**4. Rehabilitation of acidic slope**

**Figure 6.** The erosion rate on slope at different plant density of *M. malabathricum*.

526 Environmental Risk Assessment of Soil Contamination

**3.2. Carbon sequestration and carbon sink potentiality**

**Figure 7.** Soil carbon content and root length density (RLD) with depth of the species studied at different plant density.

Carbon sequestration, a natural processes in ecosystems where CO2 is absorbed from the atmosphere and stored it in plants and soil. During the photosynthesis process, plants absorb CO2 and converted into carbohydrate or starch [25]. In this way, atmospheric carbon is stored in the leaves, stems, and roots for a long period of time (Figure 8). When a tree is utilized for wood, its ability to sequester carbon is extended, and the carbon is not released until the product burns or decomposes. Vegetation plays an important role in sequestrating carbon, as one way to alleviate global warming, a global issue discussed nowadays. Whereas, carbon sink potential is defined as a natural entity, process, activity Malaysia's climate is described as typical tropical with warm, high rainfall intensity as well as humidity throughout the year. As its experiences high precipitation ranging from 2000 mm to 2500 mm per annum, the highland areas especially slopes are prone to erosion and landslides [10]. Due to the high rainfall and humid climate throughout the year in Malaysia, most of the slopes are facing the acidity problem. The acidic and infertile condition of slope does not encourage the vegetation establishment and consequently the slope turns barren. The barren slope is prone to erode when rainfall dislodge soil particles and carries them off the acidic slope. It would form rills and gullies which can trigger landslides. Rainfall hitting the soil surface can also seal the soil particles and make a crust that prevents infiltration and creates runoff.

**Figure 8.** The process of carbon sequestration [27].


Maximum Assimilation Rate (Amax), Light Compensation point (Г1), Quantum Efficiency (QE), Photosynthesis at ambient CO2 concentration (A400), Mesophyll conductance (gm), CO2 compensation point (ГCO2), LL: *Leucaena leucocephala,* PP; *Peltophorum pterocarpum*, JB: *Justicia betonica,* LC: *Lantana camara,* TE: *Thunbergia erecta*

**Table 3.** Photosynthetic components of plants grown on slope [18]

Acid soil rehabilitation is an essential process of minimizing the acidity level of the soil and providing a better environment for plant growth. This process also will help offset greenhouse gas emissions, guarantee more food for an increasing population and contribute to the economic progress of future generations. There are several methods used in rehabilitating acidic soil. However, only three methods, which are liming, planting legumes and acid tolerant plants will be discussed in this chapter.
