Ditch-buried straw return (DB-SR) is a novel soil fertility building method by combing straw incorporation and tillage rotation in rice-wheat annual double cropping system. Several benefits of DB-SR have been shown, e.g. improving carbon sequestration, nitrogen retention and soil aggregation. However, how long-term DB-SR affecting the metabolic activity and diversity of soil microbial communities is still unclear. In this study, we investigated the effects of DB-SR application after 5 years (rice season) and 5.5 years (wheat season) on functional patterns, including the overall functional activity, reflected by fluorescein diacetate hydrolase (FDA) activity, the overall growth activity, reflected by soil respiration rate, extracellular element-cycling enzyme activity, glomalin content and metabolic diversity in different soil layers. Our results first showed that DB-SR significantly increased the overall functional activity (FDA hydrolase) and growth activity (respiration rate) in 10-20 cm and 20-30 cm soils. Second, beta-glucosidase, lipase, acid phosphatase and arylsulphatase activities were significantly increased by DB-SR in different soil layers. However, urease activity was only increased by DB-SR in wheat soils, but reduced in the 0-10 cm and 20-30 cm soils after growing rice. In addition, DB-SR significantly increased the content of total glomalin and easily extracted glomalin. Finally, DB-SR significantly increased microbial metabolic diversity of carbon substrates in different soil layers. Overall, the metabolic activity and diversity of microbial communities were shown with a larger increase in 10-20 cm (above the straw layer) than 0-10 cm and 20-30 cm soil layers; and tended to increase with straw burial duration. These findings suggest that the long-term application of DB-SR is helpful to drive material transformation and nutrient supply, which can further benefit crop production in rice-wheat rotation systems.

As a novel soil tillage practice, ditch-buried straw return (DB-SR) has exhibited positive effects on soil carbon sequestration, nitrogen retention and rice yield in previous studies. However, little is known about how long-term DB-SR affects soil hydrothermal and microbial processes. Our objective is to test whether DB-SR will alter the soil water potential, temperature and microbial community in a wheat field following rice cultivation. In this study, we found significant alterations in soil water potential, temperature, and microbial communities driven by DB-SR. On average, soil water potential was significantly reduced by 37.33% and 17.56% under DB-SR to a depth of 20 cm (DB-SR-20) and 40 cm (DB-SR-40), respectively. DB-SR-20 increased soil mean daily temperature and daily range of temperature more than DB-SR-40, possibly caused by decreased water content, especially at soil depths of 10 and 15 cm. Both DB-SR-20 and DB-SR-40 led to distinct shifts in soil bacterial and fungal community composition. DB-SR-20 significantly increased the activities of peroxidase, cellobiohydrolase, urease, and acid phosphatase by 3.5%, 75.0%, 81.4% and 41.7%, respectively, but had no effects on beta-D-glucosidase activity. DB-SR-40, in contrast, significantly increased the activities of peroxidase and cellobiohydrolase by 2.4% and 36.0%, respectively, but showed no effects on urease and acid phosphatase. It did, however, reduce p-o-glucosidase activity by 15.0%. Overall functional diversity was increased by 29.9% under DBSR-20 but was not affected by DB-SR-40. Our results suggest that these improvements in soil ecological processes driven by DB-SR will promote wheat yield in a rice-wheat rotation system. (C) 2016 Elsevier B.V. All rights reserved.

