Above- and below-ground interactions with agricultural management: Effects of soil microbial communities on barley and aphids

Recent research has shown that agricultural management affects microbial biomass and community composition. We investigated the functional implications of such effects in terms of barley biomass production and nutrient acquisition, and whether changes in barley nutrient status affected aphid fecundity. Soils were collected from conventional, ley and organic arable fields and used as inocula in a glasshouse experiment. We determined microbial biomass and community composition using PLFA. We investigated barley growth and nutrient responses to the different soil inoculums, and the impact of excluding arbuscular mycorrhizal fungi (AMF). Aphids were applied to plants within clip cages and numbers of offspring counted. Microbial biomass and community composition were unaffected by agricultural management. The microbial communities altered root and shoot biomass and nutrient allocation, but had no effect on grain yield. Exclusion of AMF significantly increased shoot biomass but reduced grain yield. Aphid fecundity was not significantly affected by the microbial community or shoot nitrogen. We conclude that agricultural intensification does not necessarily have negative consequences for above- and below-ground interactions, and microbial communities from conventionally managed soils may offer equal benefit to crop productivity and nutrition as those from organically managed soils.     

Defoliation effects on Plantago lanceolata resource allocation and soil decomposers in relation to AM symbiosis and fertilization

Plants can mediate interactions between aboveground herbivores and belowground decomposers as both groups depend on plant-provided organic carbon. Most vascular plants also form symbiosis with arbuscular mycorrhizal fungi (AMF), which compete for plant carbon too. Our aim was to reveal how defoliation (trimming of plant leaves twice to 6 cm above the soil surface) and mycorrhizal infection (inoculation of the fungus Glomus claroideum BEG31), in nutrient poor and fertilized conditions, affect plant growth and resource allocation. We also tested how these effects can influence the abundance of microbial-feeding animals and nitrogen availability in the soil. We established a 12-wk microcosm study of Plantago lanceolata plants growing in autoclaved soil, into which we constructed a simplified microfood-web including saprotrophic bacteria and fungi and their nematode feeders. We found that fertilization, defoliation and inoculation of the mycorrhizal fungus all decreased P. lanceolata root growth and that fertilization increased leaf production. Plant inflorescence growth was decreased by defoliation and increased by fertilization and AMF inoculation. These results suggest a negative influence of the treatments on P. lanceolata belowground biomass allocation. Of the soil organisms, AMF root colonization decreased with fertilization and increased with defoliation. Fertilization decreased numbers of bacterial-feeding nematodes, probably because fertilized plants produced less root mass. On the other hand, bacterial feeders were more abundant when associated with defoliated than non-defoliated plants despite defoliated plants having less root mass. The AMF inoculation per se increased the abundance of fungal feeders, but the reduced and increased root AM colonization rates of fertilized and defoliated plants, respectively, were not reflected in the numbers of fungal feeders. We found no evidence of plant-mediated effects of the AM fungus on bacterial feeders, and against our prediction, soil inorganic nitrogen concentrations were not positively associated with the concomitant abundances of microbial-feeding animals. Altogether, our results suggest that (1) while defoliation, fertilization and AMF inoculation all affect plant resource allocation, (2) they do not greatly interact with each other. Moreover, it appears that (3) while changes in plant resource allocation due to fertilization and defoliation can influence numbers of bacterial feeders in the soil, (4) these effects may not significantly alter mineral N concentrations in the soil.     

Inoculating maize fields with earthworms (Aporrectodea trapezoides) and an arbuscular mycorrhizal fungus (Rhizophagus intraradices) improves mycorrhizal community structure and increases plant nutrient uptake

Earthworms and arbuscular mycorrhizal fungi (AMF) are important macrofauna and microorganisms of the rhizosphere. The effect of the inoculation of soil with earthworms (Aporrectodea trapezoides) and mycorrhiza (Rhizophagus intraradices) on the community structure of mycorrhizal fungi and plant nutrient uptake was determined with split plots in a maize field. Maize plants were inoculated or not inoculated with AMF, each treated with or without earthworms. Wheat straw was added as a feed source for earthworms. Inoculating AMF significantly increased maize yield (p?<?0.05), and the yield was further enhanced by the addition of earthworms. Alkaline phosphomonoesterase activities, soil microbial biomass carbon (SMBC) and nitrogen (SMBN) increased with the addition of both earthworms and AMF. Soil inorganic N and available K were positively affected by earthworms, while available P showed a negative relationship with AMF. Treatment with both AMF and earthworms increased shoot and root biomass as well as their N and P uptake by affecting soil phosphomonoesterase and urease activities, SMBC, SMBN, and the content of available nutrients in soil. The applied fungal inoculants were successfully traced by polymerase chain reaction with novel primers (AML1 and AML2) which target the small subunit rRNA gene. The amplicons were classified by restriction fragment length polymorphism and sequencing. Moreover, field inoculation with inocula of non-native isolates of R. intraradices appeared to have stimulated root colonization and yield of maize. Adding earthworms might influence native AMF community, and the corresponding abundance increased after earthworms were inoculated, which has positive effects on maize growth.     

