Plant and soil microbe responses to light, warming and nitrogen addition in a temperate forest

1. Temperate forests across Europe and eastern North America have become denser since the 1950s due to less intensive forest management and global environmental changes such as nitrogen deposition and climate warming. Denser tree canopies result in lower light availability at the forest floor. This shade may buffer the effects of nitrogen deposition and climate warming on understorey plant communities. 2. We conducted an innovative in situ field experiment to study the responses of co-occurring soil microbial and understorey plant communities to nitrogen addition, enhanced light availability and experimental warming in a full-factorial design. 3. We determined the effects of multiple environmental drivers and their interactions on the soil microbial and understorey plant communities, and assessed to what extent the soil microbial and understorey plant communities covary. 4. High light led to lower biomass of the soil microbes (analysed by phospholipid fatty acids), but the soil microbial structure, i.e. the ratio of fungal biomass to bacterial biomass, was not affected by light availability. The composition of the soil bacterial community (analysed by high-throughput sequencing) was affected by both light availability and warming (and their interaction), but not by nitrogen addition. Yet, the number of unique operational taxonomic units was higher in plots with nitrogen addition, and there were significant interactive effects of light and nitrogen addition. Light availability also determined the composition of the plant community; no effects of nitrogen addition and warming were observed. The soil bacterial and plant communities were co-structured, and light availability explained a large part of the variance of this co-structure. 5. We provide robust evidence for the key role of light in affecting both the soil microbial and plant communities in forest understoreys. Our results advocate for more multifactor global change experiments that investigate the mechanism underlying the (in) direct effects of light on the plant-soil continuum in forests

The functional role of temperate forest understorey vegetation in a changing world

Temperate forests cover 16% of the global forest area. Within these forests, the understorey is an important biodiversity reservoir that can influence ecosystem processes and functions in multiple ways. However, we still lack a thorough understanding of the relative importance of the understorey for temperate forest functioning. As a result, understoreys are often ignored during assessments of forest functioning and changes thereof under global change. We here compiled studies that quantify the relative importance of the understorey for temperate forest functioning, focussing on litter production, nutrient cycling, evapotranspiration, tree regeneration, pollination and pathogen dynamics. We describe the mechanisms driving understorey functioning and develop a conceptual framework synthesizing possible effects of multiple global change drivers on understorey-mediated forest ecosystem functioning. Our review illustrates that the understorey's contribution to temperate forest functioning is significant but varies depending on the ecosystem function and the environmental context, and more importantly, the characteristics of the overstorey. To predict changes in understorey functioning and its relative importance for temperate forest functioning under global change, we argue that a simultaneous investigation of both overstorey and understorey functional responses to global change will be crucial. Our review shows that such studies are still very scarce, only available for a limited set of ecosystem functions and limited to quantification, providing little data to forecast functional responses to global change

Using process-based indicator species to evaluate ecological corridors in fragmented landscapes

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Macro-detritivore identity and biomass along with moisture availability control forest leaf litter breakdown in a field experiment

Forests are structurally rich ecosystems with strong spatial variation in microclimate. Local temperature and soil moisture are important drivers of leaf litter breakdown, a key ecosystem process vital for forest functioning. Additionally, detritivore species composition and activity are equally dependent on microclimate, rendering changes in microclimate key to understand leaf litter breakdown. We investigated the interaction between microclimatic variables (i.e. temperature and moisture) and different combinations of macro-detritivores (a drought sensitive i.e. Oniscus asellus vs. a drought tolerant species i.e. Glomeris marginata) on litter breakdown of easily decomposable (high quality) Acer litter and decomposition resistant (low quality) Quercus litter in a full factorial microcosm field experiment in a temperate forest in Belgium. We hypothesize litter breakdown to be faster for high quality litter and macro-detritivore biomass and dependent on macro-detritivore identity, mediated by forest microclimate e.g. faster with higher soil moisture and warmer temperatures. We found high quality litter breakdown to be reduced by decreasing moisture availability, while it was not affected by temperature. There was no effect of moisture and temperature on litter breakdown of low quality litter. The effect of detritivore biomass on the breakdown of Quercus litter depended on detritivore identity: elevated millipede biomass increased Quercus litter breakdown, which was not the case for woodlice. There was a positive effect of macro-detritivore biomass but no effect of macro-detritivore identity on leaf litter breakdown of high quality litter. In addition, the relative consumption rates were equal between the drought sensitive (woodlouse) and the drought tolerant (millipede) species for high quality litter, but different for low quality litter. The woodlouse species was more efficient in the breakdown of low quality litter compared to our tested millipede species. Relative consumption rate was not influenced by the moisture or temperature treatments. Combining both detritivore taxa in a single microcosm had additive (non-synergistic) effects on litter breakdown, indicating that they are not complementary in their resource use. We conclude that mainly differences in moisture availability in forest ecosystems are important for litter breakdown and that detritivore identity is critical for the breakdown of especially low quality litter

