Page 15 - Read Online

Zhang et al. Carbon Footprints 2025, 4, 36 https://dx.doi.org/10.20517/cf.2025.29 Page 11 of 17

The results indicated that the enclosed alpine meadow ecosystems act as the GHG sinks, and grazing,
compared to ungrazing, significantly increased the GHG emissions (P = 0.023, 0.003 and 0.0002 for LSR,
MSR, and HSR, respectively) [Figure 5]. The net GHG balance of the fenced treatment was
-1
-1
-1,720.02 ± 844.41 kg CO -eq ha year . The GHG balance and intensity were 990.40 ± 92.25, 2,170.90 ±
2
271.12, 3,911.61 ± 484.37 kg CO -eq ha year [Figure 5] and 316,23.03 ± 2.15, 50.49 ± 10.92,
-1
-1
2
-1
90.97 ± 11.26 kg CO -eq kg LWG, for LSR, MSR and HSR, respectively (here, we assumed an average of
2
43 kg LWG per yak). The results showed increasing GHG intensities with increasing stocking rates. To
further clarify the contributions of different GHG sources to the GHG balance and the relationships
between the GHG balance and stocking rate, we used a simple linear regression [Figure 6]. We found a
linear trend between the GHG balance and the stocking rate (y = 3,057x - 1,336.8, where x indicates stocking
rate, y indicates GHG balance numbe, R = 0.87). Within the context of our study, carbon sequestration
2
emerged as a primary determinant of the GHG balance in yak-grazing farm systems. Moreover, enteric
fermentation and manure management will become the predominant sources of GHG emissions in grazing
farm systems as stocking rates increase. Thus, the mitigation practices used to reduce the GHG emissions
from yak grazing farm systems should focus on reducing enteric fermentation, manure management and
improving the organic uptake by pasture soil. Our results showed that grazing exclusion promises a large
GHG mitigation potential derived from carbon sequestration by pasture soil, which can be an alternative
farm management strategy to mitigate GHG emissions in the alpine grazing ecosystems of the QTP.

Analysis of GHG emissions and balance
The GHG balance of both grazed and ungrazed systems was significantly influenced by CO originating
2
from carbon sequestration. Pasture CH and N O fluxes accounted for 2.7% and -2.0%, respectively, of the
2
4
total GHG balance for the ungrazed scenarios. In the grazed scenarios, enteric fermentation and manure
management were the second and third most important components, contributing 34.8%-48.7% and
20.9%-32.2%, respectively, to the total GHG balance. The emissions from farm inputs were generally small,
and contributed only 0.4%-0.8% to the total GHG balance [Figure 6]. Redundancy analysis showed that
SOC stocks (ASOCS), farm inputs and manure management (Dung Patches GHG Emissions) were major
predictors of GHG balance from grassland livestock systems. Environmental factors [MAT (Mean Annual
Temperature); MAP (Mean Annual Precipitation)] have little influence on GHG balance [Figure 7].

DISCUSSION
Grazing intensity mediates soil carbon dynamics through coupled biophysical mechanisms
The depletion of topsoil organic carbon (SOC) stocks observed under grazing regimes
(990.40-3,911.61 kg CO -eq ha year ) is emblematic of the complex interplay between herbivory and
-1
-1
2
carbon cycling in alpine ecosystems . This phenomenon is driven by three synergistic mechanisms that are
[32]
amplified by the QTP’s unique environmental constraints. Yak grazing reduces aboveground net primary
productivity (ANPP) by 18%-34% (unpublished data), curtailing carbon input to soil via litter fall. The
ingested carbon undergoes rapid enteric fermentation, with only 43% of the indigestible fraction being
[33]
excreted . This “carbon diversion” is exacerbated by the QTP’s short growing season (May-October),
which limits compensatory plant growth. Isotopic tracing ( C) reveals that grazed meadows allocate 23%
δ13
less photosynthate to root exudates compared to ungrazed sites, starving rhizosphere microbes of labile
carbon . Concurrently, trampling compacts soil (BD increases by 12%-19% under HSR), reducing
[34]
macroporosity (> 50 μm pores) from 12% to 5%, thereby impeding root penetration and further
constraining belowground carbon sequestration . Metagenomic analysis of grazed soils reveals a 27%
[35]
decline in methanotrophs (e.g., Methylocystis spp.) and a 41% increase in denitrifiers (e.g.,
Pseudomonas spp.), likely driven by oxygen limitation and nitrogen enrichment from urine patches [36,37] .
This taxonomic shift correlates with functional gene abundance: particulate methane monooxygenase
(pMMO) decreases by 35%, while nirK (nitrite reduction) increases by 52%. Such changes transform grazed