Purpose
The aim of this work was to study the effect of ‘trace element-rich litter’ on the properties of two reforested polluted soils of different pH values (acidic and neutral) in terms of (1) ...availability of trace elements and (2) chemical and biochemical properties of the soil at different pH. We hypothesized that this litter would affect several parameters related to the organic matter cycle in soils, depending on initial soil pH.
Materials and methods
The experiment was carried out in three different soils: a non-polluted soil (NP) and two trace element-polluted soils (PN, neutral soil, and PA, acidic soil). Soil samples were placed in 2,000-cm
3
microcosms and were incubated for 40 weeks in controlled conditions. Each soil was mixed with its corresponding litter, NP-L, PN-L and PA-L, and soils without litter were also tested for comparison. Microbial properties such as microbial biomass carbon (MBC), β-glucosidase activity and chemical properties such as pH, CaCl
2
-soluble heavy metal concentrations, total organic carbon and water-soluble carbon (WSC) were measured after 0, 2, 4, 8, 16, 24, 32 and 40 weeks of incubation. Parameters related to soil respiration (basal respiration (
R
B
), substrate-induced respiration (
R
s), growth rate (
μ
), lag time (
t
lag
) and time from substrate addition until peak of maximum respiration rate (
t
peakmax
)) were measured after 0, 24 and 40 weeks of incubation.
Results and discussion
Available trace elements did not increase during the incubation and were always higher in soil with acid pH. Litter increased values of WSC, MBC and β-glucosidase as well as
R
B
and
R
S
, especially at the beginning of the incubation. Organic matter mineralization rates, MBC and some parameters related to soil respiration (
t
lag
and
t
peak
) were strongly affected by soil pollution with and without litter. All these properties were strongly related with pH and, to a lesser extent, with a higher trace element bioavailability in soils.
Conclusions
Acidity and trace element availability strongly affect organic matter decomposition and parameters related with the C cycle, such as MBC and soil respiration. However, despite heavy metal addition through the litter in polluted soil, organic matter input from litter is more beneficial than the removal of leaves from the soil, due to the positive effects that this causes in all parameters related to the C cycle.
