Phosphatase activity does not limit the microbial use of low molecular weight organic-P substrates in soil

Plant roots and soil microorganisms contain significant quantities of low molecular weight (MW) phosphorylated nucleosides and sugars. Consequently, upon death these can represent a significant input of organic-P to the soil. Some of these organic-P substrates must first be dephosphorylated by phosphatases before being assimilated by the soil microbial community while others can be taken up directly from soil solution. To determine whether sorption or phosphatase activity was limiting the bioavailability of low MW organic-P in soil we compared the microbial uptake and C mineralization of a range of ¹⁴C-labeled organic-P substrates [glucose-6-phosphate, adenosine monophosphate (AMP), adenosine diphosphate (ADP) and adenosine triphosphate (ATP)] to that of the parent compounds (adenosine and glucose). In a fertile grassland soil we showed that at low organic-P substrate concentrations (<0.5 mM) phosphatase activity did not limit microbial uptake or mineralization in comparison to their non-phosphorylated counterparts. However, at high substrate concentrations (1-10 mM) the mineralization of the organic-P compounds was significantly lower than that of the non-phosphorylated compounds suggesting that phosphatase activity or microbial transporter capacity limited bioavailability. Sorption to the solid phase followed the series glucose<adenosine<G-6-P<AMP<ADP=ATP. However, sorption of the organic-P compounds to the solid phase did not appear to greatly affect bioavailability. The high adenosine mineralization capacity of the microbial biomass suggests that nucleosides may represent a significant source of C and N to the soil microbial biomass. We conclude that at low organic-P substrate concentrations typical of those in soil, neither phosphatase activity nor sorption greatly limits their bioavailability.     

Effects of past and current crop management on soil microbial biomass and activity

Because soil biota is influenced by a number of factors, including land use and management techniques, changing management practices could have significant effects on the soil microbial properties and processes. An experiment was conducted to investigate differences in soil microbiological properties caused by long- and short-term management practices. Intact monolith lysimeters (0.2 m² surface area) were taken from two sites of the same soil type that had been under long-term organic or conventional crop management and were then subjected to the same 2.5-year crop rotation [winter barley (Hordeum vulgare L.), maize (Zea mais L.), lupin (Lupinus angustifolius L.), and rape (Brassica napus L. ssp. oleifera)] and two fertilizer regimes (following common organic and conventional practices). Soil samples were taken after crop harvest and analyzed for microbial biomass C and N, microbial activity (fluorescein diacetate hydrolysis, arginine deaminase activity, and dehydrogenase activity), and total C and N. The incorporation of the green manure stimulated growth and activity of the microbial communities in soils of both management histories. Soil microbial properties did not show any differences between organically and conventionally fertilized soils, indicating that crop rotation and plant type had a larger influence on the microbial biomass and enzyme activities than fertilization. Initial differences in microbial biomass declined, while the effects of farm management history were still evident in enzyme activities and total C and N. Links between enzyme activities and microbial biomass C varied depending on treatment, indicating differences in microbial community composition.     

Organic matter status and the size,activity and metabolic diversity of the soil microflora as indicators of the success of rehabilitation of mined sand dunes

The effectiveness of the rehabilitation of mined sand dunes on the northern coast of KwaZulu–Natal, South Africa, was assessed based on measurements of the total and labile organic matter content and the size, activity and metabolic diversity of the soil microflora. Soil was sampled (0–10 cm) after 0, 5, 10, 20 and 25 years of rehabilitation and compared with soil under undisturbed native forest and under long-term commercial pine forest. Following topsoil removal, stockpiling and respreading on reformed dunes, there was a massive loss of organic C such that, at time zero, organic C content was only 24% of that present under native forest. Soil organic C content increased progressively during rehabilitation until, after 25 years, it represented 93% of that present under native forest. The pattern of change in light-fraction C, KMnO₄-extractable C, water-soluble C, microbial biomass C, basal respiration and arginine ammonification rate was broadly similar to that for organic C, but the extent of the initial loss and the magnitude of the subsequent increase differed. Microbial biomass C, water-soluble C and KMnO₄-extractable C, expressed as a percentage of organic C, declined during rehabilitation as humic substances progressively accumulated. Principal component (PC) analysis of catabolic response profiles to 36 substrates revealed that the catabolic diversity of microbial communities differed greatly between native forest, commercial pine forest, 0 years and 10 years of rehabilitation. On the PC1 axis, values for soils under native forest and after 25 years rehabilitation were similar, but there was still separation on the PC2 axis. The main factor explaining variation in response profiles on the PC1 axis was organic C content; and the greatest catabolic diversity occurred in soils under native forest and after 25 years of rehabilitation.     

Soil respiration on reclaimed coal-mine spoil

Summary Measurements of soil respiration were made at a number of soil-covered reclaimed coal-mine spoil sites. Many chemical and physical soil factors likely to affect the respiration were also measured. A combination of principal component, cluster, and multiple regression analyses was used to indicate the important factors. These were found to be water-holding capacity and organic matter content. In some cases soil pH was also a controlling factor.     

