BackgroundPlant invasion affects plant community composition, biodiversity, and nutrient cycling in terrestrial ecosystems, particularly in vulnerable ecosystems. As an invasive parasitic plant, Cassytha filiformis has caused extensive damage to the native vegetation of the Paracel Islands. However, the effects of C. filiformis invasion on litter decomposition and nutrient release in native plant communities remain unclear. We conducted an in-situ decomposition experiment in native plant communities on a coral island to explore the litter decomposition dynamics varying across enzyme activities, soil properties and C. filiformis invasive degrees.ResultsThe mass loss of litter was determined during the decomposition process. The data showed that litter mass loss under severe invasion was significantly lower than in uninvaded sites after nine months of decomposition. The invasion of C. filiformis accelerated the nitrogen release and lignin decomposition with increased litter quality and polyphenol oxidase activity. Besides, soil phosphorus availability and potassium content also induced the oxidase activity. Meanwhile, the decomposition of litter organic carbon was delayed because beta-1, 4-glucosidase activity was low in the first six months. Besides, peroxidase activity maintained a high level in invasive plots, indicating that the residues of C. filiformis may have allelopathy.ConclusionOur results suggested that the invasion of C. filiformis accelerated litter mass loss and element release on coral islands by regulating litter quality and enzyme activity. However, the short-term rapid litter decomposition may result in nutrient loss, which is not conducive to the growth of native plants.

Urgent action is needed in the Amazon to halt deforestation, repair agricultural damage, and restore forests to revive ecosystemic functions such as carbon (C) storage and soil health. A critical and demanding challenge, especially in sandy soils, is ceasing the slash-and-burn in smallholder farming livelihoods to preserve ecosystem services of primary and secondary forests. Here, we examined (i) the recovery of secondary forests in structure, litter layer, and soil health, as well as C storage post-agricultural abandonment of extremely sandy Amazonian soils (> 89 % sand), and (ii) the extent of loss of these gains when a secondary forest is burned for agricultural reconversion. We tracked secondary forests at 2, 5, 10, and 20 years, including slash-and-burning the 20-year-old forest. Our methods included analyzing C stocks in soil, litter, and plants, forest vegetation ecological indexes, litter quality assessed through nitrogen (N), C, and lignocellulose contents, delta C-13 to indicate organic matter origin, and seven additional soil health indicators. Soil delta C-13 ranged from-27.1 to-28.8 parts per thousand across the sites, indicating a negligible influence of tropical grasses on the soil's organic matter and suggesting that pastures were not previously cultivated in these areas. Secondary forest growth accumulated 0.24 and 2.97 Mg C ha(- 1 )y(- 1 ) in litter and trees, respectively. Yet, soil C stocks did not show significant changes during 20 years of forest regeneration. Over 18 years, the forest increased the vegetation diversity fourfold and litter N by 41 %, improving forest structure and litter quality. This progress in organic matter aboveground contributed to improved soil biological activity and nutrient storage, facilitating soil health and multifunctionality regeneration as the forest aged. However, slash-and-burn resulted in a 67.6 Mg C ha(- 1 ) loss, reverting levels below those of the 2-year-old forest. Returning to agriculture also depleted soil cation exchange capacity, bulk density, and fauna activity, degrading soil's chemical, physical, and biological functions to levels comparable to or worse than those in the youngest forest. We conclude that Amazonian lands abandoned after long-term agriculture still offer potential for ecological restoration, with secondary forests capable of regenerating multiple ecosystem functions, even in sandy soils. However, a single slash-and-burn reverses 20 years of progress and degrades soil health further. Recognizing smallholder farmers' poverty and reliance on slash-and-burn, we advocate for educational and socioeconomic support to stop fires and encourage sustainable agriculture, including bioeconomy incentives and environmental compensation to sustain the perpetuation and benefits of secondary forests in the Amazon.

Background and aims Vascular plants and moss biocrusts are known to coexist in drylands, wherein vascular plant cover is known to be a major influencing factor for biocrusts development. Vascular plants produce litter which may affect moss biocrusts when covering them. However, to which extent the cover of litter may affect the physiology, e.g., photosynthetic activity, of moss biocrusts remains poorly understood.MethodsWe studied the effect of the litter covering on biocrust-forming mosses on the northern Chinese Loess Plateau over four-month period. We used litter from shrubs of Artemisia ordosica and Caragana korshinskii with two levels of litter thickness, and monitored moss greenness, and several indicators of moss physiological activity.ResultsLitter covering reduced moss greenness, content of chlorophyll a and b, soluble sugar, and soluble protein, suggesting a reduced photosynthetic and metabolic activity of mosses under litter cover. On the other hand, mosses covered by litter showed higher contents of malondialdehyde, proline, and catalase activity compared to those mosses without any litter cover, suggesting that litter covering increased oxidative stress in mosses and triggered a protective response against oxidative damage. Moreover, we found litter thickness exerted a more significant impact on the physiological indices of mosses than litter type.ConclusionsOur results demonstrate the detrimental effects of litter covering on the physiological activity of biocrust-forming mosses. The findings provide a mechanistic understanding of the reductions in mosses in ecosystems with high shrub cover, highlighting the importance of litter in mediating the relationships between moss biocrusts and shrub patches.

