Rhizosphere Soil Enzyme Activities Research Articles

Linking soil microbial biomass and enzyme activities to long-term manure applications and their nonlinear legacy

Long-term manure application can build soil carbon and nutrient stocks and enhance enzyme activity, but its legacy on enzyme activity after discontinued application is unclear. We quantified soil microbial biomass carbon (MBC) and potential enzyme activities in fall, spring and summer in response to long-term manure application and its discontinuation under irrigated and rain-fed conditions. Relative to the non-amended control, 43 years of annual manure applications increased MBC by 38% and 33%, and β-glucosidase, β-N- acetyl-glucosaminidase (NAGase) and acid phosphomonoesterase activities by 35% and 33%, 137% and 135%, and 67% and 90%, in bulk and soybean rhizosphere soil, respectively, while arylsulphatase activity only increased in soybean rhizosphere by 13%. Fertilizer N had no effects on MBC or most enzyme activities, which were lowest in fall. In bulk and soybean rhizosphere soil, irrigation increased MBC, and NAGase and arylsulphatase activities by 17–33%, 19–54% and 39–57%, respectively, compared to rain-fed conditions, but β-glucosidase and acid phosphomonoesterase activities increased by 25 and 12%, respectively, only in soybean rhizosphere. Legacy effects of manure applied 13 years previously were observed for MBC and all enzyme activities in bulk and soybean rhizosphere soil except MBC in bulk soil and acid phosphomonoesterase in soybean rhizosphere. Legacy effects of manure applied 29 years previously were observed for NAGase and arylsulphatase activities in bulk soil, and NAGase in soybean rhizosphere. Manure legacy effects on enzyme activities decreased with the number of years without manure, following quadratic patterns, and the effects lasted longer than those on MBC.

Effects of di-n-butyl phthalate on rhizosphere and non-rhizosphere soil microbial communities at different growing stages of wheat

The potential effects of dibutyl phthalate (DBP) on soil ecosystems and biological processes have recently aroused great concern because of the ubiquitous nature of this pollutant. However, the effects of DBP-associated disturbance on rhizosphere and non-rhizosphere soil microbial communities remain poorly understood. In the present study, we investigated the effects of DBP contamination on microbial function and soil enzyme activities in rhizosphere and non-rhizosphere soils throughout the growing season of wheat. We conducted pot experiments under glasshouse conditions and used different concentrations of DBP: 10, 20, and 40 mg kg–1. We found that the average well color development value and McIntosh index in rhizosphere and non-rhizosphere soils increased in the 10 and 20 mg kg–1 DBP treatments, but declined in the 40 mg kg–1 DBP treatment at the seedling and tillering stages, particularly, in the non-rhizosphere soil. DBP addition enhanced the Shannon-Wiener and Simpson indexes in rhizosphere and non-rhizosphere soils throughout the growing period of wheat. A principal component analysis clearly differentiated the treatments from the control, indicating that DBP led to different patterns of potential carbon utilization in rhizosphere and non-rhizosphere soils. The microbial use of amino acids was significantly increased in rhizosphere and non-rhizosphere soils after DBP addition, while the use of carbohydrates was significantly declined (p < 0.05). The dehydrogenase, urease, and acid phosphatase activities were significantly stimulated (p < 0.05) at the seedling stage, while the phenol oxidase and β-glucosidase activities were inhibited. The 40 mg kg–1 DBP treatment significantly decreased the phenol oxidase and β-glucosidase activities in rhizosphere and non-rhizosphere soils at the seedling stage, particularly in non-rhizosphere soil (p < 0.05). The microbial function and soil enzymatic activities were gradually restored following the wheat growing stage. These results offer a better understanding of the effects of DBP on the activities and functional diversity of microbial communities in farmland soils.

