Maize Agroecosystems Research Articles

Plant and arthropod diversity patterns of maize agro-ecosystems in two grassy biomes of South Africa

Intensive, large-scale cultivation has led to a postulated decrease in biodiversity worldwide, which has been ascribed to fragmentation and degradation of natural habitat bordering crop fields. Maize is the most widely planted grain crop in Grassland and Savanna Biomes of South Africa, but the effect that crop production has on surrounding species diversity and composition is unknown. This study intends to address this knowledge gap by comparing diversity patterns and species assemblages between maize fields and margins of six localities in South Africa across two biomes for plants and associated arthropods. A total of 15,019 individuals and 824 native and exotic plant species were recorded and 39 497 individuals and 1 629 morpho-species for arthropods. Although biodiversity loss was apparent in maize fields, plant and arthropod diversity remained the same for rangeland at shorter (30–100 m) and longer (100–400 m) distances from maize fields, suggesting that distance from maize fields had no effect on biodiversity patterns beyond 30 m. Plant species assemblages were best correlated with agricultural disturbance while arthropod communities were mainly correlated with biome. Our results suggest that the crop field margins (30–100 m from field edge) were not species poor ecosystems, but were surprisingly rich in plant and arthropod diversity. Field margins may therefore be of conservation value in the agricultural landscape with a diversity of species supporting important ecosystem services.

Spatial and numerical relationships of arthropod communities associated with key pests of maize

AbstractPest management largely focuses on managing individual pest species with little concern for the diverse communities that co‐occur with key pests and potentially shape their population dynamics. During anthesis, we described the foliar arthropod communities on 53 maize farms throughout the region of eastern South Dakota. The resulting communities were examined for trends in local associations in the abundances of taxa with key pests in the system (rootworms [Diabrotica spp.], European corn borers [Ostrinia nubilalis], aphids and Western bean cutworm [Striacosta albicosta]) using regression analyses. Regional spatial clustering in the abundances of key pests with members of the community was explored using Moran's I test statistic. The distributions of rootworms and European corn borer were mapped. A total of 37 185 arthropods representing at least 91 taxa were collected in South Dakota maize; there was an average of 5.06 predators and 8.29 herbivores found per plant. Key pests were never found at economically threatening levels (with one exception for Diabrotica). Numerous species were consistently numerically associated with each of the key pests across the farms during anthesis. Occasionally, these pests shared species with which they were locally associated with; for example, coccinellid egg abundances were predictive of the abundances of all key pest species except rootworm adults. Spatial analysis across the region suggested that species co‐occurred with key pests based on local characteristics surrounding the fields, rather than as a result of regional characteristics. Exceptions were documented; namely aphids and Western bean cutworms that spatially clustered with a handful of other members of the community. The results of the study point out that the abundances of key pests of maize were interconnected through indirect associations in the abundances of other members of the community. These associations may be useful for manipulating maize agroecosystems to minimize the effects of maize pests.

Damage of Maize Borer and Maize Weevil on the Yield of Transgenic Phytase Maize

The recent Chinese government approval of transgenic phytase maize for field experimentation is vital for its development of biotech maize for improved maize production. Phytase maize can potentially improve the efficiency of feed utilization by livestock and reduce environmental pollution from animal manure. Plant growth, phytochemistry, and economic characteristics of phytase maize were compared with non‐transgenic maize in field conditions. Population abundance and growth physiology of the maize borer (Ostrinia furnacalis) and the maize weevil (Sitophilus zeamais) were investigated during maize growing season and grain storage period, respectively, to assess insect pests’ occurrence and economic damage. Agronomic traits of phytase maize were generally superior to those of non‐transgenic maize, but the yield of phytase maize was only 5.5% higher than that of non‐transgenic maize. No significant difference in population dynamics of the maize borer was observed between them, while phytase maize significantly enhanced pupal weight and female fecundity of the maize borer. The length of the maize borer feeding tunnels in the stems was significantly greater in phytase maize. Moreover, significant increases in adult weight and population abundance of the maize weevil resulted in additional 2.98% losses for transgenic grains compared with non‐transgenic grains. Upon commercialization of transgenic maize in China, it will likely alter the arthropod population dynamics in the maize agroecosystem, increase plant susceptibility to lodging, and increase grain yield loss. Nevertheless, the increased insect‐induced loss (∼8%) in transgenic maize would likely be more than offset by enhanced phosphate utilization efficiency of livestock, when fed transgenic maize containing diet, and reduced environmental pollution from lower phosphate animal waste.