Arbuscular mycorrhizal fungi ( AMF) are a group of ecologically important soil microbes and show wide geographic distribution across the globe. AMF form obligate symbiosis with roots of -80% land plants. In the symbiosis, host plants provide carbon for AMF in return for several benefits, i.e., promoting nutrient uptake, tolerating drought and salt stress, resisting pathogens and herbivores, etc. AMF also can redistribute resources ( i.e., C, N and P) between plants and alter their competitive interactions, and thus drive plant population dynamics and community processes. AMF diversity is one of the most important components in soil diversity. In the past decades, AMF are found in almost all terrestrial habitats, including grassland, forest, desert, wetland, alpine meadow, polar region and mangrove, etc. This suggests that AMF have high species diversity. Although AMF diversity has a relatively long research history, most studies only tried to investigate species composition in AMF communities, little is known about the functioning of AMF diversity. In this mini⁃ review, we summarized the new advances in the AMF diversity field, including ecological functioning, determinants and assembling rules. AMF diversity has important ecological functioning. Here, we discussed three aspects: the effects on plant system diversity, stability and productivity. First, several studies reported that AMF diversity is an important determinant for plant diversity. This might be caused by mycorrhizal dependence of subordinate plants. Some studies found that host plants have some preferentially selection towards AMF. Thus, with increasing AMF diversity, subordinate plants will have a higher probability to meet their best AMF partner. Another possibility is that negative plant⁃mycorrhiza feedbacks might generate positive AMF diversity⁃plant diversity patterns. This might be caused by host selection towards specific AMF communities. Distinctive AMF communities will make host plants occupy different niche for soil resources. Secondly, AMF diversity could stabilize plant community. Two possibilities can be used to explain this pattern. One is functioning redundancy for several

The arbuscular mycorrhiza (AM) is among the most ubiquitous symbiosis in the world. A meta-analysis of 759 articles (1978–2012) was conducted to test whether ecologically important host plant traits (N-fixation and C-fixation pathway) affect the response of the plant to mycorrhizal colonization. We found that the effect of N-fixation on mycorrhizal growth response (MGR) depended on whether the plant was woody or a forb. N-fixing forbs had a higher MGR than non-N-fixing forbs, but the reverse was true for woody plants. Moreover, C4-grasses had significantly higher MGR than C3-grasses, but no significant difference was found between C3 and C4 forbs, or between C3 and C4 woody species. Overall, woody species had higher MGR than any other functional group. These results demonstrate that MGR does depend on host functional characteristics, but neither N-fixation capacity nor C-fixation pathway are apparently fundamental controllers of MGR. Instead, it would appear possible that these traits influence MGR only insofar as they influence more fundamental functions such as P demand and P supply.

In microbial ecology, the "everything is everywhere" hypothesis has long been controversial. In the present study, we performed data-mining for 18S rDNA sequences of glomeromycotan fungi in order to test this hypothesis. 18S rDNA sequences targeted using AM1–NS31 fragments were retrieved from GenBank, with a total of 1768 sequences collected from 34 sites worldwide. In total, 229, 330 and 518 operational taxonomic units (OTUs) were defined based on 97, 98 and 99 % similarity, respectively. The 97 % OTUs showed a limited geographical range of glomeromycotan fungi. Among the OTUs, 58.1 % were endemic, and 17.9 % and 9.2 % were found in two and three sites, respectively. The most widespread OTU was shared by 17 sites. Phylogenetic structure analysis demonstrated that most local communities (26 of 34) were clustered. OTUs with larger host breadth had wider geographic ranges. A significant distance–decay relationship was revealed that was independent of habitat. Cluster analysis showed that fungal composition was not related to habitat, while Fast UniFrac analysis indicated that the distribution of Glomeromycota was affected by temperature. Taken together, these results suggest that glomeromycotan fungi were not randomly distributed under natural conditions; rather, they were affected by host plants, dispersal ability and temperature. Thus, the distribution of glomeromycotan fungi argues against the hypothesis that "everything is everywhere."

