长期施肥对高原农业生态系统土壤有机碳和氮的影响

The effects of fertilization on the distributions of organic carbon (OC) and nitrogen (N) in soil aggregates and whether these effects vary with cropping system have not been well addressed.Such information is important for understanding the sequestration of OC and N in agricultural soils.In this study,the distributions of OC and N associated with soil aggregates were analyzed in different fertilization treatments in a continuous winter wheat cropping system and a legume-grain rotation system in a 27-year field experiment,to understand the effects of long-term fertilization on the distributions of OC and N in aggregates and to examine the recovery of soil OC and N in a highland agroecosystem.Manure fertilizer significantly decreased soil bulk density but increased the amount of coarse fractions and their associated OC and N stocks in the soils of both systems.Fertilizers N + phosphorus (P) and manure had similar effects on total soil OC and N stocks in both systems,but had larger effects on the OC and N stocks in ＞ 2 mm aggregates in the legume-grain rotation system than in the continuous winter wheat system.The application of P increased the OC and N stocks in ＞ 2 mm aggregates and decreased the loss of N from chemical fertilizers in the legume-grain rotation system.The results from this study suggested that P fertilizer should be applied for legume-included cropping systems and that manure with or without chemical fertilizers should be applied for semiarid cropping systems in order to enhance OC and N accumulation in soils.     

Soil microbial diversity and activity in a Mediterranean olive orchard using sustainable agricultural practices

Sustainable soil management of orchards can have positive effects on both soils and crop yields due to increases in microbial biomass, activity and complexity. The aim of this study was to investigate medium‐term effects (12 yr) of two different management practices termed ‘sustainable’ (ST) and ‘conventional’ (CT) on soil microbial composition and metabolic diversity of a rainfed mature olive orchard in Southern Italy. ST included no‐till, self‐seeding weeds (mainly graminaceous and leguminosae), and mulch derived from olive tree prunings, whilst CT was managed by frequent tillage and included severe pruning with residues removed from the orchard. Microbial analyses were carried out by culture‐dependent methods (microbial cultures and Biolog^®). Molecular methods were used to confirm the identification by light microscopy of the isolates of fungi and Streptomyces. Significantly more culturable fungi and bacteria were found in ST than in CT. The number of fungal groups in ST was also significantly greater than in CT. Overall and substrate‐specific Biolog^® metabolic diversity indices of microbial communities and soil enzyme activities were greater in ST. The results demonstrate that soil micro‐organisms respond positively to sustainable orchard management characterized by periodic applications of locally derived organic matter. This study confirms the need to encourage farmers with orchards in the Mediterranean basin to practise soil management based on organic matter inputs associated with zero tillage to improve soil functionality.     

Mycorrhizal diversity: Cause and effect?

Mycorrhizal fungi play a critical role in nutrient cycling and ecosystem function. They improve plant growth and survival through a mutualistic relationship in which photosynthates are exchanged for increased access to water and nutrients. Because the benefits realized are not equal among different plant–fungal species combinations, mycorrhizal fungi may help govern plant community structure and successional trajectories. In fact, both plant productivity and plant diversity have been shown to increase with increasing diversity of mycorrhizal fungi. The diversity and species composition of plant communities also exert a reciprocal influence on associated mycorrhizal communities, although edaphic factors may also play a role. Given this inherent bi-directionality of mycorrhizal relationships, the potential exists for positive feedback mechanisms which may promote and maintain both plant and mycorrhizal fungal diversity. This review considers recent literature on both arbuscular and ectomycorrhizal fungal–plant community relationships within a variety of environments, including artificially constructed systems and naturally occurring grasslands and forests.     