Forest litter decomposition is vital for nutrient cycling and carbon turnover. To investigate their decomposition rate, we conducted a litter bag experiment in plantation forests (PF) and natural forests (NF) in a subtropical ecosystem. Our findings showed significant seasonal variation in litter mass loss (p < 0.0001) between the two sites, indicating seasonality as the main driver of decomposition. The decay rate constant (k) expressed in day(-)(1), reflecting the fraction of litter mass lost per day due to decomposition, reveals that NF has higher k value of 0.007 day(-)(1) than PF at 0.005 day(-)(1) , indicating faster decomposition in NF. This constant is essential for predicting litter breakdown duration, highlighting decomposition dynamics between sites, suggesting that even minimal distances between forest types can affect organic matter breakdown. In both sites, litter mass loss varied significantly from the initial to the final year (p < 0.001), with peak rates during the monsoon, followed by pre-monsoon and dry periods. Mixed litter in NF experienced a 99.94 % loss after 730 days, while PF, saw 97.80 % loss. Carbon, lignin, nitrogen, and potassium concentrations were higher during the monsoon and pre-monsoon seasons at both sites. Except for phosphorus in PF, all soil parameters positively correlated with mass loss, along with litter parameters C, N, P, K, and lignin (p < 0.001). Litter decomposition was higher in NF than PF, with significant seasonal effects (p < 0.0001), highlighting seasonality over litter mixture effects. Understanding climate variability and species diversity is essential for sustainable forest management amid ongoing anthropogenic land-use changes.

Organic inputs from aboveground litter and underground roots are an important factor affecting nutrient cycling in forest ecosystems. However, we still know little about the seasonal effects of the interaction between aboveground and underground organic inputs on soil organic carbon, nutrients and microorganisms after vegetation restoration in degraded red soil. Therefore, we focused on a mixed forest dominated by Schima superba and Pinus massoniana that had been restored for 27 years on eroded and degraded red soil in a subtropical region. Five treatments were set as follows: retaining aboveground litter + retaining root + retaining mycorrhizae (LRM, control treatment), doubling aboveground litter + retaining root + retaining mycorrhizae (DLRM), removing aboveground litter + retaining root + retaining mycorrhizae (NRM), removing aboveground litter + removing root + retaining mycorrhizae (NNM), and removing aboveground litter + removing root + removing mycorrhizae (NNN). After more than three years of treatment, DLRM, NRM, NNM, and NNN treatments reduced soil moisture content by 32.0-56.8 % in the rainy season compared with the LRM treatment. Soil total nitrogen and ammonium nitrogen concentrations were the highest in the DLRM treatment. Soil ammonium concentration and pH were higher in the rainy season than those in the dry season, while soil nitrate concentration was higher in the dry season. Soil available phosphorus concentration in the dry season decreased by 64.5 % in the DLRM treatment, while they were 2.0-10.7 times of those in the LRM, NRM, NNM, and NNN treatments compared to the rainy season. Soil microbial communities were dominated by bacteria across treatments, accounting for 74.0-75.5 % of the total phospholipid fatty acid (PLFA) of soil microbes, and there was no significant difference among treatments. Except for fungi, the total PLFAs of soil microorganisms and the PLFA content of each microbial taxon were higher in the dry season than those in the rainy season. The F/B value in the rainy season was higher than that in the dry season. The PLFA contents of gram-positive bacteria and actinomyces in the DLRM and NRM treatments were higher than those in the NNM treatment, and PLFA contents of both in the dry season were 1.5 and 1.6 times of those in the rainy season, respectively. Soil total phosphorus and pH had the highest contribution to soil microbial community changes in rainy and dry seasons, respectively. Comprehensive evaluation showed that double aboveground litter addition was more conducive to soil quality improvement. In conclusion, litter, roots and mycorrhiza manipulations affected the PLFA contents of soil microorganisms through the regulation of soil physicochemical properties, rather than the proportions of each microbial taxon in the total PLFAs, which was related to the season. The results can provide a theoretical basis for soil quality improvement as driven by soil microorganisms during the restoration of degraded red soil.

