Interspecific Plant Interactions Research Articles

Interspecific plant interaction structures the microbiomes of poplar-soil interface to alter nutrient cycling and utilization.

Terrestrial plants can influence the growth and health of adjacent plants through interspecific interaction. Here, the mechanisms of interspecific plant interaction on microbial function and nutrient utilization in the plant-soil interface (non-rhizosphere soil, rhizosphere soil, and root) were studied by soybean- and potato-poplar intercropping. First, metagenomics showed that soybean- and potato-poplar intercropping influenced the composition and co-occurrence networks of microbial communities in different ecological niches, with higher stability of the microbial community in soybean intercropping. Second, the gene abundance related to carbon metabolism, nitrogen cycling, phosphorus cycling, and sulfur cycling was increased at the poplar-soil interface in soybean intercropping. Moreover, soybean intercropping increased soil nutrient content and enzymatic activity. It showed higher metabolic potential in nutrient metabolism and transportation. Third, functional microorganisms that influenced nutrient cycling and transportation in different intercropping have been identified, namely Acidobacteria, Sphingomonas, Gemmatimonadaceae, Alphaproteobacteria, and Bradyrhizobium. Therefore, intercropping can construct microbial communities to alter metabolic functions and improve nutrient cycling and absorption. Interspecific plant interactions to influence the microbiome were revealed, opening up a new way for the precise regulation of plant microbiome.IMPORTANCEPoplar has the characteristics of wide distribution, strong adaptability, and fast growth, which is an ideal tree species for timber forest. In this study, metagenomics and elemental analysis were used to comprehensively reveal the effects of interspecific plant interactions on microbial communities and functions in different ecological niches. It can provide a theoretical basis for the development and application of the precise management model in poplar.

Interspecific interactions between crops influence soil functional groups and networks in a maize/soybean intercropping system

Despite increasing evidence that intercropping systems may increase crop productivity, little is known about whether and how soil biota change under interspecific competition among plants. A field experiment with maize/soybean intercropping and the corresponding monoculture systems was conducted under four nitrogen fertilization regimes to investigate the effects of interspecific plant interactions on grain yield, soil properties (β-glucosidase and water-soluble carbohydrates), and biotic communities (bacteria, fungi, and nematodes). The soils under maize and soybean in the intercropping system were sampled separately to represent intercropped maize and intercropped soybean, respectively. Compared to monocultures, the complexity and robustness of soil networks comprising bacterial, fungal, and nematode communities increased in intercropped maize soils, but densities of plant parasitic nematodes and β-glucosidase activity were reduced. Intercropped soybean soils had lower C availability due to chronic shading by maize, but a significant increase was found in saprophytic fungi, and plant parasitic nematodes compared to soybean monoculture soils. Although intercropped soybean suffered from interspecific competition with maize, the interactions within the fungal community increased for both crop species in the intercropping system. Our study demonstrates that increased carbon uptake in maize due to increased light capture in the intercropping system can facilitate nutrient cycling by altering the abundance of functional groups of soil organisms, such as saprophytic fungi, and enhancing network complexity and stability. We detected a trade-off between productivity and soil nematode diversity in the intercropping system under nitrogen fertilization, the yield of maize increased but soil nematode richness decreased at low nitrogen level, while the yield of soybean decreased but the nematode richness increased at high nitrogen level. These findings show that both trade-offs and benefits occur in intercropping systems and highlight the role of plant-soil biota interactions in such systems.

Arbuscular mycorrhizal fungus Rhizophagus irregularis alleviates drought stress in soybean with overexpressing the GmSPL9d gene by promoting photosynthetic apparatus and regulating the antioxidant system