Mycorrhizae activity and diversity in conventional and organic apple orchards from Brazil

The aim of this study was to characterize the impacts of a conventional, an organic apple orchard and a native grassland on the activity and diversity of arbuscular mycorrhizal fungi (AMF) located at the south of Brazil during winter and summer. AMF activity was measured by the mycorrhizal inoculum potential (MIP), mycorrhizal fungal hyphal length (HL), easily extractable and total Bradford-reactive soil protein (BRSP). AMF diversity was represented by richness, Shannon diversity index and number of spores. Orchards reduced the MIP of the soil and increased the HL when compared to the grassland site. The amount of easily extractable BRSP was not different among orchards and between seasons evaluated, with overall mean value of 1.23 mg g⁻¹. However, the amount of total-BRSP was smaller in the conventional orchard (4.55 mg g⁻¹) than in the organic orchard (4.91 mg g⁻¹) and in the native grassland (5.12 mg g⁻¹). T-BRSP and total organic carbon were strongly correlated in the grassland during the winter, suggesting the contribution of this protein for carbon stocks in the native soil of this region. The organic orchard presented the highest AMF richness, but sporulation and Shannon diversity index were larger in the conventional orchard. Our data suggest that the conventional orchard promoted higher impacts on the natural condition of AMF activity, being considered an unadvisable practice to soil conservation.     

Integrated analysis of changes in soil microbiota and metabolites following long-term fertilization in a subtropical maize-wheat agroecosystem

Although the application of inorganic fertilizer is a widespread agronomic practice used to boost soil productivity and crop yields, the effects on soil microbiome and the metabolic mechanisms involved in the high-yield response of crops to long-term fertilization remain poorly described. In this study, combined metagenomic and metabolomic analyses were used to explore the mechanism of crop yield response to the 20-year application of nitrogen-phosphorus-potassium fertilizers in a subtropical ag...     

Dissolved organic nitrogen dynamics in a Mediterranean vineyard soil

Dissolved organic carbon (DOC) and nitrogen (DON) have been hypothesized to play a central role in nutrient cycling in agricultural soils. The aim of this study was to investigate the annual dynamics of DOC and DON in a Greek vineyard soil and to assess the potential role of DON in supplying N to the vines. Our results indicated that significant quantities of DOC and DON existed in soil throughout the year and that peaks in concentration appeared to correlate with discrete agronomic events (e.g. onset of irrigation and plowing). Both field and laboratory experiments showed that free amino acids were rapidly mineralized in soil and that consequently free amino acids represented only a small proportion of the soil's total soluble N. Due to rapid nitrification the soil solution N was dominated by NO₃⁻. Based upon the calculation of a plant-soil N budget and previous studies on N uptake in Vitis vinifera L., it is likely that DON uptake does not directly supply significant amounts of N to the plant. As the soil was not N limited we hypothesize that amino acids are used by the microbial community more as a source of C rather than a source of N. While we conclude that DON constitutes a significant N pool in vineyard soils further work is required to chemically characterize its constituent units and their relative bioavailability so that their overall role in N cycling can be determined.     

中国南方稻麦轮作生态系统中土壤溶解性有机氮的淋失

The rice-wheat rotation in southern China is characterized by frequent flooding-draining water regime and heavy nitrogen(N)fertilization. There is a substantial lack of studies into the behavior of dissolved organic nitrogen(DON) in the intensively managed agroecosystem. A 3-year in situ field experiment was conducted to determine DON leaching and its seasonal and yearly variations as affected by fertilization, irrigation and precipitation over 6 consecutive rice/wheat seasons. Under the conventional N practice(300kg N ha-1for rice and 200 kg N ha-1for wheat), the seasonal average DON concentrations in leachate(100 cm soil depth) for the three rice and wheat seasons were 0.6–1.1 and 0.1–2.3 mg N L-1, respectively. The cumulative DON leaching was estimated to be1.1–2.3 kg N ha-1for the rice seasons and 0.01–1.3 kg N ha-1for the wheat seasons, with an annual total of 1.1–3.6 kg N ha-1. In the rice seasons, N fertilizer had little effect(P 0.05) on DON leaching; precipitation and irrigation imported 3.6–9.1 kg N ha-1of DON, which may thus conceal the fertilization effect on DON. In the wheat seasons, N fertilization had a positive effect(P 0.01)on DON. Nevertheless, this promotive effect was strongly influenced by variable precipitation, which also carried 1.8–2.9 kg N ha-1of DON into fields. Despite a very small proportion to chemical N applied and large variations driven by water regime, DON leaching is necessarily involved in the integrated field N budget in the rice-wheat rotation due to its relatively greater amount compared to other natural ecosystems.     

