Effects of climate change on plant composition and diversity in the Gurbantünggüt Desert of northwestern China

Differential responses of the seed germination of three functional groups to low temperature and darkness in a typical steppe, Northern China

Seed germination is a key stage in the life history of plants, which has a crucial effect on plant community structure. Climate change has substantially altered the surface soil temperature and light availability, which can affect seed germination. However, whether the seed germination of different functional groups is affected by the interactions of light and temperature remains unclear. Under laboratory conditions, we examined the effects of low temperature and darkness, as well as their interaction, on the seed germination of 16 species belonging to three plant functional groups (annual and biennials, perennial grasses, and perennial forbs) in a typical steppe, Northern China. We found that low temperature had a significant negative effect on seed germination of all species. Low temperature significantly decreased the final germination percentage and germinative force of the three plant functional groups, and the germination duration of perennial grasses. Darkness significantly decreased the germinative force of perennial forbs and total seeds, and the germination duration of perennial grasses. The interactive effects of light and temperature on the seed final germination percentage and germinative force of perennial grass indicated that darkness strengthened the inhibitory effect of low temperature on the seed germination of the grass functional group. Our study indicate that the seed germination of different plant functional groups varied greatly in response to changing environmental conditions. Our results suggest that future climate change could alter the regeneration and species composition of plant communities through changing seed germination.

Vegetation dynamics and their relationships with climatic factors in the "Golden Triangle" region

The "Golden Triangle" is located on the border between Myanmar, Laos, and Thailand, and slash-and-burn cultivation is an ancient and typical land type in this region. With the development of the "The Belt and Road" strategy of China and the climate change, the vegetation information is bound to change intensively under the combined influence of alternative plantation projects and economic policies. Here we used MOD13Q1-normalized differential vegetation index (NDVI) and meteorological data to analyze the variation of vegetation coverage and its correlation with climatic factors (temperature and precipitation) during the period of 2000-2018 by using trend analysis, stability analysis, and partial correlation analysis. The results showed that the overall vegetation coverage of this region exerted the trend of improvement and became more stable over time. Spatially, the agglomeration degree became weaker as time goes during 2000-2018. The precipitation was more closely correlated with NDVI than temperature, indicating that precipitation could be the main limiting factor influencing vegetation change in this area. The correlation between NDVI and climatic factors exhibited differences among different seasons, with NDVI being less correlated with temperature and precipitation in spring and summer and more correlated with them in autumn and winter. Investigating the long-term vegetation coverage of this region and analyzing the trend of climate change is beneficial to understand the development trend of the ecological environment and resource potential in this region. Simultaneously, it can provide a favorable ecological evaluation for The Belt and Road strategy and provide important scientific suggestions and guidance for the sustainable development of ecosystems and human society under the drastic environmental changes.

Responses and comprehensive evaluation of growth characteristics of ephemeral plants in the desert-oasis ecotone to soil types

The ecological environment of the Gurbantünggüt desert-oasis ecotone is extremely fragile. Ephemeral plants are an important part of the ecosystem and play an essential role in maintaining the ecological stability of the ecotone. However, few studies have focused on the growth, soil quality and system sustainability of ephemeral plants in different soils. This study was based on two typical soil types (grey desert soil, GS; aeolian soil, AS) in the aforementioned ecotone, considered four ephemeral plants (Tetracme recurvata, TR; Tetracme contorta, TC; Malcolmia scorpioides, MS; Isatis violascens, IV) as the research object, analysed plant characteristics and soil properties, and comprehensively evaluated the ephemeral plant system by analysing the soil quality index (SQI) and sustainability index (SI). The results showed that there were significant differences in biomass and nutrient accumulation between different ephemeral plants, which were significantly affected by soil types. In the two examined soils (GS and AS), the contents of nutrients and microbial carbon (MBC) and nitrogen (MBN) in the rhizosphere soil were higher than those in the bare soil (BS), and there were significant differences among different species. The key soil factors related to total biomass in GS and AS were also different. The SQI of ephemeral plants was significantly higher than that of the BS, and varied with soil types and plant species. The species with the highest SQI of the key factor data set in GS and AS were IV and TR, respectively. The SI analysis indicated that IV in GS and MS and IV in AS were sustainable, and the plant properties can be better used to assess the sustainability of ephemeral plant systems. In conclusion, ephemeral plants improved the soil quality and system sustainability of the study ecotone. Further, the growth of ephemeral plant and rhizosphere soil properties vary with plant species and soil types; thus, selecting suitable species for large-scale planting in different soil types is of great significance for improving the ecological stability of the ecotone.

