Soil quality and microbial communities in subtropical slope lands under different agricultural management practices.

Land degradation is a major threat to ecosystem. Long-term conventional farming practices can lead to severe soil degradation and a decline in crop productivity, which are challenging for both local and global communities. This study was conducted to clarify the responses on soil physicochemical properties and microbial communities to changes in farming practices. Slope land orchards under three agricultural management practices-conventional farming (CF), organic farming (OF), and ecofriendly farming (EFF)-were included in this study. We found that soil carbon stock increased by 3.6 and 5.1 times in surface soils (0-30 cm) under EFF and OF treatments, respectively. EFF and OF significantly increased the contents of total nitrogen by 0.33-0.46 g/kg, ammonia-N by 3.0-7.3 g/kg, and microbial biomass carbon by 0.56-1.04 g/kg but reduced those of pH by 0.6 units at least, and available phosphorous by 104-114 mg/kg. The application of phosphorous-containing herbicides and chemical fertilizers might increase the contents of phosphorous and nitrate in CF soil. High abundances of Acidobacteria and Actinobacteria were observed in EFF and OF soils, likely because of phosphorous deficiency in these soils. The abundance of fungi in OF soil indicated that plants' demand for available soil phosphorous induced the fungus-mediated mineralization of organic phosphorous. High abundances of Gammaproteobacteria, Planctomycetes, Firmicutes, and Nitrospirae were observed in CF soil, possibly because of the regular use of herbicides containing phosphorous and chemical fertilizers containing high total nitrogen contents.

Air pollutant removal by four sidewalk tree species in the largest city in Taiwan.

Air pollutants pose risks to human health, especially in densely populated cities. We compared the interception of suspended particles and metal elements by four sidewalk tree species with different leaf surface wettability (based on contact angle), leaf area, and phenology in Taipei, Taiwan. Suspended particles were enriched 2.0-2.5 times in throughfall relative to rainfall due to wash-off of suspended particles deposited on leaf surfaces during rainless periods. The enrichment in throughfall was greater in tree species with larger leaf areas. Despite greater concentrations of suspended particles in rainfall during the low-leaf-area period, enrichment was greater in the high-leaf-area period, indicating that leaf area was a key factor affecting canopy interception of pollutants. Throughfall enrichment of suspended particles positively correlated with water quantity, indicating that air pollutants intercepted by tree canopies were not fully washed off by rainfall. Annually, ∼830 g of suspended particles were intercepted and washed off from one tree canopy, with a crown area of 42 m2 . Scaling up, a rough estimate of 72.7 Mg of suspended particles were intercepted annually by the 90,000 sidewalk trees in Taipei City. Copper, chromium, and aluminum were enriched in throughfall compared with rainfall. However, lead was depleted in throughfall, indicating greater interception than wash-off. Based on our results, leaf area and length of foliated period are key characteristics affecting canopy interception of particulate matter and associated metal elements, whereas leaf surface wettability is of secondary importance.

Sequestration of P fractions in the soils of an incipient ferralisation chronosequence on a humid tropical volcanic island.

BACKGROUND: Phosphorus (P) is the limiting nutrient in many mature tropical forests. The ecological significance of declining P stocks as soils age is exacerbated by much of the remaining P being progressively sequestered. However, the details of how and where P is sequestered during the ageing in tropical forest soils remains unclear. RESULTS: We examined the relationships between various forms of the Fe and Al sesquioxides and the Hedley fractions of P in soils of an incipient ferralitic chronosequence on an altitudinal series of gently sloping benches on Green Island, off the southeastern coast of Taiwan. These soils contain limited amounts of easily exchangeable P. Of the sesquioxide variables, only Fe and Al crystallinities increased significantly with bench altitude/soil age, indicating that the ferralisation trend is weak. The bulk of the soil P was in the NaOH and residual extractable fractions, and of low lability. The P fractions that correlated best with the sesquioxides were the organic components of the NaHCO3 and NaOH extracts. CONCLUSIONS: The amorphous sesquioxides, Feo and Alo, were the forms that correlated best with the P fractions. A substantial proportion of the labile P appears to be organic and to be associated with Alo in organic-aluminium complexes. The progression of P sequestration appears to be slightly slower than the chemical and mineralogical indicators of ferralisation.

Effects of field scale in situ biochar incorporation on soil environment in a tropical highly weathered soil.

