Soil Nutrient Cycling Research Articles

The long-term uncertainty of biodegradable mulch film residues and associated microplastics pollution on plant-soil health.

Biodegradable mulch film potentially offers an encouraging alternative to conventional (petroleum-based) plastic films. Since biodegradable films are more susceptible to rapid degradation, more microplastics (MPs) are likely to be generated than conventional films within the same time frame, probably leading to more severe MPs pollution and associated effects. However, the effect of biodegradable mulch film residues and associated MPs pollution on plant-soil health remains uncertainty. Here, we evaluated the potential effect of bio-MPs pollution on soil carbon (C) and nutrient (i.e., N and P) cycling, soil biology (microorganisms and mesofauna), and plant health, as these are crucial to agroecosystem functioning and the delivery of key ecosystem services. Unlike the inert (and therefore recalcitrant) C contained within petroleum-based MPs, at least 80% of the C from bio-MPs is converted to CO2, with up to 20% immobilized in living microbial biomass (i.e., < 0.05tC ha-1). Although biodegradable films are unlikely to be important in promoting soil C storage, they may accelerate microbial biomass turnover in the short term, as well as CO2 production. Compared to conventional MPs, bio-MPs degradation is more pronounced, thereby inducing greater alterations in microbial diversity and community composition. This may further alter N2O and CH4 emissions, and ultimately resulting in unpredictable consequences for global climate warming. The extent to which this may occur, however, has yet to be shown in either laboratory or field studies. In addition, bio-MPs have a large chance of forming nanoplastics, potentially causing a stronger toxic effect on plants relative to conventional MPs. Consequently, this would influence plant health, crop productivity, and food safety, leading to potential health risks. It is unclear, however, if these are direct effects on key plant processes (e.g. signaling, cell expansion) or indirect effects (e.g. nutrient deficiency or acidification). Overall, the question as to whether biodegradable mulch films offer a promising alternative to solve the conventional plastic legacy in soil over the long term remains unclear.

A test of the mycorrhizal-associated nutrient economy framework in two types of tropical rainforests under nutrient enrichments

Shifts in tree species and their mycorrhizal associations driven by global change play key roles in biogeochemical cycles. In this paper, we proposed a framework of the mycorrhizal-associated nutrient economy (MANE), and tested it using nutrient addition experiments conducted in two tropical rainforests. We selected two tropical rainforests dominated by arbuscular mycorrhizal (AM) and ectomycorrhizal (ECM) trees, and established eighteen 20 ​m ​× ​20 ​m plots in each rainforest. Six nitrogen (N) and phosphorus (P) addition treatments were randomly distributed in each rainforest with three replicates. We examined the differences in soil carbon (C) and nutrient cycling, plant and litter productivity between the two rainforests and their responses to 10-year inorganic N and P additions. We also quantified the P pools of plants, roots, litter, soil and microbes in the two rainforests. Overall, distinct MANE frameworks were applicable for tropical rainforests, in which soil C, N and P were cycled primarily in an inorganic form in the AM-dominated rainforest, whereas they were cycled in an organic form in the ECM-dominated rainforest. Notably, the effects of mycorrhizal types on soil P cycling were stronger than those on C and N cycling. The intensified N and P deposition benefited the growth of AM-dominated rainforests instead of ECM-dominated rainforests. Our findings underpin the key role of mycorrhizal types in regulating biogeochemical processes, and have important implications for predicting the ecological consequences of global changes.

