## 2 Materials and Methods
### Test Method
#### 2.4.4 Vegetation Test  
Vegetation experiments were conducted after the compressive strength tests. PC was poured into 18 wooden moulds with dimensions of 400 \(\times\) 400 \(\times\) 200 mm, and a 50 mm natural soil layer was precisely placed on the concrete, which was able to retain water and fertilizer (Figure 2). Plant seeds were evenly sown in the soil at 10-12 g/m\({}^{2}\) according to the literature and then covered with a thin layer of natural soil (5 mm). Mature seeds of _Cynodon dactylon ([PERSON]_ and _Agrostis stolonifera_ (known as Bermuda grass) were purchased from commercial seed suppliers. Mature bamboo shoots of _Sasa argenteosteritus_, e.g., _Camus_, were transplanted from the nursery garden of Sichuan Agricultural University. The effects of the concrete content on seed germination and plant growth of each species were examined with a comparative experiment that included two concrete treatments based on the particle size of the aggregates, with three replicates, and three replicate tests were also conducted for each plant under normal cultivation conditions without PC underneath as control samples. The other environmental factors were controlled in the tests. The experiments were conducted in the nursery garden of Sichuan Agricultural  
Figure 2: Sketch of the planting concrete sample used for the vegetation test. University, exposed to a natural environment. The seeds and bamboo shoots were watered every two days during the experiments. The PC containers were randomly moved every week to prevent any positional influence according to previous studies [18]. Malondialdehydedehyde (MDA)  
When damage from drought and other types of stress occurs, lipid membrane peroxidation leads to the accumulation of malondialdehydedehyde (MDA), the denaturation of proteins and nucleic acids, a decrease in membrane fluidity, and an increase in membrane permeability. Therefore, the MDA content is a commonly used index to measure the effects of adverse conditions on plants [26]. MDA is produced by the peroxidation of lipids in plant tissues or organs when plants experience ageing or drought. The main equipment used was a spectrophotometer and a centrifuge [27]. The MDA content in the plant tissues was calculated with Equation (1):  
\[C=6.45(OD_{532}-OD_{600})-0.56 OD_{450}\] \[MDA=\frac{\left(C\times V\times 10^{-3}\right)}{W} \tag{1}\]  
In this equation, \(C\) is the MDA content in the plant tissues, \(\mu\)mol/L; \(OD_{532}\), \(OD_{600}\), and \(OD_{450}\) are the absorbance values at wavelengths of 532, 600, and 450 nm, respectively; \(C\) is the MDA concentration in the extract, \(\mu\)mol/L; \(V\) is the total extract volume, mL; and \(W\) is the weight of the material, g.  
Plants tend to accumulate compatible solutes such as proline to counteract saline-alkaline conditions or low-temperature stress. To a considerable extent, proline can decrease the cytoplasmic osmotic potential and enable water absorption [28]. Free proline (Pro) forms a stable red condensate with ninhydrin under acidic conditions. Pro has a maximum absorption peak at a wavelength of 515 nm, and the red product amount is proportional to its content; thus, the Pro content in plant tissues can be determined by the colorimetric method [29]. The main equipment is a spectrophotometer, centrifuge, and oscillatory mixer. The Pro content in the plant tissues was calculated with Equation (2):  
\[C_{\text{Pro}}=\frac{C_{X}*V}{g\cdot FW} \tag{2}\]  
In this equation, \(C_{\text{Pro}}\) is the Pro content in the plant tissues, \(\mu\)g/gfw; \(C_{X}\) is the Pro concentration in the sample solution, \(\mu\)g/mL; \(V\) is the total extract volume, mL; and \(g\)\(FW\) indicates the fresh weight of the sample, g.  
Soluble protein (SP) is an important osmotic regulator and nutrient, and the overall increase and accumulation of SP can improve the water retention ability of plant cells to resist water stress. SP is often used as one of the indicators for screening resistance since it plays a protective role for cellular substances and biofilms [30].