AtoxigenicAspergillus flavus biological control of aflatoxin contamination: what is the mechanism?

The term ‘competitive exclusion’ involving physical blockage of growth or access of the toxigenic strain to the seed target has been used to describe the mechanism of biological control of aflatoxin contamination. However, recent evidence suggests that a form of intraspecific aflatoxin inhibition requiring growth of the competing strains together during the infection process in such a way that hyphae physically interact or touch is the trigger for preventing induction of aflatoxin synthesis. This direct touch-based inhibition of aflatoxin synthesis is posited to be the mechanistic basis of biological control in this system. Evidence for this idea comes from the published observations that co-culture of toxigenic and atoxigenic strains in a suspended disc system, in which the hyphae physically interact, prevents aflatoxin production. However, growth of the same strains in the same medium in the two compartments of a filter insert plate well system, separating the atoxigenic and toxigenic strains with a 0.4 μm or 3.0 μm filter, allows aflatoxin production approaching that of the toxigenic strain alone. When the strains are mixed and placed in both the insert and the well compartments, the intraspecific aflatoxin inhibition occurs as it did in the suspended disc culture system. This further suggests that neither nutrient competition nor soluble signal molecules, which should pass through the filter, are involved in intraspecific aflatoxin inhibition. When the two strains are separated by a 12 μm filter that would allow some passage of conidia or hyphae between the compartments the aflatoxin synthesis is approximately half that of the toxigenic strain alone. This phenomenon could be termed ‘competitive inclusion’ or ‘competitive phenotype conversion’. Work of others that relates to understanding the phenomenon is discussed, as well as anAspergillus flavus population biology study from the Louisiana maize agro-ecosystem which has biological control implications.

Emergence of Diverse Microbes on Application of Biofilmed Biofertilizers to a Maize Growing Soil

Diverse microbial communities in the rhizosphere perform an amazing role in plant growth and productivity. However, conventional agricultural practices such as the use of chemical fertilizer (CF) and tillage have collapsed the diversity of the microbial communities. Direct application of developed fungal-bacterial communities known as biofilmed biofertilizers (BFBFs) to the soil has been introduced recently, and observed to be multi-functional and more effective than conventional biofertilizers. However, the effect of such biofertilizers on soil microbial diversity has not been studied sufficiently world over. Therefore, the current study was carried out to investigate the effects BFBFs on bacterial, cyanobacterial and fungal species in a maize growing soil. A pot experiment was conducted under greenhouse conditions with different fertilizer treatments; 100% chemical fertilizers (CF) recommended for maize, 50% CF, 50% CF + BFBF, and no fertilizer, as the control. Microbial species richness and abundance of bacteria were evaluated after two months of plant growth. Microbial biomass carbon (MBC) was estimated by using chloroform fumigation-extraction technique. Results showed that the species richness of bacteria, fungi and cyanobacteria, and abundance of bacteria were higher in 50% CF + BFBF, compared to 50% and 100% CF. This implies that the action of BFBFs tends to break dormancy of microbial seeds in the soil, resulting in emergence of a diverse microbial community, which may support natural biocontrol of pathogens. An interesting observation was the stimulation of an additional microflora of cyanobacteria by the application of BFBF. MBC levels did not show a significant difference between any of the treatments. We recommend further testing of the BFBFs for increasing microbial diversity and ecosystem functioning and hence sustainability of maize agroecosystems. DOI: http://dx.doi.org/10.4038/cjsbs.v42i2.6612 Ceylon Journal of Science (Bio. Sci.) 42(2): 87-94, 2013