Population Dynamics and Life History Response to Precipitation Changes for a Desert Ephemeral Plant With Biseasonal Germination

The changing availability of water resources and frequent extreme drought events in the context of global change will have a profound impact on desert vegetation, especially on herbaceous populations such as ephemerals. Erodium oxyrrhynchum is the dominant species in the Gurbantunggut Desert. It can germinate both in spring and autumn, which is important for herbaceous layer coverage and productivity. Therefore, we tracked and recorded the survival and reproduction of the E. oxyrrhynchum population under different precipitation treatments and established a population matrix model, monitored the allometry and leaf traits of the plants, and compared the performance of spring-germinating and autumn-germinating plants. Our results showed that: (1) The population dynamics were significantly affected by precipitation changes; (2) drought reduced the survival rate of the plants and accelerated the completion of their life history; (3) precipitation had a significant effect on seed production and growth rate, but not on plant height and allometry; (4) biomass, leaf area, specific leaf area, and 100-grain weight of E. oxyrrhynchum also responded to changes in precipitation; and (5) autumn-germinated plants had higher productivity, whereas spring-germinated plants exhibited higher reproductive efficiency, indicating that they had difference life history strategies. In conclusion, our results suggested that, although frequent or prolonged drought can significantly inhibit population growth, species with biseasonal germination are likely to be less affected.

NDVI Dynamics and Its Response to Climate Change and Reforestation in Northern China

Vegetation is an important component of the terrestrial ecosystem that plays an essential role in the exchange of water and energy in climate and biogeochemical cycles. This study investigated the spatiotemporal variation of normalized difference vegetation index (NDVI) in northern China using the GIMMS-MODIS NDVI during 1982–2018. We explored the dominant drivers of NDVI change using regression analyses. Results show that the regional average NDVI for northern China increased at a rate of 0.001 year−1. NDVI improved and degraded area corresponded to 36.1% and 9.7% of the total investigated area, respectively. Climate drivers were responsible for NDVI change in 46.2% of the study area, and the regional average NDVI trend in the region where the dominant drivers were temperature (T), precipitation (P), and the combination of precipitation and temperature (P&T), increased at a rate of 0.0028, 0.0027, and 0.0056 year−1, respectively. We conclude that P has positive dominant effects on NDVI in the subregion VIAiia, VIAiic, VIAiib, VIAib of temperate grassland region, and VIIBiia of temperate desert region in northern China. T has positive dominant effects on NDVI in the alpine vegetation region of Qinghai Tibet Plateau. NDVI is negatively dominated by T in the subregion VIIBiib, VIIBib, VIIAi, and VIIBi of temperate desert regions. Human activities affect NDVI directly by reforestation, especially in Shaanxi, Shanxi, and Hebei provinces.