Effects of film mulching and nitrogen fertilization on rhizosphere soil environment, root growth and nutrient uptake of winter oilseed rape in northwest China

The ridge film mulching and furrow planting (RFMF) pattern has been increasingly applied to the production of wheat, maize, and potato in arid and semiarid regions of northwest China because it can significantly improve crop yield. How RFMF affects the productivity and whether it can improve the rhizosphere soil environment of winter oilseed rape (Brassica napus L.) is not clear. The main objective of the present study was to determine whether RFMF can improve rhizosphere soil environment and winter oilseed rape productivity in comparison to the conventional flat planting (FP) pattern in a three-year (2014-2017) field experiment. In combination with each planting pattern, we determined an optimal nitrogen (N) application rate among six levels: 0 (N0), 60 (N60), 120 (N120), 180 (N180), 240 (N240) and 300 (N300) kg N ha−1. Results showed that the RFMF pattern significantly improved the rhizosphere soil environment by increasing soil moisture by 0.3–5.6% and soil temperature by 0.6–3.0 °C. However, soil oxygen concentration decreased by 0.03–5.66% during the flowering stage of winter oilseed rape. In addition, the RFMF pattern markedly improved rhizosphere soil enzyme activity and microorganism abundance and thus promoted root growth, nutrient uptake, and seed yield of winter oilseed rape. The resulting optimal N application rates remarkably improved rhizosphere soil enzyme activity, microorganism abundance, root growth, nutrient uptake, and yield of winter oilseed rape in both RFMF and FP treatments. In the RFMF treatment, N240 obtained significantly greater rhizosphere soil enzyme activity, microorganism abundance, root growth parameters, nutrient uptake, and seed yield than N0, N60, N120, and N180, with no significant differences observed between N240 and N300. In conclusion, the RFMF pattern in combination with the optimal N-application rate of 240 kg ha−1 has great potential to improve rhizosphere environment and winter oilseed rape productivity in arid and semiarid regions of northwest China.

Rhizosphere Microenvironments of Eight Common Deciduous Fruit Trees Were Shaped by Microbes in Northern China.

The rhizosphere microenvironment is the site of nutrient circulation and microbial community formation, and thus is an ongoing topic of research. Although research on this topic is extensive, studies into the rhizosphere microenvironment of fruit trees remain rare. To elucidate the mechanisms driving the fruit tree rhizosphere microenvironment, we assessed soil physicochemical properties, enzyme activities, the community-level physiological profile (CLPP) and microbial diversity in rhizospheric soils of eight common deciduous fruit trees in northern China. We found that the available minerals, pH, enzyme activities, microbial utilization of six types of carbon (C) substrates, and microbial diversity in the rhizosphere varied among tree species. Redundancy analysis (RDA) showed that rhizosphere microenvironmental parameters (ammonia nitrogen content, soil pH and invertase activity) were closely related to the soil microbial community. Further analysis revealed that the soil microbial utilization of six C sources, nitrate nitrogen content, and invertase activity were negatively correlated with Ambiguous species and Alternaria; however, these groups were positively correlated with pH. The ammonia nitrogen content was positively correlated with C source utilization and negatively correlated with Ambiguous, Lysobacter, Nitrospira, Alternaria, Fusarium, and Colletotrichum. Interestingly, invertase was closely linked to the microbial community, especially fungal diversity, and was positively correlated with plant-beneficial microbes such as Mortierella, Geomyces, Lysobacter, and Chaetomium, but negatively correlated with pathogenic microbes such as Alternaria, Fusarium, and Colletotrichum. Hence, rhizosphere soil physicochemical properties, enzyme activities and microbial community were significantly affected by tree species. Additionally, a variety of environmental factors were closely related to the microbial community in the rhizospheric soils of eight species of deciduous fruit trees.

Effect of plant growth-promoting bacteria Bacillus amylliquefaciens Y1 on soil properties, pepper seedling growth, rhizosphere bacterial flora and soil enzymes

