The impact of root systems and their exudates in different tree species on soil properties and microorganisms in a temperate forest ecosystem

Stabilization of soil organic matter in Luvisols under the influence of various tree species in temperate forests

Tree species through aboveground biomass and roots are a key factors influencing the quality and quantity of soil organic matter. Our study aimed to determine the stability of soil organic matter in Luvisols under the influence of five different tree species. The study areas were located 25 km north of Krakow, in southern Poland. The study included five tree species - Scots pine (Pinus sylvestris L.), European larch (Larix decidua Mill.), pedunculate oak (Quercus robur L.), beech (Fagus sylvatica L.) and hornbeam (Carpinus betulus L.). Forest stands growing in the same soil conditions (Luvisols) with similar geological material (loess) and grain size were selected for the study. We evaluated labile and heavy fractions of soil organic matter (SOM). Additionally, basic physicochemical properties (pH, carbon and nitrogen content, base cation content) were determined in soil samples. The results of our study showed that soils under the influence of coniferous species were characterized by a higher content of carbon of free light fraction (CfLF) and carbon of occluded light fraction (CoLF) compared to deciduous species. Similar relationships were found with the nitrogen content of the free light fraction (NfLF) and nitrogen of occluded light fraction (NoLF). Higher CMAF and NMAF contents were recorded in soils influenced by deciduous species. The carbon, nitrogen and base cations content positively correlated with the C and N of free light fraction and occluded light fraction. PCA analysis confirmed the connection of C and N of heavy fractions (CMAF and NMAF) with deciduous species. Our research shows that avoiding single-species conifer stands and introducing admixtures of deciduous species, which increase SOM, is justified in forest management. The selection of suitable species will provide greater stand stability and contribute more to the carbon accumulation in the soil.

GIS-based spatial assessment of water quality, soil, and plant: a case study of Darawat Dam Sindh, Pakistan

This study applied integrated statistical approaches, including GIS mapping and the water quality index (WQI), to assess the quality of water, soil, and plant samples which collected from Darawat Dam, Sindh, Pakistan. The samples were analyzed for physicochemical parameters and metal analyses. Results of cations in water samples were in the range Na+ 26.74 to 39.67 mg/L, K+ 0.92 to 2.89 mg/L, Ca2+ 28.67 to 39.45, and Mg2+ 19.67 to 34.43 mg/L. The values of Cl- in water samples were 44.54 to 61.26 mg/L, sulfate 27.11 to 46.45 mg/L, and bicarbonate (HCO3-) 100 to 135 mg/L. The results of major and trace elements in soil samples were varied for Na+ 1259-1781 mg/kg, K+ 306-498 mg/kg, Ca2+ 689-1093 mg/kg, Mg2+ 357-795 mg/kg, Zn 194-235 mg/kg, Fe 124-242 mg/kg, Cu 25.34-33.56 mg/kg, Co 19.45-27.32 mg/kg, Mn 97.83-131 mg/kg, Ni 39.65-52.44 mg/kg, Cr 69.64-83.65 mg/kg, Cd 3.98-8.66 mg/kg, and Pb 5.34-9.62 mg/kg respectively. The major and trace elements in plant samples were varied from Na+ 3456 to 5016 mg/kg, K+ 1197 to 1654 mg/kg, Ca2+ 2367 to 2892 mg/kg, Mg2+ 1429 to 1686 mg/kg, Zn 132 to 155 mg/kg, Fe 255 to 354 mg/kg, Cu 19.54 to 28.56 mg/kg, Co 11.64 to 14.65 mg/kg, Mn 23.54 to 34.78 mg/kg, Ni 8.44 to 11.03 mg/kg, Cr 6.34 to 9.55 mg/kg, Cd 0.43 to 0.93 mg/kg, and Pb 4.33 to 6.59 mg/kg. The GIS maps were drawn for TDS, Cl-, Na+, heavy metals Cr, Cd, and WQI and these graphs showed that most of the water samples of Darawat Dam is good for human consumption. The results of electrical conductivity (EC) and total dissolved salts (TDS) of water samples were found to be from 648 to 753 µS/cm and 414 to 482 mg/L. The Darawat Dam water samples were good for drinking as well as irrigation based on the results of water quality parameters. The WQI specified that 100% of samples were excellent to good for water quality for drinking. The 100% samples were also excellent for crops. The scatter diagram disclosed that weathering and ion exchange were chief processes. The Gibbs diagram revealed that all samples showed rock dominance which confirmed the dissolution of rock as the main source for the water quality of the Dam. The hydrogeochemical facies (Piper diagram) showed that sample points were gathered in the center of the diagram which indicated mixed type water with no particular parameter effluents the water quality.

