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Article

AM Fungi Endow Greater Plant Biomass and Soil Nutrients under Interspecific Competition Rather Than Nutrient Releases for Litter

by
Bangli Wu
,
Yun Guo
,
Minhong He
,
Xu Han
,
Lipeng Zang
,
Qingfu Liu
,
Danmei Chen
,
Tingting Xia
,
Kaiping Shen
,
Liling Kang
and
Yuejun He
*
Research Center of Forest Ecology, Forestry College, Guizhou University, Guiyang 550025, China
*
Author to whom correspondence should be addressed.
Forests 2021, 12(12), 1704; https://doi.org/10.3390/f12121704
Submission received: 11 November 2021 / Revised: 29 November 2021 / Accepted: 30 November 2021 / Published: 5 December 2021
(This article belongs to the Special Issue Maintenance of Forest Biodiversity)
Browse Figures
Versions Notes

Abstract

:
Plant competition affects belowground ecological processes, such as litter decomposition and nutrient release. Arbuscular mycorrhizal (AM) fungi play an essential role in plant growth and litter decomposition potentially. However, how plant competition affects the nutrient release of litter through AM fungi remains unclear especially for juvenile plants. In this study, a competitive potting experiment was conducted using juvenile seedlings of Broussonetia papyrifera and Carpinus pubescens from a karst habitat, including the intraspecific and interspecific competition treatments. The seedlings were inoculated by AM fungus or not inoculated, and the litter mixtures of B. papyrifera and C. pubescens were added into the soil or not added. The results were as follows: Litter addition significantly increased the root mycorrhizal colonization of two species in intraspecific competition. AM fungus significantly increased the biomass of B. papyrifera seedings and nitrogen release and decreased nitrogen concentration and N/P ratio of litter and further improved the total nitrogen and N/P ratio of soil under litter. The interspecific competition interacting with AM fungus was beneficial to the biomass accumulation of B. papyrifera and improvement of soil nutrients under litter. However, intraspecific competition significantly promoted nutrient releases via AM fungus. In conclusion, we suggest that AM fungi endow greater plant biomass and soil nutrients through interspecific competition, while intraspecific competition prefers to release the nutrients of litter.

