Tropical Rainforest Soils Research Articles

Isolation and characterization of Bacillus sp. HSY32 and its toxin gene for potential biological control of plant parasitic nematode

Plant parasitic nematodes (PPNs) cause significant damage to crop production worldwide, leading to substantial economic losses. Conventional chemical nematicides are effective but frequently associated with environmental and health hazards. In response, biological control methods, particularly the use of microbial pesticides, have emerged as a sustainable and effective alternative. This study focuses on the isolation and characterization of Bacillus sp. HSY32, a bacterial strain with nematicidal properties, from a tropical rainforest soil sample in Hainan, China. Soil samples were screened for nematicidal activity, which led to the identification of the strain HSY32. Detailed observations using optical and scanning electron microscopy (SEM) revealed that HSY32 forms spores and parasporal crystal structures, which are typically associated with nematicidal Bacillus species. Genomic analysis of HSY32 showed that its genome spans 6,711,949 base pairs and contains 7915 predicted genes, with an average GC content of 35.4%. Phylogenetic analysis, utilizing 16S rRNA sequences and average nucleotide identity (ANI), established that HSY32 is closely related to Bacillus mobilis, a known species within the Bacillus genus. Further genomic analysis using local BLAST identified several toxin genes with high similarity to known nematicidal genes, including cry4Ba, cry50Ba, app6Ba, cry70Bb, and tpp36Aa. To confirm the functionality of these toxin genes, they were cloned into pET-30a expression vectors and expressed in E. coli BL21 (DE3) cells. Among the expressed proteins, the Cry4Ba-like protein, with a molecular weight of approximately 110 kDa, was found to exhibit significant nematicidal activity in bioassays. This protein demonstrated the ability to kill or inhibit the growth of PPNs, indicating its potential as a biological control agent. The successful isolation of Bacillus strain HSY32 and the identification of its novel Cry4-like toxin gene represent a significant advancement in the field of biological control of plant parasitic nematodes. The nematicidal activity of the Cry4Ba-like protein highlights the potential of HSY32 as a source of new biopesticides. Further studies are required to enhance the production and application of these biocontrol agents in agriculture, paving the way for more sustainable and eco-friendly methods to control PPNs.Graphical

Effects of two Bacillus velezensis strains isolated from different sources on the growth of Capsicum annum

Microbial inoculants offer an environmentally friendly approach to enhance plant growth and control disease. In this study, two Bacillus velezensis strains, HKSSLJEBR3 (R3) and Ya-1 were isolated from pepper plant roots and tropical rainforest soil, respectively. Both strains exhibited strong antifungal activity against Fusarium oxysporum f. sp. capsici, with inhibition rates of 48.54 ± 0.66% for R3 and 49.35 ± 1.44% for Ya-1. In greenhouse trials, R3 significantly boosted pepper growth, with a 22.12% increase in plant height, 46.44% more leaves, and 56.29% greater fresh weight. These enhancements were likely due to the strong affinity between R3 and pepper plants. Both strains also improved soil quality, with R3 increasing available potassium (AK) by 5.13% and soil organic matter (SOM) by 4.03%, while Ya-1 showed more significant increases. Metagenomic analysis revealed that both strains altered the rhizosphere microbiome, with R3 promoting Pseudomonas and suppressing Fusarium. These results suggest that the R3 strain has strong potential for enhancing pepper growth, improving soil health, and reshaping the rhizosphere microbiome.

Factors affecting the geochemistry of rare earth elements in soils in tropical rain and montane forests in Sri Lanka across an elevation gradient

Factors affecting the geochemistry of rare earth elements in soils in tropical rain and montane forests in Sri Lanka across an elevation gradient

