Mechanism by which PASP promotes plant enrichment of heavy metal Cd

Heavy metal cadmium (Cd) is a toxic element for living organisms, and Cd in cultivated soil seriously threatens human health, and removing Cd in contaminated soil is a necessary measure
to ensure the long-term safe use of soil.
Plant extraction (phytoextraction) is a green technology
to repair soil Cd pollution by using Cd high (ultra) enrichment plants to absorb and transport Cd in the soil to the aboveground part, and to remediate soil Cd pollution by harvesting plant material for harmless and resource treatment.
In addition to the uptake and enrichment capacity of plants for Cd, plant extraction efficiency is also closely related to soil conditions: on the one hand, effective nutrients in soil affect plant growth; On the other hand, the availability of Cd in soil directly determines the efficiency
of Cd uptake by plants.
Therefore, some soil amendments can be used to enhance the efficiency of plant extraction by increasing the bioavailability of mineral elements or heavy metals in the soil
.

Polyaspartic acid (PASP) is a fully degradable natural polymer with a wide range of applications
in agriculture and the environment.
The study found that PASP can effectively enhance the extraction efficiency of heavy metals from soil, but it is generally believed that PASP directly activates heavy metals or nutrients in soil through chelation, while ignoring whether the interaction between PASP and other soil factors (especially soil microorganisms) will have an impact
on plant enrichment of heavy metals 。 In order to further explore the method of enhancing the efficiency of plant extraction from the relevant mechanism, researchers from the Kunming Institute of Botany, Chinese Academy of Sciences and Yunnan Normal University studied the above problems with Bidens pilosa L.
, a highly enriched Cd plant
.

The researchers found that the addition of 3 and 6 g ^kg-1 of PASP in soil not only significantly increased the biomass of P.
< 0.
05), but also significantly (P < 0.
05) promoted the uptake of Cd by P.
ghost (Figure ¹), and finally increased the extraction efficiency of Cd by P.
ghost (total Cd enrichment in aboveground parts), respectively
。 The analysis of element content in rhizosphere soil showed that PAPS treatment significantly changed the availability of soil elements (P < 0.
05), thereby effectively promoting the uptake
of Cd and nutrients.
In addition to the direct chelation of elements by PASP, the study found that PAPS treatment enabled plant rhizosphere to recruit a variety of plant growth promoting bacteria (Figure 2), which can promote the growth and vitality of Ghost Needle under Cd stress through various mechanisms, and some plant growth promoting bacteria can also indirectly activate Cd and nutrients
in soil by secreting organic acids, siderophores and other substances 。 Among them, some plant growth promoting bacteria with potassium dissolving function may increase the soil available K content by 3.
7~21.
7 times together with PASP, in addition to plant nutrition, the increase of effective K may also have an important regulatory effect
on plant enrichment Cd.
In addition, plant physiology and metabolome analysis found that a variety of detoxification processes involving antioxidant enzymes, amino acids, organic acids and lipids in the leaves of Ghost Needle were significantly induced (P < 0.
05), which was the intrinsic basis
for maintaining growth of Ghost Needle in the case of significantly increased Cd intake.

The above results show that PASA promotes the growth and enrichment of Cd by reshaping the rhizosphere environment of plants (especially the composition of microbial communities) and regulating plant metabolic processes, which promotes the understanding of the mechanism of soil chelating agent enhancement plant extraction efficiency, and provides theoretical guidance
for the joint enhancement of plant extraction efficiency of chelating agents and plant growth-promoting bacteria 。 Polyaspartic acid enhances the Cd phytoextraction efficiency of Bidens pilosa by remolding the rhizospheric environment and reprogramming plant The topic of metabolism was published in
Chemosphere, a well-known journal in the field of environmental science.
Dr.
Li Xiong and Dr.
Tian Liyan (Yunnan Normal University) are co-first authors of the paper, and Professor Xu Jianchu and Professor Yang Yongping are the co-corresponding authors
of the paper.
The research was supported
by the Youth Innovation Promotion Association of the Chinese Academy of Sciences (2020387) and the Key Project of Basic Research Program of Yunnan Province (202101AS070045).

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Fig.
1 Effects of PASP treatment on growth and Cd enrichment of Ghost Needle Grass

Fig.
2 Changes in abundance of plant rhizosphere bacterial taxa (genus level) under PASP treatment (red font indicates potential plant growth-promoting bacteria)