Liming Lai

Distribution of three congeneric shrub species along an aridity gradient is related to seed germination and seedling emergence

In this study we aimed to determine whether a sequential distribution pattern along an aridity gradient is related to seed germination and seedling emergence of three Caragana species. The study tested the adaptive abilities of these species to major sandy environment factors including soil water potential, precipitation amount, and sand burial depth. The rank order of tolerance to drought and sand burial of the three species is C. korshinskii>C. intermedia>C. microphylla. The amount of precipitation and sand burial depth appear to be the main selective forces responsible for the geographical distribution of these species.

Soil respiration in different agricultural and natural ecosystems in an arid region.

The variation of different ecosystems on the terrestrial carbon balance is predicted to be large. We investigated a typical arid region with widespread saline/alkaline soils, and evaluated soil respiration of different agricultural and natural ecosystems. Soil respiration for five ecosystems together with soil temperature, soil moisture, soil pH, soil electric conductivity and soil organic carbon content were investigated in the field. Comparing with the natural ecosystems, the mean seasonal soil respiration rates of the agricultural ecosystems were 96%–386% higher and agricultural ecosystems exhibited lower CO2 absorption by the saline/alkaline soil. Soil temperature and moisture together explained 48%, 86%, 84%, 54% and 54% of the seasonal variations of soil respiration in the five ecosystems, respectively. There was a significant negative relationship between soil respiration and soil electrical conductivity, but a weak correlation between soil respiration and soil pH or soil organic carbon content. Our results showed that soil CO2 emissions were significantly different among different agricultural and natural ecosystems, although we caution that this was an observational, not manipulative, study. Temperature at the soil surface and electric conductivity were the main driving factors of soil respiration across the five ecosystems. Care should be taken when converting native vegetation into cropland from the point of view of greenhouse gas emissions.

Geographic variation in seed traits within and among forty‐two species of Rhododendron (Ericaceae) on the Tibetan plateau: relationships with altitude, habitat, plant height, and phylogeny

Seed mass and morphology are plant life history traits that influence seed dispersal ability, seeding establishment success, and population distribution pattern. Southeastern Tibet is a diversity center for Rhododendron species, which are distributed from a few hundred meters to 5500 m above sea level. We examined intra- and interspecific variation in seed mass and morphology in relation to altitude, habitat, plant height, and phylogeny. Seed mass decreased significantly with the increasing altitude and increased significantly with increasing plant height among populations of the same species. Seed mass differed significantly among species and subsections, but not among sections and subgenera. Seed length, width, surface area, and wing length were significantly negative correlated with altitude and significantly positive correlated with plant height. Further, these traits differed significantly among habitats and varied among species and subsection, but not among sections and subgenera. Species at low elevation had larger seeds with larger wings, and seeds became smaller and the wings of seeds tended to be smaller with the increasing altitude. Morphology of the seed varied from flat round to long cylindrical with increasing altitude. We suggest that seed mass and morphology have evolved as a result of both long-term adaptation and constraints of the taxonomic group over their long evolutionary history.

Alpine vegetation phenology dynamic over 16 years and its covariation with climate in a semi-arid region of China

Vegetation phenology is a sensitive indicator of ecosystem response to climate change, and plays an important role in the terrestrial biosphere. Improving our understanding of alpine vegetation phenology dynamics and the correlation with climate and grazing is crucial for high mountains in arid areas subject to climatic warming. Using a time series of SPOT Normalized Difference Vegetation Index (NDVI) data from 1998 to 2013, the start of the growing season (SOS), end of the growing season (EOS), growing season length (GSL), and maximum NDVI (MNDVI) were extracted using a threshold-based method for six vegetation groups in the Heihe River headwaters. Spatial and temporal patterns of SOS, EOS, GSL, MNDVI, and correlations with climatic factors and livestock production were analyzed. The MNDVI increased significantly in 58% of the study region, whereas SOS, EOS, and GSL changed significantly in <5% of the region. The MNDVI in five vegetation groups increased significantly by a range from 0.045 to 0.075. No significant correlation between SOS and EOS was observed in any vegetation group. The SOS and GSL were highly correlated with temperature in May and April-May, whereas MNDVI was correlated with temperature in August and July-August. The EOS of different vegetation groups was correlated with different climatic variables. Maximum and minimum temperature, accumulated temperature, and effective accumulated temperature showed stronger correlations with phenological metrics compared with those of mean temperature, and should receive greater attention in phenology modeling in the future. Meat and milk production were significantly correlated with the MNDVI of scrub, steppe, and meadow. Although the MNDVI increased in recent years, ongoing monitoring for rangeland degradation is recommended.

