Community Differentiation and Ecological Influencing Factors along Environmental Gradients: Evidence from 1200 km Belt Transect across Inner Mongolia Grassland, China

In this work, we conducted a 1200 km belt transect for field survey in typical and meadow steppes across Inner Mongolia Plateau in 2018. The field investigation, laboratory soil analysis, and quantitative ecology methods were utilized to explore the differentiation characteristics of the plant community, and their relationships with ecological factors. The results showed that a total of 140 vascular plants within 108 quadrats mainly comprised of Asteraceae, Poaceae, Rosaceae, and Fabaceae. Two-way Indicator Species Analysis (TWINSPAN) revealed eight vegetation typologies: I: Stipa sareptana var. krylovii + Dysphania aristata, II: Stipa grandis + Leymus chinensis, III: Stipa sareptana var. krylovii + Leymus chinensis, IV: Stipa grandis + Cleistogenes squarrosa, V: Stipa grandis + Carex duriuscula, VI: Stipa baicalensis + Leymus chinensis, VII: Carex pediformis + Stipa baicalensis, VIII: Leymus chinensis + Elymus dahuricus. Detrend Correspondence Analysis (DCA) confirmed the above eight vegetation typologies and indicated a relatively small variation. Redundancy analysis (RDA) revealed that the spatial differentiation characteristics in the typical steppe were chiefly driven by precipitation, while the influencing factor in the meadow steppe was soil nutrients, followed by temperature and precipitation. The contrast between typical and meadow steppes revealed that the spatial distribution of typical steppe was influenced by precipitation, while the contribution of heat and water in the meadow steppe was equal. The conclusion revealed that the temperature and precipitation conditions coupled with soil nutrients shaped the spatial differentiation characteristics of temperate steppe vegetation in the Inner Mongolia grassland. Therefore, this study advanced our knowledge of the spatial patterns of temperate steppe along longitude and latitude gradients, providing scientific and theoretical guidance for the biodiversity conservation and sustainable ecosystem management of the Inner Mongolia grassland.

Earthworms Modulate Impacts of Soil Heterogeneity on Plant Growth at Different Spatial Scales

Soil heterogeneity (uneven distribution of soil nutrients and/or other properties) is ubiquitous in nature and can greatly affect plant growth. As earthworm activity can influence nutrient redistribution in the soil, we hypothesize that earthworms may alter the effect of soil heterogeneity on plant growth and this effect may depend on the scale of soil heterogeneity. To test these hypotheses, we grew the clonal grass Leymus chinensis in three soil treatments (heterogeneous large vs. heterogeneous small patch vs. homogeneous soil treatment) with or without earthworms [i.e., Eisenia fetida Savigny (Lumbricidae, epigeic redworm)]. In the heterogeneous treatments, the soil consisted of patches with and without 15N-labeled litter (referred to as high- and low-quality patches, respectively), and in the homogeneous treatment, the soil was an even mixture of the two types of soil patches. Biomass of L. chinensis was significantly higher in the high- than in the low-quality patches, showing the foraging response; this foraging response occurred at both scales and under both earthworm treatments. Compared to the homogeneous treatment, the heterogeneous large patch treatment increased biomass of L. chinensis without earthworms, but decreased it with earthworms. In contrast, biomass of L. chinensis in the heterogeneous small patch treatment did not differ from that in the homogeneous treatment, irrespective of earthworms. Belowground biomass was much greater in the heterogeneous small than in the heterogeneous large patch treatment without earthworms, but it did not differ between these two scale treatments with earthworms. In the heterogeneous treatments, soil 15N was greater in the high- than in the low-quality patches, but this effect became much weaker with than without earthworms, suggesting that earthworm activity homogenized the soil. We conclude that earthworms can change the impact of soil heterogeneity on plant growth via homogenizing the soil, and that this effect of earthworms varies with patch scale. Such scale-dependent interactive effects of soil heterogeneity and earthworms could be a potential mechanism modulating plant community structure and productivity.

Ectopic Expression of a Salt-Inducible Gene, LcSAIN3, from Sheepgrass Improves Seed Germination and Seedling Growth under Salt Stress in Arabidopsis

Sheepgrass is a perennial native grass species in China, and it can tolerate high levels of salt stress with an aggressive and vigorous rhizome system. Many salt-stress-responsive genes have been identified in sheepgrass. In this study, we report the cloning and characterization of a novel salt-induced gene, LcSAIN3 (Leymus chinensis salt-induced 3), from sheepgrass. Expression analysis confirmed that LcSAIN3 was induced by PEG, ABA, and salt treatments, and the expression of LcSAIN3 was significantly increased in salt-tolerant germplasms under salt treatment. Subcellular localization analysis indicated that the GFP-LcSAIN3 protein was mainly localized in the chloroplasts. The heterologous expression of LcSAIN3 in Arabidopsis increased the seed germination rate of transgenic plants under salt, ABA, and mannitol treatments. The seedling survival rate, plant height, and fresh weight of the transgenic plants were higher than those of WT plants under salt stress. The overexpression of LcSAIN3 caused a relatively high accumulation of free proline, enhanced SOD activity, and led to the upregulation of several stress-responsive genes such as AtRD26, AtRD29B, AtSOS1, and AtP5CS1. These results suggest that LcSAIN3 could be a potential target for molecular breeding to improve plants’ salt tolerance.

