Plant and Soil最新文献

Background and Aims

Many studies have considered whether all forms of rare earth elements (REEs) in the soil are potentially bioavailable. The general consensus is that the exchangeable and carbonate-bound mineral pool is bioavailable. However, within the rhizosphere, site-specific geochemical conditions and biological weathering (due to plants, animals and microbes) may cause insoluble pools of REEs in the soil to become plant bioavailable.

Methods

This study categorized soil into four fractions using the Community Bureau of Reference (BCR) sequential extraction method. The geochemical associations of REEs with soil fractions were assessed to determine which mineral and organic pools were most bioavailable by comparing the similarity of REE fractionation patterns in local plant tissues with the BCR extraction results for compatible soils.

Results

The results showed that the residual or more recalcitrant fraction of the soil displays a convex REE pattern with distinct depletion of middle REEs (MREEs) compared with light REEs (LREEs) and heavy REEs (HREEs). Some evidence suggested that Eu may be excluded by plants, as anomalous Eu concentrations were observed when the belowground plant tissue concentrations were normalized to the BCR extraction data.

Conclusions

This study demonstrates that the REEs in belowground plant tissue are closely related, not only to exchangeable and carbonate-bound phases, but also to reducible and oxidizable soil fractions. According to the REE patterns, MREEs are more mobile than LREEs and HREEs, indicating enhanced bioavailability of MREEs.

Background and aims

Understanding of the influences of soil moisture changes on plant phenological shifts on the Qinghai–Tibetan Plateau (QTP) is insufficient mainly because previous studies focused on the climatic factors. We explored the role of soil moisture in regulating plant autumn phenology on the QTP.

Methods

Based on long-term ground observations of soil moisture, plant phenology, and meteorology, temporal and spatial changes in soil moisture and leaf senescence dates (LSD) were analyzed using ordinary least squares regression and a meta-analysis procedure. Influences of soil moisture changes on the LSD shifts were assessed through correlation analysis and support vector machine, and also compared with those of air temperature and precipitation.

Results

Nonsignificant interannual changes in soil moisture were observed, and LSD significantly delayed at a rate of 2.7 days/decade. Spatial changes of LSD were more correlated with site elevation and air temperature, and soil moisture and precipitation showed insignificant negative impacts. However, correlations between annual LSD and average soil moisture were mainly positive. Soil moisture and precipitation showed greater importance in regulating the LSD of sedges and grasses, whereas temperature exerted a larger influence on the LSD of forbs. Precipitation showed higher importance in regulating the interannual shifts in LSD, while temperature played a more important role in determining the spatial variations.

Conclusion

Soil moisture had divergent influences on the temporal and spatial shifts in LSD of different plant functional groups on the QTP. Overall, soil moisture was outweighed by temperature and precipitation in regulating autumn phenological shifts. However, soil moisture may become increasingly important in the future and forbs are expected to be more competitive if the QTP becomes warmer and drier, which will bring challenges in grassland management and utilization on the QTP.

Background and aims

White lupin (Lupinus albus) mobilize inaccessible phosphorus (P) by producing cluster root that can secrete carboxylates and enhance the phosphatase activity. Blue lupin (L. angustifolius) and yellow lupin (L. luteus) are classified in the same legume genus as white lupin, this study investigates whether blue and yellow lupins can evoke adaptation strategies under P scarcity.

Methods

For this pot experiment, three lupin species were subjected to -P, + Pi (NaH₂PO₄), and + Po (Phytate) treatments. After two months, we determined biomass and P allocation in lupins, Hedley-P fractions, exudate composition, and bacterial diversity in the rhizosheath under distinct treatments.

Results

The results indicate white lupin accumulated high P content under -P and + Po treatments, while yellow lupin exhibited similar P content under + Po and + Pi treatments. Additionally, white lupin showed higher citrate secretion, ALPase, and PHYase activities under -P condition, as well as increased PHYase and β-Glu activities under + Po treatment. Particularly, the genera Segetibacter, Granulicell, Candidatus_Methylacidiphilum, and Bryobacter, which contributed to phytate activation, were simultaneously present in the rhizosheaths of both white and yellow lupins under + Po treatment.

Conclusion

This study elucidates the multifaceted physiological responses of lupins in adapting to P-deficient and provides novel insight into the role of rhizobacteria in phytate mobilization.

Background and aims

Exploring plant community assembly mechanisms is of central interest to infer community dynamics and succession in the context of global change and intensive human activities. Our aim was to understand the grassland community assembly mechanisms and how species’ functional compositions and groups might change under ongoing climate change and shrub encroachment.