土壤深松对小麦根系活性的垂直分布及旗叶衰老的影响

土壤深松打破犁底层可改变土壤的理化性状 ,从而改善小麦根系的生长条件。与对照 (未深松 )相比 ,小麦的群体根系活性明显提高 ,垂直分布下移 ,使深层土壤的群体根系活性相对提高 ,进而对延缓地上部衰老和提高产量产生积极效应。     

Developing weed-suppressive soils through improved soil quality management

Manipulating soil microbial communities using soil and crop management practices is a basic strategy in developing sustainable agricultural systems. Sustainable farming is based, in part, on the efficient management of soil microorganisms to improve soil quality. However, the identification of biological indicators of soil quality that can be used to predict weed suppression in soils has received little attention. We investigated differences in soil microbial activity among various crop and soil management systems to assess: (i) the microbiological characteristics of these soils; (ii) determine whether any relationships existed that might be used in the development of weed suppression. Soil enzyme activity, water-stable aggregates, and the proportions of weed-suppressive bacteria were compared among seven cropping systems and one native-prairie ecosystem in mid-Missouri, USA. Assays of soil enzymes (fluorescein diacetate hydrolase, dehydrogenase, phosphatase) revealed that organic and integrated cropping systems, and the native-prairie ecosystem had the highest levels of soil activity. Weed rhizospheres from these same ecosystems also had greater proportions of bacterial isolates characterized as “growth suppressive” to green foxtail (Setaria viridis [L.] Beauv.) and field bindweed (Convolvulus arvensis L.): 15 and 10%, respectively. The proportion of water-stable soil aggregates was the greatest in soils with the highest organic matter and was found to be related to higher enzyme and weed-suppressive activity. Selected biological indicators of soil quality were associated with potential weed-suppressive activity in soil when that soil was managed for high organic matter content under reduced tillage systems. This research study provides further evidence that soil quality and sustainable agricultural practices may be linked to integrated weed management systems for the biological suppression of weeds.     

城市公园土壤和植被：自然和人为因子的影响

Various soil surface components, such as trees, shrubs and biological crusts, and human recreational activities, e.g., barbecues and trampling by visitors, may divide the area of the urban park into smaller fragments/microenvironments, differentiated by their microenvironmental conditions, which may differ in soil and vegetation characteristics. The spatial changes in the soil and vegetation characteristics and their causes were investigated in an urban park located south of Tel Aviv-Jaffa, Israel. The area of the park is 0.5 km², including groves, a lake, lawns, and rest areas. Soil was sampled in nine microenvironments, of which seven were within the park: under Ceratonia siliqua trees (CsU), under Ficus sycomorus trees (FiU), rest area between tables under F. sycomorus (FiB), rest area under tables under F. sycomorus (FiT), open area with bare soil (OaS), open area with biological crust cover (OaC), and open area covered by herbaceous vegetation (OaV). Two more microenvironments, planar and sloping open areas (CoP and CoS, respectively) in the vicinity of the park, were used as the controls. Electrical conductivity, concentrations of soluble ions (Mg²⁺, Ca²⁺, Na⁺, K⁺ and HCO₃^-), pH, contents of organic carbon, calcium carbonate and moisture, and grain size distribution were determined. In addition, herbaceous vegetation cover, number and diversity of herbaceous vegetation species were measured. It was found that soil properties and herbaceous vegetation characteristics varied within the park. Soil organic carbon, electrical conductivity, soluble salts, penetration depth, and vegetation characteristics were affected by human activities, mainly in the rest area between the tables. In contrast, the above characteristics were affected by natural factors mainly in the rest of the microenvironments, which were subjected to low levels of anthropogenic intervention. The heterogeneous structure of the park, as represented by the various microenvironments, offered new habitats and promoted the preservation of natural vegetation.     

A new coumestan with immunosuppressive activities from Flemingia philippinensis

A new coumestan, 1,3,9-trihydroxy-8-methoxycoumestan, named flemicoumestan A 1 together with nine isoflavone-related compounds were isolated from the ethyl acetate extract of the roots of Flemingia philippinensis. Their structures were elucidated and confirmed by spectroscopic methods and literature data. Compounds 3 and 4 showed strong lymphocyte proliferation inhibitory activity with an IC₅₀ value of 1.04-2.76 μM, and the low cytotoxicity with the CC₅₀ value of 71.01 and 56.36 μM, respectively.     

New furostanol saponins from Smilax aspera L. and their in vitro cytotoxicity

The occurrence of the two new cis-fused A/B rings furostanol saponins (25S)-26-O-β-d-glucopyranosyl-5β-furostan-1β,3β,22α,26-tetraol-1-O-β-d-glucopyranoside and (25S)-26-O-β-d-glucopyranosyl-5β-furostan-1β,2β,3β,5β,22α,26-hexaol and the known compounds (25S)-26-O-β-d-glucopyranosyl-5β-furostan-3β,22α,26-triol-3-O-α-l-rhamnopyranosyl-(1→2)-O-β-d-glucopyranosyl-(1→2)-O-β-d-glucopyranoside and (25S)-26-O-β-d-glucopyranosyl-5β-furostan-3β,22α,26-triol-3-O-β-d-glucopyranosyl-(1→2)-O-β-d-glucopyranoside, trans-resveratrol, (+) catechin and (−) epicatechin in the rhizomes of Smilax aspera is reported. All saponins have been isolated as their 22-OMe derivatives, which were further subjected to extensive spectroscopic analysis. The isolated furostanol saponins were evaluated for cytotoxic activity against human normal amniotic and human lung carcinoma cell lines using neutral red and MTT assays. In vitro experiments showed significant cytotoxicity in a dose dependent manner with IC₅₀ values in the range of 32.98-94.53 µM.