Short-Term Thinning Influences the Rhizosphere Fungal Community Assembly of Pinus massoniana by Altering the Understory Vegetation Diversity

Thinning can significantly promote forest productivity and ecological function. Rhizosphere fungi play an indispensable role in regulating nutrient cycling between plants and the environment, and their community composition can positively respond to anthropogenic disturbance. However, the initial effects of thinning on rhizosphere fungal community assembly have seldom been reported. In this research, we studied the alterations in the rhizosphere fungal communities of 29-year-old Pinus massoniana in East Sichuan 2 years after three different thinning intensity treatments. In addition, the responses of fungal community and functional group composition to alterations in understory vegetation and soil physiochemical properties were analyzed. Three thinning intensities were set, which were 0 (CK), 25% (LIT), and 50% (HIT), respectively. The results suggested that the richness index and Shannon index of understory vegetation increased significantly with increasing thinning intensity. The alpha diversity indices of rhizosphere fungal community and soil physiochemical properties did not show significant differences among the three treatments. The relative abundances of 17 fungal indicator species varied regularly with increasing thinning intensity, and most of them belong to Hypocreales and Eurotiales, indicating that these two orders were potential indicators for different thinning treatments. Rhizosphere fungal community assembly was determined by deterministic process, and it was driven by the diversity of understory vegetation in the initial stage of thinning. The Simpson index and Pielou index of herbs were useful measures of the main environmental factors driving the differentiation of fungal functional group composition. Based on network analysis, thinning resulted in distinct co-occurrence patterns of rhizosphere fungal functional groups. This research elucidates the initial role of thinning in rhizosphere fungal community assembly of P. massoniana and has practical significance for the functional restoration and protection of local forest ecosystem.

Impact of Oxides and Physiochemical Properties of Agricultural Soil on Bioaccumulation of Toxic Heavy Elements in Wheat Grains in Yaychi, Northeast of Iraq

To investigate the potential link between toxic heavy elements in soil with soil physiochemical properties and oxides, as well as their impact on the bioaccumulation of these elements in wheat grains. Agriculture soil and wheat grains were sampled from Yaychi area, Kirkuk northeast of Iraq. Soil physiochemical properties, oxides and toxic heavy elements contents were determined. The average concentration of toxic heavy elements in soil was in this order Ni> Cr> Pb> As> Cd> Hg, and some of these elements had exceeded their average in earth's crust and Canadian Agricultural Soil Quality Guidelines. While in wheat grains the toxic heavy elements, contents were in the following order Cr> Ni> Pb> As> Cd> Hg. The soil physiochemical properties in the study area are shown to be medium alkaline, non-saline, calcareous, non-gypsiferous, inorganic and loam texture. It became clear from the correlation matrix that the toxic heavy elements except for arsenic have significant relationships with different soil physiochemical properties and major oxides. In turn, oxides and the physiochemical properties of the soil and its type reduced the bioaccumulation of these elements in wheat grains except for arsenic, as appeared in the present study, that toxic heavy elements do not accumulate in wheat grains. And among the studied elements, arsenic had the highest bioaccumulation rate in wheat grains, because its concentration in soil has been affected by only human activities.

Tree species influences soil microbial community diversity but not biomass in a karst forest in Southwestern China

Aims The relationships between plant species and soil microorganisms remain indeterminable in different ecosystems worldwide. In karst ecosystems, soil microbial (SM) community structure and their environmental driving factors are poorly explored, and the relationships between plant species and soil microorganisms are unclear. This study aimed to characterise the general patterns of SM community composition and biomass, and to explore the relationships between tree species and soil physiochemical properties, and between SM community diversity and biomass in a karst forest. Methods The effects of tree species on SM community composition and biomass were firstly investigated on the basis of 212 soil samples collected from five dominant tree species (Lithocarpus confinis Huang, Platycarya longipes Wu, Itea yunnanensis Franch., Machilus cavaleriei H. Lév. and Carpinus pubescens Burkill) through phospholipid fatty acid (PLFA) analysis of a karst evergreen and deciduous broad-leaved mixed forest in central Guizhou Province, Southwestern China. The relationships between SM community structure and tree species and soil physiochemical properties were statistically analysed. Important Findings A total of 132 SM-PLFA biomarkers were detected. The average number of SM-PLFA biomarkers and microbial biomass in each soil sample were 65.97 and 11.22 µg g −1, respectively. Tree species influenced the number of SM-PLFA biomarkers but not the SM biomass. The number of SM-PLFA biomarkers of C. pubescens was significantly higher than that of other species (p<0.05); the numbers of SM-PLFA biomarkers amongst other species showed no significant difference. Microbial biomass showed no relationships with the soil physiochemical properties of nutrient-rich surface soils but positively correlated (p<0.05) with soil organic carbon, nitrogen and phosphorus concentrations in deeper soils. The karst forest in the plateau-surface terrain of central Guizhou Province presented a low fungal-to-bacterial ratio, low microbial biomass storage and high microbial community diversity. Specific tree species affect the SM community diversity in this kind of karst forest.