Drought is the most destructive abiotic stress and negatively affects crop growth and productivity. Modern breeding efforts have produced numerous cultivars with distinct genetic traits that improve crop growth and drought stress tolerance. Arbuscular mycorrhizal fungi (AMF) can enhance drought tolerance in soybean plants by directly providing nutrients to plants, promoting photosynthesis, or influencing interspecific plant interactions in natural communities. However, the interactions between AMF and wild and transgenic soybean genotypes remain unclear. Therefore, in the present study, we evaluated the effect of arbuscular mycorrhizal fungi on the growth performance of drought-stressed transgenic soybean lines (ZXOE-11 and ZXOE-13) overexpressing GmSPL9d gene and their wild soybean Tianlong 1 (TL1) at the seedling stage (45 d after sowing). The results showed that colonization of wild and transgenic soybean with Rhizophagus irregularis significantly decreased the adverse effects of drought on plant growth. AMF inoculation significantly increased plant biomass, root activity, chlorophyll metabolism, photosynthesis, and chlorophyll fluorescence in wild-type and transgenic plants under both control and drought stress conditions. Drought causes the production of ROS, such as hydrogen peroxide, which enhances MDA, thereby decreasing the membrane stability index (MSI). However, AMF-inoculated plants exhibited decreased ROS accumulation and increased MSI. Moreover, AMF treatment significantly improved osmolyte, nitrogen, and nitrate reductase activity under control and drought conditions, which increased the relative water content. Furthermore, AMF treatment enhanced the antioxidant systems of drought-stressed plants by increasing the activities of peroxidase, superoxide dismutase, catalase, and ascorbate peroxidase. AMF improved the growth performance, photosynthesis, and antioxidant activity of transgenic plants under drought stress conditions. The present findings indicate that the AMF contribution to soybean seedling drought tolerance was more significant for the transgenic plants than for the wild plants under drought conditions. The current findings emphasize the possibility of growth and photosynthetic variation in the degree of AMF-associated drought resistance in soybean plants. Our findings suggest that future crop breeding challenges include developing cultivars for sustainable production and maximizing crop cultivar and fungal species (AMF) combinations in drought-stressed regions.

Implications of plant N/P stoichiometry influenced by arbuscular mycorrhizal fungi for stability of plant species and community in response to nutrient limitation

Arbuscular mycorrhizal fungi (AMF) influence plant nitrogen/phosphorus (N/P) by modifying plant N and P uptake, which further affects plant stoichiometric N/P homeostasis. Plant species and community stoichiometric N/P homeostasis can impact plant species and community stability, respectively, in response to variations of soil N and P availabilities. We investigated interspecific plant interactions via AMF in regard to plant and soil microbial N/P stoichiometry across different soil N and P availabilities induced by N and P addition (0 mg N kg−1, 25 mg N kg−1, 50 mg N kg−1, 30 mg P kg−1 and 100 mg P kg−1). We selected one dominant (Bothriochloa ischaemum; C4 grass) and one subordinate (Lespedeza davurica; legume) species in a natural grassland climax community. We examined how AMF influences stoichiometric N/P homeostasis in monoculture and mixed culture systems, and the resulting consequences for temporal stability of plant species and community in response to variations in soil N and P availability.The AMF mitigated the P limitation of soil microbial communities and decreased the degree of stoichiometric N/P homeostasis of host plants in monoculture. Through their resource‐scavenging and soil organic matter mineralisation functions, AMF enhances plant ‘luxury consumption', promoting species stability in monoculture in response to soil N and P availability variations. Compared with plants in monoculture, the interaction between B. ischaemum and L. davurica via AMF increased shoot N/P under soil N‐poor conditions, leading to an enhanced degree of stoichiometric N/P homeostasis in both plant species, especially the legume.Our results suggest that interspecific plant interaction between C4 grass and legume mediated by AMF confers an advantage in complementarity in plant N acquisition under N‐poor conditions, leading to increased stability of plant communities and better maintenance of subordinate species (legume) in response to soil N deficiency.

Plant Species Interactions in the Rhizosphere Increase Maize N and P Acquisition and Maize Yields in Intercropping

