Fertilization can accelerate the pace of soil microbial community response to rest-grazing duration in the Three-river Source Region of China

Objectives Overgrazing leads to grassland degradation and productivity
decline. Rest-grazing during the regreen-up period can quickly restore
grassland and fertilization is a common restoration measure. Meanwhile,
soil microorganisms are more sensitive indicators. Therefore, the
experiment of rest-grazing time and fertilization was carried out to
explore the response of soil microorganisms to rest-grazing time and
fertilization measures. Methods A field control experiment with
rest-grazing time and fertilization as factors was conducted from the time
when grass returned to green till the livestock moved to the summer
pasture in Dawu Town of Maqin County. The primary treatment we established
was the five rest-grazing times, including rest-grazing times of 20 days,
30 days, 40 days, 50 days, and traditional grazing was used as a check
group. At the same time, the secondary treatment was nitrogen addition of
300 kg·hm-2 in each primary treatment. Results The results showed that:
the total phospholipid fatty acid (total PLFA), actinomyces (Act) and
arbuscular mycorrhizal fungi (AMF) showed an ever-increasing
biomass with the increase of rest-grazing time and the highest was at 50
days of rest-grazing, and they were all significantly higher than CK. In
addition, soil microbial biomass carbon-nitrogen ratio (MBC/MBN) had a
great influence on the change of microbial community. Applying nitrogen
fertilizer can increase the maximum value of biomass of all PLFA groups
and the biomass of all PLFA groups changed in an “inverted V” shape with
the increase of rest-grazing time. Besides, instead of MBC/MBN,
NO3--N was positively affected by the biomass of all PLFA groups, which
actively regulated the trend of microbial functions. Conclusions The
longer rest-grazing time is more conducive to the biomass of all PLFA
groups. However, applying nitrogen fertilizer could break this pattern,
namely, the 30d rest-grazing would be beneficial to the biomass of all
PLFA groups. These findings provide key information that rest-grazing
during the regreen-up period is beneficial to all PLFA groups
and fertilization could change the response of microorganisms to
rest-grazing, which provides reference measures for the restoration of
degraded alpine meadows.