蚯蚓与菌根提高玉米生长和氮磷吸收的互补效应

【目的】蚯蚓和丛枝菌根真菌处于不同的营养级,但在促进植物生长和提高土壤肥力等方面却都发挥着积极作用。研究蚯蚓菌根互作及其对玉米吸收土壤中的氮、磷养分的影响,可为提升土壤生物肥力及促进农业的可持续发展提供理论依据。【方法】本研究采用田间盆栽方式,以玉米为供试作物,研究蚯蚓(Eisenia fetida)与丛枝菌根真菌(Glomus intraradices)互作及其对玉米养分吸收的影响。试验设置P 25和175 mg/kg两个水平。每个磷水平进行接种与不接种菌根真菌以及添加与不添加蚯蚓,共8个处理。调查了玉米生长、养分吸收以及真菌浸染和土壤养分的有效性。【结果】两个磷水平下,蚯蚓和菌根在增加玉米地上部和根系生物量方面有显著正交互作用(P0.05)。接种菌根真菌的各处理显著增加了玉米的侵染率及泡囊丰度、根内菌丝丰度等菌根指标。同时添加蚯蚓和接种菌根真菌的处理(AM+E)显著提高了菌根的侵染率、菌丝密度、丛枝丰度和根内菌丝丰度但是泡囊丰度有所下降。两种磷水平下,AM+E处理玉米地上部和地下部含氮量和含磷量均显著高于其他三个处理。在低磷条件下,地上部氮磷总量的增加分别是添加蚯蚓和接菌的作用;而地下部磷总量的增加主要是菌根真菌的作用。在高磷条件下,单加蚯蚓显著增加玉米氮磷的总量,而接种菌根真菌对玉米氮磷吸收的影响未达显著性水平。在高磷条件下,单加蚯蚓的处理显著提高玉米地上地下部生物量(P0.05),而单接菌的处理效应不显著,蚯蚓菌根互作通过提高土壤微生物量碳、氮实现对玉米生长和养分吸收的调控。在低磷条件下,单接菌显著提高了玉米的生物量(P0.05),单加蚯蚓的处理具有增加玉米生物量的趋势。菌根真菌主要促进玉米对磷的吸收,蚯蚓主要矿化秸秆和土壤中的氮磷养分增加土壤养分的有效性,蚯蚓菌根互作促进了玉米根系对土壤养分的吸收并形成氮磷互补效应。【结论】无论在高磷还是低磷水平下,蚯蚓菌根相互作用都提高了玉米地上地下部生物量、氮磷吸收量同时提高了土壤微生物量碳、氮。蚯蚓菌根相互作用对植物生长的影响取决于土壤养分条件。在高磷条件下(氮相对不足),蚯蚓菌根互作通过调控土壤微生物量碳、氮调控玉米生长和养分吸收。低磷条件下,菌根主要发挥解磷作用,蚯蚓主要矿化秸秆和土壤中的氮素,蚯蚓和菌根互补调控土壤中氮、磷,从而促进植物的生长和养分吸收。     

Impacts of earthworms and arbuscular mycorrhizal fungi (Glomus intraradices) on plant performance are not interrelated