Comparative Diversity of Arthropods on Bt Maize and Non-Bt Maize in two Different Cropping Systems in South Africa

The biodiversity of an agroecosystem is not only important for its intrinsic value but also because it influences ecological functions that are vital for crop production in sustainable agricultural systems and the surrounding environment. A concern about genetically modified (GM) crops is the potential negative impact that such crops could have on diversity and abundance of nontarget organisms, and subsequently on ecosystem functions. Therefore, it is essential to assess the potential environmental risk of the release of a GM crop and to study its effect on species assemblages within that ecosystem. Assessment of the impact of Bt maize on the environment is hampered by the lack of basic checklists of species present in maize agroecosystems. The aims of the study were to compile a checklist of arthropods that occur on maize in South Africa and to compare the diversity and abundance of arthropods and functional groups on Bt maize and non-Bt maize. Collections of arthropods were carried out during two growing seasons on Bt maize and non-Bt maize plants at two localities. Three maize fields were sampled per locality during each season. Twenty plants, each of Bt maize and non-Bt maize, were randomly selected from the fields at each site. The arthropods collected during this study were classified to morphospecies level and grouped into the following functional groups: detritivores, herbivores, predators, and parasitoids. Based on feeding strategy, herbivores and predators were further divided into sucking herbivores or predators (piercing-sucking mouthparts) and chewing herbivores or predators (chewing mouthparts). A total of 8,771 arthropod individuals, comprising 288 morphospecies and presenting 20 orders, were collected. Results from this short-term study indicated that abundance and diversity of arthropods in maize and the different functional guilds were not significantly affected by Bt maize, either in terms of diversity or abundance.

Measurements of Soil Carbon Dioxide Emissions from Two Maize Agroecosystems at Harvest under Different Tillage Conditions

In this study a comparison of the soil CO2 fluxes emitted from two maize (Zea mays L.) fields with the same soil type was performed. Each field was treated with a different tillage technique: conventional tillage (30 cm depth ploughing) and no-tillage. Measurements were performed in the Po Valley (Italy) from September to October 2012, covering both pre- and postharvesting conditions, by means of two identical systems based on automatic static soil chambers. Main results show that no-tillage technique caused higher CO2 emissions than conventional tillage (on average 2.78 and 0.79 μmol CO2 m−2 s−1, resp.). This result is likely due to decomposition of the organic litter left on the ground of the no-tillage site and thus to an increased microbial and invertebrate respiration. On the other hand, fuel consumption of conventional tillage technique is greater than no-tillage consumptions. For these reasons this result cannot be taken as general. More investigations are needed to take into account all the emissions related to the field management cycle.

Comparison of six evapotranspiration models for a surface irrigated maize agro-ecosystem in Northern Italy

The approaches for the estimation of evapotranspiration (ET) can be classified in “direct” methods, based on the original Penman–Monteith (PM) equation, in which the canopy resistance rc is modelled, and “indirect” methods, based on the preliminary calculation of ET for a well-watered reference grass (ETo) with a constant rc, which is then multiplied by a crop coefficient Kc to obtain ET. Even if the latter approaches are more widely adopted for their practical simplicity, many authors show that the former often provide better ET estimates in absence of calibration of crop parameters. In this study the performances of different direct and indirect methods were evaluated in the case of a surface irrigated maize grown in the Padana Plain (Northern Italy). The “one-layer” original PM equation with three different models for rc (Monteith, Jarvis, Katerji–Perrier), the “two-layers” PM model proposed by Shuttleworth and Wallace, the “single” and “double crop coefficient” models illustrated in the Paper FAO-56 were compared to latent heat fluxes measured in 2006 by eddy-covariance techniques. Results confirm that direct methods are more performing. The FAO-56 models with generalized crop coefficients overestimate ET, especially during the middle growth stage.