Biochar has been proven as a soil amendment to improve soil environment. However, mechanistic understanding of biochar on soil physical properties and microbial community remains unclear. In this study, a wood biochar (WB), was incorporated into a highly weathered tropical soil, and after 1 year the in situ changes in soil properties and microbial community were evaluated. A field trial was conducted for application of compost, wood biochar, and polyacrylamide. Microstructure and morphological features of the soils were characterized through 3D X-ray microscopy and polarized microscopy. Soil microbial communities were identified through next-generation sequencing (NGS). After incubation, the number of pores and connection throats between the pores of biochar treated soil increased by 3.8 and 7.2 times, respectively, compared to the control. According to NGS results, most sequences belonged to Anaerolinea thermolimosa, Caldithrix palaeochoryensis, Chthoniobacter flavus, and Cohnella soli. Canonical correlation analysis (CCA) further demonstrated that the microbial community structure was determined by inorganic N (IN), available P (AP), pH, soil organic C (SOC), porosity, bulk density (BD), and aggregate stability. The treatments with co-application of biochar and compost facilitated the dominance of Cal. palaeochoryensis, Cht. flavus, and Coh. soli, all of which promoted organic matter decomposition and ammonia oxidation in the soil. The apparent increases in IN, AP, porosity, and SOC caused by the addition of biochar and compost may be the proponents of changes in soil microbial communities. The co-application of compost and biochar may be a suitable strategy for real world biochar incorporation in highly weathered soil.

Soil and biomass carbon re-accumulation after landslide disturbances.

In high-standing islands of the Western Pacific, typhoon-triggered landslides occasionally strip parts of the landscape of its vegetative cover and soil layer and export large amounts of biomass and soil organic carbon (OC) from land to the ocean. After such disturbances, new vegetation colonizes the landslide scars and OC starts to reaccumulate. In the subtropical mountains of Taiwan and in other parts of the world, bamboo (Bambusoideae) species may invade at a certain point in the succession of recovering landslide scars. Bamboo has a high potential for carbon sequestration because of its fast growth and dense rooting system. However, it is still largely unknown how these properties translate into soil OC re-accumulation rates after landslide disturbance. In this study, a chronosequence was established on four former landslide scars in the Central Mountain Range of Taiwan, ranging in age from 6 to 41 years post disturbance as determined by landslide mapping from remote sensing. The younger landslide scars were colonized by Miscanthus floridulus, while after approx. 15 to 20 years of succession, bamboo species (Phyllostachys) were dominating. Biomass and soil OC stocks were measured on the recovering landslide scars and compared to an undisturbed Cryptomeria japonica forest stand in the area. After initially slow re-vegetation, biomass carbon accumulated in Miscanthus stands with mean annual accretion rates of 2 ± 0.5 Mg C ha-1 yr-1. Biomass carbon continued to increase after bamboo invasion and reached ~40% of that in the reference forest site after 41 years of landslide recovery. Soil OC accumulation rates were ~2.0 Mg C ha-1 yr-1, 6 to 41 years post disturbance reaching ~64% of the level in the reference forest. Our results from this in-situ study suggest that recovering landslide scars are strong carbon sinks once an initial lag period of vegetation re-establishment is overcome.

Dynamic responses of DOC and DIC transport to different flow regimes in a subtropical small mountainous river.

Transport of riverine dissolved carbon (including DOC and DIC) is a crucial process linking terrestrial and aquatic C reservoirs, but has rarely been examined in subtropical small mountainous rivers (SMRs). This study monitored DOC and DIC concentrations on a biweekly basis during non-event flow periods and at 3 h intervals during two typhoon events in three SMRs in southwestern Taiwan between January 2014 and August 2016. Two models, HBV (the Hydrologiska Byråns Vattenbalansavdelning model) and a three-endmember mixing model, were applied to determine the quantities of DOC and DIC transport from different flow paths. The results show that the annual DOC and DIC fluxes were 2.7-4.8 and 48.4-54.3 t C km-2 yr-1, respectively, which were approx. 2 and 20 times higher than the global mean of 1.4 and 2.6 t C km-2 yr-1, respectively. The DIC / DOC ratio was 14.08, which is much higher than the mean of large rivers worldwide (1.86), and indicates the high rates of chemical weathering in this region. The two typhoons contributed 12%-14% of the annual streamflow in only 3 days (about 1.0% of the annual time), whereas 15.0%-23.5% and 9.2%-12.6% of the annual DOC and DIC flux, respectively, suggested that typhoons play a more important role in DOC transport than DIC transport. The end-member mixing model suggested that DOC and DIC export was mainly from surface runoff and deep groundwater, respectively. The unique patterns seen in Taiwan SMRs characterized by high dissolved carbon flux, high DIC / DOC ratio, and large transport by intense storms should be taken into consideration when estimating global carbon budgets.

