Department of Chemistry, Ashland University, Ashland, OH 44805, USA.
J Chem Ecol. 2009 Nov;35(11):1279-87. doi: 10.1007/s10886-009-9711-8. Epub 2009 Nov 10.
The difficulties of monitoring allelochemical concentrations in soil and their dynamics over time have been a major barrier to testing hypotheses of allelopathic effects. Here, we evaluate three diffusive sampling strategies that employ polydimethylsiloxane (PDMS) sorbents to map the spatial distribution and temporal dynamics of root-exuded thiophenes from the African marigold, Tagetes erecta. Solid phase root zone extraction (SPRE) probes constructed by inserting stainless steel wire into PDMS tubing were used to monitor thiophene concentrations at various depths beneath marigolds growing in PVC pipes. PDMS sheets were used to map the distribution of thiophenes beneath marigolds grown in thin glass boxes. Concentrations of the two major marigold thiophenes measured by these two methods were extremely variable in both space and time. Dissection and analysis of roots indicated that distribution of thiophenes in marigold roots also was quite variable. A third approach used 1 m lengths of PDMS microtubing placed in marigold soil for repeated sampling of soil without disturbance of the roots. The two ends of the tubing remained out of the soil so that solvent could be washed through the tubing to collect samples for HPLC analysis. Unlike the other two methods, initial experiments with this approach show more uniformity of response, and suggest that soil concentrations of marigold thiophenes are affected greatly even by minimal disturbance of the soil. Silicone tube microextraction gave a linear response for alpha-terthienyl when maintained in soils spiked with 0-10 ppm of this thiophene. This method, which is experimentally simple and uses inexpensive materials, should be broadly applicable to the measurement of non-polar root exudates, and thus provides a means to test hypotheses about the role of root exudates in plant-plant and other interactions.
监测土壤中化感化合物浓度及其随时间变化的动态一直是检验化感作用假说的主要障碍。在这里，我们评估了三种扩散采样策略，它们使用聚二甲基硅氧烷（PDMS）吸附剂来绘制非洲万寿菊（Tagetes erecta）根系分泌的噻吩的空间分布和时间动态。通过将不锈钢丝插入 PDMS 管中构建的固相根区提取（SPRE）探针用于监测在 PVC 管中生长的万寿菊下不同深度的噻吩浓度。PDMS 片用于绘制在薄玻璃盒中生长的万寿菊下噻吩的分布。这两种方法测量的两种主要万寿菊噻吩的浓度在空间和时间上都非常多变。对根系的解剖和分析表明，噻吩在万寿菊根系中的分布也非常多变。第三种方法使用 1 米长的 PDMS 微管置于万寿菊土壤中，用于重复采样而不干扰根系。微管的两端都留在土壤外，以便溶剂可以冲洗通过微管收集用于 HPLC 分析的样品。与其他两种方法不同，这种方法的初步实验显示出更一致的响应，表明即使对土壤进行最小的干扰，万寿菊噻吩的土壤浓度也会受到很大影响。当用 0-10 ppm 的这种噻吩对硅胶管微萃取进行处理时，α-三噻吩的线性响应。这种方法实验简单，使用廉价材料，应该广泛适用于非极性根分泌物的测量，从而为检验根分泌物在植物-植物和其他相互作用中的作用的假说提供了一种手段。
