Search Results (66)

Excessive fertilization is a widespread issue in onion (Allium cepa L.) production in Southwest China. This practice not only leads to environmental pollution but also decreases the marketable yield and fertilizer productivity of onions. Identifying an optimal fertilization rate is crucial for promoting high-yield and highly efficient onion cultivation. The objective of this research is to determine the appropriate amount of fertilizer by investigating the effects of different fertilization rates on the growth characteristics and bulb yield of onion. The study was conducted over two consecutive growing seasons utilizing a randomized complete block design, which included six treatments: local routine fertilizer application (F1), a 20% reduction from F1 (F2), a 40% reduction from F1 (F3), a 60% reduction from F1 (F4), an 80% reduction from F1 (F5), and no fertilizer application (F0). The results show that, at the mature stage, aboveground dry matter quantity and its accumulation rate of onion under treatment F2 were found to be the highest among all other treatments across both growing seasons. Following the onset of bulbing, dry matter accumulation initially increased but subsequently decreased with reduced fertilizer supply; notably, it was greater under treatment F2 compared to other treatments. Compared with F1, the PFPN (partial factor productivity of nitrogen fertilizer) under treatment F2 increased by 35.2% and 32.0%, and the marketable bulb yield under treatment F2 increased by 8.4% and 5.8% during the 2022–2023 and 2023–2024 growing seasons, respectively. The marketable bulb yield demonstrated extremely significant positive correlations with aboveground dry matter and the dry matter accumulation rate throughout all growth periods in both growing seasons. Furthermore, marketable bulb yield exhibited extremely significant positive correlations with dry matter translocation before the onset of bulbing and dry matter accumulation following bulbing initiation. It was concluded that the appropriate fertilizer application (F2), characterized by a fertilization rate of 339-216-318 kg ha⁻¹ for N-P₂O₅-K₂O, enhanced onion bulb yield and nitrogen fertilizer productivity by promoting post-bulbing dry matter accumulation. This study emphasizes the significance of optimizing the fertilization rate as a crucial factor in achieving high-yield and highly efficient onion cultivation by enhancing dry matter accumulation. Full article

A clear understanding of drought perceptions and adaptation behaviors adopted by farmers is an important way to cope with climate change and achieve sustainable agricultural development. Karst is a type of landscape where the dissolving of the bedrock has created sinkholes, sinking streams, caves, springs, and other characteristic features. The study took the Huajiang karst dry-hot river valley area located in the southwestern part of Guizhou as the study area and used questionnaire survey method, the index of perception and the diversity index of adaptation strategy to explore the risk perception, adaptation perception and adaptation behavior of farmers to non-climatic droughts in the subtropical karst dry-hot valleys. A total of 530 questionnaires were distributed and 520 were returned. The results show that (1) the farmers’ risk perception of drought is stronger than adaptation perception, which shows that although farmers are well aware of the possible risks posed by drought, their subjective initiative and motivation to adapt to drought are weaker; (2) in the face of drought, farmers prioritize selected non-farm measures for adaptation, followed by crop management and finally water resource management; and (3) compared to farmers in arid and semi-arid regions, those in karst hot-dry river valleys exhibit distinct adaptive behaviors in response to drought, particularly in water resource management. Full article

Sapindus delavayi is a drought-resistant tree species endemic to the dry–hot valleys of Southwestern China and is of great significance for soil and water conservation and ecological restoration. In this study, we sequenced the transcriptome of its leaves using the Illumina HiSeq 4000 platform and obtained 96.12 Gb of high-quality data (Q20 = 98.68%, Q30 = 95.62%), which were de novo assembled to obtain 89,228 unigenes (N50 = 1538 bp), of which 63,005 (70.61%) were successfully annotated to at least one database (NR, NT, SwissProt, KOG, KEGG, GO, Pfam). Overall, 53.96% of the unigenes in the S. delavayi leaves were annotated to Acer yangbiense, which belongs to the same family as S. delavayi. A total of 42,870 CDSs and 21,488 SSR loci were detected, with the highest mononucleotide repeat rate at 42.72% of the total number. Drought stress experiments identified 669–1203 differentially expressed genes (DEGs). Through our research, the first high-quality transcriptome database of S. delavayi has been constructed and its drought-resistance-related gene features have been analyzed, laying an important foundation for future functional gene mining, molecular marker development, molecular diversity studies, molecular breeding, and ecological adaptation research. Full article