The emission of CO from tropical rainforest soils

Abstract. Soil carbon monoxide (CO) fluxes represent a net balance between biological soil CO uptake and abiotic soil and (senescent) plant CO production. Studies largely from temperate and boreal forests indicate that soils serve as a net sink for CO, but uncertainty remains about the role of tropical rainforest soils to date. Here we report the first direct measurements of soil CO fluxes in a tropical rainforest and compare them with estimates of net ecosystem CO fluxes derived from accumulation of CO at night under stable atmospheric conditions. Furthermore, we used laboratory experiments to demonstrate the importance of temperature on net soil CO fluxes. Net soil surface CO fluxes ranged from −0.19 to 3.36 nmol m−2 s−1, averaging ∼1 nmol CO m−2 s−1. Fluxes varied with season and topographic location, with the highest fluxes measured in the dry season in a seasonally inundated valley. Ecosystem CO fluxes estimated from nocturnal canopy air profiles, which showed CO mixing ratios that consistently decreased with height, ranged between 0.3 and 2.0 nmol CO m−2 s−1. A canopy layer budget method, using the nocturnal increase in CO, estimated similar flux magnitudes (1.1 to 2.3 nmol CO m−2 s−1). In the wet season, a greater valley ecosystem CO production was observed in comparison to measured soil valley CO fluxes, suggesting a contribution of the valley stream to overall CO emissions. Laboratory incubations demonstrated a clear increase in CO production with temperature that was also observed in field fluxes, though high correlations between soil temperature and moisture limit our ability to interpret the field relationship. At a common temperature (25 °C), expected plateau and valley senescent-leaf CO production was small (0.012 and 0.002 nmol CO m−2 s−1) in comparison to expected soil material CO emissions (∼ 0.9 nmol CO m−2 s−1). Based on our field and laboratory observations, we expect that tropical rainforest ecosystems are a net source of CO, with thermal-degradation-induced soil emissions likely being the main contributor to ecosystem CO emissions. Extrapolating our first observation-based tropical rainforest soil emission estimate of ∼ 1 nmol m−2 s−1, global tropical rainforest soil emissions of ∼ 16.0 Tg CO yr−1 are estimated. Nevertheless, total ecosystem CO emissions might be higher, since valley streams and inundated areas might represent local CO emission hot spots. To further improve tropical forest ecosystem CO emission estimates, more in situ tropical forest soil and ecosystem CO flux measurements are essential.

Variation of Geochemical Properties of Soils in Tropical Lowland Rainforests in Sri Lanka

Tropical lowland rainforests (TLRFs) of Sri Lanka are considered as diverse ecosystems which play a vital role in climate change mitigation. In recent years, increasing deforestation leads to diminishing their potential ecosystem roles. For efficient forest conservation, knowledge of both above- and below-ground characteristics of TLRFs is required. Currently, above-ground information on TLRFs is sufficiently available but the details on the below-ground characteristics are limited. Therefore, this study was carried out to investigate pedo-geochemical properties of lowland rain forests of Kanneliya (KDN) and Pitadeniya, (PTD) in Sri Lanka. Four sampling plots with 1 ha in size (KDN1, KDN2, PTD1 and PTD2) were established, selecting altitudes of 117, 174, 509, and 618 m asl, respectively. Five representative near-surface (up to 25 cm) samples were collected from each plot for the investigation. Soil pH, electrical conductivity (EC), and cation exchange capacity (CEC) were measured while soil organic matter (SOM) content was determined by (i) Walkey-Black (WB) and (ii) Loss on ignition (LI) methods. Data were analysed by ANOVA and means were compared using Duncan‘s test. All measured parameters were significantly different (P<0.05) among the sampling plots. Soil pH and EC values were ranged between 3.43– 3.78 and 0.28–0.44 dS m-1, respectively. The highest CEC was recorded in PTD2 (11.09±3.44 cmol(+)/kg) whereas the lowest was in PTD1 (5.31±1.26 cmol(+)/kg). The highest SOM was recorded in PTD1 (17.71±4.42% in WB, 18.04±3.98% in LI) whereas the lowest was noted in PTD2 (5.81±3.07% in WB, 8.21±2.13% in LI). According to the comparison made between WB and LI methods, LI method recorded higher SOM content. The actual SOM and volatilizable water in hygroscopic mineral fractions might be the reason for the higher values in LI method. All acquired data were compared with standard interpretation data and accordingly, soils of the measured TLRFs are acidic, non-saline and non-reduced with sufficient soil aeration. Even though, TLRF vegetation produce high amount of biomass, soil CEC and SOM contents are low in the study area due to rapid microbial decomposition and absorption of dense vegetation. There was no linear relationship between measured parameters and altitude. Overall, measured soil chemical properties can be considered as ideal indicators of TLRFs conservation and therefore, it needs to be correlated with above-ground properties for understanding the behaviour of TLRFs responding to conservation strategies. 
 Keywords: Forest conservation, Soil chemical properties, Soil organic matter content, Tropical lowland rainforest

