Lignosulfonate promotes the interaction between Scots pine and an ectomycorrhizal fungus Pisolithus tinctorius in vitro

Lignosulfonate (LS) is a lignin-based polymer obtained as a by-product from paper industry, which may have potential as an amendment with macronutrients. We studied effects of LS on the interaction between Scots pine (Pinus sylvestris L.) seedlings and hypocotyl cuttings and the ectomycorrhizal (ECM) fungusPisolithus tinctorius (Pers.) Coker and Couch. The experiments were performed in vitroon the MMN agar medium containing Fe–LS chelate at the concentrations of 0, 5, 10 and 25 mg/L. Inoculation with P. tinctoriusincreased root growth of the seedlings. Fe–LS enhanced P. tinctorius induced formation of lateral roots and had a dose-dependent positive effect on the establishment of mycorrhizas on the seedlings. The growth of the fungal mycelium was improved by Fe–LS, which might cause faster and more intensive contact with the roots and, thus, better root growth and mycorrhiza formation. P.tinctorius enhanced also adventitious root formation and subsequent root growth of the hypocotyl cuttings but without any synergistic effect with Fe–LS. Our study with P. tinctorius and Scots pine in vitro indicates that a low-cost by-product Fe–LS, obtained from paper industry, may be a potential tool to improve the efficiency of fungal inoculations, thus, facilitating the early interaction between an ECM fungus and host seedling.     

Interactions between pinewood nematodes and the fungal community of pine trees

The pinewood nematode Bursaphelenchus xylophilus, is the pathogenic agent of pine wilt disease and a globally notable pine pest. Despite being a plant pathogen, B. xylophilus has a mycophagous phase during its life cycle. We assessed the capacity for polyphagy of mycetophagous pinewood nematodes, testing which of the common species of fungi in pine trees provide better food and higher population growth rates. B. xylophilus performed particularly well on airborne fungi, namely the endophytes Botrytis cinerea and Cladosporium herbarum, and the pathogens Sirococcus conigenus and Sphaeropsis sapinea. Surprisingly, growth performance was not as good on the blue stain species (Ophiostoma spp. and Leptographium spp.) which are considered natural associates of B. xylophilus in the wild. Most of the fungi nonetheless permitted positive population growth of B. xylophilus, which is polyphagous and capable of feeding on numerous fungal species with diverse ecological niches.     

Facilitation and inhibition: changes in plant nitrogen and secondary metabolites mediate interactions between above-ground and below-ground herbivores

To date, it remains unclear how herbivore-induced changes in plant primary and secondary metabolites impact above-ground and below-ground herbivore interactions. Here, we report effects of above-ground (adult) and below-ground (larval) feeding by Bikasha collaris on nitrogen and secondary chemicals in shoots and roots of Triadica sebifera to explain reciprocal above-ground and below-ground insect interactions. Plants increased root tannins with below-ground herbivory, but above-ground herbivory prevented this increase and larval survival doubled. Above-ground herbivory elevated root nitrogen, probably contributing to increased larval survival. However, plants increased foliar tannins with above-ground herbivory and below-ground herbivory amplified this increase, and adult survival decreased. As either foliar or root tannins increased, foliar flavonoids decreased, suggesting a trade-off between these chemicals. Together, these results show that plant chemicals mediate contrasting effects of conspecific larval and adult insects, whereas insects may take advantage of plant responses to facilitate their offspring performance, which may influence population dynamics.     

Multivariate path analysis of the relationships between seedling regeneration and environmental factors beneath a dwarf bamboo understory

Seedling emergence and establishment are fragile processes that determine the direction and structure of forest succession and regeneration. However, seedling emergence and establishment are easily affected by biotic and abiotic (environmental) factors. A dense and expanding understory of dwarf bamboo is one such important factor that can seriously hinder the seedling regeneration. We conducted a field experiment to investigate the emergence and establishment of canopy tree seedlings under artificially controlled densities of dwarf bamboo. We found that understory dwarf bamboo obstructed seedling emergence but reduced the death of seedlings. Although understory dwarf bamboo reduced the median retention time of seedlings, dense bamboo increased the mean survival time of seedlings. Our results suggest that understory dwarf bamboo has multiple selectivities for tree seedling emergence and establishment: high‐density dwarf bamboo was beneficial to evergreen species but lower‐density of bamboo was conducive to the survival of deciduous species, it means the dwarf bamboo potentially alters successional trajectories of forest communities. Path analysis revealed that the most important factors affecting tree seedling emergence and death were the abundance of seeds in the seed bank and the density of emerged seedlings, and that the soil temperature promoted seedling emergence but increased seedling death, the thickness of litter limited seedling emergence, and the leaf area index of the bamboo canopy limited seedling death. The present study suggests that dwarf bamboo can directly alter the microenvironment, significantly reducing light levels and soil temperature but increasing the thickness of litter and soil humus, thereby indirectly impacting the regeneration of tree seedlings. Our results indicate that various factors affected seedling emergence, and there were complex indirect relationships among these factors. In general, biological factors had a stronger influence on tree seedling regeneration than environmental factors.     

