Plant-soil feedbacks between invasive shrubs and native forest understory species lead to shifts in the abundance of mycorrhizal fungi

Aims

Non-native shrubs are important invaders of the Eastern Deciduous Forest, dramatically altering forest structure and functioning. Study of invasion mechanisms in this system has emphasized aboveground processes, and plant-soil feedbacks are relatively unexplored as a mechanism of shrub dominance. We tested whether plant-soil feedback in this habitat is affected by competition and whether arbuscular mycorrhizal fungi (AMF) are involved in plant-soil feedback.

Methods

We used a standard two-phase plant-soil feedback experiment run concurrently for each of three invasive shrub species, measuring feedback effects on AMF colonization, aboveground biomass, and the responses of native plant species in greenhouse mesocosms.

Results

Lonicera maackii and Ligustrum vulgare reduced AMF colonization of native roots, both with legacy effects (prior growth in soil) and direct effects (current growth in soil). Elaeagnus umbellata grown with natives left a legacy of increased AMF colonization of native communities.

Conclusions

Our results suggest that woody invasive species can alter the AMF associations of native plants even after the invasive is no longer present. Such consequences merit study with other native species and where environmental factors, such as light availability, might be expected to compound the effects of changes in AMF.     

Mechanisms linking plant community properties to soil aggregate stability in an experimental grassland plant diversity gradient

Background and aims

Soil aggregate stability depends on plant community properties, such as functional group composition, diversity and biomass production. However, little is known about the relative importance of these drivers and the role of soil organisms in mediating plant community effects.

Methods

We studied soil aggregate stability in an experimental grassland plant diversity gradient and considered several explanatory variables to mechanistically explain effects of plant diversity and plant functional group composition. Three soil aggregate stability measures (slaking, mechanical breakdown and microcracking) were considered in path analyses.

Results

Soil aggregate stability increased significantly from monocultures to plant species mixtures and in the presence of grasses, while it decreased in the presence of legumes, though effects differed somewhat between soil aggregate stability measures. Using path analysis plant community effects could be explained by variations in root biomass, soil microbial biomass, soil organic carbon concentrations (all positive relationships), and earthworm biomass (negative relationship with mechanical breakdown).

Conclusions

The present study identified important drivers of plant community effects on soil aggregate stability. The effects of root biomass, soil microbial biomass, and soil organic carbon concentrations were largely consistent across plant diversity levels suggesting that the mechanisms identified are of general relevance.     

Heterogeneity in arbuscular mycorrhizal fungal communities may contribute to inconsistent plant-soil feedback in a Neotropical forest

Background and aims

Plant-soil feedback may vary across host species and environmental gradients. The relative importance of these biotic versus abiotic drivers of feedback will determine the stability of plant and microbial communities across environments. If plant hosts are the main driver of soil microbial communities, plant-soil feedback may be stable across changing environments. However, if microbial communities vary with environmental gradients, feedback may also vary, limiting its capacity to predict plant distributions.

Methods

We characterized arbuscular mycorrhizal (AM) fungi across tree plantations and a primary Neotropical rainforest. We then performed a plant-soil feedback pot experiment of AM fungi from these plantations on three plant species and related feedback and AM fungal communities in the field.

Results

In the field, temporal and spatial variation in AM fungal composition was similar in magnitude to variation across plant host species. Composition of AM fungi in the pot experiment significantly differed from the field plots. Furthermore, differential feedback was explained by shifts in AM fungal composition only for one plant host species (Hyeronima alchorneoides) in the pot experiment.

Conclusions

Natural AM fungal communities were temporally and spatially heterogeneous and AM fungal communities in the greenhouse did not reflect natural soils. These factors led to heterogeneous and unpredictable feedback responses, which suggests that applying greenhouse derived plant-soil feedback trends to predict plant coexistence in natural systems may be misleading.

     

Three symbionts involved in interspecific plant-soil feedback: epichloid endophytes and mycorrhizal fungi affect the performance of rhizobia-legume symbiosis

Aims

Plants interact by modifying soil conditions in plant-soil feedback processes. Foliar endophytes of grasses exert multiple effects on host rhizosphere with potential consequences on plant-soil feedback. Here, we hypothesize that the grass-endophyte symbiosis impairs soil symbiotic potential, and in turn influences legume performance and nitrogen acquisition.