The Bacillus amyloliquefaciens Y1 strain was evaluated for its effects on soil properties, pepper seedling growth, rhizosphere bacterial flora and soil enzyme activities. Y1 solubilised insoluble phosphate, produced chitinase, and released siderophores in plate detection assay. In order to evaluate the plant growth promotion potential in vivo, strain Y1 was grown in media containing chitin powder and complex fertiliser. The pot experiment was conducted by treating pepper seedlings with C1/1 (Y1 culture, 50 ml), C2/3 (Y1 culture, 33 ml), C1/2 (Y1 culture, 25 ml), F1/1 (complex fertiliser, 50 ml), F1/2 (complex fertiliser, 25 ml), and W (water) at 10, 20, 30, 40, and 50 days after transplantation (DAT). Plants receiving Y1 had 52% (C1/2) and 68% (C1/1) more root and shoot biomass than W, and 14% (C1/1) and 18% (C2/3) more compared to F1/1 at 80 DAT. Total numbers of flowers per plant at 80 DAT were found significantly higher with the application of Y1 having 34 (C1/1), 35 (C2/3), and 22 (C1/2) compared to 4 (W), 12 (F1/1) and 10 (F1/2). In addition, chlorophyll content in pepper leaves was found to improve with the application of Y1. Furthermore, Y1 has significantly improved nutritional assimilation of total NPK, population of total culturable bacteria and chitinase producing bacteria and activities of chitinase and dehydrogenase in soil. At 60 and 80 DAT, the number of B. amyloliquefaciens at C1/1, C2/3, and C1/2 ranged from 2.3 × 10&lt;sup&gt;4&lt;/sup&gt; to 4.6 × 10&lt;sup&gt;4&lt;/sup&gt; CFU/g of soil. Our results concluded that B. amyloliquefaciens Y1 has positive effects on soil properties and can be suggested as a bio-fertiliser to minimise fertiliser application in modern agriculture.

Ectomycorrhizal fungus enhances drought tolerance of Pinus sylvestris var. mongolica seedlings and improves soil condition

Mongolian pine is an important afforestation species widely used for ecological management in northeast China. The environment in this region is very unstable and the flora are regularly subjected to drought stress. This paper reports on the influence of inoculation with the Suillus luteus on seedlings under different water conditions. Both inoculated and non-inoculated ectomycorrhizal fungi (ECMF)-S. luteus seedlings were maintained under well-watered or water-stress conditions for 3 months. The S. luteus colonization rate under water stress was higher than that in well-watered conditions. Under water stress, inoculated seedlings had greater growth than non-inoculated seedlings. In addition, under water stress, S. luteus-inoculated seedlings had greater superoxide dismutase and peroxidase activity, higher soluble protein content, lower proline content, and lower malondialdehyde content than non-inoculated seedlings. S. luteus colonization increased the rhizosphere soil-enzyme activity and the rhizosphere soil nutrition content under both well-watered and water-stress conditions. Given the positive impact on seedling growth and physiology, S. luteus shows potential for use in the arid and semi-arid regions of northeast China for afforestation.

不同油葵品种对盐碱地根际土壤酶活性及微生物群落功能多样性的影响

不同油葵品种对盐碱地根际土壤酶活性及微生物群落功能多样性的影响

青稞根腐病对根际土壤微生物及酶活性的影响

青稞根腐病对根际土壤微生物及酶活性的影响

The Effects of Cadmium Exposure on Cadmium Fractionation and Enzyme Activities in the Rhizosphere of Two Radish Cultivars (Raphanus sativus L.).

The effects of increasing Cd additions on plant growth and Cd fractionation and enzyme activities in rhizosphere soil of two radish cultivars were investigated. The results showed that Cd concentrations in shoot and root of cultivar 4 were both higher than for cultivar 19 under different Cd levels. Compared with cultivar 19, the total, shoot and root biomasses of cultivar 4 were significantly reduced with increasing Cd levels. A decrease in soil pH was observed for cultivar 4. The exchangeable Cd concentration of soil from cultivar 4 was significantly higher than for soil from cultivar 19, while the carbonate-bound Cd concentration of soil from cultivar 4 was significantly lower than for cultivar 19. Enzyme activities, especially acid phosphatase activity, were more susceptible to Cd in soil from cultivar 4. These results indicated that cultivar 19 exhibits a stronger ability to adapt to Cd stress than cultivar 4.