Methods

Here, we used standardized effect sizes (SESs) of mean pairwise distance (MPD) to evaluate community functional trait and phylogenetic relatedness patterns and infer how both aridity and shrub cover influence assembly mechanisms in the Inner Mongolia Steppe, China.

Results

Community multi-trait patterns shifted from convergence to stochasticity as aridity increased. Increasing shrub cover directly decreased the convergence of community multi-trait patterns and decreased the presence of perennial grasses as well as CWM_LDMC. Both aridity and shrub cover affected the community LDMC patterns indirectly by negatively regulating the soil nitrogen (N) content. A concave relationship between the soil N content and the community LDMC patterns indicated that abiotic filtering, niche differentiation and biotic filtering dominate community assembly at lower, medium and higher soil N contents, respectively.

Conclusion

Our results imply that the weakening of biotic filtering and enhancement of stochastic processes with the increasing aridity or shrub cover are driven by losing soil nitrogen and perennial grass which includes the dominant competitors.

Background and aims

Rhizosphere serves as a hotspot for phosphatase exudation, which is instrumental in organic P mineralization and thereby facilitates enhanced P uptake by plants. However, further exploration is required to elucidate mechanisms of P transformation regulated by microorganisms in rhizosphere hotspots.

Methods

Soil zymography was used to visualize rhizosphere hotspots associated with acid and alkaline phosphatase activities following P addition in two maize genotypes, Zhengdan958 (ZD958) and Xianyu335 (XY335). Metagenomic sequencing was used to investigate shifts in abundance and composition of P cycle genes and microbial communities within phosphatase hotspots.

Results

ZD958 exhibited higher shoot biomass than XY335 under same P conditions. Hotspots of phosphatase activity were predominantly located in the maize rhizosphere and decreased following P addition. Specifically, P addition resulted in an increase in the abundance of P-uptake and transport genes pstSCAB and a decrease in the abundance of P-starvation regulation gene phoB and inorganic P solubilization gene gcd in ZD958. The relative abundance of phytase-encoding gene (phy) significantly increased with P addition and correlated with soil available P (AP) in XY335. Among the microbial taxa containing hub genes, Streptomyces emerged as the most crucial predictor of soil AP and exhibited a significantly positive relationship with AP for both maize genotypes.

Conclusion

Our results visualized the rhizosphere phosphatase hotspots, revealing that the genes regulating P cycling differed while Streptomyces harboring P cycling hub genes improve P availability in both maize genotypes. These findings provide a scientific basis for increasing the P efficiency employing microbiology.

Graphical Abstract

Background and Aims

Roots of plants have been shown to be effective in reinforcing soils against slope failures. Two key mechanical properties in such reinforcement are the root’s tensile strength (TS) and elastic modulus (EM). However, knowledge on the combined effects of root moisture content (RMC) and root diameter on these properties is scarce. The study aims to quantify these relationships for root samples of four native Australian tree (A. costata, B. integrifolia, E. reticulatus, and E. racemosa).

Methods

A series of tensile tests were conducted and the root diameter at the fracture point and RMC were measured immediately after each test. Data were analysed using both univariate and multivariate analyses.

Results

Both TS and EM declined with increasing diameter. Power-law expressions were found to describe the relationship between TS and diameter moderately well, but less so the one between TS and RMC. Multivariate analyses yielded a double power-law for TS versus diameter and RMC with a stronger fit than univariate ones. A weaker power-law was found between EM and these 2 variables. Of the four trees tested, A. costata exhibited the highest tensile strength and elastic modulus at a 1 mm diameter, while B. integrifolia yielded the lowest.

Conclusion

Considering both diameter and RMC as explanatory variables of TS and EM yield better accounts of experimental data. This work contributes to a better understanding of reinforcement capacity of trees generally, as well as the specific performance of roots of four native Australian trees.

Background and aims

Shrubs of the genus Baccharis are considered key nurse plants for the Chilean matorral, but some species have allelopathic compounds in their leaves. These compounds can leach into the soil, casting doubt on their nurse role. We assessed the nurse effect of B. paniculata, a species with allelopathic compounds in their leaves, in a central Chilean matorral site by determining the richness and cover of species growing beneath the shrub canopy and open areas, by quantifying the microclimate beneath the canopy and by experimentally assessing the microclimate versus the soil effect of this species on planted seedlings of tree dominant tree species.

Methods

Beneath shrubs and in open areas we recorded the number and cover of species as well air and soil temperature, relative humidity of the air, photosynthetic photon flux density (PPFD) and soil water content. We planted seedlings of Lithrea caustica, Quillaja saponaria, and Cryptocarya alba in both habitats using soils from open areas and from beneath Baccharis to distinguish their effects on seedling’s photochemical efficiency and survival.