The potential impact of future climate change on the production of a major food and cash crop in tropical (sub)montane homegardens

Tropical agroforestry systems support the wellbeing of many smallholder farmers. These systems provide smallholders with crops for consumption and income through their ecological interactions between their tree, soil, and crop components. These interactions, however, could be vulnerable to changes in climate conditions; yet a reliable understanding of how this could happen is not well documented. The aim of this study is to understand how tree-soil-crop interactions and crop yield are affected by changes in climate conditions, which has implications for recognising how these systems could be affected by climate change. We used a space-for-time climate analogue approach, in conjunction with structural equation modelling, to empirically examine how warmer and drier climate conditions affects tree-soil-crop interactions and banana yield in Mt. Kilimanjaro's homegarden agroforest. Overall, the change in climate conditions negatively affected ecological interactions in the homegardens by destabilizing soil nutrient cycles. Banana yield, however, was mainly directly influenced by the climate. Banana yields could initially benefit from the warmer climate before later declining under water stress. Our findings imply that under increasingly warmer and drier climate conditions, homegarden agroforestry may not be a robust long-term farming practice which can protect smallholder's wellbeing unless effective irrigation measures are implemented.

Different Response of Soil Microbial Carbon Use Efficiency in Compound of Feldspathic Sandstone and Sand

The stoichiometry of efficient soil microbial carbon use is a sensitive index for measuring changes in soil quality and plays a crucial role in research on ecological stoichiometry in the soil nutrient cycle. To further understand the effect of feldspathic sandstone and sand compound ratios on microbial carbon use efficiency (CUE), we simulated the field conditions of the feldspathic sandstone-sand compound layer in the Mu Us sandy land and analyzed the soil C:N:P ratio, microbial biomass, extracellular enzyme activity, and microbial carbon use efficiency in soils with different compound ratios. The results demonstrated that an increase in the feldspathic sandstone content had insignificant effects on the soil C:N:P ratio. The maximum values for microbial biomass nitrogen (MBN) and microbial biomass phosphorus (MBP) were observed at compound ratios of 1:5 and 1:2, respectively. Calculations of microbial carbon use efficiency and vector analysis revealed that the microbial carbon use efficiency increased as the feldspathic sandstone content increased, P limitation existed in all compound soils, and soil with a 1:1 compound ratio may be substantially less limited. In conclusion, our research indicated that adding feldspathic sandstone to sand improved soil quality, and the compound ratio affected soil microorganisms; nevertheless, it did not significantly change soil nutrient restriction. Our study provides a theoretical basis for the development and utilization of desert land resources.

Spatial patterns of dominant bacterial community components and their influential factors in the southern Qinling Mountains, China.

Soil bacteria not only maintain the biodiversity of forest ecosystems but also affect soil nutrient cycling and ecosystem function. Nonetheless, the spatial pattern and patchy distribution of dominant bacterial community components in soil are still rarely explored. The spatial pattern and distribution of the dominant bacterial community components and their influential factors were investigated using traditional statistics, geostatistics, and kriging spatial interpolation methods in the Huoditang region of the Qinling Mountains, China. The dominant bacterial phyla were Proteobacteria, Acidobacteria, Chloroflexi, Rokubacteria, Actinobacteria, and Verrucomicrobia in this region. Among the bacterial phyla, Proteobacteria occupied an area of 2.56 km2 (the greatest) in the highest patch category, followed by Planctomycetes. Moreover, among the lowest patch category, Firmicutes occupied the lowest area (11.93 km2). The results of kriging maps showed that the dominant bacterial group presented "peak," "bimodal," and "multimodal" distributions in Huoditang. Proteobacteria, Acidobacteria, Chloroflexi, Gemmatimonadetes, Nitrospirae, and ASV (amplicon sequence variants) had significant spatial autocorrelation (< 0.68 km). Variance partitioning analysis confirmed that soil nutrients (36.5%) were the significant driving factors shaping the bacterial community structure, followed by environmental factors (28.2%) and topographic factors (7.8%). Furthermore, pH (9.1%), soil organic carbon (SOC, 6.6%), available phosphorus (AP, 4.7%), and elevation (3.9%) were the most important driving factors for the spatial distribution of bacterial community groups in the Huoditang Forest of the Qinling Mountains. The findings provide a new perspective for studying the spatial distribution characteristics and driving factors of dominant soil bacterial community components in subtropical forest ecosystems.

Grassland Degradation Has Stronger Effects on Soil Fungal Community Than Bacterial Community across the Semi-Arid Region of Northern China.