The inherent spatial heterogeneity of land types often leads to a class imbalance in remote sensing-based classification, reducing the accuracy of minority class detection. Consequently, current land use datasets are often inadequate for the specific needs of soil erosion studies. In response to the need for soil conservation in dry–hot valley regions, this study integrated multi-source remote sensing imagery and constructed three high-precision imbalanced sample datasets on the Google Earth Engine (GEE) platform to perform land use classification. The degree of class imbalance was quantified using the imbalance ratio (IR), and the impact of sample imbalance on the classification accuracy of different land use types in a typical dry–hot valley was analyzed. The results show that (1) Feature selection significantly improved both classification accuracy and computational efficiency. The period from February to April each year, between 2018 and 2023, was identified as the optimal time window for land use classification in dry–hot valleys. (2) Constructing composite images over longer time scales enhanced classification performance: using a 2020 annual composite image combined with a Gradient Tree Boosting classifier yielded the highest accuracy, indicating that longer temporal synthesis improves classification results. (3) The effect of class imbalance on classification accuracy varied by land type: woodland (the majority class) was least affected by imbalance, whereas minority classes such as cultivated land, garden plantations, and grassland were highly sensitive to imbalance. In imbalanced scenarios, minority classes are prone to omission errors, leading to notable accuracy declines; producer’s accuracy (PA) decreased by 46%, 42%, and 25% for cultivated land, garden plantations, and grassland, respectively, as IR increased (with PA dropping faster than user’s accuracy, UA). Cultivated land was especially sensitive and frequently overlooked under high imbalance conditions compared to gardens and grasslands. Despite overall accuracy improving with higher IR, the accuracy of these minority classes dropped significantly, underscoring the importance of addressing the class imbalance in land use classification for erosion-prone areas. Full article

Soil active nitrogen (N) fractions are essential for plant growth and nutrient cycling in terrestrial ecosystems. While previous studies have primarily focused on the impact of vegetation restoration on soil active nitrogen in karst ecosystems, the role of microclimate variation in rocky desertification areas has not been well explored. This study investigates soil active nitrogen fractions and key biotic and abiotic factors across four grades of rocky desertification—non-rocky desertification (NRD), light rocky desertification (LRD), moderate rocky desertification (MRD), and intense rocky desertification (IRD)—within two distinct microclimates: a dry-hot valley and a humid monsoon zone in the karst region of Guizhou Province, China. We evaluate soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), soil nitrate nitrogen (NO₃⁻-N), ammonium nitrogen (NH₄⁺-N), microbial biomass nitrogen (MBN), soluble organic nitrogen (SON), and plant diversity. Results showed that SOC, TN, and TP were significantly higher in IRD areas. Soil NO₃⁻-N, MBN, and SON initially decreased before increasing, with consistent MBN growth in the dry-hot valley. NH₄⁺-N did not differ significantly under NRD but was higher in the dry-hot valley under LRD, MRD, and IRD. The dry-hot valley had higher MBN and SON across most desertification grades. Microclimate significantly influenced soil active N, with higher levels in the dry-hot valley under LRD and MRD conditions. Plant diversity and regeneration varied markedly between the microclimates. In the dry-hot valley, Artemisia dominated herbaceous regeneration, especially in MRD areas. Conversely, the humid monsoon zone showed more diverse regeneration, with Artemisia and Bidens prevalent in MRD and NRD grades. Despite declining plant diversity with desertification, the humid monsoon zone displayed greater resilience. These findings highlight the role of microclimate in influencing soil nitrogen dynamics and plant regeneration across rocky desertification gradients, offering insights for restoration strategies in karst ecosystems. Full article

