Yuanwen Kuang

Concentrations of heavy metals and polycyclic aromatic hydrocarbons in needles of Masson pine (Pinus massoniana L.) growing nearby different industrial sources

Emissions from industrial activities pose a serious threat to human health and impose the need for monitoring both inorganic and organic pollutants in industrial areas. We selected Masson pine (Pinus massoniana L.) as potential biomonitor and collected the current (C) and previous year (C+1) needles from three industrial sites dominated by petrochemical, ceramics manufacturing, and iron and steel smelting plants and one remote site to determine heavy metals (Cu, Cd, Pb, Zn, Cr, Ni and Co) and polycyclic aromatic hydrocarbons (PAHs) in unwashed and water-washed needles. Both unwashed and washed C+1 needles showed generally higher concentrations of heavy metals and PAHs than C needles, although the washed needles more clearly spotlighted the accumulation effect of PAHs over exposure time. Water-washing resulted in a significant decrease in needle PAH concentrations with more significant effects shown in C needles. By contrast, needle heavy metal concentrations were much less affected by washing. Although heavy metals and PAHs might differ in adsorption and uptake strategies, their higher concentrations in the needles at the industrial sites indicated conspicuous contamination due to industrial emissions there. The PAH distribution patterns in pine needles accorded with the real types of energy consumption in the study sites and were efficiently used for pinpointing local pollutant sources.

Untangling the influence of phylogeny, soil and climate on leaf element concentrations in a biodiversity hotspot

Summary 1. Plant elemental properties are fundamentally important for physiology and biogeochemical cycling in ecosystems. No study has examined foliar elements and their interaction with soil and climate conditions at large geographic scales in Karst areas of China, a biodiversity hotspot in the world. Yet such information is important for understanding the functional diversity of nutrient strategies and the physiological adaptations of plants to climatic and edaphic heterogeneity. 2. We assessed the influence of phylogeny, soil type and the climate on leaf element concentrations in a clade of taxonomically diverse Karst plants from the subfamily Didymocarpoideae under an explicit phylogenetic framework. We measured leaf concentrations of seven elements and evaluated soil properties for 422 populations of 177 Didymocarpoideae species. The phylogenetic signals present in the leaf element concentrations and in soil and climatic variables were quantified at both the subfamily (Didymocarpoideae) and genus (Primulina) levels. The correlations between leaf elements and soil and climate conditions were analysed at these two phylogenetic scales. 3. The Didymocarpoideae subfamily is generally characterized by higher Ca and Mg contents relative to other plants in China. Across the subfamily, a strong phylogenetic signal is detected for all of the leaf elements analysed as well as for most soil and climate variables, whereas the genus Primulina exhibits no significant phylogenetic signal in leaf elements or in most soil variables. 4. We detected an influence of both soil and climatic conditions on leaf element concentrations. However, the patterns of the relationships between leaf elements and soil and climate variables vary at the subfamily and genus levels. The phylogeny has a stronger effect than soil and climatic factors on leaf element concentrations at the subfamily level, while the leaf element contents within the genus Primulina are mostly influenced by environmental conditions. We conclude that the influences of taxonomy, soil and climate on leaf element concentrations are dependent on the phylogenetic scale of analysis.

Distribution and Source Apportionment of Polycyclic Aromatic Hydrocarbons (PAHs) in Forest Soils from Urban to Rural Areas in the Pearl River Delta of Southern China

The upper layer of forest soils (0–20 cm depth) were collected from urban, suburban, and rural areas in the Pearl River Delta of Southern China to estimate the distribution and the possible sources of polycyclic aromatic hydrocarbons (PAHs). Total concentrations of PAHs in the forest soils decreased significantly along the urban–suburban–rural gradient, indicating the influence of anthropogenic emissions on the PAH distribution in forest soils. High and low molecular weight PAHs dominated in the urban and rural forest soils, respectively, implying the difference in emission sources between the areas. The values of PAH isomeric diagnostic ratios indicated that forest soil PAHs were mainly originated from traffic emissions, mixed sources and coal/wood combustion in the urban, suburban and rural areas, respectively. Principal component analysis revealed that traffic emissions, coal burning and residential biomass combustion were the three primary contributors to forest soil PAHs in the Pearl River Delta. Long range transportation of PAHs via atmosphere from urban area might also impact the PAHs distribution in the forest soils of rural area.