Evapotranspiration models for a maize agro-ecosystem in irrigated and rainfed conditions

A high level of accuracy in the estimation of crop evapotranspiration (ET) may lead to significant savings of economic and water resources in irrigated agriculture. Although ET is a fundamental process in many applications, it cannot be directly measured but it has to be estimated by monitoring the exchange of energy/water above the vegetated surface (micrometeorological methods), or as a residual term of the hydrological balance (lysimeters, soil water budget). The techniques to be adopted are often complex, costly and require specific equipment. Thus, since the ‘50s, many researchers have devoted their activity to the development of models for its estimation. The available approaches can be classified in “direct” methods, based on the original Penman-Monteith (PM) equation, in which the canopy resistance rc is modelled, and “indirect” methods, based on the preliminary calculation of ET for a well-watered reference grass (ET0) with a constant rc, which is then multiplied by a crop coefficient Kc and, in case, by a stress coefficient Ks to obtain ET. Even if the latter approaches are more widely adopted for their practical simplicity, many authors show that the former often provide better ET estimates in absence of calibration of crop parameters. In this study the performances of different direct and indirect methods were evaluated in the case of a surface irrigated and of a rainfed maize grown in the Padana Plain (Northern Italy). The following models were considered: the “one-layer” original PM equation with three different models for rc (Monteith, Jarvis, Katerji-Perrier), the “two-layers” PM model proposed by Shuttleworth and Wallace, the “single” and “double” crop coefficient models illustrated in the Paper FAO-56. Latent heat fluxes measured in 2006 and 2011 in an experimental maize field by eddy-covariance were used to evaluate the models accuracy. Crop, soil and meteo data monitored contextually were used for the implementation of the different models. Results confirm that direct methods are more performing for both irrigated (2006) and rainfed (2011) conditions, with the SW model providing the best results and the FAO-56 models with generalized crop coefficients overestimating ET, especially during the middle growth stage.

Estimating the contribution of rainfall, irrigation and upward soil water flux to crop water requirements of a maize agroecosystem in the Lombardy plain

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Estimating the contribution of rainfall, irrigation and upward soil water flux to crop water requirements of a maize agroecosystem in the Lombardy plain

Estimating the contribution of rainfall, irrigation and upward soil water flux to crop water requirements of a maize agroecosystem in the Lombardy plain

Impacts of elevatedCO2concentration on the productivity and surface energy budget of the soybean and maize agroecosystem in the MidwestUSA

The physiological response of vegetation to increasing atmospheric carbon dioxide concentration ([CO2 ]) modifies productivity and surface energy and water fluxes. Quantifying this response is required for assessments of future climate change. Many global climate models account for this response; however, significant uncertainty remains in model simulations of this vegetation response and its impacts. Data from in situ field experiments provide evidence that previous modeling studies may have overestimated the increase in productivity at elevated [CO2 ], and the impact on large-scale water cycling is largely unknown. We parameterized the Agro-IBIS dynamic global vegetation model with observations from the SoyFACE experiment to simulate the response of soybean and maize to an increase in [CO2 ] from 375 ppm to 550 ppm. The two key model parameters that were found to vary with [CO2 ] were the maximum carboxylation rate of photosynthesis and specific leaf area. Tests of the model that used SoyFACE parameter values showed a good fit to site-level data for all variables except latent heat flux over soybean and sensible heat flux over both crops. Simulations driven with historic climate data over the central USA showed that increased [CO2 ] resulted in decreased latent heat flux and increased sensible heat flux from both crops when averaged over 30 years. Thirty-year average soybean yield increased everywhere (ca. 10%); however, there was no increase in maize yield except during dry years. Without accounting for CO2 effects on the maximum carboxylation rate of photosynthesis and specific leaf area, soybean simulations at 550 ppm overestimated leaf area and yield. Our results highlight important model parameter values that, if not modified in other models, could result in biases when projecting future crop-climate-water relationships.

