Plant density can increase invertebrate postdispersal seed predation in an experimental grassland community

Janzen–Connell effects are negative effects on the survival of a plant’s progeny at high conspecific densities or close to its conspecifics. Although the role of Janzen–Connell effects on the maintenance of plant diversity was frequently studied, only few studies targeted Janzen–Connell effects via postdispersal seed predation in temperate grassland systems. We examined effects of conspecific density (abundance of conspecific adult plants) on postdispersal seed predation by invertebrates of three grassland species (Centaurea jacea, Geranium pratense, and Knautia arvensis) in experimental plant communities. Additionally, we examined the impact of plant species richness and different seed predator communities on total and relative seed predation (= seed predation of one plant species relative to others). We offered seeds in an exclusion experiment, where treatments allowed access for (1) arthropods and slugs, (2) arthropods only, (3) small arthropods only, and (4) slugs only. Treatments were placed in plots covering a gradient of abundance of conspecific adults at different levels of plant species richness (1, 2, 3, 4, 8 species). Two of the plant species (C. jacea and K. arvensis) experienced higher rates of seed predation and relative predation with increasing abundance of conspecific adults. For C. jacea, this effect was mitigated with increasing plant species richness. Differences in seed predator communities shifted seed predation between the plant species and changed the magnitude of seed predation of one plant species relative to the others. We exemplify density-dependent increase in seed predation via invertebrates in grassland communities shaping both the total magnitude of species-specific seed predation and seed predation of one species relative to others. Further differences in seed predator groups shift the magnitude of seed predation between different plant species. This highlights the importance of invertebrate seed predation to structure grasslands via density-dependent effects and differing preferences of consumer groups

Linking diversity, synchrony and stability in soil microbial communities

1. It is becoming well established that plant diversity is instrumental in stabilizing the temporal functioning of ecosystems through population dynamics and the so-called insurance or portfolio effect. However, it is unclear whether diversity-stability relationships and the role of population dynamics in soil microbial communities parallel those in plant communities. 2. Our study took place in a long-term land management experiment with and without perturbation to the soil ecosystem by tilling. We assessed the impacts of the soil perturbation on the diversity, synchrony and stability relationships in soil fungal and bacterial communities. 3. We found that the perturbation to the soil ecosystem not only reduced the abundance and richness of the fungal community, but it also reduced the temporal stability in both bacterial and fungal abundance. The fungal community abundance was destabilized by soil tilling due to reduced richness and increased temporal variation of individual taxa. In contrast, soil tilling destabilized the bacterial community abundance by reducing the temporal variation of individual taxa. Both bacterial and fungal community abundances were more temporally variable when taxa fluctuated more synchronously through time. 4. Our results show that land management practices, such as tilling, can destabilize soil microbial abundance by reducing the richness and disrupting the temporal dynamics belowground. However, the differences in the mechanisms that underlie the temporal variations in fungal and bacterial net abundances suggests that the mechanisms that drive the stability can differ among guilds of organisms within the same system. The different temporal responses between the fungal and bacterial communities are likely linked to changes in edaphic properties resulting from the physical alteration of the soil structure

Beyond biomass: Soil feedbacks are transient over plant life stages and alter fitness

1.) Plants influence associated soil biotic communities that in turn can alter the performance of the subsequently growing plants. Although such “plant–soil feedbacks” (PSFs) are considered as important drivers of plant community assembly, past PSF studies have mainly addressed plant biomass production. However, plant performance is not only the production of biomass but comprises a sequence of different life stages: from seed germination over vegetative growth up to the production of a viable progeny. 2.) Here, we assessed the effects of soil biotic communities that were previously conditioned for 3 years by a focal plant species monoculture or species mixtures on key plant life stages from germination and vegetative growth to flowering and the production of viable seeds. We used three common grassland herb species that were grown in a sterile substrate and inoculated with a sterile control soil or with living soils. Living soils were conditioned either by the focal species in monoculture or a four- or eight-species mixture that included the focal species to represent a decrease in the target plants’ conspecific influence on the soil communities. 3.) We show that the effect of soil biota changed from positive at the plants’ juvenile life stages to neutral or negative at the plants’ adult life stages and ultimately decreased plant fitness. A higher conspecific influence on the soil communities pronounced the positive effects at the juvenile life stage but also the negative effects at adult life stages. Further, we observed direct soil biotic effects on flower production and plant fitness that were not mediated by adult biomass production. This suggests that soil biotic effects may alter plant resource allocation and even may have transgenerational effects on plant fitness. 4.) Synthesis. We conclude that there is no overarching effect of soil biota that remains consistent at all the life stages of a plant. Thus, our results highlight the importance to consider plant life stage and ultimately plant fitness especially when plant–soil interactions are used to explain plant community dynamics

data of the soil and chemotaxis experiment

.xls file with four sheets including the data and meta-data of the soil experiment and the chemotaxis experimen

