Quantitative relationship between pollen and vegetation in northern China

205 surface pollen samples from different communities in Northern China were analyzed to understand the quantitative relationship between pollen and its original vegetation. Pollen analysis and vegetation investigation show that the pollen assemblages differ a lot in different vegetation regions. Arboreal pollen account for more than 30% in temperate broad-deciduous forests region. In temperate steppe regions, herb pollen percentages are more than 90%, where Artemisia and Chenopodiaceae are domi- nant pollen types with Artemisia percentages more than 30%. In temperate desert, Chenopodiaceae pollen percentages are more than Artemisia, where ferns are rare. Cyperaceae pollen percentages are more than 20% in sub-alpine or cold meadows. The relations between pollen percentages and vegeta- tion cover indicate that most arboreal pollen shows a close relationship with parent plant covers, most shrubby pollen types have more or less correlations, but most herbs do not show clear correlations. For arboreal pollen types, Picea pollen shows the closest correlation with spruce trees coverage, then is Quercus and Carpinus. Betula, Larix and Juglans have also high correlation coefficients with their plants coverage, but Betula pollen is of overrepresented pollen type and more than 40% in birch forest, while Larix and Juglans pollen is underrepresented and pollen percentages are more than 10% in Larix or Juglans pure forests. Pinus is of overrepresented pollen type, and pollen percentages have some relations with plants cover. Pine forest might present when Pinus pollen percentages are more than 30%. The relations between Ulmus and Populus pollen percentages and vegetation cover are not close, where they are mixed with other arbors, they cannot be recorded easily, but if their pollen percentages are more than 1%, Ulmus or Populus trees should exist. For shrubby pollen types, the correlation be- tween Vitex pollen percentages and vegetation cover is the highest, then is Corylus, Tamariaceae and Nitraria, and their pollen percentages are less than 1% where original plant are absent. Caragana and Spiraea pollen percentages have some relations with vegetation cover. The relations between pollen percentages and vegetation cover are not clear for Rosaceae and Saxifragaceae. For herb pollen types, Cyperaceae pollen has the closest correlation with vegetation cover, where pollen percentages are more than 20% when Cyperaceae are constructive or dominant species in vegetation, and pollen per- centages are less than 5% where Cyperaceae are not constructive or dominant species (cover less than 30%). Artemisia and Chenopodiaceae pollen percentages mainly have close relations with ecological regions. The relations between pollen percentages and cover are not clear for Gramineae, Legumi- nosae and Compositae.     

Water use characteristics of coexisting sand-binding vegetation in two typical soil habitats in the desert steppe of China

Understanding the water use characteristics and water relationship of coexisting vegetation in a mixed-species plantation of trees and shrubs is crucial for the sustainable restoration of degraded arid areas. This study investigated the water use characteristic of coexisting sand-binding vegetation combinations in the sierozem habitat (Populus przewalskii Maxim namely Populus-S and Caragana liouana) and aeolian sandy soil habitats (Populus przewalskii Maxim namely Populus-A and Salix psammophila) of the desert steppe. By analysing the δ²H and δ¹⁸O isotopes in xylem, soil water, groundwater and precipitation, a Bayesian MixSIAR model was employed to quantitatively assess the water utilization characteristics of plants. Throughout the growing season, in the sierozem habitat, C. liouana exhibits the highest efficiency in utilizing soil moisture above 60 cm (53.45%) and displays adaptable water use strategies. In contrast, Populus-A predominantly relies on deep soil moisture below 60 cm plus groundwater (63.89%). In the aeolian sandy soil habitat, both Populus-A and S. psammophila similarly favour deep soil moisture below the 60 cm soil plus groundwater (66.77% and 67.60%, respectively). During the transition period from the dry to the wet seasons, although both Populus-A and S. psammophila in the aeolian sandy soil habitat shifted their water sources from deeper to shallower ones, there was considerable overlap in the water sources used by Populus-A and S. psammophila. This overlap led to competition for water resources and exacerbated the depletion of deep soil moisture in both seasons. Conversely, in the sierozem habitat, the partitioning of water sources between Populus-S and C. liouana facilitated the allocation and utilization of water resources between the two species. The findings highlight the need for species-specific consideration in water resource allocation within mixed-species plantations of trees and shrubs, which is crucial for sustainable vegetation restoration in sand-binding ecosystems.     

Comparison of climatic threshold of geographical distribution between dominant plants and surface pollen in China

The geographical distribution of dominant plant species in China was georeferenced and climatic variables were interpolated into all grids.Accordingly,the percentage distributions of principal pollen taxa based on 1860 surface pollen sites in China were selected and the related climate values were interpolated with the same method. The geographical and climatic comparison between the two data-sets indicated that the climate threshold of most pollen taxa from surface pollen is coherent with plant distributions. The climatic envelopes of dominant plant are mostly accordant with those of pollen taxa at certain levels. However, some distinct offsets of the climate ranges exist between the two datasets for most pollen taxa identified at family level, such as Ericaceae,Asteraceae, Poaceae and Chenopodiaceae. The present study provides for the first time rich information on temperature and precipitation in relation to pollen and plant distribution based on the datasets on a continental scale useful for global ecological modeling and Quaternary palaeoclimate reconstruction.     

