Modeling RGB-based estimation of apple fruit maturity in the semi-arid Loess Plateau via starch-iodine staining mapping

Soil nitrogen availability is a major constraint to crop productivity in rainfed arid and semi-arid regions. The influence of straw strip mulching on nitrogen availability and transformation across soil layers remains unclear. This study investigates the effect of straw strip mulching on soil nitrogen dynamics and crop-specific variation in wheat- and potato-cultivated soils under rainfed semi-arid conditions. This study consisted of five mulching treatments, including without mulching (Tck), black plastic film mulching (Tp), straw strip mulching (Tss), plant strip without mulch (Tps), and composite strip of straw strip mulching and plant strip without mulch (Tcs) applied in wheat and potato cultivation during 2019 and 2020, and soil nitrogen fractions were determined across different soil depths. Tss mulching showed the highest increase in urease activity (48%), nitrite reductase activity (48%), microbial biomass nitrogen (52%), NH4 (11%), acid-hydrolyzed total nitrogen (10%), acid-soluble NH4 (6%), acid-hydrolyzed amino sugar (16%) and acid-hydrolyzable unknown nitrogen (59%) relative to Tck without mulching. While total nitrogen (11%) and acid-hydrolyzed amino acid (9%) were highest in the Tps treatment compared to Tck treatment, the mulching treatment had no significant effect on soil organic nitrogen-derived functional traits. Across all treatments, the 0–20 cm soil layer consistently showed the highest concentrations of observed soil traits, which declined with increasing soil depth. Furthermore, potato-cultivated soils showed consistently higher concentrations of these traits than wheat-cultivated soils, and the concentrations of these traits in 2020 exceeded those observed in 2019. This study highlights that maize straw mulching in strips significantly promotes soil organic nitrogen fractions, particularly in the upper soil layers, and promotes higher nitrogen availability in potato than in wheat-cultivated soils, and is recommended as an effective soil management practice to improve soil nitrogen availability in rainfed semi-arid Loess Plateau conditions.

The drought responses of sap flow and transpiration of a Robinia pseudoacacia plantation in the semi-arid Loess Plateau of China

Soil phosphorus (P) deficiency is an important factor limiting plant growth in the semi-arid Loess Plateau region in China. The topsoils in this area undergo repeated drying–rewetting (DRW) cycles, which can influence soil P availability, a process that may become more pronounced due to climate change. However, little is known about how soil P availability responds to DRW cycles under different land-use types. To investigate this issue, we conducted three 120-day soil culture experiments to investigate the direction and magnitude of soil available P and the responses of its influencing factors to repeated DRW cycles and their frequency and intensity under three typical land-use types (cropland, grassland, and shrubland) in Gansu Province, North-western China. The results showed that the available P concentration of cropland, grassland, and shrubland soils after repeated DRW cycles significantly decreased by 8.9%, 11.5%, and 14.2%, respectively, compared with a constant humidity control. With increasing intensity of the DRW cycles, the available P concentration of grassland and shrubland soils significantly increased by 14.3% and 15.5%, respectively, while in cropland soil P significantly decreased by 10.4%. Compared with low-frequency DRW cycles, high-frequency DRW cycles significantly reduced the available P concentration by 6.4% in grassland soil and increased it by 9.8% in shrubland soil but had no significant effect in cropland soil. Overall, the responses of soil P availability to repeated DRW cycles vary among different land-use types, and the magnitude of the soil P availability response to repeated DRW cycles depended strongly on soil microorganism biomass, phosphatase activity, and the initial soil properties, being more pronounced in grassland and shrubland soils than in cropland soils. It is therefore essential to consider land-use type when studying the effects of DRW on soil P cycling in semi-arid regions, especially in the context of climate change.

