植物群落稀有种维持机制与土壤反馈的研究进展

自Janzen-Connell(J-C)假说提出后半个世纪以来,生态学家在热带及亚热带森林对该假说开展的大量实证研究表明,由专性天敌导致的J-C效应所引起的负密度制约是维持森林多样性和决定群落组成的重要驱动力,该假说成功地解释了热带及亚热带森林的丰富多样性。土壤病原真菌所引起的植物–土壤负反馈是J-C效应最主要的表现形式。然而,对于植物–土壤负反馈是否能够维持森林群落中的大量稀有种仍然存在许多争议。基于当代物种共存理论的"稀有种优势"假说认为,只有在满足"可入侵准则"(即物种在稀有时具有种群增加的趋势)的前提下,稀有种才能在群落中与其他物种长期共存。然而,当前基于土壤反馈的实验结果与该理论预测相悖,因此在稀有种的维持机制方面仍存在较大的分歧。本文通过介绍植物–土壤反馈理论,整合了可能对稀有种维持有较大影响的因素,包括共生菌根真菌、土壤养分以及植物细根性状等在影响土壤负反馈方面的相关研究,并对这些因素如何影响群落中物种多度和稀有种在群落中的维持进行了探讨。最后,我们也从其他角度探讨了一些对稀有种维持的研究。我们认为在未来对稀有种的研究中,探讨使其长期存续的"优势"和制约其种群扩大的"限制"同等重要,将当代物种共存理论与新技术、新方法相结合对于探究稀有种的维持机制具有重要的意义,可为稀有种保护提供理论依据。

Mechanism of plant-soil feedback in a degraded alpine grassland on the Tibetan Plateau

Although biotic and abiotic factors have been confirmed to be critical factors that affect community dynamics,their interactive effects have yet to be fully considered in grassland degradation.Herein,we tested how soil nutrients and microbes regulated plant-soil feedback(PSF)in a degraded alpine grassland.Our results indicated that soil total carbon(STC;from 17.66 to 12.55 g/kg)and total nitrogen(STN;from 3.16 to 2.74 g/kg)exhibited significant(P<0.05)decrease from non-degraded(ND)to severely degraded(SD).Despite higher nutrients in ND soil generating significantly(P<0.05)positive PSF(0.52)on monocots growth when the soil was sterilized,a high proportion of pathogens(36%)in ND non-sterilized soil resulted in a strong negative PSF on monocots.In contrast,the higher phenotypic plasticity of dicots coupled with a higher abundance of mutualists and saprophytes(70%)strongly promoted their survival and growth in SD with infertile soil.Our findings identified a novel mechanism that there was a functional group shift from monocots with higher vulnerability to soil pathogens in the ND fertile soil to dicots with higher dependence on nutritional mutualists in the degraded infertile soil.The emerging irreversible eco-evolutionary in PSF after degradation might cause a predicament for the restoration of degraded grassland.

Current plant diversity but not its soil legacy influences exotic plant invasion

Current plant diversity can influence exotic plant invasion,but it is unclear whether there is a legacy effect of plant diversity on exotic plant invasion.As plant diversity can affect soil microbial communities and physio-chemical properties,which may cascade to impact subsequent exotic plant growth,we hypothesize that the soil legacy effect of plant diversity can influence exotic plant invasion.We conducted a plant–soil feedback experiment.In the conditioning phase,we trained soils by monocultures of 12 plant species from three functional groups(4 grasses,3 legumes and 5 forbs)and mixtures of 8 randomly selected species with all three functional groups from this 12-species pool.In the test phase,we grew the invasive plant Bidens pilosa with a co-occurring native grass(Arthraxon hispidus),with a co-occurring native forb(Pterocypsela indica)or with both in each type of the conditioned soils.The performance of B.pilosa relative to its native competitors varied depending on the functional type of both conditioning plant species in the conditioning phase and competing plant species in the test phase.Diversity of the conditioning plants did not influence the growth difference between B.pilosa and its native competitors.However,increasing diversity of the competing plant species reduced the performance of B.pilosa relative to its native competitors.Our results suggest that current plant diversity can reduce exotic plant invasion through increasing growth inequality between invasive and native plants,but the soil legacy effect of plant diversity may have little impact on exotic plant invasion.

