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Introduction: Soil microbial communities are key to functional processes in terrestrial ecosystems, and they serve as an important indicator of grasslands status. However, the responses of soil microbial communities and functional potential to drought stress in semiarid alpine grasslands remain unclear. Methods: Here, a field experiment was conducted under ambient precipitation as a control, -20% and -40% of precipitation to explore the responses of soil microbial diversity, community composition, and predicted functional potential to drought stress in a semiarid alpine grassland located in the northwest of China. Moreover, 16S rRNA gene and ITS sequencing were used to detect bacterial and fungal communities, and the PICRUST and FUNGuild databases were used to predict bacterial and fungal functional groups. Results: Results showed drought stress substantially changes the community diversity of bacteria and fungi, among which the bacteria community is more sensitive to drought stress than fungi, indicating that the diversity or structure of soil bacteria community could serve as an indicator of alpine grasslands status. However, the fungal community still has difficulty maintaining resistance under excessive drought stress. Our paper also highlighted that soil moisture content, plant diversity (Shannon Wiener, Pieiou, and Simpson), and soil organic matter are the main drivers affecting soil bacterial and fungal community composition and predicted functional potential. Notably, the soil microbial functional potential could be predictable through taxonomic community profiles. Conclusions: Our research provides insight for exploring the mechanisms of microbial community composition and functional response to climate change (longer drought) in a semiarid alpine grassland. [ABSTRACT FROM AUTHOR]

The plant is an important component of the riparian ecosystem, which could reflect both the environmental and functional characteristics of the riparian zone. Studies on species composition, diversity, community structure, distribution pattern, and adaptation strategies of plant communities in the riparian zone of the Three Gorges Reservoir (TGR) will help to explore the maintaining mechanism of the plant communities' ecological function under severe water-level fluctuation. The paper reviewed the plant community characteristics, functional traits as well as their eco-physiological responses and environmental adaptations in this special ecological zone. Based on this, future research orientations in this field were also prospected, which may focus on the maintenance mechanism of the plant community, suitable plants selection and their adaptation mechanism, the relationship between plant functional traits and ecosystem functions, plant niche in the riparian zone, and the connectivity of riparian zone to the surrounding environment. The results can promote the correlational research on plant communities in the riparian zone and deepen the understanding of ecosystem services the riparian ecotone provides. [ABSTRACT FROM AUTHOR]

This paper highlights the evolution and impact of the SWAP model (Soil – Water – Atmosphere – Plant), which was initiated by R.A. Feddes and colleagues fifty years ago, in 1974. Since then, the SWAP model has played a crucial role in the advancement of agrohydrology. This paper highlights some major advances that have been made, especially focussing on the last fifteen years. The domain of the SWAP model deals with the simulation of the soil water balance in both unsaturated and saturated conditions. The model solves the Richards equation using the water retention and hydraulic conductivity functions as described by the Van Genuchten – Mualem equations. Bimodal extensions of the Van Genuchten - Mualem relationships have been implemented, as well as modifications near saturation and addressing hysteresis. An important sink term in the Richards equation is root water uptake. Crop development plays an important role in a robust simulation of root water uptake. That is why a link has been made with the dynamic crop growth model WOFOST. Instead of using a prescribed crop development, a distinction between potential and actual crop development is calculated by reducing the potential photosynthesis as a result of water or oxygen stress. Since the early days of SWAP, empirical and macroscopic concepts have been used to simulate root water uptake. Recently two process-based concepts of root water uptake and oxygen stress have also been implemented. Another important sink-source term in the Richards equation is the interaction with artificial drains. In SWAP, drainage can be simulated by either using prescribed or simulated drain heads and simulation of controlled drainage with subirrigation is possible. Finally, we briefly elaborate on three studies using SWAP: water stresses in agriculture in the Netherlands, regional water productivity in China, and controlled drainage with subirrigation. We finish discussing promising developments for the near future. • Advances in soil-vegetation-atmosphere transfer modelling in the SWAP model. • Coupling of soil water dynamics with dynamic crop growth model. • Process-based root water uptake and oxygen uptake functions. • Climate-adaptive drainage with subirrigation. [ABSTRACT FROM AUTHOR]