Regional scale gradients of climate and nitrogen deposition drive variation in ectomycorrhizal fungal communities associated with native Scots pine

Ectomycorrhizal fungi commonly associate with the roots of forest trees where they enhance nutrient and water uptake, promote seedling establishment and have an important role in forest nutrient cycling. Predicting the response of ectomycorrhizal fungi to environmental change is an important step to maintaining forest productivity in the future. These predictions are currently limited by an incomplete understanding of the relative significance of environmental drivers in determining the community composition of ectomycorrhizal (ECM) fungi at large spatial scales. To identify patterns of community composition in ECM fungi along regional scale gradients of climate and nitrogen deposition in Scotland, fungal communities were analysed from 15 seminatural Scots pine (Pinus sylvestris L.) forests. Fungal taxa were identified by sequencing of the ITS rDNA region using fungal‐specific primers. Nonmetric multidimensional scaling was used to assess the significance of 16 climatic, pollutant and edaphic variables on community composition. Vector fitting showed that there was a strong influence of rainfall and soil moisture on community composition at the species level, and a smaller impact of temperature on the abundance of ectomycorrhizal exploration types. Nitrogen deposition was also found to be important in determining community composition, but only when the forest experiencing the highest deposition (9.8 kg N ha^?1 yr^?1) was included in the analysis. This finding supports previously published critical load estimates for ectomycorrhizal fungi of 5–10 kg N ha^?1 yr^?1. This work demonstrates that both climate and nitrogen deposition can drive gradients of fungal community composition at a regional scale.     

菌根真菌多样性与植物多样性的相互作用研究进展

菌根共生双方多样性影响着生态系统的过程与功能。菌根真菌-寄主植物之间的共生组合存在偏好性或特异性,这导致菌根真菌对寄主植物的效益差异和寄主植物对菌根真菌的利益差别：两者在互利共生过程中不仅相互选择,还存在相互促进与制约的关系(如互补与选择效应、竞争),从而在一定程度上决定生态系统的演化与发展。本文概述了植物多样性与菌根真菌多样性的相互影响,探讨了两者互作可能存在的调控因素与机制,对存在的问题和争议进行了总结,并提出了进一步研究的方向。深入阐明植物多样性与菌根真菌多样性之间的互作关系,将丰富生物共生学理论,增强菌根应用潜力及生物多样性的维持。     

Interannual variation in precipitation and other planting conditions impacts seedling establishment in sown plant communities

Ecological restoration can reverse biodiversity loss worldwide, yet restoration goals and outcomes vary widely, which limits this potential. Divergent restoration outcomes may stem from variation in conditions at the outset of restoration, but empirical evidence is lacking and typically confounded with site differences. Additionally, precipitation is usually cited as the source of this variation, although a wide range of conditions can vary annually. We tested for effects of planting year on seedling establishment by installing identical restorations in three different years. Within those years, we manipulated rainfall with rain‐out shelters to disentangle the effects of precipitation from other annually variable conditions. Additionally, we tested whether increasing seed mix richness buffers against adverse planting conditions. For the first growing season after planting, we followed emergence and survival of sown prairie species and nonsown weed species to determine how planting year conditions influence an establishing plant community, if at all. We found that seedling establishment differed across planting years and precipitation treatments, and that varying emergence patterns by species led to differences in the composition of the first‐year community. We also found significant variation in sown species establishment across years when precipitation was held constant, illustrating the previously overlooked role of nonprecipitation drivers on planting year effects. Higher seed mix richness did not consistently improve establishment of sown species under different planting conditions. This research provides important experimental evidence for effects of interannual variation in planting conditions on first‐year establishment. Future work will examine how these initial changes affect longer‐term assembly dynamics.     

Differentiating between effects of invasion and diversity: impacts of aboveground plant communities on belowground fungal communities

Exotic plant species can affect soil microbial communities with the potential for community and ecosystem feedbacks. Yet, separating the effects of exotics from confounded changes in plant community diversity still remains a challenge. We focused on how plant diversity and native or exotic life history affected root fungi because of their significant roles in community and ecosystem processes. Specifically, we examined how fungi colonizing plant roots were affected by plant richness (one, two or four species) replicated across a range of plant community mixtures (natives, exotics, native-exotic mixtures). Fungal biomass inside roots was affected independently by plant richness and mixture, while root fungal community composition was affected only by plant richness. Extraradical networks also increased in size with plant richness. By contrast, plant biomass was a function of plant mixture, with natives consistently smaller than exotics and native-exotic mixtures intermediate. Plant invasions may have an impact on the belowground community primarily through their effects on diversity, at least in the short-term. Disentangling the effects of diversity and invasion on belowground microbial communities can help us to understand both the controllers of belowground resilience and mechanisms of successful colonization and spread of exotic plants.     

