4.1 | Changes in soil nutrient content in response to
grazing
Our results showed that in the alpine meadow ecosystem with poor growth
environmental conditions, grazing decreased the surface soil nutrient
content and soil water content (FIG. 2(a)(c)(d)(e)) and showed a trend
of decreasing with increasing grazing intensity, with the lowest value
appearing under the MG treatment. This supports our initial hypothesis
that the response of soil nutrient content to grazing shows a linear
trend of decreasing soil function with increasing grazing intensity due
to environmental constraints. The main reasons for the decrease in soil
nutrient content are as follows. First of all, the geographical
environment of QTP is complex, and the abiotic environmental conditions
of the ecosystem are the decisive factors for the function of the
grassland ecosystem. The alpine meadow limited by the geographical
environment is mainly characterised by a thin soil layer, low soil
nutrient and soil moisture content, large diurnal temperature difference
and large soil evaporation, and other environmental conditions that are
unfavourable to growth. When the grassland is disturbed by grazing,
plants absorb a large amount of nutrients for their own recovery, growth
and reproduction, resulting in a decrease in soil nutrient content. Our
findings are also supported by previous research showing that topography
is an important limiting factor for soil nutrients in geographically
disadvantaged locations, making them more vulnerable to grazing and
gradually decreasing (Li Ying et al., 2022). In addition, the decline in
soil nutrient levels may also be related to the growth of soil
microorganisms. As a nutrient input, the excrement of grazing livestock
plays an active role in the activation of soil microorganisms and is the
energy source for accelerating the reproduction process of
microorganisms. Some studies have shown that there is nutrient
competition between vegetation and soil microorganisms(Jiang Jing &
Song Minghua, 2010) , the main source of energy for the growth of plants
and microorganisms is soil nutrients. If plants are damaged after
grazing and are in the growing season at the same time, stress responses
may occur. Plants adopt accelerated growth to compensate for the damage
and to ensure survival and reproduction, which consumes a lot of soil
nutrients. Rapid reproduction was the main reason for the decrease in
soil nutrient content. At the same time, the decrease in soil nutrient
content may also be related to the effect of moderate disturbance. Under
moderate disturbance, plant and soil micro-organisms will rearrange
their species, and the dominance of the original dominant species may be
reduced by disturbance, allowing non-dominant species to increase their
reproduction. More species require more nutrients to sustain them, and
the lack of environmental nutrients cannot support the increased
fraction of ecosystem demand, which may be the reason for the lowest
soil nutrient levels under moderate grazing. Similarly, under severe
disturbance, only a few species can adapt to high disturbance, and
plants may adopt survival strategies to survive first, and then expand
their range once the damage has exceeded their carrying capacity. Plant
activity is weakened, soil microbial species are single and soil
nutrient supply species are reduced, which may be the reason why soil
nutrient content is higher under heavy grazing than under moderate
grazing.