Soil microbes play crucial roles in grassland ecosystem functions, such as soil carbon (C) pool and nutrient cycle. Soil microbes in grasslands are susceptible to the degradation mediated by climate change and anthropogenic disturbance. However, research on how the degradation influences the diversity and community structure of different soil microbial taxa is relatively scarce. We conducted a large-scale field survey to describe the effects of four degradation levels (PD: potential degradation, LD: light degradation, MD: moderate degradation, and SD: severe degradation) on soil bacterial and fungal community in the semi-arid grasslands of northern China. We found that soil moisture, nutrients, and clay content decreased, but soil sand content increased along the increasing degradation gradient. However, the degradation had no effects on soil pH and the C:N ratio. Grassland degradation had non-significant effect on soil bacterial diversity, but it significantly affected soil bacterial community structure. The degradation decreased soil fungal diversity and had a relatively larger influence on the community structure of soil fungi than that of bacteria. The community composition and structure of soil fungi were mainly affected by soil nutrients and texture, while those of soil bacteria were mainly affected by soil pH. These results indicate that changes in soil properties induced by grassland degradation mainly drive the variation in the soil fungal community and have less effect on the soil bacterial community. This study reveals the sensitivity of soil fungal community to grassland degradation, highlighting the priority of soil fungal community for the management and restoration of degraded grasslands.

A research agenda for nonvascular photoautotrophs under climate change.

Nonvascular photoautotrophs (NVP), including bryophytes, lichens, terrestrial algae, and cyanobacteria, are increasingly recognized as being essential to ecosystem functioning in many regions of the world. Current research suggests that climate change may pose a substantial threat to NVP, but the extent to which this will affect the associated ecosystem functions and services is highly uncertain. Here, we propose a research agenda to address this urgent question, focusing on physiological and ecological processes that link NVP to ecosystem functions while also taking into account the substantial taxonomic diversity across multiple ecosystem types. Accordingly, we developed a new categorization scheme, based on microclimatic gradients, which simplifies the high physiological and morphological diversity of NVP and world-wide distribution with respect to several broad habitat types. We found that habitat-specific ecosystem functions of NVP will likely be substantially affected by climate change, and more quantitative process understanding is required on (1) potential for acclimation, (2) response to elevated CO2 , (3) role of the microbiome, and (4) feedback to (micro)climate. We suggest an integrative approach of innovative, multimethod laboratory and field experiments and ecophysiological modelling, for which sustained scientific collaboration on NVP research will be essential.

Rice-Based Integrated Farming System for Sustainable Coastal Agroecosystem of India

In comparison to industrial expansion, agriculture growth in recent years has been extremely slow. Future food demand is being impacted by the declining production of primary crops. Due to a modest shift of acreage for other purposes mainly industrialization and urbanization, net sown area in India has slightly declined in last two decades. A holistic approach is urgently required to generate positive growth rates in agriculture, particularly in coastal ecosystems. Sustainable agriculture aims to preserve the basis of natural resources, safeguard the environment, and promote wealth over a longer period. A farming system is a collection of agro-economic activities that interact and are connected in a specific agroecosystem. The term “Integrated Farming Systems” (IFS) refers to a strategic combination of one or more enterprise with crop production that produces complementary results through efficient waste and crop residue recycling and generates extra sources of income for farmers. The interdependent, connected, and interlinking production systems based on crops, animals, and related ancillary professions are what make up the IFS activity. Abundance of species diversity aids in improving soil health especially organic carbon, besides enhances ecological conditions, both of which are necessary for long-term sustainability of production system. Additionally, it inhibits the spread of pests and improves soil nutrient cycling. IFS approach with site-specific models offers gainful employment and is extremely profitable and sustainable in all environments. Along with IFS, other practices that promote fertilizer use efficiency include agroforestry, integrated nutrient management, and soil and water conservation.

Impacts of maize hybrids with different nitrogen use efficiency on root-associated microbiota based on distinct rhizosphere soil metabolites.

