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Cover crops (CC) can promote nutrient retention and recycling for main crops yet may also promote soilborne pathogens or suppress beneficial root symbionts such as arbuscular mycorrhizal fungi (AMF). We investigated how root fungal communities of main crop are affected by preceding CC monocultures and mixtures and by main crop identity. We expected that AMF abundance and diversity in main crops are promoted by AM-host CC, and suppressed by non-AM-host CC, and that mixtures of CC species can promote beneficial and suppress pathogenic root fungi. Our full-factorial field experiment comprised crop rotation in sand soil with different CC treatments (monocultures of radish [AM non-host], ryegrass, clover, vetch [AM hosts], mixtures of radish + vetch, ryegrass + clover and fallow) and two main crops (oat and endive). At peak crop growth, we investigated the root fungal communities in the main crops using microscopy and high throughput sequencing (Illumina MiSeq). Cover crop identity was of prime importance and CC legacy overruled main crop identity in determining root fungal communities in main crops. Compared with fallow, CC with ryegrass increased AMF colonization and richness in both main crops and of non-AMF in oat. Legacies of ryegrass, ryegrass + clover and vetch resulted in distinct root fungal communities in the main crops, while the legacy of CC with radish were similar to the legacy of fallow. Root fungal community in crops after clover had highest abundance of representative fungal pathogens in contrast with the other CC treatments that resulted in fungal communities where pathogens were scarce. Oppositely to expected, CC mixtures did not enhance fungal symbionts or suppressed pathogens. Overall, fungal communities in roots of the main crops in our field experiment were determined by the preceding CC species in monoculture, rather than by the CC AMF preference or functional group. This research highlights that the choice of CC determines the root fungal comm

Cover crops (CC) can promote nutrient retention and recycling for main crops yet may also promote soilborne pathogens or suppress beneficial root symbionts such as arbuscular mycorrhizal fungi (AMF). We investigated how root fungal communities of main crop are affected by preceding CC monocultures and mixtures and by main crop identity. We expected that AMF abundance and diversity in main crops are promoted by AM-host CC, and suppressed by non-AM-host CC, and that mixtures of CC species can promote beneficial and suppress pathogenic root fungi. Our full-factorial field experiment comprised crop rotation in sand soil with different CC treatments (monocultures of radish [AM non-host], ryegrass, clover, vetch [AM hosts], mixtures of radish + vetch, ryegrass + clover and fallow) and two main crops (oat and endive). At peak crop growth, we investigated the root fungal communities in the main crops using microscopy and high throughput sequencing (Illumina MiSeq). Cover crop identity was of prime importance and CC legacy overruled main crop identity in determining root fungal communities in main crops. Compared with fallow, CC with ryegrass increased AMF colonization and richness in both main crops and of non-AMF in oat. Legacies of ryegrass, ryegrass + clover and vetch resulted in distinct root fungal communities in the main crops, while the legacy of CC with radish were similar to the legacy of fallow. Root fungal community in crops after clover had highest abundance of representative fungal pathogens in contrast with the other CC treatments that resulted in fungal communities where pathogens were scarce. Oppositely to expected, CC mixtures did not enhance fungal symbionts or suppressed pathogens. Overall, fungal communities in roots of the main crops in our field experiment were determined by the preceding CC species in monoculture, rather than by the CC AMF preference or functional group. This research highlights that the choice of CC determines the root fungal communi

With the increased occurrence of climate extremes, there is an urgent need to better understand how management strategies affect the capacity of the soil microbial community to maintain its ecosystem functions (e.g. nutrient cycling). To address this issue, intact monoliths were extracted from conventional and ecological managed grasslands in three countries across Europe and exposed under common air condition (temperature and moisture) to one of three altered rain regimes (dry, wet and intermittent wet/dry) as compared to a normal regime. Subsequently, we compared the resistance and recovery of the soil microbial biomass, potential enzyme activities and community composition. The microbial community composition differed with soil management and rain regimes. Soil microbial biomass increased from the wetter to the dryer rain regime, paralleling an increase of available carbon and nutrients, suggesting low sensitivity to soil moisture reduction but nutritional limitations of soil microbes. Conversely, enzyme activities decreased with all altered rain regimes. Resistance and recovery (considering absolute distance between normal and altered rain regime) of the microbial communities depended on soil management. Conventional-intensive management showed higher resistance of two fundamental properties for nutrient cycling (i.e. bacterial biomass and extracellular enzyme activities) yet associated with more important changes in microbial community composition. This suggests an internal community reorganization promoting biomass and activity resistance. Conversely, under ecological management bacterial biomass and enzyme activities showed better recovery capacity, whereas no or very low recovery of these properties was observed under conventional management. These management effects were consistent across the three altered rain regimes investigated, indicating common factors controlling microbial communities’ response to different climate-related stresses. Synthesis and app