鄱阳湖典型洲滩湿地植物水碳稳定同位素与内在水分利用效率变化特征

在极端水文事件频发和人类活动影响加剧的背景下,鄱阳湖水文情势的异常变动给洲滩湿地植物带来了一系列影响。为进一步了解鄱阳湖湿地植物水分利用来源和内在水分利用效率(iWUE)的季节变化规律,揭示优势植物在生长过程中对不同水分变化的适应策略,于2020年12月-2021年5月在鄱阳湖国家级自然保护区蚌湖和修河之间的典型洲滩湿地上设置监测断面,对灰化苔草(Carex cinerascens)、南荻(Triarrhena lutarioriparia)植物样品及其潜在水源样品进行系统采集,测定并分析了水、碳稳定同位素的动态变化特征和指示意义。结果表明,典型洲滩湿地苔草和南荻植物茎水的氢、氧稳定同位素组成没有表现出明显差异,从冬季至春季,植物茎水的δ¹⁸O值总体上均呈现波动富集的变化趋势。苔草在春季生长期iWUE没有表现出明显变化,而南荻在萌发时期iWUE最低,之后的生长期iWUE具有显著的增长趋势。在各潜在水源当中,植物茎水的同位素组成与土层中的重力水最为相近,其次为与根系分布联系密切的土壤水。在春季降水频繁时,来源于降水且埋深较浅的重力水可能是植物利用的主要水源,而在枯水期重力水埋深较深时,植物采取降水和土壤水的混合利用模式应对水分胁迫。植物叶片有机质的δ¹⁸O值分析发现,苔草在萌发生长期iWUE的变化与光合作用能力相关的因素有关,南荻iWUE的变化主要受气孔导度变化的影响。     

Relationship between coral growth rate and sea surface temperature in the northern part of South China Sea during the past 100 a

To research the relationship between coral growth rate and sea surface temperatnre (T_ss), 5 cores of livingPorites lutea were collected from the Xisha Islands and the southern Hainan Island waters and measured. The results of the study show that there is an obviously positive correlation between the coral growth rates and theTss records from the northern part of South China Sea. The annual growth rates of the five samples ofPorites lutea during the past 100 a are in the range of 7—15 mm/a, and their mean value is 11 mm/a. The correlation coefficients between the coral growth rates and the T_ss records from the waters during 1961—1993 are in the range of 0.77—0.89. As a result, a thermometer of the coral growth rate is established. A hindcasting T_ss, in the waters from 1993 to 1961 has been obtained with an error of about 0.12—0.17°C. Based upon the calculated result, the rising rate of T_ss in the northern part of South China Sea during the past 100 a is 0.20°C. which is higher than that of the air temperature in China (0.09°C/100 a), but lower than that of the global temperature and that of T_ss in the tropical western Pacific Ocean. Project supported by the National Nutural Science Foundation of China and the Multidesciplinary Oceanographic Expedition Team of Chinese Academy of Sciences to the Nansha Islands.     

Variations in runoff,sediment load,and their relationship for a major sediment source area of the Jialing River basin,southern China

Investigation of the variations in runoff, sediment load, and their dynamic relation is conducive to understanding hydrological regime changes and supporting channel regulation and fluvial management. This study is undertaken in the Xihanshui catchment, which is known for its high sediment-laden in the Jialing River of the Yangtze River basin, southern China, to evaluate the change characteristics of runoff, sediment load, and their relationship at multi-temporal scales from 1966 to 2016. The results showed that runoff changed significantly for more months, whereas the significant changes in monthly sediment load occurred from April to September. The contributions of runoff in summer and autumn and sediment load in summer to their annual value changes were greater. Annual runoff and sediment load in the Xihanshui catchment both exhibited significant decreasing trends (p < 0.05) with a significant mutation in 1993 (p < 0.05). The average annual runoff in the change period (1994–2016) decreased by 49.58% and annual sediment load displayed a substantial decline with a reduction of 77.77% in comparison with the reference period (1966–1993) due to climate change and intensive human activity. The power functions were satisfactory to describe annual and extreme monthly runoff–sediment relationships, whereas the monthly runoff–sediment relationship and extreme monthly sediment-runoff relationship were changeable. Spatially, annual runoff–sediment relationship alteration could be partly attributed to sediment load changes in the upstream area and runoff variations in the downstream region. Three quantitative methods revealed that the main driver for significant reductions of annual runoff and sediment load is the human activity dominated by soil and water conservation measures, while climate change only contributed 22.73%–38.99% (mean 32.07%) to the total runoff reduction and 3.39%–35.56% (mean 17.32%) to the total decrease in sediment load.