Rhizosphere and bulk soil enzyme activities in a Nothotsuga longibracteata forest in the Tianbaoyan National Nature Reserve, Fujian Province, China

The rhizosphere, distinct from bulk soil, is defined as the volume of soil around living roots and influenced by root activities. We investigated protease, invertase, cellulase, urease, and acid phosphatase activities in rhizosphere and bulk soils of six Nothotsuga longibracteata forest communities within Tianbaoyan National Nature Reserve, including N. longibracteata + either Phyllostachys pubescens, Schima superba, Rhododendron simiarum, Cunninghamia lanceolata, or Cyclobalanopsis glauca, and N. longibracteata pure forest. Rhizosphere soils possessed higher protease, invertase, cellulase, urease, and acid phosphatase activities than bulk soils. The highest invertase, urease, and acid phosphatase activities were observed in rhizosphere samples of N. longibracteata + S. superba. Protease was highest in the N. longibracteata + R. simiarum rhizosphere, while cellulase was highest in the pure N. longibracteata forest rhizosphere. All samples exhibited obvious rhizosphere effects on enzyme activities with a significant linear correlation between acid phosphatase and cellulase activities (p < 0.05) in rhizosphere soils and between protease and acid phosphatase activities (p < 0.05) in bulk soils. A principal component analysis, correlating 13 soil chemical properties indices relevant to enzyme activities, showed that protease, invertase, acid phosphatase, total N, and cellulase were the most important variables impacting rhizosphere soil quality.

Impact of Imidacloprid Seed Dressing Treatment on Soil Microorganisms and Enzyme Activities in the Maize Rhizosphere

Under the field conditions, effects of imidacloprid seed dressing treatment on soil culturable microorganisms and enzyme activities in maize rhizosphere were studied. The results showed that the microbial populations for bacteria, actinomycetes and fungi in maize rhizosphere after imidacloprid treatments were lower than control. The bacteria and actinomycetes populations showed a trend of decreasing after increasing with the maize growth from the seedling stage to the maturity stage, and the fungi populations decreased with the maize growth. The urease activities of maize rhizosphere soil from different treatments showed a trend of initially increasing after decreasing, then decreasing. The invertase activities of maize rhizosphere soil from different treatments showed a trend of decreasing after increasing, and the peak value occurred at flowering stage. With the imidacloprid application, the invertase activities had been stimulated. The results may provide theoretical basis for rational seed dressing treatment.

Effects of Artificial Soil Aeration Volume and Frequency on Soil Enzyme Activity and Microbial Abundance when Cultivating Greenhouse Tomato

Core Ideas Rhizosphere soil enzymes activity showed an initial increase followed by a decrease. Soil aeration can enhance the activities of three rhizosphere soil enzymes. Aeration frequency and volume can significantly affect rhizosphere enzyme activities. Aeration can enhance the activities of non‐rhizosphere soil enzymes. Soil aeration can increase tomato yield. Artificial soil aeration can enhance soil enzyme activity, improve soil nutrient cycling, and increase crop growth and yield. We studied the response of soil microorganisms and soil enzyme activity to two levels of burial depths of subsurface tubing in combination with four levels of aeration volume and three frequency levels of supplemental soil aeration. The aeration volumes (V) were 0, 0.5, 1, and 1.5 times (CK, V1, V2, and V3, respectively) the estimated porosity of the plot rhizosphere. Burial depths (D) of subsurface tubing were 15 and 40 cm (D15 and D40). Aeration frequencies (F) levels were none and at 2‐ and 4‐d intervals (CK, F2, and F4). The results demonstrated that aeration frequency and volume positively affected soil urease, phosphatase, and catalase activity and soil microbial abundance. The impact of aeration treatment on rhizosphere soil enzyme activity was greater than its impact on non‐rhizosphere activity. When the drip irrigation tube depth was 15 cm, V2 volume with 2‐d aeration intervals led to an increase in the mean yield of first picking fruit of 75.1% compared with the unaerated control. When V3 volume with 2‐d aeration intervals was performed with a 40‐cm irrigation tube, the mean yields of the first picking fruit increased by 135.5% compared with the unaerated control. These results suggest that artificial soil aeration can improve the plant root zone environment, increase microbial abundance and soil enzyme activity, and promote nutrient uptake, thus promoting plant growth and fruit output.

Soil nitrogen content and enzyme activities in rhizosphere and non-rhizosphere of summer maize under different nitrogen application rates.

