Although it is known that plant–plant interaction is an important factor influencing plant nitrogen (N) uptake and biomass productivity, its effects on seasonal inorganic N uptake, preference, and ...allocation remain unclear. In this study, two conifer species (Picea asperata and Abies faxoniana) were planted in three different planting modes (i.e., single, intraspecific, and interspecific interaction). Using 15N stable isotope tracer, we quantified plant biomass, ammonium (NH4+), and nitrate (NO3−) uptake rate (mass) and allocation in the middle (July) and the end (September) of the growing season, respectively, followed by analyses of root traits and soil properties so as to explore the underlying mechanism. Across the two seasons, intraspecific interaction decreased plant biomass and inorganic N‐uptake rate, which triggered intense competition for both species. Intraspecific competition of P. asperata was stronger than that of A. faxoniana. In contrast, interspecific interaction revealed significant facilitative effects on A. faxoniana, particularly in September. From the middle to the late growing season, the inorganic N‐uptake rate of P. asperata reduced, whereas that of A. faxoniana increased under interspecific interaction. The seasonal variation in plant N uptake was regulated by changes in root traits (such as root nitrogen concentration, specific root length, and branching intensity) and soil N availabilities. Both species indicated a preference for NO3− across seasons. Furthermore, we observed that 15N allocation to shoots of A. faxoniana under interspecific interaction was higher than that of P. asperata and declined from July to September. These findings on how plant–plant interactions affect plant N uptake seasonally can facilitate our understanding of species co‐existence and community assembly in forest ecosystems.
•CJ and PT decreased fungal, GP bacterial abundances in the fine root rhizosphere.•PT had significantly lower acid phosphatase, dehydrogenase, and higher invertase.•Different vegetation types ...differed in the magnitude of rhizosphere effects.•SOC, TN were the main factors in regulating soil microbial community and enzymes.
Microbial communities and enzyme activity in soil are the functional link through which the vegetation type occupying a site, may alter soil processes fundamental to nutrient cycling. Roots are known to regulate soil carbon (C) input, but the impacts of different classes of roots on soil microbial community (as indexed by PLFAs) and enzyme activity are uncertain. Thus, the aim of this study was to assess how different classes of woody roots (fine roots ≤ 2 mm and coarse roots > 2 mm) in Pinus tabulaeformis (PT) and Cercidiphyllum japonicum (CJ) plantations influence the microbial community and enzyme potential activity, as compared to natural shrubland.
In the fine root rhizosphere soil, the PT and CJ plantations had lower abundances of fungal and gram-positive bacterial PLFAs, and the PT plantation had significantly lower acid phosphatase, dehydrogenase, and higher invertase activities compared to the shrubland. The shrubland and CJ plantation had distinctly higher soil microbial parameters (total, fungal, and arbuscular mycorrhizal fungal PLFAs) and enzyme activities (urease, acid phosphatase, invertase, β-glucosidase, and dehydrogenase) in the fine root rhizosphere than in the coarse root rhizosphere and bulk soils. We concluded that soil organic carbon (SOC) (much more significant) and total nitrogen (TN) were the main factors in regulating soil microbial community and enzymes.
Our findings demonstrate the importance of fine roots in regulating microbial community and function. Our results also highlight that differences between fine root rhizosphere and coarse root rhizosphere, or bulk soil are dependent on vegetation type.
