Phthalic acid esters (PAEs) are a class of lipophilic chemicals widely used as plasticizers and additives to improve various products’ mechanical extensibility and flexibility. At present, synthesized PAEs, which are considered to cause potential hazards to ecosystem functioning and public health, have been easily detected in the atmosphere, water, soil, and sediments; PAEs are also frequently discovered in plant and microorganism sources, suggesting the possibility that they might be biosynthesized in nature. In this review, we summarize that PAEs have not only been identified in the organic solvent extracts, root exudates, and essential oils of a large number of different plant species, but also isolated and purified from various algae, bacteria, and fungi. Dominant PAEs identified from natural sources generally include di-n-butyl phthalate, diethyl phthalate, dimethyl phthalate, di(2-ethylhexyl) phthalate, diisobutyl phthalate, diisooctyl phthalate, etc. Further studies reveal that PAEs can be biosynthesized by at least several algae. PAEs are reported to possess allelopathic, antimicrobial, insecticidal, and other biological activities, which might enhance the competitiveness of plants, algae, and microorganisms to better accommodate biotic and abiotic stress. These findings suggest that PAEs should not be treated solely as a “human-made pollutant” simply because they have been extensively synthesized and utilized; on the other hand, synthesized PAEs entering the ecosystem might disrupt the metabolic process of certain plant, algal, and microbial communities. Therefore, further studies are required to elucidate the relevant mechanisms and ecological consequences.

Deforestation and natural grassland conversion to agricultural land use constitute a major threat to soil and water conservation. This study aimed at assessing the status of land cover and land use (LCLU) in the Lake Kivu basin, and its related impacts in terms of soil erosion by water using the Universal Soil Erosion Equation (USLE) model. The results indicated that the Lake Kivu basin is exposed to soil erosion risk with a mean annual rate of 30 t·ha⁻¹, and only 33% of the total non-water area is associated with a tolerable soil loss (≤10 t·ha⁻¹·year⁻¹). Due to both natural factors (abundant tropical precipitation and steep slopes) and anthropogenic activities without prior appropriate conservation practices, all land-use types—namely settlement, cropland, forestland, and grassland—are exposed to a severe mean erosion rate of 41 t·ha⁻¹·year⁻¹, 31 t·ha⁻¹·year⁻¹, 28 t·ha⁻¹·year⁻¹, and 20 t·ha⁻¹·year⁻¹, respectively. The cropland that occupied 74% of the non-water area in 2015 was the major contributor (75%) to the total annual soil loss in the Lake Kivu basin. This study showed that conservation practices in the cropland cells would result in a mean erosion rate of 7 t·ha⁻¹·year⁻¹, 18 t·ha⁻¹·year⁻¹, and 35 t·ha⁻¹·year⁻¹ for terracing, strip-cropping, and contouring, respectively. The adoption of terracing would be the best conservation practice, among others, that could reduce soil erosion in cropland areas up to about 23%. The erosion risk minimization in forests and grasslands implies an increase in overstorey canopy and understorey vegetation, and control of human activities such as fires, mining, soil compaction from domestic animals grazing, and so on. Soil erosion control in settled areas suggests, among other things, the revegetation of construction sites, establishment of outlet channels, rainfall water harvesting systems, and pervious paving block with grass.

Land conversion to cropland is one of the major causes of severe soil erosion in Africa. This study assesses the current cropland extent and the related soil erosion risk in Rwanda, a country that experienced the most rapid population growth and cropland expansion in Africa over the last decade. The land cover land use (LCLU) map of Rwanda in 2015 was developed using Landsat-8 imagery. Based on the obtained LCLU map and the spatial datasets of precipitation, soil properties and elevation, the soil erosion rate of Rwanda was assessed at 30-m spatial resolution, using the Revised Universal Soil Loss Equation (RUSLE) model. According to the results, the mean soil erosion rate was 250 t·ha⁻¹·a⁻¹ over the entire country, with a total soil loss rate of approximately 595 million tons per year. The mean soil erosion rate over cropland, which occupied 56% of the national land area, was estimated at 421 t·ha⁻¹·a⁻¹ and was responsible for about 95% of the national soil loss. About 24% of the croplands in Rwanda had a soil erosion rate larger than 300 t·ha⁻¹·a⁻¹, indicating their unsuitability for cultivation. With a mean soil erosion rate of 1642 t·ha⁻¹·a⁻¹, these unsuitable croplands were responsible for 90% of the national soil loss. Most of the unsuitable croplands are distributed in the Congo Nile Ridge, Volcanic Range mountain areas in the west and the Buberuka highlands in the north, regions characterized by steep slopes (>30%) and strong rainfall. Soil conservation practices, such as the terracing cultivation method, are paramount to preserve the soil. According to our assessment, terracing alone could reduce the mean cropland soil erosion rate and the national soil loss by 79% and 75%, respectively. After terracing, only a small proportion of 7.6% of the current croplands would still be exposed to extreme soil erosion with a rate >300 t·ha⁻¹·a⁻¹. These irremediable cropland areas should be returned to mountain forest to foster environmental sustainability or further sustainable alternative erosion control techniques may be applied, such as applying Vetiver Eco-engineering Technology due to its economical soil erosion control and stabilization of steep slopes and the construction of erosion control dams to absorb and break down excess runoff from unusually intense storms in various parts of the watersheds.