Plant genotypes shape root-associated microbiota that affect plant nutrient acquisition and productivity. It is unclear how maize hybrids modify root-associated microbiota and their functions and relationship with nitrogen use efficiency (NUE) by regulating rhizosphere soil metabolites. Here, two N-efficient (NE) (ZD958, DMY3) and two N-inefficient (NIE) maize hybrids (YD9953, LY99) were used to investigate this issue under low N (60 kg N ha-1 , LN) and high N (180 kg N ha-1 , HN) field conditions. NE hybrids had higher yield than NIE hybrids under LN but not HN. NE and NIE hybrids recruited only distinct root-associated bacterial microbiota in LN. The bacterial network stability was stronger in NE than NIE hybrids. Compared with NIE hybrids, NE hybrids recruited more bacterial taxa that have been described as plant growth-promoting rhizobacteria (PGPR), and less related to denitrification and N competition; this resulted in low N2 O emission and high rhizosphere NO3 - -N accumulation. NE and NIE hybrids had distinct rhizosphere soil metabolite patterns, and their specific metabolites were closely related to microbiota and specific genera under LN. Our findings reveal the relationships among plant NUE, rhizosphere soil metabolites, root-associated microbiota, and soil nutrient cycling, and this information is informative for breeding NE crops.

Living grass mulching improves soil enzyme activities through enhanced available nutrients in citrus orchards in subtropical China.

Living grass mulching (LGM) is an important orchard floor management that has been applied worldwide. Although LGM can effectively enhance soil nutrient availability and fertility, its effects on microbial-mediated soil nutrient cycling and main drivers are unclear. Meanwhile, the variation of enzyme activities and soil nutrient availability with LGM duration have been rarely studied. This study aims to explore the effects of mulching age and soil layer on enzyme activities and soil nutrients in citrus orchards. In this study, three LGM (Vicia villosa) treatments were applied, i.e., mulching for eight years, mulching for four years, and no mulching (clean tillage). Their effects on the enzyme activities and soil nutrients were analyzed in different soil layers of citrus orchards in subtropical China, i.e., 0-10, 10-20, and 20-40cm. Compared to clean tillage, mulching for four years had fewer effects on enzyme activities and soil nutrients. In contrast, mulching for eight years significantly increased available nitrogen (N), phosphorus (P) nutrients, β-glucosidase, and cellobiohydrolase activities in the soil layer of 0-20cm. In the soil layer of 0-40cm, microbial biomass carbon (C), N, P, N-acetylglucosaminidase, leucine aminopeptidase, and acid phosphatase activities also increased (P < 0.05). Mulching for eight years significantly promoted C, N, and P-cycling enzyme activities and total enzyme activities by 2.45-6.07, 9.29-54.42, 4.42-7.11, and 5.32-14.91 times, respectively. Redundancy analysis shows that mulching treatments for eight and four years had soil layer-dependent positive effects on soil enzyme activities. Microbial C and P showed the most significant positive correlation with enzyme activities, followed by moisture content, organic C, and available N (P < 0.05). Available nutrients contributed almost 70% to affect enzyme activities significantly and were the main drivers of the enzyme activity variation. In summary, LGM could improve soil enzyme activities by increasing available nutrients. The promotion effect was more significant under mulching for eight years. Therefore, extending mulching age and improving nutrient availability are effective development strategies for sustainable soil management in orchard systems. Our study can provide valuable guidelines for the design and implementation of more sustainable management practices in citrus orchards.

