Shenglei Fu

Interactive effects of biochar and the earthworm Pontoscolex corethrurus on plant productivity and soil enzyme activities

PurposeThere is a growing interest in the use of soil enzymes as early indicators of soil quality change under contrasting agricultural management practices. In recent years, there has been increasing interest in the use of biochar to improve soil properties and thus soil quality. In addition, earthworms can also be used to ameliorate soil properties. However, there is no literature available on how biochar and earthworms interact and affect soil enzymes.The general objective of the present study was to test the suitability of adding biochar and earthworms in two tropical soils with low fertility status in order to improve their characteristics and productivity.Materials and methodsBiochars were prepared from four different materials [sewage sludge (B1), deinking sewage sludge (B2), Miscanthus (B3) and pine wood (B4)] on two tropical soils (an Acrisol and a Ferralsol) planted with proso millet (Panicum milliaceum L.). In addition, in order to investigate the interaction between earthworms and biochar, earthworm Pontoscolex corethrurus was added to half of the mesocosms, while excluded in the remaining half. The activities of invertase, β-glucosidase, β-glucosaminidase, urease, phosphomonoesterase and arylsulphatase were determined. The geometric mean of the assayed enzymes (GMea) was used as an integrative soil quality index.Results and discussionOverall, earthworms and especially biochar had a positive effect on soil quality. GMea showed B1, B2 and B3 performing better than B4; however, results were soil specific. Plant productivity increased under both biochar and earthworm addition. Fruit productivity and plant growth was enhanced by B1 and B2 but not by B3 or B4.ConclusionsEnhancements of productivity and soil enzymatic activities are possible in the presence of earthworms and the combination of the practices earthworm and biochar addition can be suggested in low fertility tropical soils. However, scientists should proceed carefully in the selection of biochars as the results of this study show a high specificity in the biochar–soil interaction.

Combining phytoextraction and biochar addition improves soil biochemical properties in a soil contaminated with Cd.

The main goal of phytoremediation is to improve ecosystem functioning. Soil biochemical properties are considered as effective indicators of soil quality and are sensitive to various environmental stresses, including heavy metal contamination. The biochemical response in a soil contaminated with cadmium was tested after several treatments aimed to reduce heavy metal availability including liming, biochar addition and phytoextraction using Amaranthus tricolor L. Two biochars were added to the soil: eucalyptus pyrolysed at 600 °C (EB) and poultry litter at 400 °C (PLB). Two liming treatments were chosen with the aim of bringing soil pH to the same values as in the treatments EB and PLB. The properties studied included soil microbial biomass C, soil respiration and the activities of invertase, β-glucosidase, β-glucosaminidase, urease and phosphomonoesterase. Both phytoremediation and biochar addition improved soil biochemical properties, although results were enzyme specific. For biochar addition these changes were partly, but not exclusively, mediated by alterations in soil pH. A careful choice of biochar must be undertaken to optimize the remediation process from the point of view of metal phytoextraction and soil biological activity.

Can Biochar and Phytoextractors Be Jointly Used for Cadmium Remediation

Phytoremediation of soils contaminated with cadmium was tested after liming (CaO) or biochar addition, using red amaranth (Amaranthus tricolor L.) as test plant species. Two biochars with contrasting characteristics were prepared from two feedstocks and added to the soil at a rate of 3% (w:w): Eucalyptus pyrolysed at 600°C (EB) and poultry litter at 400°C (PLB). Liming was carried out in two treatments (CaO1) and (CaO2) to the same pH as the treatments EB and PLB respectively. Total plant mass increased in soils amended with PLB and with a mixture of PLB and EB; however this was not sufficient to increase the efficiency of phytoextraction. Bioavailable and mobile fractions of Cd diminished after liming or biochar addition. Our study infers that, both the amount of Cd immobilized and the main mechanism responsible for this immobilization varies according to biochar properties.

The effect of biochar and its interaction with the earthworm Pontoscolex corethrurus on soil microbial community structure in tropical soils.

