Growth response of crops to soil microbial communities from conventional monocropping and tree-based intercropping systems

Background and aims

Recent studies have shown that tree-based intercropping (TBI) systems support a more diverse soil microbial community compared to conventional agricultural systems. However, it is unclear whether differences in soil microbial diversity between these two agricultural systems have a functional effect on crop growth.

Methods

In this study, we used a series of greenhouse experiments to test whether crops respond differently to the total soil microbial community (Experiment 1) and to arbuscular mycorrhizal (AM) fungal communities alone (Experiment 2) from conventionally monocropped (CM) and TBI systems.

Results

The crops had a similar growth response to the total soil microbial communities from both cropping systems. However, when compared to sterilized controls, barley (Hordeum vulgare) and canola (Brassica napus) exhibited a negative growth response to the total soil microbial communities, while soybean (Glycine max) was unaffected. During the AM fungal establishment phase of the second experiment, ‘nurse’ plants had a strong positive growth response to AM fungal inoculation, and significantly higher biomass when inoculated with AM fungi from the CM system compared to the TBI system. Soybean was the only crop species to exhibit a significant positive growth response to AM fungal inoculation. Similar to the total soil microbial communities, AM fungi from the two cropping systems did not differ in their effect on crop growth.

Conclusion

Overall, AM fungi from both cropping systems had a positive effect on the growth of plants that formed a functional symbiosis. However, the results from these experiments suggest that negative effects of non-AM fungal microbes are stronger than the beneficial effects of AM fungi from these cropping systems.     

Identity of plant,lichen and moss species connects with microbial abundance and soil functioning in maritime Antarctica

Background and aims

Plant breeding activities shape the rhizosphere microbiome but less is known about the relationship of both with the seed microbiome. We analyzed the composition of bacterial communities of seeds and rhizospheres of Styrian oil pumpkin genotypes in comparison to bulk soil to elucidate specific microbial signatures to support a concept involving plant-microbe interactions in breeding strategies.

Methods

The seed and rhizosphere microbiomes of 14 genotypes of oilseed pumpkin and relatives were analyzed using a 16S rRNA gene amplicon sequencing approach, which was assessed by bioinformatics and statistical methods.

Results

All analyzed microhabitats were characterized by diverse bacterial communities, but the relative proportions of phyla and the overall diversity was different. Seed microbiomes were characterized by the lowest diversity and dominant members of Enterobacteriaceae including potential pathogens (Erwinia, Pectobacterium). Potential plant-beneficial bacteria like Lysobacter, Paenibacillus and Lactococcus contributed to the microbial communities in significant abundances. Interestingly, strong genotype-specific microbiomes were detected for seeds but not for the rhizospheres.

Conclusions

Our study indicates a strong impact of the Cucurbita pepo genotype on the composition of the seed microbiome. This should be considered in breeding of new cultivars that are more capable of exploiting beneficial indigenous microbial communities.

     

Effects of experimental warming and nitrogen fertilization on soil microbial communities and processes of two subalpine coniferous species in Eastern Tibetan Plateau,China

Aim

This study aimed at predicting how sub-alpine coniferous ecosystems respond to global changes in the Eastern Tibetan Plateau by understanding soil microbial communities and activities, as well as variation in the quality and quantity of soil organic matter.

Methods

An experiment was conducted to examine soil microbial communities and their related soil processes in rhizospheric soil of two coniferous species that were exposed to two levels of temperature (unwarmed and infrared heater warming) and two levels of nitrogen (unfertilized and 25 g N m^?2 a^?1) from April 2007.

Results

Four-year night warming alone slightly affected the phospholipid fatty acid contents of the microbial community. However, the combination of nitrogen addition and soil warming significantly affected soil microbial composition while reducing the biomass of major microbial groups and the activities of most enzymes, especially in Abies faxoniana plots. The combination of warming and nitrogen addition increased soil labile C and N pools in Picea asperata plots and was beneficial for soil recalcitrant C, as well as for labile and total C and N pools in A. faxoniana plots.

Conclusion

Results indicated that future warming will slightly affect soil microbial communities and their related soil processes. However, warming combined with high nitrogen deposition will significantly constrain soil microbial biomass and enzyme activities, consequently increasing soil C and N pools in sub-alpine coniferous forests of this region.     

Potential soil P mobilisation capacity–method development and comparison of rhizosphere soil from different crops

Background

Phosphorus (P) deficiency is wide-spread in agricultural soils. In light of increasing P fertilizer costs, it is of interest to assess the capacity of soil microbes to mobilise native soil P and added P. There is currently no method to assess P mobilisation in situ.