To date, few attempts have been made to assess the influence of climate change on forest ecosystems and on the relationship between tree growth and climate in humid areas of low latitudes. In this paper, we studied the response of tree growth and forest ecosystem to climate change by using Fokienia hodginsii tree-ring cores from the northern Yunnan-Guizhou Plateau, southwest of China. Tree growth correlates the highest ( r = −0.64, p < 0.01) with mean temperature (July-September), but the coefficients were changing with time as revealed by a moving correlation analysis. Tree growth is significantly ( p < 0.05) and positively correlated with January-April mean temperature from AD 1961-1987, while correlations with precipitation are insignificant. In contrast, from 1988 to 2014, tree growth correlated negatively with mean temperature of previous summer and positively with precipitation of previous August-September. This indicated that the limiting factors for tree growth have changed under different climate conditions. The meteorological data suggested that from 1961 to 1987 it was cold and wet in the study area and radial growth is limited by winter and spring temperatures. This restriction is weaker if the climate is appropriate in general. However, from 1988 to 2014, the combined effects of recent warming and decreasing precipitation have led to an increasing response of tree-ring width to drought. In addition, a large proportion of mature F. hodginsii mortality occurred from 2007 to 2013, which corresponds with a drastic reduction of radial growth (narrowest in recent 100 years). The recent drought, induced by decreasing precipitation and increasing temperature, may have passed the threshold which F. hodginsii could tolerate, causing tree growth reduction, tree growth-climate relationship change, as well as catastrophic tree mortality. All these changes may lead to further responses of the local ecosystem to climate change which should be highly regarded. [ABSTRACT FROM AUTHOR]

As one of the three alpine flowers in the world and one of the ten traditional famous flowers in China, Rhododendron has high ornamental value and broad landscape applications. However, most of them are naturally distributed in high-altitude mountains, and they prefer cool and humid climate for the restriction of genetic mechanism. Drought is the key factor to restrict their ex-situ conservation and landscape application. As Rhododendron have many different species, cultivars and ecological types, distributed in a wide area, the mechanisms of different species or cultivars responses to drought stress are different. In this paper, how Rhododendron responses to drought stress and the effects of exogenous substances on improving the drought resistance of Rhododendron in China and abroad were reviewed from the aspects of seed germination, morphological and anatomical characteristics, physiological and biochemical parameters, gene expression, etc. In addition, the deficiency of current research and the future research directions were also discussed. It is proposed that the water use strategy and drought resistance mechanism of different ecological types and different drought resistances of Rhododendron should be future studied, as well as the gene regulation mechanism of mycorrhizal fungi for improving the drought resistance and the screening of excellent strains. This study provides the basis for the diversity conservation, the exploitation of drought resistance resources and the landscape applications of Rhododendron in China. [ABSTRACT FROM AUTHOR]

The main production area of Camellia vietnamensis (C. vietnamensis) is in the low mountain and hilly areas of southern China. The low survival rate of seedlings caused by drought is one of the main obstacles restricting the development of the C. vietnamensis industry. An exploration of the key adaptation mechanism of C. vietnamensis to drought stress is important in order to improve its drought resistance. We conducted a study on the morphological, physiological, biochemical, and drought resistance-related genes of five C. vietnamensis cultivars grown in Hainan province under varying degrees of drought stress. The results indicate that drought stress can lead to a decrease in the relative water content and photosynthetic capacity of C. vietnamensis leaves. Compared with the control, the drought damage index, malondialdehyde, relative electrical conductivity, soluble protein, soluble sugar and proline contents of the five C. vietnamensis cultivars increased with drought-stress duration and degree. With increasing drought-stress intensity, the activity of antioxidant enzymes and the content of related metabolites (total polyphenols, total flavonoids, tea saponins) gradually increased, and the expression levels of phenylpropanoid pathway-related genes (Cv4CL1, CvCAD1, CvCAD2, CvPOX1, CvPOX2, CvPOX3) were upregulated. Based on the results of the drought tolerance coefficients, principal component analysis, and hierarchical cluster analysis, we classified five C. vietnamensis cultivars into drought-tolerant cultivars ('Haida 1'); moderately drought-tolerant cultivars ('Haida 4' and 'Wanhai 4'); and drought-sensitive cultivars ('Wanhai 3' and 'Wanhai 1'). The results of this study provide a theoretical basis for the promotion and cultivation of C. vietnamensis and the selection of drought-resistant cultivars. [ABSTRACT FROM AUTHOR]

