Relationship between soil chemical properties and microbial metabolic patterns in intensive greenhouse tomato production systems

ABSTRACT

Intensive greenhouse production involving excessive fertilizer and organic manure application rates may affect soil chemical and biological quality. Soil samples from 50 commercial greenhouses for tomato production in northern China were collected for the evaluation of the status of soil fertility and identification of the soil chemical factor that exerts the strongest influence on microbial functional diversity. The soil total nitrogen content showed high soil fertility and was 68% higher than 1000 mg kg^?1 and 14% higher than 1500 mg kg^?1. Differential soil pH values caused statistically significant shifts in microbial metabolic activity (average well color development, AWCD) and Shannon’s diversity index using Biolog^TM ECO plates assay. The highest soil microbial functional diversity was observed at near neutral pH values. When individual data points were plotted against soil organic matter (SOM), significant positive associations with soil microbial biomass nitrogen and AWCD were observed. The canonical correspondence analysis confirmed that shifts in the soil microbial functional diversity were associated with changes in pH, total nitrogen, and SOM. This study indicated that excessive fertilization changed the community-level physiological profile of the soil microorganisms, and this effect can be a consequence of changes in soil pH under intensive greenhouse management.     

Earthworm influence on carbon dioxide and nitrous oxide fluxes from an unfertilized corn agroecosystem

Earthworms modify the soil environment through their feeding, casting, and burrowing activities, which may lead to more decomposition and respiration in aerobic microsites and more denitrification in anaerobic microsites. The objective of this study was to determine whether earthworms increase CO₂ and N₂O fluxes from an unfertilized corn agroecosystem. Earthworm populations within field enclosures (2.9 m²) were reduced by repeatedly applying carbaryl insecticide, then single and mixed populations of Lumbricus terrestris L. and Aporrectodea caliginosa (Savigny) were added. Gas samples were collected once a week for 14 weeks, from June to September 2005. Carbaryl applications reduced, but did not eliminate earthworms from enclosures. The CO₂ and N₂O fluxes were affected by the sampling date, with peak gas fluxes after rainfall events. Mean CO₂ and N₂O fluxes during the study period tended to be greater from enclosures with added earthworms than the control (no earthworms added), but were not significantly affected by earthworm treatments due to the low survival rate of introduced earthworms. Better control of earthworm populations in the field is required to fully assess the impact of earthworms on CO₂ and N₂O fluxes from temperate agroecosystems.     

不同施肥制度对玉米生育期土壤微生物量的影响

通过测定不同施肥制度下玉米土壤微生物量碳、氮的动态变化,探讨了不同施肥制度对玉米土壤的培肥效应。研究结果表明,与无肥、单施有机肥、单施化肥相比,有机肥与N、P、K肥配合施用能显著增加玉米各生育时期的土壤微生物量碳、氮,促进土壤微生物量显著增长,增强了土壤养分容量的供应强度,有利于培肥土壤。     

Soil microbial biomass and activity response to repeated drying-rewetting cycles along a soil fertility gradient modified by long-term fertilization management practices

The effects of repeated drying-rewetting (DRW) cycles on the microbial biomass and activity in soils taken from long-term field experiment plots with different fertilization (FERT) management practice histories were studied. We investigated the hypothesis that soil response to DRW cycles differs with soil fertility gradient modified by FERT management practices. The soils were incubated for 51 days, after exposure to either nine or three DRW cycles, or remaining at constant moisture content (CMC) at field capacity. We found that both DRW and FERT significantly affected soil properties including NH₄-N, NO₃-N, dissolved organic C (DOC), microbial biomass C (Cmic), basal soil respiration rate (BSR), urease activity (URE) and dehydrogenase activity (DHD). Except for NH₄-N and BSR, variation in the properties was largely explained by FERT, followed by DRW, and then their interaction. Irrespective of the soils' FERT treatment, repeated DRW cycles significantly raised the DOC and Cmic levels compared with CMC, and the DRW cycles also resulted in a significant decline in BSR and URE and increase in DHD, probably because the organisms were better-adapted to the drying and rewetting stresses. The variations in soil biological properties caused by DRW cycles showed a significantly negative relationship with the soil organic C content measured prior to the start of the DRW experiments, suggesting that soils with higher fertility are better able to maintain their original biological functions (i.e., have a higher functional stability) in response to DRW cycles.     

