Nutrient Turnover Research Articles

Plant microbiomes harbor potential to promote nutrient turnover in impoverished substrates of a Brazilian biodiversity hotspot

The substrates of the Brazilian campos rupestres, a grassland ecosystem, have extremely low concentrations of phosphorus and nitrogen, imposing restrictions to plant growth. Despite that, this ecosystem harbors almost 15% of the Brazilian plant diversity, raising the question of how plants acquire nutrients in such a harsh environment. Here, we set out to uncover the taxonomic profile, the compositional and functional differences and similarities, and the nutrient turnover potential of microbial communities associated with two plant species of the campos rupestres-dominant family Velloziaceae that grow over distinct substrates (soil and rock). Using amplicon sequencing data, we show that, despite the pronounced composition differentiation, the plant-associated soil and rock communities share a core of highly efficient colonizers that tend to be highly abundant and is enriched in 21 bacterial families. Functional investigation of metagenomes and 522 metagenome-assembled genomes revealed that the microorganisms found associated to plant roots are enriched in genes involved in organic compound intake, and phosphorus and nitrogen turnover. We show that potential for phosphorus transport, mineralization, and solubilization are mostly found within bacterial families of the shared microbiome, such as Xanthobacteraceae and Bryobacteraceae. We also detected the full repertoire of nitrogen cycle-related genes and discovered a lineage of Isosphaeraceae that acquired nitrogen-fixing potential via horizontal gene transfer and might be also involved in nitrification via a metabolic handoff association with Binataceae. We highlight that plant-associated microbial populations in the campos rupestres harbor a genetic repertoire with potential to increase nutrient availability and that the microbiomes of biodiversity hotspots can reveal novel mechanisms of nutrient turnover.

Soil nutrients shape the composition and function of fungal communities in abandoned ancient rice terraces

In recent decades, terraces abandonment has been prevalent in the hilly areas of China. Soil fungi play an important role in clarifying soil ecosystematic feedback after ancient rice terraces abandonment, but how their community composition and function shift remains unclear. Soil profiles of 0–120 cm were excavated in ancient rice terraces, dry land, and forest land (formed from ancient rice terraces abandonment), respectively. The 13C NMR and high-throughput sequencing were used to determine soil organic carbon chemical groups and fungal community, respectively, and FUNGuild was used to predict functional groups. The results showed that the soil fungal community changed from Ascomycota to Basidiomycota after ancient rice terraces abandonment. The trophic modes of dry land and forest land were transformed into pathotrophic fungi and symbiotrophic fungi, respectively. The number of nodes and edges of fungal co-occurrence networks increased by 83.8% and 644.1% in dry land, and 81.3% and 431.2% in forest land, respectively. Moreover, soil nutrients (especially DOC, TN, and TP) can more affected the variation of fungal community composition and function than soil organic carbon chemical groups. These findings indicate that soil fungal community shifts in different directions in response to ancient rice terraces abandonment, which is related to the adaptive strategies for environmental changes and may be more conducive to the acquisition and turnover of soil nutrients.

Evaluation of a subtropical maize-rice rotation system maintained under long-term fertilizer inputs for sustainable intensification of agriculture

The impacts of long-term (1996–2019) fertilizer inputs on grain yield and edaphic factors of upland maize and wetland rice rotation system were assessed for sustainable intensification of agriculture. Subtropical field treatments included swine manure compost (CP), chemical fertilizer (CF, control), no fertilizer (CK, blank), inorganic N-amended CP (CPN1 and CPN2), peat (PN1) and green manure (GMN1). Maize exhibited a significantly increased yield trend under CF, GMN1 and CP-based inputs (CP, CPN1 and CPN2), whereas rice yield displayed a non-significant marginal improvement or negative result. Principal component analysis of edaphic factors revealed distinct clustering of CP-CPN1-CPN2, CF-GMN1-CK and PN1 samples during maize-rice rotation. CP-based inputs in particular improved OM, EC, microbial metabolism and nutrient availability during crop rotation. Pronounced soil microbial activity and Bacterial abundances were recorded during maize cultivation. In contrast, low aerobic metabolism coupled with high Bacterial and Archaeal species richness, diversity and evenness were found during rice cultivation. In conclusion, increasing maize yield trends observed under long-term CP-based inputs were on par with CF and GMN1 amendments that concurrently acidified soil. Numerically dominant aerobic Bacteria appear to drive nutrient recycling and promote maize grain yield, whereas metabolically lethargic diverse prokaryotes constrained nutrient turnover stagnating the rice yield.

