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Forests suffer from heavy losses due to the occurrence of fires. A prediction model based on environmental condition, such as meteorological and vegetation indexes, is considered a promising tool to control forest fires. The construction of prediction models can be challenging due to (i) the requirement of selection of features most relevant to the prediction task, and (ii) heavily imbalanced data distribution where the number of large-scale forest fires is much less than that of small-scale ones. In this paper, we propose a forest fire prediction method that employs a sparse autoencoder-based deep neural network and a novel data balancing procedure. The method was tested on a forest fire dataset collected from the Montesinho Natural Park of Portugal. Compared to the best prediction results of other state-of-the-art methods, the proposed method could predict large-scale forest fires more accurately, and reduces the mean absolute error by 3–19.3 and root mean squared error by 0.95–19.3. The proposed method can better benefit the management of wildland fires in advance and the prevention of serious fire accidents. It is expected that the prediction performance could be further improved if additional information and more data are available.

Recycling sewage sludge (SS) to soil potentially causes soil heavy metal (HM) pollution and plant phytotoxicity. Biochar plays an important role in alleviating HM phytotoxicity, and responses vary with the feedstocks and usage of biochar. However, the effect of plant adaptability on biochar-mediated alleviation is poorly understood. Here, SS-derived biochar (SB) and rice straw-derived biochar (RB) applied at rates of 1.5% and 3% (W/W, SB1.5, SB3, RB1.5, and RB3) were used to improve the properties of soil amended with SS at 50% (W/W). Alleviation of phytotoxicity by biochar was further analyzed with SS-sensitive plant Monstera deliciosa and SS-resistant plant Ruellia simplex. Results revealed that both SB and RB significantly decreased the soil's bulk density and increased water retention. They also changed soil organic matter content and HMs fractionation. The addition of SB or RB alleviated the SS phytotoxicity, and they significantly promoted the growth and the root morphology and physiological index of M. deliciosa. But for R. simplex, these significant changes only synchronously occurred in SB3 treatment. The alleviation in M. deliciosa was more prominent and more closely connected with soil property changes than in R. simplex. Also, more soil property predictors were observed to play an important role in M. deliciosa growth than in R. simplex growth. These results indicated that biochar alleviating HMs phytotoxicity in SS-amended soil is associated with the changes of soil property. Moreover, the alleviation varies more prominently with plant adaptability than with biochar feedstocks and usage.

The handling of sewage sludge (SS) and urban plant litter (UPL) has become an important concern. Immobilizing heavy metals (HMs) is regarded as a necessary process for recycling SS in agriculture and forestry. Here, HM removal and HM phytotoxicity in SS during vermicomposting with different additive UPLs was investigated. The results show that vermicomposting with additive UPL significantly reduced the content of HMs, and increased organic carbon content and the proportion of macroaggregates in SS. This process also significantly immobilized HMs by mainly transforming extractable and reducible HMs into residual products. The litters of Dracontomelon duperreanum and Bauhinia purpurea increased oxidizable HMs in SS and the accumulation capacity of HMs of earthworms during vermicomposting. The Cd content in vermicomposts with the B. purpurea litter addition was decreased by 31% relative to the initial SS. Maize in vermicomposts with UPL additions, especially with B. purpurea litter, exhibited significan5tly higher seed germination rates, seedling biomass, root activity, and a lower accumulation of HMs than in SS compost without UPL additions. These results suggest that vermicomposting with additive UPL can alleviate the phytotoxicity of HMs in SS and provides a new method for simultaneously recycling SS and UPL.

