[en] Highlights: • Pooling multiple soil cores is superior to a non-pooling strategy. • Pooling a small number of soil cores (i.e. 5 or 9) is enough. • Distribution of α diversity varies with sampling strategies and sequencing depth. • Retaining 100,000 reads after taxonomic clustering is enough to cover common species. Due to the massive quantity and broad phylogeny, an accurate measurement of microbial diversity is highly challenging in soil ecosystems. Initially, the deviation caused by sampling should be adequately considered. Here, we attempted to uncover the effect of different sampling strategies on α diversity measurement of soil prokaryotes. Four 1 m² sampling quadrats in a typical grassland were thoroughly surveyed through deep 16S rRNA gene sequencing (over 11 million reads per quadrat) with numerous replicates (33 soil sampling cores with total 141 replicates per quadrat). We found the difference in diversity was relatively small when pooling soil cores before and after DNA extraction and sequencing, but they were both superior to a non-pooling strategy. Pooling a small number of soil cores (i.e., 5 or 9) combined with several technical replicates is sufficient to estimate diversities for soil prokaryotes, and there is great flexibility in pooling original samples or data at different experimental steps. Additionally, the distribution of local α diversity varies with sampling core number, sequencing depth, and abundance distribution of the community, especially for high orders of Hill diversity index (i.e., Shannon entropy and inverse Simpson index). For each grassland soil quadrat (1 m²), retaining 100,000 reads after taxonomic clustering might be a realistic option, as these number of reads can efficiently cover the majority of common species in this area. Our findings provide important guidance for soil sampling strategy, and the general results can serve as a basis for further studies.

[en] Highlights: • Soil conditioned by pre-successional species had a positive feedback on the future plant species. • The feedback of different successional species to soil microbial communities was mainly positive. • The main microbial groups affecting the replacement of species during succession varied across taxonomic levels. Plant–soil feedback (PSF) is an important driver of plant community dynamics. The role of plant species in PSF has been emphasized for secondary succession processes; however, microbial responses to PSF and the underlying mechanisms responsible for their effects on plant succession remain poorly understood, particularly in semiarid grassland ecosystems. Here, we conducted a greenhouse experiment using soil collected from early-, mid-, and late-successional plant communities to measure net pairwise PSF for species grown under monoculture. Soils conditioned by pre-successional species had a positive feedback effect on subsequent plant species, whereas soil conditioned by subsequent plant species had a negative feedback effect on pre-successional species. The feedback effect of plants from different successional stages on soil bacterial and fungal communities was mainly positive. However, the bacterial genera in the soil conditioned by early- and mid-successional species and fungal classes in the soil conditioned by early- successional species had a negative feedback effect on late-successional species. Thus, the effects of soil fungal and bacterial communities on species in other successional stages varied with taxonomic level. Our results provide insight into the manner in which soil microbial communities influence PSF responses during secondary succession processes.

[en] Highlights: • Nitrogen addition elevated soil respiration in the grassland. • Phosphorus addition did not affect soil respiration, but augments the effects of nitrogen addition on soil respiration. • Plant cover and litter biomass played an important role in regulating the response of soil respiration to nitrogen addition. Soil respiration is one of the largest carbon (C) sources in terrestrial ecosystems and is sensitive to soil nutrient variation. Although nitrogen (N) availability affects soil respiration, other nutrients, such as phosphorous (P), which play pivotal roles in plant growth and microbial activity, may also affect soil respiration. In addition, N and P have been widely reported to interactively affect plant growth; however, their interactive effects on soil respiration have rarely been studied. Therefore, we conducted a short-term, two-factor experiment (from 2013 to 2015) to determine whether N and P addition can interactively affect soil respiration in a northern Chinese steppe. Nitrogen addition elevated soil respiration by 9.5%, whereas P addition did not affect soil respiration in the studied steppe across all treatments. However, neither N nor P addition significantly affected soil respiration alone in the experiment. Furthermore, N and P interactively affected soil respiration. Nitrogen addition did not affect soil respiration in the ambient P plots, but significantly elevated soil respiration (by 17.7%) in P addition plots across the three growing seasons. The effects of N addition on soil respiration were primarily correlated with the responses of vegetation cover and litter biomass to N addition in the experiment. Our results demonstrate that P addition augments the effects of N addition on soil respiration. Soil nutrient contents should be incorporated into predictive models for terrestrial C cycle response to N addition.

No abstract available

[en] Highlights: • We investigated plant communities in wetlands 7-17 years after restoration. • Plant communities did not approach those characterising natural riparian wetlands. • Target species dispersal from source populations may restrict restoration success. • Continuous high nutrient input may be another major constraint for recovery. For more than two decades, wetland restoration has been successfully applied in Denmark as a tool to protect watercourses from elevated nutrient inputs from agriculture, but little is known about how the flora and fauna respond to restoration. The main objective of this study was therefore to: (1) examine plant community characteristics in 10 wetland sites in the River Odense Kratholm catchment, restored between 2001 and 2011 by re-meandering the stream and disconnecting the tile drains, and (2) explore whether the effects of restoration on plant community characteristics change with the age of the restoration. Specifically, we hypothesised that plant community composition, species richness and diversity would improve with the age of the restoration and eventually approach the state of natural wetland vegetation. We found that the prevailing plant communities could be characterised as humid grasslands, moist fallow fields and improved grasslands, whereas the abundance of natural wetland plant communities (e.g., rich fens, fen-sedge beds and humid grasslands) was lower in both the recently restored as well as in older restored wetlands. Additionally, species richness and diversity did not seem to improve with the age of the restoration. We suggest that the continued high nutrient input at the restored sites in combination with restricted dispersal of wetland plant species may hamper the recovery of natural plant communities and that the sites therefore may stay botanically poor for many decades.