Ditch-buried straw return (DBSR) is a novel farming system that not only efficiently eliminates the need to burn straw, but also shows positive effects on soil carbon sequestration and crop yields. Implementation of DBSR, however, may penetrate the tillage pan, increasing the risk of N leaching losses. We therefore determined whether N retention could be increased by DBSR in order to reduce the risk of N loss to the environment. A four-year field experiment and a complementary greenhouse experiment were conducted to test the effects of DBSR on N retention in a rice-wheat rotation system. We found that DBSR altered the spatial distribution of fertilizer N. N content was significantly increased above but reduced below the straw layer in the field experiment. The greenhouse experiment further confirmed the N retention effects by the straw layer. In theory, a maximum of 9.09mg urea-N could be adsorbed by one gram dry wheat straw. Our results suggest that DBSR has the potential to increase N retention in the soil, thus increasing crop uptake and minimizing leaching N loss in the rice-wheat rotation system.

为弄清丛枝菌根(arbuscular mycorrhiza,AM)真菌群落随宿主植物演化的变异规律,通过对MaarjAM数据库进行数据挖掘,根据每个分子虚拟种(virtual taxa,VT)包含的DNA序列不少于5条的标准,筛选出188种菌根植物.通过分析植物与其根内AM真菌的关系发现:AM真菌的物种丰富度随着寄主植物的分化而增加;在不同的植物系统类群中,AM真菌的物种丰富度显著不同;在起源时间较晚的被子植物和裸子植物中,AM真菌的物种丰富度显著高于起源较早的苔类、角苔类和蕨类植物类群,而与寄生植物共生的AM真菌物种丰富度与早期植物无显著差异;不同寄主植物进化类群间AM真菌组成差异显著.以上结果表明:AM真菌群落随着寄主植物进化而发生变化.在进化过程中,寄主植物倾向于选择保留共生效率较高的AM真菌.

Our aim was to explore the way that root system type affects mycorrhizal growth response of plants.

BACKGROUND:Crop residue management and nitrogen loss are two important environmental problems in the rice-wheat rotation system in China. This study investigated the effects of burial of straw on water percolation, nitrogen loss by leaching, crop growth and yield. Greenhouse mesocosm experiments were conducted over the course of three simulated cropping seasons in a rice1-wheat-rice2 rotation. RESULTS:Greater amounts of straw resulted in more water percolation, irrespective of crop season. Burial at 20 and 35 cm significantly reduced, but burial at 50 cm increased nitrogen leaching. Straw at 500 kg ha(-1) reduced, but at 1000 kg ha(-1) and at 1500 kg ha(-1) straw increased nitrogen leaching in three consecutive crop rotations. In addition, straw at 500 kg ha(-1) buried at 35 cm significantly increased yield and its components for both crops. CONCLUSIONS:This study suggests that N losses via leaching from the rice-wheat rotation may be reduced by the burial of the appropriate amount of straw at the appropriate depth. Greater amounts of buried straw, however, may promote nitrogen leaching and negatively affect crop growth and yields. Complementary field experiments must be performed to make specific agronomic recommendations.

Naturally, simultaneous interactions occurred among plants, herbivores, and soil biota, that is, arbuscular mycorrhizal fungi (AMF), nematodes, and fungal pathogens. These multiple interactions play fundamental roles in driving process, structure, and functioning of ecosystems. In this study, we conducted a meta-analysis with 144 papers to investigate the interactions between AMF and plant biotic stressors and their effects on plant growth performance. We found that AMF enhanced plant tolerance to herbivores, nematodes, and fungal pathogens. We also found reciprocal inhibition between AMF and nematodes as well as fungal pathogens, but unidirectional inhibition for AMF on herbivores. Negative effects of AMF on biotic stressors of plants depended on herbivore feeding sites and actioning modes of fungal pathogens. More performance was reduced in root-feeding than in shoot-feeding herbivores and in rotting- than in wilt-fungal pathogens. However, no difference was found for AMF negative effects between migratory and sedentary nematodes. In return, nematodes and fungal pathogens generated more reduction of root colonization in Non-Glomeraceae than in Glomeraceae. Our results suggested that AMF positive effects on plants might be indirectly mediated by competitive inhibition with biotic stressors of plants. These positive and negative interactions make potential contributions to maintaining ecosystem stability and functioning.