Sewage sludge (SS) application on forest plantation soils as a fertilizer/soil amendment is increasingly becoming a forestry management measure. However, the potential risk of SS-derived potentially toxic elements (PTEs) is still a cause for concern. This research was carried out to evaluate PTEs behavior in SS applied as an amendment for forestland application purposes. Speciation and transformation perspectives on residual effects during a 3-year field experiment were evaluated. Sewage sludge was applied to soils under Eucalyptus urophylla S.T. Blake, Schima superba Gardn. et Champ, and Pinus elliottii Engelm plantations at 30 Mg·ha−1 (dry weight). We investigated the total concentrations of Cu, Zn, Pb, Cd, and Ni, as well as their concentrations of five fractions: exchangeable (F1), bound to carbonates (F2), Fe–Mn oxides (F3), organic matter (F4), and residual (F5) along with the 0–10 cm of a surface A horizon (topsoil) one day, one, two, and three years after SS application, respectively. Sewage sludge caused significant increase in PTEs total concentrations and proportion of fraction F1 or F2. The mobility index and potential ecological risk confirmed that the risk was linked to the presence of these PTEs, especially for Cd. The total concentration and corresponding ecological risks of PTEs in most cases decreased, suggesting a potential loss of PTEs from the topsoil system. The percentage of all PTEs in fractions F1–F4 decreased and that in F5 increased with time. These results illustrate that the residual and mobility of PTEs in the topsoil during SS utilization was lower than expected and more attention should be paid to the risk of PTEs transferring to other environments.

The ecological effects of eucalypt plantations (EPs) have garnered increasing attention. To understand their effect on soil quality at a landscape scale, and to determine whether soil quality parameters differ due to different stand types, we evaluated soil characteristics in twenty-one groups of EPs, Pinus massoniana Lamb. plantations (PMPs) and natural broadleaved forests (NBFs) across Guangdong Province, China. Both the physical characteristics of soil hydrology and the properties of soil nutrients in A and B horizons were determined. Results showed that, compared to NBFs, EPs and PMPs produced a shallower litter layer, reduced canopy density, higher soil bulk density, significantly lower total porosity, non-capillary porosity, total water volume, and hygroscopic water in the A horizon (P

Recycling sludge as a soil amendment has become a viable option for sludge disposal. However, such application can lead to soil pollution because of its enrichment in contaminants, especially heavy metals. To identify an effective means to ensure the ecological safety of sewage sludge landscape utilization, a glasshouse experiment was conducted by mixing sewage sludge at 0%, 15%, 30%, 60%, and 100% (V/V) amendment ratios to landscape soils and planting five common landscape plants (Aphelandra ruellia, Syngonium podophyllum, Schefflera odorata, Alocasia macrorrhiza, and Dianella ensifolia). Sludge amendment significantly improved fertility and moisture retention capacity of soil, but dramatically increased the contents of Cd, Pb, Cu, and Zn. Compared with lateritic red soil (CK), sludge amended-soils increased the relative growth rate of landscape plants and enhanced their nutrient uptake and heavy metals accumulation. A rate of 30% or less of sludge application showed positive growth effects for all five landscape plants, and did not cause potential ecological risks of heavy metals to landscape soils. However, rates of 60% or higher posed very high potential ecological risk in multiple metals, particularly in Cd. Interestingly, S. odorata, A. ruellia and A. macrorrhiza could alleviate the ecological risks of Cd, Cu and Zn, respectively, and these results were confirmed by data of relative changes in heavy metal contents in post-experiment soil. Our results suggest that attention to reducing the environmental risks of heavy metals in sludge utilization as landscape soil-amendments should not only be paid to controlling the application dosage of sludge but also to planting suitable plant species.

Previous studies show that pupating in soil is essential for Heortia vitessoides Moore (Lepidoptera: Crambidae) to complete its life cycle. However, little is known of the process. In the present study, we observed soil-burrowing and pupal-chamber construction by prepupae of H. vitessoides in 0.5-cm-wide acrylic plate interlayers. In bioassays, we also investigated pupation behaviors and pupal physiology and morphology in response to soil moistures of 5%, 25%, 45%, and 65% water saturation. Prepupae burrowed significantly deeper in soils with higher levels of soil moisture and constructed larger pupal chambers at 65% water saturation. H. vitessoides pupae also had significantly greater percentage biomass loss and lower body water content when the soil moistures were lower. Interestingly, pupae in 5% saturated soil were smaller and showed a significantly higher surface-to-volume ratio than at other soil moisture levels, which might pose challenges in water conservation.

