To clarify the alleviative effect of exogenous abscisic acid (ABA) on Medicago sativa under drought stress, we conducted an experiment with the drought-tolerant cultivar Dryland and drought-sensitive cultivar WL354HQ. With four treatments including water spray control, exogenous ABA treatment, drought treatment, and drought + ABA treatment, we analyzed the effects of exogenous ABA on the physiological characteristics of M. sativa seedlings with different drought tolerance. The results showed that drought stress significantly inhibited seedling growth, induced severe oxidative stress and osmotic adjustment responses, and suppressed photosynthetic capacity. Compared with drought treatment, the drought + ABA treatment significantly alleviated the inhibition of drought on seedling growth. Specifically, root length of drought-tolerant and drought-sensitive cultivars increased significantly by 34.6% and 9.8%, respectively. Meanwhile, membrane lipid peroxidation in plant cells was effectively alleviated. Malondialdehyde (MDA) content in leaves and roots of the drought-tolerant cultivar significantly decreased by 20.0% and 54.9%, respectively. Excessive proline accumulation was inhibited. Proline content in leaves and roots decreased by 19.8% and 64.0% in the drought-tolerant cultivar, and by 3.5% and 20.2% in the drought-sensitive cultivar. The photosynthetic stability of the drought-tolerant cultivar was superior to that of the drought-sensitive cultivar. Specifically, leaf transpiration rate was significantly decreased by 62.5% and 49.1%, and net photosynthetic rate was significantly reduced by 58.9% and 32.7% in drought-tolerant and drought-sensitive cultivars, respecti-vely. In conclusion, ABA mitigated drought stress in M. sativa by coordinating osmotic adjustment and oxidative defense systems, and the alleviatory effect was stronger in the drought-tolerant cultivar.
Estuarine marsh is one of the most sensitive ecosystems to global change and human activities. Estuarine marsh generally acts as a sink of exogenous nitrogen (N), with significant effects on N-cycling. Under the scenario of enhanced N and sulfur (S) loads in the Minjiang River estuary, it is of great significance to explore the responses of N distribution in plant-soil system. We conducted a field experiment with four treatments (T0, control; TN, high N load treatment, 98.0 g N·m-2·a-1; TS, high S load treatment, 216.0 g S·m-2·a-1; and TNS, high N and S load treatment, 98.0 g N·m-2·a-1 + 216.0 g S·m-2·a-1) in a typical Phragmites australis marsh in the Minjiang River estuary. We investigated nitrogen distribution patterns in the plant-soil system under elevated N and S inputs. Results showed that high N and S load significantly altered the contents of total nitrogen (TN), ammonium (NH4+-N) and nitrate (NO3--N) in marsh soils. Compared with the T0 treatment, the TN, NH4+-N and NO3--N contents in the TN treatment increased by 9.1%, 1.3% and 13.4%, the TN content in the TS treatment increased by 9.4%, while the NH4+-N and NO3--N contents decreased by 2.7% and 33.6%, respectively. The TN and NH4+-N contents in the TNS treatment decreased by 13.3% and 6.7%, respectively, while NO3--N content increased by 37.9%. Under different treatments, the TN contents were consistently higher in leaves and lower in roots of P. aus-tralis. Compared with the T0 treatment, root TN contents increased by 1.5% under the TN treatment but decreased by 7.0% and 15.4% under the TS and TNS treatments, while those in leaves in the TN, TS and TNS treatments increased by 10.4%, 1.9% and 7.9%, respectively. Among different treatments, the N stocks in the plant-soil system in the TN and TS treatments were much higher, while that in the TNS treatment was the lowest. Under different N and S loading conditions, P. australis adapted to environmental variations by altering its N uptake and translocation strategies. It adopted a "limited uptake and limited translocation" strategy under high N loading condition, a "massive uptake and massive translocation" strategy under high S loading condition, and a "limited uptake but massive translocation" strategy under high N and S loading condition.