Efficacy of teak and pine litter extract with several solvent against wood termites (Cryptotermes cynocephalus light)

Termites are social insects that play an important role in the decomposition and nutrient turnover. In addition, termites are also categorized as pests that eat wood or materials composed of cellulose. Some form of control one of them has been done by making biopesticides. Various types of raw materials have been used from agricultural, plantation and forestry crop groups. Termite mortality is one indicator to determine extract bioactivity by calculating the percentage of the number of termites that died after being given treatment at a certain time. Compound content bioactive substances such as alkaloids, phenolics and other chemicals that can be used to kill and controlling insects in the environment. This study examines the effectiveness teak litter extract and pine litter extract with various solvents against wood termites through experimental research activities in the laboratory. The content of teak litter extract levels and pine litter obtained by 2.5%. Based on the termite mortality value test, the highest toxicity in the ethyl acetate extract, which is at week 3, it has reached 100% at a concentration of 1% which is. In addition, based on testing the retention value of the test paper, The highest percentage of weight loss was in the control, followed by the n-hexane fraction 49.55%. Whereas in testing the level of termite consumption, the highest percentage was in the aquades fraction.

Different effects of litter and root inputs on soil enzyme activities in terrestrial ecosystems

Soil extracellular enzymes are involved in the decomposition of plant litter and soil organic matter, and their activities are of critical significance to soil carbon and nutrient turnover in terrestrial ecosystems. However, the coupling of litter and root inputs and soil enzyme activities across terrestrial ecosystems still remains not fully understood. In this study, we compiled 788 paired observations to evaluate changes in soil β-1,4-glucosidase (BG), β-d-cellobiosidase (CBH), phenol oxidase (PHO), β-1,4-N-acetyl-glucosaminidase (NAG), and acidic phosphatase (AP) activities after the removal of litter, living roots, and both litter and living roots in different ecosystems (forests, grasslands, croplands and tundra). Soil BG, NAG, and AP activities were decreased by 22.5 %, 16.6 % and 28.7 %, respectively, after removing both litter and living roots, but these effects varied in different ecosystems. Removing both litter and living roots decreased soil BG and CBH activities in forests and BG activity in croplands but increased soil CBH activity in croplands. Soil NAG activity was decreased by 15.1 % in forests but increased by 6.1 % in croplands after both litter and living roots were removed, while soil AP activity was decreased significantly across all of the studied ecosystems after both litter and living root removal. However, litter addition greatly increased soil BG, CBH, NAG and AP activities, suggesting that soil enzyme activities involved in carbon, nitrogen and phosphorus cycling were strongly controlled by plant carbon input, with an additive effect of litter and root inputs observed for C-degrading enzymes. Our synthesis also found that these enzymatic responses to plant carbon input were strongly controlled by edaphic and not climatic factors across terrestrial ecosystems. These results suggested that soil enzyme activities increased after litter addition to accelerate the decomposition of litter input but decreased after litter removal. Removing both litter and root inputs had a similar but additive effect on soil enzyme activities across sites. Although these responses varied greatly among ecosystems and litter types, edaphic factors predominantly controlled enzymatic responses over terrestrial ecosystems. Our results highlighted the importance of plant inputs in enzymatically involved carbon and nutrient cycles in terrestrial ecosystems.

