Plant and Soil最新文献

Background and aims

In arable soil, the formation of occluded phosphate restricts the bioavailability of phosphorus (P). Straw incorporation effectively increases available P, but it stimulates CH₄ emission from paddy fields. Periphytic biofilms (PB), growing at soil-water interface, exert significant impacts on physical, chemical and biological characteristics of paddy soil. However, the effects of PB decomposition on P bioavailability remain unclear.

Methods

We conducted a microcosm experiment to explore the pathways how PB decomposition affected Olsen-P by comparing it with straw (ST) decomposition from perspectives of soil porosity, DOM compounds, reducing environment and microbial functions.

Results

Both PB and ST decomposition significantly increased soil Olsen-P concentration, but their pathways differed substantially. PB decomposition primarily enhanced Olsen-P by augmenting soil porosity, recalcitrant DOM compounds, bacterial species richness, bpp gene abundance, and facilitating Fe³⁺ reduction. Conversely, ST decomposition predominantly enhanced P bioavailability by augmenting soil reducibility.

Conclusion

PB biomass decomposition has more significant effects on soil Olsen-P than ST by influencing soil porosity, DOM, microbial community and reducing environment characteristics. These insights will offer valuable perspectives for leveraging PB biomass to improve soil P availability and reduce P input in paddy ecosystems.

Root exudation of carboxylates is a key response to phosphorus (P) limitation for many plant species. However, sampling and quantitative and qualitative determination of root exudates under field conditions faces various challenges. Recently, multiple studies have demonstrated that manganese (Mn) concentration in mature leaves may serve as a proxy for rhizosheath carboxylate concentration. In this issue of Plant and Soil, the paper by Yan and co-authors shows that leaf Mn concentration ([Mn]) was higher in P-limited forests of southern China than in forests of northern China that exhibit higher soil [P]. This study revealed the potential relationships between rhizosheath carboxylates and leaf [Mn] in the studied Chinese flora, and indicates a potential common strategy (i.e. root carboxylate exudation) among plants, including many mycorrhizal plants, in P-limited forests. Despite the fact that there is great variation among plant species, and the molecular basis underlying the positive correlation between plant Mn uptake and root release of carboxylates remains largely unexplored, this study has paved the road for an easy and reliable way to assess rhizosheath carboxylates in forest ecosystems. In combination with the handheld X-ray fluorescence spectroscopy system that enables non-destructive analysis of [Mn] in dried mature leaves (e.g., herbarium specimens), researchers are now able to estimate the patterns of root-released carboxylates for a broad range of plant species under various environmental conditions, in an easy, rapid and low-costs way.

Background and aims

Alpine shrublands are critical for global carbon dynamics due to their widespread occurrence in cold-climate regions and vulnerability to environmental shifts, including increased nitrogen deposition. Although nitrogen deposition affects litter turnover and accumulation, the precise mechanisms governing litter dynamics, including production, chemical composition, and decomposition rates, remain uncertain for these ecosystems.

Methods

To address this knowledge gap, our study investigated the effects of different nitrogen additions on litter production, chemistry, and decomposition rates in an alpine shrubland ecosystem on the eastern margin of the Qinghai–Tibetan Plateau of China over a four-year period.

Results

Our results showed that nitrogen addition did not significantly affect litter production or chemical properties, including carbon, nitrogen, phosphorus, lignin, and cellulose concentrations. Consequently, the annual input of litter-derived carbon and nutrients remained unchanged. However, we observed a significant reduction in litter decomposition rates at nitrogen additions of 50 and 100 kg ha⁻¹ yr⁻¹, whereas no such effect was observed at nitrogen additions of 20 kg ha⁻¹ yr⁻¹.

Conclusions

Our study revealed that high nitrogen deposition reduces litter decomposition in alpine shrublands, which coincides with increased litter accumulation, with consequences for carbon and nutrient cycling.

Aims

The stability of soil organic matter (SOM) is influenced by its chemical structure as well as by biological and environmental factors. However, the specific mechanisms by which pore space gaseous O₂/CO₂ concentrations affect SOM are not well understood.

Methods

The experimental design involved a 2 (Chinese photinia planted and bare land) × 2 (O₂ aeration levels) × 2 (CO₂ aeration levels) design compared to 2 non-aeration treatments, to investigate the impact of pore space O₂/CO₂ concentration on soil enzymes, soil organic carbon (SOC), light fraction organic carbon (LFOC), dissolved organic carbon (DOC) and microbial carbon (MBC).

Results

The injection of 21% O₂ led to a significant increase in the activities of catalase, urease, saccharase, invertase, and polyphenol oxidase enzymes. Significant increases in the contents of SOC, LFOC, DOC, and MBC were observed when comparing the effects of injecting 21% O₂ into the soil with 15% O₂, with the differences between treatments on carbon turnover rate increasing over time. Additionally, vegetation treatments were observed to increase DOC, MBC, and SOC. Changes in pore space gaseous CO₂ concentration from 0.03% to 0.4% had no significant effect on soil microorganisms, soil enzymes, or SOC turnover.