Results

No woody species grew beneath B. paniculata. Air temperature was similar in both habitats, but soil temperature and PPFD were lower, and soil moisture was higher beneath shrubs. Seedling’s photochemical efficiency and survival were generally higher beneath canopies but were negatively affected by soil from beneath Baccharis shrubs.

Conclusion

Our findings question the nurse role of B. paniculata in the Chilean matorral, emphasizing the need to consider other shrub species for restoration initiatives for central Chile.

Background and aims

Anthropogenic activities have substantially elevated nitrogen (N) deposition globally and affect ecosystem processes, including soil carbon (C) storage potential. Phosphorus (P) can become a limiting factor for plant production in instances of N deposition, yet the responses of ecosystem C cycles to P enrichment are poorly understood, particularly in sensitive alpine ecosystems.

Methods

We conducted a short-term field study to appraise the effects of N and P addition on ecosystem CO₂ emissions and CH₄ uptake in three typical alpine grasslands, alpine meadow, alpine steppe, and cultivated grassland on the Qinghai-Tibet Plateau (QTP). The closed chamber technique was employed to monitor the fluxes of CO₂ and CH₄. Environmental factors, including plant biomass and diversity and soil nutrients, and the abundance of C-cycling genes were analyzed to investigate the factors regulating CO₂ and CH4 fluxes.

Results

The results showed that: (i) N and P addition tended to increase CO₂ emissions and CH₄ uptake. Furthermore, P addition weakened the positive effects of N on CH₄ uptake across the three grasslands, but the interaction of N and P addition on CO₂ emissions varied across the three grasslands. (ii) N and P addition affected the fluxes of CO₂ and CH₄ both directly and indirectly through their impacts on soil and plant factors rather than C-cycling functional genes. 

Conclusions

These results indicate that in the context of increasing N deposition in the QTP, short-term P addition is not an effective method for mitigating global warming potential and improving soil C sequestration in alpine grassland ecosystems.

Background and Aims

Mutualistic root symbioses, particularly those involving mycorrhizal fungi and nitrogen-fixing bacteria, are pivotal to ecosystem productivity and stability. Plant-soil feedbacks (PSFs) and climate serve as primary regulators of these symbiotic interactions, determining their establishment, maintenance, and diversity. PSFs, encompassing the complex interactions between plants and soil biota, modulate nutrient uptake and ultimately influence plant growth and development. Climate not only shapes the abundance, composition and performance of soil biota, but also directly impacts the distribution and response of plant symbioses to environmental shifts including rising temperatures and modified precipitation patterns.

Results

This review compiles recent advancements in the ecology and diversity of mycorrhizal and nitrogen-fixing associations, emphasizing the interaction between soil biota and climate, and their implications for ecosystem functions in the context of climate change. It also identifies key gaps in our understanding, such as the molecular mechanisms at play, the genetic variability involved, and the impact of global environmental changes on symbiotic networks.

Conclusion

Addressing these questions is essential for a more profound comprehension of the complex plant-soil dynamics that sculpt terrestrial ecosystems.

Background and aims

According to the carbon (C) saturation concept, the capacity of soils to accumulate stabilized organic C is limited by the number of binding sites on mineral surfaces. The concept and its application are highly debated. Therefore, we aimed at testing this theory using field experimental data.

Methods

Soils were sampled from four long-term field experiments with different amounts of organic fertilisation going up to extreme high C inputs (20 Mg C ha⁻¹ yr⁻¹) five times higher than in common agricultural practice. Soils were fractionated by particle size to obtain sand-sized, coarse silt and fine silt plus clay fractions.

Results

We found a linear relation between C input and soil organic carbon stocks (SOC) even with vast amounts of organic C inputs to the soil at three experimental sites. Across all experiments, C stocks in the sand-sized fraction increased on average by 146%, whereas C stocks in the fine silt plus clay fraction (< 20 µm) increased by just 17% without distinct saturation behaviour. The C sequestration efficiency (amount of C retained as SOC per amount of C input) tended to increase with initial SOC content which is not in line with the saturation theory.

Conclusion

The experiments were subject to C inputs via organic fertilisation that would and should rarely be reached in agricultural practice due to negative side effects. Even under these artificial conditions experiments did not show a distinct saturation behaviour.

Initial SOC stocks or SOC in the mineral-associated fraction did not appear to limit the potential of soils to sequester additional SOC. It can be concluded that C sequestration is mainly limited by the availability of C inputs from biomass.