Structure and Diversity of Soil Bacterial Communities in Offshore Islands.

The effects of biogeographical separation and parent material differences in soil bacterial structure and diversity in offshore islands remain poorly understood. In the current study, we used next-generation sequencing to characterize the differences in soil bacterial communities in five offshore subtropical granite islands (Matsu Islets, MI) of mainland China and two offshore tropical andesite islands (Orchid [OI] and Green Islands [GI]) of Taiwan. The soils of OI and GI were more acidic and had higher organic carbon and total nitrogen content than MI soils. The bacterial communities were dominated by Acidobacteria and Proteobacteria but had different relative abundance because soils were derived from different parent material and because of geographic distance. Non-metric multi-dimensional scaling revealed that the communities formed different clusters among different parent material and geographically distributed soils. The alpha-diversity in bacterial communities was higher in tropical than subtropical soils. Mantel test and redundancy analysis indicated that bacterial diversity and compositions of OI and GI soils, respectively, were positively correlated with soil pH, organic carbon, total nitrogen, microbial biomass carbon and nitrogen. These results suggest that variations in soil properties of offshore islands could result from differences in soil parent material. Distinct soils derived from different parent material and geographic distance could in turn alter the bacterial communities.

Unusual Roles of Discharge, Slope and SOC in DOC Transport in Small Mountainous Rivers, Taiwan.

Riverine dissolved organic carbon (DOC), responsible for riverine productivity, is rarely documented in subtropical small mountainous rivers (SMRs) where high rainfall and steep slopes are the main features. This study investigated the DOC export at eight sites in three Taiwan SMRs to characterize the dynamics and controlling factors of DOC transport. Results showed that the mean DOC concentration of ~0.78 mg L-1 is much lower than the global average of ~5.29 mg L-1. However, the mean DOC yield, ~22.51 kg-C ha-1 yr-1, is higher than the global average of 14.4-19.3 kg-C ha-1 yr-1. Comparing with worldwide rivers from literature, the annual discharge, slope, and SOC (soil organic carbon) are controlling factors as expected, though they influence in different ways. SOC stock likely regulated by elevation-dependent biomes dominate the DOC supply, while slope restrains the DOC generation due to shallow soil depth and fast runoff velocity. However, the abundant discharge flushing this persistent low supply leads to a large DOC export in the SMRs. Furthermore, the DOC dynamics during typhoon periods showed a clockwise hysteresis, suggesting that the DOC is mainly from the riparian zone or downslope area during the rising limb of the hydrograph. This study elucidates the DOC transport in SMRs and provides an atypical yet significant piece of understanding on DOC transport in a global context.

In-situ biochar application conserves nutrients while simultaneously mitigating runoff and erosion of an Fe-oxide-enriched tropical soil.

Climate change gives rise to rapid degradation of rural soils in sloping subtropical and tropical areas and might further threaten environmental sustainability. In this study, we conducted an integrated evaluation of the effects of wood biochar (WB) application mixed with a green waste dreg compost (GWC) on runoff quality, soil losses, and agricultural productivity for a highly weathered tropical soil. A conventional agriculture method, in which soils are treated with anionic polyacrylamide (PAM), was also conducted for comparison. The amounts of runoff and soil loss, and nutrient retention were evaluated a year after WB application. Soil fertility was also investigated through a year pot experiment with rape (Brassica campestris L.) cultivation. Our results showed that the WB application not only effectively increased soil pH, soil organic carbon (SOC) and exchangeable K+ but also increased the production of rape plants. Significant reduction of runoff and the increases of inorganic nitrogen (IN) and total phosphorus (TP) were found in the WB-treated soil. Compared to the control, the co-application of WB and GWC, particularly for the WB at 4%, decreased runoff by 16.8%, soil loss by 25%, and IN loss (via runoff) by 41.8%. Meanwhile, compared to the control and PAM treatments, the co-application of WB and GWC improved soil acidity and the contents of SOC, IN, TP, and exchangeable K+. The co-application of WB and GWC could be an alternative agricultural strategy to obtain benefits to agricultural productivity and environmental sustainability.

Short-term biochar application induced variations in C and N mineralization in a compost-amended tropical soil.

