The amount of organic matter was different between both the two
soil depths (0–0.1 m and 0.1–0.3 m) and the four types of green space
soils (Table 2). The amount of organic matter was higher at the
0–0.1 m depth than at the 0.1–0.3 m depth for the four types of green
space soils, and was highest in the PROT soil and the lowest in the
STREET soil (Table 4). According to the Chinese soil fertility classes
(Table 5), the amount of organic matter in the 0–0.1 m depth of the
STREET soil can be considered as low, while the other sites fall into the
low to moderate class. At the 0.1–0.3 m depth, the amount of organic
matter present in the STREET soil can be considered as extremely low,
with the PARK and ATTACH soils belonging to the low class and the
PROT soils fitting into the low to moderate class. Therefore, there was
a minimal amount of organic matter regardless of the green space
type or depth, especially in the STREET soil. The most common cause
of low levels of organic constituents is that there is generally little
attempt made to replicate a topsoil during the course of planting.
Although green space soils are usually covered by vegetation, which
would be expected to accumulate organic matter in the upper layers,
the amount of organic matter in the topsoil is relatively low due to the
destruction of the original surface organic horizon and a lack of accumulation
of organic matter. Similarly, other urban-soil studies reported an
insufficient supply of organic matter to urban topsoils (Biasioli et al.,
2006) and urban road soils (Jim, 1998). The shortage of organic constituents
in urban soils has unfavorable physical and chemical effects. Soil
structural formation andmaintenance is difficultwithout organicmatter
as the crucial aggregating agent, and results in low-grade structure and
relatively low-strength aggregates (Jim, 1998).