Water-stable aggregates and organic matter pools in a calcareous vineyard soil under four soil-surface management systems

Abstract. Vineyards in Champagne, France are generally situated on slopes where the soils are subject to erosion. Therefore it is important to find a soil‐surface management practice that protects the soil against water erosion. We assessed the potential of mulches or grass covers to stabilize soil aggregates in a calcareous sandy loam from a vineyard in Champagne after 9 years under different management systems. Four different treatments were studied: (i) a bluegrass (Poa pratensis) surface cover between the vine rows (GC) with bare soil under the vines (R); two organic mulches of (ii) coniferous (CB) or (iii) poplar (PB) bark that covered the entire soil surface, and (iv) bare soil between the rows as a control. The bark amendments were applied every 3 years at rates of 61 and 67 t ha^?1 for the PB and CB treatments, respectively. The kinetics of soil disaggregation in water fitted a power law (A=K t^?D), in which K was the fraction of water‐stable >200 μm aggregates remaining after 1 hour of wet‐sieving. In the 0–5 cm layer, aggregate stability was greater for GC (K=21.7), CB (K=15.2) and PB (K=13.6) than for the control (K=10.5) and R (K=11.8). In the 0–20 cm layer, CB also stabilized soil aggregates (K=14.0–15.0); but PB did not. Structural stability was more strongly related to total organic carbon (R²=0.64, P <0.001) than to microbial biomass carbon (R²=0.54, P<0.001). A bluegrass cover enhanced structural stability in the 0–5 cm and 0–20 cm layers (K=14.2), probably because of intense root development and rhizodeposition enhancing microbially produced metabolites, such as carbohydrates. Establishing grass cover or applying bark mulch are effective agricultural practices that improve soil aggregate stability and thus should reduce soil erosion. The vegetative growth of the vines was greater on the soils amended with bark mulches and less on the grass covered soils compared with the control soil; however, no difference in wine quality was observed among the different treatments.     

菜茶果园红壤微生物量磷与土壤磷以及磷植物有效性之间的关系研究

对有机质水平差异较大的7种菜茶果园红壤和1种红壤性水稻土进行了微生物量P与土壤P以及P植物有效性之间的相关性研究。结果表明，红壤微生物量P与土壤全P、土壤有机P以及土壤速效P之间存在明显正相关，相关系数分别为0.840， 0.897和0.944。红壤微生物量P尤以与土壤速效P关系最为密切，红壤微生物量P有可能作为红壤供P能力的一个活指标；盆栽试验表明，微生物量C与黑麦草产量呈显著正相关，与黑麦草吸P量以及单位黑麦草吸P量相关性不明显；而微生物量P与黑麦草产量、黑麦草吸P量以及单位黑麦草吸P量之间均呈显著正相关，相关性依次增强；红壤微生物量P在指示土壤植物有效P上的作用不仅体现在植物的产量和植物吸P量上， 更体现在植物的品质～单位重量植物的吸P量上。     

Mineralization of carbon and nitrogen from cowpea leaves decomposing in soils with different levels of microbial biomass

Soils with greater levels of microbial biomass may be able to release nutrients more rapidly from applied plant material. We tested the hypothesis that the indigenous soil microbial biomass affects the rate of decomposition of added green manure. Cowpea (Vigna unguiculata L.) Walp.] leaves were added to four soils with widely differing microbial biomass C levels. C and N mineralization of the added plant material was followed during incubation at 30°C for 60 days. Low levels of soil microbial biomass resulted in an initially slower rate of decomposition of soil-incorporated green manure. The microbial biomass appeared to adjust rapidly to the new substrate, so that at 60 days of incubation the cumulative C loss and net N mineralization from decomposing cowpea leaves were not significantly affected by the level of the indigenous soil microbial biomass.     