Soil organic matter and water-stable aggregates under different tillage and residue conditions in a tropical dryland agroecosystem

Changes in the proportions of water-stable soil aggregates, organic C, total N and soil microbial biomass C and N, due to tillage reduction (conventional, minimum and zero tillage) and crop residue manipulation (retained or removed) conditions were studied in a tropical rice–barley dryland agroecosystem. The values of soil organic C and total N were the highest (11.1 and 1.33 g kg⁻¹ soil, respectively) in the minimum tillage and residue retained (MT+R) treatment and the lowest (7.8 and 0.87 g kg⁻¹, respectively) in conventional tillage and residue removed (CT−R) treatment. Tillage reduction from conventional to minimum and zero conditions along with residue retention (MT+R,ZT+R) increased the proportion of macroaggregates in soil (21–42% over control). The greatest increase was recorded in MT+R treatment and the smallest increase in conventional tillage and residue retained (CT+R) treatment. The lowest values of organic C and total N (7.0–8.9 and 0.82–0.88 g kg⁻¹ soil, respectively) in macro- and microaggregates were recorded in CT−R treatment. However, the highest values of organic C and total N (8.6–12.6 and 1.22–1.36 g kg⁻¹, respectively) were recorded in MT+R treatment. The per cent increase in the amount of organic C in macroaggregates was greater than in microaggregates. In all treatments, macroaggregates showed wider C/N ratio than in microaggregates. Soil microbial biomass C and N ranged from 235 to 427 and 23.9 to 49.7 mg kg⁻¹ in CT−R and MT+R treatments, respectively. Soil organic C, total N, and microbial biomass C and N were strongly correlated with soil macroaggregates. Residue retention in combination with tillage reduction (MT+R) resulted in the greatest increase in microbial biomass C and N (82–104% over control). These variables showed better correlations with macroaggregates than other soil parameters. Thus, it is suggested that the organic matter addition due to residue retention along with tillage reduction accelerates the formation of macroaggregates through an increase in the microbial biomass content in soil.     

Conservation planning of vertebrate diversity in a Mediterranean agricultural-dominant landscape

To improve effectiveness of protected areas, selection of priority areas should include consideration of three main components, namely special conservation elements, focal species and representation. We present a three-track approach related to these components for vertebrate conservation planning in Castilla-La Mancha, central Spain. As special conservation elements, we identified Priority Areas for Conservation of species using five criteria: species richness, geographic rarity, species vulnerability, a Combined Index of these three criteria, and a Standardised Biodiversity Index (SBI) that integrate the three criteria and four studied taxa. The Natura 2000 Network was used to include conservation areas for focal species. We evaluated the representation of every landscape type in the existing conservation areas. To delineate the spatial configuration for vertebrate conservation, we combined the identified Priority Areas for Conservation, existing conservation areas and connectivity areas by cost–distance analysis. The Combined Index was the most efficient criterion analyzed to identify Priority Areas for Conservation. The Natura 2000 Network showed a high percentage of coincidence with identified Priority Areas for Conservation, whereas the natural protected areas network had a low percentage of coincidence. Six agricultural landscapes were inadequately represented in the current conservation network. According to our multi-track approach, ∼29% of study area was required to capture 100% of vertebrate species and all landscape types. Our results show that the existing conservation areas are insufficient to guarantee the conservation of biodiversity in the study region. Additional areas with outstanding features of diversity, connectivity areas, and establishment of targets for off-reserve conservation are of fundamental importance for strengthening biodiversity conservation.     

Microbial functional diversity,metabolic quotient,and invertase activity of a sandy loam soil as affected by long-term application of organic amendment and mineral fertilizer

Purpose  

Organic and inorganic fertilizers are used primarily to increase nutrient availability to plants. Monitoring balanced versus unbalanced fertilization effects on soil microbes could improve our understanding of soil biochemical processes and thus help us to develop sound management strategies. The objective of this study was to investigate the effects of long-term fertilization regimes on soil microbial community functional diversity, metabolic activity, and metabolic quotient and to find out the main factors that influence these parameters.     