Soil TPH concentration estimation using vegetation indices in an oil polluted area of eastern China.

Assessing oil pollution using traditional field-based methods over large areas is difficult and expensive. Remote sensing technologies with good spatial and temporal coverage might provide an alternative for monitoring oil pollution by recording the spectral signals of plants growing in polluted soils. Total petroleum hydrocarbon concentrations of soils and the hyperspectral canopy reflectance were measured in wetlands dominated by reeds (Phragmites australis) around oil wells that have been producing oil for approximately 10 years in the Yellow River Delta, eastern China to evaluate the potential of vegetation indices and red edge parameters to estimate soil oil pollution. The detrimental effect of oil pollution on reed communities was confirmed by the evidence that the aboveground biomass decreased from 1076.5 g m−2 to 5.3 g m−2 with increasing total petroleum hydrocarbon concentrations ranging from 9.45 mg kg−1 to 652 mg kg−1. The modified chlorophyll absorption ratio index (MCARI) best estimated soil TPH concentration among 20 vegetation indices. The linear model involving MCARI had the highest coefficient of determination (R 2 = 0.73) and accuracy of prediction (RMSE = 104.2 mg kg−1). For other vegetation indices and red edge parameters, the R2 and RMSE values ranged from 0.64 to 0.71 and from 120.2 mg kg−1 to 106.8 mg kg−1 respectively. The traditional broadband normalized difference vegetation index (NDVI), one of the broadband multispectral vegetation indices (BMVIs), produced a prediction (R 2 = 0.70 and RMSE = 110.1 mg kg−1) similar to that of MCARI. These results corroborated the potential of remote sensing for assessing soil oil pollution in large areas. Traditional BMVIs are still of great value in monitoring soil oil pollution when hyperspectral data are unavailable.

Organic matter and water addition enhance soil respiration in an arid region.

Climate change is generally predicted to increase net primary production, which could lead to additional C input to soil. In arid central Asia, precipitation has increased and is predicted to increase further. To assess the combined effects of these changes on soil CO2 efflux in arid land, a two factorial manipulation experiment in the shrubland of an arid region in northwest China was conducted. The experiment used a nested design with fresh organic matter and water as the two controlled parameters. It was found that both fresh organic matter and water enhanced soil respiration, and there was a synergistic effect of these two treatments on soil respiration increase. Water addition not only enhanced soil C emission, but also regulated soil C sequestration by fresh organic matter addition. The results indicated that the soil CO2 flux of the shrubland is likely to increase with climate change, and precipitation played a dominant role in regulating soil C balance in the shrubland of an arid region.

Effects of Added Organic Matter and Water on Soil Carbon Sequestration in an Arid Region

It is generally predicted that global warming will stimulate primary production and lead to more carbon (C) inputs to soil. However, many studies have found that soil C does not necessarily increase with increased plant litter input. Precipitation has increased in arid central Asia, and is predicted to increase more, so we tested the effects of adding fresh organic matter (FOM) and water on soil C sequestration in an arid region in northwest China. The results suggested that added FOM quickly decomposed and had minor effects on the soil organic carbon (SOC) pool to a depth of 30 cm. Both FOM and water addition had significant effects on the soil microbial biomass. The soil microbial biomass increased with added FOM, reached a maximum, and then declined as the FOM decomposed. The FOM had a more significant stimulating effect on microbial biomass with water addition. Under the soil moisture ranges used in this experiment (21.0%–29.7%), FOM input was more important than water addition in the soil C mineralization process. We concluded that short-term FOM input into the belowground soil and water addition do not affect the SOC pool in shrubland in an arid region.

Strong light inhibits germination of Artemisia sphaerocephala and A. ordosica at low temperature and its relevance to revegetation in sandy lands of Inner Mongolia, China

Artemisia sphaerocephala and A. ordosica are two dominant shrub species in Mu Us sandy land (Inner Mongolia, China) and are widely used for vegetation restoration. However, there are two different conclusions about the effect of light on their germination: light promotes germination versus light inhibits germination. The aim of this study was to evaluate these two conclusions and relate the results to instances of failure of these two species to germinate well when air-dispersed in revegetation projects. The effects of fluctuating temperature, light/dark, source (population), position on mother plant, storage condition, and storage time were tested on germination of achenes of these two species. At low temperature, final percent germination (FPG) of achenes in dark and nearly dark conditions was significantly higher than those in light. At 10:20°C, achenes of both A. sphaerocephala and A. ordosica had higher FPG in dark than in light regardless of source, position on mother plants or storage condition. At suboptimum (5:15°C) and supraoptimal (25:35°C) temperatures, germination of A. sphaerocephala and A. ordosica achenes was inhibited in both light and darkness. It was concluded that light inhibits germination of A. sphaerocephala and A. ordosica achenes at low (10:20°C) temperature but not at high (15:25°C) temperature. Since the temperature in Mu Us sandy land is around 10:20°C in early June, when air sowing is done, achenes should germinate best when they are covered by a thin layer of sand.

