[Impacts of Climate Change and Human Activities on Vegetation Restoration in Typical Grasslands of China].

Grasslands, as one of the key ecosystems relevant to the terrestrial ecosystem carbon and water cycles as well as the ecological security in China, are very sensitive to climate change and human activities. However, the relative contributions of climate change and human activities on the vegetation restoration in those regions are still controversial. Using ecosystem net primary production (NPP) as an ecological indicator, this study quantified the relative roles of climate change and human activities on vegetation restoration in Chinese typical grasslands (northern temperate grasslands and Qinghai-Tibet Plateau alpine grasslands) by comparing the trends of actual NPP derived from MODIS and potential NPP estimated by the Thornthwaite Memorial model during 2000-2020. The results showed that approximately 93% of the grasslands in the study area experienced a recovering tendency, with an average increase of NPP (carbon) by 2.12 g·(m2·a)-1(P<0.01). Therein, nearly half of the vegetation-restored areas were jointly-dominated by climate change and human activities, whereas approximately 36% and 10% of the restored areas were controlled individually by climate change and human activities, respectively. In addition, the share of climate-change dominated areas differed greatly by grassland types, characterized by a much larger area percentage in the alpine grasslands than that in the temperate grasslands and an increasing area share with a drying background climate. This study suggested that human activities were not primarily responsible for the vegetation restoration in northern temperate grasslands and Qinghai-Tibet Plateau alpine grasslands, but they could decrease and even cancel the possible vegetation degeneration caused by worsening climate in a few regions. Long-term monitoring of vegetation dynamics and a multi-method comparison are needed in future studies.

[Spatial-temporal Variations and Their Driving Forces of the Ecological Vulnerability in the Loess Plateau].

The Loess Plateau is one of the most eco-fragile regions in China, and therefore the scientific evaluation of its ecological vulnerability provides a premise for the effective implication of ecological protection and management practices. However, previous studies have mainly focused on the ecological vulnerability in a small region, which cannot reflect the overall picture of the ecological vulnerability in the Loess Plateau. Based on the "exposure-sensitivity-adaptation" framework, this study investigated the spatial-temporal patterns and their driving forces of the ecological vulnerability in the Loess Plateau from 2000 to 2015 through a combined use of the analytic hierarchy process, spatial principal component analysis, and Geodetector analysis. The results showed that the ecological vulnerability was overall at a moderate to high level, and the vulnerability was clearly higher in the northwestern part of the Loess Plateau than that in the southeastern counterparts. Additionally, the ecological vulnerability differed greatly by land use type. The ecological vulnerability decreased after an increase from 2000 to 2015 and in general decreased slightly throughout the study period. Therein, approximately 64% of the total land area experienced an upward or downward trend in the vulnerability. Vegetation coverage and precipitation were the two main factors contributing to the spatial-temporal variability in the ecological vulnerability, and there were significant interactions among all the used indicators. This study suggests that climate change and human activities may help reduce the ecological vulnerability over the Loess Plateau, although their contributions are limited.

[Effects of Myospalax baileyi disturbance on plant community at alpine meadow in Three Rivers Headwater Region, China.] / é«˜åŽŸé¼¢é¼ å¹²æ‰°å¯¹ä¸‰æ±ŸæºåŒºé«˜å¯’è‰ç”¸ç¾¤è½ç‰¹å¾çš„å½±å“.

Plateau zokor (Myospalax baileyi) is one of the major rodent species at the alpine meadow in Three Rivers Headwater Region. They eat plant roots, excavate many tunnels and deposit soil on the surface, which result in many exposed mounds to cover the aboveground part of plants. Here, taking plateau zokor mound density in a plot as their disturbance degree, we selected seven plots with different plateau zokor mound densities and one control plot which was not disturbed by plateau zokor to explore the effects of M. baileyi disturbance on community composition, species diversity and productivity. The results showed that, with the increases of available mound density, the dominant species were changed from Cyperaceae and Gramineae species to forb species, including Poly-gonum viviparum, Potentilla anserine, and Polygonum sibiricum. The community coverage and height were significantly decreased. Light or intermediate disturbance by plateau zokor improved species diversity, whereas the evenness index showed no significant change. The changes of community productivity did not support the 'intermediate disturbance hypothesis'. With the increases of plateau zokor disturbance, the aboveground biomass, belowground biomass, total biomass of community significantly decreased. Our findings revealed the effects of plateau zokor's activity on plant community at alpine meadow and presented important information for the management and restoration of degraded grassland and the sustainable utilization of grassland in Three Rivers Headwater Region.

[Impact of the Beijing and Tianjin Sand Source Control Project on the grassland soil organic carbon storage: a case study of Xilingol League, Inner Mongolia, China].