Evaluating tillage optimization, soil thresholds, and drivers for maize yield and WUE in China's semiarid loess Plateau: A meta-analysis

Tillage and nitrogen management enhance nitrogen-cycling microbes and maize yield under plastic film mulching in the semi-arid loess plateau, China

Biodegradable microplastics induce more soil nitrous oxide emission than conventional in semi-arid Loess Plateau.

Global climate change-induced extreme drought has triggered widespread forest growth decline and tree mortality worldwide, making the processes of forest decline and their responses to environmental conditions a major research focus. In the Longtan Catchment of the Loess Plateau, Chinese pine (Pinus tabulaeformis Carr.) plantations exhibit varying levels of degradation, yet the growth trends and climate-growth relationships across different health gradients remain poorly understood. We developed tree-ring width chronologies for Chinese pine plantations representing five distinct health conditions: healthy, relatively healthy, slightly declining, moderately declining, and severely declining. Standard dendrochronological techniques were employed to compare growth rates, chronology statistical quality, and the sensitivity of radial growth to climate variables during both the growing and non-growing seasons. The results showed that the healthy chronology exhibited a clear increasing trend in growth rate over time and relatively high statistical quality. In contrast, declining chronologies showed no evident long-term increase in growth rate and were characterized by lower chronology quality. Regarding climate responses, the strength of climate signals during the growing season decreased progressively with increasing decline severity. While healthy trees displayed strong positive correlations with climate variables, these relationships weakened and shifted toward negative associations in the moderately and severely declining stages. Similarly, positive climate signals in the non-growing season declined markedly along the health gradient, weakening substantially in the severely declining stage. These findings deepen our understanding of growth decline and its environmental drivers in the Loess Plateau. The health-dependent sensitivity shifts identify a critical window for proactive intervention. Our study suggests that early detection and timely density regulation, such as thinning during mild-to-moderate decline, are essential. Furthermore, management strategies should prioritize conserving non-growing-season water-especially spring moisture-to mitigate the risk of severe forest decline and support sustainable ecological restoration.

IntroductionWater scarcity severely constrains the sustainability of plantations in semi-arid regions by reducing soil water availability and increasing drought stress. Thinning is a crucial silvicultural practice for forest restoration and water regulation, yet the responses of soil water content (SWC) to varying thinning intensities during a dry year and a normal year remain insufficiently understood.MethodsThis study evaluated the effects of thinning on SWC in Chinese pine (Pinus tabuliformis) plantations on the Loess Plateau of China, with five thinning intensities: 0% (control), 15% (light), 30% (moderate), 45% (heavy), and 60% (extremely heavy). SWC at depths of 0 -200 cm was repeatedly monitored during the growing seasons of 2023 (dry year) and 2024 (normal year). Vegetation structure, rainfall redistribution, and soil properties were periodically measured.ResultsThinning increased mean 0 -200 cm profile SWC by 4.96 -18.06% in the dry year (2023) and by 5.33 -18.87% in the normal year (2024), compared with the 0% thinning control. Although SWC in 2024 was higher than in 2023, thinning exerted a similar effect on SWC in both study years, with the 30% thinning intensity yielding the most pronounced positive improvement in deep SWC (30 -200 cm; +19.14% -25.26%). Thinning significantly improved the temporal stability of deep SWC in 2024, and the 15% and 30% thinning treatments consistently exhibited relatively low coefficient of variation values during the monitored observation period. Redundancy analysis (RDA) indicated that SWC was positively associated with net precipitation in both soil layers and in both study years. Additionally, deep SWC exhibited a positive association with soil organic carbon during both years, as well as with fine-root traits in 2024.DiscussionBased on the above results and the regional soil water carrying capacity, we recommend prioritizing an initial thinning intensity of approximately 30% (≈2,000 stems ha−1) to alleviate soil desiccation in Chinese pine plantations. This finding informs adaptive eco-rehabilitation strategies for plantation restoration on the Loess Plateau and other semi-arid regions and provides a practical basis for improving soil-water regulation and plantation resilience under increasing climatic stress.