Suspended soils enrich local forest floor soils during the rainy season in a tropical monsoon rainforest of Hainan Island, South China.

Epiphytic plants are abundant in rainforests and often serve as traps for litter and dust falling from the canopy. As it accumulates, this material can form nutrient rich soils, which are likely involved in local nutrient cycling and ecological processes. To explore spatial and temporal variation in the influence of suspended soils on local nutrient cycles, we compared the physical, chemical and biological properties of suspended soils from the locally-dominant epiphytic Bird's nest fern (Asplenium nidus L.) to those of three types of forest floor soils (soil collected from upslope, downslope, and underneath the host tree) in a tropical monsoon rainforest in Bawangling National Nature Reserve on Hainan Island, China. Suspended and forest floor soils were all acidic, with suspended soils having much higher organic matter (66.84%) and water content (~ 300%) than forest floor soils. Suspended soils contained significantly more available nitrogen, phosphorous, and potassium and had much higher urease, cellulase, and catalase activities, indicating that they harbored diverse microbial communities with higher decomposition and biomineralization activity. Physicochemical traits of suspended soil and soil collected from under the host tree were significantly more similar in the rainy season than in the dry season, suggesting that suspended soils may contribute to local nutrient cycling as they are flushed out of epiphytic plants and enrich stemflow and forest floor soils. Thus, suspended soils play a role in local nutrient cycling, especially during the rainy season. This study provides empirical support for the seasonality and heterogeneity of forest floor soil enrichment by suspended soils in tropical monsoon rainforests.

Land Use Effects on Soil Organic Carbon Index and Nitrogen Pools of a Tropical Coastal Plain Sands in Southern Nigeria

Land use types can of considerable interest in efforts to quantify soil organic C and nitrogen (N) cycling, both of which are important for soil stability and fertility. A study was carried out on a tropical rainforest soils in southern Nigeria to quantify soil organic carbon and nitrogen pools and other indices under forested, 5-year fallow, cocoa plantation and a 5-year continuous cassava land uses. Soil samples were collected at 0-15 cm and 15-30 cm depths for measurement of these indices. Results revealed that total organic carbon (TOC and total nitrogen (TN) varied significantly among the different land uses. TOC of 30.2 g kg-1 was higher (p<0.05) in forested soils at in the 0-15 cm top soil and 22.3 g kg-1 in the subsoil. Total N was statistically significant (p<0.05) at 2.61 and 2.01 in forested and 5-year fallowed soils, respectively. The carbon pool index (CPI) was significant at 1.63 in forested soils, while nitrogen pool index (NPI) 1.30 in similar soil (p<0.05) in 0-15 cm topsoil. In 15-30 cm subsoil, CPI and NPI values were in the order of forested > cocoa plantation > 5-year cassava cultivation, with the least values of 0.44 CPI and 0.35 NPI found in 5-year cassava plots. It was concluded that CPI and NPI are valuable indicators for analyzing changes in soil quality induced by maintaining a 5-year fallow. It was found that forested and 5-year fallow land uses can be used to improved C and N stock, as well as the structural and hydraulic properties of the soils.