Earthworms and arbuscular mycorrhizal fungi (AMF) might interactively impact plant productivity; however, previous studies reported inconsistent results. We set up a three-factorial greenhouse experiment to study the effects of earthworms (Aporrectodea caliginosa Savigny and Lumbricus terrestris L.) and AMF (Glomus intraradices N.C. Schenck & G.S. Sm.) on the performance (productivity and shoot nutrient content) of plant species (Lolium perenne L., Trifolium pratense L. and Plantago lanceolata L.) belonging to the three functional groups grasses, legumes and herbs, respectively. Further, we investigated earthworm performance and plant root mycorrhization as affected by the treatments. Our results accentuate the importance of root derived resources for earthworm performance since earthworm weight (A. caliginosa and L. terrestris) and survival (L. terrestris) were significantly lower in microcosms containing P. lanceolata than in those containing T. pratense. However, earthworm performance was not affected by AMF, and plant root mycorrhization was not modified by earthworms. Although AMF effectively competed with T. pratense for soil N (as indicated by δ¹⁵N analysis), AMF enhanced the productivity of T. pratense considerably by improving P availability. Remarkably, we found no evidence for interactive effects of earthworms and AMF on the performance of the plant species studied. This suggests that interactions between earthworms and AMF likely are of minor importance.     

Herbivory of an invasive slug in a model grassland community can be affected by earthworms and mycorrhizal fungi

Invasion of non-native species is among the top threats for the biodiversity and functioning of native and agricultural ecosystems worldwide. We investigated whether the herbivory of the slug Arion vulgaris (formerly Arion lusitanicus; Gastropoda), that is listed among the 100 worst alien species in Europe, is affected by soil organisms commonly present in terrestrial ecosystems (i.e. earthworms—Annelida: Lumbricidae and arbuscular mycorrhizal fungi—AMF, Glomerales). We hypothesized that slug herbivory would be affected by soil organisms via altered plant nutrient availability and plant quality. In a greenhouse experiment, we created a simple plant community consisting of a grass, a forb, and a legume species and inoculated these systems with either two earthworm species and/or four AMF taxa. Slugs were introduced after plants were established. Earthworms significantly reduced total slug herbivory in AMF-inoculated plant communities (P?=?0.013). Across plant species, earthworms increased leaf total N and secondary metabolites, AMF decreased leaf thickness. Mycorrhizae induced a shift in slug feeding preference from non-legumes to legumes; the grass was generally avoided by slugs. AMF effects on legume herbivory can partly be explained by the AMF-induced increase in total N and decrease in C/N ratio; earthworm effects are less clear as no worm-induced alterations of legume plant chemistry were observed. The presence of earthworms increased average AMF colonization of plant roots by 140 % (P?<?0.001). Total shoot mass was significantly increased by AMF (P?<?0.001). These data suggest that the feeding behavior of this invasive slug is altered by a belowground control of plant chemical quality and community structure.     

Earthworms can modify effects of hydrochar on growth of Plantago lanceolata and performance of arbuscular mycorrhizal fungi

Hydrothermal carbonization (HTC) is a method to produce carbonized material at relatively low temperatures (180–250 °C) under pressure and aqueous conditions. The product is called hydrochar and can be used as a soil amendment. However, applied in high dosages it may have detrimental effects on plants or soil biota. The potential impact of hydrochar amendment on beneficial soil organisms such as arbuscular mycorrhizal fungi (AMF) and earthworms and their interactions are not well understood. The goal of the present study was to determine effects of hydrochar on plant growth and soil biota and to evaluate interactions of earthworms and hydrochar on plant and AMF performance and to identify underlying mechanisms. In a greenhouse experiment, we investigated the effect of hydrochar at different addition rates (control, 1% and 10%, v/v) with or without the earthworm Aporrectodea caliginosa on the growth of Plantago lanceolata L. and the performance of its AMF. We observed a positive interaction between earthworms and 10% hydrochar on shoot and root biomass: added as a single treatment hydrochar had a negative effect on plant growth at this dosage, but plant biomass increased significantly when hydrochar was added together with earthworms. Root colonization by AMF increased significantly with increasing concentration of hydrochar, but was not affected by earthworms. Contrastingly, extraradical hyphal length of AMF was reduced by earthworms, but not affected by hydrochar. Thus, hydrochar and earthworms affected the performance of AMF, albeit of different AMF structures and in different directions. Our results indicate that earthworms may play an important role in alleviating the negative impacts of high dosages of hydrochar on plant growth; such interactions should move into focus of future research on potential effects of HTC materials.     