1. Introduction

Litter is an essential carrier for carbon storage and nutrient cycling in terrestrial ecosystems [1] and is the main source of nutrients that flow into the soil through decomposition and nutrient release [2], which is closely related to the aboveground and belowground ecological process [3]. The decomposition of litter in the soil contributes significantly to the productivity of the terrestrial ecosystem [4]. Moreover, the nutrients released from litter influences the nutrient turnover between plants and soil, and this is mainly controlled by litter chemistry [5].
The chemical properties of litter affect the litter mass-loss rate [6], thus, affecting its decomposition in the soil at different stages [7]. Generally, most plants return to the soil in the form of litter, which provides substantial nutrients and energy for the soil [3,8]. This process is affected by soil microorganisms, which are considered to be the major drivers of biogeochemical cycles [9,10,11].
Hence, the significance of soil microorganisms on ecosystem processes cannot be ignored. Arbuscular mycorrhizal (AM) fungi are essential to soil functional microorganisms and form a symbiotic relationship with the roots in over 80% of terrestrial plant species [12] and play a critical role in soil chemical properties and plant communities by affecting the plant nutrient uptake [13]. Research has shown that AM fungi can improve N and P acquisition for plants [14]. N and P are generally thought to be the main elements that limit plant growth and terrestrial ecosystem productivity [15], and the acquisition of these nutrients may depend on the effect of AM fungi on litter decomposition.
Several studies have suggested that AM fungi can influence litter breakdown [16,17], and consequently accelerate the release of litter nutrients [18,19]. For instance, AM fungi can promote the decomposition of complex organic materials in soil through the function of saprophytes [20]. AM fungal extraradical mycelium can penetrate into the litter to facilitate the decomposition [21].
Nutrients released from litter are mainly returned to the soil, and only small amounts are transferred to host plants via AM hyphae [22]. However, these transfers of nutrients can change the competitive relationship between plants [23]. Despite the importance of AM fungi in competitive plant relationships and litter nutrient release, how competition affects decomposition and nutrient release in the presence of AM fungi has not yet been addressed.
Belowground competition is an important force in structuring plant communities [24] and affects the distribution of plant species and the diversity of plant communities [25]. Additionally, belowground competition is more intense than aboveground competition because plant roots compete for soil nutrients [26]. AM fungi can regulate the plant competition associated with plant roots through interconnected mycorrhizal networks that exchange C, N and P among different species and change the nutrient status between plants and soil [27,28].
Aponte et al. [29] proposed that plant competition indirectly affects the decomposition rate by inducing changes in the microbial community. Specifically, interspecific differences drive litter mass changes that positively affect the decomposition process [30], but intraspecific differences are generally considered to influence plant residue breakdown more intensely due to almost complete niche overlap [31]. Meanwhile, AM fungi play an important role in mediating intra- and interspecific competitions [32].
Therefore, AM fungi and competitive plant interactions could affect plant nutrient acquisition strategies [28]. The variable nutrient acquisition strategies of plants reflect the difference in litter decomposition rates and mediate the population of decomposer organisms [33], which may have different impacts on the decomposition and release of litter nutrients, especially in nutrient-poor environments.
The southwest of China is the largest karst distribution area in the world. It is a typical fragile ecosystem characterized by nutrient deficiency that severely restricts the primary productivity of plants [34]. Furthermore, the small amount of litter reduces the nutrient turnover of the karst ecosystem [35]. AM fungi are widely distributed in karst areas and can coexist with woody plants, such as Broussonetia papyrifera [36]. AM fungi can also regulate plant nutrient competition in karst regions.
For instance, Shen et al. [37] reported that AM fungi confer in invasive plants a competitive advantage in nutrient acquisition compared to native species, and Xia et al. [38] showed that AM fungi change plant root phenotypic traits and resource acquisition strategies to increase host competitiveness. Additionally, AM fungi could promote litter decomposition and the transfer of N from litter to host plants by enhancing the interaction among plants in karst habitats [21].
Therefore, plant competition affects the decomposition and nutrient release of litter via AM fungi. However, the effects of AM fungi on the release of litter nutrients associated with intra- versus interspecific competitions in karst soils remains unclear. Thus, our aim is to clarify the role of AM fungi in the nutrient release of litter under intra- and interspecific competitions. We hypothesized that:
Hypothesis 1 (H1).
The interspecific competition increases more plant biomass and soil nutrients than the intraspecific competition when associated with AM fungi and litter in karst soil.
Hypothesis 2 (H2).
AM fungi can promote the nutrient release of litter in karst soil.
We verify the arbuscular mycorrhizal roles in soil nutrient maintenance and forest ecosystem management of karst areas.

2. Materials and Methods

2.1. Experimental Treatments

A potting experiment was conducted in a plastic pot (22 × 20 × 28 cm, caliber × bottom diameter × height) in which there is a 1 cm hole in the bottom of the pot for draining water. The experimental treatments included competition patterns, AM fungus and litter addition. The competition pattern contained the intraspecific competition treatment (Intra-) and the interspecific competition treatment (Inter-) using seedlings of Broussonetia papyrifera and Carpinus pubescens, which are common plant species from karst habitat. Two seedlings of B. papyrifera or C. pubescens were monoculture in a pot as the Intra-treatment, in contrast to mixed planting for two species as the Inter-treatment.
A 100 g of AM inoculum of the fungus Claroideoglomus etunicatum was taken into the growth substrate of soil in each pot as the inoculated M+ treatment, or a sterilized inoculum of 100 g of C. etunicatum was applied into the substrate as the control of M−. The litter addition wrapped with 10 g litter mixture (5 g B. papyrifera and 5 g C. pubescens) in 1 mm aperture nylon mesh bag (5.0 cm × 5.0 cm) was regarded as the L+ treatment and was not added as the L− treatment (Figure 1).
The litters were soaked in 2% H2O2 for 3 min and oven-dried for 48 h at 65 °C before the experimental treatment. The initial chemistry of the litter mixtures had nitrogen 1.368 mg g−1 and phosphorus 0.268 mg g−1. A 1300 g of growth substrate of limestone soil (Calcaric regosols, FAO) [36] was sterilized at 121 °C and 0.14 Mpa for one hour and was then placed into a pot before the start of the experiment. The growth substrate had a pH of 6.93, total nitrogen of 0.718 g kg−1, total phosphorus of 0.491 g kg−1, available nitrogen of 201.3 mg kg−1 and available phosphorus of 233.15 mg kg−1.
Specifically, 550 g of growth substrate was added into the bottom of each pot. Then, the litter bag was placed on the growth substrate and covered with 500 g of sterilized substrate. Finally, five seeds of B. papyrifera and C. pubescens were sterilized with 1/1000 solution of KMnO4 for 10 min and rinsed with sterile water three times, and were placed into the pot and covered with 250 g soil substrate. Two plants were retained after three weeks of seedling growth in each pot (Figure 1). There were 40 pots with five replicates for each treatment in this experiment.
In particular, the AM inoculum contained colonized root pieces, hyphae and approximately 100 spores per gram, and an extra 10 mL of filtrate was taken into M− from 100 g of inoculum and dissolved into 1000 mL sterilized water in order to maintain a consistent microflora with the inoculated treatment except for the AM fungus. Additionally, C. etunicatum had been initially isolated from a local karst site in Guizhou of southwest China, purchased from the Institute of Nutrition Resources, Beijing Academy of Agricultural and Forestry Sciences (BGA0046).
The soil, plant seeds and litter were collected from a typical karst habitat in Huaxi District, Guiyang city, Guizhou Province, China. The plants were cultured in a greenhouse at Guizhou University, China (106°22′ E, 29°49′ N, 1120 m above sea level). All materials of plants and soil were harvested for determination after 24 weeks.