Litter-derived nitrogen reduces methane uptake in tropical rainforest soils

Litter comprises a major nutrient source when decomposed via soil microbes and functions as subtract that limits gas exchange between soil and atmosphere, thereby restricting methane (CH4) uptake in soils. However, the impact and inherent mechanism of litter and its decomposition on CH4 uptake in soils remains unknown in forest. Therefore, to declare the mechanisms of litter input and decomposition effect on the soil CH4 flux in forest, this study performed a litter-removal experiment in a tropical rainforest, and investigated the effects of litter input and decomposition on the CH4 flux among forest ecosystems through a literature review. Cumulative annual CH4 flux was −3.30 kg CH4-C ha−1 y−1. The litter layer decreased annual accumulated CH4 uptake by 8% which greater in the rainy season than the dry season in the tropical rainforest. Litter decomposition and the input of carbon and nitrogen in litter biomass reduced CH4 uptake significantly and the difference in CH4 flux between treatment with litter and without litter was negatively associated with N derived from litter input. Based on the literature review about litter effect on soil CH4 around world forests, the effect of litter dynamics on CH4 uptake was regulated by litter-derived nitrogen input and the amount soil inorganic nitrogen content. Our results suggest that nitrogen input via litter decomposition, which increased with temperature, caused a decline in CH4 uptake by forest soils, which could weaken the contribution of the forest in mitigating global warming.

Isolation, identification, and characterization of phosphate solubilizing bacteria, Paenibacillus sp., from the soil of Danum Valley Tropical Rainforest, Sabah, Malaysia

While phosphorus (P) is a vital element for the plant to grow, only 0.1% of the phosphate soil is directly to be uptake by plants. Consequently, P fertilizer, which is mostly taken from unrenewable resources of phosphate rock, is practically added into the croplands. Nevertheless, as the demand for this fertilizer kept increasing, the availability of resources and environmental issues are currently raising wide concerns. Alternatively, soil phosphate solubilizing bacteria (PSB) is promising to be further developed as a biofertilizer to increase the availability of P elements for plants. This study aims to screen and characterize novel PSB from the tropical rainforest soil. The soil samples were collected from the Danum Valley tropical rainforest, Sabah. Phosphatase solubilizing bacteria were then screened using the NBRIP Agar selective media. The screening results yielded five colonies, designated as PSB1, PSB2, PSB3, PSB4, and PSB5, displaying halos, with an average diameter of 10mm. Further, 16s rRNA gene sequence analysis using BLASTn suggested that PSB1, PSB2, PSB3, PSB4, and PSB5 were designated as Bacillus sp. PSB01, Pseudomonas oryzyhabitans PSB02, Staphylococcus pasteuri PSB03, Paenibacillus sp. PSB04, and Staphylococcus pasteuri PSB05, respectively. Interestingly, the Paenibacillus group is a promising biofertilizer and is currently used in the global agriculture industry. Accordingly, Paenibacillus sp. PSB04 was then selected for further characterization using Gram staining and observed under scanning electron microscope (SEM). The Gram staining revealed that Paenibacillus sp. PSB04 is a Gram-negative bacterium with a rod shape, which is in good agreement with the SEM result. The specific phosphatase activity of the extracellular fraction of this bacterium was 7378.12 U mg-1 which is the highest activity compared to previous studies. This study provides an early insight into an excellent phosphate solubilizing bacterium for the agriculture industry obtained from Danum Valley.

Resistance and resilience of soil prokaryotic communities in response to prolonged drought in a tropical forest.

Global climate changes such as prolonged duration and intensity of drought can lead to adverse ecological consequences in forests. Currently little is known about soil microbial community responses to such drought regimes in tropical forests. In this study, we examined the resistance and resilience of topsoil prokaryotic communities to a prolongation of the dry season in terms of diversity, community structure and co-occurrence patterns in a French Guianan tropical forest. Through excluding rainfall during and after the dry season, a simulated prolongation of the dry season by five months was compared to controls. Our results show that prokaryotic communities increasingly diverged from controls with the progression of rain exclusion. Furthermore, prolonged drought significantly affected microbial co-occurrence networks. However, both the composition and co-occurrence networks of soil prokaryotic communities immediately ceased to differ from controls when precipitation throughfall returned. This study thus suggests modest resistance but high resilience of microbial communities to a prolonged drought in tropical rainforest soils.