Effect of biochar on the growth of Poncirus trifoliata (L.) Raf. seedlings in Gannan acidic red soil

Soil acidification has become a serious problem for citrus cultivation in China. As a soil amendment, biochar is expected to increase soil pH as well as soil fertility. In this study, we assessed the effect of biochar on Trifoliate orange, the most frequently used citrus rootstock, in a pot experiment using acidic red soil from the Gannan citrus production area. Plant height and shoot diameter of Poncirus trifoliata (L.) Raf. seedlings increased significantly after biochar was added to soils. This positive effect was further evidenced by the increased plant biomass and leaf net photosynthetic rate. The root system architecture (RSA) was evaluated based on root length, root surface area, root volume and root tip. Biochar amendment significantly increased the total absorptive surface area of the root system. Due to the significant role of arbuscular mycorrhizal fungi (AMF) in citrus root nutrient uptake, the AMF colonization and community in Poncirus roots were investigated. The AMF colonization rate was not significantly affected by biochar, whereas AMF diversity increased upon biochar treatment. In addition, the biochar treatment resulted in increases in soil pH, organic matter and mineral nutrients. Together, our results suggest that the positive effects of biochar on the growth performance of Poncirus seedlings can be attributed to the substantial augmentation of soil fertility, increased soil pH, optimized RSA and improved AMF species composition.     

Do interactions with soil organisms mediate grass responses to defoliation?

Defoliation-induced changes in grass growth and C allocation are known to affect soil organisms, but how much these effects in turn mediate grass responses to defoliation is not fully understood. Here, we present results from a microcosm study that assessed the role of arbuscular mycorrhizal (AM) fungi and soil decomposers in the response of a common forage grass, Phleum pratense L., to defoliation at two nutrient availabilities (added inorganic nutrients or no added nutrients). We measured the growth and C and N allocations of P. pratense plants as well as the abundance of soil organisms in the plant rhizosphere 5 and 19 d after defoliation. To examine whether defoliation affected the availability of organic N to plants, we added ¹⁵N-labelled root litter to the soil and tracked the movement of mineralized ¹⁵N from the litter to the plant shoots.When inorganic nutrients were not added, defoliation reduced P. pratense growth and root C allocation, but increased the shoot N concentration, shoot N yield (amount of N in clipped plus harvested shoot mass) and relative shoot N allocation. Defoliation also reduced N uptake from the litter but did not affect total plant N uptake. Among soil organisms, defoliation reduced the root colonization rates of AM fungi but did not affect soil microbial respiration or the abundance of microbe-grazing nematodes. These results indicate that interactions with soil organisms were not responsible for the increased shoot N concentration and shoot N yield of defoliated P. pratense plants. Instead, these effects apparently reflect a higher efficiency in N uptake per unit plant mass and increased relative allocation of N to shoots in defoliated plants. The role of soil organisms did not change when additional nutrients were available at the moment of defoliation, but the effects of defoliation on shoot N concentration and yield became negative, apparently due to the reduced ability of defoliated plants to compete for the pulse of inorganic nutrients added at the moment of defoliation.Our results show that the typical grass responses to defoliation—increased shoot N concentration and shoot N yield—are not necessarily mediated by soil organisms. We also found that these responses followed defoliation even when the ability of plants to utilize N from organic sources, such as plant litter, was diminished, because defoliated plants showed higher N-uptake efficiency per unit plant mass and allocated relatively more N to shoots than non-defoliated plants.     

Above- and below-ground plant inputs both fuel soil food webs

Soil food webs depend almost exclusively on plant derived resources; however, it is still subject to debate how plants affect soil biota. We tested the effects on soil decomposers of three components of soil inputs of plant species identity: presence of live plants (representing rhizodeposits), identity of shoot litter input and identity of root litter input; using all combinations of these for Trifolium pratense and Plantago lanceolata. We assessed impacts on soil microorganisms, Collembola, Oribatida and earthworms in a full-factorial greenhouse experiment. Species identity of shoot litter input had greatest effect on decomposers, following by species identity of live plant. Microbial carbon use efficiency and Oribatida density were significantly higher in the presence of T. pratense shoot litter input than in that of P. lanceolata shoot litter input, while earthworm body mass ratio was significantly higher in the presence of P. lanceolata plants than in that of T. pratense plants. Oribatida density was at minimum in the presence of P. lanceolata plants, shoot and root litter input, resulting in a significant three-way interaction and pointing to the relevance of all investigated plant input pathways. Live plant identity effects were not due to differences in living root biomass among species and treatments. Detrimental P. lanceolata effects may have been due to significantly lower N concentrations than in T. pratense tissue. Our results indicate that both above- and below-ground plant inputs into soil determine the performance of decomposers, and thus suggest due consideration of both types of inputs fueling soil food webs in future studies.     