This study investigates the hydrological processes and water body transformation mechanisms in the Yuanmou dry–hot valley, focusing on precipitation, well water, spring water, river water, and reservoir water, during both wet and dry seasons. The spatiotemporal characteristics and significance of the hydrogen and oxygen stable isotopes across these water bodies were analyzed. Key findings included the following: (i) Seasonal variations in precipitation, river water, and shallow groundwater were minimal, and were primarily driven by differences in water vapor sources and transport distances during wet and dry seasons. The seasonal effects of mid-deep groundwater and reservoir water were influenced by leakage recharge from deep aquifers and temperature variations, respectively. (ii) The groundwater line-conditioned excess (lc-excess) deviated significantly from the Local Meteoric Water Line, indicating that precipitation recharge occurred primarily through slow infiltration piston flow with significant isotopic fractionation. (iii) River water was recharged by precipitation, deep groundwater, and spring water; well water by precipitation and lateral groundwater inflow; spring water by deep groundwater; and reservoir water by precipitation, groundwater, and water transfer, with strong evaporation effects. (iv) Using a binary isotope mass balance model, the recharge ratios of precipitation and groundwater to surface water were calculated to be 40% and 60%, respectively. Additionally, during the wet season, the proportion of groundwater recharge to river water increased. This study provides valuable insights into hydrological cycle processes in dry–hot valleys and offers a scientific basis for the sustainable development and management of water resources in arid regions. Full article

Trunk sap flow is essential for assessing plant water use efficiency and adaptation, yet the mechanisms underlying drought resistance and water utilization strategies in dry and hot valleys remain poorly understood. This study investigates the sap flow dynamics of four tree species (Albizia kalkora, Diospyros dumetorum, Terminalia franchetii, and Acacia auriculiformis) in a dry and hot valley using Granier’s thermal diffusion probe method. The aims were to analyze interspecific differences and their response mechanisms to environmental factors using a fitted model of sap flow density and transpiration variables, supplemented by Pearson’s and Mantel’s tests. The results showed that (1) the trunk sap flow of each tree species is significantly higher in the wet season than in the dry season. (2) In the dry and wet seasons, the average trunk sap flow rates were in the order Albizia kalkora > Diospyros dumetorum > Terminalia franchetii > Acacia auriculiformis. (3) The correlation between environmental factors and trunk sap flow was in the order photosynthetically active radiation > atmospheric temperature > saturated water vapor pressure difference > relative humidity > wind speed. (4) Deciduous plants demonstrated stronger water-conducting capacities than evergreen plants and native plants exhibited better drought resistance than introduced plants. (5) Acacia auriculiformis and Albizia kalkora were identified as rainfall-sensitive plants, while Diospyros dumetorum and Terminalia franchetii were rainfall-insensitive. By optimizing species selection based on water use efficiency, rainfall sensitivity, and environmental conditions such as light and temperature, this research contributes to enhancing the stability and resilience of ecosystem restoration in arid regions. Full article

During winter 2023–2024, the Charente River experienced four successive flood events in six months, including one major flood and three moderate ones. These grouped floods affected a huge territory in the Charente valley, in particular the Territoire à Risque d’Inondation Important (TRI, i.e., Major Flood Risk Area) between Angoulême and Saintes (46 municipalities). Although they produced little immediate damage due to their slow kinematics and low flow speeds, they had a major impact on the functioning of the territory through prolonged house flooding and infrastructure disruption. This repeated flood sequence is all the more remarkable in that it occurs after the February 2021 extreme flood and a backdrop of severe and prolonged drought initiating in 2019. This article proposes to analyze grouped floods, a complex and little-studied hydrological phenomenon, from a geohistorical perspective in order to demonstrate that they are not emergent events and to look for historical precedents that show that these particular events have already occurred in the past but have been neglected or underestimated until now. Among past grouped flood sequences extending back to 1700, a significant similarity arises with the 1859–1860 flood sequence. In both cases, the first annual flood occurred early in the year in response to an early storm season and followed an uncommon hot and dry summer. Although the floods of 2023–2024 are well documented through both meteorological and hydrological data, as well as the surrounding context, the floods of 1859–1860 remain poorly constrained. By gathering a wide range of documentary sources and instrumental data, we try to better understand the context and the course of this past sequence of grouped floods, with particular emphasis on the first annual flood, the November 1859 flood. The analysis of similarities and divergences between sequences of past and recent grouped floods makes it possible to improve knowledge of their formation and course in order to better anticipate these particular events in the context of climate change. Full article