Methods

The soil P mobilisation potential was assessed by incubating low P soil for up to 30?days with poorly available P sources; C and N were added to increase microbial activity and ensure that only P was limiting microbial growth.

Results

The increase in microbial P from day 0 to day 15 showed that microbes were able to mobilise P from FePO₄ and phytate. The P mobilisation potential (sum of microbial and resin P) of the rhizosphere soil decreased in the following order: faba bean > chickpea and white lupin > wheat. After 10?days, up to 80% of the mobilised P was microbial P, whereas after 30?days, almost all P mobilised was resin P.

Conclusions

The method developed in this study is useful assessing not only potential of a soil to mobilise P but also, by using different poorly available P sources, the mechanisms of P mobilisation.     

Influence of organic residues and soil incorporation on temporal measures of microbial biomass and plant available nitrogen

Aims

Despite our current understanding of plant nitrogen (N) uptake and soil N dynamics in arable systems, the supply and demand of N are infrequently matched as a result of variable seasonal and soil conditions. Consequently, inefficiencies in N utilisation often lead to constrained production and can contribute to potential environmental impacts. The aim of this study was to examine the influence of plant residue quality (C/N ratio) and extent of residue incorporation into soil on temporal changes in soil mineral N and the associated plant N uptake by wheat in the semi-arid agricultural production zone of Western Australia.

Methods

Oat (Avena sativa); lupin (Lupinus angustifolius) and field pea (Pisum sativum) were incorporated into a Red-Brown Earth using varying degrees of mechanical disturbance (0 to 100% residue incorporated). Soil samples for inorganic N (NO ₃ ^? and NH ₄ ⁺ ) profiles (0?C50?cm), microbial biomass-C (0?C50?cm) and plant N uptake were taken throughout the growing season of the subsequent wheat (Triticum aestivum) crop. Grain yield and yield components were determined at harvest.

Results

Despite observed treatment effects for plant residue type and soil disturbance, fluctuations in inorganic N were more readily influenced by seasonal variability associated with wet-dry cycles. Treatment effects resulting from residue management and extent of soil disturbance were also more readily distinguished in the NO ₃ ^? pool. The release of N from crop residues significantly increased (p?=?0.05) with greater soil-residue contact which related to the method of incorporation; the greater the extent of soil disturbance, the greater the net supply of inorganic N. Differences in microbial biomass-C were primarily associated with the type of plant residue incorporated, with higher microbial biomass generally associated with legume crops. No effect of residue incorporation method was noted for microbial biomass suggesting little effect of soil disturbance on the microbial population in this soil.

Conclusions

Despite differences in the magnitude of N release, neither crop type nor incorporation method significantly altered the timing or pattern of N release. As such asynchrony of N supply was not improved through residue or soil management, or through increased microbial biomass in this semi-arid environment. N fluxes were primarily controlled by abiotic factors (e.g. climate), which in this study dominated over imposed agricultural management practices associated with residue management.     

Biogeochemical transformations of amino acids in soil assessed by position-specific labelling

Background and aims

Amino acid turnover in soil is an important element of terrestrial carbon and nitrogen cycles. This study accounts for their driver - the microbial metabolism - by tracing them via the unique isotopic approach of position-specific labeling.

Methods

Three ¹⁴C isotopomers of alanine at five concentration levels combined with selective sterilization were used to distinguish sorption mechanisms, exoenzymatic and microbial utilization of amino acids in soil.

Results

Sorption and microbial uptake occurred immediately. Unspecific microbial uptake followed a linear kinetic, whereas energy-dependent uptake followed Michaelis-Menten. Less than 6 % of the initially added alanine was sorbed to soil, but after microbial transformation products were bound to the soil matrix at higher proportions (5–25 %). The carboxyl group (C-1) was rapidly oxidized by microorganisms, whereas C-2 and C-3 positions were preferentially incorporated into microbial biomass. Dependency of C metabolization on amino acid concentration reflected individual alanine transformation pathways for starvation, maintenance and growth conditions.

Conclusions

This study demonstrates that position-specific labeling determines the mechanisms and rates of C cycling from individual functional groups. This approach reflected underlying metabolic pathways and revealed the formation of new organic matter. We therefore conclude that position-specific labeling is a unique tool for detailed insights into submolecular transformation pathways and their regulation factors.     