To mitigate food shortage due to global warming, developing sustainable management practices to stabilize soil organic matter (SOM) and sequester more carbon (C) in the cultivated soils is necessary, particularly in subtropical and tropical areas. A short-term (56 days) incubation experiment was conducted to evaluate the influences of rice husk biochar (RHB) and manure compost (MC) application on C mineralization and nitrogen (N) immobilization in a sandy loam soil. The RHB was separately incorporated into the soil at application rates of 2 and 4% (w/w) either with or without 1% (w/w) compost. Our results displayed that macroaggregates (≥2 mm) were obviously increased by 11% in soil amended with RHB + MC at the end of incubation. In addition, the experimental results presented that the C mineralization of the soil rapidly increased during the first week of incubation. However, the co-application of compost with biochar (RHB + MC) revealed that CO2 emission was significantly decreased by 13-20% compared to the soil with only MC. In addition, the mineralized N in the soil was lower in RHB + MC-amended soil simultaneously than only MC-amended soil, indicating that biochar addition induced N immobilization. The physical protection of compost by its occlusion into aggregates or adsorption on surface of RHB as proved by the micromorphological observation was the main reason for lower C and N mineralization in soil amended with RHB + MC. Overall results revealed that RHB + MC treatment can decrease the decomposition of compost and sequester more C in the tropical agricultural soils.

Soil ingestion rates for children under 3 years old in Taiwan.

Soil and dust ingestion rates by children are among the most critical exposure factors in determining risks to children from exposures to environmental contaminants in soil and dust. We believe this is the first published soil ingestion study for children in Taiwan using tracer element methodology. In this study, 66 children under 3 years of age were enrolled from Taiwan. Three days of fecal samples and a 24-h duplicate food sample were collected. The soil and household dust samples were also collected from children's homes. Soil ingestion rates were estimated based on silicon (Si) and titanium (Ti). The average soil ingestion rates were 9.6±19.2 mg/day based on Si as a tracer. The estimated soil ingestion rates based on Si did not have statistically significant differences by children's age and gender, although the average soil ingestion rates clearly increased as a function of children's age category. The estimated soil ingestion rates based on Si was significantly and positively correlated with the sum of indoor and outdoor hand-to-mouth frequency rates. The average soil ingestion rates based on Si were generally lower than the results from previous studies for the US children. Ti may not be a suitable tracer for estimating soil ingestion rates in Taiwan because the Ti dioxide is a common additive in food. To the best of our knowledge, this is the first study that investigated the correlations between soil ingestion rates and mouthing behaviors in Taiwan or other parts of Asia. It is also the first study that could compare available soil ingestion data from different countries and/or different cultures. The hand-to-mouth frequency and health habits are important to estimate the soil ingestion exposure for children. The results in this study are particularly important when assessing children's exposure and potential health risk from nearby contaminated soils in Taiwan.

Contribution of urban runoff in Taipei metropolitan area to dissolved inorganic nitrogen export in the Danshui River, Taiwan.

A previous study has demonstrated that Danshui River has almost the highest dissolved inorganic nitrogen (DIN) yield in the world and exports most of the DIN in the form of ammonium unlike the world's large rivers. However, the DIN sources are poorly constrained. In this study, the contributions of major sources in the Taipei metropolitan area to the DIN export in the Danshui River were investigated. It is observed that ammonium is the major DIN species in the downstream reaches, resulting from the ammonium-dominated inputs of the effluents of wastewater treatment plants (WWTP) and rain water pumping stations (RWPS). DIN concentrations in the downstream (urban) reaches are substantially elevated. The upstream tributaries annually discharge ∼2709 t DIN to the downstream reaches. However, the DIN discharge off the downstream reaches rises to ∼17,918 t, resulting from the contribution of RWPS-collected water, i.e., ∼14,632 t, and the effluents of two WWTP, i.e., ∼577 t. RWPS-collected water inherently contains the contribution of atmospheric deposition, ∼2937 t DIN. This finding implies that ∼11,695 t (∼66 % of the downstream output) DIN flux off the Danshui River is from urban runoff and can be attributed to human activities in the Taipei metropolitan area. To improve the water quality in the Danshui River, water quality controls in urban runoff are important.

Magnified Sediment Export of Small Mountainous Rivers in Taiwan: Chain Reactions from Increased Rainfall Intensity under Global Warming.