Evapotranspiration models for a maize agro-ecosystem in irrigated and rainfed conditions

A high level of accuracy in the estimation of crop evapotranspiration (ET) may lead to significant savings of economic and water resources in irrigated agriculture. Although ET is a fundamental process in many applications, it cannot be directly measured but it has to be estimated by monitoring the exchange of energy/water above the vegetated surface (micrometeorological methods), or as a residual term of the hydrological balance (lysimeters, soil water budget). The techniques to be adopted are often complex, costly and require specific equipment. Thus, since the ‘50s, many researchers have devoted their activity to the development of models for its estimation. The available approaches can be classified in “direct” methods, based on the original Penman-Monteith (PM) equation, in which the canopy resistance rc is modelled, and “indirect” methods, based on the preliminary calculation of ET for a well-watered reference grass (ET0) with a constant rc, which is then multiplied by a crop coefficient Kc and, in case, by a stress coefficient Ks to obtain ET. Even if the latter approaches are more widely adopted for their practical simplicity, many authors show that the former often provide better ET estimates in absence of calibration of crop parameters. In this study the performances of different direct and indirect methods were evaluated in the case of a surface irrigated and of a rainfed maize grown in the Padana Plain (Northern Italy). The following models were considered: the “one-layer” original PM equation with three different models for rc (Monteith, Jarvis, Katerji-Perrier), the “two-layers” PM model proposed by Shuttleworth and Wallace, the “single” and “double” crop coefficient models illustrated in the Paper FAO-56. Latent heat fluxes measured in 2006 and 2011 in an experimental maize field by eddy-covariance were used to evaluate the models accuracy. Crop, soil and meteo data monitored contextually were used for the implementation of the different models. Results confirm that direct methods are more performing for both irrigated (2006) and rainfed (2011) conditions, with the SW model providing the best results and the FAO-56 models with generalized crop coefficients overestimating ET, especially during the middle growth stage.

玉米农田空气动力学参数动态及其与影响因子的关系

Based on continuous observation data of 16 m gradient weather observation tower from 2006 to 2008 at Jinzhou agricultural ecosystem research station,dynamic characteristics of aerodynamic parameters roughness(z0) and zero-plane displacement(d) over a rainfed maize agroecosystem and their relationships with controlling factors during growing seasons are analyzed.The results showed that d appears about 10 days after jointing when plant height(h) is about 1.40 m and increases from 0.80—1.00 m to 1.00—1.40 m after tasseling stage.z0 is smaller than 0.20 m before tasseling stage and comes to the maximum about 0.4m before and after milk stage.d/h and z0/h are 0.40—0.54 and 0.10—0.14,and are decreasing and increasing with LAI,respectively,before h comes to the maximum.Before d appears,negative exponent and positive linear relationships between z0 and wind speed at 2 m(u 2),z0 and LAI or h are found.Yet,after d appears,relationship between u 2 and z0 +d is more notable than those between u 2 and z0 or d.At the same time,positive exponent relationships between z0 or d and LAI or h respectively are found.LAI and h influence more to z0 than to d and z0 +d with greater role for the latter.Those relationships are more conspicuous from d appearing to h coming to the maximum.These research conclusions will play an important reference role for setting up aerodynamic parameterization and improving land surface process model.

Impact of long-term nitrogen fertilization and rotation with soybean on the diversity and phosphorus metabolism of indigenous arbuscular mycorrhizal fungi within the roots of maize (Zea mays L.)

A clear understanding of the importance of arbuscular mycorrhizal fungi (AMF) to phosphorus (P) nutrition in intensively managed maize cropping systems will impact how we currently manage these systems, particularly tillage, fertilization and crop rotation decisions. The influence of nitrogen (N) fertilizer (0, 50, 100, 150 and 300kgha−1) and crop rotation of maize (Zea mays L.) with soybean (Glycine max L.) versus monoculture maize on AMF communities and P metabolism in maize roots were investigated in a 13-year irrigated field trial located in SE Nebraska, USA. Maize roots were sampled at four growth stages (V6, V12, R1 and R4) and analyzed for AMF biomass and species composition using AMF-specific fatty acid biomarkers and DGGE-cloning of 18s rDNA, respectively. The activities of AMF-derived alkaline phosphatase (ALP), acid phosphatase (ACP) and polyphosphate (Poly P) were measured as indicators of P metabolism. The biomass of AMF in maize roots increased from V6 to R4 stage, and was not significantly influenced by N fertilizer addition or by rotation with soybean. The Shannon–Weiner diversity index (H′) and richness of AMF phylotypes varied with phenology, but was not influenced by crop rotation. Richness and H′ of AMF phylotypes decreased mainly under the highest N rate. Detection of AMF-derived ALP, ACP and Poly P in maize roots provided indirect evidence for P uptake via AMF in highly productive maize agroecosystems. AMF-associated P uptake was not affected by N application, but was higher under maize monoculture. We conclude that N fertilization at agronomic rates has minimal impact on overall AMF diversity as measured by H′ and colonization of maize roots; however, the frequency of AMF phylotypes varied with N fertilization level and may have important implications for agroecosystem management.