Background: Drought stress severely impedes plant growth, and only a limited number of species exhibit long-term resistance to such conditions. Pinus sylvestris var. mongolica, a dominant tree species in arid and semi-arid regions of China, exhibits strong drought resistance and plays a crucial role in the local ecosystem. However, the molecular mechanisms underlying this resistance remain poorly understood. Results: Here, we conducted transcriptome sequence and physiological indicators analysis of needle samples during drought treatment and rehydration stages. De-novo assembly yielded approximately 114,152 unigenes with an N50 length of 1,363 bp. We identified 6,506 differentially expressed genes (DEGs), with the majority being concentrated in the heavy drought stage (4,529 DEGs). Functional annotation revealed enrichment of drought-related GO terms such as response to water (GO:0009415: enriched 108 genes) and response to water deprivation (GO:0009414: enriched 106 genes), as well as KEGG categories including MAPK signaling pathway (K04733: enriched 35 genes) and monoterpenoid biosynthesis (K21374: enriched 27 genes). Multiple transcription factor families and functional protein families were differentially expressed during drought treatment. Co-expression network analysis identified a potential drought regulatory network between cytochrome P450 genes (Unigene4122_c1_g1) and a core regulatory transcription factor Unigene9098_c3_g1 (PsNAC1) with highly significant expression differences. We validated PsNAC1 overexpression in Arabidopsis and demonstrated enhanced drought resistance. Conclusions: These findings provide insight into the molecular basis of drought resistance in P. sylvestris var. mongolica and lay the foundation for further exploration of its regulatory network. [ABSTRACT FROM AUTHOR]

Pinus taeda is an important forest tree species for plantations because of its rapid growth and high yield of oleoresins. Although P. taeda plantations distribute in warm and wet southern China, drought, sometime serious and long time, often occurs in the region. To explore drought tolerance of P. taeda and usage of beneficial microorganisms, P. taeda seedlings were planted in pots and were inoculated with root endophytic fungus Serendipita indica and finally were treated with drought stress for 53 d. Metabolome and proteome of their needles were analyzed. The results showed that S. indica inoculation of P. taeda seedlings under drought stress caused great changes in levels of some metabolites in their needles, especially some flavonoids and organic acids. Among them, the levels of eriocitrin, trans-aconitic acid, vitamin C, uric acid, alpha-ketoglutaric acid, vitamin A, stachydrine, coumalic acid, itaconic acid, calceolarioside B, 2-oxoglutaric acid, and citric acid were upregulated more than three times in inoculated seedlings under drought stress, compared to those of noninoculated seedlings under drought stress. KEGG analysis showed that some pathways were enriched in inoculated seedlings under drought stress, such as flavonoid biosynthesis, ascorbate and aldarate metabolism, C5-branched dibasic acid metabolism. Proteome analysis revealed some specific differential proteins. Two proteins, namely, H9X056 and H9VDW5, only appeared in the needles of inoculated seedlings under drought stress. The protein H9VNE7 was upregulated more than 11.0 times as that of non-inoculated seedlings under drought stress. In addition, S. indica inoculation increased enrichment of water deficient-inducible proteins (such as LP3-1, LP3-2, LP3-3, and dehydrins) and those involved in ribosomal structures (such as A0A385JF23). Meanwhile, under drought stress, the inoculation caused great changes in biosynthesis and metabolism pathways, mainly including phenylpropanoid biosynthesis, cutin, suberine and wax biosynthesis, and 2-oxocarboxylic acid metabolism. In addition, there were positive relationships between accumulation of some metabolites and enrichment of proteins in P. taeda under drought stress. Altogether, our results showed great changes in metabolome and proteome in inoculated seedlings under drought stress and provided a guideline to further study functions of metabolites and proteins, especially those related to drought stress. [ABSTRACT FROM AUTHOR]

Plants of the Clematis genus are attractive ornamental plants due to their various flower colors and patterns, and they play an important role as ground cover plants in landscaping. However, the application of Clematis plants in landscaping in arid and semi-arid areas is limited. This study used five common wild Clematis species in Gansu Province as experimental materials, including Clematistangutica, Clematis glauca, Clematis intricata, Clematis nannophylla, and Clematis fruticosa. By simulating different intensities of drought stress with polyethylene glycol (PEG), the germination behavior of seeds and the physiological and biochemical responses of seedlings of these five species to drought stress were observed. The results showed that 15% PEG stress significantly inhibited the seed germination of the five species, which was also the drought threshold for seed germination of C. fruticosa. C. tangutica exhibited the strongest tolerance to drought stress in seed germination. Seedlings of the five Clematis plants showed different levels of tolerance to drought stress, mainly demonstrating higher tolerance to 10% and 20% concentrations of PEG stress, while a 30% concentration of PEG stress caused varying degrees of damage to the seedlings of the five Clematis species. PCA analysis indicated that seedlings of C. intricata and C. glauca had higher scores under drought stress. These findings can provide a theoretical basis for the selection of urban landscaping plant species in arid and semi-arid regions of northwest China. [ABSTRACT FROM AUTHOR]