Chinese fir (Cunninghamia lanceolata (Lamb.) Hook) is an important native tree species in China. Consecutive cropping traditionally occurs in Chinese fir plantations (CFPs), but this practice has resulted in productivity declines in subsequent rotations. This study was designed to better understand the change of soil properties in the continuous cropping CFPs. We investigated soil pH, soil organic matter (SOM), and nutrient contents in different soil layers and in rhizosphere soil (RS) and non-rhizosphere soil (NRS) under CFPs of different ages and in different rotations. In the upper (0–20 cm) soil layer, soil pH decreased, while SOM increased, beneath mature CFPs with consecutive rotations. Total nitrogen (TN), available potassium, and available phosphorus contents in the upper soil layers did not differ significantly with consecutive rotations. Soil pH in RS was significantly lower than in NRS under mature plantations of the third rotation. Soil organic matter, TN, and available nitrogen did not differ between RS and NRS. Available phosphorus in RS was consistently lower than in NRS, and was highly deficient in the third rotation. We conclude that no severe soil nutrient degradation occurred in the continuous cropping CFPs examined in this study, with soil acidification and phosphorus deficiency being two primary problems observed.

Recycling sewage sludge (SS) as a soil amendment potentially causes soil heavy metals (HMs) contamination. This study investigated the potential roles of landscape plants co-planting in SS-amended soil remediation. Three landscape trees Mangifera persiciforma, Bischofia javanica, and Neolamarckia cadamba (NC), and three ground cover plants Dianella ensifolia, Syngonium podophyllum, and Schefflera odorata (SO) were selected for the tree-ground cover co-planting. Species in different co-planting treatments exhibited diversified effects on the growth, root morphology, HMs uptake, and HMs accumulation. Five plant characteristics including total root length, total surface of roots (diameter

Application of sewage sludge to forested land has been regarded as a promising method for sewage sludge disposal, because it can improve soil fertility and productivity. It is also likely to alter the soil nutrient cycle, which is mainly mediated by soil microorganisms. However, how the soil bacterial community responds to the application of sewage sludge in subtropical planted forests is poorly understood. Unlike farmland soil, forestland soil is covered with leaf litter, which might influence the effects of sewage sludge on the soil bacterial community. In this study, we investigated the effects of sewage sludge application (30 t/ha) on the soil bacterial community at 0–10 cm depth in three forest plantations (Eucalyptus urophylla, Pinus elliottii, and Schima superba) in southern China. The treatments included sewage sludge addition (treatment S), sewage sludge addition and leaf litter removal (treatment SLR), and a control (CK). The composition of the soil bacterial community differed in the three forest plantations and was affected by treatment S, but the effects of treatment S were not greatly altered by litter removal in the three forest plantations. At the community level, the composition of the soil bacterial community was significantly related to soil pH, available phosphorus (P) and potassium (K), and cadmium (Cd). At the phylum level, the relative abundance of Actinobacteria, Bacteroidetes, and Chloroflexi was increased by treatments S and SLR, while that of Acidobacteria, Proteobacteria, and Verrucomicrobia was decreased. The changes in the abundance of these bacteria were significantly related to the increase in the contents of available nutrients and heavy metals. Sewage sludge application resulted in an increased number of positive interactions among bacterial taxa, lower modularity, and higher connectivity, which indicated an unstable bacterial community. Changes in the composition, co-occurrence pattern, and keystone taxa of the bacterial community might reflect adaptation to sewage sludge application.