Influence of integrated weed management system on N-cycling microbial communities and N2O emissions

Aims

Integrated weed management, which allows reducing the reliance of cropping systems on herbicides, is based on the use of specific combinations of innovative agricultural practices. However the impact of the introduction of these practices in cropping systems may influence soil functioning such as biogeochemical cycling. Here, we investigated N₂O emissions and the abundances of N-cycling microorganisms in 11-year old cropping systems (i.e. conventional reference and integrated weed management) in order to estimate the environmental side-effects of long-term integrated weed management.

Methods

N₂O emissions were continuously measured using automated chambers coupled with infrared analysers. Abundances of ammonia oxidizers and denitrifiers together with total bacteria and archaea were determined monthly from 0 to 10 and 10–30 cm soil layer samples by quantitative Polymerase Chain Reaction (qPCR). The relationship between N₂O emissions and microbial abundances during the study were investigated as were their relationships with soil physicochemical parameters and climatic conditions.

Results

Over 7 months, the system with integrated weed management emitted significantly more N₂O with cumulated measured emissions of 240 and 544 g N-N₂O ha^?1 for conventional and integrated systems, respectively. Abundances of microbial guilds varied slightly between systems, although ammonia-oxidizing bacteria were more abundant in the reference system (1.7 10⁶ gene copies g^?1 dry weight soil) compared to the integrated system (1.0 10⁶ gene copies g^?1 dry weight soil). These differences revealed both the long-term modification of soil biogeochemical background and the functioning of microbial processes due to 11 years of alternative field management, and the short-term impacts of the agricultural practices introduced as part of weed management during the cropping year.

Conclusions

The abundances of the different microbial communities involved in N cycling and the intensity of N₂O emissions were not related, punctual high N₂O emissions being more dependent on favourable soil conditions for nitrifying and denitrifying activities. Future studies will be performed to check these findings for other pedoclimatic conditions and to examine the impact of such cropping systems.     

Soil substrate utilization pattern and relation of functional evenness of plant groups and soil microbial community in five low mountain NATURA 2000

Background and aims

Species rich, semi-natural grassland systems provide several ecosystem functions. The goal was to assess how aboveground composition and evenness affects soil substrate utilization pattern and soil microbial functional evenness.

Methods

At five German NATURA 2000 grassland sites, the interactions of plant functional groups (graminoids, forbs and legumes) and belowground microbial functional evenness were investigated in relation to soil properties and sampling date. Functional evenness of soil microorganisms was measured with high spatial resolution by community level physiological profiling (CLPP) using multi-SIR (substrate-induced respiration) at three sampling dates during the vegetation period. Evenness indices were used to compare plant functional group diversity and soil microbial functional diversity.

Results

All sites differed in the consistently high soil microbial functional evenness, which was strongly predicted by soil pH, but not by plant functional groups or aboveground plant dry matter production. However, soil microbial functional evenness was particularly decreased by an increasing legume proportion and showed seasonal changes, probably driven by shifts in resource availability and soil water content.

Conclusions

Our results suggest that changes in soil chemical properties or in a single key plant functional group may have stronger effects on soil microbial functional evenness than changes in plant functional group evenness.     

Comparison of different methods for determining lignin concentration and quality in herbaceous and woody plant residues

Background

The development and dispersal of seeds as well as their transition to seedlings represent perhaps the most critical stages of a plant’s life cycle. The endophytic and epiphytic microbial interactions that take place in, on, and around seeds during these stages of the plant’s life cycle may have profound impacts on plant ecology, health, and productivity. While our understanding of the seed microbiota has lagged far behind that of the rhizosphere and phyllosphere, many advances are now being made.

Scope

This review explores the microbial associations with seeds through various stages of the plant life cycle, beginning with the earliest stages of seed development on the parent plant and continuing through the development and establishment of seedlings in soil. This review represents a broad synthesis of the ecological and agricultural literature focused on seed-microbe interactions as a means of better understanding how these interactions may ultimately influence plant ecology, health, and productivity in both natural and agricultural systems. Our current understanding of seed-microbe associations will be discussed, with an emphasis on recent findings that specifically highlight the emerging contemporary understanding of how seed-microbe associations may ultimately impact plant health and productivity.