Distribution pattern of Tugai forests species diversity and their relationship to environmental factors in an arid area of China

Ecological restoration of degraded riparian Tugai forests is a key driver to combat desertification in arid regions. Previous studies have focused mainly on changes in groundwater as the underlying mechanisms of Tugai forest’s decline. We evaluated species composition and diversity of Tugai forest and their relationship to groundwater, soil salinity, and soil nutrient. Using 73 quadrats (100 m × 100 m) from 13 transects located perpendicularly to river in the upper reaches of the Tarim River. Eighteen plant species belonging to sixteen genera and eight families were recorded, and the dominant species included Populus euphratica, Phragmites communis, and Tamarix ramosissima. Three P. euphratica stand ages were detected: young stand, mature stand, and old stand. There were significant differences in species diversity, groundwater depth, groundwater salinity, distance from the quadrat to the river channel, soil moisture content, pH, electrical conductivity, total salt, Cl⁻, SO₄²⁻, Ca²⁻, Mg²⁺, Na⁺, K⁺, soil organic carbon, and soil organic matter across the stand ages. Seven species were identified as indicators of the three stand ages. Redundancy analysis indicated that the Tugai forest diversity indices were negatively correlated with groundwater depth, groundwater salinity, and distance from the river, and positively associated with electrical conductivity, total salt, pH, Cl⁻, SO₄²⁻, CO₃²⁻, soil organic matter, soil organic carbon, and soil moisture content. Plant diversity was the highest at 3–6 m groundwater depth, followed by 0–3 m and then 6–9 m, with the lowest recorded at > 9 m. The appropriate groundwater depth for herbs was about 1–4 m, whereas the depth for trees and shrubs was about 3–6 m. The groundwater depth < 6 m was deemed suitable for the growth of desert riparian forests. This results provide a scientific reference for the ecological restoration and protection for Tugai forests in arid areas.

Impact of groundwater depth and soil salinity on riparian plant diversity and distribution in an arid area of China

Riparian plant diversity in arid regions is sensitive to changes in groundwater. Although it is well known that groundwater has a significant influence on plant diversity, there have been few studies on how groundwater and soil salinity impact plant community in desert riparian ecosystems. Therefore, we surveyed 77 quadrats (100 m × 100 m) to examine the relationship between groundwater depth, groundwater salinity, soil salinity and plant community in the upper reaches of the Tarim River. Data were analyzed with two-way indicator species analysis (TWINSPAN), detrended canonical correspondence analysis (DCCA) and principal component analysis (PCA). The results indicated that Populus euphratica, Tamarix ramosissima, and Phragmites australis were the dominant plants among trees, shrubs and herbs, respectively. Five plant community types were classified. There were significant differences in species diversity, soil moisture, soil salinity, groundwater depth and groundwater salinity across the community types. The composition and distribution of plant community are significantly influenced by groundwater depth, groundwater salinity, soil moisture, distances from the river to the quadrats, soil pH, electrical conductivity, total salt, CO₃²⁻, Cl⁻, SO₄²⁻, Ca²⁺, Mg²⁺, Na⁺ and K⁺. Shallow groundwater depth, low groundwater salinity, and high soil moisture and soil salinity were associated with higher plant diversity.

Future N deposition and precipitation changes will be beneficial for the growth of Haloxylon ammodendron in Gurbantunggut Desert, northwest China

Evaluation of precipitation and nitrogen (N) deposition in desert ecosystems helps to elucidate the reaction of desert ecosystems to future environmental changes. An in-situ field experiment was established to examine the influence of a long-term enhanced precipitation and N deposition on the photosynthetic traits and physiological characteristics of Haloxylon ammodendron in the Gurbantunggut Desert, northwest China, throughout the growing season in 2014-2016. Results showed a significant interaction between precipitation and N applications. Increased precipitation and N deposition and their coupling could significantly improve photosynthetic capacity, alter the variability in amplitude of water potential and change the content of substances regulating osmotic pressure in H. ammodendron. According to the comprehensive evaluation of H. ammodendron's adaptability using six different water and N coupling models, a combination of a 30% increase in precipitation and a 30 kg N ha^-1 yr^-1 addition in nitrogen deposition, or the addition of N at a concentration of 60 kg N ha^-1 yr^-1 with natural precipitation were beneficial to H. ammodendron growth and development. Hence, changes in the future global environment can be anticipated to be beneficial to H. ammodendron growth.