Effects of long-term organic and mineral fertilizers on bulk density and penetration resistance in semi-arid Mediterranean soil conditions

Soil aggregation is of great importance in agriculture due to its positive effect on soil physical properties, plant growth and the environment. A long-term (1996-2008) field experiment was performed to investigate the role of mycorrhizal inoculation and organic fertilizers on some of soil properties of Mediterranean soils (Typic Xerofluvent, Menzilat clay-loam soil). We applied a rotation with winter wheat (Triticum aestivum L.) and maize (Zea mays L.) as a second crop during the periods of 1996 and 2008. The study consisted of five experimental treatments; control, mineral fertilizer (300-60-150 kg N-P-K ha⁻¹), manure at 25 t ha⁻¹, compost at 25 t ha⁻¹ and mycorrhiza-inoculated compost at 10 t ha⁻¹ with three replicates. The highest organic matter content both at 0-15 cm and 15-30 cm soil depths were obtained with manure application, whereas mineral fertilizer application had no effect on organic matter accumulation. Manure, compost and mycorrhizal inoculation + compost application had 69%, 32% and 24% higher organic matter contents at 0-30 cm depth as compared to the control application. Organic applications had varying and important effects on aggregation indexes of soils. The greatest mean weight diameters (MWD) at 15-30 cm depth were obtained with manure, mycorrhiza-inoculated compost and compost applications, respectively. The decline in organic matter content of soils in control plots lead disintegration of aggregates demonstrated on significantly lower MWD values. The compost application resulted in occurring the lowest bulk densities at 0-15 and 15-30 cm soil depths, whereas the highest bulk density values were obtained with mineral fertilizer application. Measurements obtained in 2008 indicated that manure and compost applications did not cause any further increase in MWD at manure and compost receiving plots indicated reaching a steady state. However, compost with mycorrhizae application continued to significant increase (P < 0.05) in MWD values of soils. Organic applications significantly lowered the soil bulk density and penetration resistance. The lowest penetration resistance (PR) at 0-50 cm soil depth was obtained with mycorrhizal inoculated compost, and the highest PR was with control and mineral fertilizer applications. The results clearly revealed that mycorrhiza application along with organic fertilizers resulted in decreased bulk density and penetration resistance associated with an increase in organic matter and greater aggregate stability, indicated an improvement in soil structure.     

Contribution of earthworm activity to the infiltration of nitrogen in a wheat agroecosystem

The effect of earthworms on leachate volume and leachate N losses was investigated in a rice–wheat rotation agroecosystem over the wheat growing season. Corn residues (<2 cm) were added to field microcosms as either mulch or incorporated into the soil. Earthworms were added to half of the microcosms at a population density and age structure simulating a natural earthworm population. With earthworms present, leachate volume was >30% higher, but this result was not statistically significant (P>0.05). Earthworms significantly increased mineral N losses in the mulching treatment (P<0.05). There was a reduced fertilizer N (urea-¹⁵N) loss when earthworms were present, but the reduction was not significant (P>0.05). Our results indicate that earthworm activity can accelerate leachate production and N loss to a certain extent under wheat, and that native soil N (including mineral N and organic N) and/or organic matter N (corn residue N) are more likely sources for N leaching than urea-N.     

