Why should the grassland of the Qinghai-Tibet Plateau return to green ahead of schedule and postpone yellowing?

Schematic diagram (provided by interviewee)

On February 27, the reporter learned from the Institute of Tibetan Plateau of the Chinese Academy of Sciences that Luo Tianxiang, a researcher in the ecosystem pattern and process team of the institute, and his collaborators monitored the phenology of the three dominant species of Purple Flower Needle Grass, Bigiflora Songweeda and Pinnacle Cerea from 2013 to 2014, simultaneously recorded temperature, precipitation, soil temperature and soil moisture, and analyzed the effects of 2 degrees Celsius warming and 15% and 30% rainfall on the phenological changes of dominant species in the alpine grassland-meadow transition zone. It was clarified that the increase in rainfall led to the early greening and postponement of the yellowing of vegetation in the alpine grassland of the Qinghai-Tibet Plateau, which was not related to warming. The relevant research results were published in the authoritative journal “Total Environmental Science” in the field of environmental science and ecology.

Luo Tianxiang, the corresponding author of the paper, introduced that the Qinghai-Tibet Plateau has the highest altitude and largest alpine meadows and grasslands in the world, and its formation and distribution are mainly controlled by the Indian monsoon climate. How the dominant species on the Qinghai-Tibet Plateau adapt to both cold and arid climates is key to understanding the response of alpine grassland vegetation phenology to climate change.

In the early stage, the research team established an infrared warming and automatic rainfall control experimental platform at the National Field Scientific Observation and Research Station of Namtso Alpine Lake and Environment in Tibet on the northern slope of Nianqing Tanggula Mountain in the middle of the Qinghai-Tibet Plateau for data monitoring.

Luo Tianxiang said that in the past 30 years, the Qinghai-Tibet Plateau has experienced rapid warming, accompanied by increased precipitation. It is expected that by the end of the 21st century, the annual average temperature of the Qinghai-Tibet Plateau will increase by 2.8-4.9 degrees Celsius, and the annual precipitation will increase by 15-21%. In this context of warmth and humidification, there is great controversy over whether the main driver of vegetation phenological change in alpine grassland is warming or rainfall. Previous warming experiments have rarely paid attention to the influence of precipitation changes, and there are few cases of two-factor control experiments combining temperature and precipitation changes.

Ma Pengfei, the first author of the paper and a doctoral student at the Qinghai-Tibet Plateau, introduced that the experimental observation data of two consecutive years showed that the increase in rainfall generally led to the early rejuvenation period of the three dominant species of Purple Flower Needle Grass, Large-flowered Songweed and Pinnacle Ceremonia, while the warming delayed the rejuvenation period or had no significant effect. Both warming and rainfall could significantly delay the yellowing period of the three dominant species, and there was no interaction between warming and rainfall. The greening period of the three dominant species came at the same time or slightly later than the rainy season, and the increase of spring precipitation brought the rainy season earlier and promoted the rejuvenation of vegetation.

The results of the research team showed that alpine vegetation phenology was more sensitive to precipitation changes. Under the conditions of 2 degrees Celsius warming and more than 15% rainfall, the prolongation of the growth season of dominant species in alpine grassland was mainly affected by the delay of autumn phenology. Under the background of warming and humidification of the Qinghai-Tibet Plateau, this study provides important scientific support for us to correctly understand the response mechanism of alpine grassland ecosystems to climate change. (Source: China Science News Han Yangmei)

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