Biochar effects on soil microbial abundance and community structure are keys for understanding the biogeochemical cycling of nutrients and organic matter turnover, but are poorly understood, in particular in tropical areas. We conducted a greenhouse experiment in which we added biochars produced from four different feedstocks [sewage sludge (B1), deinking sewage sludge (B2), Miscanthus (B3) and pine wood (B4)] at a rate of 3% (w/w) to two tropical soils (an Acrisol and a Ferralsol) planted with proso millet (Panicum milliaceum L.). The interactive effect of the addition of earthworms was also addressed. For this purpose we utilized soil samples from pots with or without the earthworm Pontoscolex corethrurus, which is a ubiquitous earthworm in tropical soils. Phospholipid fatty acid (PLFA) measurements showed that biochar type, soil type and the presence of earthworms significantly affected soil microbial community size and structure. In general, biochar addition affected fungal but not bacterial populations. Overall, biochars rich in ash (B1 and B2) resulted in a marked increase in the fungi to bacteria ratio, while this ratio was unaltered after addition of biochars with a high fixed carbon content (B3 and B4). Our study remarked the contrasting effect that both, biochar prepared from different materials and macrofauna, can have on soil microbial community. Such changes might end up with ecosystem-level effects.

Biochar alters the resistance and resilience to drought in a tropical soil

Soil microbes play a key role in nutrient cycling and carbon sequestration. Global change can alter soil microbial population composition and behavior. Biochar addition has been explored in the last years as a way to mitigate global warming. However, responses of microbial communities to biochar addition in particular in relation to abiotic disturbances are seldom documented. An example of these disturbances, which is predicted to be exacerbated with global warming, is regional drought. It has been known that fungal-based food webs are more resistant to drought than their bacterial counterparts. Our study found that biochar addition can increase the resistance of both the bacterial and fungal networks to drought. Contrary to expected, this result was not related to a change in the dominance of fungal or bacteria. In general, soil amended with biochar was characterized by a faster recovery of soil microbial properties to its basal values. Biochar addition to the soil also suppressed the Birch effect, a result that has not been previously reported.

Effects of understory removal and N-fixing species seeding on soil N2O fluxes in four forest plantations in southern China

Abstract The magnitude, temporal, and spatial patterns of nitrous oxide (N2O) fluxes in plantations are still largely unknown; however, they are crucial for our understanding and management of global greenhouse gas emissions. The objective of this study was to determine the effects of forest management practices, such as the understory removal and nitrogen (N)-fixing species (Cassia alata [C. alata]) seeding, on soil N2O fluxes in four forest plantations in southern China. Fluxes of N2O were measured in a Eucalyptus urophylla plantation (EUp), an Acacia crassicarpa plantation (ACp), 10 native species-mixed plantation (Tp), and 30 native species-mixed plantation (THp) by a static chamber method from June 2007 to May 2008 in Guangdong province, China. Four forest management treatments, including understory removal and replacement with C. alata (UR+CA), understory removal only (UR), C. alata seeding only (CA), and (4) control without any disturbances (CK), were applied in the four forest plantations. The results showed that N2O fluxes were higher under UR treatment as compared to CK in EUp (16.9 μg m−2 h−1), ACp (16.3 μg m−2 h−1), Tp (14.4 μg m−2 h−1), and THp (14.4 μg m−2 h−1) during the study period. Soil N2O fluxes under CA treatment tended to be enhanced in EUp (18.1 μg m−2 h−1), ACp (18.3 μg m−2 h−1), Tp (19 μg m−2 h−1), and THp (16.6 μg m−2 h−1), having higher values in CA than in CK. There were positive relationships between N2O fluxes and soil temperature (P < 0.01), soil moisture (P < 0.01), and nitrate (NO3)–N concentrations (P < 0.05). Our results indicated that soil NO3–N, soil temperature, and moisture are the primary controlling variables for soil N2O fluxes. The present study improved our understanding of soil N2O fluxes in forest plantations under different management practices.

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.