2.2. Measurements of the Root Mycorrhizal Colonization, Spore Density, Hyphal Length, Plant Biomass and the Concentrations of Nitrogen and Phosphorus in Litter and Soil

All materials containing the soil substrates, plants and residual litter were harvested for determination. The plant tissues, including roots, stems and leaves, were weighed after being dried at 65 °C for constant weight, and then added together for the total biomass of the plant individual. The spore density of C. etunicatum was determined in soil using the method described by Biermann and Linderman [39], and the hyphal length was determined using the gridline intersect method [40].
The root mycorrhizal colonization rate was used the magnified gridline intersection method from Mcgonigle et al. [41]. Nitrogen and phosphorus concentrations regarding the residual litter and soil materials were determined using the Kjeldahl method [42] and the molybdenum-antimony anti-colorimetric method [43]. The available nitrogen (AN) and the available phosphorus (AP) of soil were determined, respectively, by the alkali hydrolysis diffusion method [44] and the colorimetry method [45].

2.3. Calculations of the Release of Nitrogen and Phosphorus

Decomposing traits, including the mass-loss rate and nutrient release of litter, were calculated via the equation referenced from Bragazza et al. [46] and Wu [47] as follows:
Litter mass-loss rate (%) = [(W0 − W1)/W0] × 100%
Litter nutrient release = [(X0W0 − X1W1)/X0W0] × X0W0
where the W0 and W1 are the initial and final litter weights, respectively; meanwhile, X0 and X1 are the initial and final litter nutrient concentrations of nitrogen and phosphorus, respectively. Positive or negative values mean the net mineralization or net immobilization, respectively.

2.4. Statistical Analysis

For comparing Intra- and Inter- competition when analyzing nutrients of litter and soil, these data were integrated through all monoculture treatments combined the respective B. papyrifera with C. pubescens seedlings as intraspecific competition data, except for the mycorrhizal colonization rate and plant biomass for each species. All data were tested for normality and homogeneity of variance before analysis. Two-way ANOVAs were applied for analyzing the effects of AM fungus (M+ vs. M−) and competition pattern (Intra- vs. Inter-) and their interactions on decomposing traits of litter and soil nutrients under L+ or L−. All statistical analyses were performed using the SPSS 25.0 software, and all the graphs were drawn through the Origin 2018 software.

3. Results

3.1. The Root Mycorrhizal Colonization of Two Plants and The Spore Density and Hyphal Length in Different Competition and Litter Treatments when Inoculated with AM Fungus

The significant Inter- > Intra- of mycorrhizal colonization was presented in C. pubescens under L− (Table 1). However, there was no significant difference in mycorrhizal colonization of the two species in Intra- and Inter- competitions under L+. In addition, a significant L+ > L− was observed for mycorrhizal colonization of two species in Intra-treatment. The soil spore density of the Inter-treatment was significantly greater than the Intra-treatment under L+ but not for under L−.
A significant L+ > L− of spore density was presented in Inter-treatment; there was no significant difference between L+ and L− under Intra- and Inter-treatments for the hyphal length (Table 1). This indicates that litter addition significantly increased the root mycorrhizal colonization of two species except for interspecific competition conditions; the intraspecific competition decreased the spore density, while the interspecific competition increased the spore density in this experiment.