With the increased occurrence of climate extremes, there is an urgent need to better understand how management strategies affect the capacity of the soil microbial community to maintain its ecosystem functions (e.g. nutrient cycling). To address this issue, intact monoliths were extracted from conventional and ecological managed grasslands in three countries across Europe and exposed under common air condition (temperature and moisture) to one of three altered rain regimes (dry, wet and intermittent wet/dry) as compared to a normal regime. Subsequently, we compared the resistance and recovery of the soil microbial biomass, potential enzyme activities and community composition. The microbial community composition differed with soil management and rain regimes. Soil microbial biomass increased from the wetter to the dryer rain regime, paralleling an increase of available carbon and nutrients, suggesting low sensitivity to soil moisture reduction but nutritional limitations of soil microbes. Conversely, enzyme activities decreased with all altered rain regimes. Resistance and recovery (considering absolute distance between normal and altered rain regime) of the microbial communities depended on soil management. Conventional-intensive management showed higher resistance of two fundamental properties for nutrient cycling (i.e. bacterial biomass and extracellular enzyme activities) yet associated with more important changes in microbial community composition. This suggests an internal community reorganization promoting biomass and activity resistance. Conversely, under ecological management bacterial biomass and enzyme activities showed better recovery capacity, whereas no or very low recovery of these properties was observed under conventional management. These management effects were consistent across the three altered rain regimes investigated, indicating common factors controlling microbial communities’ response to different climate-related stresses. Synthesis and app

1. Organic farming (OF) enhances top soil organic carbon (SOC) stocks in croplands compared with conventional farming (CF), which can contribute to sequester C. As farming system differences in the amount of C inputs to soil (e.g. fertilization and crop residues) are not enough to explain such increase, shifts in crop residue traits important for soil C losses such as litter decomposition may also play a role. 2. To assess whether crop residue (leaf and root) traits determined SOC sequestration responses to OF, we coupled a global meta-analysis with field measurements across a European-wide network of sites. In the meta-analysis, we related crop species averages of leaf N, leaf-dry matter content, fine-root C and N, with SOC stocks and sequestration responses in OF vs. CF. Across six European sites, we measured the management-induced changes in SOC stocks and leaf litter traits after long-term ecological intensive (e.g. OF) vs. CF comparisons. 3. Our global meta-analysis showed that the positive OF-effects on soil respiration, SOC stocks, and SOC sequestration rates were significant even in organic farms with low manure application rates. Although fertilization intensity was the main driver of OF-effects on SOC, leaf and root N concentrations also played a significant role. Across the six European sites, changes towards higher leaf litter N in CF also promoted lower SOC stocks. 4. Our results highlight that crop species displaying traits indicative of resource-acquisitive strategies (e.g. high leaf and root N) increase the difference in SOC between OF and CF. Indeed, changes towards higher crop residue decomposability was related with decreased SOC stocks under CF across European sites. 5. Synthesis and applications. Our study emphasizes that, with management, changes in crop residue traits contribute to the positive effects of organic farming (OF) on soil carbon sequestration. These results provide a clear message to land managers: the choice of crop species, and m

Substantial amounts of nutrients are lost from soils through leaching. These losses can be environmentally damaging, causing groundwater eutrophication and also comprise an economic burden in terms of lost agricultural production. More intense precipitation events caused by climate change will likely aggravate this problem. So far it is unresolved to which extent soil biota can make ecosystems more resilient to climate change and reduce nutrient leaching losses when rainfall intensity increases. In this study, we focused on arbuscular mycorrhizal (AM) fungi, common soil fungi that form symbiotic associations with most land plants and which increase plant nutrient uptake. We hypothesized that AM fungi mitigate nutrient losses following intensive precipitation events (higher amount of precipitation and rain events frequency). To test this, we manipulated the presence of AM fungi in model grassland communities subjected to two rainfall scenarios: moderate and high rainfall intensity. The total amount of nutrients lost through leaching increased substantially with higher rainfall intensity. The presence of AM fungi reduced phosphorus losses by 50% under both rainfall scenarios and nitrogen losses by 40% under high rainfall intensity. Thus, the presence of AM fungi enhanced the nutrient interception ability of soils, and AM fungi reduced the nutrient leaching risk when rainfall intensity increases. These findings are especially relevant in areas with high rainfall intensity (e.g., such as the tropics) and for ecosystems that will experience increased rainfall due to climate change. Overall, this work demonstrates that soil biota such as AM fungi can enhance ecosystem resilience and reduce the negative impact of increased precipitation on nutrient losses.