Understanding the impacts of eco-construction project on grassland soil carbon storage is crucial to assess the effectiveness of the project and its role in carbon cycling of the grassland ecosystems. Using IPCC carbon budget inventory method, this paper analyzed the influence of Beijing and Tianjin Sand Source Control Project (BTSSCP) on the grassland soil carbon storage between 2000 and 2006 in Xilingol League, Inner Mongolia, and evaluated the time needed to reach the maximal soil carbon density for three management practices (i. e. , sown pasture, aerial sowing pasture, and grazing exclosure). Results showed that the BTSSCP significantly increased soil carbon storage, with a carbon sequestration of 59.26 x 10(4) t C from 2000 to 2006. The rate and effectiveness of soil carbon sequestration varied significantly with management practices, with the highest rate in sown pasture (0.25 t C x hm(-2) x a(-1)) while a greater benefit of soil carbon sequestration in the grazing exclosure (63 million yuan). Compared with other grassland vegetations, lowland meadow and temperate meadow steppe both had higher carbon sequestration rates of 0.14 t C x hm(-2) x a(-1). Long time would be needed to reach the maximum soil carbon density in grassland under the three practices, yet shorter for sown pasture with average of 57.75 years.

Relationships between C3 plant foliar carbon isotope composition and element contents of grassland species at high altitudes on the Qinghai-Tibet Plateau, China.

Relationships of foliar carbon isotope composition (δ(13)C) with foliar C, N, P, K, Ca, Mg contents and their ratios of 219 C3 species leaf samples, obtained in August in 2004 to 2007 from 82 high altitude grassland sites on the Qinghai-Tibet Plateau China, were examined. This was done with reference to the proposition that foliar δ(13)C increases with altitude and separately for the life-form groups of graminoids, forbs and shrubs and for the genera Stipa and Kobresia. For all samples, foliar δ(13)C was negatively related to foliar K, P and ∑K+ Ca+ Mg, and positively correlated to foliar C, C/N and C/P. The significance of these correlations differed for the taxonomic and life-form groups. Lack of a relationship of foliar δ(13)C with foliar N was inconsistent with the majority of studies that have shown foliar δ(13)C to be positively related to foliar N due to a decrease of Ci/Ca (the ratio between intercellular and atmospheric concentration of CO2) and explained as a result of greater photosynthetic capacity at higher foliar N concentration. However this inconsistency relates to other high altitude studies that have found that photosynthetic capacity remains constant as foliar N increases. After accounting for the altitudinal relationship with foliar δ(13)C, of the elements only the K effect was significant and was most strongly expressed for Kobresia. It is concluded that factors critical to plant survival and growth at very high altitudes, such as low atmospheric pressure and low temperatures, may preclude expression of relationships between foliar δ(13)C and foliar elements that have been observed at lower altitudes.

[Allelopathic interactions between invasive plant Solidago canadensis and native plant Phragmites australis].

Taking the seeds of invasive plant Solidago canadensis and native plant Phragmites australis from their mono- and co-dominant communities as allelopathic acceptors, this paper analyzed the differences in the seed germination rate and sprout length after treated with five level (12.5, 25, 50, 100, and 200 mg x mL(-1)) S. canadensis and P. australis extracts, aimed to understand the allelopathic interactions between the two species. The 1000-grain weight and seed germination rate under distilled water treatment of the two species in co-dominated community were greater than those in mono-dominant community. Low level (12.5 and 25 mg x mL(-1)) S. canadensi extracts slightly promoted the seed germination rates of S. canadensis in both mono- and co-dominant communities, but high level (50, 100, and 200 mg x mL(-1)) S. canadensi extracts had strong inhibition effect, especially for the S. canadensis in co-dominated community. No significant patterns were observed about the effects of P. australis extract on S. canadensis seed germination. The sprout length of S. canadensis seeds in both mono- and co-dominant communities decreased with increasing level of S. canadensis extract, but decreased in a fluctuation way with increasing level of P. australis extract. After treated with the extracts of P. australis or S. canadensis, the seed germination rate of P. australis in mono-dominant community was significantly greater than that in co-dominant community (P < 0.05), but there was no significant difference between these two extracts.

Assessment of effects of climate change and grazing activity on grassland yield in the Three Rivers Headwaters Region of Qinghai-Tibet Plateau, China.

Inter-annual dynamics of grassland yield of the Three Rivers Headwaters Region of Qinghai-Tibet Plateau of China in 1988-2005 was analyzed using the GLO-PEM model, and the herbage supply function was evaluated. The results indicate that while grassland yield in the region showed marked inter-annual fluctuation there was a trend of increased yield over the 18 years of the study. This increase was especially marked for Alpine Desert and Alpine Steppe and in the west of the region. The inter-annual coefficient of variation of productivity increased from the east to the west of the region and from Marsh, Alpine Meadow, Alpine Steppe, Temperate Steppe to Alpine Desert grasslands. Climate change, particularly increased temperatures in the region during the study period, is suggested to be the main cause of increased grassland yield. However, reduced grazing pressure and changes to the seasonal pattern of grazing could also have influenced the grassland yield trend. These findings indicate the importance of understanding the function of the grassland ecosystems in the region and the effect of climate change on them especially in regard to their use to supply forage for animal production. Reduction of grazing pressure, especially during winter, is indicated to be critical for the restoration and sustainable use of grassland ecosystems in the region.