Soil qualities and change rules of Eucalyptus grandis × Eucalyptus urophylla plantation with different slash disposals

Slash disposal changes soil quality by affecting soil properties and nutrient cycling, and the appropriate disposal approaches remain controversial. This work aimed to explore the impact of different slash disposal methods on soil qualities. For this purpose, a Eucalyptus grandis × Eucalyptus urophylla plantation that had been cultivated in 2002 and felled for the third time in 2016 was established in Hezhou City, China. Burning forest (BF, for moderate intensity fire) and no-burning forest (NF) were set in the plantation, and the native evergreen broadleaf forest near the plantation was used as the control (CK). Soils were sampled quarterly in 2017, and 27 indicators that represent soil physical, chemical, and biological properties were analyzed and compared through the analysis of the sustainability index (SI), which adopts five indices to calculate soil quality. The obtained data showed that the indicators of BF and NF, except for the total potassium content, were much lower than those of CK. The physical properties (Max-WHC, CWHC, Min-WHC, MMC, CPD, TPD) of NF were significantly better (29.07%, 30.98%, 29.61%, 52.08%, 21.89%, 19.76%) than those of BF, unlike the chemical properties of BF (SOM, TN, ACa, AFe, AMn, ACu, AZn) were significantly better than those of NF (45.61%, 81.33%, 12.78%, 23.18%, 96.13%, 144.30%, 114.04%). The enzymatic activities of NF (URE, APHO) were significantly better (43.33%, 156.58%)than those of BF, except the activities of INV (− 25.21%). Results of SI showed that the soil quality of CK was much better than that of BF, and NF the worst. But it exhibited the most unevenness of CK, followed by NF, and BF the best. The change rules of BF and NF were contrasting, and soil quality reached the same level after half a year. In summary, the soil qualities, either BF or CK, were not comparable to that of CK. BF increased the soil quality fleetly and transiently, and NF was sustainable for the eucalyptus plantation.

Micromorphology, mineralogy, and geochemistry of ferromanganese nodules in tropical soils and their impacts on heavy metal sequestration

Ferromanganese nodules (FMNs) are important products of soil-forming processes that can reflect the historical pedogenic environment and affect the elemental cycle in the soil. Despite extensive investigations on the morphology, microstructure, and components of FMNs, non-destructive observation of the 3D microstructure and elemental distribution feature of FMNs remains difficult, owing to the limitations of conventional measurement techniques and instrumental accuracy. In this study, the micromorphological, mineralogical and geochemical characteristics of FMNs in basalt-derived soils in tropical China were examined using different techniques, including scanning electron microscopy, X-ray diffraction, chemical extraction, and synchrotron radiation-based X-ray microtomography and microfluorescence mapping. Mn and Fe in FMNs were found to be inversely distributed in concentric rings, with Mn mainly enriched in the interior and Fe mainly distributed at the edge of the nodule. A line scan of the cross-section of FMNs revealed symmetrical distributions of the peak Fe and Mn contents and Fe:Mn ratios, indicating alternating dry/wet conditions and oxidation/reduction reactions during the formation of FMNs. FMNs were significantly enriched in P and various heavy metals, including Ba, Co, Cu, and Ni. The enrichment factors of P, Ba, Co, Cu, and Ni were in the range of 1.20–4.68, 8.34–27.12, 12.92–24.74, 2.51–3.55, and 2.75–3.58, respectively, reflecting the potential of FMNs to influence the soil nutrient cycle and heavy metal sequestration. Factor analysis further verified the adsorption of heavy metals by FMNs and indicated that the formation of FMNs was accompanied by an increase in Mn-bearing mineral and a decrease in phyllosilicate. Our study demonstrates that FMNs provide important information for understanding changes in pedogenic environment and heavy metal behavior in tropical soils.

Soil stoichiometry characteristics under different land use types in the Horqin Sandy Land, China