Methods

Soil was conditioned in pots, growing Lolium multiflorum with or without the fungal endophyte Epichloë and with or without arbuscular mycorrhizal fungi (AMF). Then, Trifolium repens grew in all types of conditioned soils with high or low rhizobia availability.

Results

Endophyte soil conditioning reduced AMF spores number and rhizobial nodules (?27 % and ?38 %, respectively). Seedling survival was lower in endophyte-conditioned soil and higher in mycorrhizal soils (?27 % and +24 %, respectively). High rhizobia-availability allowed greater growth and nitrogen acquisition, independent of soil conditioning. Low rhizobia-availability allowed both effects only in endophyte-conditioned soil.

Conclusion

Endophyte-induced changes in soil (i) hindered symbiotic potential by reducing AMF spore availability or rhizobia nodulation, (ii) impaired legume survival irrespective of belowground symbionts presence, but (iii) mimicked rhizobia effects, enhancing growth and nitrogen fixation in poorly nodulated plants. Our results show that shoot and root symbionts can be interactively involved in interspecific plant-soil feedback.

     

Giant Ragweed Invasion is Not Well Controlled by Biotic Resistance

The effect of native plant restoration on invasion by giant ragweed (Ambrosia trifida), an invasive species, is currently unknown. We hypothesized that (1) functional group identity would be a good predictor of biotic resistance to A. trifida, and (2) mixtures of species would be more resistant to invasion than monocultures. Using seven functional traits, 37 native and non-native plants were divided into three functional groups that differed primarily in longevity and woodiness. We conducted a competition experiment using an additive competition design with A. trifida and monocultures or mixtures of 14 species. Biotic resistance was evaluated by calculating a relative competition index (RCI_avg) based on the average performance of A. trifida in treatments compared with that in control. In monocultures, RCI_avg of resident plants did not significantly differ among the three functional groups or within each functional group. The highest RCI_avg (40%) was observed for some fast-growing annuals (FG1) such as Zea mays and Secale cereal, which were strong competitors. RCI_avg of resident plants was not significantly greater in mixtures than in monocultures. Taken together, the results show that plant diversity did not control invasion by A. trifida and that giant ragweed invasion cannot be well controlled by biotic resistance.     

Litter species traits, but not richness, contribute to carbon and nitrogen dynamics in an alpine meadow on the Tibetan Plateau

Aims

Litter, as afterlife of plants, plays an important role in driving belowground decomposition processes. Here we tested effects of litter species identity and diversity on carbon (C) and nitrogen (N) dynamics during litter decomposition in N-limited alpine meadow soil from the Qinghai–Tibet Plateau.

Methods

We incubated litters of four meadow species, a sedge (“S”, Kobresia humilis), a grass (“G”, Elymus nutans), a herb (“H”, Saussurea superba), and a legume (“L”, Oxytropis falcata), in monoculture and in mixture with meadow soil. CO₂ release was measured 21 times during the incubation, and soil available N and microbial biomass C and N were measured before and after the experiment.

Results

The organic C decay rate did not differ much among soils amended with monocultures or mixtures of litter, except in the H, S, L, and S+H treatments, which had much higher decay rates. Potential decomposable C pools were lowest in the control, highest in the L treatment, and intermediate in the S treatment. Mineralized N was completely immobilized by soil microbes in all treatments except the control, S+L, and S+G+L treatments. Litter mixtures had both additive and non-additive effects on CO₂-C emission (mainly antagonistic effects), net N mineralization (mainly synergistic), and microbial biomass C and N (both). Overall, these parameters were not significantly correlated with litter species richness. Similarly, microbial C or N was not significantly correlated with litter N content or C/N. However, cumulative CO₂-C emission and net N mineralization were positively correlated with litter N content and negatively correlated with litter C/N.

Conclusions

Litter N content and C/N rather than litter species richness drove the release of CO₂-C and net available N in this ecosystem. The antagonistic effects of litter mixtures contributed to a modest release of CO₂-C, but their synergistic effects enhanced net available N. We suggest that in alpine meadow communities, balancing species with high and low N contents will benefit soil carbon sequestration and plant competition for available N with soil microbes.     

Effects of condensed tannins in conifer leaves on the composition and activity of the soil microbial community in a tropical montane forest

Background and aims

Condensed tannins, a dominant class of plant secondary metabolites, play potentially important roles in plant-soil feedbacks by influencing the soil microbial community. Effects of condensed tannins on the soil microbial community and activity were examined by a short-term tannin-addition experiment under field and laboratory conditions.

