A tremendous high number of herbal products such as spices, herbal teas, or phytopharmaceuticals, contain significant amounts of toxic alkaloids. These widespread contaminations are mainly due to the uptake of alkaloids from the soil. Due to their alkalinity, it is obvious that the import of alkaloids is strongly affected by the pH of the rhizosphere. This so far unconsidered issue was analyzed in a model study by applying various alkaloids to hydroponically grown barley seedlings, adjusted to several pH values, i.e., 5, 6, 7, and 8. In most cases, the resulting concentration of the alkaloids imported into the barley leaves ranged from about 0.8 to 7.7 μmol/g d.w. However, caffeine was imported to a higher extent, resulting in concentration up to 19 μmol/g d.w. In contrast, the uptake of monocrotaline (0.04–0.13 μmol/g d.w.) and atropine (just traces) was quite lower. For sparteine, no uptake was recorded. Apart from caffeine, the uptake of alkaloids strongly depends on the pH in the medium. Accordingly, these experiments demonstrated the significance of the rhizosphere pH for the alkaloid uptake. Both parameters, the overall concentration of alkaloids as well as the share of the unprotonated alkaloids, are determined by the pH. Accordingly, for the first time, it became obvious that the alkaloidal contaminations of plant derived commodities significantly depend on the pH of the rhizosphere during the cultivation of the crop plants. Moreover, the extent of alkaloid accumulation in acceptor plants is also influenced by the rate of transpiration. In consequence, the uptake of the various alkaloids and its pH-dependency might be quite different and no general prediction on the extent of alkaloid uptake can be made.

大量的草药产品（例如香料，凉茶或植物性药物）都含有大量的有毒生物碱。这些广泛的污染主要是由于从土壤中吸收了生物碱。由于它们的碱度，显然生物碱的输入受到根际pH的强烈影响。在模型研究中，通过将各种生物碱应用于水培大麦幼苗，并调节至多个pH值（即5、6、7和8），对这一至今尚未考虑的问题进行了分析。大麦叶的范围从约0.8到7.7μmol/ g dw。但是，咖啡因的进口量较高，导致浓度高达19μmol/ g dw。相反，单芥子碱的摄取量为（0.04-0.13μmol/ g dw ）和阿托品（仅微量）较低。对于斯巴汀，未记录到摄取。除咖啡因外，生物碱的摄取在很大程度上取决于培养基中的pH。因此，这些实验证明了根际pH对于生物碱吸收的重要性。这两个参数，即生物碱的总浓度以及未质子化生物碱的份额均由pH值决定。因此，第一次变得明显的是，植物来源商品的生物碱污染在农作物的栽培过程中极大地取决于根际的pH。而且，受体植物中生物碱积累的程度也受蒸腾速率的影响。结果，