Extraradical Mycorrhizal Hyphae Promote Soil Carbon Sequestration through Difficultly Extractable Glomalin-Related Soil Protein in Response to Soil Water Stress.
Soil water stress (WS) affects the decomposition of soil organic carbon (SOC) and carbon (C) emissions. Glomalin, released by arbuscular mycorrhizal fungi into soil that has been defined as glomalin-related soil protein (GRSP), is an important pool of SOC, with hydrophobic characteristics. We hypothesized that mycorrhizal fungi have a positive effect on SOC pools under soil WS for C sequestration in GRSP secreted by extraradical mycorrhizal hyphae. A microsystem was used to establish a root chamber (co-existence of roots and extraradical mycorrhizal hyphae) and a hyphal chamber (the presence of extraradical mycorrhizal hyphae) to study changes in plant growth, leaf water potential, soil aggregate stability, SOC, GRSP, C concentrations in GRSP (CGRSP), and the contribution of CGRSP to SOC after inoculating Rhizophagus intraradices with trifoliate orange (Poncirus trifoliata) in the root chamber under adequate water (AW) and WS. Inoculation with R. intraradices alleviated negative effects on leaf water potential and plant growth after 7 weeks of WS. Soil WS decreased SOC and mean weight diameter (MWD), while AMF inoculation led to an increase in SOC and MWD in both chambers, with the most prominent increase in the hyphal chamber under WS. The C concentration in easily extractable GRSP (EE-GRSP) and difficultly extractable GRSP (DE-GRSP) was 7.32 - 12.57 and 24.90 - 32.60 mg C/g GRSP, respectively. WS reduced CGRSP, while AMF mitigated the reduction. Extraradical mycorrhizal hyphae increased GRSP production and CGRSP, along with a more prominent increase in DE-GRSP under WS than under AW. Extraradical mycorrhizal hyphae increased the contribution of CDE-GRSP to SOC only under WS. CEE-GRSP and CDE-GRSP were significantly positively correlated with SOC and MWD. It is concluded that extraradical mycorrhizal hyphae prominently promoted C sequestration of recalcitrant DE-GRSP under soil WS, thus contributing more organic C accumulation and preservation in aggregates and soil C pool.
Wang YJ
，He XH
，Meng LL
，Zou YN
，Wu QS
... -
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Elevated CO(2) increases glomalin-related soil protein (GRSP) in the rhizosphere of Robinia pseudoacacia L. seedlings in Pb- and Cd-contaminated soils.
Glomalin-related soil protein (GRSP), which contains glycoproteins produced by arbuscular mycorrhizal fungi (AMF), as well as non-mycorrhizal-related heat-stable proteins, lipids, and humic materials, is generally categorized into two fractions: easily extractable GRSP (EE-GRSP) and total GRSP (T-GRSP). GRSP plays an important role in soil carbon (C) sequestration and can stabilize heavy metals such as lead (Pb), cadmium (Cd), and manganese (Mn). Soil contamination by heavy metals is occurring in conjunction with rising atmospheric CO2 in natural ecosystems due to human activities. However, the response of GRSP to elevated CO2 combined with heavy metal contamination has not been widely reported. Here, we investigated the response of GRSP to elevated CO2 in the rhizosphere of Robinia pseudoacacia L. seedlings in Pb- and Cd-contaminated soils. Elevated CO2 (700 μmol mol-1) significantly increased T- and EE- GRSP concentrations in soils contaminated with Cd, Pb or Cd + Pb. GRSP contributed more carbon to the rhizosphere soil organic carbon pool under elevated CO2 + heavy metals than under ambient CO2. The amount of Cd and Pb bound to GRSP was significantly higher under elevated (compared to ambient) CO2; and elevated CO2 increased the ratio of GRSP-bound Cd and Pb to total Cd and Pb. However, available Cd and Pb in rhizosphere soil under increased elevated CO2 compared to ambient CO2. The combination of both metals and elevated CO2 led to a significant increase in available Pb in rhizosphere soil compared to the Pb treatment alone. In conclusion, increased GRSP produced under elevated CO2 could contribute to sequestration of soil pollutants by adsorption of Cd and Pb.
Jia X
，Zhao Y
，Liu T
，Huang S
，Chang Y
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Differential Effects of Exogenous Glomalin-Related Soil Proteins on Plant Growth of Trifoliate Orange Through Regulating Auxin Changes.
Multiple functions of glomalin released by arbuscular mycorrhizal fungi are well-recognized, whereas the role of exogenous glomalins including easily extractable glomalin-related soil protein (EE-GRSP) and difficultly extractable glomalin-related soil protein (DE-GRSP) is unexplored for plant responses. Our study was carried out to assess the effects of exogenous EE-GRSP and DE-GRSP at varying strengths on plant growth and chlorophyll concentration of trifoliate orange (Poncirus trifoliata) seedlings, along with changes in root nutrient acquisition, auxin content, auxin-related enzyme and transporter protein gene expression, and element contents of purified GRSP. Sixteen weeks later, exogenous GRSP displayed differential effects on plant growth (height, stem diameter, leaf number, and biomass production): the increase by EE-GRSP and the decrease by DE-GRSP. The best positive effect on plant growth occurred at exogenous EE-GRSP at ½ strength. Similarly, the GRSP application also differently affected total chlorophyll content, root morphology (total length, surface area, and volume), and root N, P, and K content: positive effect by EE-GRSP and negative effect by DE-GRSP. Exogenous EE-GRSP accumulated more indoleacetic acid (IAA) in roots, which was associated with the upregulated expression of root auxin synthetic enzyme genes (PtTAA1, PtYUC3, and PtYUC4) and auxin influx transporter protein genes (PtLAX1, PtLAX2, and PtLAX3). On the other hand, exogenous DE-GRSP inhibited root IAA and indolebutyric acid (IBA) content, associated with the downregulated expression of root PtTAA1, PtLAX1, and PtLAX3. Root IAA positively correlated with root PtTAA1, PtYUC3, PtYUC4, PtLAX1, and PtLAX3 expression. Purified EE-GRSP and DE-GRSP showed similar element composition but varied in part element (C, O, P, Ca, Cu, Mn, Zn, Fe, and Mo) concentration. It concluded that exogenous GRSP triggered differential effects on growth response, and the effect was associated with the element content of pure GRSP and the change in auxins and root morphology. EE-GRSP displays a promise as a plant growth biostimulant in citriculture.
Liu RC
，Gao WQ
，Srivastava AK
，Zou YN
，Kuča K
，Hashem A
，Abd Allah EF
，Wu QS
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《Frontiers in Plant Science》
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