Role and Variation of the Amount and Composition of Glomalin in Soil Properties in Farmland and Adjacent Plantations with Reference to a Primary Forest in North-Eastern China

Abstract

The glycoprotein known as glomalin-related soil protein (GRSP) is abundantly produced on the hyphae and spores of arbuscular mycorrhizal fungi (AMF) in soil and roots. Few studies have focused on its amount, composition and associations with soil properties and possible land-use influences, although the data hints at soil rehabilitation. By choosing a primary forest soil as a non-degraded reference, it is possible to explore whether afforestation can improve degraded farmland soil by altering GRSP. In this paper, close correlations were found between various soil properties (soil organic carbon, nitrogen, pH, electrical conductivity (EC), and bulk density) and the GRSP amount, between various soil properties and GRSP composition (main functional groups, fluorescent substances, and elements). Afforestation on farmland decreased the EC and bulk density (p < 0.05). The primary forest had a 2.35–2.56-fold higher GRSP amount than those in the plantation forest and farmland, and GRSP composition (tryptophan-like and fulvic acid-like fluorescence; functional groups of C–H, C–O, and O–H; elements of Al, O, Si, C, Ca, and N) in primary forest differed from those in plantation forest and farmland (p < 0.05). However, no evident differences in GRSP amount and composition were observed between the farmland and the plantation forest. Our finding highlights that 30 years poplar afforestation on degraded farmland is not enough to change GRSP-related properties. A longer period of afforestation with close-to-nature managements may favor the AMF-related underground recovery processes.

Glomalin contributed more to carbon, nutrients in deeper soils, and differently associated with climates and soil properties in vertical profiles

“…Long-term land uses could affect fractions of glomalin and SOC in the Indo-Gangetic plain 10 . The primary forests had 2.35–2.56-fold higher GRSP amount than those in the plantation forests and farmlands 14 , while the GRSP amount significantly correlated with soil bulk density and soil water 47 . However, from land uses changes were not well-defined to date.…”

“…Deep soil carbon and nutrient depletion have been observed in forests in NE China 34 , and also in other different studies, such as Amazonian forests 41 , reforestation on grasslands 42 and croplands 43 . Most of the glomalin compositional traits were stable with soil physiochemical changes 14,44 showing that this kind of glomalin-related nutrients may possibly restrict the nutrient supply for subsoil microbial activities. Actually, the absence of fresh organic carbon, an essential source of energy for soil microbes, the stability of organic carbon in deep soil layers is maintained 20 .…”

“…The surface-deep soil differences in factors regulating glomalin distribution, i.e., lower nutrient (SOC)- but higher physicochemical (pH)-regulations on glomalin in the deep soils were found when compared with the surface soils, provided a new evidence of the deep soil organic matter importance for terrestrial C and nutrient cycle from the view point of AMF and glomalin contributions 34,38 . The soil conditioning function of GRSP has well reported, and understanding of how to improve GRSP accumulation in soil is important for the GRSP-oriented degraded soil rehabilitation 14,44 . Long-term land uses could affect fractions of glomalin and SOC in the Indo-Gangetic plain 10 .…”

“…GRSP amount received increasing attention over the past few years for the anti-erosion ability of GRSP in soil aggregate formation 3–5 and the physical networking function of AM hyphae 6 , loading capacity for heavy metals 2 , maintaining soil fertility 7 , increasing soil C capture 8–11 and enhancing the availability of polycyclic aromatic hydrocarbons in soil 12 . Many studies proved that GRSP has a complex composition of asparagine-linked carbohydrate chains 13,14 and it is a mixture of organic matter, amino acids and carbohydrates along with some aliphatic methines, methylenes 3 and possibly some auto-fluorescent compounds tightly bound with metal ions 15,16 . However, limited information is available regarding glomalin variation at vertical soil profiles and underlying mechanism related soil properties and climatic variations, and this information will benefit the local degraded soil improvements and exact evaluations of AMF-importance 14,16,17 .…”

“…Many studies proved that GRSP has a complex composition of asparagine-linked carbohydrate chains 13,14 and it is a mixture of organic matter, amino acids and carbohydrates along with some aliphatic methines, methylenes 3 and possibly some auto-fluorescent compounds tightly bound with metal ions 15,16 . However, limited information is available regarding glomalin variation at vertical soil profiles and underlying mechanism related soil properties and climatic variations, and this information will benefit the local degraded soil improvements and exact evaluations of AMF-importance 14,16,17 .…”