Ectomycorrhizal (ECM) fungi colonization and function depend on soil water and nutrient supply. To study the effects of resource supply on ECM colonization and inorganic nitrogen (N) uptake by roots ...of Picea asperata seedlings, we conducted a study at the end of a 5‐year long experiment consisting of five watering regimes (40, 50, 60, 80, and 100% of field capacity) and three NH4NO3 application rates (0 N0, 20 N1, and 40 N2 g N m−2 year−1). We measured fluxes of ammonium (NH4+) and nitrate (NO3−) into colonized and uncolonized roots using noninvasive microtest technology. We found that, across the N supply levels, ECM colonization rate increased by 53 ± 14% from the highest to the lowest level of water supply. Across the watering regimes, the fraction of mycorrhizal root tips was 39 ± 4% higher under native N supply compared to roots grown under N additions. As expected for conifers, both colonized and uncolonized roots absorbed NH4+ at a higher rate than NO3−. N additions reduced the instantaneous ion uptake rates of uncolonized roots grown under low water supply but enhanced the fluxes into roots grown under sufficient soil water availability. Soil water supply improves inorganic N uptake by uncolonized roots but reduces the efficiency of colonized roots. Under the lowest water supply regime, the uptake rate of NH4+ and NO3− by colonized roots was 40–80% of those by uncolonized roots, decreasing to 20–30% as soil water supply improved. Taken together, our results suggest that the role ectomycorrhizae play in the nutrient acquisition of P. asperata seedling likely diminishes with increasing availability of soil resources.
Abstract
Plant nitrogen (N) uptake is affected by plant–plant interactions, but the mechanisms remain unknown. A 15N-labeled technique was used in a pot experiment to analyze the uptake rate of ...ammonium (NH4+) and nitrate (NO3−) by Abies faxoniana Rehd. et Wils and Picea asperata Mast. in single-plant mode, intraspecific and interspecific interactions. The results indicated that the effects of plant–plant interactions on N uptake rate depended on plant species and N forms. Picea asperata had a higher N uptake rate of both N forms than A. faxoniana, and both species preferred NO3−. Compared with single-plant mode, intraspecific interaction increased NH4+ uptake for A. faxoniana but reduced that for P. asperata, while it did not change NO3− uptake for the two species. The interspecific interaction enhanced N uptake of both N forms for A. faxoniana but did not affect the P. asperata compared with single-plant mode. NH4+ and NO3− uptake rates for the two species were regulated by root N concentration, root nitrate reductase activity, root vigor, soil pH and soil N availability under plant–plant interactions. Decreased NH4+ uptake rate for P. asperata under intraspecific interaction was induced by lower root N concentration and nitrate reductase activity. The positive effects of interspecific interaction on N uptake for A. faxoniana could be determined mainly by positive rhizosphere effects, such as high soil pH. From the perspective of root–soil interactions, our study provides insight into how plant–plant interactions affect N uptake, which can help to understand species coexistence and biodiversity maintenance in forest ecosystems.
Purpose of this study was to investigate different responses of two contrasting
Populus davidiana populations to exogenous abscisic acid (ABA) application under well-watered and water-stressed ...conditions, and to further elucidate the role of ABA in drought tolerance. Two contrasting populations were from the wet and dry climate regions in China, respectively. Exogenous ABA was applied to the leaves by spraying and changes in plant growth and structure, gas exchange, endogenous ABA concentration and water use efficiency were monitored. The results demonstrated that exogenous ABA application significantly decreased height growth (Ht), total biomass (Tb), total leaf area (La), specific leaf area (Sla), net photosynthesis (A) and transpiration (E), and significantly increased root/shoot ratio (Rs), transpiration efficiency (WUE
T), instantaneous water use efficiency (WUE
i) and carbon isotope composition (
δ
13C) under well-watered and water-stressed conditions. These morphological and physiological responses to exogenous ABA application showed that ABA could play an important role to control drought tolerance in
P. davidiana populations. However, distinct population differences were found in ABA-induced growth reduction, gas exchange decrease and water use efficiency increase. Compared with the wet climate population, the dry climate population was more responsive to exogenous ABA application, resulting in lower Ht, Tb, La, Sla, A and E, and higher Rs, WUE
T, WUE
i and
δ
13C under all experimental treatments. Our results provide strong evidence for adaptive differentiation between populations of