CAN Canopy Addition of Nitrogen Better Illustrate the Effect of Atmospheric Nitrogen Deposition on Forest Ecosystem

Increasing atmospheric nitrogen (N) deposition could profoundly impact community structure and ecosystem functions in forests. However, conventional experiments with understory addition of N (UAN) largely neglect canopy-associated biota and processes and therefore may not realistically simulate atmospheric N deposition to generate reliable impacts on forest ecosystems. Here we, for the first time, designed a novel experiment with canopy addition of N (CAN) vs. UAN and reviewed the merits and pitfalls of the two approaches. The following hypotheses will be tested: i) UAN overestimates the N addition effects on understory and soil processes but underestimates those on canopy-associated biota and processes, ii) with low-level N addition, CAN favors canopy tree species and canopy-dwelling biota and promotes the detritus food web, and iii) with high-level N addition, CAN suppresses canopy tree species and other biota and favors rhizosphere food web. As a long-term comprehensive program, this experiment will provide opportunities for multidisciplinary collaborations, including biogeochemistry, microbiology, zoology, and plant science to examine forest ecosystem responses to atmospheric N deposition.

Analysis of polycyclic aromatic hydrocarbons in tree-rings of Masson pine (Pinus massoniana L.) from two industrial sites in the Pearl River Delta, south China

Concentrations of polycyclic aromatic hydrocarbons (PAHs) were examined and potential sources of PAHs were identified from the dated tree-rings of Masson pine (Pinus massoniana L.) near two industrial sites (Danshuikeng, DSK and Xiqiaoshan, XQS) in the Pearl River Delta of south China. Total concentrations of PAHs (∑PAHs) were revealed with similar patterns of temporal trends in the tree-rings at both sites, suggesting tree-rings recorded the historical variation in atmospheric PAHs. The differences of individual PAHs and of ∑PAHs detected in the tree-rings between the two sites reflected the historical differences of airborne PAHs. Regional changes in industrial activities might contribute to the site-specific and period-specific patterns of the tree-ring PAHs. The diagnostic PAH ratios of Ant/(Ant + PA), FL/(FL + Pyr), and BaA/(BaA + Chr)) revealed that PAHs in the tree-rings at both sites mainly stemmed from the combustion process (pyrogenic sources). Principal component analysis further confirmed that wood burning, coal combustion, diesel, and gasoline-powered vehicular emissions were the dominant contributors of PAHs sources at DSK, while diesel combustion, gasoline and natural gas combustion, and incomplete coal combustion were responsible for the main origins of PAHs at XQS. Tree-ring analysis of PAHs was indicative of PAHs from a mixture of sources of combustion, thus minimizing the bias of short-term active air sampling.

Reconstruction of soil pH by dendrochemistry of Masson pine at two forested sites in the Pearl River Delta, South China

