Tree mycorrhizal effect on litter-leached DOC amounts and biodegradation is highly dependent on leaf habits in subtropical forests of southern China

Litter-leached dissolved organic carbon (DOC) plays an essential role in regulating biogeochemical cycles in forests. However, it is unclear how tree litter-leached DOC amounts and biodegradation vary with mycorrhizal types and leaf habits. We collected leaf litter from 14 common tree species belonging to different mycorrhizal types (arbuscular mycorrhizal, AM; and ectomycorrhizal, ECM) and leaf habits (deciduous broadleaf, evergreen broadleaf, and evergreen coniferous) in subtropical forests of southern China. We used a soaking experiment to determine litter-leached DOC, dissolved total nitrogen (DTN), and dissolved total phosphorus (DTP) amounts, and DOC aromaticity and molecular weight, and then assessed leaf litter-leached DOC biodegradation using a 42-day incubation experiment. AM broadleaf tree litter produced greater amounts of DOC with lower aromatic content and molecular weight than ECM broadleaf tree litter. In contrast, AM evergreen coniferous litter leached lower amounts of DOC with greater aromaticity than ECM evergreen coniferous litter. In the litter leachates, AM broadleaf trees often had higher DOC:DTN ratio than ECM broadleaf trees, while AM evergreen coniferous species had a lower DOC:DTP ratio than ECM evergreen coniferous species. For both deciduous and evergreen broadleaf trees, AM species had greater DOC biodegradation than ECM species due to the lower aromatic content and molecular weight. However, litter-leached DOC biodegradation did not differ between AM and ECM evergreen coniferous trees. Tree mycorrhizal associations can indicate the interspecific variations of litter-leached DOC amounts and biodegradation, but such tree mycorrhizal effect is highly dependent on leaf habit in subtropical forests.