The present investigation studied the chemical composition of the essential oils extracted from Dracocephalum integrifolium Bunge growing in three different localities in northwest China and evaluated the phytotoxic, antimicrobial and insecticidal activities of the essential oils as well as their major constituents, i.e., sabinene and eucalyptol. GC/MS analysis revealed the presence of 21–24 compounds in the essential oils, representing 94.17–97.71% of the entire oils. Monoterpenes were the most abundant substances, accounting for 85.30–93.61% of the oils; among them, sabinene (7.35–14.0%) and eucalyptol (53.56–76.11%) were dominant in all three oils, which occupied 67.56–83.46% of the total oils. In general, phytotoxic bioassays indicated that the IC₅₀ values of the oils and their major constituents were below 2 μL/mL (1.739–1.886 mg/mL) against Amaranthus retroflexus and Poa annua. Disc diffusion method demonstrated that the oils and their major constituents possessed antimicrobial activity against Bacillus subtilis, Pseudomonas aeruginosa, Escherichia coli, Saccharomyces cerevisiae, and Candida albicans, with MIC values ranging from 5–40 μL/mL (4.347–37.712 mg/mL). The oils, sabinene and eucalyptol also exhibited significant pesticidal activity, with the mortality rates of Aphis pomi reaching 100% after exposing to 10 μL oil/petri dish (8.694–9.428 mg/petri dish) for 24 h. To the best of our knowledge, this is the first report on the chemical composition, phytotoxic, antimicrobial and insecticidal activity of the essential oils extracted from D. integrifolium; it is noteworthy to mention that this is also the first report on the phytotoxicity of one of the major constituents, sabinene. Our results imply that D. integrifolium oils and sabinene have the potential value of being further exploited as natural pesticides.

With high resolution and wide coverage, satellite precipitation products like Global Precipitation Measurement (GPM) could support hydrological/ecological research in the Tianshan Mountains, where the spatial heterogeneity of precipitation is high, but where rain gauges are sparse and unevenly distributed. Based on observations from 46 stations from 2014–2015, we evaluated the accuracies of three satellite precipitation products: GPM, Tropical Rainfall Measurement Mission (TRMM) 3B42, and the Climate Prediction Center morphing technique (CMORPH), in the Tianshan Mountains. The satellite estimates significantly correlated with the observations. They showed a northwest–southeast precipitation gradient that reflected the effects of large-scale circulations and a characteristic seasonal precipitation gradient that matched the observed regional precipitation pattern. With the highest correlation (R = 0.51), the lowest error (RMSE = 0.85 mm/day), and the smallest bias (1.27%), GPM outperformed TRMM and CMORPH in estimating daily precipitation. It performed the best at both regional and sub-regional scales and in low and mid-elevations. GPM had relatively balanced performances across all seasons, while CMORPH had significant biases in summer (46.43%) and winter (−22.93%), and TRMM performed extremely poorly in spring (R = 0.31; RMSE = 1.15 mm/day; bias = −20.29%). GPM also performed the best in detecting precipitation events, especially light and moderate precipitation, possibly due to the newly added Ka-band and high-frequency microwave channels. It successfully detected 62.09% of the precipitation events that exceeded 0.5 mm/day. However, its ability to estimate severe rainfall has not been improved as expected. Like other satellite products, GPM had the highest RMSE and bias in summer, suggesting limitations in its way of representing small-scale precipitation systems and isolated deep convection. It also underestimated the precipitation in high-elevation regions by 16%, suggesting the difficulties of capturing the orographic enhancement of rainfall associated with cap clouds and feeder–seeder cloud interactions over ridges. These findings suggest that GPM may outperform its predecessors in the mid-/high-latitude dryland, but not the tropical mountainous areas. With the advantage of high resolution and improved accuracy, the GPM creates new opportunities for understanding the precipitation pattern across the complex terrains of the Tianshan Mountains, and it could improve hydrological/ecological research in the area.

The allelopathy definition accepted by the International Allelopathy Society is any process or phenomenon via which organisms such as plants, microorganism, viruses, and fungi release specific metabolites, known as allelochemicals, into the environment that affect the growth and development of other surrounding plants, resulting in mutual inhibition or promotion of the organisms. Allelopathy in donor plants is either self-induced or induced by specific external biotic and abiotic factors. The external factors may determine the types and quantities of allelochemicals released into the environment by a donor plants. Biotic factors inducing allelopathy include plant competition, herbivory by animals and insects, and soil-borne pathogens. For example, competing plants produce allelochemicals in response to competing weeds. Plants may emit signaling chemicals from their roots to induce the production of protective metabolites against organisms, herbivores, or competitors. Additionally, herbivory is a selection pressure that triggers defensive measures in plants, such as the synthesis of allelochemicals in response to injury. Moreover, some leaves release volatile substances that help the plant to deter or attract herbivores or pests that attack leaves. Likewise, root compounds may be produced in response to soil-borne pathogens. Furthermore, some abiotic factors, including light, temperature, drought, CO₂, and nutrient deficiency, can also induce plants to release allelochemicals. Therefore, it is pertinent to understand this natural phenomenon in plants and how external factors lead plants to exert allelopathy to compete, defend themselves, and survive in a challenging environment.