Abstract• Soil acidification is a global concern. Base cation (Ca, Mg, Mn and Al) concentrations, as well as their molar ratios, were measured in tree rings of Masson pines (Pinus massoniana L.) from Dinghushan and Xiqiaoshan to reconstruct the historical changes in soil acidification in the Pearl River Delta, south China.• In Dinghushan, Ca and Mn xylem concentrations yielded significant correlations with the higher soil pHs, and Ca and Mg with the lower soil pHs. In Xiqiaoshan, only xylem Mn concentration correlated significantly with the soil pH in both layers. Significant correlations between xylem molar ratios and soil pH were revealed for Ca/Mn, Mg/Mn, Mn/Al and Ca/Al in the upper soils and for the same ratios except for Ca/Al in the deeper soils in Dinghushan. The same correlations were revealed for Ca/Mn, Mg/Mn and Mn/Al at both depths in Xiqiaoshan.• Soil pHs at 0–10 cm and 10–40 cm depths at the study sites were reconstructed by the molar ratios of Mg/Mn and Ca/Mn in the xylem of Masson pines, respectively.• Cation molar ratios in the xylem of Masson pine were superior to the single Ca, Mg, Mn and Al for soil acidity reconstruction in the Delta of China.Résumé• L’acidification du sol est un phénomène important à l’échelle mondiale. Les concentrations en cations (Ca, Mg, Mn et Al) aussi bien que leurs rapports molaires dans les cernes des pins (Pinus massoniana L.) de Dinghushan et Xiqiaoshan ont été mesurées pour reconstruire les changements historiques d’acidification du sol dans le delta de la Pearl River, dans le sud de la Chine.• À Dinghushan, les concentrations en Ca et Mn du xylème présentent des corrélations significatives avec les pH de la partie supérieure du sol, Ca et Mg, avec les pH de la partie inférieure du sol. À Xiqiaoshan, seule la concentration en Mn du xylème est corrélée significativement avec les pH du sol dans les deux horizons. Des corrélations significatives entre rapports molaires dans le xylème et les pH du sol ont été mises en évidences pour Ca/Mn, Mg/Mn, Mn/Al et Ca/Al dans les parties supérieures des sols et pour les mêmes rapports sauf Ca/Al dans les parties profondes des sols à Dinghushan. Des corrélations semblables ont été révélées pour Ca/Mn, Mg/Mn et Mn/Al dans les deux profondeurs à Xiqiaoshan.• Les pH du sol à 0–10 cm et 10–40 cm de profondeur dans les sites d’étude ont été reconstruits à partir des rapports molaires de Mg/Mn et Ca/Mn dans le xylème des pins. Les rapports molaires des cations dans le xylème des pins étaient supérieurs au seul Ca, Mg, Mn et Al pour la reconstruction de l’acidité du sol dans le Delta de la Chine.

Sensitivity analyses of woody species exposed to air pollution based on ecophysiological measurements

AbstractGoal, Scope and BackgroundAir pollution has been of a major problem in the Pearl River Delta of south China, particularly during the last two decades. Emissions of air pollutants from industries have already led to damages in natural communities and environments in a wide range of the Delta area. Leaf parameters such as chlorophyll fluorescence, leaf area (LA), dry weight (DW) and leaf mass per area (LMA) had once been used as specific indexes of environmental stress. This study aims to determine in situ if the daily variation of chlorophyll fluorescence and other ecophysiological parameters in five seedlings of three woody species,Ilex rotunda, Ficus microcarpa andMachilus chinensis, could be used alone or in combination with other measurements for sensitivity indexes to make diagnoses under air pollution stress and, hence, to choose the correct tree species for urban afforestation in the Delta area.MethodsFive seedlings of each species were transplanted in pot containers after their acclimation under shadowing conditions. Chlorophyll fluorescence measurements were made in situ by a portable fluorometer (OS-30, Opti-sciences, U.S.A). Ten random samples of leaves were picked from each species for LA measurements by area-meter (CI-203, CID, Inc., U.S.A). DW was determined after the leaf samples were dried to a constant weight at 65°C. LMA was calculated as the ratio of DW/LA. Leaf N content, was analyzed according to the Kjeldhal method, and the extraction of pigments was carried out according Lin et al.Results and DiscussionThe daily mean Fv/Fm (Fv is the variable fluorescence and Fm is the maximum fluorescence) analysis showed thatIlex rotunda andFicus microcarpa vittz more highly resistant to pollution stress, followed byMachilus chinensis, implying that the efficiency of photosystem II inI. rotunda was less affected by air pollutants than the other two species. Little difference in daily change of Fv/Fm inI. rotunda between the polluted and the clean site was also observed. However, a relatively large variation of Fv/Fm appeared in the other two species, particularly inM. chinensis, suggesting that they were more sensitive to air pollutants thanI. rotunda. The mean LA was reduced for all species growing at the polluted site. The mean LMA for all species exceeded the sclerophylly threshold given by Cowling and Campbell and increased for those under pollution stress, which could be explained as one of the acclimation strategies for plants to air pollution stress. Little difference in leaf chlorophyll content was observed inF. microcarpa andM. chinensis, while remarkable differences were found inI. rotunda growing at the polluted and the clean site. Content of leaf carotenoids was largely reduced inI. rotunda growing at the polluted site, but increased inF. microcarpa andM. chinensis, compared with plants growing at the clean site. Plants growing at the clean site had a lower leaf N content than those growing at the polluted site. In addition, species with a higher resistance to pollution stress showed less difference in leaf N content than those sensitive species.ConclusionBased on Fv/Fm measurements of the three woody species,I. rotunda showed the highest resistance to air pollutants from ceramic industries, followed byF. microcarpa. M. chinensis was the most sensitive species to air pollution, had lowest capacities to cope with the air pollution stress, which was consistent with visual injury symptoms observed in the crown profiles of plants at the polluted site. Fv/Fm, LAM, LA, leaf pigments and N content could be used alone or in combination to diagnose the extent of the physiological injury. The ratio of Fv/Fm, however, was the best and most effective parameter.Recommendation and OutlookTree species which have higher air-pollutant resistance, as diagnosed by such ecophysiological parameters, should be considered first and planted widely for urban afforestation or forest regeneration in areas where the forest was seriously degraded or forest health was markedly effected by the same kind of air pollutants.