Background: Cunninghamia lanceolata (Chinese fir), is one of the most important timber trees in China. With the global warming, to develop new resistant varieties to drought or heat stress has become an essential task for breeders of Chinese fir. However, classification and evaluation of growth status of Chinese fir under drought or heat stress are still labor-intensive and time-consuming. Results: In this study, we proposed a CNN-LSTM-att hybrid model for classification of growth status of Chinese fir seedlings under drought and heat stress, respectively. Two RGB image datasets of Chinese fir seedling under drought and heat stress were generated for the first time, and utilized in this study. By comparing four base CNN models with LSTM, the Resnet50-LSTM was identified as the best model in classification of growth status, and LSTM would dramatically improve the classification performance. Moreover, attention mechanism further enhanced performance of Resnet50-LSTM, which was verified by Grad-CAM. By applying the established Resnet50-LSTM-att model, the accuracy rate and recall rate of classification was up to 96.91% and 96.79% for dataset of heat stress, and 96.05% and 95.88% for dataset of drought, respectively. Accordingly, the R2 value and RMSE value for evaluation on growth status under heat stress were 0.957 and 0.067, respectively. And, the R2 value and RMSE value for evaluation on growth status under drought were 0.944 and 0.076, respectively. Conclusion: In summary, our proposed model provides an important tool for stress phenotyping in Chinese fir, which will be a great help for selection and breeding new resistant varieties in future. [ABSTRACT FROM AUTHOR]

Unpredictable drought–heatwave events occur frequently worldwide, causing low water availability (drought) and high temperatures (hot), with consequences for forest decline and mortality. Our knowledge of the potential instantaneous reactions and subsequent recovery of water-related physiological processes and vegetation indices in hot drought events remains unclear. Here, we investigated how the 2022 summer drought–heatwave event in the subtropical regions of China affected hydraulic traits and NDVI values in the forests of four common subtropical tree species. During the hot drought, the NDVI values of all four forests decreased (−31%~−23%), accompanied by leaf scorch and tree crown dieback. Among the four species, a hot drought event caused an instantaneous descent in hydraulic conductivity (Ks, −72%~−31%), stomatal conductance (gs, −94%~−50%), and midday water potential (−40%~−169%), with severe drought-induced stem xylem embolism. A trade-off was found between resistance and resilience in hot-drought-induced hydraulic dysfunction, as species with lower declines in Ks and gs during the hot drought had a shorter recovery in the post-stress phase. This study highlights that the 2022 hot drought event had severe negative instantaneous impacts on the forests of four subtropical tree species, which were reflected both in water-related physiological processes in the field and in remote sensing data from satellites. [ABSTRACT FROM AUTHOR]

Pinus massoniana is a major fast-growing timber tree species planted in arid areas of south China, which has a certain drought-resistant ability. However, severe drought and long-term water shortage limit its normal growth and development. Therefore, in this study, physiological indices, and the transcriptome sequencing and cloning of AP2/ERF transcription factor of P. massonsiana were determined to clarify its molecular mechanism of drought stress. The results showed that stomatal conductance (Gs) content was significantly decreased, and superoxide dismutase (SOD) activity, and malondialdehyde (MDA) and abscisic acid (ABA) content were significantly increased under drought stress. Transcriptomic analysis revealed that compared to the control, 9, 3550, and 4142 unigenes with differential expression were identified by comparing plants subjected to light, moderate or severe drought. AP2/ERF with high expression was screened out for cloning. To investigate the biological functions of ERF1, it was over-expressed in wild-type Populus davdianaand × P. bolleana via the leaf disc method. Under drought stress, compared to wild-type plants, ERF1 over-expressing poplar lines (OE) maintained a higher photosynthetic rate and growth, while the transpiration rate and stomatal conductance significantly decreased and water use efficiency was improved, indicating that drought tolerance was enhanced. This study provides an insight into the molecular mechanism of drought stress adaptation in P. massoniana. [ABSTRACT FROM AUTHOR]

Drought stress poses a serious threat to Pinus massoniana seedling growth in southern China. Trichoderma species, as beneficial microorganisms, have been widely used in agriculture to enhance plant growth and drought tolerance, but the interaction mechanisms remain unclear. To investigate the effect of drought-resistant Trichoderma longibrachiatum inoculation on P. massoniana growth under drought stress, the plant physiological indicators and rhizosphere microbiome diversity were measured to identify Trichoderma-activated mechanisms. Trichoderma longibrachiatum inoculation significantly promoted P. massoniana growth under drought treatment, and enhanced nitrogen, phosphorus, and potassium absorption compared with those of non-inoculated seedlings. Trichoderma longibrachiatum treatment alleviated the damage to cell membranes and needle tissue structure, and significantly increased antioxidant enzyme activities, osmotic substance contents, and photosynthesis in P. massoniana in response to drought stress. Soil nutrient contents, activities of sucrase, phosphatase, and urease as well as the relative abundances of the dominant genera Burkholderia, Rhodanobacter, and Trichoderma were elevated in the rhizosphere soil of P. massoniana inoculated with T. longibrachiatum under drought stress. A network analysis showed that certain crucial dominant taxa driven by T. longibrachiatum inoculation, including Penicillium, Trichoderma, Simplicillium, Saitozyma, Burkholderia, Bradyrhizobium, Sinomonas, and Mycobacterium, had more correlations with other microorganisms in the soil. Trichoderma longibrachiatum enhanced P. massoniana seedling growth under drought stress by regulating physiological responses and soil microbial community. [ABSTRACT FROM AUTHOR]