Methods

Condensed tannins were extracted from the leaves of a dominant conifer (Dacrydium gracilis) in a tropical montane forest on Mt. Kinabalu, Borneo. The extracted tannins were added to soils beneath the conifer and a dominant broadleaf (Lithocarpus clementianus) to evaluate the dependence of the response to tannin addition on the initial composition of the soil microbial community.

Results

Enzyme activities in the field tannin-addition treatment were lower than in the deionized-water treatment. Carbon and nitrogen mineralization were also inhibited by tannin-addition. The fungi-to-bacteria ratio after tannin-addition was higher compared with the distilled-water treatment in the laboratory experiment.

Conclusions

Based on our results, we suggest that the higher concentration of condensed tannins in the leaf tissues of Dacrydium than in those of Lithocarpus is a factor influencing the microbial community and activity. This may have influences on subsequent plant performance, which induces plant-soil feedback processes that can control dynamics of the tropical montane forest ecosystem.     

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.

     

Soil retention of 15N in a simulated N deposition study: effects of live plant and soil organic matter content

Background and aims

The impacts of atmospheric nitrogen (N) deposition on terrestrial ecosystem processes remain controversial, mostly because of the uncertainty regarding the fates of deposited N. We conducted a 16-week simulated deposition study to experimentally trace N in a greenhouse plant-soil system.

Methods

Using a two-way factorial design, we added (¹⁵NH₄)₂SO₄ solution twice a week to pots containing different soil organic matter (SOM) content and with or without a live plant (Salix dasyclados). The recoveries of ¹⁵N in soil, plant biomass, and leaching solution were quantified.

Results

We found most ¹⁵N was retained in soil (18.0–59.2%), with significantly more ¹⁵N recovered from high-SOM soils than from low-SOM soils. Plant presence significantly increased ¹⁵N retention in soil. Plant biomass accounted for 10–20% of the ¹⁵N input, with proportionally more ¹⁵N assimilated when plants were grown in low-SOM soils. Leaching loss of ¹⁵N was relatively low (10–17%).

Conclusion

Our study suggests that SOM content and plant presence significantly affect the fates of deposited N. Indeed, N would be preferentially retained in soils with high SOM content and live plant, while plants would assimilate more deposited N when grown in low SOM soils. Global biogeochemical models thus need to incorporate such soil-specific N retention and plant N assimilation.     

Competition overwhelms the positive plant–soil feedback generated by an invasive plant

Invasive plant species can modify soils in a way that benefits their fitness more than the fitness of native species. However, it is unclear how competition among plant species alters the strength and direction of plant–soil feedbacks. We tested how community context altered plant–soil feedback between the non-native invasive forb Lespedeza cuneata and nine co-occurring native prairie species. In a series of greenhouse experiments, we grew plants individually and in communities with soils that differed in soil origin (invaded or uninvaded by L. cuneata) and in soils that were live vs. sterilized. In the absence of competition, L. cuneata produced over 60% more biomass in invaded than uninvaded soils, while native species performance was unaffected. The absence of a soil origin effect in sterile soil suggests that the positive plant–soil feedback was caused by differences in the soil biota. However, in the presence of competition, the positive effect of soil origin on L. cuneata growth disappeared. These results suggest that L. cuneata may benefit from positive plant–soil feedback when establishing populations in disturbed landscapes with few interspecific competitors, but does not support the hypothesis that plant–soil feedbacks influence competitive outcomes between L. cuneata and native plant species. These results highlight the importance of considering whether competition influences the outcome of interactions between plants and soils.     

Bacterial endophytes and root hairs

Aims

This study aimed to measure the effect of plant diversity on N uptake in grasslands and to assess the mechanisms contributing to diversity effects.

Methods

Annual N uptake into above- and belowground organs and soil nitrate pools were measured in the Jena experiment on a floodplain soil with mixtures of 2–16 species and 1–4 functional groups, and monocultures. In mixtures, the deviation of measured data from data expected from monoculture performance was calculated to assess the contribution of complementarity/facilitation and selection.