P. davidiana.
Mycorrhizae and their hyphae play critical roles in soil organic carbon (SOC) accumulation. However, their individual contributions to SOC components and stability under climate warming conditions ...remain unclear. This study investigated the effects of warming on the SOC pools of Picea asperata (an ectomycorrhizal plant) and Fargesia nitida (an arbuscular mycorrhizal plant) mycorrhizae/hyphae on the eastern Tibetan Plateau. The results indicated that mycorrhizae made greater contributions to SOC accumulation than hyphae did by increasing labile organic carbon (LOC) components, such as particle organic carbon (POC), easily oxidizable organic carbon, and microbial biomass carbon, especially under warming conditions. Plant species also had different effects on SOC composition, resulting in higher mineral-associated organic carbon (MAOC) contents in F. nitida plots than in P. asperata plots; consequently, the former favored SOC stability more than the latter, with a lower POC/MAOC. Partial least-squares path modelling further indicated that mycorrhizae/hyphae indirectly affected LOC pools, mainly by changing soil pH and enzyme activities. Warming had no significant effect on SOC content but did change SOC composition by reducing LOC through affecting soil pH and iron oxides and ultimately increasing SOC stability in the presence of mycorrhizae for both plants. Therefore, the mycorrhizae of both plants are major contributors to the variation of SOC components and stability under warming conditions.
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•Mycorrhizal roots made greater contributions to SOC pools than the external hyphae.•Warming favored SOC stability in the presence of mycorrhizal roots for both plants.•POC was the main contributor for SOC variation.
The effects of mycorrhiza and its external hyphae on the response of soil microbes to global warming remain unclear. This study investigates the role of mycorrhiza and its hyphae in regulating soil ...microbial community under warming by examining the microbial biomass and composition in the ingrowth cores of arbuscular mycorrhiza (AM) plant, Fargesia nitida, and ectomycorrhiza (ECM) plant, Picea asperata, with/without mycorrhiza/hyphae and experimental warming. The results showed that warming significantly increased the biomass of all soil microbes (by 19.89%–137.48%) and altered the microbial composition in both plant plots without mycorrhiza/hyphae. However, this effect was weakened in the presence of mycorrhiza or hyphae. In F. nitida plots, warming did not significantly affect biomass and composition of most soil microbial groups when mycorrhiza or hyphae were present. In P. asperata plots, warming significantly increased the total and ECM fungi (ECMF) biomass in the presence of hyphae (p < 0.05) and the total, Gn, and AM fungi (AMF) biomass in the presence of mycorrhiza (p < 0.05). Meanwhile, the response of enzyme activities to warming was also altered with mycorrhiza or hyphae. Additionally, soil microbial community composition was mainly influenced by soil available phosphorus (avaP), while enzyme activities depended on soil avaP, dissolved organic carbon (DOC), and nitrate concentrations. Our results indicate that mycorrhiza and its hyphae are essential in regulating the response of microbes to warming.
Mycorrhiza and hyphae can regulate the response of soil microbial community to warming. Display omitted
•Both ECM and AM mycorrhiza/hyphae increased the biomass of soil microbes.•The response of microbes to warming was altered with mycorrhiza/hyphae presence.•Soil microbes in P. asperata plots were more sensitive to warming than F. nitida.