To clarify the distribution pattern of Quercus variabilis under the combined influences of climate change and habitat fragmentation, we used 87 occurrence records and 9 climatic variables, and applied the MaxEnt model and ArcGIS to simulate the current and future suitable habitats of Q. variabilis across China under SSP126 and SSP585 scenarios. The results showed that the MaxEnt model performed well (area of receiver operating characteristic curve was 0.884). The main climatic factors influencing the distribution of Q. variabilis were the minimum temperature of the coldest month, precipitation of the wettest quarter, maximum temperature of the warmest month, and mean temperature of the wettest quarter. During 1970-2000, the area of highly suitable habitats for Q. variabilis was approximately 104.92×104 km2, mainly located in central, eastern, southwestern, and southeastern China. Under both SSP126 and SSP585 scenarios, the total suitable habitat expanded during 2021-2100, but its structure shifted. The highly suitable area declined significantly (by 44.8%-50.5%), moderately suitable habitat also contracted (by 1.7%-34.4%) except for a slight increase under SSP126 during 2021-2040, and poorly suitable area increased (by 41.7%-104.5%). This trend suggested the increases in fragmentation and the decline of overall suitability of Q. variabilis habitats. The findings would provide scientific guidance for region-specific management and the long-term sustainable utilization of Q. variabilis resources.
Cable bacteria are a type of filamentous conductive microorganisms with the capacity of centimeter level long-range electron transfer (LDET). As a "biological cable" in the environment, they play a key role as geochemi-cal engineers in the rhizosphere microenvironment. They also drive a series of interconnected redox reactions by constructing a unique bioelectrochemical network that connects root oxygen secretion (ROL) with deep sulfide oxidation. We reviewed the colonization patterns of cable bacteria in the rhizosphere and their interactions with plants. LDET could efficiently drive the in-situ formation of sulfide detoxification and iron oxide barriers, deeply couple the sulfur iron phosphorus cycle, significantly reduce methane emissions from ecosystems such as rice paddies, and improve phosphorus fixation and retention efficiency. The interaction between cable bacteria and plants has great potential for applications in organic pollutant degradation, heavy metal stabilization, ecosystem restoration, and greenhouse gas emission reduction. This review would provide new research ideas and theoretical references for deepening the understanding of microbial-plant symbiosis and transforming it into ecological engineering strategies, such as rhizosphere remediation and greenhouse gas emission reduction.
Open-pit coal mines are widely distributed in China, and the ecological monitoring of which is susceptible to geographical heterogeneity in hydrothermal conditions, vegetation types, and soil characteristics. To achieve accurate cross-regional monitoring, it is essential to evaluate the applicability of ecological quality assessment indices. Based on Google Earth Engine and uniform Landsat 8 OLI data, we used the standardized remote sensing ecological index (RSEIs), land surface ecological status composition index (LSESCI), new remote sensing-based ecological index (RSEInew), and surface coal mine ecological index (SurMEI) to evaluate ecological quality of open-pit coal mines in four typical climatic-geomorphologic zones (arid Gobi, semi-arid grassland, semi-arid plateau, and karst plateau). Through comparative analysis of the evaluation results of four indices, combined with correlation analysis, spatial distribution identification, land cover response assessment, and validation with synchronous field measurement data from typical mining areas, we analyzed the adaptability and limitations of each index in open-pit coal mines across different climatic-geomorphologic zones. The results showed that the ecological quality assessment based on SurMEI exhibited the best performance (mean correlation coefficient of 0.810) in the four typical climatic-geomorphologic zones, demonstrating good adaptability in cross-regional evaluations. The performance disparities among the other three indices arose from mismatches between their index structures and regionally dominant ecological processes. RSEIs overestimated disturbances in humid areas due to excessive sensitivity to the normalized difference bare soil index. LSESCI exhibited misclassification in complex terrains, owing to instability of the brightness component derived from the tasseled cap transformation. RSEInew failed in arid zones because of the weak discriminative power of its added PM2.5 indicator. Furthermore, spatiotemporal analysis based on SurMEI revealed significant differences in ecological restoration potential across different climatic-geomorphologic zones, with the highest potential in the karst plateau, intermediate in the semi-arid region (including grassland and plateau), and the lowest in the arid Gobi, indicating that ecological restoration should follow the principle of "zonal management". This study would provide a theoretical basis for accurate monitoring of ecological quality and model optimization for open-pit coal mines across different climatic-geomorphologic zones.