The aim of the study was to examine interspecific plant interactions that contribute to plant nitrogen (N) and phosphorus (P) acquisition and are likely the reason for overyielding in intercropping. We conducted a field and a rhizobox experiment with the same soil. Maize (Zea mays L.) was grown alone or intercropped with the companions faba bean (Vicia faba L.), soy (Glycine max (L.) Merr.), blue lupin (Lupinus angustifolius L.), or white mustard (Sinapis alba L.). We determined the isotopic N signature (δ15N) of maize as well as soil parameters (pH, phosphatase activity, nitrate) in the field experiment. We analyzed phosphatase activities and rhizosphere pH by soil zymography and pH imaging in the rhizobox experiment. Maize N and P contents were larger in intercropping than monocropping, especially with soy and lupin in the field, indicating intercropping advantages for maize N and P acquisition. Intercropping with legumes decreased maize δ15N in the field, suggesting that 11–20% of maize aboveground biomass N was transferred from legumes to maize. Soil zymography revealed high phosphatase activities in the rhizosphere of lupin and faba bean. pH imaging showed a rhizosphere alkalinization by mustard, and a rhizosphere acidification by faba bean. These changes in the companions’ rhizosphere likely mobilized P and were also beneficial for maize in intercropping. Taken together, our study provides evidence that the companions’ ability to mobilize N and P in the rhizosphere promotes increases in maize nutrient contents and causes maize overyielding in intercropping and thus can contribute to fertilizer savings.

Adoption of Food Species Mixtures from Farmers’ Perspectives in Germany: Managing Complexity and Harnessing Advantages

Many agronomic studies have shown the advantages of species mixtures (SM), but for food grain production, they represent only a small niche. Empirical studies that investigate reasons for SM adoption in food grain production are scarce. Here we present an in-depth study based on qualitative expert interviews with nine farmers. By means of interpretative analysis and reconstruction, socially shared models of SM adoption were built to identify the five main factors for SM adoption: (1) perceived relative mixture performance compared to sole crops, (2) suitability within the farm context (3), challenges and opportunities in mixture management due to increased complexity, (4) knowledge and technology as resources to handle mixture management and (5) quality standards in the food value chain. Relative performance was perceived as higher for SM than for sole crops for crop protection, nutrient efficiency, farm diversification, total yield stability and grain quality. The yield stability of individual crop species in SM was perceived as lower and grain impurities higher, requiring increased separation efforts. The economic potential of SM was perceived as highly variable, depending on crop value and post-harvest efforts to attain food quality. Reconstructing the mixture management process revealed that the interspecific plant interactions and emergent mixture attributes increased the cropping system complexity and affected the entire farming process. Adopting SM required knowledge about species interactions, mixture attributes and equipment settings. Large knowledge gaps for food SM were identified. The complexity of SM also provided opportunities for farmers to design mixtures that allow competition control (alternate rows) or avoid separation (relay mixtures). The main conclusions are: (1) increased complexity is a basic property of SM compared to sole crops, enabling advantages and increasing the option space to develop new sustainable cropping systems, (2) specific knowledge and technology are required for SM and are not accessible for most farmers, requiring new information channels and (3) new food SM should be developed more systematically, taking into account mixture properties and their effects on the farming process, as well as needs from the food value chain.

Flowering segregation and pollinator distinctiveness contribute to coexistence in an extremely generalist plant group

Background Flowering time determines potential plant mates, and it is related to gene flow within and among plant populations arising from different selective forces and interspecific interactions between plants with similar pollination niches. However, these effects on flowering phenology of plants with generalist pollination systems have received little attention and hence our knowledge of the contribution of generalised pollination systems on the evolution of adaptative traits, such as the flowering time contains lacunae. Aims To verify the effective contribution of interspecific plant interactions in a generalised pollination system to the structuring of flowering phenology. Methods We recorded the reproductive phenophases of four Baccharis species in a subtropical grassland. We evaluated their flowering patterns by a niche overlap index and compared it with a null model. We used ecological network metrics from insect visitors recorded to determine the pollinator network structure. Results A staggered flowering pattern and distinctiveness of insect pollinators with non-signal of modularity and a variation in the Baccharis-pollinators network structure throughout the year were observed. The distinctiveness on pollinators with a strong bee-dependence added to temporal divergence on flowering among the species leads to no negative effects on fruit set. Conclusion The temporal segregation on flowering peaks and low pollinator similarity appear to underlie to coexistence of Baccharis species studied in southern Brazil.

Does the intensive grazing and aridity change the relations between the dominant shrub Artemisia kopetdaghensis and plants under its canopies?