Host trees allocate photosynthates to ectomycorrhizal symbionts (ECMs) in exchange for soil nutrients, and the carbon allocation has profound effects on forest carbon sequestration. However, it is ...still a challenge to precisely quantify the amount of carbon allocated to ECMs and to identify factors affecting this allocation. Here, we estimated tree species-specific differences and the dynamics of carbon allocation to ECMs by 13CO2 labeling along seedling development, and explored mechanisms underlying these differences from the perspective of ECM fungal community across four tree species (evergreen Picea asperata and Quercus aquifolioides, deciduous Larix gmelinii and Betula albosinensis) and three development stages (early, middle and late of the growing season). Results showed that the proportion of 13C allocated to ECMs (P13CECMs) and ECM fungal community composition varied across tree species and seedling development. P13CECMs was higher in deciduous (3.3 ± 0.7%) trees than in evergreen trees (1.6 ± 0.3%), and higher at the late (5.2 ± 0.7%) than middle (1.8 ± 0.3%) and early (0.3 ± 0.1%) growing season. The relative abundance of the four ECM exploration types (contact, short-, medium- and long-distance) was 7.8–14.8%, nearly 50%, 25.2–31.2%, and nearly 10%, respectively, and varied significantly for contact and medium-distance types. The relative abundance of contact type was higher in deciduous than evergreen trees, and higher at the late than mid-growing stage, but the opposite was true for medium-distance type. Across tree species and seedling development, P13CECMs was positively correlated with the relative abundance of contact type, but negatively correlated with that of medium-distance type. The results suggest that carbon allocation to ECMs is tightly associated with ECM fungal community composition and highlight the critical role of ECM fungal community composition in carbon budges of forest ecosystem.
•Deciduous had greater P13CECMs than evergreen trees.•Trees had higher P13CECMs at the late than middle and early growing stages.•Contact and medium-distance types varied with tree species and seasons.•P13CECMs was tightly associated with ECM fungal community composition.
Despite increasing knowledge of plant interactions on the aboveground parts, little is known about the belowground mechanisms underlying such interactions. Here, we selected Picea asperata and Abies ...faxoniana, two dominant species of subalpine forests, to investigate the effects of planting patterns (isolation and intra- and interspecific interactions) on soil microbial communities. High-throughput 16S rRNA and ITS gene sequencing were performed to explore the bacterial and fungal community structures of the soils. The fungal community changed more under interactions of two species than isolation. Intra- and interspecific interactions had different effects on the fungal community. However, neither intra- nor interspecific interactions had effects on bacterial community composition. Compared with bacteria, fungi were more strongly affected by soil properties, such as the nitrate nitrogen concentration, total nitrogen concentration, pH, and β-1,4-N-acetyl-glucosaminidase activity. These results indicated that fungi were more susceptible than bacteria to plant interactions. Fungal community composition and structure, especially those of ectomycorrhizal fungi, were changed by intra- and interspecific interactions. In inter- and intraspecific interactions with P. asperata, the relative abundance of the ectomycorrhizal fungal Inocybe and Trichophaea increased, which may be one of important factors directly or indirectly affecting belowground interactions.
•P. asperata had a positive effect on the growth of A. faxoniana.•Fungal community was more sensitive to plant interactions than bacterial community in short time.•P. asperata induced an increment in the abundance of Inocybe and Trichoderma under interspecific interactions.•P. asperata mainly affected microbial community in interspecific interactions.
The functional traits of roots play an important role in nutrient acquisition in plants, which affects the outcome of plant–plant interactions. However, few studies have comprehensively investigated ...the plastic responses of plant root traits to plant–plant interactions. A pot experiment was conducted to quantify the effects of intraspecific and interspecific interactions on seedling growth and on multiple root traits of two coniferous species, Picea asperata Mast. and Abies faxoniana Rehd. et Wils. The results showed that plant–plant interactions changed the root physiology of these two species but had no effect on the morphological, architectural, and biotic traits of their root system. Intraspecific interaction resulted in lower root nitrogen content and stronger resource competition than interspecific interaction. Under intraspecific interaction, P. asperata had lower root vigor and nitrate reductase activity, which impeded the acquisition and utilization of the limited resources, and thus resulted in marginally decreased total biomass, where the total biomass for A. faxoniana was not significantly affected. Under interspecific interaction, the high total biomass of A. faxoniana could be explained by rhizosphere interactive effects and reduced metabolic (carbon and nitrogen) costs due to lower root exudative outputs. Our results demonstrate that root physiological responses can explain the effects of short-term plant–plant interactions on plant growth.
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