Fluvial sediment export from small mountainous rivers in Oceania has global biogeochemical significance affecting the turnover rate and export of terrestrial carbon, which might be speeding up at the recognized conditions of increased rainfall intensity. In this study, the historical runoff and sediment export from 16 major rivers in Taiwan are investigated and separated into an early stage (1970-1989) and a recent stage (1990-2010) to illustrate the changes of both runoff and sediment export. The mean daily sediment export from Taiwan Island in the recent stage significantly increased by >80% with subtle increase in daily runoff, indicating more sediment being delivered to the ocean per unit of runoff in the recent stage. The medians of the runoff depth and sediment yield extremes (99.0-99.9 percentiles) among the 16 rivers increased by 6.5%-37% and 62%-94%, respectively, reflecting the disproportionately magnified response of sediment export to the increased runoff. Taiwan is facing increasing event rainfall intensity which has resulted in chain reactions on magnified runoff and sediment export responses. As the globe is warming, rainfall extremes, which are proved to be temperature-dependent, very likely intensify runoff and trigger more sediment associated hazards. Such impacts might occur globally because significant increases of high-intensity precipitation have been observed not only in Taiwan but over most land areas of the globe.

Impacts of biochar on physical properties and erosion potential of a mudstone slopeland soil.

Food demand and soil sustainability have become urgent issues recently because of the global climate changes. This study aims to evaluate the application of a biochar produced by rice hull, on changes of physiochemical characteristics and erosion potential of a degraded slopeland soil. Rice hull biochar pyrolized at 400°C was incorporated into the soil at rates of 2.5%, 5%, and 10% (w/w) and was incubated for 168 d in this study. The results indicated that biochar application reduced the Bd by 12% to 25% and the PR by 57% to 92% after incubation, compared with the control. Besides, porosity and aggregate size increased by 16% to 22% and by 0.59 to 0.94 mm, respectively. The results presented that available water contents significantly increased in the amended soils by 18% to 89% because of the obvious increase of micropores. The water conductivity of the biochar-amended soils was only found in 10% biochar treatment, which might result from significant increase of macropores and reduction of soil strength (Bd and PR). During a simulated rainfall event, soil loss contents significantly decreased by 35% to 90% in the biochar-amended soils. In conclusion, biochar application could availably raise soil quality and physical properties for tilth increasing in the degraded mudstone soil.

Using EDDS and NTA for enhanced phytoextraction of Cd by water spinach.

A greenhouse experiment was used to test the applicability of [S,S]-Ethylenediaminedisuccinic acid (EDDS) and nitrilotriacetic acid (NTA) at rates of 2.5 mmol kg(-1) and 5.0 mmol kg(-1), respectively, to increase the uptake of Cd by water spinach (Ipomoea aquatic Forsk) in soils with 2.5-30 mg Cd kg(-1). The addition of EDDS and NTA significantly increased water soluble Cd in soils. However, the Cd concentration in the root and shoot was higher in the NTA treatment than in the EDDS treatment. No instance of Cd hyperaccumulation was observed; however, the 5.0 mmol kg(-1) NTA treatment for soil with 30 mg Cd kg(-1) caused the Cd concentration to increase to 86 mg kg(-1), which is close to the critical concentration (100 mg kg(-1)) of a hyperaccumulator. The total Cd uptake in the treatments of EDDS and NTA for soils with 2.5, 5.0, and 10 mg Cd kg(-1) was acceptable, and was higher than the control. The level of 5.0 mmol kg(-1) EDDS was excessively high for enhanced phytoextraction in soils with 20 and 30 mg Cd kg(-1). Water spinach for Cd phytoextraction is a viable alternative to using herbaceous hyperaccumulators.

Sorption of paraquat on clay components in Taiwan's oxisol.

The sorption of herbicides in soils is mainly influenced by clay components. The objectives of this study were to evaluate the contribution of clay components on paraquat sorption. The surface soils (0-20 cm) of a Laopi pedon (Fine, mixed, Hyperthermic Typic Hapludox) were separated clays into whole (< 2.0 microm), coarse (0.2-2.0 microm), and fine (< 0.2 microm) fractions with the treatments of removals of organic matter (OM) and free Fe (Fed) oxides. Results indicated that sorption isotherm of paraquat was fitted by the nonlinear Freundlich equation with R2 values ranged in 0.79-0.96, respectively. The shape of paraquat adsorption isotherm on the fine fraction was H-type, but their shapes on the whole and coarse fractions were L-types. The fine clay fractions gave higher contribution on paraquat sorption than the coarse clay fractions identified by their K(f) values. Organic matter associated with fine clay fraction had high CEC contributing to relatively high affinity for paraquat. The DCB treatment created high-affinity sites for paraquat on the fine clay, but had little effect on paraquat sorption for the coarse clay. Chemisorption is the major mechanism for retention of paraquat on clay components, not ion exchange. However, the silicate clay had the highest affinity for paraquat and free Fe compound had the lowest.