Data from: Beyond biomass: soil feedbacks are transient over plant life-stages and alter fitness

1. Plants influence associated soil biotic communities that in turn can alter the performance of the subsequently growing plants. Although such ‘plant-soil feedbacks’ (PSFs) are considered as important drivers of plant community assembly, past PSF studies have mainly addressed plant biomass production. However, plant performance is not only the production of biomass, but comprises a sequence of different life-stages: from seed germination over vegetative growth up to the production of a viable progeny. 2. Here we assessed the effects of soil biotic communities that were previously conditioned for three years by a focal plant species monoculture or species mixtures on key plant life-stages from germination and vegetative growth to flowering and the production of viable seeds. We used three common grassland herb species that were grown in a sterile substrate and inoculated with a sterile control soil, or with living soils. Living soils were conditioned either by the focal species in monoculture, or a four- or eight-species mixture that included the focal species to represent a decrease in the target plants’ conspecific influence on the soil communities. 3. We show that the effect of soil biota changed from positive at the plants’ juvenile life-stages to neutral or negative at the plants’ adult life-stages, and ultimately decreased plant fitness. A higher conspecific influence on the soil communities pronounced the positive effects at the juvenile life-stage, but also the negative effects at adult life-stages. Further, we observed direct soil biotic effects on flower production and plant fitness that were not mediated by adult biomass production. This suggests that soil biotic effects may alter plant resource allocation and even may have trans-generational effects on plant fitness. 4. Synthesis. We conclude that there is no overarching effect of soil biota that remains consistent at all the life-stages of a plant. Thus, our results highlight the importance to consider plant life-stage and ultimately plant fitness especially when plant soil interactions are used to explain plant community dynamics

Plant responses to soil inoculation treatments at different life-stages

Plant responses to soil inoculation treatments at different life-stage

FE_Data

FE_Dat

Data from: Linking diversity, synchrony and stability in soil microbial communities

1. It is becoming well established that plant diversity is instrumental in stabilizing the temporal functioning of ecosystems through population dynamics and the so-called insurance or portfolio effect. However, it is unclear whether diversity-stability relationships and the role of population dynamics in soil microbial communities parallel those in plant communities. 2. Our study took place in a long-term land management experiment with and without perturbation to the soil ecosystem by tilling. We assessed the impacts of the soil perturbation on the diversity, synchrony and stability relationships in soil fungal and bacterial communities. 3. We found that the perturbation to the soil ecosystem not only reduced the abundance and richness of the fungal community, but it also reduced the temporal stability in both bacterial and fungal abundance. The fungal community abundance was destabilized by soil tilling due to reduced richness and increased temporal variation of individual taxa. In contrast, soil tilling destabilized the bacterial community abundance by reducing the temporal variation of individual taxa. Both bacterial and fungal community abundances were more temporally variable when taxa fluctuated more synchronously through time. 4. Our results show that land management practices, such as tilling, can destabilize soil microbial abundance by reducing the richness and disrupting the temporal dynamics belowground. However, the differences in the mechanisms that underlie the temporal variations in fungal and bacterial net abundances suggests that the mechanisms that drive the stability can differ among guilds of organisms within the same system. The different temporal responses between the fungal and bacterial communities are likely linked to changes in edaphic properties resulting from the physical alteration of the soil structure

A new species of Elaphoglossum sect: Lepidoglossa subsect: Muscosa (dryopteridacae) with cristate spores

A new species from the Bolivian highlands is described as Elaphoglossum cristatum. It is very similar to E. engelii but is characterized by a (for subsect. Muscosa unique) cristate perispore structure with irregular deposits (versus papillate spores), more densely ciliate petiole scales (50–80 versus 10–30 cilia per scale), somewhat thicker blade texture, denser scale cover, and paler, more reddish rhizome scales