Dazhi Wen

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.

Structural and physiological responses of two invasive weeds, Mikania micrantha and Chromolaena odorata , to contrasting light and soil water conditions

To better understand the requirement of light and soil water conditions in the invasion sites of two invasive weeds, Mikania micrantha and Chromolaena odorata, we investigated their structural and physiological traits in response to nine combined treatments of light [full, medium and low irradiance (LI)] and soil water (full, medium and low field water content) conditions in three glasshouses. Under the same light conditions, most variables for both species did not vary significantly among different water treatments. Irrespective of water treatment, both species showed significant decreases in maximum light saturated photosynthetic rate (Pmax), photosynthetic nitrogen-use efficiency, and relative growth rate under LI relative to full irradiance; specific leaf area, however, increased significantly from full to LI though leaf area decreased significantly, indicating that limited light availability under extreme shade was the critical factor restricting the growth of both species. Our results also indicated that M. micrantha performed best under a high light and full soil water combination, while C. odorata was more efficient in growth under a high light and medium soil water combination.

Nutrient limitation on ecosystem productivity and processes of mature and old-growth subtropical forests in China.

Nitrogen (N) is considered the dominant limiting nutrient in temperate regions, while phosphorus (P) limitation frequently occurs in tropical regions, but in subtropical regions nutrient limitation is poorly understood. In this study, we investigated N and P contents and N:P ratios of foliage, forest floors, fine roots and mineral soils, and their relationships with community biomass, litterfall C, N and P productions, forest floor turnover rate, and microbial processes in eight mature and old-growth subtropical forests (stand age >80 yr) at Dinghushan Biosphere Reserve, China. Average N:P ratios (mass based) in foliage, litter (L) layer and mixture of fermentation and humus (F/H) layer, and fine roots were 28.3, 42.3, 32.0 and 32.7, respectively. These values are higher than the critical N:P ratios for P limitation proposed (16–20 for foliage, ca. 25 for forest floors). The markedly high N:P ratios were mainly attributed to the high N concentrations of these plant materials. Community biomass, litterfall C, N and P productions, forest floor turnover rate and microbial properties were more strongly related to measures of P than N and frequently negatively related to the N:P ratios, suggesting a significant role of P availability in determining ecosystem production and productivity and nutrient cycling at all the study sites except for one prescribed disturbed site where N availability may also be important. We propose that N enrichment is probably a significant driver of the potential P limitation in the study area. Low P parent material may also contribute to the potential P limitation. In general, our results provided strong evidence supporting a significant role for P availability, rather than N availability, in determining ecosystem primary productivity and ecosystem processes in subtropical forests of China.

Phosphatase activity in relation to key litter and soil properties in mature subtropical forests in China

Phosphatase-mediated phosphorus (P) mineralization is one of the critical processes in biogeochemical cycling of P and determines soil P availability in forest ecosystems; however, the regulation of soil phosphatase activity remains elusive. This study investigated the potential extracellular activities of acid phosphomonoesterase (AcPME) and phosphodiesterase (PDE) and how they were related to key edaphic properties in the L horizon (undecomposed litter) and F/H horizon (fermented and humified litter) and the underlying mineral soil at the 0-15cm depth in eight mature subtropical forests in China. AcPME activity decreased significantly in the order of F/H horizon>L horizon>mineral soil horizon, while the order for PDE activity was L horizon=F/H horizon>mineral soil horizon. AcPME (X axis) and PDE (Y axis) activities were positively correlated in all horizons with significantly higher slope in the L and F/H horizons than in the mineral soil horizon. Both AcPME and PDE activities were positively related to microbial biomass C, moisture content and water-holding capacity in the L horizon, and were positively related to soil C:P, N:P and C:N ratios and fine root (diameter≤2mm) biomass in the mineral soil horizon. Both enzyme activities were also interactively affected by forest and horizon, partly due to the interactive effect of forest and horizon on microbial biomass. Our results suggest that modulator(s) of the potential extracellular activity of phosphatases vary with horizon, depending on the relative C, P and water availability of the horizon.

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.

Relationships of phosphorus fractions to organic carbon content in surface soils in mature subtropical forests, Dinghushan, China

Exploring the relationship between the accumulation of soil organic carbon (C) and the form and availability of soil phosphorus (P) is important for improved understanding of soil P availability and its regulation of C storage in forest ecosystems. Here, we investigated the relationships among soil organic C, sequentially extracted P fractions and P sorption index in 32 surface soils (0–0.15 m depth) across eight mature subtropical forests (80–400 years) in Dinghushan, China. Results showed that soil organic P (Po) accounted for 40–63% (mean 54%) of soil total P. Soil organic C was significantly positively correlated with both the content and the percentage of soluble inorganic P (Pi), Al-Po and Fe-Po fractions and the content of the Al-Pi fraction. The content of soil total Po increased significantly with soil organic C, whereas the percentage of soil total Po tended to increase with soil organic C only when soil organic C was low (<30 Mg/ha) but was relatively stable when soil organic C was high (≥30 Mg/ha). Moreover, soil organic C was highly correlated with P sorption index. Our results suggest that accumulation of organic C may increase, rather than decrease, the availability of P in surface soil in mature subtropical forests.

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.

Altitudinal patterns and controls of plant and soil nutrient concentrations and stoichiometry in subtropical China.

Altitude is a determining factor of ecosystem properties and processes in mountains. This study investigated the changes in the concentrations of carbon (C), nitrogen (N), and phosphorus (P) and their ratios in four key ecosystem components (forest floor litter, fine roots, soil, and soil microorganisms) along an altitudinal gradient (from 50 m to 950 m a.s.l.) in subtropical China. The results showed that soil organic C and microbial biomass C concentrations increased linearly with increasing altitude. Similar trends were observed for concentrations of total soil N and microbial biomass N. In contrast, the N concentration of litter and fine roots decreased linearly with altitude. With increasing altitude, litter, fine roots, and soil C:N ratios increased linearly, while the C:N ratio of soil microbial biomass did not change significantly. Phosphorus concentration and C:P and N:P ratios of all ecosystem components generally had nonlinear relationships with altitude. Our results indicate that the altitudinal pattern of plant and soil nutrient status differs among ecosystem components and that the relative importance of P vs. N limitation for ecosystem functions and processes shifts along altitudinal gradients.