Non-microbial methane emissions from tropical rainforest soils under different conditions.

Non-microbial methane (NM-CH4), emissions from soil might play a significant role in carbon cycling and global climate change. However, the production mechanisms and emission potential of soil NM-CH4 from tropical rainforest remain highly uncertain. In order to explore the laws and characteristics of NM-CH4 emission from tropical rainforest soils. Incubation experiments at different environmental conditions (temperatures, soil water contents, hydrogen peroxide) and for soils with different soil organic carbon (SOC) contents were conducted to investigate the NM-CH4 emission characteristics and its influence factors of soils (0-10cm) that collected from a tropical rainforest in Hainan, China. Incubation results illustrated that soil NM-CH4 release showed a linear increase with the incubation time in the first 24 hours at 70 °C, whereas the logarithmic curve increase was found in 192 h incubation. Soil NM-CH4 emission rates under aerobic condition were significantly higher than that of under anaerobic condition at first 24 h incubation. The increasing of temperature, suitable soil water contents (0-100%), and hydrogen peroxide significantly promoted soil NM-CH4 emission rates at the first 24 h incubation. However, excessive soil water contents (200%) inhibited soil NM-CH4 emissions. According to the curve simulated from the NM-CH4 emission rates and incubation time at 70 °C of aerobic condition, soil would no longer release NM-CH4 after 229 h incubation. The NM-CH4 emissions were positively corelated with SOC contents, and the average soil NM-CH4 emission potential was about 6.91 ug per gram organic carbon in the tropical mountain rainforest. This study revealed that soils in the tropical rainforest could produce NM-CH4 under certain environment conditions and it supported production mechanisms of thermal degradation and reactive oxygen species oxidation. Those results could provide a basic data for understanding the soil NM-CH4 production mechanisms and its potential in the tropical rainforest.

The role of geochemistry in organic carbon stabilization against microbial decomposition in tropical rainforest soils

Abstract. Stabilization of soil organic carbon (SOC) against microbial decomposition depends on several soil properties, including the soil weathering stage and the mineralogy of parent material. As such, tropical SOC stabilization mechanisms likely differ from those in temperate soils due to contrasting soil development. To better understand these mechanisms, we investigated SOC dynamics at three soil depths under pristine tropical African mountain forest along a geochemical gradient from mafic to felsic and a topographic gradient covering plateau, slope and valley positions. To do so, we conducted a series of soil C fractionation experiments in combination with an analysis of the geochemical composition of soil and a sequential extraction of pedogenic oxides. Relationships between our target and predicting variables were investigated using a combination of regression analyses and dimension reduction. Here, we show that reactive secondary mineral phases drive SOC properties and stabilization mechanisms together with, and sometimes more strongly than, other mechanisms such as aggregation or C stabilization by clay content. Key mineral stabilization mechanisms for SOC were strongly related to soil geochemistry, differing across the study regions. These findings were independent of topography in the absence of detectable erosion processes. Instead, fluvial dynamics and changes in soil moisture conditions had a secondary control on SOC dynamics in valley positions, leading to higher SOC stocks there than at the non-valley positions. At several sites, we also detected fossil organic carbon (FOC), which is characterized by high C/N ratios and depletion of N. FOC constitutes up to 52.0 ± 13.2 % of total SOC stock in the C-depleted subsoil. Interestingly, total SOC stocks for these soils did not exceed those of sites without FOC. Additionally, FOC decreased strongly towards more shallow soil depths, indicating decomposability of FOC by microbial communities under more fertile conditions. Regression models, considering depth intervals of 0–10, 30–40 and 60–70 cm, showed that variables affiliated with soil weathering, parent material geochemistry and soil fertility, together with soil depth, explained up to 75 % of the variability of SOC stocks and Δ14C. Furthermore, the same variables explain 44 % of the variability in the relative abundance of C associated with microaggregates vs. free-silt- and-clay-associated C fractions. However, geochemical variables gained or retained importance for explaining SOC target variables when controlling for soil depth. We conclude that despite long-lasting weathering, geochemical properties of soil parent material leave a footprint in tropical soils that affects SOC stocks and mineral-related C stabilization mechanisms. While identified stabilization mechanisms and controls are similar to less weathered soils in other climate zones, their relative importance is markedly different in the tropical soils investigated.