Food origin influences microbiota and stable isotope enrichment profiles of cold-adapted Collembola (Desoria ruseki).

Collembola are a group of globally distributed microarthropods that can tolerate low temperature and are active in extremely cold environments. While it is well known that animal diets can shape their microbiota, the microbiota of soil animals is not well described, particularly for animals with limited food resources, such as Collembola active in winter at low temperatures. In this study, we explored the effects of three different food sources; corn litter (agriculture grain residuals), Mongolian oak litter (natural plant residuals), and yeast (common food for Collembola culture), on the microbiota of a winter-active Collembola species, Desoria ruseki. We found that microbial diversity and community composition of the Collembola were strongly altered after feeding with different food sources for 30 days. Collembola individuals fed on corn litter harbored the highest bacterial richness and were dominated by a representative of Microbacteriaceae. In contrast, those fed on yeast exhibited the lowest bacterial richness and were primarily colonized by Pseudomonas. The microbial communities associated with the winter-active Collembola differed significantly from those observed in the food. Collembola nutrient turnover also differed when cultured with different food sources, as indicated by the C and N stable isotopic signatures. Our study highlights microbial associations with stable isotopic enrichments of the host. Specifically, the Arthrobacter was positively correlated with δ13C enrichment in the host. Representatives of Microbacteriaceae, Micrococcaceae, TM7a, Devosia, and Rathayibacter were positively correlated with δ15N enrichment of the host. Our study indicates that food sources are major determinants for Collembola microbiota that simultaneously alter consumers' isotopic niches, thereby improving our understanding of the roles played by host-microbiota interactions in sustaining soil biodiversity during the winter.

Nutrient turnover by large sulfur bacteria on the Namibian mud belt during the low productivity season

Surface sediments of the coastal mud belt in the Benguela Upwelling System (BUS) off Namibia host extensive communities of chemotrophic large sulfur bacteria (LSB) of the family Beggiatoaceae such as Thiomargarita spp. and Candidatus Maribeggiatoa spp. In order to understand the role of these bacteria in N and P cycling, biogeochemical data from three sites in the mud belt were simulated with a biogeochemical model including LSB catabolic pathways. Organic carbon remineralization was dominated by the reduction of sulfate to hydrogen sulfide (5.0–7.7 mmol C m−2 d−1). At the two stations where LSB were observed, produced hydrogen sulfide was almost completely oxidized by LSB using nitrate as the electron acceptor. Modeled rates of nitrate reduction to N2 by LSB were over two times higher than nitrate reduction to ammonium. This points toward a potential negative feedback by LSB on primary production. Furthermore, loss of fixed N strongly enriched the benthic fluxes in P relative to N. Although the model included intracellular polyphosphate accumulation by LSB and subsequent breakdown to phosphate, a clear link between polyphosphate dynamics and hydroxyapatite precipitation and burial could not be clearly substantiated. This is partly due to simplifying assumptions in the model and analytical uncertainties in distinguishing between authigenic hydroxyapatite and allochthonous hydroxyapatite (e.g., fish bones), both of which are major components of particulate P in the BUS. Our modeling suggests a significant control of LSB on benthic N and P fluxes to the water column. Given the extensive coverage of LSB on the shelf (>30,000 km2), more accurate forecasts of nutrient cycling and primary production in the BUS necessitate a closer inspection of benthic P sources and sinks in the mud belt and a clearer understanding of the controls on the end product of nitrate reduction by LSB.