A field experiment was conducted on fluvo-aquic soil in the North China Plain to study the effects of nitrogen application rate on soil nitrogen contents and enzyme activities in rhizosphere and non-rhizosphere of summer maize. The results showed that the soil enzyme activities under different nitrogen application rates showed similar seasonal patterns. In comparison to no nitrogen ferti-lizer treatment, all nitrogen application treatments significantly increased NO3--N contents in rhizosphere and non-rhizosphere soils, NH4+-N content in rhizosphere soil and the activities of β-N-acetylglucosaminidase, β-glucosidase, β-xylosidase and Cellobiohyrolase. During the whole summer maize growing season, the NO3--N content in non-rhizosphere soil was significantly higher than that in rhizosphere soil. The NH4+-N content in non-rhizosphere soil was also significantly higher than that in rhizosphere soil at filling stage but significantly lower at seedling and maturity stages. Furthermore, soil enzyme activities in rhizosphere soil were significantly higher than those in non-rhizosphere soil. Effect of nitrogen application on soil organic carbon content was not significant. Soil total nitrogen content increased significantly when the nitrogen application rate was 0-180 kg·hm-2 but decreased significantly when the rate was higher than 180 kg·hm-2. Generally, a proper rate of nitrogen fertilizer application could significantly increase soil enzyme activities and total nitrogen content, and then improve soil biochemistry properties.

Cry1Ac Transgenic Sugarcane Does Not Affect the Diversity of Microbial Communities and Has No Significant Effect on Enzyme Activities in Rhizosphere Soil within One Crop Season.

Cry1Ac transgenic sugarcane provides a promising way to control stem-borer pests. Biosafety assessment of soil ecosystem for cry1Ac transgenic sugarcane is urgently needed because of the important role of soil microorganisms in nutrient transformations and element cycling, however little is known. This study aimed to explore the potential impact of cry1Ac transgenic sugarcane on rhizosphere soil enzyme activities and microbial community diversity, and also to investigate whether the gene flow occurs through horizontal gene transfer. We found no horizontal gene flow from cry1Ac sugarcane to soil. No significant difference in the population of culturable microorganisms between the non-GM and cry1Ac transgenic sugarcane was observed, and there were no significant interactions between the sugarcane lines and the growth stages. A relatively consistent trend at community-level, represented by the functional diversity index, was found between the cry1Ac sugarcane and the non-transgenic lines. Most soil samples showed no significant difference in the activities of four soil enzymes: urease, protease, sucrose, and acid phosphate monoester between the non-transgenic and cry1Ac sugarcane lines. We conclude, based on one crop season, that the cry1Ac sugarcane lines may not affect the microbial community structure and functional diversity of the rhizosphere soil and have few negative effects on soil enzymes.

Variation of rhizosphere environmental factors of sugarbeet seedlings under Na2CO3 stress and their correlation.

To study the effect of saline-alkali stress on dry mass, rhizosphere soil enzyme activities and soil microbial quantities, pot experiments were designed two sugar beet varieties, 'KWS0143' (strong tolerance to saline-alkali) and 'Beta464' (weak tolerance to saline-alkali) planted in different Na2CO3 concentrations [0% (control), 0.4%, 0.8% and 1.2% of soil], and the dry mass of seedlings,soil enzyme activities and amount of microbiology in soil were recorded. The results showed that compared with the control, the dry mass of seedlings was significantly increased in the treatment of 0.4% Na2CO3, while it was significantly decreased in the 0.8% and 1.2% Na2CO3 treatments. Significant differences among treatments were observed. The soil urease, alkali phosphatase and peroxidase activities in the root rhizosphere of seedlings presented a similar tendency under different concentrations of Na2CO3. Compared with the control, the enzyme activities with the treatment 0.4% Na2CO3 were not significantly enhanced, while those in the treatment of 0.8% and 1.2% Na2CO3 were significantly reduced. All the soil enzymes' activities in 'KWS0143 were higher than in 'Beta464'. The 0.4% Na2CO3 did not lead to significant change of soil microbial community, but 0.8% and 1.2% Na2CO3 sharply decreased the amount of soil bacteria, fungi and actinomycets (P<0.05). The amount of rhizosphere soil microbe in 'KWS0143' was higher than in 'Beta464'. There were significantly positive correlation among the dry mass, soil enzymes and soil microbe of the two varietie. Path coefficient analysis showed the determinant coefficient of 'KWS0143' dry mass was in order of sctinomycetes > bacteria > peroxidase > urease > fungi > alkali phosphatase, while that 'Beta464' dry mass was in order of actinomycetes > peroxidase > urease > fungi > alkali phosphatase > bacteria.

