Effect of Environmental Factors on Cd Accumulation of Tagetes erecta L._水生态环境综合治理与保护（江西水问题研究与实践丛书）-QQ阅读男生玄幻网

书名：水生态环境综合治理与保护（江西水问题研究与实践丛书）
作者名：江西省水利科学研究院
本章字数：3539字
更新时间：2021-04-16 21:51:38

Effect of Environmental Factors on Cd Accumulation of Tagetes erecta L.

Shasha，Fu

Jiangxi Provincial Institute of Water Sciences

Xinfa，Xu

Jiangxi Provincial Institute of Water Sciences

Rongfang，Li

Jiangxi Provincial Institute of Water Sciences

Peidong，Tai

Institute of Applied Ecology

A hydroponic culture experiment was conducted to study the effect of temperature and nutrient level on Cd accumulation in Tagetes erecta L..In the first experiment，shoot Cd accumulation and transpiration rate at different temperature was determined.Cd accumulation was lower with higher transpiration rate at 35℃ than that of 25℃ or 15℃ with lower transpiration rate.In the other experiment，cadmium accumulation of plants varies significantly under the condition of different nutrient supplication.Contents of Cd in roots were not high，but the contents of Cd in shoots were the highest when plants were cultivated in 0.05-fold Hoagland's solution.Roots Cd accumulation decreased as the concentration of single nutrient element（N，P，S）decrease or absence，and shoots Cd accumulation decrease in the condition of sulfur deficiency and sulfur absence.It was shown that transpiration is not the primary factor affecting Cd accumulation in Tagetes erecta L.，but growth rate of plants has certain correlation with Cd accumulation；contents of Cd in roots are most affected by the supplication of nutrient elements，yet shoots accumulation is relatively lagging behind；different nutrient element has some different effect on Cd accumulation，and the effects of nitrogen and sulfur on the shoots Cd accumulation are the greatest.

关键词:cadmium-temperature-nutrient level-accumulation

1 Introduction

Cadmium is a highly toxic heavy metal for all living organisms.It is released into the environment by industrial discharges，mining wastes，and so on.Environmental remediation using plants to accumulate heavy metals has been proposed，termed phytoextraction；the phytoextraction of Cd from contaminated soils is indicated in some cases^［1］.Hyperaccumulation of Cd in higher plants is a rare phenomenon.The mechanisms of Cd accumulation have not been clear.

Environmental temperature and nutrient levels are closely related to the plant growth that may have an important impact on Cd accumulation，but it is not widely reported that the effect of temperature on Cd accumulation of plants or some correlative study on the mechanism.Nitrogen，phosphorus and sulfur are macronutrient of plants and they are required for synthesis of protein，nucleic acids and phospholipids.In addition，they are structural constituents of Cd chelating ligands ^［2-7］ or may affect the synthesis of these ligands.Therefore，N，P and S nutrition may play important roles in Cd accumulation.Much research has been done to study the effect of N or P nutrition on plant Cd accumulation ^［8-13］.However，there was no consistent conclusion about the relationship between the N，P level and Cd accumulation.There have been few studies concerning the effect of S nutrition on Cd accumulation^［¹⁴^，¹⁵^］.The relationship between N，P or S nutrition and Cd accumulation in plant tissues is of great significance in our understanding Cd accumulation mechanisms.Although some papers have investigated the effect of N，P or S nutrition on Cd accumulation，the results are not completely consistent and the mechanisms are still unclear.

（T.erecta）is a popular and common horticultural plant in China.It not only has the ornamental value，but also has important economic value.The results of Lal et al.^［16］ showed that T.erecta had a potential to be an alternative crop for phytoremediation of soil and providing other environmental benefits like minimizing the risks of Cd entering into the food chain.In view of this，T.erecta was chosen as the test plant in the present study.The effect of temperature，N，P and S on growth and Cd accumulation in T.erecta was studied under hydroponic culture condition for the purpose of illuminating the mechanism of Cd accumulation in T.erecta and providing some theoretical basis for the phytoremediation of Cd contaminated soil.

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2 Material and methods

2.1 Plant Material

Seeds of T.erecta were bought from Shenyang Agricultural University.The seeds were germinated in water-soaked vermiculite，and transferred for further growth in pots with 500mL full Hoagland's solution（HS）.Each pot contained one seedling.Pots were kept in a culture chamber with temperature of 25℃ and 12h day（photon flux density of 200μmols^-1m^-2）/night cycle.The solutions were replaced every 3 days.