3.2. The Biomass of B. papyrifera and C. pubescens Seedlings in Different Competition and Litter Treatments

A significant M+ > M− of biomass was presented in B. papyrifera seedlings regardless of Intra- and Inter- under litter and no litter addition treatments (Figure 2a,c). However, the biomass of C. pubescens seeding was not significantly different when comparing M+ to M− under Intra- or Inter- competition (Figure 2b), except for the biomass of M+ was significantly less than the biomass of M− in Intra-treatment (Figure 2d). The significant Inter- > Intra- of biomass were presented in B. papyrifera seedlings under M+ of litter or no litter addition and also M− of litter addition (Figure 2a,c) but not for C. pubescens seedlings even presenting a not significant Inter- > Intra- under no litter (Figure 2d).

3.3. The Concentration and Release of Residual Litter Nutrients on Nitrogen and Phosphorus in Competition Interacting with AM Fungus

The mass-loss rate was not significantly different among AM fungus (M), competition (C) and their interactions M × C (Table 2), and there was no significant difference between M+ and M− in the litter mass-loss rate under Intra- and Inter- competitions (Figure 3a). AM fungus (M) significantly affected the N concentration, N/P ratio and the N and P releases of residual litter but not the P concentration (Table 2). The significant M+ < M− were presented with the N concentration, N/P ratio and P release under Intra-treatment (Figure 3b,d,f).
However, the significant M+ > M− were presented for N release and P concentration under Intra-treatment (Figure 3c,e). The competition pattern (C) significantly affected the N and P concentrations, N/P ratio and the N and P releases of residual litter. The significant Inter- > Intra- of N concentration (Figure 3b) and the significant Inter- < Intra- of N release (Figure 3e) were presented under M+ or M− treatment.
The P concentration and P release under M− showed Inter- > Intra- or Inter < Intra-, respectively, while there were no significant differences between Inter- and Intra-treatments under M+ (Figure 3c,f). The N/P ratio of Inter-treatment was greater than Intra-treatment but was not significant under M+ or M− in the residual litter (Figure 3d). The interaction of M × C significantly affected the concentrations of N and P but not for the N/P ratio and the releases of N and P (Table 2).

3.4. The Nutrients of Nitrogen and Phosphorus in Two Competition Soil with AM Fungus and Litter Treatments

Under the litter addition, the AM fungus (M) significantly affected the total nitrogen (TN) and N/P ratio but not for the total phosphorus (TP), the available nitrogen (AN) and the available phosphorus (AP) (Table 3). The significant M+ > M− of the TN and N/P ratio was found under Intra- and Inter-treatments (Figure 4a,c); however, a significant M+ < M− of TP was found under Intra-treatment (Figure 4b). The competition pattern (C) significantly affected the TN but did not significantly affect the TP and N/P ratio; furthermore, the interaction of M × C significantly affected TN and TP via the two-way ANOVAs analysis (Table 3).
Under M+, the TN and TP of Inter-treatment were significantly greater than Intra-treatment (Figure 4a,b). In addition, the AM fungus (M), competition pattern (C) and their interaction did not significantly affect AN and AP, and there were no differences of AN and AP among Intra- and Inter- compared with other soil nutrients under the M+ and M− treatments (Figure 4d,e).
Under the no litter addition, the AM fungus (M) significantly affected TP and N/P ratio but not for TN, AN and AP (Table 3); the TN and N/P ratio were showed as M+ > M− under Intra-, but the TP was showed as M+ < M− under Intra- and Inter- (Figure 5a–c). The competition pattern (C) significantly affected the TN but not for the TP, the N/P ratio and the AN and AP (Table 3), by significantly increasing the TN of Intra-treatment (Figure 5a). The interaction of M × C did not significantly affect the nutrients of TP, AN, AP and N/P ratio via this experiment (Table 3).