Alteration in Forest Soil Biogeochemistry through Coarse Wood Debris in Northeast China

Coarse woody debris (CWD) has a strong influence on nutrient dynamics and hinders its availability through fixation. The CWD decaying logs, with two states (three and four) impacting on carbon (C) capture, nutrient dynamics and enzymatic properties, were investigated under and away (50 cm) from the logs in three forest types, i.e., the Picea koraiensis-Abies nephrolepis-Pinus koraiensis forest (PAPF), Betula costata-Pinus koraiensis forest (BPF) and Tilia amurensis-Pinus koraiensis forest (TPF). The results showed that soil organic carbon (OC), nitrogen (N), soil pH, other soil nutrients and enzymatic activity were significantly affected by the forest types, decay class and distance from decaying logs in three forests. The CWD, with decay class IV under CWD, resulted in the optimum OC 64.7 mg g−1, N 6.9 mg g−1 and enzymatic activity in the PAPF forest, and the distance effect was negligible for all the forests. A lower soil pH value of 3.8 was observed at decay class IV in the soil collected from the immediate vicinity of the deadwood. CWD play a key role in decaying logs in forest ecosystems to enhance C and the nutrient budget with the improved enzymatic activity of the soil. It was concluded from this research that CWD is a critical factor in the nutrient cycling process of forest ecosystems that contributes functionally to the forest floor by inducing the spatial heterogeneity of enzymatic activity, C and nutrient turnover.

Phosphorus Nutrition and Water Relations of European Beech (Fagus sylvatica L.) Saplings Are Determined by Plant Origin

Climate change, specifically the increasing frequency and intensity of summer heat and drought, has severe influences on the performance of beech forests, including decline in growth, reduced nutrient turnover, enhanced mortality, and a shift in spatial distribution northwards and towards higher elevations. The present study aimed to characterize the physiological responses of Croatian beech saplings originating from 10 natural forest stands to experimentally applied water deprivation in a common-garden experiment. The aim was to evaluate the extent to which external factors such as climate, as well as nitrogen (N) and phosphorus (P) availability in the soil of the natural habitats, control the response of beech saplings to water deprivation. For this purpose, beech saplings from 10 forest stands that differed in terms of soil type, chemical soil properties, as well as climate were collected in winter, cultivated in an artificial soil substrate under controlled conditions for one year, and then subjected to 29 days of water deprivation. Responses to water deprivation were observed in the antioxidative system (total ascorbate, reduced ascorbate, oxidized ascorbate, and redox state) in leaves and fine roots. The latter allowed us to categorize saplings as adapted or sensitive to water deprivation. P over N availability in the soil rather than climatic conditions in the natural habitats controlled the response of beech saplings to the water-deprivation event. The categorization of saplings as adapted or sensitive to water deprivation was related to genetic parameters. The results of this multidisciplinary study (tree physiology, climate, and genetic data) are considered to be highly significant and beneficial for the adaptation of European beech forests to changing climatic conditions.

Crab contributions as an ecosystem engineer to sediment turnover in the Yellow River Delta

Burrowing crabs are widely distributed and have large populations in estuarine wetlands. Crab excavation can have potentially significant bioturbation effects on the vertical structure of sediments, and the processes of nutrients deposition and mineralization. However, the effects of crab micro activities on the geochemical cycling processes of the whole estuarine ecosystems are not clear, specifically the contributions of burrowing crabs to sediment and nutrients turnover in coastal ecosystems. Due to the lack of knowledge on crab burrowing behavior and borrow morphology, it is difficult to accurately estimate the excavation and turnover volumes of crabs. Therefore, this study examined the bioturbation activity of the crab Helice tientsinensis in western Pacific estuary ecosystems by analyzing their burrow morphology and local sediment properties. The common burrow shapes of Helice tientsinensis were J- and Y-shaped burrows. Burrow morphological characteristics such as total burrow depth, curve burrow length, burrow volume, and opening diameter significantly differed among tidal zones. Crab carapace size, water depth, soil hardness, and bulk density were the main factors driving burrow morphology. Sediment excavation by crabs was ~50 times greater than the deposition of sediment into crab burrows. The net transported amounts of sediment (31.66–33.18 g·d-1·m-2) and nutrients (total nitrogen: 0.075–0.090 g·d-1·m-2, total carbon: 3.96–4.55 g·d-1·m-2, and organic matter: 0.44–0.77 g·d-1·m-2) were mainly from the belowground sediment to the surface. These results highlighted the important role of crabs in sediment and nutrients cycling within coastal estuary ecosystems.

