Microbial activity promoted with organic carbon accumulation in macroaggregates of paddy soils under long-term rice cultivation
While soil organic carbon (SOC) accumulation and stabilization has been increasingly the focus of ecosystem properties, how it could be linked to soil biological activity enhancement has been poorly assessed. In this study, topsoil samples were collected from a series of rice soils shifted from salt...
| Main Authors: | , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2016-12-01
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| Series: | Biogeosciences |
| Online Access: | http://www.biogeosciences.net/13/6565/2016/bg-13-6565-2016.pdf |
| Summary: | While soil organic carbon (SOC) accumulation and stabilization has been
increasingly the focus of ecosystem properties, how it could be linked to
soil biological activity enhancement has been poorly assessed. In this study,
topsoil samples were collected from a series of rice soils shifted from salt
marshes for 0, 50, 100, 300 and 700 years from a coastal area of
eastern China. Soil aggregates were fractioned into different sizes of coarse
sand (200–2000 µm), fine sand
(20–200 µm), silt (2–20 µm) and clay
(< 2 µm), using separation
with a low-energy dispersion protocol. Soil properties were determined to
investigate niche specialization of different soil particle fractions in
response to long-term rice cultivation, including recalcitrant and labile
organic carbon, microbial diversity of bacterial, archaeal and fungal
communities, soil respiration and enzyme activity. The results showed that
the mass proportion both of coarse-sand (2000–200 µm) and clay
(< 2 µm) fractions increased with prolonged rice
cultivation,
but the aggregate size fractions were dominated by fine-sand
(200–20 µm) and silt (20–2 µm) fractions across the chronosequence. SOC was
highly enriched in coarse-sand fractions (40–60 g kg<sup>−1</sup>) and moderately in
clay fractions (20–25 g kg<sup>−1</sup>), but was depleted in silt fractions
(∼ 10 g kg<sup>−1</sup>). The recalcitrant carbon pool was higher
(33–40 % of SOC) in both coarse-sand and clay fractions than in fine-sand
and silt fractions (20–29 % of SOC). However, the ratio of labile organic
carbon (LOC) to SOC showed a weakly decreasing trend with decreasing size of
aggregate fractions. Total soil DNA (deoxyribonucleic acid) content in the size fractions followed a
similar trend to that of SOC. Despite the largely similar diversity
between the fractions, 16S ribosomal gene abundance of bacteria and of
archaeal were concentrated in both coarse-sand and clay fractions. Being the
highest generally in coarse-sand fractions, 18S rRNA gene abundance of fungi
decreased sharply but the diversity gently, with decreasing size of the
aggregate fractions. The soil respiration quotient (ratio of respired CO<sub>2</sub>–C
to SOC) was the highest in the silt fraction, followed by the fine-sand fraction, but
the lowest in coarse-sand and clay fractions in the rice soils cultivated over
100 years, whereas the microbial metabolic quotient was lower in coarse-sand-sized fractions than in other fractions.
Soil respiration was higher in the silt
fraction than in other fractions for the rice soils. For the size fractions
other than the clay fraction, enzyme activity was increased with prolonged rice
cultivation, whereas soil respiration appeared to have a decreasing trend.
Only in the coarse-sand fraction was both microbial gene abundance and enzyme
activity well correlated to SOC and LOC content, although the chemical
stability and respiratory of SOC were similar between coarse-sand and clay
fractions. Thus, biological activity was generally promoted with LOC
accumulation in the coarse-sand-sized macroaggregates of the rice soils,
positively responding to prolonged rice cultivation management. The finding
here provides a mechanistic understanding of soil organic carbon turnover
and microbial community succession at fine scale of soil aggregates that
have evolved along with anthropogenic activity of rice cultivation in the
field. |
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| ISSN: | 1726-4170 1726-4189 |