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Mediation of Arbuscular Mycorrhizal Fungi on Plant Density Effects under Different Water Levels: Phenomena and Mechanism

Author: XuLiMing
Tutor: ChenXin
School: Zhejiang University
Course: Ecology
Keywords: exponent of density regulation(α) B-D relationship(Biomass-Density relationship) density effect plant interactions facilitation competition Relative Interaction Index(RII) arbuscular mycorrhizal fungi(AMF) water stress Medicago sativa L. Lespedeza formosa (Vog.) Koehne root compartment
CLC: Q948
Type: Master's thesis
Year: 2010
Downloads: 114
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Abstract

-3/2 self-thinning law, which describes the plant individual biomass and density relationship, reflects the population density effects and population dynamics. The exponent of self-thinning or exponent of density regulation （a） is -3/2 . However, the -3/2 self-thinning law is facing challenges that the exponent might not be a constant and could be regulated by abiotic and biological factors such as water, soil microbes, etc. It is well known that plant interactions （neighbor effects） is a main factor regulating plant density effects. Whereas plant interactions per se is mediated by many factors. Arbuscular mycorrhizal fungi （AMF）, one of the most important soil microbes, can form symbiosis with over 80% terrestrial plants and improves plants nutrient acquisition. Therefore, the mediation of AMF on plant interactions and then on density effects is well worth researching. Here, we first tested whether AMF would influence on density effects of two species Medicago sativa L. and Lespedeza formosa （Vog.） Koehne through greenhouse experiments, then carried out a root compartments experiment to explore the mechanism of AMF mediating plant interactions, thereby the density effects. Main results obtained from these experiments are as follows:1. AMF colonization and influence of water, AMF and plant density on the growth of Medicago sativa and L. Formosa under greenhouse experimentAMF colonization decreased under drought stress （annual precipitation of 312mm）. The interaction of water and AMF treatments significantly influenced the AMF root colonization of L Formosa. AMF treatments did not impact but water and density treatments significantly impacted individual biomass of shoot and root of both species.2. Impacts of water, AMF and density on the growth of M. sativa and plant density effectsThe biomass root/shoot （R/S） differed significantly among water, AMF or density treatments, with the highest under the treatment of "drought stress-low AMF" reaching to 0.68 at the density of 1000 plants/m². Under drought stress, high AMF lowers R/S. While under sufficienct water condition （annual precipitation of 1455mm）, high AMF improved the growth of low-density plants and decreased R/S. However, under high density AMF increased R/S.High AMF enhanced the individual competition of high densitiy population under either water level, resulting in the B-D relationship line forming a steeper slope. But under drought stress, individual biomass significantly decreased with a lower density of 400 plants/m², while under sufficienct water condition that significantly decreased with a higher density of 2200 plants/m². Drought stress decreased |α| value of both shoots and roots under either AMF treatment comparing with sufficient water treatment. Under drought stress, high AMF decreased the roots |α| while increased that of shoots. Under sufficienct water condition values of |α| of both shoots and roots were highest under high AMF treatment, with the shoots |α| of 1.023 and the roots |α| of 1.226 respectively.3. Impacts of water, AMF and density on the growth of L. formosa and plant density effectsNo significant difference of effects of AMF on plant density effects of L. formosa was found under either water treatments. AMF tended to stimulate both individual biomass of shoots and roots, especially the root biomass under drought stress. Water treatments significantly impact R/S. Highest R/S （0.63） occurred at the density of 500 plants/m² under "drought stress-high AMF" treatment. Both water and density treatments had significant effects on the plant height. None of the treatment had significant influence on the plant crown diameter. High AMF did not enhanced individual competition under either water level. Thus, in the B-D relationship line, no steeper slope was found. Drought stress decreased |α| value of both shoots and roots under either AMF treament. Under drought stress, high AMF increased |α| value of roots while decreased that of shoots. Under sufficienct water condition |α| values of both shoots and roots were highest under low AMF treatment, with the shoots |α| of 1.199 and the roots |α| of 0.956 respectively.4. Effects of water, root system interaction on the growth of M. sativa and plant interactions in the controlled root-compartment experimentBoth water levels （annual precipitation, Wl:312mm, W2:632mm, W3:920mm, W4:1455mm） and root system interaction treatments significantly affected the shoot and root biomass, and plant height of target plants.Root system regulated plant interactions differently under different water levels. Under the lowest water level （W1）, the treatment with AMF passing through promoted the growth of target plants, whereas the treatment with the whole root interaction inhibited the growth of target plants. Under other water levels, the treatment with the whole root interaction facilitated the growth of target plants while the treatment with AMF passing through decreased the growth of target plants. Thus, the "whole root interaction" treatment showed to have the lowest RII for shoots and roots under the lowestwater level. While the treatment with AMF passing through showed the lowest RII for shoots and shoots under higher water conditions.R/S presented highest in the treatment with the whole root interaction under all water treatments. In treatments of no-neighbor and the whole root interaction, R/S decreased with water increasing.Data of ¹⁵N showed nitrogen could be transferred between the neighbor and target plants through the common mycelial networks, implying that through mediating nutrient acquisition AMF could affect interaction between neighbor and target plants.

Mediation of Arbuscular Mycorrhizal Fungi on Plant Density Effects under Different Water Levels: Phenomena and Mechanism

Abstract

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