Conclusions

The diversity and dynamics of seed microbiomes represent the culmination of complex interactions with microbes throughout the plant life cycle. The richness and dynamics of seed microbiomes is revealing exciting new opportunities for research into plant-microbe interactions. Often neglected in plant microbiome studies, the renaissance of inquiry into seed microbiomes is offering exciting new insights into how the diversity and dynamics of the seed microbiome with plant and soil microbiomes as well as the microbiomes of dispersers and pollinators. It is clear that the interactions taking place in and around seeds indeed have significant impacts on plant health and productivity in both agricultural and natural ecosystems.

     

Impact of the plant community composition on labile soil organic carbon, soil microbial activity and community structure in semi-natural grassland ecosystems of different productivity

Aims

The main objective was to describe the effects of plant litter on SOC and on soil microbial activity and structure in extensively managed grasslands in Central Germany that vary in biomass production and plant community composition.

Methods

The decomposition of shoot and root litter was studied in an incubation experiment. Labile C and N were isolated by hot water extraction (C_HWE, N_HWE), while functional groups of microbes were identified by PLFA analysis and microbial activity was measured using a set of soil exo-enzymes.

Results

The plant community composition, particulary legume species affected SOC dynamics and below-ground microbial processes, especially via roots. This was reflected in about 20% lower decomposition of root litter in low productivity grassland soil. The C_HWE soil pool was found to be a key driver of the below-ground food web, controlling soil microbial processes.

Conclusions

Below-ground responses appear to be related to the presence of legume species, which affected the microbial communities, as well as the ratio between fungal and bacterial biomass and patterns of soil enzyme activity. Low productivity fungal-dominated grasslands with slow C turnover rates may play an important role in SOC accumulation. The approach used here is of particular importance, since associated biological and biochemical processes are fundamental to ecosystem functioning.     

Dynamics of plant nutrient uptake as affected by biopore-associated root growth in arable subsoil

Background and aims

Soil microbial communities influence nutrient cycling, chemistry and structure of soil, and plant productivity. In turn, agronomic practices such as fertilization and crop rotation alter soil physical and chemical properties and consequently soil microbiomes. Understanding the long-term effects of agronomic practices on soil microbiomes is essential for improving agronomic practices to optimize these microbial communities for agricultural sustainability. We examine the composition and substrate-utilization profiles of microbial communities at the Morrow Plots in Illinois.

Methods

Microbial community composition is assessed with 16S rRNA gene sequencing and subsequent bioinformatic analyses. Community- level substrate utilization is characterized with the BIOLOG EcoPlate.

Results

Fertilizer and rotation treatments significantly affected microbial community structure, while substrate utilization was affected by fertilizer, but not crop-rotation treatments. Differences in relative abundance and occurrence of bacterial taxa found in fertilizer treatments can explain the observed differences in community level substrate utilization.

Conclusion

Long-term fertilization and crop-rotation treatments affect soil microbial community composition and physiology, specifically through chronic nutrient limitation, long-term influx of microbes and organic matter via manure application, as well as through changes in soil chemistry. Relatively greater abundance of Koribacteraceae and Solibacterales taxa in soils might prove useful as indicators of soil degradation.

     

Effects of forest wildfire on soil microbial-community activity and chemical components on a temporal-seasonal scale

Background

Soil response and rehabilitation after wildfires are affected by natural environmental factors such as seasonality, and other time-dependent changes, such as vegetation recovery (e.g., % soil cover). These changes affect soil microbial-community activity. During summer 2006, almost 1,200 hectares (ha) of coniferous forest in northern Israel, including Byria Forest, burned.

Methods

Soil samples were collected seasonally from severely burned and unburned areas, on a time scale of 7?days to 4?years after wildfire. Chemical and microbial parameters of the forest soil system were examined.

Results

Results obtained show that increase in total soluble nitrogen (TSN) in burned areas may limit microbial activity during the first year after wildfire. Two years after wildfire, soil TSN levels in burned areas decreased to unburned levels after plant growth, allowing the microbial community to proliferate.

Conclusions

Wildfire had a significant impact on TSN, soil moisture (SM), and microbial nitrogen (MBN) compared to seasonality. These parameters are recommended for monitoring post-fire soil state. The direct effect of wildfire on soil constituents at the study site was stronger during the first 2–4?years. Indirect changes due to vegetation cover could have a longer effect on burned soil systems and should be further examined.     

Interaction between contrasting rice genotypes and soil physical conditions induced by hydraulic stresses typical of alternate wetting and drying irrigation of soil

Background and aims

Drought events, agricultural practices and plant communities influence microbial and soil abiotic parameters which can feedback to fodder production. This study aimed to determine which soil legacies influence plant biomass production and nutritional quality, and its resistance and recovery to extreme weather events.