Characterization and land evaluation of three tropical rainforest soils derived from the coastal plain sands of southeastern Nigeria

Soils on coastal plain sands of southeastern Nigeria have hitherto been referred to as fragile sandy and acidic soils of low base saturation, cation exchange capacity (CEC) and fertility, as evidenced by the extensive land degradation evident in the region. This underscores the need for the characterization of the soils for sustainable use. Three profile pits were therefore dug on the upper, middle and bottom slopes of three towns in the rainforest belt underlain by the coastal plain sands. The results showed that the topsoil of the soils was generally sandy, with relatively more clayey subsoil. The pH ranged from extremely acidic (< 4.4) to slightly acidic (6.1- 6.5). They had low organic matter, low total nitrogen, low effective CEC, low Al saturation and moderate base saturation. The soils of the upper and the middle slopes were classified as Arenic Kandiudult by the United States Department of Agriculture’s (USDA) Soil Taxonomy or as Chromic Acrisols by the World Reference Base (WRB) for Soil Resources classification system, while that of the bottom slope was classified as a TypicDystrudept (USDA Soil Taxonomy) / Dystric Cambisol (WRB classification system). The upper slope had a USDA land capability class of IIes and a United States Bureau for Reclamation (USBR) land capability class of 2v/C. The middle slope and the bottom slope both had USDA and USBR capability class of IVs and 3v/C, respectively. Though moderately to marginally irrigable, the soils can still produce increased and sustainable agricultural yield if the appropriate land use and husbandry practices are adopted.
 Key words: Coastal plain sands, land use planning, soil characterization, toposequence, tropical rainforest

Application of nitrogen fixing bacteria and poultry droppings for enhanced bioremediation of crude oil polluted-soil

The exploration, production and refining of crude oil has led to severe environmental degradation in the oil producing communities of the Niger Delta region of Nigeria. Enhanced bioremediation of tropical rainforest soil artificially polluted with crude oil, bioaugmented with nitrogen fixing bacteria (NFB) and biostimulated with poultry droppings was carried out ex situ. Soil sample was collected at 15cm depth from tropical rainforest soil of the University of Port Harcourt, Nigeria. The NFB was isolated from roots of leguminous plant Arachis hypogea, identified as Nitrobacter species. Bioaugmentation by application of NFB served as option A, option B (biostimulation by application of poultry droppings), option C (No amendment) served as the control. Bioremediation was monitored for 28 days for interval of 14 days, and determined using the percentage ratio of total petroleum hydrocarbon (TPH) losses for each period to TPH at initial day (day zero). Results of total culturable heterotrophic bacterial (TCHB) counts showed that highest range in option B (1.9×104- 2.4×109Cfu/g) than in option A (7.8×106 -2.29×107Cfu/g) and C (6.75×106 -2.6×107Cfu/g) respectively. Similarly, hydrocarbon utilizing bacterial (HUB) counts had higher range in option B (1.20×105 - 1.9×107Cfu/g) than in option A (8.30×104 - 2.30×105Cfu/g) and option C control (4.3×104 −1.69×105 Cfu/g) respectively. Changes in physicochemical parameters during the study showed reductions in nitrate, phosphate and TPH in all the options expect pH which showed slight increase in option C (6.20-6.24). Characterization and identification for bacteria revealed the following HUB genera Pseudomonas, Citrobacter, Bacillus, Corynebacterium, Micrococcus, Klebsiella, Staphylocuccus and Nitrobacter). The percentage losses in TPH from gas chromatography (GC) results showed the following; option A (44.24%) option B (61.08%) and option C - control (27.28%) respectively. The results from this study showed that option B, the application of poultry droppings as biostimulant was more efficient than the application of NFB in enhanced bioremediation of crude oil polluted soil, hence the use of poultry droppings which is available as organic waste, eco-friendly and cost-effective is recommended asbiostimulant for enhanced bioremediation in environmental cleanup of crude oil impacted-sites of the Niger Delta region of Nigeria.
 Key Words: Bioremediation, Crude oil polluted-soil, Biostimulation, Bioaugumentation, Poultry droppings, Nitrogen fixing bacteria.