4. Discussion

4.1. Intraspecific and Interspecific Competition Mediated The Accumulation of Plant Biomass and Soil Nutrients and The Releases of Litter Nutrient via AM Fungi

In this study, the interspecific competition significantly increased the biomass of B. papyrifera than the intraspecific competition via AM fungus regardless of litter addition (Figure 2a,c), which indicated that interspecific competition endowed plant biomass accumulation an advantage over the intraspecific competition. Matos et al. [48] found that interspecific competition enhanced the biomass accumulation of Bidens pilosa and Ipomoea grandifolia than the intraspecific competition; Heuermann et al. [49] also observed that interspecific competition greatly increased the biomass of catch plants.
In addition, the interspecific competition significantly increased the soil N and P compared with intraspecific competition under AM fungus inoculation and litter addition (Figure 4a,b), indicating that interspecific competition was more beneficial to increase soil nutrients when compared with the intraspecific competition, which was similar to the previous studies. For instance, the interaction of interspecific plants can positively influence soil properties and, thus, reducing soil nutrients loss, while this was not obvious in competitive intraspecific plants [50].
Additionally, when compared to intraspecific competition, interspecific competition could enhance soil nutrient availability through altering the densities of plants intercropping [51]. Therefore, the interspecific competition confers greater soil nutrients than intraspecific competition; this exactly verified the hypothesis of H1. Overall, the interspecific competition plays an important role in plant biomass accumulation and soil nutrient improvement in nutrient-limited karst soil.
The competition significantly affected the N and P releases of litter (Table 2), and the N and P releases in the intraspecific competition were all greater than in interspecific competition (Figure 3e,f), indicating that intraspecific competition was an important factor affecting the nutrient release of litter in nutrient strategies of competitive plants.
Yang et al. [52] proposed that the intraspecific competition was the main competition mode, which greatly intensified the plant nutrient acquisitions due to niche overlap, thus, driving the decomposition of organic matter and nutrient release [53]. Meanwhile, Tedersoo et al. [54] discovered that the interspecific competition reduced the nutrient demands of plants due to niche differentiation, thus, slowing down litter decomposition and nutrient release [55]. These results supported that intraspecific competition promoted the greater nutrient releases for litter when compared with the interspecific competition in this experiment.

4.2. Arbuscular Mycorrhizal Fungi Regulate the Release of Nitrogen and Phosphorus in Decomposing Litter

AM fungus significantly increased the N release of litter under intra- and interspecific competitions (Figure 3e), indicating that N release positively responded to AM fungus, which was consistent with the study of Hodge et al. [56] and Tan et al. [19], who found that AM fungi stimulated N release during the process of litter decomposition. The N release of litter via AM fungi was mainly achieved through two pathways. One is that AM fungi accelerated N release through decomposing nitrogen compounds in the litter [57], and the other is that AM fungi could facilitate the transformation of organic N into inorganic N; thereby, the N was released from decomposed litter [58].
Previous studies have shown that AM fungi can directly or indirectly affect the decomposition of litter and then promote nutrient release. Directly, the length of AM fungal extraradical mycelium can generally exceed 13-fold of the root length [59], which penetrates into the litter to facilitate the decomposition [21]. Indirectly, AM fungi accelerated decomposition by altering the fungal community composition associated with litter breakdown [60]. In addition, AM fungi hyphal exudates could stimulate litter decomposition by increasing soil enzyme activity [61].
Therefore, AM fungi contribute to the nutrient release of litter directly or indirectly; this exactly verifies the hypothesis of H2. Nevertheless, whether most of the released nutrients are transferred to host plants or soil through AM fungi remains unclear. Therefore, isotope tracing experiments are necessary to explore the nutrient transport among competitive plants via AM mycelium in the future.