Microbial community structure and activity in a Colorado Rocky Mountain forest soil scarred by slash pile burning

Tree thinning and harvesting produces large amounts of slash material which are typically disposed of by burning, often resulting in severe soil heating. We measured soil chemical properties and microbial community structure and function over time to determine effects of slash pile burning in a ponderosa pine forest soil. Real time data were collected for soil temperature, heat flux, and soil moisture contents in one of two slash piles burned in April 2004. During the burn, soil temperatures reached 300 °C beneath the pile center and 175 °C beneath the pile edge. Slash pile burning increased soil pH, extractable N and P, and decreased total C levels within the first 15 cm of soil. Burning reduced soil bacterial biovolumes within the first 15 cm of soil and fungal biovolumes within the first 5 cm of soil. One month after the burn, soil microbial communities under the pile center were enriched in Gram-positive bacterial fatty acid markers compared to communities from under the pile edge and control (nonburned) soil. Fifteen months later, soil chemical properties had not returned to background levels, and microbial community structure in fire-affected soil, regardless of pile location, was distinct from communities of control soil. In fire-affected soil, concentrations of fungal fatty acid biomarkers were low and arbuscular mycorrhizal fungal biomarkers were absent, regardless of pile location. Slash pile burning also reduced fungal and bacterial respiration and resulted in large fluctuations in microbial potential N mineralization and immobilization activities. By altering soil properties important to soil conservation and plant reestablishment, slash pile burning negatively impacts forest ecosystems at localized scales.     

The feeding ecology of earthworms – A review

Current knowledge of earthworm feeding ecology is reviewed, with particular reference to food selection, ingestion, digestion and assimilation, and the use of novel techniques to advance understanding of the functional significance of these processes.

Traditional research methods including direct observation of feeding behaviour, gut content analysis, choice tests, and litter bags have provided a wealth of information on earthworm feeding. However, there is a lack of the mechanistic, quantitative information required to characterise adequately their functional role in soil ecosystem processes such as soil C sequestration and loss, decomposition of organic residues, the maintenance of soil structure and trophic interactions with plants and microorganisms.

Stable isotope ratio analysis of light elements (C, N, and S) offers a powerful research tool to reveal and quantify trophic relationships of earthworms in soil food webs, while molecular techniques can further enhance understanding of the interactions between earthworms and microorganisms and their functional significance.     

中国四川盆地地区侵蚀斜坡土壤酶活性研究

Determining how soil erosion affects enzyme activity may enhance our understanding of soil degradation on eroded agricultural landscapes. This study assessed the changes in enzyme activity with slope position and erosion type by selecting water and tillage erosion-dominated slopes and performing analyses using the ¹³⁷Cs technique. The ¹³⁷Cs data revealed that soil loss occurred in the upper section of the two eroded slope types, while soil accumulation occurred in the lower section. The invertase activity increased downslope and exhibited a pattern similar to the ¹³⁷Cs data. The spatial patterns of urease and alkaline phosphatase activities were similar to the ¹³⁷Cs inventories on the water and tillage erosion-dominated slopes, respectively. On both the eroded slope types, the invertase activity and soil organic carbon content were correlated, but no correlation was observed between the alkaline phosphatase activity and total phosphorus content. Nevertheless, the urease activity was correlated with the total nitrogen content only on the water erosion-dominated slopes. The enzyme activity-to-microbial biomass carbon ratios indicated high activities of invertase and urease but low activity of phosphatase on the water erosion-dominated slopes compared with the tillage erosion-dominated slopes. Both the invertase activity and the invertase activity-to-microbial biomass carbon ratio varied with the slope position. Changes in the urease activity-to-microbial biomass carbon ratio were significantly affected by the erosion type. These suggested that the dynamics of the invertase activity were linked to soil redistribution on the two eroded slope types, whereas the dynamics of the urease and alkaline phosphatase activities were associated with soil redistribution only on the water or tillage erosion-dominated slopes, respectively. The erosion type had an obvious effect on the activities of invertase, urease and alkaline phosphatase. Soil redistribution might influence the involvement of urease in the N cycle and alkaline phosphatase in the P cycle. Thus, enzyme activity-to-microbial biomass ratios may be used to better evaluate microbiological activity in eroded soils.