Results

N uptake varied from <1 to 45 g?N m^?2 yr^?1, and was higher in grasslands with than without legumes. On average, N uptake was higher in mixtures (21?±?1 g?N m^?2 yr^?1) than monocultures (13?±?1 g?N m^?2 yr^?1), and increased with species richness in mixtures. However, compared to N uptake expected from biomass proportions of species in mixtures, N uptake of mixtures was only slightly higher and a significant surplus N uptake was confined to mixtures containing legumes and non-legumes.

Conclusions

In our study, high N uptake of species rich mixtures was mainly due to dominance of productive species and facilitation by legumes whereas complementarity among non-legumes was of minor relevance.     

The effects of leaf litter evenness on decomposition depend on which plant functional group is dominant

Background and aims

Climbing plants are increasing in dominance in the subtropical forests of South China and other areas around the world, altering patterns of plant dominance and evenness in community. We investigated how changes in species’ identity and patterns of leaf litter evenness affected decomposition of litter mixtures.

Methods

We used litter-bag method to study the influence of different relative abundance mixtures (75 % : 25 %; 50 % : 50 %; 25 % : 75 %) of plant litter from two functional groups (climbing plants and trees) on decomposition rates in a subtropical forest in Guangdong, China.

Results

We found negative non-additive effects of mixing litter overall and species composition affected decomposition rates the most. In addition, when climbing plants were dominant, even mixtures decomposed slower significantly than uneven mixtures. Evenness did not affect decomposition rates, however, when trees were dominant. The magnitude of antagonistic effects increased with increasing dominance of climbing plants but decreased with time, suggesting a strong negative feedback between litter proportion of climbing plant and decomposition rates at the initial stage.

Conclusion

The evenness in leaf litter composition affects rates of decomposition, but these effects depend on which plant functional group is dominant. Thus, we should pay more attention to shifts in identity of dominant species and patterns of community evenness.     

Allelopathic invasive tree (<Emphasis Type="Italic">Rhamnus cathartica</Emphasis>) alters native plant communities

Many plants release allelopathic chemicals that can inhibit germination, growth, and/or survival in neighboring plants. These impacts appear magnified with the invasion of some non-native plants which may produce allelochemicals against which native fauna have not co-evolved resistance. Our objective was to examine the potential allelopathic impact of an invasive non-native shrub/tree on multiple plant species using field observation and experimental allelopathy studies. We surveyed and collected an invasive, non-native tree/shrub (Rhamnus cathartica) at Tifft Nature Preserve (a 107-ha urban natural area near Lake Erie in Buffalo, NY). We also surveyed understory plant communities in the urban forest to examine correlations between R. cathartica abundance and local plant community abundance and richness. We then used experimental mesocosms to test if patterns observed in the field could be explained by adding increased dosages of R. cathartica to soils containing five plant species, including native and non-native woody and herbaceous species. In the highly invaded urban forest, we found that herbaceous cover, shrubs and woody seedlings negatively covaried with R. cathartica basal area and seedlings density. In the mesocosm experiments, R. cathartica resulted in significant decreases in plant community species richness, abundance, and shifted biomass allocation from roots. Our results provide evidence that R. cathartica is highly allelopathic in its invaded range, that R. cathartica roots have an allelopathic effect and that some plant species appear immune. We suggest that these effects may explain the plant’s ability to form dense monocultures and resist competitors, as well as shift community composition with species-specific impacts.     

Field application of a DNA-based assay to the measurement of roots of perennial grasses

Background and aims

DNA-based methods present new opportunities for overcoming the difficulties of accurately identifying and quantifying roots of different plant species in field soils. In order to quantify species-specific root biomass from measurements of DNA, consideration needs to be given to replication and ability to recover roots for calibration purposes in order to account for spatial, temporal and inter- and intra-species variation in DNA content of roots and distribution of roots within the soil profile.

Methods

This paper develops the field application of a DNA-based technique for direct quantification of roots in soils. The method was applied to a field experiment to investigate differences in root growth of acid-soil resistant and sensitive genotypes of perennial pasture grasses in an acid soil. DNA was extracted directly from soil and species-specific DNA was quantified using quantitative real-time PCR prior to estimation of root biomass.

Results

Root growth of the perennial grasses was quantified using the DNA-based technique, although separate calibration procedures were needed to convert DNA content to root mass for each species, soil layer and sampling date. Compared to acid-soil resistant genotypes, lesser root growth in acid soil layers and reduced above-ground dry matter production was observed for acid-soil sensitive genotypes.