Conclusions

This study demonstrates that higher concentrations of pore space gaseous O₂ stimulate the activity of soil microorganisms, affecting the carbon turnover rate and its stability. These findings provide important evidence of SOC responses to variations in pore space gaseous O₂.

Background and aims

Worldwide wind speed decline (i.e., global terrestrial stilling) and rapid forest fragmentation have been widely documented. The internal hydrothermal conditions within fragmented forests are particularly susceptible to wind speed changes, potentially influencing carbon emissions through soil respiration. However, the qualitative and quantitative effects of the wind speed decline on soil carbon emissions in fragmented forests, as well as corresponding underlying mechanisms, remain highly uncertain.

Methods

We comprehensively investigated the influences of wind speed changes on soil respiration in a fragmented subtropical forest in Eastern China, based on field experiments and model experimental simulations using the Community Land Model version 5 (CLM5).

Results

Wind speed decreased by 0.09 m s⁻¹ decade⁻¹ from late 1950s to early 2020s at the fragmented forest site and resulted in an increase in soil respiration of 4.14 g C m⁻² decade⁻¹, consisting of a 5.83 g C m⁻² decade⁻¹ increase in heterotrophic respiration and a 1.85 g C m⁻² decade⁻¹ decrease in autotrophic respiration. Although CLM5 accurately simulated seasonal soil respiration dynamics, it clearly underestimated the wind speed decline-induced increases in soil respiration. Observations indicated that the negative impact of wind speed on soil carbon emissions was driven by the desiccating microclimate created by dry external air brought in by the wind, while CLM5 proposed wind-induced cooling caused by increased latent heat loss, i.e., primarily canopy transpiration.

Conclusion

This study quantitatively evaluates for the first time the impact of declining wind speed on soil respiration in fragmented forests of eastern China, providing valuable insights for future model improvements.

Background and aims

Phytoremediation is an environment friendly, sustainable, and aesthetically pleasing technology for remediating heavy metal polluted soil. Earthworms are ubiquitous macrofauna in the soil ecosystem that play an important role in maintaining soil health and fertility. However, the understanding of earthworms' effect on phytoremediation remains limited.

Methods

In a greenhouse experiment, Lolium multiflorum was subjected to three levels of cadmium (0, 20, or 100 mg kg⁻¹) fully crossed with two levels of earthworm treatments (i.e., with or without Eisenia foetida Savigny).

Results

Plant growth was inhibited while the root-shoot ratio and nitrogen accumulation in shoots were increased under 100 mg kg⁻¹ cadmium. Earthworms interacted with cadmium level to affect the total phosphorus content in soil. Furthermore, earthworms enriched specific microorganisms and significantly influenced bacterial communities under 0 and 20 mg kg⁻¹ cadmium. We observed a significant enrichment of specific microbial species in cadmium polluted soil when earthworms were present. Earthworms’ presence increased the sensitivity of fungal communities in soils polluted with cadmium.

Conclusions

Both earthworms and cadmium had certain impacts on the growth of plants, soil properties and microbial communities in root-zone soil. Moreover, the results suggest that earthworms may alleviate some negative effects of cadmium on soil microorganisms. The findings highlight the effect of earthworm on plant performance, soil properties, and root-zone microbial communities under cadmium stress, providing valuable insights into its role in phytoremediation of soils polluted with metals.

Aims

Salt stress presents a significant impediment to crop growth and development. However, the effects of indigenous arbuscular mycorrhizal fungi (AMF) and the addition of exogenous AMF on soybean growth strategies under salt stress remain poorly understood. The purpose of this study was to examine the impact of different AMF sources on soybean growth strategies under salt stress conditions.

Methods

In this study, we established three different salt stress gradients (1, 2, and 4 g NaCl kg⁻¹ soil) along with two AMF treatments (indigenous AMF and added exogenous AMF) to evaluate soybean growth parameters, enzymes, and soil indicators.

Results

Under salt stress, exogenous AMF significantly increased mycorrhizal colonization in soybean, resulting in a notable enhancement in phosphorus (P) and potassium (K) concentration while reducing nitrogen (N) absorption. Additionally, the addition of exogenous AMF demonstrated the capacity to enhance soybean salt tolerance by lowering soybean sodium (Na) and malondialdehyde (MDA) content, catalase (CAT) activity, and increasing K⁺/Na⁺ ratio and acid phosphatase (A-Pase) activity. In contrast, in the indigenous AMF treatment, rhizosphere A-Pase activity in soybean exhibited predominantly positive correlations with each trait, and the K⁺/Na⁺ ratio relied more on mycorrhizal colonization and CAT activity. Soybean biomass was influenced both directly and indirectly, with the K⁺/Na⁺ ratio serving as a crucial pivot in the indirect pathway.