Impact of waterlogging and heat stress on rice rhizosphere microbiome assembly and potential function in carbon and nitrogen transformation

ABSTRACT The impacts of rhizosphere microorganisms on the turnover of nutrients are affected by many environmental factors. In this study, rice plants were subjected to deep flooding and heat stress for one week at the jointing stage. Rhizospheric soil was sampled for the analysis of rice rhizosphere bacterial assembly and functional groups responsible for carbon and nitrogen transformation. Compared with the control, both deep flooding and heat stress increased bacterial alpha diversity. Moreover, heat stress and the interactions of heat stress and deep flooding improved the bacterial cooperation. Heat stress reduced the relative abundance of Actinobacteria and Firmicutes, which are responsible for organic carbon decomposition. The relative abundance of the gene encoding lignin-degrading catalases under deep flooding and heat stress treatments reduced by 6% and 8%, respectively. The interaction of heat stress and deep flooding increased the relative abundance of the nifD gene by 5%, may slowed down nitrate reduction to nitrite. Our results highlight the effects of heat and flooding stress on the bacteria-mediated mechanisms responsible for regulating organic carbon sequestration and nitrogen cycling in rhizosphere of paddy fields.

Current Challenges and Pitfalls in Soil Metagenomics.

Soil microbial communities are essential components of agroecological ecosystems that influence soil fertility, nutrient turnover, and plant productivity. Metagenomics data are increasingly easy to obtain, but studies of soil metagenomics face three key challenges: (1) accounting for soil physicochemical properties; (2) incorporating untreated controls; and (3) sharing data. Accounting for soil physicochemical properties is crucial for better understanding the changes in soil microbial community composition, mechanisms, and abundance. Untreated controls provide a good baseline to measure changes in soil microbial communities and separate treatment effects from random effects. Sharing data increases reproducibility and enables meta-analyses, which are important for investigating overall effects. To overcome these challenges, we suggest establishing standard guidelines for the design of experiments for studying soil metagenomics. Addressing these challenges will promote a better understanding of soil microbial community composition and function, which we can exploit to enhance soil quality, health, and fertility.

Temperature dependence of ecosystem carbon, nitrogen and phosphorus residence times differs between subtropical and temperate forests in China

Residence times of ecosystem carbon (τe,C), nitrogen (τe,N) and phosphorus (τe,P) are closely related to efficacies of carbon and nutrients conservation within an ecosystem. However, estimates of τe,C, τe,N and τe,P together are very limited for forest ecosystems, and little is known about the environmental controls. Here we estimated τe,C, τe,N and τe,P of 127 undisturbed forests based on observed carbon, nitrogen and phosphorus stocks and compiled 30 key variables related to climate, vegetation, soil and terrain for the sites. We then performed a variation partitioning analysis to identify dominant controls on τe,C, τe,N and τe,P, and used segmented regression to identify possible thresholds in the dependence of τe,C, τe,N and τe,P on temperature. Climate, particularly average minimum temperature of the coldest month of a year (Tmin), was the main driver of τe,C, τe,N and τe,P. In regions with Tmin < 0 °C, τe,C and τe,P decreased with increasing Tmin; and in regions with Tmin > 0 °C, both τe,C and τe,P increased with increasing Tmin, as a result of a significant increase in total ecosystem carbon pool and a decrease in external phosphorus input, respectively. Our results challenge the use of a single temperature-dependent function of ecosystem carbon or nutrient turnover rate in global land models, and highlight the importance of other factors, such as soil weathering stage, clay content, in influencing the responses of carbon and nutrients cycles in subtropical forests to global warming.