Allelopathy is an underlying and controversial mechanism for detrimental environmental effects in the management of Eucalyptus plantations. However, little attention has been paid to the dynamics of allelochemicals and phytotoxicity in soil fauna during litter decomposition. To explore the relationship between the dynamics of phytotoxicity and allelochemicals, a decomposition experiment was conducted using 4-year-old and 8-year-old Eucalyptus grandis litter (0, 10, 20, 30, and 45 days). The acute toxicity of Eisenia fetida was assessed, and a chemical analysis of the eucalyptus leaves was performed. Biochemical markers, including total protein, acetylcholinesterase (AChE) activity, and oxidative stress levels (SOD and MDA) were measured. A comet assay was used to determine DNA damage in E. fetida cells. The results showed that after 20-30 days of decomposition, E. grandis litter exhibited stronger phytotoxic effects on E. fetida in terms of growth and biochemical levels. After 20 days of decomposition, the weight and total protein content of E. fetida first decreased and then increased over time. SOD activity increased after 20 days but decreased after 30 days of decomposition before increasing again. MDA content increased after 20 days, then decreased or was stable. AChE activity was inhibited after 30 days of decomposition and then increased or stabilized with further decomposition. Soluble allelochemicals, such as betaine, chlorogenic acid, and isoquercitrin, significantly decreased or disappeared during the initial decomposition stage, but pipecolic acid significantly increased, along with newly emerging phenolic fractions that were present. More allelochemicals were released from 8-year-old litter than from 4-year-old E. grandis litter, resulting in consistently more severe phytotoxic responses and DNA damage in E. fetida. Scientific management measures, such as the appropriate removal of leaf litter in the early stages of decomposition, might help support greater biodiversity in E. grandis plantations.

We tested the hypothesis that the number of seedlings from the soil seed bank (SSB) in forests polluted by heavy metals and disturbed by recent fires decreases. It was also assumed that the consequences of pollution and fires for the soil seed bank are additive. We estimated the number of seedlings from the SSB of pine forests located near the Karabash copper smelter (KCS) (contaminated by Cu, Zn, Pb, and Cd) and from uncontaminated forests of the Ilmen State Reserve (ISR). In both areas, samples of the forest litter and humus horizon were taken from forests recently exposed to ground fires and long-term unburned forests. Samples were exhibited from June to September, conducting seven rounds of counting seedlings. Small peculiarities of the emergence of seedlings on the samples of the forest litter and the humus horizon were established. However, the regularities of the reaction of SSB to pollution and fire disturbances did not depend on the soil horizon. The number of seedlings on substrates from contaminated forests was 5-8 times lower than the number of seedlings on substrates from background forests. A decrease in the number of seedlings on polluted substrates was accompanied by an increase in the share of dicots in the total number of seedlings. The relationship between the number of seedlings and the age of fires was not found. The additivity of the consequences of pollution and fires has also not been established. Of the two types of damage, pollution and fires, the pollution factor is of leading importance for SSBs. The results indicate a low recovery capacity of the herb-shrub layer of polluted forests.

The decomposition of returned straw is increasing facing the negative impacts by metal nanoparticles (NPs), however, which may be modulated by soil fauna and this modulation effect is unclear. Here, the interactive effects of ZnO NPs with soil fauna on wheat straw decomposition were investigated in a potted rice cropping system. The results showed that ZnO NP below middle concentrations did not significantly influence straw decomposition, and mass loss was mainly driven by microfauna and microbes. High concentrations of ZnO NPs significantly impeded decomposition, mainly by reducing the complexity of fungal communities. This negative effect was ascribed to the promotion of Zn solubilization by bacterial taxa such as unclassified Acidobacteria, Bacteroidetes and Gemmatimonadetes. ZnO NPs had a greater impact on soil microorganisms than on fauna, reduced microbial activity, promoted the released straw nutrients entering into the soil by damaging nutrient transferring microorganisms and dominated the effects on soil stoichiometry. However, soil fauna significantly increased the activities of C- and N-releasing enzymes, decreased the activity of P-releasing enzymes, regardless of ZnO NP concentration, and promoted straw C decomposition. ZnO NPs altered soil microbial community composition, but these changes were modulated by soil fauna. Nonetheless, nutrient transport by fungi such as Ascomycota and Zygomycota and grazing by fauna were the predominant modulators on straw stoichiometry. The results of this study revealed that rational control of soil fauna will be helpful for promoting straw decomposition and efficient recycling of straw nutrients by crops under ZnO NP contamination. High ZnO NP concentrations inhibit straw decomposition mainly by reducing diversity of fungal community.The negative effects of ZnO NPs are ascribed to Zn solubilization by bacterial taxa such as unclassified Acidobacteria, Bacteroidetes and Gemmatimonadetes.ZnO NPs have greater impact on soil microorganisms than on fauna, reduce microbial activity, promote the released nutrients into soil and dominate the effects on soil stoichiometry.Fungal transport (e.g., Ascomycota and Zygomycota) and fauna grazing are the predominant modulators on straw stoichiometry.

