Regulation of soil organic carbon dynamics by microbial communities
during reforestation of Chinese fir plantations after clearcutting
Abstract
Reforestation after forest clearcutting is an effective measure to
increase soil organic carbon (SOC) sequestration. However, the soil C
balance and functions of microbial communities under reforestation
remain to be determined. Samples of organic (0-2 cm) and mineral (2-10
cm) horizons were collected from the 7-, 15-, 20-, 29-, and 36-year-old
forest stands of Chinese fir developed after plantation clearcutting in
subtropical climate zone under the condition of phosphorus limitation.
Particulate organic carbon (POC), mineral-associated organic carbon
(MAOC), microbial phospholipid fatty acids (PLFAs), and enzymatic
activities for C, nitrogen (N), and phosphorus (P) acquisition were
analyzed. The lowest contents of POC (10 %) and MAOC (13 %) in the
organic horizon were found in 7-year-old stands due to the slow tree
regrowth and extensive decomposition of SOC in the first years of forest
regrowth. POC (2.0x) and MAOC (0.8x) increases in the organic horizon
with forest age were attributed to the stand development and
accumulation of above and belowground litter. The organic horizon had a
higher POC: MAOC ratio than the mineral (0.7-1.1 vs. 0.2-0.5),
indicating lower SOC stability in the first one. A positive correlation
of the Gram-positive to Gram-negative bacteria (G+:G-) ratio with the
POC: MAOC ratio may point to developing specific substrate utilization
strategies for microbial communities. Microorganisms were limited by C
and P; however, the C limitation was alleviated in the 36-year-old plots
in the organic horizon due to increased litter input. Microbial C and P
limitations increased with total PLFAs and the G+:G- ratio, indicating
the strong influence of community structure on nutrient acquisition from
SOC. Thus, soil C sequestration under reforestation of Chinese fir can
be controlled by microbial community structure and metabolic limitation,
which both shifted with the stand age.