The stoichiometry characteristics of carbon (C), nitrogen (N), and phosphorus (P) is an important indicator of soil quality and ecosystem nutrient limitations. Exploring the effects of land use type and soil depth on soil nutrient stoichiometry can clarify soil nutrient cycling. In this study, we collected soil samples from sites with five different land use types (irrigated cropland, rainfed cropland, sandy grassland, fixed dunes, and mobile dunes) in the Horqin Sandy Land, and evaluated the influences of land use type and soil depth on the contents and stoichiometry characteristics of soil organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP). We found that: 1) SOC (3.23 g·kg-1), TN (0.37 g·kg-1), and TP (0.15 g·kg-1) contents and stoichiometry characteristics (C:N, C:P, N:P was 9.07, 25.56, 2.97, respectively) to a depth of 10 cm in the Horqin Sandy Land were significantly lower than the mean values of soils in China. 2) Soil stoichiometry characteristics differed significantly among land use types. The contents of SOC, TN, and TP to a depth of 100 cm were highest in irrigated cropland, followed by sandy grassland, rainfed cropland, fixed dunes, and mobile dunes. The C:N ratios in sandy grassland, irrigated cropland, and rainfed cropland were significantly higher than those in the fixed dune and mobile dune sites. C:P ratios in the sandy grassland, fixed dunes, irrigated cropland, and rainfed cropland were significantly higher than that in the mobile dunes. The N:P ratio differed little among the five land use types. 3) SOC and TN contents in the sandy grassland, fixed dunes, irrigated cropland, and rainfed cropland decreased with increasing soil depth. SOC, TN, and C:P in the mobile dunes and TP and C:N in all land use types showed no variation among depths. The C:P ratio of sandy grassland, fixed dunes, irrigated cropland, and rainfed cropland and the N:P ratio of sandy grassland decreased with increasing soil depth. 4) SOC, TN, and TP contents and the C:N ratio were significantly negatively correlated with the contents of medium and fine sands and with soil bulk density, but significantly positively correlated with silt+clay, and very fine sand contents. Desertification led to losses of SOC and nutrients in the Horqin Sandy Land, and exacerbated soil N deficiency. Inputs of water and ferti-lizer helped cropland to maintain a relatively high level of soil nutrients.

Stochastic processes contribute to arbuscular mycorrhizal fungal community assembly in paddy soils along middle and lower Yangtze River

Arbuscular mycorrhizal fungi (AMF) are extensively distributed in environment, and have key effects on regulating soil structure, nutrient cycles, crop productivity, and ecological processes in agricultural ecosystems. However, the biogeographic patterns and underlying ecological processes shaping AMF community assembly remain unclear. The present study examined AMF community composition and diversity in paddy soils along middle and lower reaches of the Yangtze River, and the driving factors and processes of AMF community assembly were assessed based on MiSeq sequencing. The results showed that soil pH, total N and Olsen-P, and soil organic matter (SOM) levels affected AMF community diversity. In addition, there were 4 orders, 8 families along with 8 genera within our study area, where Glomus was the most dominant genus. Moreover, AMF community composition was under the influence of geographic distance and soil characteristics such as pH, SOM, N and P contents, and enzyme activities. However, the contribution of deterministic processes was less than stochastic processes by the null model analysis, suggesting that stochastic processes was the dominant ecological processes shifting AMF community assembly in paddy soils along middle and lower reaches of the Yangtze River. The results sheds more lights on patterns as well as mechanisms driving the assembly of AMF communities within the agricultural ecosystems.

Land-Use Types Influence the Community Composition of Soil Mesofauna in the Coastal Zones of Bohai Bay, China

Soil faunal communities play key roles in maintaining soil nutrient cycling. Affected by different land-use types, soil environment and soil faunal communities change significantly. However, few studies have focused on the aforementioned observations in coastal zones, which provide suitable habitats for many species of concern. Here, we investigated the changes in soil mesofaunal communities under different land-use types, including cotton fields, jujube trees, ash trees, a saline meadow, and wetlands. The variations in land-use types affected the community composition and diversity of soil mesofauna in the coastal zones. The taxa of soil mesofauna had different responses to land-use types in the coastal zones. Isotomidae was regarded as an indicator taxon of the coastal cropland regions. Entomobryidae was considered to be an indicator taxon of coastal artificial trees. Meanwhile, Onychiuridae and three taxa (Brachycera, Armadillidiidae, and Gammaridae) were indicator taxa of the coastal terrestrial ecosystem and the coastal wetland ecosystem, respectively. Thus, we suggested that specific soil mesofaunal taxa were considered to be appropriate bioindicators for land-use types in the coastal zones. The results of this study were helpful to develop guidelines for coastal biodiversity and ecosystem conservation in the future.