Arbuscular mycorrhizal fungi reduce decomposition of woody plant litter while increasing soil aggregation

The decomposition of plant organic matter and the stability of soil aggregates are important components of soil carbon cycling, and the relationship between decomposition rate and arbuscular mycorrhizal fungi (AMF) has recently received considerable attention. The interaction of AMF with their associated microorganisms and the consequences for litter decomposition and soil aggregation still remain fairly unclear. In a laboratory pot experiment we simultaneously tested the single and combined effects of one AMF species (Rhizophagus irregularis) and a natural non-AMF microbial community on the decomposition of small wooden sticks and on soil aggregation. To disentangle effects of hyphae and roots we placed mesh bags as root exclusion compartments in the soil. The decomposition of the wooden sticks in this compartment was significantly reduced in the presence of AMF, but not with the non-AMF microbial community only, compared to the control, while aggregation was increased in all treatments compared to the control. We suggest that AMF directly (via localized nutrient removal or altered moisture conditions) or indirectly (by providing an alternative carbon source) inhibited the activity of decomposers, leading to different levels of plant litter degradation under our experimental settings. Reduced decomposition of woody litter in presence of AMF can be important for nutrient cycling in AMF-dominated forests and in the case of woody plants and perennials that develop lignified roots in grasslands.     

地上和地下植食者互作对水稻氮分配及土壤活性氮的影响

植物茎叶和根系植食者虽然在空间上隔离,但二者的相互作用被认为是联系地上和地下部生态系统的基础。土壤氮素有效性通过植物影响植食者已得到大量研究的证实,但有关地上和地下部植食者互作对土壤氮素影响的研究却鲜有报道。以水稻褐飞虱和潜根线虫分别作为地上和地下的植食者,采用两因素交互试验设计,两个褐飞虱水平(未接种褐飞虱、接种褐飞虱),两个潜根线虫水平(未接种潜根线虫、接种潜根线虫),探讨二者的交互作用对水稻氮吸收和土壤活性氮(微生物生物量氮、可溶性有机氮以及铵态氮和硝态氮)的影响。结果表明,褐飞虱和潜根线虫相互抑制,二者的共存加剧了对水稻茎叶和根系生长的危害。褐飞虱未影响水稻茎叶和根系含氮量,而潜根线虫显著降低了水稻根系含氮量(p0.05)。褐飞虱和潜根线虫对土壤活性氮的影响表现出强烈的交互作用,在未接潜根线虫的处理中,褐飞虱显著提高了微生物生物量氮含量(p0.05),显著降低了硝态氮含量(p0.05);潜根线虫显著影响了微生物生物量氮含量和土壤活性氮总量。总之,褐飞虱和潜根线虫的相互抑制关系对土壤活性氮的影响格局较为复杂,相比褐飞虱,潜根线虫趋向于提高土壤活性氮水平,这可能影响与氮转化有关的土壤生态功能。     

Earthworm (Aporrectodea trapezoides)–mycorrhiza (Glomus intraradices) interaction and nitrogen and phosphorus uptake by maize

The interactive impacts of arbuscular mycorrhizal fungi (AMF, Glomus intraradices) and earthworms (Aporrectodea trapezoides) on maize (Zea mays L.) growth and nutrient uptake were studied under near natural conditions with pots buried in the soil of a maize field. Treatments included maize plants inoculated vs. not inoculated with AMF, treated or not treated with earthworms, at low (25 mg kg⁻¹) or high (175 mg kg⁻¹) P fertilization rate. Wheat straw was added as feed for earthworms. Root colonization, mycorrhiza structure, plant biomass and N and P contents of shoots and roots, soil available P and NO₃⁻–N concentrations, and soil microbial biomass C and N were measured at harvest. Results indicated that mycorrhizal colonization increased markedly in maize inoculated with AMF especially at low P rate, which was further enhanced by the addition of earthworms. AMF and earthworms interactively increased maize shoot and root biomass as well as N and P uptake but decreased soil NO₃⁻–N and available P concentrations at harvest. Earthworm and AMF interaction also increased soil microbial biomass C, which probably improved root N and P contents and indirectly increased the shoot N and P uptake. At low P rate, soil N mobilization by earthworms might have reduced potential N competition by arbuscular mycorrhizal hyphae, resulting in greater plant shoot and root biomass. Earthworms and AMF interactively enhanced soil N and P availability, leading to greater nutrient uptake and plant growth.     