Responses of bryosphere fauna to drought across a boreal forest chronosequence

Projected changes in precipitation regimes can greatly impact soil biota, which in turn alters key ecosystem functions. In moss-dominated ecosystems, the bryosphere (i.e., the ground moss layer including live and senesced moss) plays a key role in carbon and nutrient cycling, and it hosts high abundances of microfauna (i.e., nematodes and tardigrades) and mesofauna (i.e., mites and springtails). However, we know very little about how bryosphere fauna responds to precipitation, and whether this response changes across environmental gradients. Here, we used a mesocosm experiment to study the effect of volume and frequency of precipitation on the abundance and community composition of functional groups of bryosphere fauna. Hylocomium splendens bryospheres were sampled from a long-term post-fire boreal forest chronosequence in northern Sweden which varies greatly in environmental conditions. We found that reduced precipitation promoted the abundance of total microfauna and of total mesofauna, but impaired predaceous/omnivorous nematodes, and springtails. Generally, bryosphere fauna responded more strongly to precipitation volume than to precipitation frequency. For some faunal functional groups, the effects of precipitation frequency were stronger at reduced precipitation volumes. Context-dependency effects were found for microfauna only: microfauna was more sensitive to precipitation in late-successional forests (i.e., those with lower productivity and soil nutrient availability) than in earlier-successional forests. Our results also suggest that drought-induced changes in trophic interactions and food resources in the bryosphere may increase faunal abundance. Consequently, drier bryospheres that may result from climate change could promote carbon and nutrient turnover from fauna activity, especially in older, less productive forests.

Distinct roles for soil bacterial and fungal communities associated with the availability of carbon and phosphorus under aerated drip irrigation

Soil bacteria and fungi play key roles in organic matter decomposition and nutrient turnover. Aerated drip irrigation (ADI) is beneficial for improving soil nutrients but its effects on bacterial and fungal communities are less known. In this study, a two-season ADI field experiment comprising three dissolved oxygen concentrations (10, 15, and 20 mg·L–1, referred to as A1, A2, and A3) and a control treatment (groundwater without aerated, CK) was conducted in a tomato plantation in Shandong, China. Soil bacterial and fungal communities were examined using high-throughput sequencing targeting 16 S rRNA and ITS genes, respectively. The ADI treatments increased fungal community diversity but did not significantly affect bacterial community diversity. However, bacterial communities were more connected within the module, with more stable network structures in the ADI treatments. In contrast, fungal networks had lower modularity values and a significant negative correlation with soil available phosphorus (AP). The ADI treatments increased the bacterial phylum Gemmatimonadetes and Firmicutes and a few aerobic taxa and strongly enriched the fungal phylum Mortierellomycota and phosphorus-dissolving taxa (Humicola, Mycothermus, and Myceliophthora). In addition, the A2 treatment enhanced functional groups related to carbon and phosphorus cycling while decreasing Plant Pathogen functional groups. The most important environmental factors affecting bacterial and fungal communities were soil organic carbon (SOC) and AP, respectively. Structural equation modeling (SEM) demonstrated that ADI directly affected soil bacterial and fungal communities and indirectly promoted SOC, AP content, and tomato yield. Overall, our findings highlight the importance of bacterial and fungal taxonomic communities, co-occurrence networks, and functions related to regulating soil carbon and phosphorus availability, providing novel evidence for the application of ADI to improve soil fertility and crop productivity.