Isolation and identification of entomopathogenic fungi and their evaluation against Tribolium confusum, Sitophilus zeamais, and Rhyzopertha dominica in stored maize

The objective of this study was to isolate and identify native entomopathogenic fungi from different components of maize agroecosystem, and evaluate their virulence against Tribolium confusum, Rhyzopertha dominica, and Sitophilus zeamais, three insect pest vectors of aflatoxigenic fungi. Paecilomyces and Metarhizium were the most abundant genera isolated from the soil. Identification of fungal cultures by DNA extraction, amplification, and sequencing showed that all isolates macro- and micromorphological identified as P. lilacinus were Purpureocillium lilacinum. The isolate JQ926223 showed the lowest LT50 for T. confusum (4, 66 days) and R. dominica (9, 38 days), and the isolate JQ926212 demonstrated similar LT50 for the three insects evaluated between the range of 11, 7 to 14, 95 days. Maximum mortality rate was observed for the isolate JQ926223. The isolates of Purpureocillium lilacinum JQ926223 and JQ926212 may be considered good candidates for biologic control in the ecosystem of stored maize.

Arbuscular mycorrhizal root colonization and soil P availability are positively related to agrodiversity in Mexican maize polycultures

In Los Tuxtlas, Mexico, the local Popoluca people maintain the traditional management of their maize agroecosystems. However, it is not known whether the loss of agrodiversity over recent decades has affected mycorrhizal populations, nutrient availability, and crop productivity. This study utilized linear mixed effect models to analyze the relationship between agrodiversity (three, six, and greater than or equal to eight cultivated species) and (a) arbuscular mycorrhizal fungi (AMF) inoculum potential, measured as the most probable number (MPN) of propagules and colonization level, (b) nutrient availability, and (c) aboveground maize productivity. We also investigated the relationship between soil nutrient content and inoculum potential. Soil samples were taken before planting, and during flowering, in the 2009 maize cycle. We found that AMF colonization level of maize roots and P availability increased with planted species richness, but that this effect only occurred at the flowering sampling date. Plots with a higher MPN of propagules presented increased C and NO3− contents and lower C/N ratio than those with lower MPN of propagules, regardless of agrodiversity. Soils that produced the highest maize root colonization level also featured high P availability and N content. We conclude that decreased agrodiversity in these traditional systems does not significantly affect the soil MPN of propagules, but may have a negative impact on the ability of the mycorrhizal community to colonize maize roots, as well as reducing the availability of P, which is often the most limiting nutrient in tropical soils.

Spatio-temporal dynamics of an indigenous arbuscular mycorrhizal fungal community in an intensively managed maize agroecosystem in North China