Arbuscular mycorrhizal fungi improve the growth of pioneer tree species of tropical forests on savanna and tropical rainforest soils under nursery conditions

Background: Tropical rainforests and savannas are often spatially distributed at close distances. The combined effects of soil type and arbuscular mycorrhizal fungi (AMF) might contribute to explain the preference of tropical rainforest tree species for forest areas over those of savannas. However, few studies have examined such effects on pioneer tropical tree species.
 Objective: Evaluate the effects of soil type and inoculation with an AMF consortium on the growth of seedlings of pioneer tree species of tropical rainforest.
 Methods: A factorial 2 x 2 experiment was conducted to evaluate the role of soil type (rainforest or savanna) and native AMF consortium on growth (height and stem diameter) of four native pioneer tree seedling species under tree nursery conditions.
 Results and conclusions: The highest growth was detected on rainforest soils inoculated with AMF. Uninoculated plants growing on savanna soils rendered the lowest performance. AMF inoculation could be a valuable procedure in ecological restoration projects of tropical forests.

Taxonomy of New and Known Species of Crateronematidae (Nematoda: Dorylaimida) from Western Ghats, India

New species of CrateronemaSiddiqi, 1969 and ChrysonemaThorne, 1929 are described and illustrated from the tropical rain forest soils in India. Crateronema tropicumsp. nov. is characterized by its long body (0.65–0.85 mm); cuticle with distinct transverse striations; lateral chords about one-third of the corresponding body diameter; lip region offset by constriction; pharyngeal expansion 42–53% of total neck length; vulva post-equatorial pore-like; tail elongate conoid, ventrally curved. Chrysonema minorsp. nov. is characterized by long body (0.67–0.85 mm); cuticle with fine transverse striations; lateral chords about one-third to two-fifths of the corresponding body diameter; lips amalgamated, lip region slightly offset by constriction; odontostyle about 0.6–1.0 times lip region diameter long; pharyngeal expansion 41–53% of total neck length; vulva equatorial pore-like; tail elongate conoid, ventrally curved. Males with 14–15 µm long dorylaimoid arcuate spicules, lateral guiding pieces and three ventromedian supplements. Crateronema aestivumSiddiqi, 1969 is redescribed and the photomicrographs are provided for this species for the first time. Diagnostic compendium and keys to valid species of Crateronema and Chrysonema is provided.

Drivers of difference in CO2 and CH4 emissions between rubber plantation and tropical rainforest soils

With large area of primary tropical rainforest converted into rubber (Hevea brasiliensis) plantation in Southeast Asia, it is necessary to examine the change in soil CO2 and CH4 emissions, and their underlying drivers in tropical rainforest (TRF) and rubber plantation. In TRF and RP in Xishuangbanna Southwest China, we measured the soil CO2 , CH4 , temperature, and water content once each week from 2003 to 2008, and twice weeks in 2013 and 2014. Additionally, the concentrations of soil carbon (C) and nitrogen (N) fractions from 2013 to 2014 were observed. Inputs of litter and live, dead, decomposed fine roots dynamics were also included. TRF transplanted to RP did not change significantly the annual soil CO2 emissions (TRF, 359 ± 91 and RP 352 ± 41 mg CO2 m−2 h−1) but decreased soil CH4 uptake significantly (TRF, −0.11 ± 0.18 mg CH4 m−2 h−1) RP, −0.020 ± 0.087 mg CH4 m−2 h−1). The most important influence on soil CO2 and CH4 emissions in the RP was the leaf area index and soil water content, respectively, whereas the soil water content, soil temperature, and dead fine roots were the most important factors in the TRF. Variations in the soil CO2 and CH4 caused by land-use transition were individually explained by soil temperature and fine root growth and decomposition, respectively. The results show that land-use change varied the soil CH4 and CO2 emission dynamics and drivers by the variation of soil environmental and plant's factors.