Genotypic Identification of Trees Using DNA Barcodes and Microbiome Analysis of Rhizosphere Microbial Communities

DNA barcodes can provide accurate identification of plants. We used previously reported DNA primers targeting the internal transcribed spacer (ITS1) region of the nuclear ribosomal cistron, internal transcribed spacer (ITS2), and chloroplast trnL (UAA) intron to identify four trees at Bergen Community College. Two of the four trees were identified as Acer rubrum and Fagus sylvatica. However, Quercus was only identified at the genus level, and the fourth tree did not show similar identification between barcodes. Next-generation sequencing of 16S rRNA genes showed that the predominant bacterial communities in the rhizosphere mainly consisted of the Pseudomonadota, Actinomycetota, Bacteroidota, and Acidobacteriota. A. rubrum showed the most diverse bacterial community while F. sylvatica was less diverse. The genus Rhodoplanes showed the highest relative bacterial abundance in all trees. Fungal ITS sequence analysis demonstrated that the communities predominantly consisted of the Ascomycota and Basidiomycota. Quercus showed the highest fungi diversity while F. sylvatica showed the lowest. Russula showed the highest abundance of fungi genera. Average similarity values in the rhizosphere for fungi communities at the phylum level were higher than for bacteria. However, at the genus level, bacterial communities showed higher similarities than fungi. Similarity values decreased at lower taxonomical levels for both bacteria and fungi, indicating each tree has selected for specific bacterial and fungal communities. This study confirmed the distinctiveness of the microbial communities in the rhizosphere of each tree and their importance in sustaining and supporting viability and growth but also demonstrating the limitations of DNA barcoding with the primers used in this study to identify genus and species for some of the trees. The optimization of DNA barcoding will require additional DNA sequences to enhance the resolution and identification of trees at the study site.

Metabolic niches in the rhizosphere microbiome: dependence on soil horizons, root traits and climate variables in forest ecosystems

Understanding belowground plant-microbial interactions is important for biodiversity maintenance, community assembly and ecosystem functioning of forest ecosystems. Consequently, a large number of studies were conducted on root and microbial interactions, especially in the context of precipitation and temperature gradients under global climate change scenarios. Forests ecosystems have high biodiversity of plants and associated microbes, and contribute to major primary productivity of terrestrial ecosystems. However, the impact of root metabolites/exudates and root traits on soil microbial functional groups along these climate gradients is poorly described in these forest ecosystems. The plant root system exhibits differentiated exudation profiles and considerable trait plasticity in terms of root morphological/phenotypic traits, which can cause shifts in microbial abundance and diversity. The root metabolites composed of primary and secondary metabolites and volatile organic compounds that have diverse roles in appealing to and preventing distinct microbial strains, thus benefit plant fitness and growth, and tolerance to abiotic stresses such as drought. Climatic factors significantly alter the quantity and quality of metabolites that forest trees secrete into the soil. Thus, the heterogeneities in the rhizosphere due to different climate drivers generate ecological niches for various microbial assemblages to foster beneficial rhizospheric interactions in the forest ecosystems. However, the root exudations and microbial diversity in forest trees vary across different soil layers due to alterations in root system architecture, soil moisture, temperature, and nutrient stoichiometry. Changes in root system architecture or traits, e.g. root tissue density (RTD), specific root length (SRL), and specific root area (SRA), impact the root exudation profile and amount released into the soil and thus influence the abundance and diversity of different functional guilds of microbes. Here, we review the current knowledge about root morphological and functional (root exudation) trait changes that affect microbial interactions along drought and temperature gradients. This review aims to clarify how forest trees adapt to challenging environments by leveraging their root traits to interact beneficially with microbes. Understanding these strategies is vital for comprehending plant adaptation under global climate change, with significant implications for future research in plant biodiversity conservation, particularly within forest ecosystems.