The plant cuticle is the outermost layer of the aerial organs and an important barrier against biotic and abiotic stresses. The climate varies greatly between the north and south of China, with large differences in temperature and humidity, but Chinese chestnut is found in both regions. This study investigated the relationship between the wax layer of chestnut leaves and environmental adaptation. Firstly, semi-thin sections were used to verify that there is a significant difference in the thickness of the epicuticular wax layer between wild chestnut leaves in northwest and southeast China. Secondly, a whole-genome selective sweep was used to resequence wild chestnut samples from two typical regional populations, and significant genetic divergence was identified between the two populations in the CmCER1-1, CmCER1-5 and CmCER3 genes. Thirty-four CER genes were identified in the whole chestnut genome, and a series of predictive analyses were performed on the identified CmCER genes. The expression patterns of CmCER genes were classified into three trends—upregulation, upregulation followed by downregulation and continuous downregulation—when chestnut seedlings were treated with drought stress. Analysis of cultivars from two resource beds in Beijing and Liyang showed that the wax layer of the northern variety was thicker than that of the southern variety. For the Y-2 (Castanea mollissima genome sequencing material) cultivar, there were significant differences in the expression of CmCER1-1, CmCER1-5 and CmCER3 between the southern variety and the northern one-year-grafted variety. Therefore, this study suggests that the CER family genes play a role in environmental adaptations in chestnut, laying the foundation for further exploration of CmCER genes. It also demonstrates the importance of studying the adaptation of Chinese chestnut wax biosynthesis to the southern and northern environments. [ABSTRACT FROM AUTHOR]

Background: Agroforestry has been advocated as a climate-smart agricultural approach to counter extreme climate and as an important sustainable intensification practice to meet Sustainable Development Goals (SDGs). However, its efficacy remains under dispute in drylands where resources, especially water, are limited. Aim and methods: This study aimed to study how annual bioenergy crops, soybean (Glycine max) and canola (Brassica rapa), influence soil water availability and fine root distribution in a young apple orchard exposed to varying to drought intensity on the semiarid Loess Plateau of China. Drought was simulated by reducing natural precipitation by 15% (moderate drought) and 25% (severe drought). Result and conclusions: Intercropping soybean and canola increased the fine root biomass (FRB) of apple trees in the 80–180 cm soil layer, improved moisture status below the 80 cm soil layer in the wet season, and promoted apple tree growth. Under moderate drought, FRB in the 0–80 cm soil layer increased, making use of the shallow soil water replenished by precipitation. However, the trees switched to absorbing soil water in the 80–180 cm in the dry season. Under severe drought, the apple trees increased FRB in the 0–80 cm and 180–280 cm soil layers and increased the proportion of the total roots in the 180–280 cm layer, aggravating the deep soil desiccation and inhibiting apple tree growth. These findings offer insights into drought effects on root plasticity and soil management practices in rainfed orchards. [ABSTRACT FROM AUTHOR]

Drought-induced forest canopy die-back and tree mortality have been commonly recorded in the lithoid mountainous regions of northern China. However, the capacity of trees to regulate their carbon and water balance in response to drought remains inadequately understood. We measured tree growth, intrinsic water use efficiency (iWUE), vulnerability, and canopy health during drought events using dendrochronology, C isotope measurements, and a tree canopy health survey in a mixed plantation of Quercus variabilis and Robinia pseudoacacia. Resistance (Rt), recovery (Rc), resilience (Rs), and increased amplitude in iWUE compared to the indices 3 years before drought (iWUEr) were calculated for each species across the dominant tree (D), codominant tree (CD), and suppressed tree (S). Our results revealed that D and CD showed lower Rt, higher Rc, and higher iWUEr than S. After exposure to multiple sequential drought events, Q. variabilis showed an increasing trend in Rt, and R. pseudoacacia showed a decreasing trend in Rc. R. pseudoacacia exhibited a more conservative strategy towards drought, resulting in a negative SRt-iWUEr (slope of the linear model fitted to capture the trend between Rt and iWUEr) during drought events than Q. variabilis. For individual trees, lower Rc or positive SRt-iWUEr Q. variabilis and negative SRt-iWUEr R. pseudoacacia were more susceptible to canopy die-back. In conclusion, our study offers a new perspective for improved management practices in the design of silvicultural actions for forestry plantations in lithoid mountainous areas with increasing drought risk. [ABSTRACT FROM AUTHOR]