The temporal and spatial dynamics of arbuscular mycorrhizal fungal (AMF) spore communities and biomass were studied in an intensively managed maize agroecosystem located in the North China Plain, one of the most important regions for cereal production in China. Maize roots and soils from three depths (0–30, 30–60 and 60–90 cm) were sampled in conventional agricultural management (CAM) and recommended agricultural management (RAM) systems at V6 (six leaf collar), V12 (twelve leaf collar), R1 (silking) and R6 (physiological maturity) stage of maize. The dynamics of percent root colonization by AMF, extra-radical hyphal length density (HLD), AMF fatty acid biomarkers (C16:1w5 and C18:1w7) and spore density were analyzed. AMF spore species were identified according to their morphological characteristics. Maize roots were rapidly and heavily colonized by arbuscular mycorrhizal (AM) fungi even under intensive agricultural management. The abundance of arbuscules and hyphal coils within maize roots peaked during early reproductive growth suggesting a period of high P demand by maize. This was preceded by increased concentration of the AMF biomarker C16:1w5 in the soil at the V12 growth stage, and led to a peak in soil HLD at R1. Twenty seven AMF species belonging to five genera were isolated in total, and dominant species such as Glomus aggregatum, Glomus claroideum, Glomus etunicatum, Glomus geosporum and Glomus mosseae occurred widely across growth stage, soil depth and management system. Rare species occurred mainly at a particular growth stage or soil depth. The effects of growth stage, soil depth and management system on spore relative abundance differed among AMF species. The highest species richness and diversity occurred at the R1 stage and may stem from increased C supply to the fungus during peak arbuscular development within the roots. The AMF community and biomass were mainly affected by soil depth and growth stage rather than agroecosystem management. The abundance of AMF biomass and species found deep in the soil profile highlights the potential for P uptake by AMF from lower soil depths under intensive maize management.

Field Studies on the Relationship betweenFusarium verticillioidesand Maize (Zea maysL.): Effect of Biocontrol Agents on Fungal Infection and Toxin Content of Grains at Harvest

Maize (Zea maysL.) is a staple food for the majority of the world's population.Fusarium verticillioides(Sacc.) Nirenberg (Teleomorph:Gibberella moniliformisWineland; synonym:F. moniliformis) is both a saprophyte and a parasite of maize and can also be found as an endophyte. The presence of this fungus in maize constitutes an imminent risk due to its ability to produce fumonisins, mycotoxins with proven carcinogenic effects. The present work investigated biocontrol activity ofBacillus amyloliquefaciensandMicrobacterium oleovoransagainstF. verticillioidesinfection and fumonisin B1production in field-grown maize during four consecutive growing seasons. Treatment withB. amyloliquefaciensconsistently reducedF. verticillioidesinoculum and fumonisin content of harvested grains.F. verticillioidescount and fumonisin levels correlated negatively with rainfall regimes; however, none of these parameters showed significant correlation with yields. Treatment with these biocontrol agents may improve phytosanitary quality of the grains and reduce toxicological risk in the maize agroecosystem.

Responses of soil respiration in non-growing seasons to environmental factors in a maize agroecosystem, Northeast China

Based on continuous three-year measurements (from 2004 to 2007) of eddy covariance and related environmental factors, environmental controls on variation in soil respiration (R s) during non-growing season were explored in a maize agroecosystem in Northeast China. Our results indicated that during non-growing seasons, daily R s was 1.08–4.08 g CO2 m−2 d−1, and the lowest occurred in late November. The average R s of non-growing season was 456.06 ± 20.01 g CO2 m−2, accounting for 11% of the gross primary production (GPP) of the growing season. Additionally, at monthly scale, the lowest value of R s appeared in January or February. From the beginning to the end of non-growing season, daily R s tended to decrease first, and then increase to the highest. There was a significant quadratic curve relationship between R s and soil temperature at 10 cm depth when soil temperature was more than 0°C (P<0.001), with the explaining ratio of 38%–70%. When soil water content was more than 0.1 m3 m−3, soil moisture at 10 cm depth was significantly parabolically correlated with R s (P<0.001), explaining the rate of 18%–60%. Based on all the data of soil temperature of more than 0°C, a better model for R s was established by coupling soil temperature and moisture, which could explain the rate of up to 53%–79%. Meanwhile, the standard error of regression estimation between the values of prediction and observation for R s could reach 2.7%–11.8%. R s in non-growing season can account for 22.4% of R s in growing season, indicating that it plays a critical role in assessing the carbon budget in maize agroecosystem, Northeast China.