Abstract. While we know that understory vegetation affects the soil
microbial biomass and extracellular enzyme activities in subtropical Chinese
fir (Cunninghamia lanceolata) forests, we are less certain about the
degree of its influence. We determined the degree to which the soil abiotic
and biotic properties, such as PLFAs and extracellular enzyme activities,
were controlled by understory vegetation. We established a paired treatment
in a subtropical Chinese fir plantation, which comprised one plot from which
the understory vegetation and litter were removed (None) and another from
which the litter was removed but the understory vegetation was left intact
(Understory). We evaluated how the understory vegetation influenced the soil
abiotic properties, the bacterial, fungal, and actinobacterial PLFAs, and the
activities of five hydrolases and two oxidative enzymes. The dissolved
organic carbon (DOC), particulate organic carbon, soil organic carbon,
ammonia nitrogen (NH4+–N), and total nitrogen contents and soil
moisture were 18 %, 25 %, 12 %, 34 %, 8 %, and 4 % lower in the
None treatments than in the Understory treatments, respectively (P<0.05).
Soil bacterial, fungal, and total PLFAs, and the potential activities of
β-1,4-glucosidase (βG), β-1,4-N-acetylglucosaminidase,
phenol oxidase, and peroxidase, were as much as 24 % lower in None
treatments than in Understory treatments (P<0.05). The specific activities
of C-acquiring enzymes were as much as 41 % higher (P<0.05), and the
ratio of C- to N-acquiring enzymes was also higher in the None treatments
than in the Understory treatments. This suggests that in the absence of
understory vegetation microbes invested more in C acquisition than N
acquisition because the carbon (C) inputs were less labile. The negative
relationship between DOC and AP shows that DOC is consumed when P-acquiring
enzymes are produced. The positive correlation between NH4+–N
and βG suggested the increased availability of N promoted the
decomposition of C. More extracellular enzymes that degrade soil organic
matter are produced when there is understory vegetation, which leads to
losses of soil C. On the other hand, the soil C sink is maintained by
increased inputs of C. We can therefore conclude that understory vegetation
contributes to C sequestration in Chinese fir forests and suggest that
understory should be maintained to sustain soil quality in subtropical
Chinese fir plantations.
Understory vegetation plays the key role in sustaining soil microbial biomass and extracellular enzyme activities