Biochar Effects on Soil Physiochemical Properties in Degraded Managed Ecosystems in Northeastern Bangladesh

A body of emerging research shows the promise of charcoal soil amendments (“biochars”) in restoring fertility in degraded agricultural and forest soils. “Sustainable biochars” derived from locally produced waste biomass and produced near the application site are of particular interest. We tested the effects of surface applications of wood-derived biochars (applied at 7.5 t·ha−1) on soil physiochemical properties (N, P, K, pH, soil moisture content, organic matter content, and bulk density) in three land-use types: agriculture (Camellia sinensis monoculture), agroforestry (C. sinensis with shade trees), and secondary forest (Dipterocarpus dominated) assessed over seven months. We found significant positive effects of biochar on soil physiochemical properties in all land-use types, with the strongest responses in the most degraded tea monoculture sites. Although biochar had no significant effect on soil N and K, it improved soil P—the primary nutrient most commonly limiting in tropical soils. Biochar also enhanced soil moisture and organic matter content, reduced bulk density, and increased soil pH in monoculture sites. Our results support the general hypothesis that biochar can improve the fertility of degraded soils in agricultural and forest systems in Bangladesh and suggest that biochar additions may be of great benefit to the most degraded soils.

Effects of Different Ages of Robinia pseudoacacia Plantations on Soil Physiochemical Properties and Microbial Communities

Robinia pseudoacacia is widely planted on the Loess Plateau as a strong drought-tolerant and salt-tolerant species for vegetation restoration. However, this mode of pure plantation has triggered great concern over the soil ecosystem. The aim of this study was to explore the effects of the plantation on soil physiochemical properties, soil microorganisms, and the relationship between them in Robinia pseudoacacia plantations of different ages. Four different ages of Robinia pseudoacacia stands, including 10-year-old, 15-year-old, 25-year-old, and 40-year-old (abbreviated as Y10, Y15, Y25, and Y40, respectively) were selected, and 20 soil physicochemical and biological indicators were determined. The variation in soil microbial biomass was influenced by sampling depth, and consistent with the variations in TN (soil total nitrogen) and SOC (soil organic carbon) during 25 years’ artificial forestation. Soil moisture increased significantly at Y15 and then decreased at Y40 but other soil properties remained relatively stable. The contents of phosphor lipid fatty acid (PLFA) of different microbial groups followed the order of B (Bacteria) > G− (Gram-negative) > G+ (Gram-positive) > A (Actinomycetes) > F (Fungi). The ratios of F/B (Fungi to Bacteria) and Sat/Mono (Saturated PLFAs to Monosaturated PLFAs) of different ages of plantations showed a similar trend, i.e., declined first, then rose, and declined again. The ratios of Cy/Pre (Cyclopropyl PLFAs to Precursor PLFAs) and G+/G− (Gram-positive to Gram-negative) of the soil of all ages of plantations showed a trend of slow growth and a trend of rapid growth, respectively. Redundancy analysis showed that the contents of individual PLFAs and total PLFA were positively correlated with SOC and TN, but variations of soil PLFA ratios mostly depended on other soil properties. After artificial forestation, the ratios of F/B and Sat/Mono were lower than before forestation, while the ratio of Cy/Pre varied with different soil layers. The ratio of G+/G− increased with the increase in afforestation time, peaking at the 25th year. The contents of individual PLFAs and total PLFA may be sensitive indicators of SOC and TN within 25 years’ plantation. Lower ratio of F/B and higher G+/G− suggest that the sustainability of the ecosystem is weaker and the fertility of the soil is lower after plantation of Robinia pseudoacacia.