Trade-off and decoupling of biomass allocation and nutrient content in three grassland community types on the semiarid Loess Plateau

Abstract The variability of raindrop size distribution (DSD) across terrain gradients plays a critical role in regulating rainfall microphysics and kinetic energy (KE), yet this variability remains underexplored in semiarid regions. This study utilized six summers (2019–24) of 92 disdrometer observations across Shaanxi Province, China, to demonstrate the pronounced south–north DSD gradient across terrains: While the site-averaged mass-weighted mean diameter ( D m ) increased, the normalized intercept parameter (log 10 N w ) decreased rapidly from mountains to plateaus. The humid Qinling–Daba Mountains exhibit higher seasonal rainfall (>800 mm) dominated by a high concentration of small raindrops, while the semiarid Loess Plateau shows frequent occurrences of large raindrops. This DSD shift drives higher KE in the Loess Plateau (25/28 stations > 20 J m −2 mm −1 ) than in the Qinling–Daba Mountains (only 2/25 stations > 20 J m −2 mm −1 ), thus amplifying soil erosion risks due to vulnerable loessial substrates. Despite the spatial heterogeneity, the site-averaged D m –log 10 N w pairs demonstrate consistent evolution throughout Shaanxi along with the increase in rain rate. We further establish D m as a universal microphysical constraint, deriving robust estimators for KE, accretion/evaporation rates, and mass-weighted terminal velocity of DSD. These relationships overcome the limitations of traditional methods by encoding terrain-mediated DSD heterogeneity through the D m parameter. Consequently, they are practical for facilitating high-accuracy estimation of key microphysical quantities and process rates without full DSD resolution. Our findings offer critical semiarid DSD benchmarks for improving model microphysics parameterization, advancing remote sensing–based KE retrievals, and designing targeted soil conservation strategies for erosion hotspots. Significance Statement Six years of measurements from 92 disdrometers across diverse terrains in Shaanxi Province, China, are applied to investigate the spatial variability of raindrop size distributions. Results indicate that heavy rainfall in the southern mountains is characterized by many small raindrops but with weak energy per drop. Conversely, the rainfall in the semiarid Loess Plateau is comprised of more large-size raindrops, resulting in a higher impact energy per rainfall unit despite a lower rainfall amount. This phenomenon amplifies the destructive potential of storms, exacerbating soil erosion in vulnerable plateau landscapes. Empirical relationships that employed the mean raindrop size are developed to predict rainfall energy and cloud processes more precisely. Our findings contribute to facilitate the improvement of flood and erosion forecasts.

In the semi-arid Loess Plateau of China, afforestation frequently leads to soil water depletion, threatening ecosystem sustainability. Although mixed-species plantations are encouraged to enhance resource use efficiency, their effects on deep soil water and root distribution strategies remain unclear. This study compared soil water content (SWC), deep soil water deficit (SWD), and fine root distribution in pure and mixed plantations of Robinia pseudoacacia, Platycladus orientalis, and Hippophae rhamnoides to assess whether species mixing intensifies consumption for deep soil water. Soil moisture and root samples were collected with a maximum depth of 20 m across five stand types in August 2018 and during the 2019 growing season. Results showed that mixed stands exhibited shallower water depletion depth and lower SWC below 2 m than pure stands, but a more severe deep soil water deficit, with observed SWD exceeding the expected values by 12% in the R. pseudoacacia-P. orientalis mixture (MRP) and 22% in the H. rhamnoides-P. orientalis mixture (MHP), indicating intensified water consumption below 2 m. In the MRP, the maximum rooting depth was shallower than in the corresponding pure stands. Within the mixture, species-specific root plasticity was observed: the normalized fine root length density (FRLD) of P. orientalis was four times greater in mixture than in pure stand, whereas that of R. pseudoacacia was 62% lower, suggesting divergent foraging strategies. Correlation analyses indicated that SWC was differently associated with root traits between pure and mixed stands, with relationships varying by soil depth. Mixed-effects models confirmed that both plantation type and soil depth significantly influenced FRLD and Root dry weight density (RDWD), while specific root length (SRL) was mainly affected by plantation type and its interaction with depth. These findings demonstrated that mixed-species afforestation intensifies deep soil water competition. Therefore, sustainable management should prioritize the selection of species with complementary root foraging strategies and the optimization of planting densities in semi-arid regions.