Conclusions

The DNA-based method allowed genotypic differences in root growth to be assessed directly in soil and was advantageous for rapid processing of a large number of samples. However, high replication was still required to overcome spatial variability and separate calibrations were required for different species and soil depths across sampling times. The technique demonstrated greater root growth of acid-soil resistant perennial grasses which was beneficial for their establishment and persistence.     

The optimum Se application time for reducing Cd uptake by rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.) and its mechanism

Background and aims

Intraspecific aggregation of plant individuals can promote species coexistence by delaying competitive exclusions. However, such impacts may differ among species with contrasting spatial architecture and rely on the spatial distribution of resources.

Methods

We grew a phalanx clonal plant Carex neurocarpa (with aggregated ramets) and a guerilla one Bolboschoenus planiculmis (with diffused ramets) in monocultures or in 1:1 mixtures with an even or a clustered distribution pattern of the two species in homogeneous or heterogeneous soils.

Results

After 16 months, shoot biomass and ramet number were greater in mixtures than in monocultures in C. neurocarpa, but smaller in B. planiculmis. However, the growth of neither C. neurocarpa nor B. planiculmis differed between even and clustered mixtures. Soil nutrient heterogeneity did not significantly affect the growth of either species, but increased relative yield of B. planiculmis and decreased that of C. neurocarpa.

Conclusions

The relative importance of intra- vs. interspecific competition depends on the spatial architecture of plants, and soil nutrient heterogeneity slows down competitive exclusion by decreasing differences in competitive ability between plants. However, our results do not support the idea that intraspecific aggregation of individuals alters competitive interactions between species.

     

Competitive interaction between the exotic plant Rhus typhina L. and the native tree Quercus acutissima Carr. in Northern China under different soil N:P ratios

Background and aims

Anthropogenic nitrogen (N) and phosphorus (P) input has changed the relative importance of nutrient elements. This study aimed to examine the effects of different nutrient conditions on the interaction between exotic and native plants.

Methods

We conducted a greenhouse experiment with a native species Quercus acutissima Carr. and an exotic species Rhus typhina L. grown in monocultures or mixtures, under three N:P ratios (5, 15 and 45 corresponding to N-limited, basic N and P supply and P-limited conditions, respectively). After 12 weeks of treatment, traits related to biomass allocation, leaf physiology and nutrient absorption were determined.

Results

R. typhina was dominant under competition, with a high capacity for carbon assimilation and nutrient absorption, and the dominance was unaffected by increasing N:P ratios. R. typhina invested more photosynthate in leaves and more nutrients in the photosynthetic apparatus, enabling high biomass production. Q. acutissima invested more photosynthate in roots and more nutrients in leaf persistence at the expense of reduced carbon assimilation capacity.

Conclusions

Different trade-offs in biomass and nutrient allocation of the two species is an important reason for their distinct performances under competition and helps R. typhina to maintain dominance under different nutrient conditions.     

Signal effects of the lectin from the associative nitrogen-fixing bacterium Azospirillum brasilense Sp7 in bacterial–plant root interactions

Aims

We compared the degree of arbuscular mycorrhizal fungi (AMF) colonization on an invasive, Triadica sebifera, and two native, Baccharis halimifolia and Morella cerifera, woody species that occur in coastal Mississippi, USA. Specifically, we investigated how the degree of colonization affects growth of these species and assessed potential allelopathic effects of T. sebifera on the two native species.

Methods

A field study and a greenhouse experiment were used to determine the degree of AMF colonization on focal woody species. Seedling growth of these species was compared between active (fungicide untreated) and AMF-suppressed (fungicide treated) soils in the greenhouse experiment. In a second greenhouse experiment, we tested the potential allelopathic effects of T. sebifera on the native species by growing the natives in soils from T. sebifera invaded or uninvaded regions, with and without activated carbon (AC).

Results

The invasive species, Triadica sebifera, exhibited a higher degree of AMF colonization compared to the native species and significantly higher total biomass in active soils compared to AMF-suppressed soils. Seedling biomass and AMF colonization of native B. halimifolia and M. cerifera did not differ between T. sebifera invaded and uninvaded soils, irrespective of the application of AC.

Conclusions

Results suggest that invasive T. sebifera benefits from the presence of AMF, which might facilitate establishment of this invader. Results also suggest that allelopathy is not a likely mechanism of T. sebifera invasion in coastal transition ecosystems. A higher degree of AMF colonization, relative to native co-occurring species, may partly explain the successful invasion of T. sebifera into coastal plant communities of the southeastern USA.     