The interspecific plant interactions along grazing and aridity stress gradients represent a major research issue in plant ecology. However, the combined effects of these two factors on plant–plant interactions have been poorly studied in the northeast of Iran. To fill this knowledge gap, 144 plots were established in 12 study sites with different grazing intensities (high vs. low) and climatic characteristics (arid vs. semiarid) in northeastern Iran. A dominant shrub, Artemisia kopetdaghensis, was selected as the model species. Further, we studied changes in plant life strategies along the combined grazing and aridity stress gradients. In this study, we used relative interaction indices calculated for species richness, Shannon diversity, and species cover to determine plant–plant interactions using linear mixed‐effect models (LMM). The indicator species analysis was used to identify the indicator species for the undercanopy of shrub and for the adjacent open areas. The combined effects of grazing and aridity affected the plant–plant interactions and plant life strategies (CSR) of indicator species. A. kopetdaghensis showed the highest facilitation effect under high stress conditions (high grazing, high aridity), which turned into competition under the low stress conditions (low grazing, low aridity). In the arid region, the canopy of the shrub protected ruderals, annual forbs, and grasses in both high and low grazing intensities. In the semiarid region and high grazing intensity (low aridity/high grazing), the shrubs protected mostly perennial forbs with C‐strategy. Our findings highlight the importance of context‐dependent shrub management to restore the vegetation damaged by the intensive grazing.

Mechanistic understanding of interspecific interaction between a C4 grass and a C3 legume via arbuscular mycorrhizal fungi, as influenced by soil phosphorus availability using a 13 C and 15 N dual-labelled organic patch.

Arbuscular mycorrhizal fungi (AMF) can improve plant nutrient acquisition, either by directly supplying nutrients to plants or by promoting soil organic matter mineralization, thereby affecting interspecific plant relationships in natural communities. We examined the mechanism by which the addition of P affects interspecific interactions between a C4 grass (Bothriochloa ischaemum, a dominant species in natural grasslands) and a C3 legume (Lespedeza davurica, a subordinate species in natural grasslands) via AMF and plant growth, by continuous 13 C and 15 N labelling, combined with soil enzyme analyses. The results of 15 N labelling revealed that P addition affected the shoot uptake of N via AMF by B.ischaemum and L.davurica differently. Specifically, the addition of P significantly increased the shoot uptake of N via AMF by B.ischaemum but significantly decreased that by L.davurica. Interspecific plant interactions via AMF significantly facilitated the plant N uptake via AMF by B.ischaemum but significantly inhibited that by L.davurica under P-limited soil conditions, whereas the opposite effect was observed in the case of excess P. This was consistent with the impact of interspecific plant interaction via AMF on arbuscular mycorrhizal (AM) benefit for plant growth. Our data indicate that the capability of plant N uptake via AMF is an important mechanism that influences interspecific relationships between C4 grasses and C3 legumes. Moreover, the effect of AMF on the activities of the soil enzymes responsible for N and P mineralization substantially contributed to the consequence of interspecific plant interaction via AMF for plant growth.

Managing biotic interactions during early seagrass life stages to improve seed‐based restoration

Abstract Seagrasses are declining globally, and effective restoration actions to promote the recovery of degraded meadows are urgently needed. Harnessing positive plant interactions during early life stages is considered a valuable strategy to improve terrestrial and coastal habitat restoration. Yet, its application to seagrass restoration is still in infancy, and very little is known on the role played by biotic interactions in shaping newly established populations. We assessed the feasibility of manipulating intraspecific and interspecific plant interactions to enhance seed‐based restoration success using the seagrass Posidonia oceanica as a model. Specifically, we investigated in mesocosm whether seed germination increased with increasing seed density and whether increasing seedling density and planting a pioneer seagrass promoted facilitation among seedlings. To do this, seedlings were grown either as a single individual or in clumps of medium and high density, with and without Cymodocea nodosa, for 2 years encompassing their most critical growth stage. Germination of P. oceanica seeds was not affected by seed density. Posidonia oceanica seedlings planted at medium and high density showed higher survival than those planted individually but only in the presence of C. nodosa. Seedlings planted at medium and at high density with C. nodosa performed better than those grown at low density or without C. nodosa due to a positive joint effect of intraspecific and interspecific interaction. Cymodocea nodosa plants grown with P. oceanica seedlings at high density were larger than those grown alone, indicating a mutualistic relationship. Synthesis and applications. Our results show that in seagrasses positive interactions during early life stages can be promoted by planting seedlings in dense clumps in association with an early successional species. The incorporation of this novel nature‐based approach in seed‐based restoration could accelerate the recolonization of degraded seagrass habitats. In planning future seed‐based restoration interventions, managers should assess both intraspecific and interspecific interactions established by seedlings of target species for identifying proper planting density/spatial configuration and potential benefactor species promoting facilitative mechanisms to maximize seedling planting success.