Differential effect of arbuscular mycorrhizal fungal communities from ecosystems along management gradient on the growth of forest understorey plant species

Arbuscular mycorrhizal fungi (AMF) are important functional components of ecosystems. Although there is accumulating knowledge about AMF diversity in different ecosystems, the effect of forest management on diversity and functional characteristics of AMF communities has not been addressed. Here, we used soil inoculum representing three different AM fungal communities (from a young forest stand, an old forest stand and an arable field) in a greenhouse experiment to investigate their effect on the growth of three plant species with contrasting local distributions - Geum rivale, Trifolium pratense and Hypericum maculatum. AM fungal communities in plant roots were analysed using the terminal restriction fragment length polymorphism (T-RFLP) method. The effect of natural AMF communities from the old and young forest on the growth of studied plant species was similar. However, the AMF community from the contrasting arable ecosystems increased H. maculatum root and shoot biomass compared with forest inocula and T. pratense root biomass compared to sterile control. According to ordination analysis AMF inocula from old and young forest resulted in similar root AMF communities whilst plants grown with AM fungi from arable field hosted a different AMF community from those grown with old forest inocula. AMF richness in plant roots was not related to the origin of AMF inoculum. G. rivale hosted a significantly different AM fungal community to that of T. pratense and H. maculatum. We conclude that although the composition of AM fungal communities in intensively managed stands differed from that of old stands, the ecosystem can still offer the ‘symbiotic service’ necessary for the restoration of a characteristic old growth understorey plant community.     

Effects of Collembola on root properties of two competing ruderal plant species

Plant roots compete for nutrients mineralised by the decomposer community in soil. By affecting microbial biomass and activity Collembola influence the nutrient availability to plants. We investigated the effect of Collembola (Protaphorura fimata Gisin) on growth and competition between of two plant species, Cirsium arvense L (creeping thistle) and Epilobium adnatum Griseb. (square-stemmed willow herb), in a laboratory experiment. Two seedlings of each plant species were planted in rhizotrons either in combination or in monoculture (intra- and interspecific competition). Interspecific competition strongly reduced total biomass of C. arvense whereas E. adnatum suffered most from intraspecific competition. Collembola neither affected the competitive relationship of the two plant species nor shoot and root biomass. Although Collembola did not affect total root biomass they influenced root morphology of both plant species. Roots grew longer and thinner and had more root tips in presence of Collembola. Root elongation is generally ascribed to the exploitation of nutrient rich patches in soil. We hypothesise that changes in root morphology in presence of Collembola are due to Collembola-mediated changes in nutrient availability and distribution.     

磷肥对酸性红壤上玉米不同部位丛枝菌根真菌群落的影响

为了研究不同磷肥水平下酸性红壤上玉米不同部位丛枝菌根真菌(Arbuscular mycorrhizal fungi, AMF)群落多样性和组成结构,明确玉米不同部位AMF群落的分布特征及对磷肥的响应差别,为提高酸性红壤磷素利用提供理论依据。本实验设置三个磷肥水平：不施磷、低磷(25 mg P /kg)和高磷(100 mg P /kg),玉米培养4周后,测定玉米生物量和土壤理化性质,利用高通量测序技术检测玉米根部、根际和非根际土壤AMF群落结构和多样性。结果显示,随着磷肥水平增加,玉米生物量显著提高,高磷处理下玉米地上部磷含量显著高于不施磷和低磷处理。取样部位(根部、根际和非根际)显著影响了AMF群落优势属球囊霉属(Glomus)、巨孢囊霉属(Paraglomus)和近明球囊霉属(Claroideoglomus)相对丰度,但是磷肥影响不显著。类似的,取样部位而不是磷肥显著影响了AMF群落香农指数和物种丰富度。非度量多维标度(NMDS)结果显示,根部样品与非根际和根际土壤样品群落距离更远,而相同取样部位中不同磷肥水平间群落组成更为相似；置换多元方差分析(PERMANOVA)进一步表明,取样部位而不是磷肥显著影响了AMF群落组成结构,主要表现在根部样品与根际和非根际土壤不同。因此,酸性红壤上玉米不同部位对AMF群落的影响明显高于磷肥作用,表明AMF应用于酸性红壤时应重点考虑作物部位的特性。     