Exploring the gene flow and its causes in complex habitats of forest trees is valuable for understanding species’ adaptive evolution. Pinus yunnanensis var. tenuifolia (PYT) is mainly distributed in the dry–hot valleys along the Nanpan-Hongshui rivers in southwest China, an ecologically fragile area. In this study, we analyzed 1056 seeds from eleven natural populations of PYT across its range using twelve cpSSR markers to explore haplotype polymorphisms and correlations with environmental factors. The results revealed a high genetic diversity (H_E = 0.83), with the private haplotypes significantly exceeding the shared haplotypes. A genealogical structure was observed among the populations, with a moderate differentiation (F_ST = 0.162). The population clustering and haplotype network demonstrated localized areas of pollen exchange, especially in the middle and lower reaches of the river. Redundancy analysis showed that, as the populations were closer to the river, genetic diversity tended to decrease significantly, implying that the pollen dispersal is restricted by the foehn effect in the valley. Variability in genetic differentiation among the offspring populations was primarily influenced by geographic factors, such as mountains and rivers, which, along with local environmental adaptations, shaped the pollen distribution pattern. These findings may facilitate the sustainable management and conservation of PYT and other species under similar habitats. Full article

The lower reaches of the Jinsha River, serving as a vital ecological barrier in southwestern China and playing a crucial role in advancing targeted poverty alleviation efforts, remain underexplored in terms of the coupling between ecological and economic development, creating a gap in understanding the region’s sustainable development potential. This study combines the remote sensing ecological index (RSEI) derived from MODIS data and the biodiversity richness index (BRI) based on land use data to create the ecological environment index (EEI) using a weighted approach. It also develops the economic development index (EDI) from economic data using the entropy weight method. By integrating the EEI and EDI, the study calculates key metrics, including the ecological–economic coupling degree (EECD), coupling coordination degree (EECCD), and relative development degree (EERDD), and examines their spatiotemporal changes from 2000 to 2020. Additionally, the study applies a geographic detector model to identify the spatial drivers of the EEI, an obstacle factor diagnosis model to pinpoint the main barriers to EDI, and a neural network model to uncover the underlying forces shaping EECCD. The results indicate that: (I) From 2000 to 2020, the overall improvement rate of the ecological and economic subsystems was greater than that of the ecological–economic coupling system. The entire region is still in the Running-In Stage, and the coordination level has been upgraded from near imbalance to marginal coordination. About 85% of the counties’ EERDDs are still in the EDI Behind EEI Stage. (II) The structural composition of the EEI shows a pattern of low Dry Hot Valley Area and high in other areas, mainly driven by natural factors, although human activities had a notable impact on these interactions. (III) Originating from an impact model primarily driven by economic factors and supplemented by ecological factors, both EDI and EECCD exhibit a pattern of high in the south and low in the north, with improvements spreading northward from the urban area of Kunming. The development gradient differences between 24 poverty-stricken counties and 16 non-poverty-stricken counties have been reduced. (IV) For the six types of ecological–economic coupling development zones, it is essential to adopt localized approaches tailored to the differences in resource and environmental characteristics and development stages. Key efforts should focus on enhancing ecological protection and restoration, increasing financial support, implementing ecological compensation mechanisms, and promoting innovative models for sustainable development. Full article

