土壤重金属胁迫对桑树营养代谢的影响

Effects of Soil Heavy Metal Stress on Nutrient Metabolism of Mulberry Trees

摘要: 为了解决重金属污染土壤的合理利用及蚕桑产业可持续发展问题，选取桂西北某锰矿区周边受到不同程度重金属污染的12个桑园作为研究样地，以远离矿区的非污染区3个桑园作为对照样地，采集了调查样地的桑园土壤样品及桑树根部和桑叶样品，测定了土壤样品的基本理化特性及土壤和植物样品的铜、锌、铬、镉、锰5种重金属元素含量，还测定了桑叶样品的叶绿素、可溶性糖、水溶性蛋白质及总氨基酸含量，并对相关检测指标与桑叶营养代谢生理指标的相关性进行了比较分析，结果表明：1) 在被测的5种重金属元素中，锰含量最高，锌含量次之，调查样地桑园土壤及桑叶重金属含量的高低排序均为Mn > Zn > Cr > Cu > Cd，桑树根部重金属含量的高低排序为Mn > Zn > Cu > Cd > Cr，虽然不同重金属元素在桑树体内的累积情况不同，但大部分调查样地的重金属含量高低排序为土壤 > 根 > 叶；2) 在桑树营养代谢生理指标中，叶绿素含量与土壤pH呈显著的负相关，与土壤全磷和速效磷含量均呈极显著的正相关；3) 不同调查样地桑叶的可溶性糖、水溶性蛋白质及总氨基酸含量差异较大，而叶绿素含量差异相对较小。根据实验结果的分析讨论可知：1) 土壤重金属胁迫对桑树营养代谢各种生理指标均有一定的影响，其影响大小因重金属元素差异及作用浓度高低而不同；2) 在土壤重金属复合胁迫条件下，各种重金属元素之间存在复杂的相互作用，共同影响桑树的营养代谢过程；3) 桑树从土壤中吸收的重金属主要累积在根部，转移到地上部分叶片的重金属相对较少，低浓度的重金属对桑树营养代谢有一定促进作用；4) 桑树叶片中的重金属元素含量对其营养代谢具有直接的影响，而土壤中的重金属元素，则通过桑树根部的吸收和转运，间接影响桑树的营养代谢过程；5) 桑树具有较强的重金属抗耐性，在其耐受的范围内，可通过增加体内可溶性糖、水溶性蛋白质、总氨基酸等渗透调节物质的含量或其他代谢调节机制，增强其对重金属胁迫的抗性，从而维持正常的生长发育。

Abstract: In order to solve the problems of rational utilization of heavy metal polluted soil and sustainable development of the sericulture industry, 12 mulberry fields around a manganese mining area in northwest Guangxi were selected as research plots, and 3 mulberry fields in non-polluted areas far from the mining area were used as control plots. Soil samples of mulberry fields, as well as samples of mulberry tree roots and leaves, were collected from the survey plots, the basic physicochemical properties of soil samples and the content of five heavy metal elements, including copper, zinc, chromium, cadmium, and manganese, in soil and plant samples were determined. The chlorophyll, soluble sugar, water-soluble protein, and total amino acid content of mulberry leaf samples were also measured, and the correlation between relevant detection indicators and physiological indicators of mulberry leaf nutrition metabolism was compared and analyzed. The results showed that: 1) Among the five heavy metal elements tested, manganese content was the highest, followed by zinc content. The order of heavy metal content in the surveyed mulberry field soil and mulberry leaves was Mn > Zn > Cr > Cu > Cd, and the order of heavy metal content in the roots of mulberry trees was Mn > Zn > Cu > Cd > Cr. Although the accumulation of different heavy metal elements in the mulberry tree body was different, the order of heavy metal content in most surveyed plots was soil > roots > leaves; 2) In the physiological indicators of nutritional metabolism in mulberry trees, chlorophyll content is significantly negatively correlated with soil pH, and highly positively correlated with soil total phosphorus content and available phosphorus content; 3) There are significant differences in the content of soluble sugars, water-soluble proteins, and total amino acids in mulberry leaves from different survey sites, while the differences in chlorophyll content are relatively small. According to the analysis and discussion of the experimental results, it can be concluded that: 1) Soil heavy metal stress has a certain impact on various physiological indicators of mulberry tree nutrition metabolism, and the magnitude of the impact varies depending on the differences in heavy metal elements and the concentration of action; 2) Under soil heavy metal compound stress conditions, there are complex interactions between various heavy metal elements, which jointly affect the nutritional metabolism process of mulberry trees; 3) The heavy metals absorbed by mulberry trees from the soil mainly accumulate in the roots, and the heavy metals transferred to the aboveground leaves are relatively less. Low concentrations of heavy metals have a certain promoting effect on the nutritional metabolism of mulberry trees; 4) The content of heavy metal elements in mulberry leaves has a direct impact on their nutritional metabolism, while heavy metal elements in soil indirectly affect the nutritional metabolism process of mulberry trees through absorption and transportation by mulberry roots; 5) Mulberry trees have strong resistance to heavy metal stress. Within their tolerance range, they can enhance their resistance to heavy metal stress by increasing the content of osmoregulatory substances such as soluble sugars, water-soluble proteins, total amino acids, or other metabolic regulatory mechanisms, thereby maintaining normal growth and development.