Some plants like it warmer: Increased growth of three selected invasive plant species in soils with a history of experimental warming

Soil warming can affect plant performance by increasing soil nutrient availability through accelerating microbial activity. Here, we test the effect of experimental soil warming on the growth of the three invasive plant species Trifolium pratense (legume), Phleum pratense (grass), and Plantago lanceolata (herb) in the temperate-boreal forest ecotone of Minnesota (USA). Plants were grown from seed mixtures in microcosms of soils with three different warming histories over four years: ambient, ambient +1.7 °C, and ambient +3.4 °C. Shoot biomass of P. pratense and P. lanceolata and plant community root biomass increased significantly in soils with +3.4 °C warming history, whereas T. pratense responded positively but not significantly. Soil microbial biomass and N concentration could not explain warming effects, although the latter correlated significantly with the shoot biomass of P. lanceolata. Our results indicate that soil with a warming history may benefit some invasive plants in the temperate-boreal ecotone with potential impacts on plant community composition. Future studies should investigate the impact of warming-induced differences in soil organisms and nutrients on plant invasion.     

Resource dynamics in an early-successional plant community are influenced by insect exclusion

The exclusion of insects from terrestrial ecosystems may change productivity, diversity and composition of plant communities and thereby nutrient dynamics. In an early-successional plant community we reduced densities of above- and below-ground insects in a factorial design using insecticides. Beside measuring vegetation dynamics we investigated the effects of insect exclusion on above- and below-ground plant biomass, below-ground C and N storage by plants, litter quality, decomposition rate, soil water content, soil C:N ratio, nutrient availability and soil microbial activity and biomass.The application of soil insecticide had only minor effects on above- and below-ground biomass of the plant community but increased carbon content in root biomass and total carbon and nitrogen storage in roots. In one of the three investigated plant species (Cirsium arvense), application of soil insecticide decreased nitrogen concentration of leaves (−12%). Since C. arvense responded positively to soil insecticide application, this effect may be due to drought stress caused by root herbivory. Decomposition rate was slightly increased by the application of above-ground insecticide, possibly due to an impact on epigeic predators. The application of soil insecticide caused a slightly increased availability of soil water and an increased availability of mineralised nitrogen (+30%) in the second season. We explain these effects by phenological differences between the plant communities, which developed on the experimental plots. Microbial biomass and activity were not influenced by insecticide application, but were correlated to above-ground plant biomass of the previous year. Overall, we conclude that the particular traits of the involved plant species, e.g. their phenology, are the key to understand the resource dynamics in the soil.     

Soil arthropods beneficially rather than detrimentally impact plant performance in experimental grassland systems of different diversity

Impacts of belowground insecticide application on plant performance and changes in plant community structure almost uniformly have been ascribed to reduced belowground herbivory, although recent studies reported distinct side effects on detritivore soil animals, particularly on Collembola. Consequently, it remains controversial if the resulting soil feedbacks on plants are due to alterations in arthropod herbivory or to changes in the activity of detritivores. We investigated the impacts of the application of a commonly used belowground insecticide (chlorpyrifos) on soil animals and soil feedbacks on model plant species representing two main plant functional groups of grassland communities, the grass Lolium perenne and the forb Centaurea jacea.Insecticide application decreased soil insect herbivore densities considerably. However, also Collembola densities and diversity decreased markedly due to insecticide application and this was most pronounced in Entomobryidae, Isotomidae, Hypogastruridae, and Sminthuridae. While densities of other detritivore taxa were not affected or even increased (Oribatida) in insecticide subplots, that of predators mostly decreased.Both model plant species built considerably more biomass in control subplots than in insecticide subplots irrespective of characteristics of the resident plant community. This suggests that soil feedbacks on plants were not due to belowground herbivory and highlights the significance of alternative mechanisms responsible for insecticide-mediated soil feedbacks on plants. The deterioration of model plant species’ performances in insecticide subplots most likely was due to decreased densities of Collembola resulting in the deceleration of nutrient cycling and plant nutrition. The results suggest that it is oversimplistic to only ascribe insecticide-mediated soil feedbacks on plants to belowground herbivores. The results further indicate that in the present study the impact of arthropod detritivores on plant productivity was more important than that of belowground herbivores. This emphasizes that plant-soil arthropod interactions in grassland might be based on both facilitative and antagonistic interrelationships.