Response of soil respiration and ecosystem carbon budget to vegetation removal in Eucalyptus plantations with contrasting ages

Reforested plantations have substantial effects on terrestrial carbon cycling due to their large coverage area. Although understory plants are important components of reforested plantations, their effects on ecosystem carbon dynamics remain unclear. This study was designed to investigate the effects of vegetation removal/understory removal and tree girdling on soil respiration and ecosystem carbon dynamics in Eucalyptus plantations of South China with contrasting ages (2 and 24 years old). We conducted a field manipulation experiment from 2008 to 2009. Understory removal reduced soil respiration in both plantations, whereas tree girdling decreased soil respiration only in the 2-year-old plantations. The net ecosystem production was approximately three times greater in the 2-year-old plantations (13.4 t C ha−1 yr−1) than in the 24-year-old plantations (4.2 t C h−1 yr−1). The biomass increase of understory plants was 12.6 t ha−1 yr−1 in the 2-year-old plantations and 2.9 t ha−1 yr−1 in the 24-year-old plantations, accounting for 33.9% and 14.1% of the net primary production, respectively. Our findings confirm the ecological importance of understory plants in subtropical plantations based on the 2 years of data. These results also indicate that Eucalyptus plantations in China may be an important carbon sink due to the large plantation area.

Non‐target effects of herbicides on soil nematode assemblages

BACKGROUND Herbicides are used extensively to control weeds. However, little is known about the non-target effects of herbicides on soil nematode assemblages. The objective of this study was to determine whether herbicides affect the abundance of nematodes in specific trophic groups. Meta-analysis was performed, and the calculated effect size, lr, quantified the impact of herbicides on the abundance of total nematodes and five trophic groups (bacterivores, fungivores, plant parasites, omnivores and predators). RESULTS Measurements of lr indicated that herbicides decreased abundance of both fungivores and predators; however, abundance of bacterivores, plant parasites and omnivores increased. Overall, total nematode abundance tended to increase in response to herbicide application. CONCLUSION The decrease in predator abundance suggests that herbicide application disturbs soil food webs. The increase in bacterivore and decrease in fungivore abundance suggest that bacterivores are more tolerant and both fungivores and predators more sensitive to herbicide applications. Herbicides also have non-target effects on omnivores, which may be due to the increased amount of food resources for omnivores after weed control. Additionally, the use of herbicides may result in a risk of an increase in plant-parasitic nematode abundance.

Consistent effects of canopy vs. understory nitrogen addition on the soil exchangeable cations and microbial community in two contrasting forests.

Anthropogenic N deposition has been well documented to cause substantial impacts on the chemical and biological properties of forest soils. In most studies, however, atmospheric N deposition has been simulated by directly adding N to the forest floor. Such studies thus ignored the potentially significant effect of some key processes occurring in forest canopy (i.e., nitrogen retention) and may therefore have incorrectly assessed the effects of N deposition on soils. Here, we conducted an experiment that included both understory addition of N (UAN) and canopy addition of N (CAN) in two contrasting forests (temperate deciduous forest vs. subtropical evergreen forest). The goal was to determine whether the effects on soil exchangeable cations and microbial biomass differed between CAN and UAN. We found that N addition reduced pH, BS (base saturation) and exchangeable Ca and increased exchangeable Al significantly only at the temperate JGS site, and reduced the biomass of most soil microbial groups only at the subtropical SMT site. Except for soil exchangeable Mn, however, effects on soil chemical properties and soil microbial community did not significantly differ between CAN and UAN. Although biotic and abiotic soil characteristics differ significantly and the responses of both soil exchangeable cations and microbial biomass were different between the two study sites, we found no significant interactive effects between study site and N treatment approach on almost all soil properties involved in this study. In addition, N addition rate (25 vs. 50 kg N ha(-1) yr(-1)) did not show different effects on soil properties under both N addition approaches. These findings did not support previous prediction which expected that, by bypassing canopy effects (i.e., canopy retention and foliage fertilization), understory addition of N would overestimate the effects of N deposition on forest soil properties, at least for short time scale.