Intergenerational effects of ocean acidification on reproductive traits of an estuarine copepod

Copepods are an important part of the marine food web because of their high biomass productivity and nutrient turnover rate compared to other zooplankton in the marine ecosystem. Despite their great ecological role in the ocean, there is only limited information available on the consequences of ocean acidification (OA) induced by the future increase in CO2 on the planet. More specifically, there is almost no information about the impact of OA on the European copepod Calanipeda aquaedulcis Kritschagin, 1873. Therefore, the present investigation hypothesized that OA would not produce negative multigenerational effects on the survival and reproductive performance of this copepod species. Here we assessed, the multigenerational (F1 and F2) effect of OA on eight important reproductive traits (maturity, prosome length, fertility, egg release, hatching success, survival rate, reproductive performance, and the total number of adults per generation). For this study, C. aquaedulcis were collected from the Guadalquivir River (southwest of Spain) and were exposed to four different pH gradients (pH 8.1 as control and pH 7.5, 7.0, 6.5 as acidified conditions) to mimic the future seawater acidification scenarios. The survival rate from nauplius to adult, C. aquaedulcis was significantly reduced by pHs and across generations. Besides, results also indicated that there were marked effects on fertility, reflected by a significantly lower number of eggs per female in each generation. Similarly, hatching success also showed a decreasing pattern towards low pH, and importantly, F1 females had lower hatching success than F0 females. While a beneficial parental effect was detected in the offspring in response to OA, it was insufficient to offset the negative effects caused by it. The findings presented here appear to have ecological significance, as decreasing the reproductive performance of copepods may have a negative impact on the marine food web, as ichthyofaunal feeding and growth are heavily reliant on this component of the food web.

Soil nutrient cycling and bacterial community structure in response to various green manures in a successive Eucalyptus (Eucalyptus urophylla × Eucalyptus grandis) plantation

AbstractSuccessive cultivation of short‐rotation eucalyptus plantations often cause serious decline in soil quality in China, which limits sustainable production. Green manure application is a potential strategy for improving soil fertility while ensuring ecological sustainability. Nevertheless, the impacts of various green manure species on soil quality in eucalyptus plantations remain unclear. In the present study, we investigated how soil nutrient cycling and bacterial communities respond to various green manure species (Legume and Gramineae), namely Tephrosia candida, Sesbania cannabina, Lolium perenne, and Pennisetum purpureum (PP). A batch experiment was conducted using eucalyptus plantation (E. urophylla × E. grandis) soil mixed with green manures for 60 days. According to the results, the PP treatment had the highest soil respiration rate among the five treatments, suggesting that PP application had the optimal effects on soil organic matter and residue decomposition. Furthermore, applying green manure increased bacterial diversity significantly when compared to CK (soil without green manure). Among the treatments, the PP treatment increased bacterial functional groups associated with the nitrogen cycle significantly, which result in rapid nutrient turnover. The rapid decomposition under PP may be responsible for the structural and functional changes in bacterial communities. Overall, the PP green manure is the optimal amendment for rapid nutrient supply in degraded eucalyptus plantations over the short term. Our results could facilitate sustainable management of successive eucalyptus plantations; nevertheless, extra investigations are needed to verify the long‐term impacts of PP green manure in the field.

Effects of rape/common vetch intercropping on biomass, soil characteristics, and microbial community diversity

Legume–brassica intercropping is widely used to increase productivity in modern, sustainable agricultural systems. However, few studies have assessed the linkages between soil properties and soil microorganisms. Soil microorganisms play a key role in soil nutrient turnover and plant community composition. To elucidate the responses of soil microbial community diversity and structure to intercropping, we conducted a 2-year experiment based on common vetch (CV) monoculture, rape (R) monoculture, and common vetch–rape intercropping (IRCV) with phosphorus (P) addition in alkaline soil. The microbial communities of bacteria and fungi in the rhizosphere soil were examined based on high-throughput sequencing targeting the 16S rRNA and ITS genes, respectively. In addition, we analyzed changes in soil properties and enzyme activities. Intercropping significantly increased dry matter (up to 98.86% and 81.48%, respectively dry matter is the aboveground biomass.) compared with common vetch monoculture. Intercropping decreased soil bulk density and pH and enhanced soil available phosphorus (AP) by 14.54–34.38%, 7.25–22.67%, soil organic matter (SOM) by 15.57–22.85, 6.82–15.57%, soil sucrase (Suc.) by 13.69–16.10%, 35.57–40.24% compared to monoculture common vetch and rape, respectively. However, bacterial alpha diversity was higher under rape monoculture than IRCV. In addition, the dominant soil bacterial phyla Proteobacteria (1.25–3.60%), Gemmatimonadetes (7.88–15.16%), Bacteroidetes (9.39–11.76%), and Rokubacteria (0.49–5.69%) were present at greater abundance with IRCV relative to those with CV and R, but phyla Chloroflexi was significantly decreased by 11.56–12.94% with IRCV compared with the other two treatments. The redundant analysis showed that SOM and AP were positively correlated with the dominant bacterial and fungal flora. Common vetch–rape intercropping resulted in increased biomass and altered soil microbial community composition as well as soil properties. Our results showed that intercropping systems positively improve soil microbial activity; this strategy could help in the cultivation of multiple crops and improve soil properties through sustainable production.