地中海生态系统中可溶性有机N研究

Dissolved organic nitrogen (DON) in soils has recently gained increasing interest because it may be both a direct N source for plants and the dominant available N form in nutrient-poor soils, however, its prevalence in Mediterranean ecosystems remains unclear. The aims of this study were to i) estimate soil DON in a wide set of Mediterranean ecosystems and compare this levels with those for other ecosystems; ii) describe temporal changes in DON and dissolved inorganic nitrogen (DIN) forms (NH4+ and NO3? ), and characterize spatial heterogeneity within plant communities; and iii) study the relative proportion of soil DON and DIN forms as a test of Schimel and Bennett’s hypothesis that the prevalence of different N forms follows a gradient of nutrient availability. The study was carried out in eleven plant communities chosen to represent a wide spectrum of Mediterranean vegetation types, ranging from early to late successional status. DON concentrations in the studied Mediterranean plant communities (0-18.2 mg N kg-1) were consistently lower than those found in the literature for other ecosystems. We found high temporal and spatial variability in soil DON for all plant communities. As predicted by the Schimel and Bennett model for nutrient-poor ecosystems, DON dominance over ammonium and nitrate was observed for most plant communities in winter and spring soil samples. However, mineral-N dominated over DON in summer and autumn. Thus, soil water content may have an important effect on DON versus mineral N dominance in Mediterranean ecosystems.     

Soil organic C variability and microbial functions in a Mediterranean agro-forest ecosystem

Five soils characterised by different agro-forest managements, typical of Mediterranean environment and with increasing human impact were chosen in Sardinia (Italy): two vineyards with different management systems, a rotation hay crop-pasture and a forest (Quercus suber L.). The study aimed to investigate the relationships between C storage and microbial functionality in soil under different managements. Pools of total organic C and microbial biomass C were determined, as well as the loss of organic C due to microbial respiration (basal and cumulative) and several microbial indices (metabolic, mineralization, and microbial quotient) as indicators of the microbial efficiency in the use of energy and the degree of substrate limitation for soil microbes. Enzymes were chosen on their relevance in the C (β-cellobiohydrolase, N-acetyl-β-glucosaminidase, β-glucosidase, α-glucosidase), N (leucine aminopeptidase), S (arylsulphatase) and P (acid phosphatase) cycling and were used as indicators of functional diversity in soil. Organic C pools and enzyme activities on average increased noticeably in soils with a lower human impact showing the highest values in forest and the lowest in the vineyards, following the trend of organic matter availability. The trend in functional diversity reflected the increase of microbial pool and organic C availability: the vineyards showed a lower Shannon’s diversity index, whilst pasture and forest sites reached the maximum levels of functional diversity. These soils showed an increase of microbial efficiency in the use of available resources and the decrease of substrate limitation for soil microbes.     

Soil organic carbon distribution drives microbial activity and functional diversity in particle and aggregate-size fractions

Chemical and functional characterizations of particle-size and aggregate fractions of soils were performed to investigate whether accessibility and decomposability of organic matter regulate functions and diversity of the soil microbial community at the micro-habitat scale. Soils were physically fractionated into particle size fractions, free-particulate organic matter (F-POM), macro-aggregates (250–2000 μm) and micro-aggregates (53–250 μm). Organic C was enriched in silt and clay, micro-aggregates and F-POM fractions. Enzymes showed the greatest activity in the fine fractions (silt and clay) and F-POM, and were largely influenced by organic C content. MicroResp-CLPP (Community Level Physiological Profile) showed the lowest catabolic responses in the sand and the highest in the fine fraction and micro-aggregates. In general, organic C availability drove soil activity and functional diversity: soils with the higher amount of organic C showed the higher catabolic activity. However, this response was variable within soil fractions, where organic C accessibility, as well as microbial selection and distribution, affected functional diversity.     

Soil microbiome biomass,activity, composition and CO2 emissions in a long-term organic and conventional farming systems

The implementation of environmentally friendly agricultural policies has increased the need to compare agricultural aspects of conventional (CON) and organic farming (ORG) systems. The objective of the present work was to compare the effects of an organic and conventional long-term experiment on bacterial and fungal biomass and activity, as well as soil CO₂ emission and readily available nitrogen forms in a soil cultivated with Helianthus annuus L. The microbial biomass was more active and abundant in ORG as well as soil CO₂ emission. Despite being less abundant, fungi were more active than bacteria in both ORG and CON experiments. 16S rRNA gene sequencing showed that the ORG treatment had a significantly greater bacterial richness than CON. Cyanobacteria, Actinobacteria and Proteobacteria were the most abundant phyla contributing more than others to the differences between the two systems. Moreover, the soil ${\mathit{NH}}_4^{+}$ and ${\mathit{NO}}_2^{-}$ content was not significantly different between ORG and CON, while ${\mathit{NO}}_3^{-}$ was less in ORG. ORG sunflower yield was significantly less compared with CON. While much remains to be discovered about the effects of these agricultural practices on soil chemical properties and microbial diversity, our findings may contribute to this type of investigation.     