4.3. Arbuscular Mycorrhizal Fungi Differentially Affected Plant Biomass and Soil Nutrients

AM fungus significantly increased the biomass of B. papyrifera seedlings under intra- and interspecific competitions in this study (Figure 2a,c), which was accordant with AM fungi enhancing the biomass of Cinnamomum camphora [62]. Wu et al. [63] also proposed that AM fungi facilitated the biomass accumulation of Populus cathayana seedlings.
In this experiment, the AM fungus had no significant effect on the biomass of C. pubescens compared with B. papyrifera (Figure 2a–d), indicating that the two plants differently responded to AM fungus in biomass production, which proved that the AM fungi had the selectivity in regulating plant growth. For example, AM fungi enabled the preferential allocation of nutrient resources to high-quality host plants and aggravated the growth differences between plants [64].
Meanwhile, when two plants were mixed, one of the plants obtained higher N and P and subsequently promoted the biomass accumulation than the neighboring plant through AM fungi [65]. Smith and Read [12] and Helgason and Fitter [66] also agreed that there was a selectivity between specific AM fungi and host plants. Thereby, AM fungi are essential for plant growth, but the mutual selection is not excluded between AM fungi and host plant, precisely as the B. papyrifera and C. pubescens seedlings presented further growth under interspecific or intraspecific competition.
In this experiment, AM fungus increased soil N and P under interspecific competition with litter addition (Figure 4a,b) compared with no litter addition (Figure 5a,b), which indicated that AM fungi improved soil nutrients in the presence of litter. Several studies reported that AM fungi could increase soil N content by stimulating the secretion of soil urease [67] and P content through improving the phosphatase activity [68]. In addition, the nutrients released from the decomposing litter were transferred to the surrounding soil through AM fungi, thus, affecting the soil nutrient turnover [69].
Litter is the main source of soil nutrients, and AM fungi could significantly increase the soil N and P during decomposition [19]. Moreover, AM fungus significantly increased the soil N/P ratio under litter addition, indicating that AM fungi facilitated the soil nitrogen accumulation more than phosphorus (Figure 4c). Verbruggen et al. [70] showed that AM fungi could regulate the soil N/P ratio, and a higher N/P ratio means that the contribution of AM fungi to nitrogen was greater than phosphorus.
It is possible that AM fungi prevented soil N loss through expanding nutrient interception zone [71] or acquired mobile N by absorbing NH4+ and NO3− ions in the soil [72]. Overall, these studies showed that AM fungi could improve soil nutrients associated with litter, and the improvement in nitrogen is greater than for phosphorus. However, the specific mechanism of how AM fungi regulating soil nutrients through litter needs to be further explored in the future.

5. Conclusions

In this experiment, AM fungus affected the plant growth, litter nutrient release and soil nutrients differently under intra- and interspecific competitions via litter. The litter addition had a significant improvement on the root mycorrhizal colonization of B. papyrifera and C. pubescens in intraspecific competition. The AM fungus exerted a positive influence on the biomass of B. papyrifera, the litter N release and soil TN and N/P ratio while showing the opposite effects for the N concentration, P release and N/P ratio of litter in two competitive patterns under litter addition.
The interspecific competition interacting with AM fungus enhanced the biomass accumulation of B. papyrifera and the N concentration and N/P ratio of litter, as well as the TN and TP of soil under litter addition; however, the intraspecific competition regulated by AM fungus significantly improved the N and P releases of litter. In conclusion, the interspecific competition conferred more significant benefits over intraspecific competition in enhancing plant biomass and soil nutrients, while the intraspecific competition instead increased litter nutrient releases when associated with AM fungi in karst soil.

Author Contributions

Conceptualization, Y.H.; Data analysis, Y.G., M.H., D.C., T.X., K.S., Q.L. and L.K.; methodology, X.H., M.H. and L.Z.; writing—original draft preparation, B.W.; writing—review and editing, B.W. and Y.H. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by National Natural Science Foundation of China (31660156, 31360106), the Science and Technology Project of Guizhou Province ([2021] General-455, [2016] Supporting-2805), the Guizhou Hundred-level Innovative Talents Project (Qian-ke-he platform talents [2020]6004), the First-class Disciplines Program on Ecology of Guizhou Province (GNYL [2017]007) and the Talent-platform Program of Guizhou Province ([2017]5788, [2018]5781).

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflict of interest.