Bacterial biomarkers are linked more closely to wheat yield formation than overall bacteria in fertilized soil

AbstractSoil bacteria play pivotal roles in agroecosystem functioning. However, the immense diversity of soil bacterial communities masks the effects of some species, such as bacterial biomarkers, on soil nutrient cycling and crop growth. We analyzed biological and chemical soil parameters of five fertilization treatments (CK, LN, CN, HN, LNM: 0, 150, 200, 250 kg N hm−2, 150 kg N hm−2 + 15,000 kg hm−2 sheep manure). The random forest models were used to select bacterial biomarkers and assess the contributions of bacterial biomarkers and overall bacteria to wheat yield. Moreover, we used a partial least squares path modelling to explore the relationship between fertilization, bacterial biomarkers, carbon (C) and nitrogen (N) cycling functions, soil nutrients, and wheat yield. The results showed that bacterial biomarkers are better predictors of wheat yield than overall bacteria, explaining 52.54% and 16.00% of the variation in yield, respectively. Bacterial biomarkers affected wheat production by increasing soil organic carbon, and available nitrogen content. The LNM treatment significantly improved the relative abundance of beneficial biomarkers, such as Sphingomonadales, Xanthomonadaceae, Lysobacter, and Streptomyces, compared to the LN treatment. In addition, the LNM treatment promoted chitinlysis, cellulolysis, xylanolysis, aromatic hydrocarbon degradation, and aerobic ammonia oxidation, relative to the other inorganic N treatments (LN, CN, and HN). Our results emphasize the role of bacterial biomarkers in wheat yield formation, providing new insights into maintaining agricultural productivity by taking advantage of soil bacterial biomarkers.

Parasitic plants indirectly regulate decomposition of soil organic matter

Abstract Parasitic plants have been shown to affect soil‐organic‐matter (SOM) decomposition, but the mechanism is unknown. As arbuscular mycorrhizal fungi (AMF) can affect decomposition and compete with parasitic plants for carbon, we hypothesized that parasitic plants can indirectly regulate SOM decomposition by suppressing the effects of AMF on decomposition. To test this hypothesis, we conducted two container experiments in which the herbaceous plant Bidens pilosa was inoculated with the AMF Rhizophagus intraradices or not, and Cuscuta australis or not. In one experiment, we provided SOM within hyphae‐in‐growth bags as 13C‐/15 N‐labelled maize leaves and in the other experiment as phytate‐P. We assessed growth and nutrient uptake of B. pilosa, growth of C. australis, the SOM remaining in the hyphae‐in‐growth bags, and the bacterial communities. Parasitization increased the 13C and decreased the organic P remaining in the bags, but only in the presence of the extraradical AMF hyphae. AMF decreased the 13C and increased the organic P remaining in the absence of the parasite, but not in the presence of the parasite. Our results demonstrate that parasitic plants can regulate the decomposition of organic materials indirectly by suppressing the effect of the extraradical AMF hyphae on decomposition. In other words, parasitic plants can regulate SOM decomposition indirectly via a multitrophic cascading effect. Our study helps to unravel the mechanisms of a sophisticated hidden ecological process, and is an important step forward in elucidating the roles of parasitic plants in soil nutrient cycling. Read the free Plain Language Summary for this article on the Journal blog.