Influence of rhizosphere ventilation on soil nutrient status, root architecture and the growth of young peach trees

The peach tree root respiration rate is high, which requires large amounts of oxygen. When the rhizosphere oxygen content is poor, the root respiration and energy metabolism are restrained which will have negative impacts on peach trees growth, fruit quality and yield, especially during high temperature and rainy season. Our objectives were to investigate the relationship between rhizosphere ventilation and orchard soil enzyme activity, nutrient status, root architecture and growth of young peach trees. Two-year-old ‘Chunmei’ peach (Prunus persica L. Batsch) was subjected to various treatments (Treatment 1 [T1]: ventilation every three days; T2: ventilation every six days; T3: natural ventilation; Control: no ventilation) under field cultivation conditions. The soil oxygen content decreased and subsequently increased during the growth period, reaching a minimum in August. The rhizosphere soil oxygen content was higher under ventilation treatment than control, and T1 markedly increased the rhizosphere soil oxygen content. The rhizosphere soil available K and organic matter decreased while the rhizosphere soil available N and available P content increased and the soil enzyme activity was improved under ventilation treatments. The root activity and root nitrate reductase activity increased under ventilation treatments. Under T1, the total root surface area, total root length and number of first lateral root and second lateral root were increased significantly, but the average root diameter and the average length of first lateral root was reduced significantly, the branching angle between first lateral root and vertically downward direction was decreased, the number of small angle was increased. T1improved leaf functions and increased the net photosynthetic rate. Under T1, the leaf chlorophyll content and leaf protective enzyme activity (Superoxide dismutase, Guaiacol peroxidase and Catalase) increased markedly in the middle- and late-growth period and leaf senescence was postponed. The total nitrogen, phosphorus and potassium contents of young peach roots, shoots and leaves, as well as shoot growth, leaf weight and leaf area, increased under T1.

Nutrients, microbial community structure and functional gene abundance of rhizosphere and bulk soils of halophytes

Salt marshes occupy the transition zone between terrestrial and marine ecosystem and provide habitat for salt tolerant plant species-halophytes. Dominant halophytes such as Salicornia brachiata, Aeluropus lagopoides and Suaeda maritima play significant role in carbon sequestration, nutrient mineralization, nutrient cycling and improving micro-environment. There are scanty reports on the rhizosphere microbial communities of halophytes. Whether the rhizosphere of halophytes harbors unique microbial communities or has species specificity is yet to be established. In the present study, we have determined microbial community structure and functional genes abundance as well as major nutrients and three key enzyme activities in both rhizosphere and bulk soil of three halophytes (Salicornia, Aeluropus and Suaeda) growing on salty marsh of coastal Gujarat, India. The NH4-N and available K were significantly higher in the rhizosphere than in the bulk soil in all the cases. The rhizosphere of Suaeda was characterized by significantly higher concentrations of organic carbon, total N, NH4-N and available P as compared to other two halophytes. The rhizopsheric soil had significantly higher concentrations of total PLFA, GM+ve, GM−ve and total bacterial PLFA biomarkers compared to the bulk soil. Among halophytes, significantly higher concentrations of total PLFA, GM+ve, GM−ve, total bacterial and actinomycetes biomarker PLFAs were recorded in Suaeda and Aeluropus in comparison to Salicornia. The NMS analysis of PLFA profiles revealed a significant difference in microbial community structure in Salicornia compared to Aeluropus and Suaeda. Similarly, rhizosphere microbial community structure of Salicornia was significantly different from Suaeda and Aeluropus. In rhizosphere soils, significantly higher abundance (molar%) of GM−ve, GM+ve, total bacterial and actinomycetes PLFAs were observed in Aeluropus and Suaeda compared to Salicornia. Activities of β-glucosidase and urease were significantly higher in rhizosphere than in the bulk soil. The abundance of 16S rRNA, cbbL and nifH genes, detected by the quantitative RT-PCR was significantly varied among soils and halophytes. The results exhibited high bacterial diversity, abundance of CO2 and N-fixing bacteria, which can be explored further for their role in C and N cycling for sustainable agriculture and environment management.