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Forests 12 01704 g001 550
Figure 1. Diagram of the experimental design. The woody plant of Broussonetia papyrifera and Carpinus pubescens seedlings were inoculated by AM fungus of Claroideoglomus etunicatum. The litter bags = a 10 g of litter mixture of B. papyrifera and C. pubescens. Intra- = intraspecific competition of B. papyrifera or C. pubescens; Inter- = interspecific competition of B. papyrifera and C. pubescens.
Figure 1. Diagram of the experimental design. The woody plant of Broussonetia papyrifera and Carpinus pubescens seedlings were inoculated by AM fungus of Claroideoglomus etunicatum. The litter bags = a 10 g of litter mixture of B. papyrifera and C. pubescens. Intra- = intraspecific competition of B. papyrifera or C. pubescens; Inter- = interspecific competition of B. papyrifera and C. pubescens.
Forests 12 01704 g001
Forests 12 01704 g002 550
Figure 2. The biomass of B. papyrifera and C. pubescens seedlings through the treatments of competition pattern, AM fungus and with (a,b) or without (c,d) litter addition. Abbreviations: M+ = with AM fungus; M− = without AM fungus; Intra- = intraspecific competition; Inter- = interspecific competition; the *, ** and *** mean different difference between Intra- and Inter- treatments under M+ or M− at p < 0.05, p < 0.01 and p < 0.001, respectively; while the ‘ns’ means a not significant difference; the different lowercase letters (a,b) means a significant difference between M+ and M− treatments under Intra- or Inter- (p < 0.05).
Figure 2. The biomass of B. papyrifera and C. pubescens seedlings through the treatments of competition pattern, AM fungus and with (a,b) or without (c,d) litter addition. Abbreviations: M+ = with AM fungus; M− = without AM fungus; Intra- = intraspecific competition; Inter- = interspecific competition; the *, ** and *** mean different difference between Intra- and Inter- treatments under M+ or M− at p < 0.05, p < 0.01 and p < 0.001, respectively; while the ‘ns’ means a not significant difference; the different lowercase letters (a,b) means a significant difference between M+ and M− treatments under Intra- or Inter- (p < 0.05).
Forests 12 01704 g002
Forests 12 01704 g003 550
Figure 3. The residual litter on mass-loss rate (a), on the concentrations of nitrogen and phosphorus (b,c) and N/P ratio (d) and nutrient release of nitrogen and phosphorus (e,f) in two competition soils through AM fungus treatment. Abbreviations: see Figure 2 for explanations of M+, M−, Intra-, Inter-, * and **, the lowercase letters (a,b) and the ns.
Figure 3. The residual litter on mass-loss rate (a), on the concentrations of nitrogen and phosphorus (b,c) and N/P ratio (d) and nutrient release of nitrogen and phosphorus (e,f) in two competition soils through AM fungus treatment. Abbreviations: see Figure 2 for explanations of M+, M−, Intra-, Inter-, * and **, the lowercase letters (a,b) and the ns.
Forests 12 01704 g003
Forests 12 01704 g004 550
Figure 4. The soil nutrient properties on the total nitrogen and phosphorus (a,b) and the N/P ratio (c) and the available nitrogen and phosphorus (d,e) in two competition soils through AM fungus under litter addition treatment. Abbreviations: see Figure 2 for explanations of M+, M−, Intra-, Inter-, ** and ***, the lowercase letters (a,b) and the ns.
Figure 4. The soil nutrient properties on the total nitrogen and phosphorus (a,b) and the N/P ratio (c) and the available nitrogen and phosphorus (d,e) in two competition soils through AM fungus under litter addition treatment. Abbreviations: see Figure 2 for explanations of M+, M−, Intra-, Inter-, ** and ***, the lowercase letters (a,b) and the ns.
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Forests 12 01704 g005 550
Figure 5. The soil nutrient properties on the total nitrogen and phosphorus (a,b) and the N/P ratio (c) and the available nitrogen and phosphorus (d,e) in two competition soils through AM fungus under none-litter addition treatment. Abbreviations: see Figure 2 for explanations of M+, M−, Intra-, Inter- and **, the lowercase letters (a,b) and the ns.
Figure 5. The soil nutrient properties on the total nitrogen and phosphorus (a,b) and the N/P ratio (c) and the available nitrogen and phosphorus (d,e) in two competition soils through AM fungus under none-litter addition treatment. Abbreviations: see Figure 2 for explanations of M+, M−, Intra-, Inter- and **, the lowercase letters (a,b) and the ns.
Forests 12 01704 g005
Table
