3.1 Effect mechanism of optimal water and fertilizer management
on soil microbial biomass C and N of Panax notoginseng
This study found significant differences (p<0.05) in soil
microbial biomass C and N and enzyme activities at different growth
periods under the same water and fertilizer optimal management, and the
changes tended to increase first and then decrease with the growth time
of Panax notoginseng. The soil microbial biomass C and N content ranged
from high to low in flowering, fruiting period, seedling period, and
rooting period, with the highest in flowering (rainy season) and the
lowest in rooting period (dry season). Bargali, K et al. found that soil
microbial biomass carbon of different forest types showed significant
seasonal changes, with the minimum value in winter and the maximum value
in the rainy season(Bargali et al.,2018).Lepcha, N.T. et al.studied the
effects of land use types and seasonal changes in the eastern Himalayas
on soil microbial biomass carbon and nitrogen and found that soil
microbial biomass carbon and nitrogen of different land use types showed
strong seasonal differences (p<0.001), with the peak occurring
in the rainy season and the lowest in winter(Lepcha et al.,2020). In
this study, the highest soil microbial biomass C and N content occurred
in the flowering season (rainy season) and the lowest in the root growth
period (dry season) because the dry and wet seasons in the study area
were distinct, with rainy summer, dry winter and spring, abundant
rainfall in summer, humid air, and small evaporation. The soil
temperature and humidity were suitable for the growth, reproduction, and
decomposition activities of soil microorganisms, and microbial increase
promoted the conversion and accumulation of soil microbial biomass C and
N content. Huang et al. found that the interaction between increased
irrigation amount and season had significant effects on MR, MBC, and MBN
but significantly increased in summer and autumn, with no effect in
spring and winter. Rehydration in summer and autumn increased bacterial
biomass as well as bacterial and fungal diversity and abundance(Huang et
al.,2018), which was in contrast to the finding by Li et al. that soil
microbial biomass carbon and nitrogen in the Mediterranean
agro-ecological system had the lowest value in summer and the highest
value in autumn(Li et al.,2014) because of the different climatic types
in the two regions. The Mediterranean region was hot and dry in summer
and warm and rainy in winter, in contrast to the rainy summer and dry
winter and spring in the studied region.
This study found significant differences (p<0.05) between soil
microbial biomass C and N and enzyme activities in the same growth
period under different water and fertilizer optimal management, and the
soil microbial biomass C and N content increased with the increase of
irrigation and fertilizer application amount, of which, the W2F4
treatment at the rooting period and the W3F4 treatment at the seedling,
flowering and fruiting periods greater than the other treatments in all
reproductive stages. The study showed that long-term fertilization
improved soil microbial biomass carbon (SMBC) and dehydrogenase
activities, and organic fertilizers had a greater effect on SMBC and
dehydrogenase activities than mineral fertilizers(Luo et
al.,2015).Increases in lower soil elemental and microbial biomass
stoichiometry (SMBC:SMBP and SMBN:SMBP) and LAP were mainly due to the
combined use of manure and mineral fertilizers accelerating SOC and N
mineralization(Yang et al.,2015).In this study, the worst treatments for
soil microbiomass carbon, nitrogen and enzyme activity were W1F2 and
W1F1 for both the rooting and seedling periods, respectively, and W2F1
and W1F1 for both the flowering and fruiting periods, respectively.