In cocoa agroforestry systems, cycling of leaves, pods, and branches are key for organic matter sustenance. We investigated annual total litterfall, annual nutrient stocks in total litterfall, cocoa pods and beans, as well as cocoa leaf decomposition rates in cocoa agroforestry systems under conventional and organic management in Suhum Municipality, Eastern Region of Ghana. The study was conducted using six cocoa agroforests for each management selected from a total of four villages. Litterfall was collected monthly using litterboxes and a litterbag technique was employed to study the rates of leaf decomposition and nutrient release for 12 months. In June and July, total litterfall in organic farms were 94% and 65%, respectively, higher than in conventional farms, but management had no effect on average annual total litterfall of 8.8 t ha-1 yr-1 litterfall. Due to the trees' reduced transpiration, 61% of the annual total litterfall occurred during the dry season. Whereas average leaf litter nitrogen (N) concentration was 17% higher in the rainy season than dry season, potassium (K) concentration was 38% higher during the dry season than rainy season. This likely reflected the contribution of N rich green leaves to litterfall in the rainy season and plant coping strategy to drought leading to K accumulation. Cocoa leaf decomposition was not affected by management. Annual potassium (K) and calcium (Ca) stocks in cocoa pod husk were four and nine-fold, respectively, higher than in cocoa beans. We conclude that organic versus conventional management had no effect on litterfall and cocoa leaf decomposition rather season influenced litterfall quantity and chemistry. Irrespective of management the spreading of cocoa pod husk after harvest will improve internal nutrient cycling in cocoa agroforestry systems.

Recent studies have highlighted the crucial role of abiotic processes, such as photodegradation and microclimatic fluctuation, in accelerating dryland litter decomposition. In grasslands, substantial amounts of dead plant material persist upright above the soil surface after senescence, experiencing distinct microclimatic conditions compared to surface litter. However, our understanding of how ultraviolet (UV) exposure and microclimatic conditions influence their decomposition is limited. To address this knowledge gap, we conducted a field experiment manipulating UV radiation for both soil surface litter and standing litter and monitored their microclimatic conditions in a semi-arid grassland. Our findings indicate that UV exposure enhanced the decomposition of soil surface litter by alleviating the constraint of lignin on litter decomposition, while having no significant influence on standing litter. Although the mean levels of thermal-hydric conditions were lower, more intense fluctuation of temperature and air humidity was detected in standing litter. These higher-level microclimatic fluctuations facilitated the release of dissolved organic carbon, potentially increasing the availability of labile substrates to microbes. Meanwhile, standing litter released more photo-sensitive phenols, leading to decreased sensitivity to UV exposure. Consequently, while UV exposure initially increased standing litter decomposition during the early stage, its influence eventually diminished. These findings underscore the critical yet differing roles of microclimatic conditions and UV exposure in the decomposition of standing and surface litter. Relying solely on knowledges derived from surface litter decomposition and microclimate conditions may not accurately capture the patterns of grassland litter degradation. The limited precipitation in drylands is widely believed to restrict litter decomposition. However, the observed litter decomposition rates in these regions often exceed model predictions based on climatic conditions. In arid and semi-arid steppes, the sparse vegetation cover results in intense ultraviolet (UV) radiation reaching soil surface, thereby triggering photodegradation of the recalcitrant compounds in litter. Additionally, substantial dead plant materials persist standing for months to years, and undergoes more intense warm-cold and wet-dry cycles. However, there have been limited studies assessing the intricate interplay between UV radiation and microclimate fluctuations on litter decomposition in drylands. In this study, we found that UV radiation facilitated the degradation of recalcitrant compounds and enhanced litter degradability of soil surface litter. More intense temperature and humidity fluctuations increased the concentration of dissolved organic carbon in standing litter. This increase could provide more labile substrate to decomposers, consequently accelerating litter decomposition. Moreover, microclimatic fluctuation enhances the loss of photo-sensitive compounds in litter, reducing litter's sensitivity to UV exposure. Our study highlighted the significant role played by the interaction between climatic conditions and UV radiation in driving litter decomposition in water-limited steppes, contributing to a better understanding of carbon turnover in dryland ecosystem. The degradation of soil surface litter was mainly driven by warmer and wetter microclimate and ultraviolet (UV) exposure Greater microclimatic fluctuation in standing litter enhanced the release of dissolved labile carbon, thereby accelerating its decomposition Greater microclimatic fluctuation increased the loss of photo-sensitive compound and weakened sensitivity of standing litter to UV radiation