Methods

In a greenhouse experiment, soil legacy effects on Lolium perenne were examined, first under optimal conditions, and subsequently during and after drought. We used subalpine grassland soils previously cultivated for two years with grass communities of distinct functional composition, and subjected to combinations of climatic stress and simulated management.

Results

The soil legacy of climatic stress increased biomass production of Lolium perenne and its resistance and recovery to a new drought. This beneficial effect resulted from higher nutrient availability in soils previously exposed to climatic stresses due to lower competitive abilities and resistance of microbial communities to a new drought. This negative effect on microbial communities was strongest in soils from previously cut and fertilized grasslands or dominated by conservative grasses.

Conclusion

In subalpine grasslands more frequent climatic stresses could benefit fodder production in the short term, but threaten ecosystem functioning and the maintenance of traditional agricultural practices in the long term.

     

Topsoil organic matter properties in contrasted hedgerow vegetation types

Background and aims

Hedges, semi-natural landscape components, have the ability to integrate both agronomic and environmental functions and to provide several ecosystem services. The aim of this study was to test whether hedgerow vegetation is a determinant of soil organic matter properties in ancient agricultural lands.

Methods

We complemented cluster analysis and ordination to determine the extent to which two types of hedges that were distinct in character-plant species also differed between each other in concentration and composition of two major constituents of soil organic matter, namely humic substances and dissolved organic matter.

Results

The two types of hedges were associated with significant differences in humic carbon content, hormone-like activity and molecular size of humic substances, which, in general, were more similar to those typical of forest than of agricultural soils. Moreover, we detected between-group differences in several phenolic acids.

Conclusions

Variation of the topsoil biochemical properties of hedges may be explained by variation in their vegetation characteristics, similar to other ecosystems. Spontaneous vegetation in hedges perform an important role in controlling the variability of surface soil properties that influence the evolution of soil organic matter and nutrient availability in agricultural lands.     

Application of LCSA to used cooking oil waste management

Purpose

Used cooking oil (UCO) is a domestic waste generated as the result of cooking and frying food with vegetable oil. The purpose of this study is to compare the sustainability of three domestic UCO collection systems: through schools (SCH), door-to-door (DTD), and through urban collection centres (UCC), to determine which systems should be promoted for the collection of UCO in cities in Mediterranean countries.

Methods

The present paper uses the recent life cycle sustainability assessment (LCSA) methodology. LCSA is the combination of life cycle assessment (LCA), life cycle costing, and social life cycle assessment (S-LCA).

Results and discussion

Of the three UCO collection systems compared, the results show that UCC presents the best values for sustainability assessment, followed by DTD and finally SCH system, although there are no substantial differences between DTD and SCH. UCC has the best environmental and economic performance but not for social component. DTD and SCH present suitable values for social performance but not for the environmental and economic components.

Conclusions

The environmental component improves when the collection points are near to citizens’ homes. Depending on the vehicle used in the collection process, the management costs and efficiency can improve. UCO collection systems that carry out different kind of waste (such as UCC) are more sustainable than those that collect only one type of waste. Regarding the methodology used in this paper, the sustainability assessment proposed is suitable for use in decision making to analyse processes, products or services, even so in social assessment an approach is needed to quantify the indicators. Defining units for sustainability quantification is a difficult task because not all social indicators are quantifiable and comparable; some need to be adapted, raising the subjectivity of the analysis. Research into S-LCA and LCSA is recent; more research is needed in order to improve the methodology.     

Addition of a volcanic rockdust to soils has no observable effects on plant yield and nutrient status or on soil microbial activity

Background and Aims

Rising costs and pressure on supplies of commercial mineral fertilizers and increasing markets for organically produced foods and feeds have led to a growing interest in soil amendments to supply plant nutrients. Rockdust is a by-product of quarrying and its effectiveness to supply plants with nutrients has been a contested issue and there have been no assessments of its effect on soil biota other than plants. The aim of this study was to assess the effect of a commercially-available volcanic rockdust application on crop growth and element concentrations for a wide range of macro and microelements and the response of soil microbial communities to rockdust due to the potential alteration in soil mineralogy.

Methods

A three-year controlled outdoor-growing experiment was conducted on three different soil types with two wheat cultivars in the first year following rockdust application and with forage species in the third year.

Results

Our results show that the tested rockdust had no positive or negative effect on plant growth or nutrient composition. In addition, the microbial response to added substrates, a sensitive measure of changes in soil environment, were unaltered by the rockdust.