The Loess Plateau (China) is an ecologically fragile region where understanding the impact of forest naturalness on soil carbon content is critical for ecological restoration and enhancing carbon sequestration. This study investigates this relationship in the Cuiying Mountain area (Yuzhong County, Lanzhou City), a representative landscape of the semi-arid Loess Plateau. The Cuiying Mountain ecosystem is characterized by coniferous forests and Gray-cinnamon soils. We assessed forest naturalness using several key indicators: herb coverage, shrub coverage, tree biodiversity, and stand structural attributes. The results revealed a generally low level of forest naturalness at Cuiying Mountain. Although herb coverage was high, shrub coverage was minimal (2.1%), and tree biodiversity was low (Shannon index = 0.09). The stand structure was simple, characterized by considerable variation in individual tree sizes and a single canopy layer (mean mingling degree = 0.14). This structural simplicity aligns with the area’s history of plantation management. Furthermore, analysis of soil physicochemical properties and their relationship with plant diversity identified plant diversity as a significant factor influencing soil carbon content. The strongest correlation was observed between plant species number and topsoil organic carbon (r = 0.77), indicating a particularly pronounced effect of plant diversity on surface soil organic carbon. In summary, while forest naturalness at Cuiying Mountain is generally low, increased plant diversity enhances the accumulation of litter/root exudates and carbonates, suggesting that enhancing plant diversity is an effective strategy for increasing total soil carbon content. This study provides valuable insights for refining ecological restoration practices and strengthening the soil carbon sink function in forest ecosystems across the Loess Plateau and similar semi-arid regions.

Modulating effects of herbicide-safener co-application on rhizosphere microbiota and soil function in proso millet (Panicum miliaceum L.).

The carbon metabolism activity of rhizosphere soil microbial communities is an essential indicator for assessing soil ecosystem health, as it directly affects soil nutrient cycling and the stability of organic matter. However, there is a limited understanding of the carbon metabolism characteristics of rhizosphere soil microorganisms in alfalfa (Medicago sativa L.) of different ages and their relationships with soil physicochemical properties. This study used Biolog EcoPlates to evaluate the carbon metabolism activity, functional diversity, and carbon-source utilization preferences of rhizosphere soil microbial communities in 5-, 7-, and 9-year-old alfalfa grasslands on the semi-arid Loess Plateau of western China. We analyzed the relationships between soil physicochemical properties and microbial carbon metabolism characteristics, considering their potential covariation. The results showed that, with the extension of alfalfa planting years, the rhizosphere soil water content decreased significantly, pH decreased slightly, but soil organic carbon, total nitrogen, and total phosphorus contents increased significantly. The rhizosphere soil microbial community of 9-year-old alfalfa exhibited the highest carbon metabolism activity, Shannon diversity index, and carbon-source utilization. Rhizosphere soil microorganisms from different-aged alfalfa showed significantly different preferences for carbon-source utilization, with microorganisms from 9-year-old alfalfa preferentially utilizing carbon sources such as N-acetyl-D-glucosamine, D-mannitol, and D-cellobiose. Redundancy analysis revealed that soil water content was among the most important factors influencing the carbon metabolism activity of rhizosphere soil microbial communities while acknowledging that the relative contributions of soil water content, organic carbon, and nitrogen require careful interpretation, owing to their potential collinearity. This study demonstrates that, under rain-fed conditions in the semi-arid Loess Plateau, the continuous cultivation of alfalfa for nine years led to a significant decrease in soil water content but enhanced the rhizosphere soil nutrient status and microbial carbon metabolism activity, with no apparent signs of microbial functional degradation, although soil water depletion was observed. These findings highlight the complex interactions among multiple soil factors in influencing microbial carbon metabolism, providing valuable microbiological insights for understanding the sustainability of alfalfa grasslands and a theoretical basis for the scientific management of alfalfa grasslands in the semi-arid Loess Plateau region. Future research should consider longer planting periods to determine the critical age of alfalfa grassland degradation under semi-arid conditions and its associated microbial mechanisms.