Higher flavonoids yield can increase economic and industrial efficiency of Ginkgo biloba Linn. leaf-harvesting plantation. However, high-temperature limits ginkgo leaf flavonoids production in warm climates regions. Few studies have reported on methods that may improve ginkgo leaf flavonoids yield by increasing leaf productivity and flavonoids content simultaneously. This study investigated the effects of combined application of fertilizer for bud growth (FBG) and fertilizer for leaf growth (FLG) on the growth, productivity and flavonoids accumulation of ginkgo leaves, aiming to optimize fertilization schemes for improving leaf flavonoids yield of ginkgo in high-temperature regions. Results revealed that FBG significantly improved twig bud break, twig number, and twig elongation, and increased leaf number (up to 446±27.38 per four-year-old seedling) in spring. Topdressing FLG in summer moderated the decline of leaf SPAD (soil and plant analyzer development) values, modulated leaf nutrient content, and significantly increased single leaf dry weight, antioxidative enzyme activities, and leaf flavonoids content. Dry leaf productivity, flavonoids content, and flavonoids yield of four-year-old ginkgo with combined application of FBG and FLG was 103±16.05 g/plant, 6.54±0.13 mg/g, and 615.71±58.22 mg/plant, respectively, which were comparably high in reference to those in the central production region. These results suggest that the integrated application of FBG and FLG is an effective approach for improving ginkgo leaf flavonoids yield in high-temperature regions.

Enriched planting of native tree species in monoculture plantation forests is a commonly recommended forest practice. However, its effect on various ecological processes is generally lacking. Here, we carried out an experiment in a 16-year-old Eucalyptus plantation in South China to assess the effects of enriched planting of native tree species on surface water, soil erosion and nutrient losses. Two treatments were conducted in 2008: (1) enriched planting of native broadleaved tree species with uniform thinning of 60% of Eucalyptus trees (TEP); and (2) enriched planting of native broadleaved tree species without thinning (NEP). The original Eucalyptus plantation stands was used as the control (CK). Runoff plots (total n = 9, 3 for each treatment or CK) were established in 2009, and surface water flow, sediment, nitrogen (N) and phosphorus (P) losses were monitored from major rainfall events in 2010–2012. Results showed that enriched planting in Eucalyptus plantation significantly reduced surface water flow and soil erosion. Compared with CK, TEP and NEP reduced annual surface water flow by 29–43% and 11–16%, and reduced annual soil erosion by 38–54% and 20–33% throughout the study period, respectively. TEP and NEP had significantly lower annual mean concentrations of N and P in surface water. Compared with CK, TEP reduced annual N and P losses through surface water by 42–60% and 44–64%, respectively, while NEP reduced them by 25–28% and 24–34%, respectively. N and P losses were significantly related to surface water flow. Between the two treatments, TEP was better for retaining water and soil, and for preventing nutrient loss. These results clearly demonstrated that the enriched planting of native tree species effectively retained surface water and nutrients.

Improving soil fertility is a critical component of abandoned rare-earth mine land (ARL) revegetation. To study the effects of sewage sludge (SS), earthworms, and Jatropha curcas in ARL revegetation, SS (40% in mass ratio) and earthworms (0, 40, 60, and 80 individual adult Eisenia fetida kg−1) were applied to abandoned rare-earth mine land soil (ARLS) and then J. curcas was grown in a potting experiment. The organic carbon, nutrients (N, P, K) and heavy metals (HMs; Cd, Cu, Zn) contents in ARLS and the biomass and nutrients uptake in J. curcas were significantly increased by SS amendment. Application of 80 individual E. fetida kg−1 significantly increased availability of P and K in SS-amended ARLS relative to other treatments. Earthworms increased the height, ground diameter and biomass of J. curcas, but the promotion of biomass became weaker as earthworm density increased. After J. curcas harvest, the contents of Cd, Cu and Zn in SS-amended ARLS were reduced by 15%, 23%, and 19%, respectively. With the joint application of J. curcas and earthworms, a much larger decrease in contents of Cd (34–40%), Cu (31–44%) and Zn (24–29%) in SS-amended ARLS were observed, and the HMs ecological risks were reduced from “moderate potential” to “low potential”. Moreover, J. curcas and earthworms together exerted more reduction in the exchangeable fraction HMs in SS-amended ARLS than J. curcas alone. Our results suggest that the integrated application of SS, earthworms and J. curcas is an effective approach for ARL revegetation.