Conclusions

The addition of exogenous AMF can enhance soybean salt tolerance by regulating nutrient and sodium absorption, enzyme activity, and MDA content. Meanwhile, indigenous AMF promotes salt tolerance in soybeans by global regulating trait associations.

Aims

One of the most important questions of our time is how ecosystems will be transformed by climate change. Here, we used a five-year field experiment to investigate the effects of climate warming on the cover and function of a sub-Arctic alpine ecosystem in the highlands of Iceland dominated by biocrust, mosses and vascular plants.

Methods

We used Open Top Chambers (OTCs) to simulate warming; standard surface and Normalised Difference Vegetation Index (NDVI) analyses to measure plant cover and function; gas analyzers to monitor biocrust respiration; and the Tea Bag Index approach to estimate mass loss, decomposition and soil carbon stabilization rates.

Results

Contrary to our initial hypothesis of warming accelerating an ecological succession of plants growing on biocrust, we observed a warming-induced decreased abundance of vascular plants and mosses —possibly caused by high temperature summer peaks that resemble heat waves— and an increase in the cover of biocrust. The functional responses of biocrust to warming, including increased litter mass loss and respiration rates and a lower soil carbon stabilization rates, may suggest climate-driven depletion of soil nutrients in the future.

Conclusion

It remains to be studied how the effects of warming on biocrusts from high northern regions could interact with other drivers of ecosystem change, such as grazing; and if in the long-term global change could favor the growth of vascular plants on biocrust in the highlands of Iceland and similar ecosystems. For the moment, our experiment points to a warming-induced increase in the cover and activity of biocrust.

Background and aims

The domestication of modern crop cultivars involved significant changes in key agronomic traits relative to their wild relatives. This study aimed to investigate the effects of crop domestication on leaf phosphorus (P)-use strategies, particularly photosynthetic P-use efficiency (PPUE), under low plant-available soil P conditions.

Methods

Ten crop species and their wild relatives were grown in pots under low plant-available soil P conditions to compare leaf PPUE, the concentration and percentage of five leaf P fractions, and investigate the correlation of these P fractions with PPUE.

Results

Domesticated crops exhibited significantly higher area-based (A_area) and mass-based (A_mass) photosynthesis rate, and PPUE (63%, 74% and 69%, respectively) than their wild relatives under low plant-available P condition. Domesticated crops demonstrated a 49% higher metabolite-P concentration but an 18% lower lipid-P concentration than their wild relatives. Domestication significantly reduced P allocation to lipid-P (20%) and inorganic-P (9%), coupled with increased partitioning to metabolite-P (67%) and residual-P (43%). PPUE was positively correlated with A_area, A_mass, metabolite-P concentration, and the percentage of leaf P allocated to the metabolite-P fraction, while being negatively correlated with leaf P concentration, nucleic acid-P, inorganic-P concentration, and the percentage of leaf P allocated to inorganic-P fraction.

Conclusion

Crop domestication enhanced PPUE by increased photosynthesis rates and a shift in leaf P allocation to different P fractions. Greater allocation to P-containing metabolites but reduced investment in inorganic P provide crucial mechanistic insights for enhanced PPUE under P-limited condition, unravelling strategies aimed at improving crop P-use efficiency under low-limited environment.

Background and aims

The degradation of Moso bamboo (Phyllostachys edulis) forests was reported to dominate soil organic carbon (SOC) accumulation via primarily increased litterfall and root secretions. However, to what extent degradation affects SOC fractions and the mechanisms underlying different degraded durations for SOC stability remain uncertain.

Methods

The vegetation spatial structure, basic soil physiochemical properties, SOC and its components, and microbial traits in four degradation categories of Moso bamboo forests were analyzed. Multiple statistical analyses were further conducted to explore the underlying mechanisms controlling the changing SOC pool size and stability under degradation.

Results

Significantly higher SOC pools (5.40% to 33.62%) and POC/SOC ratios (11.26% to 30.68%), lower MAOC/SOC ratios (5.93% to 18.28%), and thus SOC stability, were reduced by degradation. Degraded Moso bamboo forests had higher age mingling (18.17%), more aggregated distribution (35.76%), and more intense competition (48.87%). This impacted increases in C inputs into soil from aboveground plants and, therefore, increased SOC and POC contents in the topsoil. Moreover, degradation reduced bacterial diversity and shifted the community from K- to r-strategists; fungal diversity remained unaffected, and saprotrophic fungi (r-) dominated the fungal community composition in soil. Consequently, microorganisms were highly involved in the shift from MAOC to POC, with implications for bacterial community diversity, life-history strategy, and increasing saprotrophic fungi. These alterations led to increased SOC storage but decreased its stability.

Conclusions

Overall, degradation-induced changes in plants, microbial communities, SOC fractions, and SOC stability are key processes for understanding plant-soil interactions under global change.