Ecological Effects of Oil Pollution on Soil-Plant System

With industrial production and application of oil,oil pollution has become a worldwide and serious environmental problem.Ecological effects of oil pollution on soil,plant individuals,plant community and ecosystem are summed up systematically in this paper.There are many toxicants such as BTEX(benzene,toluene,ethylbenzene,and xylene) and PAHs(polycyclic aromatic hydrocarbons) in oils and petrochemicals.These oil pollutants transfer into the soil-plant system and affect the quality of underground water.Thus,oil pollution affects not only soil-plant system(including its composition,structure,function and service),but also human health through food chain.Oil pollution affects soil water condition,porosity and other physical properties;as well as soil carbon,nutrient and other chemical properties.It influences the composition and diversity of soil microbial community,soil enzymes and other biological properties.In most cases,oils pose oxidative stress to plants.Cell membranes are damaged by penetration of hydrocarbon molecules,leading to the leakage of cell contents.Oils usually reduce photosynthesis rates by destroying chloroplast membranes.Oil pollution often inhibits plant germination,growth,flowering and fruiting.However,low dose of oils may promote the growth of some plants.The effects of oil pollution on plant individuals can be classified into four categories: Promoting,no effect,sublethal and lethal.Correspondingly,plant responds in three ways(adaptation,tolerance and death).Thus,there are three basic patterns in which oil pollution affects plant community and finally reduces its biomass,species diversity and vegetation cover.The combination of the changes of plant community and the alternation of soil environment reduces the productivity,stability and health of ecosystem.Finally,functions and services of ecosystem are decreased by oil pollution.Oil pollutants can be biologically remediated and degraded by microorganisms,plants and mycorrhizae.These biological processes can be enhanced by nutrient addition and aeration.Vegetation indices,red edge effect and other remote sensing technologies are potential methods to monitor ecological effects of oil pollution.Overall,indices of different hierarchical levels in the soil-plant system respond to oil pollutants acutely or chronically.Linking these responses with ecological effects of oil pollution is one of the important and difficult issues in future researches.Therefore,multi-scaled and systematic researches should be carried out,and these researches should integrate indoor controlled experiments,outdoor controlled experiments and field investigations.With these researches,the system of hierarchical indices for ecological effects of oil pollution should be established to quantify the relationships between oil pollutants and indices of ecological effects.Then the ecological effects of oil pollution could be mechanically interpreted with simulations of some models,and the effects of oil pollution on soil-plant system could be comprehensively understood.These efforts will provide theoretical foundation and practical guidelines for ecological risk assessment,remediation and control of oil pollution.

The effect of photosynthetic parameters on species acclimation in an arid mountainous region of China

Understanding the mechanisms of how environmental factors limit species distribution along environmental gradients is a central question in ecology. This study aimed to understand species acclimation in view of photosynthetic parameters in an arid mountainous region. We measured some photosynthetic parameters and light and CO 2 photosynthesis response curves for all plant communities with seven dominant species in 13 sites along an elevation gradient in the Qilian Mountains in arid northwestern China. The results showed that species in xerothermic environments had low maximum rate of carboxylation (Vcmax) (14.5 μmol m -2 s -1 ) and maximum rate of electron transport (Jmax) (22.7 μmol m -2 s -1 ), high light compensation points (60.0 μmol m -2 s -1 ) and light saturation points (1150.7 μmol m -2 s -1 ), high dark respiration rates (5.3 μmol m -2 s -1 ), and high maximum photosynthetic rates (Amax) (18.1 μmol m -2 s -1 ) compared with species in mesic environments. Photosynthesis parameters did not vary with temperature, precipitation, and altitude in different communities dominated by the same species, Picea crassifolia. However, some photosynthesis parameters varied with temperature, precipitation, and altitude in communities dominated by species other than spruce at different elevations. Selected photosynthesis parameters could be used to measure species adaptation to environmental gradients in arid mountain regions.