Heteropogon contortus is a valuable pasture species that is widely used for vegetation restoration in dry-hot valleys of China. However, to date, its morphological and physiological responses to drought, and the underlying mechanisms are not well understood. This study was aimed to investigate the morphological and physiological changes of H. contortus under drought stress during the dry-hot season. Heteropogon contortus was planted in pots and subjected to four levels of soil water treatments: above 85 % (control), 70–75 % (light stress), 55–60 % (moderate stress) or 35–40 % (severe stress) of field capacity. Within the total stress period (0–29 days), H. contortus grew rapidly in the light stress, whereas severe stress had a negative impact on growth. Aboveground biomass decreased together with increasing drought stress, whereas root biomass increased. Consequently, the root/shoot ratio of the severe stress treatment increased by 80 % compared to that of the control treatment. The ratio of bound water/free water (BW/FW) was the most sensitive parameter to drought and showed a value under severe stress that was 152.83 % more than that in the control treatment. Although leaf water potential (LWP) and leaf relative water content (RWC) decreased with progressive water stress, H. contortus managed to maintain a relatively high RWC (nearly 70 %) in the severe stress condition. We also detected a significant reduction (below 0.6) in the ratio of variable fluorescence/maximum fluorescence (Fv/Fm) in the severe stress treatment. Our results show that H. contortus adapts to drought mainly by avoidance mechanisms, and its morphological and physiological characteristics are inhibited under severe stress, but can recover at a certain time after re-watering. These findings might help limited water resources to be fully used for vegetation management in the studied region.

Sewage irrigation has a strong influence on the physical, chemical, and biological properties of soil. However, the effects of sewage irrigation on the pore characteristics of soil are not well understood. This study compares the effects of sewage irrigation and groundwater irrigation on computed tomography (CT)-measured pore parameters and examines the relationships between CT-measured pore parameters and soil physicochemical and microbial properties. Intact soil cores were collected from S1 irrigated with sewage for 25 years, S2 irrigated with sewage for 52 years, and CK irrigated with groundwater. Various soil pore characteristics were determined, including the total pore number, macropore number (>1 mm diam.), coarse mesopore number (0.264–1 mm diam.), total porosity, macroporosity, coarse mesoporosity, and circularity. The results indicated that sewage irrigation significantly affected soil pore number and porosity. Compared with S1 and S2, CK exhibited a higher average total pore number (91), macropore number (40), coarse mesopore number (51), total porosity (2.08%), macroporosity (1.90%), and coarse mesoporosity (0.18%) throughout the 50–350 mm layer. At depths of 200–350 mm, S2 exhibited the lowest average total pore number (33), macropore number (13), coarse mesopore number (21), total porosity (0.42%), macroporosity (0.35%), and coarse mesoporosity (0.07%) among the three sites. In addition, the average pore numbers and porosity at depths of 200–350 mm decreased with increasing sewage irrigation time. There were significant positive correlations between pore features (including pore numbers and porosity) and soil properties (phosphorus content and fungi numbers). Our results suggest that decreased macropore numbers and macroporosity in the sewage-irrigated farmland may strongly intensify the accumulation of metals and nutrients in the upper layer. The findings of this study are useful for understanding the negative effects of sewage irrigation on soil pore structure and are critical for developing sustainable strategies in agriculture.

Diatoms constitute an important part of the phytoplankton community in lakes and reservoirs and play a significant role in regulating ecological balance. Danjiangkou Reservoir is the water source area of the middle route of China’s South-to-North Water Diversion project. In order to explore the spatial and temporal distribution and know the governing factors of the diatom community, 18srRNA sequencing was carried out from seven sampling sites of the reservoir. At the same time, the concentration of nutrients present in the collected sample water was also determined. The results showed that a total of 51 genera and 96 species were thriving the community of diatoms in Danjiangkou Reservoir. Discostella was dominant in summer and autumn, accounting for 98.84% and 62.71% of the diatom abundance, respectively. Aulacoseira was dominant in spring and winter, accounting for 60.62% and 60.90%, respectively. Discostella and Aulacoseira showed significant differences in seasonal variation (p < 0.05). The colinear network of diatoms changed significantly with the seasons, mainly consisting of Aulacoseira, Discostella, and Stephanodiscus. RDA redundancy analysis showed that water temperature (WT), total nitrogen (TN), NH₄⁺-N, pH, and electrical conductivity (Cond) were the main environmental factors driving the changes in diatom community structure.