Community-aggregated plant traits interact with soil nutrient heterogeneity to determine ecosystem functioning

Background and aims

Spatial distribution of soil nutrients (soil heterogeneity) and availability have strong effects on above- and belowground plant functional traits. Although there is ample evidence on the tight links between functional traits and ecosystem functioning, the role played by soil heterogeneity and availability as modulators of such relationship is poorly known.

Methods

We conducted a factorial experiment in microcosms containing grasses, legumes and non-legume forbs communities differing in composition to evaluate how soil heterogeneity and availability (50 and 100 mg N) affect the links between traits and ecosystem functioning. Community-aggregated specific leaf area (SLA_agg) and specific root length (SRL_agg) were measured as both relevant response traits to soil heterogeneity and availability, and significant effect traits affecting ecosystem functioning (i.e., belowground biomass, β-glucosidase and acid phosphatase activities, and in situ N availability rate).

Results

SRL_agg was negatively and significantly associated to β-glucosidase, phosphatase and N availability rate in the high nutrient availability and heterogeneous distribution scenario. We found a significant negative relationship between SLA_agg and availability rate of mineral-N under low nutrient availability conditions.

Conclusions

Soil heterogeneity modulated the effects of both traits and nutrient availability on ecosystem functioning. Specific root length was the key trait associated with soil nutrient cycling and belowground biomass in contrasted heterogeneous soil conditions. The inclusion of soil heterogeneity into the trait-based response-effect framework may help to scale from plant communities to the ecosystem level.     

Soils as agents of selection: feedbacks between plants and soils alter seedling survival and performance

Soils are one of the first selective environments a seed experiences and yet little is known about the evolutionary consequences of plant-soil feedbacks. We have previously found that plant phytochemical traits in a model system, Populus spp., influence rates of leaf litter decay, soil microbial communities and rates of soil net nitrogen mineralization. Utilizing this natural variation in plant-soil linkages we examined two related hypotheses: (1) Populus angustifolia seedlings are locally adapted to their native soils; and (2) Soils act as agents of selection, differentially affecting seedling survival and the heritability of plant traits. We conducted a greenhouse experiment by planting seedlings from 20 randomly collected P. angustifolia genetic families in soils conditioned by various Populus species and measured subsequent survival and performance. Even though P. angustifolia soils are less fertile overall, P. angustifolia seedlings grown in these soils were twice as likely to survive, grew 24% taller, had 27% more leaves, and 29% greater above-ground biomass than P. angustifolia seedlings grown in non-native P. fremontii or hybrid soils. Increased survival resulted in higher trait variation among seedlings in native soils compared to seedlings grown in non-native soils. Soil microbial biomass varied significantly across soil environments which could explain more of the variation in seedling performance than soil texture, pH, or nutrient availability, suggesting strong microbial interactions and feedbacks between plants, soils, and associated microorganisms. Overall, these data suggest that a “home-field advantage” or a positive plant soil feedback helps maintain genetic variance in P. angustifolia seedlings.     

Disturbances by desert rodents are more strongly associated with spatial changes in soil texture than woody encroachment

Background and Aims

Soil texture is an important determinant of ecosystem structure and productivity in drylands, and may influence animal foraging and, indirectly, plant community composition.

Methods

We measured the density and composition of surface disturbances (foraging pits) of small, soil-foraging desert vertebrates in shrubland and grasslands, both with coarse- and fine-textured soils. We predicted that the density and functional significance of disturbances would be related more to differences in texture than shrub encroachment.

Results

Soil texture had a stronger influence on animal foraging sites than shrub encroachment. There were more disturbances, greater richness and abundance of trapped seed, and greater richness of germinating plants on coarse- than fine-textured soils. Pits in coarse soils trapped 50 % more litter than those in finer soils. Apart from slightly more soil removal and greater litter capture in shrubland pits, there were no effects of encroachment.

Conclusions

Although the process of woody encroachment has been shown to have marked effects on some ecosystem properties, it is likely to have a more subordinate effect on surface disturbances and therefore their effects on desert plant communities than soil texture. Our results highlight the importance of animal activity in shaping desert plant communities, and potentially, in maintaining or reinforcing shrub dominant processes.