For the two experiments，healthy seedlings of about 3 g fresh weights were selected.The plants were treated with 0.1mg Cd L^-1（added as CdCl₂·2.5H₂O solution），a concentration which is nonphytotoxic to T.erecta and other details as described below.At least three seedlings were used for each treatment.

2.2 Experiment Design

Effect of temperature on Cd accumulation（Experiment 1）.Seedlings of T.erecta were cultivated in illumination incubators at the temperature of 15℃（low temperature），25℃（optimum temperature）and 35℃（high temperature）respectively，and sampled after 1～5 days.Net photosynthetic rate and stomatal conductance were determined by the portable photosynthesis analyzer（LI6400，LI-COR）.Transpiration was determined by weighting the water loss.

Effect of nutrient level on Cd accumulation（Experiment 2）.0.05-fold HS and 0.25-fold HS were prepared by dilution of Cd-containing HS by a factor of 20 and 4，respectively.The nutrient solution of sulfate absence（0 S），sulfate deficiency（0.25 S），phosphate absence（0 P），phosphate deficiency（0.25 P），nitrate absence（0 N）and nitrate deficiency（0.25 N）were prepared by replacing sulfate salts（Mg²⁺，Mn²⁺，Zn²⁺，Cu²⁺），monopotassium phosphate（KH₂PO₄）and nitrate salts（KNO₃，Ca（NO₃）₂）in complete Hoagland's nutrient solution by appropriate amounts of chloride salts in the preparation of the Cd-containing HS，respectively.The control of this experiment was the normal plants grown in Cd-containing HS.The plants were harvested after 15 days treatment.

Determination of Cd content.At the time of harvest，plants were divided into roots and shoots and then fresh weighs were determined.Plant samples were successively washed thoroughly in tap water，distilled water and double distilled water.The Cd level was determined by atomic absorption spectrophotometer after wet-ashing of dry mater in a HNO₃/HClO₄ mixture（4：1，v/v）［17］.

2.3 Results

Effect of temperature on Cd accumulation.Temperature has significant impact on the transpiration rate，net photosynthetic rate，growth rate（Table 1 and Fig.1）.It was shown that the higher temperature is，the greater transpiration rate is.The transpiration rate of plants cultivated at 35℃ is about two times that of plants at 15℃ and 25℃.The net photosynthesis rate was the least when temperature is 15℃，and there is not any difference between that of 25℃ and 35℃.Temperature also significantly affected the growth of plants.The growth rate was the highest at 25℃ and plants almost stop growing at 35℃.

Table 1 Physiologic indexes of marigold under different temperatures and illuminations

Fig.1 The effect of temperatures on transpiration rate

Cd accumulation in shoots increased gradually with Cd exposure duration increasing，no matter what the cultivation temperature is（Fig.2）.Cd content in shoots was the highest at 25℃；followed by 15℃，Cd content was about two-thirds of content at 25℃；when the cultivation temperature is 35℃，the value was the lowest which is less than half of content at 25℃.The differences of Cd content were more and more with the growing cultivation periods.

Fig.2 The effect of temperatures on Cd accumulation in shoots

Fig.3 The effect of temperatures on Cd accumulation in roots

Temperature also had some influence on Cd content in roots（Fig.3）.Cd content in roots was the least when temperature is 35℃，and there is no difference between that of 15℃ and 25℃.The order of Cd concentration in roots was 25℃&gt；15℃&gt；35℃ in 5 days.

Effect of nutrient level on Cd accumulation.Biomass and root-shoot ratio were also determined in the treatment of 0.1mg Cd L^-1 and different nutrient levels（Fig.4）.The plants growing in normal nutrient solution（1 Hoagland）containing 0.1mg Cd L^-1 were selected as the Control in this experiment.It could be seen that plants biomass in most treatment were less than that of Control，except for the sulfate absence（0 S）and sulfate deficiency（0.25 S）.All of data did not have significant difference（p&lt；0.05）.However，root-shoot ratio were impacted significantly.Compared to the Control，the ratios increased significantly in the treatment of phosphorous deficiency，nitrogen deficiency and nitrogen absence，but decreased significantly in the treatment of sulfur deficiency.

Fig.4 The effect of nutrient levels on biomass and root-shoot ratio

Cd accumulation in roots and shoots varied from different treatments of nutrient solutions（Fig.5，Fig.6）.Cd contents in shoots were less impacted by the level of nutrient.Few differences were observed in most treatments，except for the treatments of sulfate absence（0 S）and sulfate deficiency（0.25 S）.Cd contents in shoots of these two treatments were about 30%less than that of Control.