Introduction: Eukaryotic plankton plays crucial roles in ecosystem processes, impacting aquatic ecosystem stability. This study focuses on Danjiangkou Reservoir, a canyon lake in central China, that acts as the water source of the Mid-route of the South-to-North Water Diversion Project.Methods: In this study, high-throughput 18S rDNA gene sequencing was employed to investigate eukaryotic plankton community at four water depths (0.5 m, 5 m, 10 m, and 20 m). The environmental factors including pH, water temperature (WT), nitrate nitrogen (NO₃⁻-N), ammonia nitrogen (NH₄⁺-N), total nitrogen (TN), conductivity (Cond), and dissolved oxygen (DO) in reservoir areas were measured, and their correlations with abundance and diversity of eukaryotic plankton were analyzed.Results: The results showed the presence of 122 genera of eukaryotic plankton from 38 phyla. Eukaryotic plankton communities were mainly composed of Eurytemora, Thermocyclops, Sinocalanus, Mesocyclops, and Cryptomonas. In particular, significant differences in the diversity of eukaryotic plankton communities were found in vertical distribution. The diversity and abundance of eukaryotic plankton communities in 7 sampling sites decreased with the increase of depth from 0.5 to 10 m, while the diversity and abundance of plankton communities increased at 20 m. RDA analysis indicated that pH, depth, WT, NH₄⁺-N, DO, Cond, and NO₃⁻-N could influence the vertical distribution of the eukaryotic plankton community in the Danjiangkou Reservoir. Among these eukaryotic plankton, Eurytemora, Thermocyclops, and Volvox were negatively correlated with pH and WT and positively correlated with depth.Discussion: This study revealed a novel perspective on the distribution of the eukaryotic plankton community in Danjiangkou Reservoir, particularly in terms of vertical variation, which will be helpful to comprehensively understand ecological processes and to further ensure the water quality safety in this canyon-style reservoir.

Using field slope farmland plots, this study planted the typical crop of maize (Zea mays L.) and investigated the effects of varied chemical fertilizer (organic compound fertilizer of potassium nitrate, containing 17% each of nitrogen, phosphorus, and potassium) application levels (0.5 times the common fertilizer amount (CK, 0.75 t·hm⁻² to 2.5 CK) on the soil fertility in the Yuanmou dry-hot River Valley. The results showed that the soil chemical properties, microbial properties, and enzyme activities increased with the increase of fertilizer application levels from CK to 2.0 CK. However, a declining trend showed both under 0.5 CK level and the 2.5 CK level, and higher in fertilizer application level 3 (1.5 CK) and level 4 (2.0 CK) compared to level 1 (1 CK). Soil chemical properties, microbial properties, and enzyme activities in five-degree slope cropland topsoil were higher than these in 10-degree slope cropland topsoil. Five parameters (available N, nitrifying bacteria, inorganic phosphorus bacteria, organic matter, and invertase) in five-degree slope cropland and three parameters (organic matter, ammonifying bacteria, and total P) in 10-degree slope cropland, which had the greatest weight in the principal components analysis, were selected to calculate the soil quality index (SQI). The SQI calculated by integrating all critical parameters indicated that the highest SQI values were found in fertilizer levels 1.5 CK (0.71) and 2.0 CK (0.69), followed by CK (0.64), and the lowest were found in 0.5 CK (0.62) and 2.5 CK (0.61) in five-degree slope cropland soil. The highest SQI values were found in fertilizer levels 1.5 CK (0.26) and 2.0 CK (0.29), followed by CK (0.23), and the lowest were found in 0.5 CK (0.14) and 2.5 CK (0.20) in 10-degree slope cropland soil. The final SQI values implied that the fertilization treatment 2 (CK), fertilization treatment 3 (1.5 CK) and fertilization treatment 4 (2.0 CK) could improve the soil fertility, whereas the fertilization treatment 1 (0.5 CK) and fertilization treatment 5 (2.5 CK) could decrease the soil fertility. In view of the impact of slope, the soil qualities of five-degree slope cropland of five fertilization treatments were higher than in 10-degree slope cropland. The SQI values in five-degree slope cropland soil were found higher than the SQI values in 10-degree slope cropland soil by 68.65%, 64.20%, 62.22%, 57.46%, and 67.01%, respectively. For this study, the range of fertilization tolerance was 0.75–1.50 t·hm⁻² (organic compound fertilizer of potassium nitrate) in 10-degree slope plot scale and 0.75–1.13 t∙hm⁻² in five-degree slope cropland soil.