Conclusions

As the rockdust had no nutrient or toxic effect it can probably be considered as an inert material which at least causes no harm but equally has no demonstrable ecological or agricultural benefit.     

Assessment of carbon sustainability under different tillage systems in a double rice cropping system in Southern China

Purpose

Adoption of the carbon (C)-friendly and cleaner technology is an effective solution to offset some of the anthropogenic emissions. Conservation tillage is widely considered as an important sustainable technology and for the development of conservation agriculture (CA). Thus, the objective of this study was to assess the C sustainability of different tillage systems in a double rice (Oryza sativa L.) cropping system in southern China.

Methods

The experiment was established with no-till (NT), rotary tillage (RT), and conventional tillage (CT) treatments since 2005. Emission of greenhouse gasses (GHG), C footprint (CF), and ecosystem service through C sequestration in different tillage systems were compared.

Result and discussion

Emission of GHG from agricultural inputs (Mg CO₂-eq ha^?1 year^?1) ranged from 1.81 to 1.97 for the early rice, 1.82 to 1.98 for the late rice, and 3.63 to 3.95 for the whole growing season, respectively. The CF (kg CO₂-eq kg^?1 of rice year^?1) in the whole growing seasons were 1.27, 1.85, and 1.40 [excluding soil organic carbon (SOC) storage] and 0.54, 1.20, and 0.72 (including SOC storage) for NT, RT, and CT, respectively. The value of ecosystem services on C sequestration for the whole growing seasons ranged from ¥3,353 to 4,948 ha^?1 year^?1 and followed the order of NT > CT > RT. The C sustainability under NT was better than that under RT for the late, but reversed for the early rice. However, NT system had better C sustainability for the whole cropping system compared with CT.

Conclusions

Therefore, NT is a preferred technology to reduce GHG emissions, increase ecosystem service functions of C sequestration, and improve C sustainability in a double rice cropping region of Southern China.     

Long-term effects of organic amendments on the recovery of plant and soil microbial communities following disturbance in the Canadian boreal forest

Background and Aims

Ecosystem recovery following disturbance requires the reestablishment of key soil biogeochemical processes. This long-term 7 year study describes effects of organic material, moisture, and vegetation on soil microbial community development in the Athabasca Oil Sands Region of Western Canada.

Methods

Phospholipid fatty acid analysis was used to characterize and compare soil microbial community composition and development on reclaimed and natural forest sites. Additionally, we conducted a laboratory moisture manipulation experiment.

Results

The use of forest floor material as an organic amendment resulted in a greater percent cover of upland vegetation and placed the soil microbial community on a faster trajectory towards ecosystem recovery than did the use of a peat amendment. The soil microbial composition within the reclaimed sites exhibited a greater response to changes in moisture than did the soil microbial communities from natural sites.

Conclusion

Our research shows that the use of native organic amendment (forest floor) on reclaimed sites, and the associated establishment of native vegetation promote the development of soil microbial communities more similar to those found on natural forest sites. Additionally, soil microbial communities from natural sites may be more resistant to changes in soil moisture than those found on reclaimed sites.     

Temporal variation in microbial and plant biomass during summer in a Mediterranean high-mountain dry grassland

Aims

We assessed the temporal changes on microbial biomass in relation to changes in soil moisture, dissolved organic carbon and plant biomass during the summer season in a Mediterranean high-mountain grassland.

Methods

Temporal variations were tested by two-way ANOVA. The relationships among microbial biomass, plant biomass, soil water content, soil organic carbon, dissolved organic carbon and total soil nitrogen during the summer season were assessed by means of structural equation modeling.

Results

Microbial biomass did not show variation, while dissolved organic carbon and root biomass decreased throughout the summer. Aboveground plant biomass peaked in the middle of the summer, when soil water content was at its minimum. Soil water content directly and negatively affected soil microbial biomass, and positively affected dissolved organic carbon. Moreover soil microbial biomass and dissolved organic carbon were negatively related. Plant biomass effects on soil microbial biomass were driven by root biomass, which indirectly affected soil microbial biomass through effects on soil organic carbon and soil nitrogen.

Conclusions

The temporal dynamic of microbial biomass during the summer season appeared to differ from previous observations in temperate alpine communities, and indicated the drought resistance of the microbial community during the summer in Mediterranean high-mountain grasslands. During the dry period, microbial biomass may play an alternative role in soil carbon conservation.