# Linking Ecological Stoichiometry to Biomass Allocation in Plants Under Cadmium and Petroleum Stress in the Yellow River Delta

## TL;DR

This study shows how petroleum pollution affects plant growth in the Yellow River Delta by altering soil and plant nutrient ratios, and how adding nitrogen and phosphorus can help restore vegetation.

## Contribution

The study identifies petroleum as the main driver of changes in plant stoichiometry and biomass allocation in Suaeda salsa under combined cadmium and petroleum stress.

## Key findings

- Petroleum pollution increases soil C/N and C/P ratios, reducing plant nutrient uptake and biomass accumulation.
- Soil stoichiometric ratios have a greater influence on Suaeda salsa biomass allocation under petroleum stress than under control conditions.
- Adding nitrogen and phosphorus can mitigate the negative effects of petroleum pollution on plant growth.

## Abstract

Cadmium and petroleum contamination are among the major threats to the wetland ecosystem in the Yellow River Delta. Therefore, understanding how plants grow and regulate nutrient uptake under such pollution stress is essential for effective ecological restoration. Most scientists working in this field aim to understand how plants adjust the balance of carbon, nitrogen, and phosphorus to optimize biomass allocation and enhance the remediation potential in complex environments. Here, we provide evidence that petroleum pollution is the primary driver of changes in the stoichiometric characteristics and reductions in the biomass of halophytic plants (Suaeda salsa). Firstly, petroleum contamination significantly increases the soil carbon-to-nitrogen ratio and carbon-to-phosphorus ratio, thereby suppressing plant nutrient uptake. Secondly, this nutrient limitation leads to a decline in total biomass accumulation. As soil stoichiometric ratios play a dominant role in plant growth, appropriate supplementation with nitrogen and phosphorus can mitigate the adverse effects of pollution stress and improve restoration outcomes. Our findings have important implications for vegetation rehabilitation in the Yellow River Delta and provide a theoretical basis for the management of contaminated soils.

Cadmium and petroleum are the main pollutants in coastal wetland ecosystems that affect plant nutrient balance and growth. Scholars have discovered how saline plants adapt to single stresses. How plant ecology and physiology correspond to complex cadmium and petroleum pollution, especially regarding the pollution impacts on carbon (C), nitrogen (N), and phosphorus (P) stoichiometry and biomass allocation in coastal wetland plants, remains unclear, limiting their application in regard to pollution remediation. This study focuses on Suaeda salsa, a popular species used in vegetation restoration in the Yellow River Delta’s coastal wetlands. Through the use of pot experiments, the dynamic changes in plant–soil ecological stoichiometry and biomass allocation were systematically investigated in response to individual and combined cadmium (0, 5, and 10 mg kg−1) and petroleum (0, 6, and 12 g kg−1) treatments. Compared with the control (CK), petroleum stress significantly increased the total nitrogen (TN) and plant total phosphorus (TP) contents, but did not substantially impact the total carbon (TC) content, resulting in 19.7% and 26.6% decreases in the plant C/N and C/P ratios, respectively. The soil organic carbon (SOC) content increased significantly under petroleum stress, whereas the TN and TP contents did not notably change, considerably increasing the soil C/N and C/P ratios, which were 1.5 times and 1.3 times greater than those of the CK, respectively. Cadmium stress alone or with petroleum stress did not significantly affect the C, N, or P stoichiometry or biomass allocation in S. salsa. The soil C/N/P stoichiometry redundancy analysis revealed that the contribution rates (especially the soil C/P and C/N ratios) to the total biomass and its allocation in S. salsa (64.5%) were greater than those of the control group plants (35.5%). The correlation analysis revealed that the total growth biomass of S. salsa was negatively correlated with the soil carbon content, C/N ratio, and C/P ratio, but positively correlated with the plant C/N and C/P ratios. The aboveground biomass proportion in S. salsa was significantly negatively correlated with the soil N/P ratio. The belowground biomass proportion exhibited the opposite trend. Petroleum pollution was the main factor driving S. salsa stoichiometry and growth changes, increasing the soil C/N and C/P ratios, reducing the nitrogen and phosphorus nutrient absorption capacities in plant roots, limiting plant nitrogen and phosphorus nutrients, and inhibiting biomass accumulation. Appropriate N and P supplementation alleviated plant growth inhibition due to petroleum pollution stress, which was conducive to improving vegetation ecological restoration in the Yellow River Delta.