Influences of soil cadmium content on bind and fruit cadmium contentsin watermelon

Abstract:【Objective】Watermelons are Cucurbitaceae plants, which are juicy and sweet, refreshing andloved by people everywhere. It is a fruit for summer consumption. The Hunan region has a long history ofwatermelon cultivation, with its wide open areas, an annual planting space of about 140 000 hectares, whichranks fourth in the country, providing considerable economic benefit, and it also represents an importanthorticultural crop for the Hunan region. The increased development of the economy and society, the exploi⁃tation of minerals, smelting, transportation and the use of mineral fertilizers, has caused cadmium (Cd) to be⁃come one of the main pollutants in the environment. The most effective way to control Cd contaminated soilis to cultivate and grow crop varieties with a low accumulation of non-edible plants and edible organs.They will not only provide for the gradual elimination of cadmium in the soil, but also provide for the rational use of the land, and to ensure sustainable land output. Within the Hunan province, heavy metal exceedsthe standards as part of the adjustment of the planting structure, while also having a mild and moderate areathat makes it ideal for watermelon planting. However, cadmium exceeded the standard allowed in the production of the watermelon fruit, with the cadmium content in excess of the standard, and therefore, thethreshold value of the cadmium content of the soil and the cadmium content of the watermelon fruit is a significant issue of concern, and also represents an important reference for the planting structure adjustment.【Methods】By using the potted soil method, and respectively digging soil with different levels of cadmiumpollution in Zhuzhou County of Hunan Province as follows: T1 (Cd: 1.9 mg·kg- 1, pH 5.6); T2 (Cd: 3.59mg·kg-1, pH 5.34); T3 (Cd: 7.03 mg·kg-1, pH 5.48), detection of the Cd content、soil physical and chemicalindicator of the soil in the laboratory, and digging the soil from the experimental field of the College of horti⁃culture and landscape architecture, Hunan Agricultural University (Cd: 0.21 mg·kg-1, pH 5.12) for compari⁃son, we obtained a pot that is 44 cm wide, 48 cm long, 26 cm high. On April 10th, the following was imple⁃mented: 2 leaves and 1 heart of the watermelon seedlings were planted in a pot with 1 plant per pot, usingsingle vine pruning, with each plant having 1 melon. Our approach is to grow 5 pots per treatment, and repeat 3 times. Three of the watermelon plants which were consistent with the growth of the fruit were selectedfor further testing. The cadmium content of the roots, lower stem leaves (fruit section under section 4 tobase), middle stem leaves (4 section around the fruit), upper stem leaves (4 section from fruit to stem tip)and the fruit of watermelon were analyzed.【Results】The results show that the Cd content in the roots of allthe cultivars increased with the increase of Cd concentration in the soil, T3 > T2 > T1 > CK, The root Cdcontent in the‘Heimawangzi’was 2.64 times, 5.63 times and 6.02 times higher than that in the control. Inthe Cd content in the root‘Heimeiniang’, each treatment was 3.56 times, 4.56 times and 5.66 times higherthan in the control. The cadmium content in all treatments of the‘Heimawangzi’lower stem leaves in⁃creased by 2.04 times, 6.22 times and 10.80 times compared to the control; the cadmium content in thetreatments of the‘Heimeiniang’of the lower stem leaves were increased by 3.37 times, 4.79 times and10.3 times compared to the contro; 25.46 mg·kg-1 was the highest Cd content in the lower part of the‘Heimawangzi’in the T3 soil. The accumulation amount of Cd in the middle leaves was significantly lower thanthat in the lower part. The‘Heimawangzi’central stem and leaf cadmium content increased 137.57% ,432.56%and 611.18%, and th‘e Heimeiniang’for each treatment increased 227.2%, 380.31%and 756.95%compared to the control. The upper stems and leaves represent the tender newborn portions of the plants,and the accumulation of cadmium is relatively small. The contents of Cd in the upper leaves of the watermel⁃ons were significantly different in the various soil treatments. The‘Heimawangzi’of the upper leaves increased by 152.93%, 399.98% and 563.05% and the‘Heimeiniang’increased 170.54%, 418.82% and619.55% compared to the control. The Cd content in the watermelon fruit was positively correlated with theCd content in the soil, and increased with the increase of the Cd content in the soil. The cadmium contentof the watermelon fruits was lower than that of the national standard. T3 with high cadmium content in the‘Heimawangzi’reached 0.036 mg·kg^-1, 0.011 mg·kg^-1 higher than in the‘Heimeiniang’. The enrichmentcoefficient of Cd in the watermelon fruit was much lower than that in the root and stem. The Cd was primarily accumulated in the lower part of the stem and leaf, while the control was enriched in the root. The trans⁃fer coefficient of cadmium in different parts of the watermelon increased with the increase of the cadmiumcontent in the soil.【Conclusion】According to the fitting equation of the cadmium content in the soil andfruit of the different cadmium contents during the fruit ripening stage，we observed that the fruit cadmiumcontent reached the national standard allowable value 0.05 mg·kg^-1, and the soil cadmium content‘Heimawangzi’and‘Heimeiniang’corresponded to the 10.04 mg·kg^-1, and 12.69 mg·kg^-1 values.