Interactions between functionally diverse fungal mutualists inconsistently affect plant performance and competition

Plants form mutualistic relationship with a variety of belowground fungal species. Such a mutualistic relationship can enhance plant growth and resistance to pathogens. Yet, we know little about how interactions between functionally diverse groups of fungal mutualists affect plant performance and competition. We experimentally determined the effects of interaction between two functional groups of belowground fungi that form mutualistic relationship with plants, arbuscular mycorrhizal (AM) fungi and Trichoderma, on interspecific competition between pairs of closely related plant species from four different genera. We hypothesized that the combination of two functionally diverse belowground fungal species would allow plants and fungi to partition their symbiotic relationships and relax plant–plant competition. Our results show that: 1) the AM fungal species consistently outcompeted the Trichoderma species independent of plant combinations; 2) the fungal species generally had limited effects on competitive interactions between plants; 3) however, the combination of fungal species relaxed interspecific competition in one of the four instances of plant–plant competition, despite the general competitive superiority of AM fungi over Trichoderma. We highlight that the competitive outcome between functionally diverse fungal species may show high consistency across a broad range of host plants and their combinations. However, despite this consistent competitive hierarchy, the consequences of their interaction for plant performance and competition can strongly vary among plant communities.     

动物与植物种子更新的关系Ⅱ．动物对种子的捕食、扩散、贮藏及与幼苗建成的关系

植物的繁殖体总是面临来自各类生物（如昆虫、脊椎动物、真菌）的捕食风险。因动物捕食引起的种子死亡率影响植物的适合度、种群动态、群落结构和物种多样性的保持。种子被捕食的时间和强度成为植物生活史中发芽速度、地下种子库等特征的主要选择压力,而种子大小、生境类型等因素也影响动物对植物种子的捕食。捕食者饱和现象被认为是植物和种子捕食者之间的高度协同进化作用的结果,是限制动物破坏种子、提高被扩散种子存活率的一种选择压力。大部分群落中的大多数植物种子被动物扩散。种子扩散影响种子密度、种子被捕食率、病原体攻击率、种子与母树的距离、种子到达的生境类型以及建成的植株将与何种植物竞争,从而影响种子和幼苗的存活,最终影响母树及后代植物的适合度。种子被动物扩散后的分布一般遵循负指数分布曲线,大多数种子并没有扩散到离母树很远的地方。捕食风险、生境类型、植被盖度均影响动物对种子的扩散。植物结实的季节和果实损耗的过程也体现了其对扩散机会的适应。许多动物有贮藏植物种子的行为。动物贮藏植物繁殖体的行为,一方面调节食物的时空分布,提高了贮食动物在食物缺乏期的生存概率;另一方面也为种子萌发提供了适宜条件,促进了植物的扩散。于是,植物与贮食动物形成了一种协同进化关系,这种关系可能是自然界互惠关系（mutualism)的一种。影响幼苗存活和建成的因子包括种子贮蒇点的微生境、湿度、坡向、坡度、林冠盖度等。许多果食性动物吃掉果肉后,再将完好的种子反刍或排泄出来。种子经动物消化道处理后,发芽率常有所提高。     

A comparison between reclamation stockpile and boreal forest seed banks and plant communities

Soil stockpiles are essential to the reclamation of large‐ and small‐scale mining and other industrial sites. However, stockpiling soils can lead to the degradation of seed banks. This study examines the diversity, composition, depth of seed storage, and relationships between the aboveground and seed bank plant communities in stockpiles and compares them to the nearby boreal forest. The seed bank and aboveground vegetation sampled at eight stockpiles and six mature forest sites were near Fort McMurray (57.337°N, 111.755°W) and Cold Lake (54.695°N, 110.730°W), Alberta, Canada. Seed bank samples were taken from the forest floor (LFH) and depths of 0–5, 5–10, 10–20, 20–30, >50 cm. Aboveground vegetation cover was also estimated at these locations. The seed bank composition was determined using the seedling emergence method in a greenhouse. Stockpile seed banks had higher seedling abundance and species richness than nearby forested sites but were dominated by grasses and non‐native forbs. Most seeds germinated from the surface layer, with 92% of seeds germinating from the LFH layers in the forested sites, and 68% from the 0 to 5 cm layer in the stockpiles. Mature forest sites had more similar aboveground and seed bank communities than the stockpiles. Overall, integrating information on seed bank and aboveground plant communities would improve reclamation decisions, rather than relying on aboveground vegetation alone.     