In heterogeneous landscapes with temporary water deficit characteristics in southwestern China, understanding the electrophysiological and morphological characteristics of Bletilla striata under different water conditions can help to better evaluate its suitability for planting plants in specific locations and guide planting and production. Using B. striata seedlings as experimental materials, the maximum field capacity (FC) was 75–80% (CK: control group), 50–60% FC (LS: light drought stress), 40–45% FC (MS: moderate drought stress), and 30–35% FC (SS: severe drought stress). In terms of physiological response, the activities of peroxidase (POD) and catalase (CAT) decreased under drought conditions, but the activity was well under the LS treatment, and the contents of proline (Pro) and malondialdehyde (MDA) increased. In terms of morphological responses, under drought conditions, root lengths of the rhizomes (except the LS treatment) were significantly reduced, the leaf lengths were reduced, and the biomass was significantly reduced. The stomatal size reached the maximum under the LS treatment, and the stomatal density gradually decreased with the increase in drought degree. In terms of electrophysiological responses, drought significantly decreased the net photosynthetic rate (PN) of B. striata, stomatal conductance (gs), and transpiration rate (Tr), but effectively increased the water use efficiency (WUE). The effective thickness of leaves of B. striata increased under drought conditions, and drought promoted the formation of leaf morphological diversity. Our results showed that drought stress changed the physiological and morphological characteristics of B. striata, and under light drought conditions had higher physiological activity, good morphological characteristics, higher cellular metabolic energy and ecological adaptability. Appropriate drought can promote the improvement of the quality of B. striata, and it can be widely planted in mildly arid areas. [ABSTRACT FROM AUTHOR]

Dark septate endophytes (DSEs) usually colonize plant roots, especially in stress environments. However, their relationship with plants ranges from beneficial to harmful and has remained largely uncharacterized. In the present study, 14 DSE species grouped into 11 genera were isolated from the roots of a desert plant, Artemisia ordosica, which is widely distributed in northwest China. Three dominant DSE species—Paraphoma chrysanthemicola (Pc), Alternaria chartarum (Ac), and Acrocalymma vagum (Av)—were selected and tested for their resistance to drought in vitro. Furthermore, we characterized the responses of A. ordosica under drought conditions in relation to the presence of these DSEs following inoculation. The results showed that all three strains grew well under in vitro drought stress, and the biomass of Ac and Av was significantly higher than that of the unstressed control. The effects of DSE inoculation on the growth of A. ordosica under drought stress varied according to the different DSE species but were generally beneficial. Under drought stress, Av and Pc promoted plant growth, antioxidant enzyme activity, and root development of the hosts. The Ac strain conferred obvious positive effects on the antioxidant enzyme activity of the hosts. In general, Av and Pc demonstrated better application potential for improving the drought resistance of A. ordosica. [ABSTRACT FROM AUTHOR]

Drought is the main limiting factor for plant growth in karst areas with a fragile ecological environment. Cinnamomum migao H.W. Li is an endemic medicinal woody plant present in the karst areas of southwestern China, and it is endangered due to poor drought tolerance. Arbuscular mycorrhizal fungi (AMF) are known to enhance the drought tolerance of plants. However, few studies have examined the contribution of AMF in improving the drought tolerance of C. migao seedlings. Therefore, we conducted a series of experiments to determine whether a single inoculation and coinoculation of AMF (Claroideoglomus lamellosum and Claroideoglomus etunicatum) enhanced the drought tolerance of C. migao. Furthermore, we compared the effects of single inoculation and coinoculation with different inoculum sizes (20, 40, 60, and 100 g; four replicates per treatment) on mycorrhizal colonization rate, plant growth, photosynthetic parameters, antioxidant enzyme activity, and malondialdehyde (MDA) and osmoregulatory substance contents. The results showed that compared with nonmycorrhizal plants, AMF colonization significantly improved plant growing status; net photosynthetic rate; superoxide dismutase, catalase, and peroxidase activities; and soluble sugar, soluble protein, and proline contents. Furthermore, AMF colonization increased relative water content and reduced MDA content in cells. These combined cumulative effects of AMF symbiosis ultimately enhanced the drought tolerance of seedlings and were closely related to the inoculum size. With an increase in inoculum size, the growth rate and drought tolerance of plants first increased and then decreased. The damage caused by drought stress could be reduced by inoculating 40–60 g of AMF, and the effect of coinoculation was significantly better than that of single inoculation at 60 g of AMF, while the effect was opposite at 40 g of AMF. Additionally, the interaction between AMF and inoculum sizes had a significant effect on drought tolerance. In conclusion, the inoculation of the AMF (Cl. lamellosum and Cl. etunicatum) improved photosynthesis, activated antioxidant enzymes, regulated cell osmotic state, and enhanced the drought tolerance of C. migao, enabling its growth in fragile ecological environments. [ABSTRACT FROM AUTHOR]