Fig.5 The effect of nutrient levels on Cd accumulation in shoots

Fig.6 The effect of nutrient levels on Cd accumulation in roots

Cd contents in roots were more impacted by the level of nutrient.The contents in most treatments were 30%～60%less than that of Control，except for treatment of 0.25 Hoagland in which Cd content was almost the same as that of Control.

3 Discussion

Temperature and nutrition are both key factors of plant growth.At the same time，they have effects on the Cd accumulation and adsorption in T.erecta in different degrees（Fig.2，Fig.3，Fig.5，Fig.6）.

The growth rate of plants is low at low temperature（15℃），so that the amount of Cd accumulation in shoots is relatively low.The growth rate of plants is the lowest in high temperature stress（35℃），and the amount of Cd accumulation in shoots is still the lowest，despite of the highest transpiration.It can be seen that Cd accumulation in shoots does not depend on transpiration.This is consistent with the results of Perfus-Barbech et al.^［18］They made a comparison of Cd accumulation between two types of Arabidopsis thaliana L.（mutant abi1-1 and wild-type）which have different transpiration rate，and did not find any differences，so they speculated that metal ions uptake of plants does not depend on the transpiration.However，there are some opposite views.For example，Salt et al.^［19］found that contents of Cd in leaves of B.juncea treated with ABA decreased rapidly，so they suggested that Cd accumulation in leaves depend on the transpiration.As few research about the mechanism of Cd accumulation in shoots have been reported，there are still disputes on this issue which needs further research.

The growth rate of plants is the highest at the optimum temperature（25℃），and the amount of Cd accumulation in shoots is also the highest，correspondingly.There are not much differences of Cd contents in roots when the cultivation temperature is 25℃ and 15℃，but are higher than the value at 35℃.The higher growth rate is the more Cd accu mulation in shoots is，but has not any significant effect on Cd accumulation in roots.That implies high temperature（35℃）seriously interfere with the metabolism of T.erecta.As a result，Cd accumulation is depressed significantly both in shoots and roots.That only the amount of Cd accumulation in shoots at 15℃ is significantly less than the amount at 25℃ can be attribute to the lower growth rate of plants.So Cd accumulation in shoots of T.erecta maybe closely relate to the growth.

Low level of nutrient supplication has not great impact on the growth rate in short period，and even increases the plant biomass in some conditions.Deficiency or absence of singular nutrient element does not affect biomass significantly，but maybe significantly increases the root-shoot ratio（such as phosphorous deficiency，nitrogen deficiency and nitrogen absence）.

The amount of nutrients affects Cd accumulation of T.erecta in different degrees.Overall speaking，the nutrients have more effects on the Cd accumulation in roots.Plants living in the condition of nutrition deficiency may satisfy the need of shoots firstly，and then may satisfy the need of roots.As a consequence，lack of nutrients in roots will be firstly observed which is consistent with the trend of Cd amounts in roots.Cd accumulation is the lowest in roots and the highest in shoots in the treatment of 0.05 Hoagland.Deficiency or absence of singular nutrient element decrease Cd accumulation in roots of T.erecta in different degrees and sulfur deficiency or absence lead to the decrease of Cd amount in shoots.It is well known that nitrogen，phosphorous and sulfur are not only the essential nutrients to the growth of plants，but also the important elements which may constitute the Cd-ligands in plants，such as metallothionein，phytochelatins，glutathione，amino acids，phosphates and so on.^［²⁰^，²¹^］It can be suggested that nutrients deficiency or absence will change the synthesis of ligands and thus affect Cd accumulation in plants.

In conclusion，temperature and nutrients obviously affect Cd accumulation of T.erecta.Transpiration is not the primary factor affecting Cd accumulation in T.erecta，but growth rate of these plants has certain correlation with Cd accumulation；contents of Cd in roots are most affected by the supplication of nutrient elements，yet shoots accumulation is relatively lagging behind；different nutrient element has some different effect on Cd accumulation，and the effects of nitrogen and sulfur on the shoots Cd accumulation are the greatest.

Acknowledge

The authors would like to thank Special Fund for Water resource-scientific Research in the Public Interest（No.201001054），National Science Foundation of China（No.21077113），National Science Foundation of China（No.20977095）and Innovative Program of the Chinese Academy of Sciences（KZCX2-YW-446）for financial support to this research.