of different water treatments on the germination of soil seed bank at lower reaches of Tarim River

基于国内外在土壤种子库研究中对种子萌发方法认识的基础上,选择不同水分处理下开展了塔里木河下游三个典型退化区土壤种子库的种子萌发实验,目的是:(1)验证不同水分梯度下土壤种子库萌发的数量和种类存在明显差异,从而为今后选择适宜水分条件进行土壤种子库研究提供依据;(2)通过土壤种子库的萌发实验,找出一个最适宜于本区植被种子萌发的土壤水分区间。实验于2005年3月和8月分别进行。在第一次实验中,以本区沙土地平均的饱和含水率28%为基准,选择5.6%、11.2%、16.8%、22.4%、28%和33.6%等6个水分梯度进行种子库种子萌发的实验,从萌发结果看,萌发种子的数量和种类在不同水分处理下有较显著的差异,其中当土壤含水量在12%以下几乎没有种子萌发,而后随着水分梯度的增大,萌发种子的数量和种类有一个明显的增加,但当水分梯度超过饱和含水率后萌发种子的数量和种类也呈下降的趋势;相应地,根据首次实验的结论又进行了第二次萌发实验,通过设定16.8%、22.4%、23.2%、24.4%、25.6%、26.8%、28.0%、30.5%和33.6%等9个水分梯度的种子萌发实验,发现塔里木河下游土壤种子库中出现的不同植物的种子均有各自独特的髓水分变化的萌发规律,而多数植物种子萌发的最大值并不是在饱和含水率或超过这一水分条件下,而是在稍低于饱和含水率时,如胡杨和柽柳在土壤种子库中的种子均是在25.6%时出现萌发数量的最大值,而这对于指导今后开展的恢复实践是有意义的。通过对萌发实验结果的讨论,可以得出以下初步的结论或建议:(1)在土壤种子库研究中由于水分梯度选择上的差异将会造成土壤种子库实验结果在种子数量和种类上均出现较大的差异,因此必须根据研究区生境的特点选择适宜的水分梯度;(2)从塔里木河下游主要建群植物恢复的角度考虑,目前从理论上看,最适宜塔里木河下游天然植被种子萌发的土壤水分区间是[23.2%,26.8%]。

On the basis of cognitions of seed germination methods in studies from home and abroad on soil seed bank, the seed germination experiments of soil seed bank were carried out under different water treatments in three zones in lower reaches of Tarim River. Average saturated water content 28% as the reference of the sandy land in this area, the first experiment was gone under six water gradients 5.6%, 11.2%, 16.8%, 22.4%, 28% and 33.6%, and the results showed that germinated seeds under different water treatments differed significantly in number and species, of which, few seeds germinated when soil water content was below 12% then both number and species of germinated seeds increased obviously along with water gradient enlarging and decreased when water gradient was higher than the saturated water content. According to above results, the second germination experiment was made at nine water gradients 16.8%, 22.4%, 23.2%, 24.4% 25.6%, 26.8%, 28.0%, 30.5% and 33.6%, revealing that seeds of different plant species in the soil seed bank in lower Tarim River had their unique germinating laws with water dynamics and that the maximum germinating of most plant seeds appeared neither at the saturated water content nor at higher but at a little lower water content, such as Populus euphratica and Tamarix spp. at 25.6%, which was meaningful for future restoring practice. On these results, the paper got the following conclusions ： （ 1 ） different water gradients in soil seed bank studies would make experimental results great different in number and species, thus it was necessary to select suitable water gradients according to the habi- tat characteristic of the study area; （2） considering to the restoration of the main constructive plants in lower reaches of Tarim River, the most optimum soil water interval for natural vegetation seeds germinating was [ 23.2%, 26.8% ] in theory at present.