Dynamics of Bacterial Community and Fermentation Quality in Leymus chinensis Silage Treated With Lactic Acid Bacteria and/or Water

This study aimed to reveal the bacterial community and fermentation quality of Leymus chinensis silage during the fermentation process. L. chinensis was harvested at the heading stage, and ensiled with lactic acid bacteria (LAB, L), water (W), or a combination of both (LW) in vacuum-sealed plastic bags. As a control silage, untreated L. chinensis silage was also assessed. The samples were taken at 0, 5, 15, 35, and 60 days after ensiling. The bacterial community structure was assessed by plate cultivation and Illumina sequencing, and the fermentation parameters were also analyzed. Fresh L. chinensis contained low moisture (509 g/kg) and LAB (3.64 log colony-forming units/g fresh weight). Control silage displayed higher pH and lower lactic acid (LA) than other treatments during ensilage (p < 0.05); moreover, LW-treatment had lower pH from 5 to 35 days and greater LA at 5 days than L- and W-treatments (p < 0.05). During the fermentation process, Lactobacillus in L- and LW-treatments was the most dominant bacterial genus (>97%), had higher abundance than that in control silage and W-treatment (p < 0.05), and correlated negatively with other main genera and pH, and positively with LA and acetic acid (p < 0.05). Moreover, Lactobacillus had considerable abundance in W-treatment from 5 to 15 days (81.38–85.86%). Enterobacteriaceae had the most abundance among bacteria in control silage during ensiling (49.31–69.34%), and in W-treatment from 35 to 60 days (47.49–54.15%). The L-, W-, and LW-treatments displayed the aggregated bacterial community at 5 and 15 days, with W-treatment diverging from L- and LW-treatments at 35 and 60 days. Overall, the low moisture and/or insufficient LAB in fresh L. chinensis led to Enterobacteriaceae dominating bacterial community and contributing to the high pH and low LA in control silage during the fermentation process. Applying L, W, or LW contributed to Lactobacillus succession, LA production, and pH reduction during early stage of fermentation; moreover, treating with L and LW displayed more efficiency. Lactobacillus dominated the entire ensilage process in L- and LW-treatments and the early stage of fermentation in W-treatment, and contributed to the satisfactory fermentation quality of L. chinensis silage. The L- and LW-treatments displayed a similar pattern of bacterial succession during ensiling.

Differences in the Seed Germination of Leymus chinensis (Poaceae) Ecotypes Reveal Distinct Strategies for Coping With Salinity Stress: A Common Garden Experiment

Soil salinity is important abiotic stress affecting various ecosystems worldwide such as grassland. Distinct ecotypes often evolve within species by natural selection to facilitate adaptation to different types of environmental stress. Leymus chinensis is a perennial rhizomatous grass that is widely distributed in the eastern Eurasian steppe; it has two main ecotypes, namely, yellow-green (YG) and gray-green (GG), which differ in their strategy for coping with salinity stress. Few studies have examined the seed germination of the two ecotypes under salinity stress. In this study, the seed germination and seedling growth of two ecotypes of L. chinensis in response to different levels of salinity (NaCl) stress [0 (control), 20, 50, 100, and 200 mM] were examined. Then, ungerminated seeds were placed under normal conditions to evaluate seedling growth following exposure to salt stress (i.e., regermination). The germination percentage was significantly higher, and the mean germination time was significantly shorter in the GG ecotype than in the YG ecotype at all NaCl concentrations. As the salinity level increased, the radicle length of the two ecotypes decreased; however, GG had longer radicles and a higher number of radicles, even at 200 mM NaCl when no radicle protruding from the seed coat was detected in YG. The shoot length of GG was significantly longer than that of YG at all NaCl levels. After salinity stress was removed, the seed germination percentage increased as the original concentration of NaCl applied increased, but the total germination percentage did not significantly differ among NaCl concentrations. The total seed germination percentage of GG was approximately 80%, whereas that of the YG was approximately 20%. The seedling length of regerminated seeds for both GG and YG was similar. The thousand-grain weight of GG was significantly higher than that of YG. GG was more salt-tolerant than YG and might be better capable of surviving in harsher environments, suggesting that GG might be particularly useful for saline grassland restoration.