Determination of the Effect of Co-cultivation on the Production and Root Exudation of Flavonoids in Four Legume Species Using LC-MS/MS Analysis.

Flavonoids play a key role in the regulation of plant–plant and plant–microbe interactions, and factors determining their release have been investigated in most of the common forage legumes. However, little is known about the response of flavonoid production and release to co-cultivation with other crop species. This study investigated alterations in the concentration of flavonoids in plant tissues and root exudates in four legumes [alfalfa (Medicago sativa L.), black medic (Medicago polymorpha L.), crimson clover (Trifolium incarnatum L.), and subterranean clover (Trifolium subterraneum L.)] co-cultivated with durum wheat [Triticum turgidum subsp. durum (Desf.) Husn.]. For this purpose, we carried out two experiments in a greenhouse, one with glass beads as growth media for root exudate extraction and one with soil as growth media for flavonoid detection in shoot and root biomass, using LC–MS/MS analysis. This study revealed that interspecific competition with wheat negatively affected legume growth and led to a significant reduction in shoot and root biomass compared with the same legume species grown in monoculture. In contrast, the concentration of flavonoids significantly increased both in legume biomass and in root exudates. Changes in flavonoid concentration involved daidzein, genistein, medicarpin, and formononetin, which have been found to be involved in legume nodulation and regulation of plant–plant interaction. We hypothesize that legumes responded to the co-cultivation with wheat by promoting nodulation and increasing exudation of allelopathic compounds, respectively, to compensate for the lack of nutrients caused by the presence of wheat in the cultivation system and to reduce the competitiveness of neighboring plants. Future studies should elucidate the bioactivity of flavonoid compounds in cereal-legume co-cultivation systems and their specific role in the nodulation process and inter-specific plant interactions such as potential effects on weeds.

Border-row proportion determines strength of interspecific interactions and crop yields in maize/peanut strip intercropping

Strip intercropping enables increases in yields and ecological services in agriculture. Crop yields of species grown in strip intercropping are often related to the yield responses (increases or decreases) in the outer rows of the strips: the border rows. This suggests that the yield response can be modulated by changing the proportion of border rows in the field. Here we studied the relationship between component species yields and proportion of border rows in strip intercrops of maize (Zea mays L.) and peanut (Arachis hypogaea Linn.). We tested four different intercrops with equal proportions of maize and peanut but a different number of rows per strip: M2P2 (2 rows maize intercropped with 2 rows peanut), M4P4, M6P6, M8P8, and sole maize (SM) and sole peanut (SP). The border-row proportions were 1, 0.5, 0.33 and 0.25 for the intercropping M2P2 to M8P8, respectively, and 0 for the pure stands. Yield responded positively to the proportion of border rows for maize, but negatively for peanut, confirming the dominance of maize in this system. Kernel number per ear of maize and pod number per plant of peanut were the main yield components that responded to the border-row proportion. Across three years, relative maize yield (yield in intercropping divided by yield in monoculture), varied from 0.76 in M2P2 to 0.56 in M8P8, while relative peanut yield varied from 0.19 in M2P2 to 0.39 in M8P8. Relative yield total was not significantly different from one in any of the mixtures. Yield of intercropped maize in border rows was 48% higher than in inner rows and the sole crop, in part due to a significantly higher kernel number per ear (13%). Yield of intercropped peanut in border rows was on average 29% lower than in inner rows and 48% lower than in sole peanut. Yield responses in border rows were independent from the border-row proportion. The results show that relative crop yields responded strongly to variation in border-row proportion resulting from variation in strip width from 1 to 4 m. Strip width thus provides a mechanism to control the strength of interspecific plant interactions and relative yields in strip intercropping.

