Chengyi Li

Grazing exclusion is an effective measure of restoring patchily degraded alpine meadows, but a controversy still surrounds it as whether it will have a continuously positive ecological impact on degraded alpine meadows as the duration of exclosure prolongs. Under grazing exclosure, plateau pika disturbance can also alter soil characteristics. To address the uncertaint effects of long-term exclosure and plateau pika disturbance on soil biochemistry in alpine meadows, this study compared soil properties in a 10-year enclosed meadow encompassing both pika-active (FP) and pika-free (FN) zones to those of a regularly grazed area (CK). The results indicated that the light fraction organic carbon content and microbial biomass carbon content in FN were significantly higher than those in CK, but the dissolved organic carbon content and leucine aminopeptidase activity were significantly lower than those in CK. The SOC fractions and soil enzyme activities in FP were significantly lower than those in CK and FN (P < 0.05). Long-term exclosure and plateau pika disturbance significantly altered the composition of the soil bacterial and fungal communities, and the soil bacterial diversity in FN was significantly lower than that in CK and FP. Changes in bacterial diversity were significantly correlated with SOC fractions. Therefore, long-term exclosure on SOC fractions, enzyme activities, and microbial diversity in degraded alpine meadows brings out minimal positive effects, and plateau pika disturbance is not conducive to maintaining ecosystem balance in the alpine meadow.

Three degradation stages of alpine swamp wetland (none, light and severe degeneration levels) were addressed through measuring the respiratory components rate of ecosystem during the peak period of vegetation growth (July to August), so as to analyze the impacts of degradation on ecosystem respiration and its components in alpine swamp wetland on the Qinghai-Tibet Plateau. Two methods which are root separation and herbicide spraying, were used for determination and measurement of respiratory components. The results showed that degradation of alpine swamp wetland can significantly increase soil respiration rate and microbial respiration rate. Moreover, the proportion of vegetation respiration and microbial respiration in ecosystem respiration changed significantly (P < 0.05). There was a significant positive correlation between vegetation respiration and ecosystem respiration rate at all the degradation levels (P < 0.05). Canopy respiration and ecosystem respiration were highly correlated between none and severe degraded wetlands (P < 0.05), it was also found that there was significant positive correlation among soil respiration rate, root respiration rate and ecosystem respiration in light degraded wetland. There was a positive correlation between root respiration and soil respiration in none and light degraded wetland (P < 0.05). The Q₁₀ change ranges of ecosystem respiration, vegetation respiration, canopy respiration, soil respiration, root respiration and soil microbial respiration during the degradation stage of alpine swamp wetland were 1.41–1.50, 1.81–1.94, 4.46–6.93, 1.41–2.40, 2.84–5.97 and 1.99–3.74, respectively. The degradation of alpine wetland affects firstly the ecosystem respiration and its components, and then will affect the carbon cycle process. Therefore, it is very important to protect and restore the alpine wetland on the Qinghai-Tibet Plateau.

The melting of permafrost and the degradation of alpine meadow ecosystems caused by climate warming and high-intensity human activities have imposed serious threats to local and global ecological security. In order to estimate the effects of climate warming and grazing interference on the photosynthesis and respiration of alpine meadow plant community in permafrost regions, warming – infrared radiator is applied to simulate the climate warming (increasing temperature by +2°С). The winter grazing level is simulated by mowing the aboveground biomass of all plants. The responses of permafrost meadow community in terms of photosynthesis, respiration, surface soil temperature and moisture, as well as the carbon balance to simulated different climate warming and grazing level were analyzed and discussed. The results showed that: (1) the surface soil temperature in climate warming and grazing plots is significantly higher than in Ck plots (P < 0.01); (2) warming and warming + grazing plots enhanced community photosynthesis and respiration (P < 0.01); (3) warming and warming + grazing treatments increased community aboveground biomass (P < 0.05); (4) the photosynthetic rate increased in the second year, then decreased in the third year when both temperature and grazing level increased during the growing season. However, the ecosystem respiration increasingly increased year by year; (5) compared with the control groups, warming and grazing treatments resulted in an increase in carbon sequestration of the permafrost meadow community during the growing season.