China, particularly the cotton-growing province of Xinjiang, is experiencing acute agricultural water shortages, stifling the expansion of the cotton sector. Discovering drought resistance genes in cotton and generating high-quality, drought-resistant cotton varieties through molecular breeding procedures are therefore critical to the cotton industry's success. The drought-resistant cotton variety Xinluzhong No. 82 and the drought-sensitive cotton variety Kexin No. 1 were utilised in this study to uncover a batch of drought-resistant candidate genes using whole transcriptome sequencing. The following are the key research findings: A competing endogenous RNA network (ceRNA) was built using complete transcriptional sequencing to screen the core genes in the core pathway, and two drought-related candidate genes were discovered. It was found that γ-aminobutyric acid aminotransferase (GhGABA-T, Gohir.A11G156000) was upregulated at 0 h vs. 12 h and downregulated at 12 h vs. 24 h. L-Aspartate oxidase (GhAO, Gohir.A07G220600) was downregulated at 0 h vs. 12 h and upregulated at 12 h vs. 24 h. GABA-T is analogous to a pyridoxal phosphate-dependent transferase superfamily protein (POP2) in Arabidopsis thaliana and influences plant drought resistance by controlling γ-aminobutyric acid (GABA) concentration. The analogue of GhAO in A. thaliana is involved in the early steps of nicotinamide adenine dinucleotide (NAD) production as well as in plant antioxidant responses. This study revealed that gene expression regulatory networks can be used for rapid screening of reliable drought resistance genes and then utilised to validate gene function. [ABSTRACT FROM AUTHOR]

Under extreme drought and climate change, golden pear trees have experienced problems such as yield reduction, dryness and death. This suggests that we know very little about the mechanisms regulating pear tree growth, assuming that meteorological factors positively influence plant sap flow. Based on this, we used the heat ratio method to monitor the sap flow of pear trees from June to December 2020, and recorded the changes in various environmental factors. The results showed that: (1) Sap flow velocity has obvious radial variability in tree sections; the sap flow velocity during the day was significantly higher than that at night (p < 0.05) and was higher in the growing season than in the non-growing season. (2) All environmental factors, except relative humidity and precipitation, were positively correlated with sap flow, vapor pressure deficit and photosynthetically active radiation, which are the key factors affecting daytime flow, and vapor pressure deficit and plant water potential are the key factors affecting nighttime flow. The linear regression results also showed that the daytime sap flow had a significant positive effect on the nighttime sap flow (p < 0.05). (3) The contribution of night flow to total daily flow varied from 17.3% to 50.7%, and most of the non-growing season values were above 40%. The results show that nighttime sap flow accounts for a significant portion of the pear tree's water budget. Continuous irrigation during fruit enlargement and non-growing seasons will increase fruit yield and maintain plant sap flow activity to avoid death due to drought. [ABSTRACT FROM AUTHOR]

Extensive studies have shown that the success of invasive plants in large environmental gradients can be partly attributed to related factors, including phenotypic plasticity and rapid evolution. To enhance their ability to compete and invade, invasive plants often show higher morphological and physiological plasticity to adapt to different habitat conditions. In the past two decades, invasive species have expanded to some new habitats in North and Northwest China, including arid oasis agricultural zones, which are disturbed by human activities, and the ecosystem itself is very fragile. To evaluate the ecological adaptability of invasive plants widely distributed in North and Northwest China, we studied the physiological response and tolerance mechanism of different geographical populations of Solanum rostratum Dunal to different drought-stress gradients in extremely arid regions (Xinjiang population) and semi-arid regions (Inner Mongolia population). The results showed that with the aggravation of drought stress, S. rostratum from different geographical populations adopted different physiological mechanisms to drought stress. Xinjiang population was mostly affected by root/shoot ratio and chlorophyll fluorescence characteristics, showing higher plasticity in the net and total photosynthetic rates, while the Inner Mongolia population mainly relied on the accumulation of osmotic adjustment substances, higher leaf dry matter content, and increased malondialdehyde to cope with drought stress. Based on these results, we concluded that the physiological responses of S. rostratum invading different habitats in northern China to drought stress were significantly different. The drought resistance of the Xinjiang population was higher than that of the Inner Mongolia population. In general, S. rostratum can be widely adapted to both harsh and mild habitats through phenotypic plasticity, threatening agricultural production and ecological environment security in northern China. [ABSTRACT FROM AUTHOR]

