Differential effects of conifer and broadleaf litter inputs on soil organic carbon chemical composition through altered soil microbial community composition

A strategic selection of tree species will shift the type and quality of litter input, and subsequently magnitude and composition of the soil organic carbon (SOC) through soil microbial community. We conducted a manipulative experiment in randomized block design with leaf litter inputs of four native subtropical tree species in a Pinus massoniana plantation in southern China and found that the chemical composition of SOC did not differ significantly among treatments until after 28 months of the experiment. Contrasting leaf litter inputs had significant impacts on the amounts of total microbial, Gram-positive bacterial, and actinomycic PLFAs, but not on the amounts of total bacterial, Gram-negative bacterial, and fungal PLFAs. There were significant differences in alkyl/O-alkyl C in soils among the leaf litter input treatments, but no apparent differences in the proportions of chemical compositions (alkyl, O-alkyl, aromatic, and carbonyl C) in SOC. Soil alkyl/O-alkyl C was significantly related to the amounts of total microbial, and Gram-positive bacterial PLFAs, but not to the chemical compositions of leaf litter. Our findings suggest that changes in forest leaf litter inputs could result in changes in chemical stability of SOC through the altered microbial community composition

Labile substrate availability controls temperature sensitivity of organic carbon decomposition at different soil depths

The decomposition of soil organic carbon (SOC) is intrinsically sensitive to temperature. However, the degree to which the temperature sensitivity of SOC decomposition (as often measured in Q(10) value) varies with soil depth and labile substrate availability remain unclear. This study explores (1) how the Q(10) of SOC decomposition changes with increasing soil depth, and (2) how increasing labile substrate availability affects the Q(10) at different soil depths. We measured soil CO2 production at four temperatures (6, 14, 22 and 30 A degrees C) using an infrared CO2 analyzer. Treatments included four soil depths (0-20, 20-40, 40-60 and 60-80 cm), four sites (farm, redwood forest, ungrazed and grazed grassland), and two levels of labile substrate availability (ambient and saturated by adding glucose solution). We found that Q(10) values at ambient substrate availability decreased with increasing soil depth, from 2.0-2.4 in 0-20 cm to 1.5-1.8 in 60-80 cm. Moreover, saturated labile substrate availability led to higher Q(10) in most soil layers, and the increase in Q(10) due to labile substrate addition was larger in subsurface soils (20-80 cm) than in surface soils (0-20 cm). Further analysis showed that microbial biomass carbon (MBC) and SOC best explained the variation in Q(10) at ambient substrate availability across ecosystems and depths (R-2 = 0.37, P < 0.001), and MBC best explained the variation in the change of Q(10) between control and glucose addition treatment (R-2 = 0.14, P = 0.003). Overall, these results indicate that labile substrate limitation of the temperature sensitivity of SOC decomposition, as previously shown in surface soils, is even stronger for subsoils. Understanding processes controlling the labile substrate availability (e.g., with rising atmospheric CO2 concentration and land use change) should advance our prediction of the fate of subsoil SOC in a warmer world.U.S. Department of Energy's Office of Science through the Midwestern Regional Center of the National Institute for Climatic Change Research at Michigan Technological University [DE-FC02-06ER64158]; U.S. National Science Foundation, Division of Environmental Biology's Ecosystem Studies Program [DEB-1354098]; Overseas Foundation of the Chinese Academy of Sciences; National Science Foundation of China [31270492]; Office of 985 Project at Peking UniversitySCI(E)[email protected]