Landscape plants have great potentials in heavy metals (HMs) removal as sewage sludge compost (SSC) is increasingly used in urban forestry. We hypothesize that woody plants might perform better in HMs phytoremediation because they have greater biomass and deeper roots than herbaceous plants. We tested the differences in growth responses and HMs phytoremediation among several herbaceous and woody species growing under different SSC concentrations through pot experiments. The mixing percentage of SSC with soil at 0%, 15%, 30%, 60, and 100% were used as growth substrate for three woody (Ficus altissima Bl., Neolamarckia cadamba (Roxb.) Bosser, and Bischofia javanica Bl.) and two herbaceous (Alocasia macrorrhiza (L.) G. Don and Dianella ensifolia (L.) DC) plants. Results showed that the biomass, relative growth rate, and nutrient uptake for all plants increased significantly at each SSC concentration compared to the control; woody plants had higher biomass and nutrient use efficiency than herbaceous plants. All plants growing in SSC-amended soils accumulated appreciable amounts of HMs and reduced the contents of HMs present in the substrates. The woody plants were generally more effective than herbaceous plants in potentials of HMs phytoextraction, but A. macrorrhiza showed higher bioconcentration and translocation of Cu and Zn and D. ensifolia had higher bioconcentration and translocation of Cd than woody plants. The optimal application concentrations were 30% or less for woody plants and 15% for herbaceous plants for plant growth and ecological risk control, respectively. Intercropping suitable woody and herbaceous landscape plants in urban forestry might have promising potentials to minimize the ecological risks in the phytoremediation of SSC.

Forest productivity is dependent on soil quality, which in turn is related to litter; yet there is limited understanding of the relationships between litter and soil quality. The effects of litter removal treatment on tree growth and soil properties were examined in a Pinus caribaea stand with the aim of providing an understanding of consequences of litter removal on soil patterns. This knowledge is important for planning appropriate long-term forest management. Three pairs of 30 × 30 m2 plots (each pair a control and treatment) were established in the center of a P. caribaea stand in April 2002. The controls were left undisturbed with an intact litter layer, while litter was removed monthly from treated plots. The diameter and height of the P. caribaea decreased and soil quality was degraded over the experimental period in litter-removed (treated) plots. Litter removal also produced a significant increase in soil bulk density at 0–20 and 20–40 cm depths. The capillary porosity, capillary moisture...

Application of sewage sludge compost (SSC) as a fertilizer on landscaping provides a potential way for the effective disposal of sludge. However, the response of landscape trees to SSC application and the impacts of heavy metals from SSC on soil are poorly understood. We conducted a pot experiment to investigate the effects of SSC addition on Mangifera persiciforma growth and quantified its uptake of heavy metals from SSC by setting five treatments with mass ratios of SSC to lateritic soil as 0%:100% (CK), 15%:85% (S15), 30%:70% (S30), 60%:40% (S60), and 100%:0% (S100). As expected, the fertility and heavy metal concentrations (Cu, Zn, Pb and Cd) in substrate significantly increased with SSC addition. The best performance in terms of plant height, ground diameter, biomass and N, P, K uptake were found in S30, implying a reasonable amount of SSC could benefit the growth of M. persiciforma. The concentrations of Cu, Pb and Cd in S30 were insignificantly different from CK after harvest, indicating that M. persiciforma reduced the risk of heavy metal contamination of soil arising from SSC application. This study suggests that a reasonable rate of SSC addition can enhance M. persiciforma growth without causing the contamination of landscaping soil by heavy metals.