Acidity and conductivity of Pinus massoniana bark as indicators to atmospheric acid deposition in Guangdong, China.

Barks of Pinus massonianm collected from two polluted sites, Qujiang and Xiqiaoshan, and from the relatively clean site Dinghushan were used to evaluate the pollution indication by the determination of their acidity and conductivity. The acidity of the inner and outer barks from the polluted sites was significantly higher than those from the clean site, suggesting that the acidity of the bark occurred in concurrent with the air pollution. The significant lower pH values of the outer bark than the inner bark collected from all sites indicated that the outer bark was more sensitive than the inner bark in response to acid pollution, implying that the outer bark is more preferable when used as indication of atmospheric acid pollution. The conductivities of the inner barks differed significantly among the three sites, with higher values at the clean site. However, the significant differences were not observed among these sites. Furthermore, the pH values for the inner and outer barks were not correlated with the conductivity, which did not coincide with some other studies.

Homogeneity of δ15N in needles of Masson pine (Pinus massoniana L.) was altered by air pollution

The present study investigated the changes of delta(15)N values in the tip, middle and base section (divided by the proportion to needle length) of current- and previous-year needles of Masson pine (Pinus massoniana L.) from two declining forest stands suffering from air pollution, in comparison with one healthy stand. At the healthy stand, delta(15)N in the three sections of both current- and previous-year needles were found evenly distributed, while at the polluted stands, delta(15)N values in the needles were revealed significantly different from the tip to the base sections. The results implied that the distribution of delta(15)N among different parts or sections in foliages was not always homogeneous and could be affected by air pollution. We suggested that the difference of delta(15)N values among pine needle sections should be reconsidered and should not be primarily ignored when the needle delta(15)N values were used to assess plant responses to air pollution.

A structural equation model analysis of phosphorus transformations in global unfertilized and uncultivated soils

Understanding the soil phosphorus (P) cycle is a prerequisite for predicting how environmental changes may influence the dynamics and availability of P in soil. We compiled a database of P fractions sequentially extracted by the Hedley procedure and its modification in 626 unfertilized and uncultivated soils worldwide. With this database, we applied structural equation modeling to test hypothetical soil P transformation models and to quantify the importance of different soil P pools and P transformation pathways in shaping soil P availability at a global scale. Our models revealed that soluble inorganic P (Pi, a readily available P pool) was positively and directly influenced by labile Pi, labile organic P (Po), and primary mineral P, and negatively and directly influenced by secondary mineral P; soluble Pi was not directly influenced by moderately labile Po or occluded P. The overall effect on soluble Pi was greatest for labile Pi followed by the organic P pools, occluded P, and then primary mineral P; the overall influence from secondary mineral P was small. Labile Pi was directly linked to all other soil P pools and was more strongly linked than soluble Pi to labile Po and primary mineral P. Our study highlights the important roles of labile Pi in mediating P transformations and in determining overall P availability in soils throughout the world.