Non-photosynthetic vegetation (NPV) significantly impacts ecosystem degradation, drought, and wildfire risk due to its flammable and persistent litter. Yet, the accurate estimation of NPV in heterogeneous landscapes, such as dry–hot valleys, has been limited. This study utilized multi-source time-series remote sensing data from Sentinel-2 and GF-2, along with field surveys, to develop an NDVI-DFI ternary linear mixed model for quantifying NPV coverage (f_NPV) in a typical dry–hot valley region in 2023. The results indicated the following: (1) The NDVI-DFI ternary linear mixed model effectively estimates photosynthetic vegetation coverage (f_PV) and f_NPV, aligning well with the conceptual framework and meeting key assumptions, demonstrating its applicability and reliability. (2) The RGB color composite image derived using the minimum inclusion endmember feature method (MVE) exhibited darker tones, suggesting that MVE tends to overestimate the vegetation fraction when distinguishing vegetation types from bare soil. On the other hand, the pure pixel index (PPI) method showed higher accuracy in estimation due to its higher spectral purity and better recognition of endmembers, making it more suitable for studying dry–hot valley areas. (3) Estimates based on the NDVI-DFI ternary linear mixed model revealed significant seasonal shifts between PV and NPV, especially in valleys and lowlands. From the rainy to the dry season, the proportion of NPV increased from 23.37% to 35.52%, covering an additional 502.96 km². In summary, these findings underscore the substantial seasonal variations in f_PV and f_NPV, particularly in low-altitude regions along the valley, highlighting the dynamic nature of vegetation in dry–hot environments. Full article

Extensive and profound landscape alterations significantly contribute to ecological vulnerability in environmentally delicate regions. Existing research primarily emphasizes ecological risks caused by landscape alterations, while overlooking vulnerable characteristics of landscape functions; particularly lacking are studies on the driving mechanism of landscape ecological risk through the reciprocal relationship between landscape pattern risk and function risk. Based on these issues, this paper constructed a landscape pattern risk index (LPRI), a landscape function risk index (LFRI), and a landscape ecological risk index (LERI) in the counties of the dry–hot valley of the Jinsha River in southwest China. By employing a coupling degree and a coordination model, we analyzed temporal and spatial variations in the interaction between two types of ecological risk, thereby revealing the driving mechanisms of landscape ecological risk. The results indicated that the average LPRI values of the study area were 0.373, 0.327, and 0.427, respectively, while the average LFRI values were 0.451, 0.356, and 0.442 in 2000, 2010, and 2020, respectively. More than 90% of the study area exhibited a medium coupling relationship between the two types of ecological risks. The area proportion of the coupling coordination regions has increased from 25.58% to 31.07% from 2010 to 2020. The two types of risk exhibited a low level of constraint inhibition. Extremely evident expansion of high pattern–function risk areas and the area increase of coupling coordination region resulted in the acceleration of regional landscape ecological risk level. Increasing competition between market-driven land-use activities and ecological regulations from the government has rendered the diversification of landscape ecological risk sources and its underlying mechanisms intricate. This study serves as a model reference for assessing landscape ecological risk and a theoretical basis for sustainable landscape management and ecological regulation in the Yangtze River basin. Full article

Yuanjiang dry–hot valley is located in the southwest of mainland China. It is a sparsely vegetated area with a fragile arid ecosystem. Although the valley previously had forest cover, it has become a tropical montane savannah in recent decades. Mechanisms controlling plant species distribution in such dry–hot valleys are unclear. Clarifying this will be beneficial to sustainable ecosystem management in dry–hot valleys. This study explored the relationship between diversity patterns of plant species and their environments in the lowland of this dry–hot valley. To achieve this, transects and plots were arranged along the river channel. Alpha and beta diversity indices were calculated to quantify biodiversity changes between species and environments. Estimated species, rarity, and abundance indices were also utilized to examine the correlation among species, their population size, and their environment: Species_estimated (expected number of species in t pooled plots), Singletons (the number of species with only one individual in t pooled plots), Uniques (the number of species living in one plot in t pooled plots), ACE (species richness estimator with coverage-based abundance), ICE (species richness estimator with coverage-based incidence), and Chao2 (species richness estimator extrapolated from Singletons). Fifty years of meteorological records, including temperature and precipitation, were utilized as climate variables. The results indicated the following findings: (1) alpha diversity was higher closer to the river, whereas the beta diversity was higher towards the lower sections of the river (Bray–Curtis < 0.5), but this trend was reversed in the perpendicular transects; (2) total phosphorous (TP) and total potassium (TK) were higher on flatter ground, tending to be associated with raised nitrogen (TN) and organic matter (OM); (3) soil nutrients were higher towards the lower sections of the river, corresponding to an increased number of species; (4) water supply determined plant distribution, with soil condition determining water retention; (5) the estimated species and their rarity and abundance indices were associated with proximity to the river, indicating heterogeneity of habitats and soil condition; and (6) fern species could be used as indicators representing the xeric environment of Yuanjiang dry–hot valley. Plant cover was reduced at low altitudes, with high temperatures and a low water supply. These results draw attention to the need for specific policy formation to protect the microhabitats and manage the environment of the Yuanjiang valley. Full article