Fertilization is indispensable to the establishment success of many eucalypt plantations. Split application of fertilizer has proven effective in agronomic systems; however, its potential impact on eucalypt tree growth and fertilizer uptake efficiency (FUE) is not well understood. This study investigated the effects of split fertilizer applications on seedling growth and biomass production, nutrient uptake, and FUE for the Guanglin No. 9 clone [hybrid of Eucalyptus grandis (Hill ex Maiden) × Eucalyptus urophylla S.T. Blake]. Three application timings and a control were established at rates of 125 and 250 g inorganic fertilizer (16N–7P–7K) per seedling. Split application played a more pronounced role than fertilization rate in eucalypt seedling growth and biomass accumulation. Compared to a single-time application, split applications increased eucalypt seedling height and root collar diameter growth, biomass, and nutrient uptake. The ratio of root to seedling dry mass showed a decreasing trend with split applications, whereas ratios of stem and branch to seedling dry mass tended to increase with split applications. Split applications also significantly improved FUE compared to the single-time application treatment. Findings of this study suggest that split applications of inorganic fertilizer with two application times could be an appropriate fertilization method to improve seedling growth and FUE of this eucalypt clone.

The relationships between above-ground stem, branch, leaf masses and stand density index (SDI) were analysed in Populus×euramericana (Dode) Guinier stands in Jiangsu Province, China. The allometric equations developed in this study accurately estimated masses of above-ground and specific above-ground tree components in stands with different SDIs. The relationship between the mean above-ground mass w and the ratio of stem to the above-ground (wS/w) was examined. With increasing w, the stem mass ratio wS/w increased. Mean masses of above-ground and tree components decreased significantly with increasing SDI at age 9 years, indicating the presence of competition-induced limitations to growth. The mean above-ground mass‐SDI and mean component mass‐SDI were strongly correlated with above-ground mass-SDI and tree component mass‐SDI, respectively. An equation describing the relationship between the mean leaf area u and SDI was developed, which fitted well for the u-SDI data. Stem mass increment exponentially increased with increasing leaf area index.

Growing fruit trees on the slopes of rolling hills in South China was causing serious environmental problems because of heavy application of chemical fertilizers and soil erosion. Suitable sources of fertilizers and proper rates of applications were of key importance to both crop yields and environmental protection. In this article, the impact of four fertilizers, i.e., inorganic compound fertilizer, organic compound fertilizer, pig manure compost, and peanut cake (peanut oil pressing residue), on chestnut (Castanea mollissima Blume) growth on a slope in South China, and on the total N and total P concentrations in runoff waters have been investigated during two years of study, with an orthogonal experimental design. Results show that the organic compound fertilizer and peanut cake promote the heights of young chestnut trees compared to the control. In addition, peanut cake increases single-fruit weights and organic compound fertilizer raises single-seed weights. All the fertilizers increased the concentrations of total N and total P in runoff waters, except for organic compound fertilizer, in the first year experiment. The observed mean concentrations of total N varied from 1.6 mg/L to 3.2 mg/L and P from 0.12 mg/L to 0.22 mg/L, which were increased with the amount of fertilizer applications, with no pattern of direct proportion. On the basis of these experiment results, organic compound fertilizer at 2 kg/tree and peanut cake at 1 kg/tree are recommended to maximize chestnut growth and minimize water pollution.

Eutrophication of surface water bodies is a problem of increasing environmental and ecological concern worldwide and is particularly serious in China. In the present study, oxidation ditches were connected to a lake receiving municipal sewage sludges. Two 24 m 2 (width 2 m, length 12 m) parallel plastic oxidation ditches material were installed on a lake near the inlet of the municipal sewage. Zizania caduciflora and Canna generalis were grown in the ditches with plastic floating supporters for the removal of N and P from the sewage. The experiment was conducted firstly with municipal sewage in autumn–winter seasons for about 150 days under the following conditions: 2 m 3 /h influent flow, 0.75 kW jet-flow aerator (air/water of 5), 18 h HRT (hydrological retention time) and a return ratio of 10. Then it was run with the polluted lake water in summer–autumn for about 160 days with an aerator of 1.25 kW and an influent of 6 m 3 /h (air/water 3.3, HRT 6 h). The performance was quite stable during the experimental period for the municipal sewage treatment. The average removal rates of COD (chemical oxygen demand), SS (suspended solids), TP (total phosphorus), NH 4 + -N and inorganic-N were 70.6, 75.8, 72.6, 52.1 and 50.3%, respectively. For the polluted lake water treatment, the average concentrations of COD, NH 4 + -N and TP were 42.7, 13.1 and 1.09 mg/L, respectively, in the influent and were 25.1, 6.4 and 0.38 mg/L, respectively, in the effluent. The capacity of the plants to remove N and P by direct uptake was limited, but the indirect mechanisms also occurred. The proposed process, transforming the natural lake into a wastewater treatment plant, could evidently reduce the costs of the sewage collection, the land space requirement and the construction compared with conventional sewage treatment plants, and is especially suited to conditions in south China and south-east Asia.