The conversion of degraded ecosystems to perennial vegetation in water-limited regions creates conflicting demands for soil water maintenance and carbon sequestration. However, current understanding of these competing demands is limited. In this study, to quantify the trade-off resulting from land-use conversion (converting cropland into forest, shrub, and grassland) in the Loess Plateau, 2775 observations of soil organic carbon (SOC) stocks (to a depth of 100 cm) and 2654 observations of soil water storage (SWS) (to a depth of 500 cm) from peer-reviewed papers and measured data were synthesized. The results showed that (1) land-use conversion greatly influenced the trade-off, and in general, converting cropland into natural grassland and evergreen trees performed relatively better in carbon sequestration and soil water maintenance; (2) in rainfall zones less than 550 mm, natural grassland exhibited higher advantages in increasing SOC stock but maintained a lower SWS depletion, while forest was a better choice for rainfall greater than 550 mm; and (3) with increasing restoration age, SOC stock and SWS depletion both increased significantly; nevertheless, natural grassland appeared to be sustainable and stable to achieve a win–win result. Moreover, with increasing age, an accumulation of 0.7 Mg ha−1 SOC stock in the upper 100 cm was associated with an approximately 5.14 mm SWS decrease in the 0–500 cm soil layers. Overall, this study provides practical insights for land and water managers on how to achieve win–win results for soil- and water-related ecosystem services during ecological restoration in water-limited regions.

Trait and evolutionary differences among coexisting species are increasingly used to comprehend the processes shaping communities. However, they do not consistently yield congruent insights due to methodological limitations and scale dependence. Utilizing two plastid DNA genes (rbcL and matK) and one nuclear DNA gene (internal transcribed spacer, ITS), we first constructed the phylogenies of 147 woody species from 98 line transects in the forest areas of the Loess Plateau and subsequently measured three functional traits. Five plots (2500 m2) were constructed within Quercus forests to analyze the functional and phylogenetic structures at three spatial scales (100, 400, 2500 m2) and two vertical structural layers (tree colonization and shrub layer). In contrast to the phylogenetic convergence observed at the genus level, using plant DNA barcodes, we found that the entire forest communities and the tree layer exhibited phylogenetic randomness across all three spatial scales; even the shrub layer showed phylogenetic overdispersion with increasing scale. Specific leaf area (SLA) exhibited functional convergence in both the shrub and tree layers. In contrast, seed mass (SM) and plant height (PH) displayed distinct functional structures. In the tree layer, these traits showed phylogenetic overdispersion, while in the shrub layer, they demonstrated functional convergence. This contrast highlights the different ecological roles and processes at play in the two layers. Specifically, the scale dependency of assembly patterns in the shrub layer was more pronounced than in the tree layer for both functional and phylogenetic structures. Our findings underscore the significance of employing DNA barcodes to assess the phylogenetic structure of communities with closely related coexisting species and emphasize niche-based functional assembly and multi-process phylogenetic assembly among vertical structural layers in the Quercus community. Decoupling functional and phylogenetic disparities between species could facilitate the understanding of complex species differences influencing community assembly.

Declining water constraints at the cost of water storage for ecosystem on China's Loess Plateau.

Favorable climate conditions for rice cultivation existed 5000 years ago in the semi-arid Loess Plateau of China

Rainfall partitioning in the Robinia pseudodcacia plantations with different thinning intensities in the semiarid Loess Plateau of China