Species and functional responses of ants to inter-row tillage and vegetation in organic Mediterranean vineyards

Ants are arthropods providing crucial ecosystem services such as soil structuring, nutrient cycling, seed dispersal and pest predation. Thus, their abundance and diversity need to be considered in approaches to improve sustainability of land use such as Mediterranean viticulture. In our study, we tested whether (1) inter-row vegetation and the absence of tillage increase the species richness and/or functional diversity of ants in vineyards and (2) ground cover vegetation drives ant species composition. We included 23 Mediterranean organic vineyards in our analyses and distinguished three types of inter-row management: all inter-rows tilled, half of the inter-rows tilled, and all inter-rows are untilled and covered by vegetation. The occurrence of ant species was analysed in six pitfall traps per vineyard. Around each trap, the floristic composition of inter-row vegetation was analysed in 2 × 2 m² plots. We found that inter-row tillage significantly affected ant species richness, being higher in partially than in fully tilled vineyards whereas untilled vineyards were not different from the other tillage types. Grass cover and the perennial/annual rate were positively correlated with ant species richness. Ant functional diversity and the frequency of most predatory ants were not correlated neither with plant functional groups nor with tillage type. In conclusion, ant communities benefit from inter-row vegetation and/or absence of soil disturbance but partial inter-row tillage of vineyards may be tolerated and even benefit several species. In particular, grasses and perennial plant species favour ants in our system and need to be considered in inter-row sowing.

Distinct roles of bacteria and fungi in mediating soil extracellular enzymes under long-term nitrogen deposition in temperate plantations

Soil microbes decompose soil organic matter by producing various extracellular enzymes, and also regulate soil carbon (C) and nutrient cycles. However, how shifts in soil microbial community under long-term nitrogen (N) deposition govern soil extracellular enzyme activities (EEAs) is not known. Here, we conducted a decade-long N fertilization experiment consisting of control, low-N (2 g N m−2 year−1), medium-N (5 g N m−2 year−1), and high-N (10 g N m−2 year−1) treatments in a N-limited temperate plantation in northern China. The diversity and community composition of fungi and bacteria were determined with bacterial 16S rRNA genes and fungal internal transcribed spacer genes sequencing. Soil EEAs involved in C, N, and phosphorus (P) cycles were also measured. The results showed that high-N addition increased fungal diversity and altered microbial community composition. In particular, rare fungal diversity and rare bacterial community composition were more sensitive to N addition. N addition improved β-1,4-glucosidase (BG) and acid phosphatase (AP) activities by altering bacterial community composition, and inhibited leucine aminopeptidase (LAP) and polyphenolic oxidase (PPO) activities by affecting fungal functional groups. Specifically, shifts in bacterial community composition caused by N addition were reflected in the significant increase in the dominant class Thermoleophilia, which could be an indicator of secreted hydrolase involved in C and P cycles. Symbiotrophic fungi were more closely associated with LAP for acquiring N and PPO. Our data provide a novel view of the link between major extracellular enzymes and specific microbial taxa under the background of N deposition.

Canada Goldenrod Invasion Regulates the Effects of Soil Moisture on Soil Respiration

Canada goldenrod (Solidago canadensis L.) is considered one of the most deleterious and invasive species worldwide, and invasion of riparian wetlands by S. canadensis can reduce vegetation diversity and alter soil nutrient cycling. However, little is known about how S. canadensis invasion affects soil carbon cycle processes, such as soil respiration, in a riparian wetland. This study was conducted to investigate the effects of different degrees of S. canadensis invasion on soil respiration under different moisture conditions. Soil respiration rate (heterotrophic and autotrophic respiration) was measured using a closed-chamber method. S. canadensis invasion considerably reduced soil respiration under all moisture conditions. The inhibition effect on autotrophic respiration was higher than that on heterotrophic respiration. The water level gradient affects the soil autotrophic respiration, thereby affecting the soil respiration rate. The changes in soil respiration may be related to the alteration in the effective substrate of the soil substrate induced by the invasion of S. canadensis. While the effects of S. canadensis invasion were regulated by the fluctuation in moisture conditions. Our results implied that S. canadensis invasion could reduce the soil respiration, which further potentially affect the carbon sequestration in the riparian wetlands. Thus, the present study provided a reference for predicting the dynamics of carbon cycling during S. canadensis invasion and constituted a scientific basis for the sustainable development and management of riparian wetlands invaded by alien plants.