A Preliminary Study On Amount And Composition Variation Of Glomalin Related Soil Protein In NE China And Their Roles In Soil Function

Arbuscular mycorrhizal fungi (AMF) reportedly produce glomalin related soil protein (GRSP), a glycoprotein that has the potential to increase soil carbon (C), nitrogen (N) storage and regulate soil physics. Fewer studies have focused on soil properties and AMF secretions of GRSP, although the data may hints soil rehabilitation practices. Firstly, spatial variations in concentration, composition of GRSP (total GRSP, TG; easily extractable GRSP, EEG) in poplar shelterbelts in Northeastern China, and possible relations with soil physicochemical properties were explored. Secondly, variations of soil properties, GRSP amount and composition in farmland, adjacent plantations with reference to primary forests, and their possible correlations in Northeastern China were also observed. Finally, many previous researches of GRSP were summarized, and to explore and analyze the research direction of GRSP in the future. This study reached the following results:(1) For TG concentration, the biggest variation of inter-sites was 3.14 fold, and the biggest variation of inter-depths was 2.98 fold, and the variation for EEG was respectively 3.95 fold and 2.58 fold. Changing TG and EEG concentration could regulate bulk density and moisture (p< 0.05). TG mainly consists of 7 kinds of functional traits and 7 kinds of fluorescent substances, with characteristic X-ray diffraction peak at 2θ=19.8° and 129.3 nm grain size as well as 1.08% low crystallinity. Similar inter-sites variations were found in traits related with infrared spectrum peaks (1.12-2.10 folds), X-ray diffraction data (1.41-2.71 folds),3-D fluorescent data (1.18-4.50 folds). Soil pH is mainly responsible for GRSP amount and GRSP composition (stretching of aliphatic C-H, Si-O-Si, polysaccharide C-O and O-H bending of-COOH, relative crystallinity) (p< 0.05). These basic data in poplar shelterbelt forests are good for understanding of the underlying mechanism of GRSP in soil functional maintenance.(2) Results clearly manifested soil properties (SOC, N, pH, EC, bulk density) were closely correlated with TG concentration (R2= 0.41-0.85) (p<0.05). Soil properties were respectively significant related with part of main functional traits, fluorescent substances and elements (p< 0.05). Plantation forest have improved EC and bulk density in degraded farmland, especially EC of plantation forest have approached the level of primary forest (p< 0.05). However, for TG amount, primary forest had 2.35-fold and 2.56-fold higher TG amount than plantation forest and farmland (p< 0.05). With GRSP composition:tryptophan-like, fulvic acid-like, functional groups of stretching of aliphatic C-H, C-O and O-H bending of -COOH, structural OH, Al, O, Si, C, Ca, N in primary forest were different from those in plantation forest and farmland (p<0.05), while no differences were found in farmland and plantation forest (p>0.05). Therefore, although GRSP played an important role in regulating soil function, afforestation on farmland could not significantly improve GRSP amount and composition, in other words,30-year poplar afforestation on farmland is not enough to recover GRSP to the level of un-degraded primary forest, it still needs a much longer time.(3) On average, a general tendency of EEG (forest:1.95 g/kg> farmland:1.89 g/kg> grassland (shrub):0.75 g/kg) and TG (farmland:3.54 g/kg> forest:3.47 g/kg> grassland (shrub):1.81 g/kg) was observed in many references, but these differences were not statistical significant owing to large intra-vegetation variations (p> 0.05). Moreover, a positive correlation between TG concentration and EEG concentration was observed. GRSP (TG and EEG) concentration could significantly regulate SOC, N, bulk density, soil aggregate stability (p<0.05). Many researchers have also proved that TG was composed of glycosylate protein, aromatics, carboxyl, carbohydrate, lipid, humics, amino acid and some elements (for example C, N, O, H, Si, Fe, Cr, etc.). Marked correlations between soil pH and GRSP (amount and composition traits) were also observed. These findings highlight the importance of GRSP in soil functional maintenance, and unexpected complexity of GRSP compositions. In future, more attentions should be addressed on studies of composition and characteristic.