Plant-plant interactions and N fertilization shape soil bacterial and fungal communities

The impact of conspecific and heterospecific neighboring plants on soil bacterial and fungal communities has never been explored in a forest ecosystem. In the present study, we first investigated soil microbial communities in three plantations: Larix kaempferi monoculture, L. olgensis monoculture and their mixture. Then, a two-year growth experiment was conducted to investigate the effects of intra- and inter-specific interactions of L. kaempferi and L. olgensis on rhizosphere microbial communities at two different nitrogen levels. The results demonstrated clear differences in the beta-diversity and composition of bacteria and fungi among the three plantations, which implied the presence of different effects of plant-plant interactions on soil microbial communities. The results of the pot experiment showed that L. kaempferi suffered from greater neighbor effects from its conspecific neighbor regardless of N fertilization, although the effect declined when L. kaempferi was grown with L. olgensis under N fertilization. Changes in intra- and inter-specific plant interactions significantly impacted the chemical and biological properties of soil under N fertilization, with lower concentrations of NH4+, and lower soil microbial biomass (CMic) and soil carbon nitrogen biomass (NMic) under intra-specific plant interactions of L. kaempferi (KK) compared to inter-specific interactions of L. kaempferi and L. olgensis (KO). N fertilization increased bacterial and fungal alpha diversities in the rhizosphere soil of KO. For the beta diversity, the PERMANOVA results demonstrated that there was a significant impact of intra- and inter-specific plant interactions on soil microbial communities, with KK significantly differing from intra-specific plant interactions of L. olgensis (OO) and KO. The two plant species and N fertilization showed specific effects on the soil microbial composition, particularly on the fungal community. Both L.olgensis and N fertilization increased the abundance of Ascomycota but reduced that of Basidiomycota, and even shifted the dominance from Basidiomycota to Ascomycota under KO combined with N fertilization.

Interspecific Plant Interactions Reflected in Soil Bacterial Community Structure and Nitrogen Cycling in Primary Succession.

Past research demonstrating the importance plant–microbe interactions as drivers of ecosystem succession has focused on how plants condition soil microbial communities, impacting subsequent plant performance and plant community assembly. These studies, however, largely treat microbial communities as a black box. In this study, we sought to examine how emblematic shifts from early successional Alnus viridus ssp. sinuata (Sitka alder) to late successional Picea sitchensis (Sitka spruce) in primary succession may be reflected in specific belowground changes in bacterial community structure and nitrogen cycling related to the interaction of these two plants. We examined early successional alder-conditioned soils in a glacial forefield to delineate how alders alter the soil microbial community with increasing dominance. Further, we assessed the impact of late-successional spruce plants on these early successional alder-conditioned microbiomes and related nitrogen cycling through a leachate addition microcosm experiment. We show how increasingly abundant alder select for particular bacterial taxa. Additionally, we found that spruce leachate significantly alters the composition of these microbial communities in large part by driving declines in taxa that are enriched by alder, including bacterial symbionts. We found these effects to be spruce specific, beyond a general leachate effect. Our work also demonstrates a unique influence of spruce on ammonium availability. Such insights bolster theory relating the importance of plant–microbe interactions with late-successional plants and interspecific plant interactions more generally.

Importance of intra- and interspecific plant interactions for the phytomanagement of semiarid mine tailings using the tree species Pinus halepensis

The objective of this work was to evaluate the effects of plant interactions (intra- and interspecific) on the growth and metal(loid) uptake of the tree species Pinus halepensis to determine its suitability for the phytomanagement of semiarid mine tailings. The pioneer tailings colonizer grass Piptatherum miliaceum was selected for assessing interspecific interactions. The experiment was conducted following a pot experimental design employing mine tailings soil. Pots containing single individuals of P. halepensis or P. miliaceum and pots containing combinations with pines (two pines per pot, or one pine and one grass per pot) were used. The analyses included the determination of plant biomass, foliar element status and stable isotope composition, metal(loid) uptake and its translocation to different plant organs. P. halepensis strongly favoured the growth of P. miliaceum by increasing 9-fold the latter's biomass and alleviating its P limitation. In this interspecific treatment P. halepensis showed a strong N limitation (N/P = 7), which negatively affected its growth, (to about half the biomass of that obtained for the other treatments) and exhibited a significant increase in some metals translocation (especially Cd) into aerial parts. Interestingly, P. miliaceum showed a decrease in the root to leaves translocation factor for most of metals when growing together with pines. The effects of the intraespecific combination on growth and metal uptake in P. halepensis were less relevant than those obtained for the interspecific one. Further research should be focused on testing the behaviour of plant co-cultures under the addition of N or P amendments which could alleviate the negative effects of plant competition.