The land application of sewage sludge has the potential risk of transferring heavy metals to soil or groundwater. The agricultural reuse of sludge leachate could be a cost-effective way to decrease metal contamination. Sludge leachate collected during the phytoremediation of sludge by co-cropping with Sedum alfredii and Zea mays was used for irrigating vegetables in a field experiment. Results indicate that the concentrations of Cu, Zn, Pb, and Cd in sludge leachates complied with the National Standards for agricultural irrigation water in China. For the vegetable crop Ipomoea aquatica, nutrients obtained only from the sludge leachate were not sufficient to support growth. For the second crop, Brassica parachinensis, no differences in biomass were observed between the treatment with leachate plus a half dose of inorganic fertilizer and the treatment with a full dose of inorganic fertilizers. The concentrations of heavy metals in I. aquatica and B. parachinensis were not significantly affected by the application of sludge leachates. Compared with initial values, there were no significant differences in Zn, Cd, Cu, and Pb concentrations in soil following treatment with sludge leachate. This study indicates that on range lands, sludge phytoremediation can be conducted at the upper level, and the generated sludge leachate can be safely and easily used in crop production at the lower level.

Previous soil pot and field experiments demonstrated that co-cropping the hyperaccumulator Sedum alfredii with maize increased Zn phytoextraction by S. alfredii and decreased Zn uptake by maize shoots. This hydroponic experiment was conducted to investigate whether the facilitation of Zn phytoextraction by S. alfredii resulted from improved dissolution in this co-cropping system and its relation to root exudates. S. alfredii and maize were mono- and co-cropped (without a root barrier) in nutrient solution spiked with four Zn compounds, ZnS, ZnO, Zn3(PO4)2 and 5Zn·O2CO3·4H2O (represented as ZnCO3) at 1000 mg/L Zn for 15 days without renewal of nutrient solution after pre-culture. The root exudates were collected under incomplete sterilization and analyzed. The results indicated that the difference in Zn salts had a greater influence on the Zn concentration in maize than for S. alfredii, varying from 210–2603 mg/kg for maize shoots and 6445–12476 mg/kg for S. alfredii in the same order: ZnCO3 > ZnO > Zn3(PO4)2 > ZnS. For the four kinds of Zn sources in this experiment, co-cropping with maize did not improve Zn phytoextraction by S. alfredii. In most cases, compared to co-cropped and mono-cropped maize, mono-cropped S. alfredii resulted in the highest Zn2+ concentration in the remaining nutrient solution, and also had a higher total concentration of low molecular weight organic acids (LMWOA) and lower pH of root exudation. Root exudates did partly influence Zn hyperaccumulation in S. alfredii.

The productions, seasonal dynamics, macronutrient contents and decomposition rates of the litterfalls of four typical stands, e.g., Pinus massoniana plantation, secondary evergreen broadleaved forest, Acacia mangium plantation and Schima superba-Acacia mangium plantation at the scenic Baiyunshan of Guangzhou were studied. The litterfall productions of four stands in 1998 were 8.34, 6.77, 6.31 and 11.54 t.hm-2, respectively. The seasonal dynamics of litterfall amounts demonstrated the single-peak model with the peak period in June and July. The total amounts of macronutrients returned to the forest land by means of litters in the four stands in 1998 were 26.30, 69.81, 54.9 and 152.24 kg.hm-2, respectively. The annual decomposition rates of the litterfalls were 24.4%, 53.4%, 52.4% and 57.4%.