[en] In the context of roadside revegetation activities in rural regions, revegetation objectives commonly are to establish plant communities with a diversity of species that would otherwise be absent on the predominantly agricultural landscape. To determine the efficacy of revegetation in providing plant communities of high biodiversity value, we quantified species richness, floristic quality, and success in seeding efforts. We evaluated the outcome of roadside seedings conducted by Nebraska Department of Transportation (NDOT) for five NDOT landscape regions spanning Nebraska. Our assessment occurred on average 13.2 years (range: 10–17) post-revegetation, thus, providing insight into what established plant communities can be expected after a decade or more. Biomass production declined on an east to west gradient, but the component species responsible for this gradient were unique to each region. We found species richness was greatest in the western regions of Nebraska with the Sandhills supporting the highest richness. This rangeland-dominated region exhibited the highest floristic quality index, a tool commonly used to identify areas of high conservation value. Our findings indicate that the roadside vegetation is landscape-dependent in that neighboring plant communities influence botanical composition of roadside vegetation. Thus, less diverse seeding mixtures could be used on roadsides with a diversity of desirable native plant species in neighboring land (i.e., Sandhills rangeland). Conversely, in roadsides surrounded by cropland or plant communities with many non-native, weedy species, seeding complex mixtures with a diversity of desirable and highly competitive native species is likely necessary. Nebraska roadsides are viewed as a resource where plant communities with a diversity of native grassland species can be established; however, persistence of many seeded, native species is minimal (mostly forbs) because of the competiveness of both seeded and invasive grasses.

No abstract available

No abstract available

[en] Highlights: • Meadow degradation can significantly alter soil microbial community. • The spatial turnover rate of microorganisms increased with meadow degradation. • Environmental heterogeneity affects the fungal community in degraded meadow. • Dispersal limitation promotes the spatial turnover rate of microbial community. The alpine meadow ecosystem, as the main ecosystem of the Qinghai-Tibet Plateau, has been heavily degraded over the past several decades due to overgrazing and climate change. Although soil microorganisms play key roles in the stability and succession of grassland ecosystems, their response to grassland degradation has not been investigated at spatial scale. Here, we systematically analyzed the spatial turnover rates of soil prokaryotic and fungal communities in degraded and undegraded meadows through distance-decay relationship (DDR) and species area relationship (SAR), as well as the community assembly mechanisms behind them. Although the composition and structure of both fungal and prokaryotic communities showed significant changes between undegraded and degraded meadows, steeper spatial turnover rates were only observed in fungi (Degraded Alpine Meadow β = 0.0142, Undegraded Alpine Meadow β = 0.0077, P < 0.05). Mantel tests indicated that edaphic variables and vegetation factors showed significant correlations to the β diversity of fungal community only in degraded meadow, suggesting soil and vegetation heterogeneity both contributed to the variation of fungal community in that system. Correspondingly, a novel phylogenetic null model analysis demonstrated that environmental selection was enhanced in the fungal community assembly process during meadow degradation. Interestingly, dispersal limitation was also enhanced for the fungal community in the degraded meadow, and its relative contribution to other assembly process (i.e. selection and drift) showed a significant linear increase with spatial distance, suggesting that dispersal limitation played a greater role as distance increased. Our findings indicated the spatial scaling of the fungal community is altered during meadow degradation by both niche selection and dispersal limitation. This study provides a new perspective for the assessment of soil microbial responses to vegetation changes in alpine areas.

[en] Highlights: • S-selected species dominate in non-degraded and degraded alpine grasslands. • Grassland degradation shifts plant communities from S- to R-strategy. • Sedges/grasses exhibit stronger S strategy to tolerate degraded-stressful conditions. • Forbs adapt to resource deficient and disturbed conditions with flexible R-strategy. The replacement of dominant sedges/grasses with secondary forbs is common in alpine rangelands, but the underlying plant ecological strategies and their relevance to leaf traits and their variabilities of different plant functional groups remain largely unknown. Here, we measured key leaf traits and analyzed the competitor, stress-tolerator and ruderal (CSR) strategies of major species with different functional groups (sedges, grasses and forbs) in an alpine meadow along a degradation gradient on the Tibetan Plateau. Our results indicated that S-selected species were dominant in both non-degraded (C:S:R = 1:95:4%) and severely degraded (C:S:R = 2:87:11%) meadows. However, there was a shift from S- to R-strategy in the communities after rangeland degradation. More specifically, sedges and grasses with a “conservative” strategy maintained stronger S-strategy to tolerate degraded and stressful conditions. In contrast, forbs with an “opportunistic” strategy (increase 9.5% in R-score) tended to adapt to degraded stages. Moreover, 51.1% and 23.9% of the increased R-scores in forbs were accounted by leaf mass per area and specific leaf area, respectively. Generally, higher leaf water and nitrogen contents coupled with larger variations in leaf traits and flexible SR strategies in forbs enabled them to capitalize on lower soil water and nutrient availability. Our findings highlighted that the contrasting strategies of plant species in response to the decrease in available resources might lead to niche expansion of secondary forbs and loss of diversity in the degraded alpine meadow. The emerging alternative stable states in the degraded rangelands might bring about a predicament for rangeland restoration.