Arbuscular mycorrhizal fungi contribute to overyielding by enhancing crop biomass while suppressing weed biomass in intercropping systems

Intercropping often produces more biomass than the average of the corresponding monocultures, particularly in sustainable, low-input agriculture. Characterizing plant-plant interactions is fundamental for a better understanding of the ecological functioning of intercropping. However, there is little information on whether mycorrhizal networks exhibit different effects upon intra- and interspecific plant interactions in intercropping systems. Microcosms with one inner and three outer compartments were used. The inner compartment was separated from the outer compartments by a 30-μm nylon mesh or a solid barrier or remained open to allow full interactions between plants grown in the different compartments, creating three treatments, namely −Roots−CMNs (solid barrier), −Roots+CMNs (mesh), and +Roots+CMNs (no barrier). Either faba bean (Vicia faba) or maize (Zea mays) was grown as the donor plant in the inner compartment. Maize was combined with maize, wheat (Triticum aestivum) or the weed species foxtail (Setaria viridis) as the neighboring plant species. Faba bean was combined with faba bean, maize, or foxtail. The low-P soil was inoculated with the arbuscular mycorrhizal fungus (AMF) Funneliformis mosseae or remained uninoculated. In the absence of AMF, plant growth was restricted by P deficiency and root interactions did not significantly affect plant-plant interactions. The presence of AMF enhanced plant biomass (maize by 104.5 %, faba bean by 61.6 %) and nutrient (N and P) uptake. Significant overyielding occurred in treatments where roots and hyphal networks of all plant species intermingled. The weed (foxtail) was suppressed by interspecific interactions while maize and faba bean benefitted from a mycorrhizal network and the presence of intermingling roots. In low-P soils, mycorrhizal networks contribute to overyielding in intercropping by enhancing the biomass and nutrient uptake of the mycorrhiza-dependent plant species. The biomass depression of weed species by AMF and/or root interactions may have ecological implications in weed control in intercropping systems.

A Review of Processes Behind Diversity—Productivity Relationships in Forests

Through complementarity interactions, mixed-species forests can be more productive than monocultures, and this effect can increase with tree-species richness. However, this is not always the case. This review examines the processes and stand structural attributes that can influence diversity-productivity relationships (DPRs); how they influence resource availability, resource uptake, and resource-use efficiency; and also describes some important differences between tree-diversity versus grassland-diversity experiments. The size of the complementarity effects caused by these processes and stand structures varies along spatial and temporal gradients in resource availability and climate. These spatial and temporal dynamics have now been examined in many studies, and the general patterns are summarized using a simple framework; complementarity is predicted to increase as the availability of resource “X” declines (or climatic condition X becomes harsher) if the species interactions improve the availability, uptake, or use efficiency of resource X (or interactions improve climatic condition X). Importantly, this framework differs from the stress-gradient hypothesis to account for a wider range of inter-specific plant interactions (not only facilitation) by considering contrasting methods used to quantify species interactions while accounting for stand structure. In addition, complementarity (as opposed to facilitation) for a given species combination can increase as growing conditions improve in forests, contrary to predictions of the stress-gradient hypothesis with regards to facilitation. This review indicates that while the effects of tree-species diversity on growth and other forest functions are now receiving a lot of attention, far less is known about the effects of structural diversity on growth or forest functioning. Direct measurements of the processes, as opposed to focusing mainly on growth responses, could greatly contribute to our understanding of structural diversity effects.