Weak but persistent provenance effects modulate the response of Quercus robur (Fagaceae) seedlings to elevated temperature

Background and aims: Clinal variation in bud phenology and growth has repeatedly been reported in common garden experiments for many tree species. The response of the seedlings generated from such translocated trees has not been studied yet, despite its relevance regarding the role of transgenerational plasticity in the adaptation of long-living trees in the face of climate change. Here, we aim to understand the effects of warming on bud burst, germination success and growth performance of tree seedlings of different origins (provenances) but that shared their maternal environment. Methods: We collected seeds from a mature provenance trial of five different provenances of oak (Quercus robur, Fagaceae) and seeds were grown in two common gardens at two different latitudes representing a mean annual temperature difference of nearly 2°C in Belgium and Denmark. We assessed seed germination, bud burst time and biomass of seedlings in two common gardens. Results: We observed an interaction between provenances and common gardens in seedlings’ bud burst time indicating the prevalence of an environmental effect at the site of origin (provenance), which depends on the seedlings’ growing environment (across the two common gardens). The germination success and shoot biomass were reduced across all provenances in the southern common garden. Conclusions: Our results indicate that the environment of origin influences the bud phenology of seedlings and this provenance effect is dependent on the seedlings’ growing environment. In addition, our results suggest that the effect of warming might differ between provenances and that the environmental history of the previous generations is likely to influence the response of tree seedlings as well

Soil microbial community and plant cover

The data file contains three datasets.The folder PrimerClipped contains the primerclipped V3-V4 region 16SrRNA gene amplicon sequence files. The excel file Plant cover contains plant species and cover in each plot. The PLFA concentrations file contains all PLFA biomarkers. The READ ME file indicates the details of sequence files

Win some, lose some : mesocosm communities maintain community productivity despite lower phosphorus availability because of increased species diversity

Aims: The restoration of degraded ecosystems typically focuses on establishing assemblages of target species, but successful recovery should also be evaluated by the ecosystem's functioning to guarantee long-term persistence. We investigated how the processes underlying community assembly (i.e. species loss, species gain and changes in abundance of resident species) influenced ecosystem functioning in experimental grassland communities in different states of restoration. Location: A greenhouse experiment in northern Flanders, Belgium. Methods: We set up a mesocosm experiment with communities of 19 planted species, ranging from slow-growing species from poorly productive Nardus grasslands to fast-growing species from highly productive Lolium perenne grasslands. We categorised the mesocosms into different grassland restoration states based on known abiotic and biotic restoration barriers for semi-natural grassland restoration: soil phosphorus levels and soil biota communities. After two growing seasons, we used the CAFE approach, an ecological application of the Price equation, to partition the effects of plant community assembly on ecosystem functioning (here community productivity) for the different restoration states. Results: Adding soil biota communities sampled from reference Nardus grasslands vs more intensively managed grasslands did not have a significant effect on either plant species richness or biomass productivity. Lower soil phosphorus concentrations (i.e. abiotic restoration) resulted in a higher plant species richness. However, the net effect on productivity was close to zero. The increase in productivity caused by species gains was compensated through decreases in productivity caused by species loss and by decreases in the abundance or functioning of species that are present in both abiotically degraded and abiotically restored states. Conclusions: Not only species richness but also species identity resulted in changes in ecosystem functioning (i.e. productivity), even though the net functional effects were close to zero. More specifically, we found that species richness-driven increases in productivity were counterbalanced by resource-driven and species identity-driven reductions in productivity

Phytomining to re-establish phosphorus-poor soil conditions for nature restoration on former agricultural land

Aims: To restore species-rich grasslands on former agricultural land, typically phosphorus-poor soil conditions need to be re-established. Here we assess the potential of phosphorus extraction by biomass production, i.e. phytomining. We compare two techniques: (i) 'mowing', i.e. cutting and removing hay two or three times a year, and (ii) 'P-mining', i.e. mowing with yield maximization by adding growth-limiting nutrients other than phosphorus (i.e. nitrogen and potassium). Methods: In a five-year field experiment at three fields situated along a soil phosphorus gradient, we studied phosphorus removal through both biomass assessment and changes in two soil phosphorus pools: bioavailable phosphorus (P-Olsen) and slowly cycling phosphorus (P-Oxalate). Results: Phosphorus-mining doubled the phosphorus removal with biomass compared to mowing, and phosphorus removal with biomass was lower at fields with an initially lower concentration of P-Olsen in the soil. The P-Olsen concentrations decreased significantly during the experiment with the largest decreases in phosphorus-rich plots. Changes in the P-Olsen and P-Oxalate stocks were correlated with the amount of phosphorus removed with biomass. Conclusions: Phosphorus-mining effectively increases phosphorus removal compared to mowing, but becomes less efficient with decreasing soil phosphorus concentrations. Restoring phosphorus-poor soil conditions on formerly fertilized land remains a challenge: phytomining most often needs a long-term commitment