In the context of rising temperatures and increasing humidity in Northwest China, substantial gaps remain in understanding the mechanisms of land–atmosphere cloud–precipitation coupling across the northeastern Tibetan Plateau (TP), Loess Plateau (LP), and Huangshui Valley (HV). This study addresses these gaps by investigating cloud properties and precipitation patterns utilizing the Fengyun-4 Satellite Quantitative Precipitation Estimation Product (FY4A-QPE) and ERA5 datasets. We specifically focus on Lanzhou, a pivotal city within the LP, and Xining, which epitomizes the HV. Our findings reveal that diurnal variations in precipitation are significantly less pronounced in the eastern regions compared to northeastern TP. This discrepancy is attributed to marked diurnal fluctuations in convective available potential energy (CAPE) and wind shear between 200 and 500 hPa. While both cities share similar wind shear patterns and moisture transport directions, Xining benefits from enhanced snowmelt and effective water retention in surrounding mountains, resulting in higher precipitation levels. Conversely, Lanzhou suffers from moisture deficits, with dry, hot winds exacerbating the situation. Notably, precipitation in Xining is strongly correlated with CAPE, influenced by diurnal variability, and intensified by valley and lake–land breezes, which drive afternoon convection. In contrast, Lanzhou’s precipitation exhibits a weak relationship with CAPE, as even elevated values fail to generate significant cloud formation due to insufficient moisture. The ongoing trends of warming and humidification may lead to improved precipitation patterns, especially in the HV, with potential ecological benefits. However, concentrated rainfall during summer afternoons and midnights raises concerns regarding extreme weather events, highlighting the susceptibility of the HV to geological hazards. This research underscores the need to further explore the uncertainties inherent in precipitation dynamics in these regions. Full article

A plant species can have diverse hydraulic strategies to adapt to different environments. However, the water transport divergence of co-occurring species in contrasting habitats remains poorly studied but is important for understanding their ecophysiology adaptation to their environments. Here, we investigated whole-branch, stem and leaf water transport strategies and associated morphology traits of 11 co-occurring plant species in Yuanjiang valley-type savanna (YJ) with dry–hot habitats and Xishuangbanna tropical seasonal rainforest (XSBN) with wet–hot habits and tested the hypothesis that plants in YJ have a lower water transport efficiency than co-occurring species in XSBN. We found high variation in whole-branch, stem and leaf hydraulic conductance (K_shoot; K_stem and K_leaf) between YJ and XSBN, and that K_stem was significantly higher than K_leaf in these two sites (K_stem/K_leaf: 16.77 in YJ and 6.72 in XSBN). These plants in YJ with significantly lower K_shoot and K_leaf but higher sapwood density (WD) and leaf mass per area (LMA) showed a lower water transport efficiency regarding less water loss and the adaptation to the dry–hot habitat compared to co-occurring species in XSBN. In contrast, these co-occurring plants in XSBN with higher K_shoot and K_leaf but lower WD and LMA tended to maximize water transport efficiency and thus growth potential in the wet–hot habitat. Our findings suggest that these co-occurring species employ divergent hydraulic efficiency across YJ and XSBN so that they can benefit from the contrasting hydraulic strategies in adaptation to their respective habitats. Full article