Long-term response of tropical Andisol properties to conversion from rainforest to agriculture

Short-term changes in tropical rainforest soil properties and their impact on C cycling following land-use conversion to agriculture have received intensive study. However, long-term, land-use changes have not been explored for tropical Andisols, whose high carbon stocks and several distinctive properties may differ in their response to land-use conversion. Thus, the primary objective of this study was to assess changes in selected soil properties of Andisols in response to long-term (>100 years) changes of land use from tropical rainforests to agriculture. Soils were sampled by horizon to a depth of 110–140 cm in pine forests (PF), tea plantation (TP) and horticultural crops with either intensive cultivation (IH) or bare fallow (FH) cropping systems. Selected physical, chemical and biological soil properties were characterized, including microbial biomass carbon (MBC) and laboratory CO2 mineralization rates. Results showed that land-use change from rainforest to agriculture resulted in increased soil bulk density and meso/micropores that contributed to increased plant-available water retention capacity. Soil carbon and nitrogen stocks in the upper 1 m of soil were higher in agricultural soils (25–29 kg C m−2; 1.7 – 2.3 kg N m−2) than pine forest soil (17 kg C m−2; 1 kg N m−2) with a redistribution of organic matter from topsoil to subsoil horizons. Organic matter quality was also affected by land-use conversion with the horticultural soils having lower rates of carbon mineralization per unit soil carbon (PF > TP > IH > FH) and lower microbial biomass, especially in topsoil horizons. The MBC sharply decreased in the topsoil horizon due to land-use change from forest (330 mg kg−1) to agricultural production (<118 mg kg−1). The intensive horticultural soil receiving recent additions of horse manure had higher extractable mineral N (especially NO3), reduced P fixation, increased available P, higher pH, and higher concentrations of exchangeable base cations (Ca2+, Mg2+ and K+) and micronutrients (Zn, Mn and Cu). The Andisols in this study demonstrated strong resilience to long-term degradation of soil properties following conversion from rainforest to agronomic land use. Further, this study demonstrates the ability of these Andisols to sequester additional C upon conversion to selected agriculture practices, thereby providing a positive impact on C mitigation.

The Use of Different Cropping Systems for Pepper (Capsicum Annum) Seed Production in Tropical Rain Forest Soils of Nigeria

A cropping system that involved the use of intercropping and planting patterns was used to test the profitability of producing pepper seeds. The triple replicated randomized complete block design experiment was carried out during the wet and dry seasons of 2018 at the Teaching and Research Soils of the Rivers State University Port Harcourt. The planting patterns were: Sole pepper (control), strip rows, double alternate rows and scattered pattern while maize and okra were used as inter crops. During the wet and dry seasons, the control (sole pattern) outperformed the other patterns in fresh pepper fruit yield (6000kg/ha, 5503kg/ha) but not in fruit number and fruit seed yield which were not significantly different from that of strip rows. Also, the strip rows fresh maize cobs yield (9573.3kg/ha, 6133.33kg/ha) and okro pods yield (2453kg/ha, 2470.67kg/ha) in wet and dry seasons respectively were high. With Land equivalent ratio of 2.3 and 1.62 in both seasons, the strip row pattern proved to be more stable, sustainable and profitable. This cropping system (pepper, maize and okra inter crop on strip row pattern) is therefore very profitable since it allows poor resource farmers to harvest different crop produce (maize cobs and okro pods) for use and sale until the maturation, processing and sale/use of the pepper seeds.

Interaction between Some Soil Physicochemical Properties and Weather Variables on Sub-humid Tropical Rainforest Soils of Cross River State, Southeastern Nigeria

Interaction between Some Soil Physicochemical Properties and Weather Variables on Sub-humid Tropical Rainforest Soils of Cross River State, Southeastern Nigeria