Soil enzyme activities after application of fungicide Quadris&lt;sup&gt;R&lt;/sup&gt; at increasing concentration rates

The study aimed to assess the effects of fungicide QuadrisR on activities of soil enzymes contributed to soil nutrient turnover. A batch laboratory experiment with QuadrisR-amended (0 mg/kg ds (dry soil) – 35.00 mg/kg ds) loamy sand soil was conducted, and shifts in soil physical environments and enzyme activities (beta-glucosidase, urease, acid and alkaline phosphatases, arylsulfatase and dehydrogenase) were evaluated on experimental days 1, 30, 60, 90 and 120. The results indicated that QuadrisR changed both soil properties and enzyme activities. The most sensitive environmental parameter to fungicide input was soil pH. The most suscaptable to QuadrisR enzymes were dehydrogenase and arylsulfatase, and the most resistant – urease. The mean overall dehydrogenase activity decreased by 33%, whereas the profile of arylsulfatase activity tended to permanent decrease over time. The general pattern of enzyme responses to QuadrisR was an immediate-early (days 1 – 30) decline of enzyme activities after fungicide application, except that of arylsulfatase. Beta-glucosidase manifested a temporal profile of steady-state stimulation under the lowest (2.90 mg/kg ds) and low sensitivity to the higher (14.65 mg/kg ds and 35.00 mg/kg ds) fungicide concentrations.

Increasing nitrogen addition rates suppressed long-term litter decomposition in a temperate meadow steppe

AbstractPlant litter decomposition is critical for the carbon (C) balance and nutrient turnover in terrestrial ecosystems, and is sensitive to the ongoing anthropogenic biologically nitrogen (N) input. Previous studies evaluating the N effect on litter decomposition relied mostly on short-term experiments (&amp;lt;2 years), which may mask the real N effect on litter decomposition. Therefore, long-lasting experiments are imperative for the overall evaluation of the litter decomposition dynamics under N enrichment. We conducted a relative long-term (4-year) N-addition experiment with N levels ranging from 0 to 50 g N m−2 yr−1 to identify the potential abiotic and biotic factors in regulating the decomposition process of litterfall from the dominant species Leymus chinensis. The results showed a consistent decrease of decomposition rate with increasing N-addition rates, providing strong evidence in support of the inhibitory effect of N addition on decomposition. The N-induced alterations in soil environment (acidification and nutrient stoichiometry), microbial activity (microbial biomass and enzyme activity), changes of litter quality (residual lignin and nutrient content) and plant community (aboveground productivity and species richness) jointly contributed to the lowered decomposition. During the whole decomposition process, the changes of litter quality, including accumulation of lignin and the concentrations of nutrient, were mainly driven by the soil and microbial activity in this N-enriched environment. The findings help clarify how increasing N input rates affect long-term litter decomposition, and advance the mechanistic understanding of the linkages between ecosystem N enrichment and terrestrial C cycling.