Effects of phosphine on enzyme activities and available phosphorus in rhizospheric and non-rhizospheric soils through rice seedlings

The objective of this study was to investigate phosphine-induced changes in enzyme activities (acid phosphatase (ACP), urease, invertase, dehydrogenase) and effects of phosphine on available phosphorus in rhizospheric and non-rhizospheric soils. Rice seedlings, as model plant, were exposed to different ambient concentrations of phosphine (0, 1.4, 4.2 and 7.0 mg m−3) for a period of 30 days, and the enzyme activities and available phosphorus in both rhizospheric and non-rhizospheric soils were monitored for different phosphine concentrations and exposure times. In the first 2 weeks in the rhizospheric soil, the activities of urease, invertase and dehydrogenase increased slowly with phosphine exposure time in both rhizospheric and non-rhizospheric soils, although ACP activity displayed a slight drop in the rhizosphere; however, the activities of all these enzymes dramatically increased with phosphine concentration and exposure time after 15 days. Enzyme activities in rhizosphere soil are generally greater than those in non-rhizosphere soil, exhibiting effects of the rhizosphere. Increase in phosphine exposure concentrations also increased the available phosphorus in rhizosphere and non-rhizosphere soils. Phosphine exposure increases soil enzyme activities and available phosphorus in both rhizosphere and non-rhizosphere which is beneficial for rice growth.

Impacts of the transgenic CrylAc and CpTI insect-resistant cotton SGK321 on selected soil enzyme activities in the rhizosphere

Transgenic CrylAc and CpTI insect-resistant cotton SGK321 is widely adopted for many years in several regions of China, however the understanding of its potential effects on soil enzyme activities is not studied. The impacts of transgenic cotton SGK321 on dehydrogenase, urease and phosphatase activities in rhizosphere soil were investigated in a two-year field study in Northern China. Rhizosphere soil enzyme activities between transgenic cotton SGK321 and its non-transgenic parental cotton Shiyuan 321 were found to differ at senescence. However compared to the plant growth stages and cotton cultivar, the impacts of the transgenic trait were minor or transient. The principal component analysis also showed no significant or minor difference in the activities of dehydrogenase, urease and phosphatase in the rhizosphere soil of transgenic cotton SGK321 and its counterpart. Our results indicated that the transgenic cotton SGK321 has no apparent impact on dehydrogenase, urease and phosphatase activities in rhizosphere soil.

Rhizosphere priming effects on soil carbon and nitrogen mineralization

Living roots and their rhizodeposits affect microbial activity and soil carbon (C) and nitrogen (N) mineralization. This so-called rhizosphere priming effect (RPE) has been increasingly recognized recently. However, the magnitude of the RPE and its driving mechanisms remain elusive. Here we investigated the RPE of two plant species (soybean and sunflower) grown in two soil types (a farm or a prairie soil) and sampled at two phenological stages (vegetative and mature stages) over an 88-day period in a greenhouse experiment. We measured soil C mineralization using a continuous 13C-labeling method, and quantified gross N mineralization with a 15N-pool dilution technique. We found that living roots significantly enhanced soil C mineralization, by 27–245%. This positive RPE on soil C mineralization did not vary between the two soils or the two phenological stages, but was significantly greater in sunflower compared to soybean. The magnitude of the RPE was positively correlated with rhizosphere respiration rate across all treatments, suggesting the variation of RPE among treatments was likely caused by variations in root activity and rhizodeposit quantity. Moreover, living roots stimulated gross N mineralization rate by 36–62% in five treatments, while they had no significant impact in the other three treatments. We also quantified soil microbial biomass and extracellular enzyme activity when plants were at the vegetative stage. Generally, living roots increased microbial biomass carbon by 0–28%, β-glucosidase activity by 19–56%, and oxidative enzyme activity by 0–46%. These results are consistent with the positive rhizosphere effect on soil C (45–79%) and N (10–52%) mineralization measured at the same period. We also found significant positive relationships between β-glucosidase activity and soil C mineralization rates and between oxidative enzyme activity and gross N mineralization rates across treatments. These relationships provide clear evidence for the microbial activation hypothesis of RPE. Our results demonstrate that root–soil–microbial interactions can stimulate soil C and N mineralization through rhizosphere effects. The relationships between the RPE and rhizosphere respiration rate and soil enzyme activity can be used for explicit representations of RPE in soil organic matter models.