Kinetics of added organic matter decomposition in a Mediterranean sandy soil

Carbon mineralization kinetics of 17 organic materials were studied in a Mediterranean sandy soil. These added organic matters (AOM) used in the organic fertilizer industry differed in their origin and composition: plant residues from the agri-food industry, animal wastes, manures (plant and animal origin), composts at different composting times and organic fertilizers. The mixtures AOM-soils were incubated under aerobic conditions at 28°C during 6 months. Soil moisture was maintained at 75% water holding capacity and respired-CO₂ was regularly trapped into alkali media in closed chambers, then checked by HCl titration. Analyses of CO₂ were performed in triplicate at 17 sampling occasions. The mineralized AOM fraction (MAOMF) varied according to the AOM origin: from 12–33% of added C for composts, to 65–90% for animal-originated AOM, with many intermediate patterns for plant-originated AOM.Seven decomposition models from the literature were fitted to actual MAOMF: (a) three consecutive models with two 1st-order-kinetic compartments and three parameters (m1, humification; m2, exchange; m3, decomposition), (b) three parallel models (m4, with two compartments and three parameters; m8, a 1st-order plus 0-order model with three parameters; m5, a three-compartment model with four parameters), and (c) m7, a model with one 2nd-order-kinetic compartment and two parameters. Additionally, m6, a simplified version of m5 was proposed. Models m2 and m7 did not match with actual data or gave a poor fit. By the correlation parameters, the most simple model m4 was chosen instead of the consecutive models m1 and m3. Residual sums of squares were always greater—but not significantly—in m8 than in m4, which confirmed the superiority of the models with two 1st-order compartments against 1st-order plus 0-order models for incubation times higher than 100 days. Model m5 (most of its parameters being not correlated) gave the best predictions of our data. The proposed m6 version gave predictions with similar precision as m4 and appeared powerful with only two parameters (very labile and stable fractions of the AOM). A compromise between the precision of the predictions and the simplicity of the formulae allowed the recommendation of the well-known m4 model, and above all the simpler m6 model.     

Pinus halepensis Mill. plantations did not restore organic carbon,microbial biomass and activity levels in a semi-arid Mediterranean soil

Maquis is a dense evergreen shrub layer which, in semi-arid Mediterranean lands, is commonly linked to the presence of well-conserved soils with large contents of mineralizable substrates. It was our aim to test whether: (i) maquis promotes soil microbial biomass and activity, and (ii) mature pine plantations without a shrubby understory support microbial biomass and activity levels comparable to those of stands with maquis. Surface soil samples were taken in four sites that sustain pine plantations (PP), maquis with pines (MP), maquis (MQ) and grasslands (GS). Microbial biomass was inferred from the C content in the soil microbiota. The ATP content in fresh samples and the CO₂–C production from incubated samples were used to assess microbial activity, as was the activity of β-glucosidase and alkaline phosphatase. Topsoils under maquis (MP and MQ) were the most fertile, both chemically (high organic carbon contents) and physically (low bulk density, high aggregate stability) and showed by far the largest levels of microbial biomass and activity. These levels in soils under PP, which sustained a successful plantation in terms of tree canopy density but lacked the shrubby understory, were significantly smaller than those of the adjacent shrubland with pines (MP). Redundancy analysis extracted a main axis explaining 67% of the variation of the microbiological soil properties, which was interpreted as an environmental gradient of soil fertility. Along this axis, the samples were separated according to the presence or absence of a maquis dominated by late-successional species; other factors such as soil type, slope position and aspect were less influential. The effects of afforestation practices on the detritus-based system should be considered in the design of future forest restoration strategies in desertification-threatened lands.