The relative importance of biotic and abiotic processes for structuring plant communities through time

Summary The question of the relative importance of biotic interactions versus abiotic drivers for structuring plant communities is highly debated but largely unresolved. Here, we investigate the relative importance of mean July air temperature, nitrogen (N) availability and direct plant interactions in determining the millennial‐scale population dynamics through the Holocene (10 700–5200 cal. years bp) for four temperate tree taxa in the Scottish Highlands. A variety of dynamic population models were fitted to our palaeoecological time‐series data to determine the mechanism(s) by which each driver affected the population biomass dynamics of Betula (birch), Pinus (pine), Alnus (alder) and Quercus (oak). Akaike information criterion weights identified the best model(s) for describing the relationship between each population and driver. The relative importance of these drivers was then assessed by the ability of each model to predict the observed population biomass dynamics. We also measured the change in goodness‐of‐fit of each model over time. We found that models of intra‐ and interspecific plant interactions described the plant population dynamics better than temperature‐ or N‐dependent population growth models over the 5000‐year study period. The best‐fitting models were constant over time for pine, alder and oak. However, the plant–N availability and plant–temperature models provided a progressively better fit to the birch data when temperatures rose and N availability declined, suggesting increasing importance of these abiotic factors coincident with changing conditions. Synthesis. Multiple mechanistic models were applied to palaeoecological data to infer the most likely processes driving millennial‐scale plant biomass dynamics in a woodland ecosystem. Direct plant interactions provided a better explanation for population biomass dynamics than growing season temperature or N availability over the full study period. The relative importance of all drivers we assessed here varied by species and – in the case of birch – over time in response to warming and reduced N availability.

Early competition shapes maize whole-plant development in mixed stands.

Mixed cropping is practised widely in developing countries and is gaining increasing interest for sustainable agriculture in developed countries. Plants in intercrops grow differently from plants in single crops, due to interspecific plant interactions, but adaptive plant morphological responses to competition in mixed stands have not been studied in detail. Here the maize (Zea mays) response to mixed cultivation with wheat (Triticum aestivum) is described. Evidence is provided that early responses of maize to the modified light environment in mixed stands propagate throughout maize development, resulting in different phenotypes compared with pure stands. Photosynthetically active radiation (PAR), red:far-red ratio (R:FR), leaf development, and final organ sizes of maize grown in three cultivation systems were compared: pure maize, an intercrop with a small distance (25cm) between maize and wheat plants, and an intercop with a large distance (44cm) between the maize and the wheat. Compared with maize in pure stands, maize in the mixed stands had lower leaf and collar appearance rates, increased blade and sheath lengths at low ranks and smaller sizes at high ranks, increased blade elongation duration, and decreased R:FR and PAR at the plant base during early development. Effects were strongest in the treatment with a short distance between wheat and maize strips. The data suggest a feedback between leaf initiation and leaf emergence at the plant level and coordination between blade and sheath growth at the phytomer level. A conceptual model, based on coordination rules, is proposed to explain the development of the maize plant in pure and mixed stands.

Soil organisms shape the competition between grassland plant species

Decomposers and arbuscular mycorrhizal fungi (AMF) both determine plant nutrition; however, little is known about their interactive effects on plant communities. We set up a greenhouse experiment to study effects of plant competition (one- and two-species treatments), Collembola (Heteromurus nitidus and Protaphorura armata), and AMF (Glomus intraradices) on the performance (above- and belowground productivity and nutrient uptake) of three grassland plant species (Lolium perenne, Trifolium pratense, and Plantago lanceolata) belonging to three dominant plant functional groups (grasses, legumes, and herbs). Generally, L. perenne benefited from being released from intraspecific competition in the presence of T. pratense and P. lanceolata. However, the presence of AMF increased the competitive strength of P. lanceolata and T. pratense against L. perenne and also modified the effects of Collembola on plant productivity. The colonization of roots by AMF was reduced in treatments with two plant species suggesting that plant infection by AMF was modified by interspecific plant interactions. Collembola did not affect total colonization of roots by AMF, but increased the number of mycorrhizal vesicles in P. lanceolata. AMF and Collembola both enhanced the amount of N and P in plant shoot tissue, but impacts of Collembola were less pronounced in the presence of AMF. Overall, the results suggest that, by differentially affecting the nutrient acquisition and performance of plant species, AMF and Collembola interactively modify plant competition and shape the composition of grassland plant communities. The results suggest that mechanisms shaping plant community composition can only be understood when complex belowground interactions are considered.