Plant diversity promotes soil fungal pathogen richness under fertilization in an alpine meadow

Aims The effects of fertilization on fungal plant pathogens in agricultural soils have been studied extensively.However,we know little about how fertilization affects the relative abundance and richness of soil fungal plant pathogens in natural ecosystems,either through altering the soil properties or plant community composition.Methods Here,we used data from a 7-year nitrogen(N)addition experiment in an alpine meadow on the Qinghai-Tibetan Plateau to test how N addition affects the relative abundance and richness of soil fungal plant pathogens,as determined using Miseq sequencing of ITS1 gene biomarkers.We also evaluated the relative importance of changes in soil properties versus plant species diversity under N addition.Important Findings Using general linear model selection and a piecewise structural equation model,we found that N addition increased the relative abundance of soil fungal plant pathogens by significantly altering soil properties.However,higher host plant species richness led to higher soil fungal plant pathogen richness,even after excluding the effects of N addition.We conclude that the relative abundance and richness of soil fungal plant pathogens are regulated by different mechanisms in the alpine meadow.Continuous worldwide N inputs(through both fertilizer use and nitrogen deposition)not only cause species losses via altered plant species interactions,but also produce changes in soil properties that result in more abundant soil fungal plant pathogens.This increase in pathogen relative abundance may seriously threaten ecosystem health,thus interrupting important ecosystem functions and services.

Similarity in fine-to-total root mass ratio leads to comparative plant-soil feedbacks between co-occurring native and invasive plants

Aims Soil biota can affect plant-plant interactions and non-native plant invasions via plant-soil feedback(PSF).Understanding the drivers underlying interspecific variations in PSF is im portant for predicting the role of soil biota in non-native plant invasions.Recent studies found that PSF could be predicted by plant traits.The success of plant invasions is also linked with plant traits,suggesting a potential linkage between PSF and plant invasion via plant traits,but has not yet been tested.Here,we compared PSF between six phylogenetically paired co-occurring native and invasive plants,and explored the potential linkage between PSF with plant root traits.Methods We conducted a two-phase PSF experiment.Field collected soils were conditioned by the six plant species for 3 months firstly,then seedllings of these plants were grown in living or sterilized soils that had been conditioned by conspecific vs.heterospecific(the conge ner/confamilial species)individuals.We estimated effects of biota in conspecific(conspecific PSF)or heterospecific(heterospecific PSF)soils relative to sterilized soils,and the relative effects of biota in conspecific vs.heterospecific soils(PSF-away)on plant biomass.Important Findings In general,soil biota suppressed plant growth,and there were no differences in conspecific PSF,heterospecific PSF and PSF-away between native and invasive plants.PSF increased with rising plant fineto-total root mass ratio in the presence of soil biota,and its value was comparable between native and invasive plants.Our results indicate that similarity in plant fine-to-total root mass ratio that predicted PSF may have partially led to the comparable PSFs between these native and invasive plants.Studies exploring the linkages among plant traits,PSF and plant invasions with more plants,in particular phylogenetically distant plants,are needed to improve our understanding of the role of soil biota in plant invasions.

An invading annual plant benefits less from soil biota and has reduced competitive power with a resident grass

Aims Interactions between plants and their soil biota,arbuscular mycorrhizal fungi(AMF)in particular,may play a vital role in the establishment and the range expansion of exotic plants in new environments.However,whether there are post-introduction shifts in dependence on AMF and how dependency interacts with competition remains poorly understood.Methods We conducted a common garden greenhouse experiment to examine how native(USA)and invasive(China)populations of the plant species Plantago virginica,respond to soil biota,and whether these responses change in the presence of a competitor.Important Findings We found that while native populations consistently had a higher AMF colonization rate and benefited from AMF in both biomass and seed production,invasive populations received less benefit from AMF,and even showed reduced biomass with AMF in the presence of a competitor.This low mycorrhizal dependency in invasive populations correlated with greater suppression by an indigenous competitor for the invader.The different responses of the invasive and native populations to AMF suggest that alteration of mycorrhizal dependency has occurred during the invasion of P.virginica into China.Our findings suggest that this reduced dependency incurs a cost during interspecific competition.