Table 1. The root mycorrhizal colonization of Broussonetia papyrifera and Carpinus pubescens, the spore density and the hyphal length through the treatments of competition pattern and with or without litter addition under AM fungus inoculation.
Table 1. The root mycorrhizal colonization of Broussonetia papyrifera and Carpinus pubescens, the spore density and the hyphal length through the treatments of competition pattern and with or without litter addition under AM fungus inoculation.
TreatmentsMycorrhizal Colonization Rate (%)Spore Density (g soil−1)Hyphae Length (m soil−1)
Broussonetia papyriferaCarpinus pubescens
Intra-L+63.3 ± 4.6 ax39.0 ± 7.1 ax8.6 ± 1.3 by15.2 ± 4.1 ax
L−44.7 ± 2.1 ay14.6 ± 0.9 by12.5 ± 0.6 ax9.9 ± 1.7 ax
Inter-L+59.3 ± 5.3 ax17.4 ± 4.3 ax17.9 ± 0.6 ax20.6 ± 8.9 ax
L−46.0 ± 3.3 ax23.0 ± 1.6 ax4.4 ± 0.2 by21.9 ± 7.6 ax
Abbreviations: M+ = with AM fungus; M− = without AM fungus; Intra- = intraspecific competition; Inter- = interspecific competition; L+ = with litter addition; L− = without litter addition; the different lowercase letters (a,b) means a significant difference between Intra- and Inter-treatments under L+ or L− (p < 0.05); the different lowercase letters (x,y) means a significant difference between L+ and L− treatments under Intra- or Inter- (p < 0.05). The values are the mean ± SE.
Table
Table 2. Two-Way ANOVAs for the effects of AM fungus (M+ vs. M−) and competition pattern (Intra- vs. Inter-) on the concentrations and releases of nitrogen and phosphorus and N/P ratio in residual litter.
Table 2. Two-Way ANOVAs for the effects of AM fungus (M+ vs. M−) and competition pattern (Intra- vs. Inter-) on the concentrations and releases of nitrogen and phosphorus and N/P ratio in residual litter.
FactorsdfLitter Mass-
Loss Rate (%)		N Concentration
(mg g−1)		P Concentration
(mg g−1)		N/P RatioN Release
(mg g−1)		P Release
(mg g−1)
FpFpFpFpFpFp
M11.9360.17624.3020.0003.9070.06020.6750.00010.7460.0035.1130.033
C10.1150.73746.6800.00015.9090.0014.2700.05028.1230.0009.2590.006
M × C12.5370.1234.4950.0455.1700.0320.0000.9940.7920.3820.8350.370
Abbreviations: M = AM fungus treatments; C = Competition pattern treatments. p < 0.05 and p < 0.01 indicate significant differences, and p < 0.001 indicates highly significant differences.
Table
Table 3. Two-Way ANOVAs for the effects of AM fungus (M+ vs. M−) and competition pattern (Intra- vs. Inter- ) on total nitrogen and phosphorus and the N/P ratio and the available nitrogen and phosphorus of soil under L+ and L− treatments.
Table 3. Two-Way ANOVAs for the effects of AM fungus (M+ vs. M−) and competition pattern (Intra- vs. Inter- ) on total nitrogen and phosphorus and the N/P ratio and the available nitrogen and phosphorus of soil under L+ and L− treatments.
FactorsdfTotal Nitrogen
(mg g−1)		Total Phosphorus
(mg g−1)		N/P RatioAvailable Nitrogen
(mg kg−1)		Available Phosphorus
(mg kg−1)
FpFpFpFpFp
L+M164.4090.0001.7840.1939.5220.0050.0060.9400.5910.449
C141.4460.0002.5780.1200.4010.5320.2540.6190.1010.753
M × C134.9430.0004.8140.0370.0010.9770.7900.3820.9470.340
L−M11.2440.27515.9420.00011.1480.0031.1410.2954.0090.056
C19.0460.0060.0020.9690.0130.9093.8710.0600.1290.723
M × C13.0190.0940.9490.3390.0010.9810.1810.6740.6270.436
Abbreviations: L+ = with litter addition treatment; L− = without litter addition treatment; M = AM fungus treatments; C = Competition pattern treatments. p < 0.05 and p < 0.01 indicate significant differences, and p < 0.001 indicates highly significant differences.
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Wu, B.; Guo, Y.; He, M.; Han, X.; Zang, L.; Liu, Q.; Chen, D.; Xia, T.; Shen, K.; Kang, L.; et al. AM Fungi Endow Greater Plant Biomass and Soil Nutrients under Interspecific Competition Rather Than Nutrient Releases for Litter. Forests 2021, 12, 1704. https://doi.org/10.3390/f12121704

AMA Style

Wu B, Guo Y, He M, Han X, Zang L, Liu Q, Chen D, Xia T, Shen K, Kang L, et al. AM Fungi Endow Greater Plant Biomass and Soil Nutrients under Interspecific Competition Rather Than Nutrient Releases for Litter. Forests. 2021; 12(12):1704. https://doi.org/10.3390/f12121704

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Wu, Bangli, Yun Guo, Minhong He, Xu Han, Lipeng Zang, Qingfu Liu, Danmei Chen, Tingting Xia, Kaiping Shen, Liling Kang, and et al. 2021. "AM Fungi Endow Greater Plant Biomass and Soil Nutrients under Interspecific Competition Rather Than Nutrient Releases for Litter" Forests 12, no. 12: 1704. https://doi.org/10.3390/f12121704

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