Tree growth declines and mortality were associated with a parasitic plant during warm and dry climatic conditions in a temperate coniferous forest ecosystem

Insects and pathogens are widely recognized as contributing to increased tree vulnerability to the projected future increasing frequency of hot and dry conditions, but the role of parasitic plants is poorly understood even though they are common throughout temperate coniferous forests in the western United States. We investigated the influence of western hemlock dwarf mistletoe (Arceuthobium tsugense) on large (≥45.7 cm diameter) western hemlock (Tsuga heterophylla) growth and mortality in a 500 year old coniferous forest at the Wind River Experimental Forest, Washington State, United States. We used five repeated measurements from a long‐term tree record for 1,395 T. heterophylla individuals. Data were collected across a time gradient (1991–2014) capturing temperature increases and precipitation decreases. The dwarf mistletoe rating (DMR), a measure of infection intensity, varied among individuals. Our results indicated that warmer and drier conditions amplified dwarf mistletoe effects on T. heterophylla tree growth and mortality. We found that heavy infection (i.e., high DMR) resulted in reduced growth during all four measurement intervals, but during warm and dry intervals (a) growth declined across the entire population regardless of DMR level, and (b) both moderate and heavy infections resulted in greater growth declines compared to light infection levels. Mortality rates increased from cooler‐wetter to warmer‐drier measurement intervals, in part reflecting increasing mortality with decreasing tree growth. Mortality rates were positively related to DMR, but only during the warm and dry measurement intervals. These results imply that parasitic plants like dwarf mistletoe can amplify the impact of climatic stressors of trees, contributing to the vulnerability of forest landscapes to climate‐induced productivity losses and mortality events.     

Effects of different clipping intensities on above- and below-ground production in simulated herbaceous plant communities

We studied the effect of clipping on above- and below-ground production in different plant communities through a factorial experiment. We designed five pasture systems with different species composition, perennials/annuals ratio and soil water availability, recreating different altitudinal locations, and simulated a gradient of grazing intensity by clipping with different heights and frequencies. Response patterns of above- and below-ground production were similar, increasing with the higher clipping frequency and decreasing with altitude. These results suggest that high grazing intensity stimulate above-ground production, but only in certain situations of species composition, density, diversity, perennials/annuals ratio and water availability. This stimulus, however, is unsustainable over time, and the lower clipping frequencies are those that favour the maintenance of production.     

Reduced mycorrhizae on Juniperus monosperma with mistletoe: the influence of environmental stress and tree gender on a plant parasite and a plant-fungal mutualism

Summary We examined how an important plant mutualist (fungal mycorrhizae) interacted with a common tree parasite, a xylem-tapping mistletoe (Phoradendron juniperium Engelm.) growing on one-seeded juniper (Juniperus monosperma Engelm.). We also examined how host tree gender and environmental stress might be involved in this interaction. Four major patterns were observed. First, the mycorrhizal levels of trees of both sexes were negatively correlated with mistletoe density. In comparisons of heavily and lightly infested trees at the stressful site, high mistletoe levels were associated with 27% less mycorrhizae on male trees and 38% less mycorrhizae on the roots of female trees. Second, the reduction of mycorrhizae on trees with high mistletoe levels was slightly but significantly greater for female trees than male trees. These results are consistent with the hypothesis that severe mistletoe infestation suppresses mycoresis and that this suppression is more severe in female trees because of their greater energetic investment in reproduction. Third, female junipers growing in the stressful ash and cinder fields averaged three-fold higher levels of mistletoe infestation than male trees. Fourth, no differences in mistletoe infestation were observed between male and female trees growing in the more favorable soils. Comparisons with other systems suggest that both mistletoes and herbivores have similar interactions with mycorrhizae.     

Links between plant and fungal communities across a deforestation chronosequence in the Amazon rainforest

Understanding the interactions among microbial communities, plant communities and soil properties following deforestation could provide insights into the long-term effects of land-use change on ecosystem functions, and may help identify approaches that promote the recovery of degraded sites. We combined high-throughput sequencing of fungal rDNA and molecular barcoding of plant roots to estimate fungal and plant community composition in soil sampled across a chronosequence of deforestation. We found significant effects of land-use change on fungal community composition, which was more closely correlated to plant community composition than to changes in soil properties or geographic distance, providing evidence for strong links between above- and below-ground communities in tropical forests.