This study aimed to explore dark septate endophytes (DSE) that may improve the cultivation of medicinal plants in arid ecosystems. We isolated and identified eight DSE species (Acremonium nepalense , Acrocalymma vagum , Alternaria chartarum , Alternaria chlamydospora , Alternaria longissima , Darksidea alpha , Paraphoma chrysanthemicola , and Preussia terricola) colonizing the roots of wild licorice (Glycyrrhiza uralensis) in the desert areas of northwest China. Moreover, we investigated the osmotic stress tolerance of the DSE using pure culture, along with the performance of licorice plants inoculated with the DSE under drought stress in a growth chamber, respectively. Here, five species were first reported in desert habitats. The osmotic-stress tolerance of DSE species was highly variable, A. chlamydospora and P. terricola increased the total biomass and root biomass of the host plant. All DSE except A. vagum and P. chrysanthemicola increased the glycyrrhizic acid content; all DSE except A. chartarum increased the glycyrrhizin content under drought stress. DSE × watering regimen improved the glycyrrhizic acid content, soil organic matter, and available nitrogen. Structural equation model analysis showed that DSE × watering regimen positively affected soil organic matter, and total biomass, root length, glycyrrhizic acid, and glycyrrhizin (Shapotou site); and positively affected soil organic matter, available phosphorus, and glycyrrhizin (Minqin site); and positively affected the root length (Anxi site). DSE from the Shapotou site accounted for 8.0, 13.0, and 11.3% of the variations in total biomass, root biomass, and active ingredient content; DSE from the Minqin site accounted for 6.6 and 8.3% of the variations in total biomass and root biomass; DSE from the Anxi site accounted for 4.2 and 10.7% of the variations in total biomass and root biomass. DSE × watering regimen displayed a general synergistic effect on plant growth and active ingredient contents. These findings suggested that the DSE–plant interactions were affected by both DSE species and DSE originating habitats. As A. chlamydospora and P. terricola positively affected the total biomass, root biomass, and active ingredient content of host plants under drought stress, they may have important uses as promoters for the cultivation of licorice in dryland agriculture. [ABSTRACT FROM AUTHOR]

Autophagy has been reported to be an adapt function of plant cells under various stresses. In this report, autophagy-related gene expressions and carbohydrate concentrations in Caragana korshinskii leaf cells under drought stress were investigated. Leaf samples of C. korshinskii plants of an estimated 15-year-old were collected from three sites with different drought stress (annual precipitation range, 325.8 to 440.8 mm) at the Loess Plateau in northwestern China. Autophagy was observed in C. korshinskii samples from all three sites and was revealed by autophagosomes in the cytoplasm of mesophyll cells and increased chloroplasts degradation observed by transmission electron microscopy. Furthermore, with the drought stress increase, autophagy-related gene expressions were upregulated and leaf concentration of sucrose was increased, while concentrations of monosaccharide sugars such as glucose, fructose and galactose were decreased. The results suggested that drought stress induced autophagy gene expression, which may serve as a survival mechanism for nutrient remobilisation. [ABSTRACT FROM AUTHOR]

Background: Raw second-generation (2G) lignocellulosic biomass materials have the potential for development into a sustainable and renewable source of energy. Poplar is regarded as a promising 2G material (P. davidiana Dode×P. bolleana Lauch, P. bolleana, P. davidiana, P. euphratica, et al). However, their large-scale commercialization still faces many obstacles. For example, drought prevents sufficient irrigation or rainfall, which can reduce soil moisture and eventually destroy the chloroplast, the plant photosynthetic organelle. Heterosis is widely used in the production of drought-tolerant materials, such as the superior clone "Shanxinyang" selected from the offspring of Populus davidiana Dode×Populus bolleana Lauch. Because it produces good wood and is easily genetically transformed, "Shanxinyang" has become a promising material for use in tree genetics. It is also one of the most abundant biofuel plants in northern China. Understanding the genetic features of chloroplasts, the cp transcriptome and physiology is crucial to elucidating the chloroplast drought-response model. Results: In this study, the whole genome of "Shanxinyang" was sequenced. The chloroplast genome was assembled, and chloroplast structure was analysed and compared with that of other popular plants. Chloroplast transcriptome analysis was performed under drought conditions. The total length of the "Shanxinyang" chloroplast genome was 156,190 bp, the GC content was 36.75%, and the genome was composed of four typical areas (LSC, IRa, IRb, and SSC). A total of 114 simple repeats were detected in the chloroplast genome of "Shanxinyang". In cp transcriptome analysis, we found 161 up-regulated and 157 down-regulated genes under drought, and 9 cpDEGs was randomly selected to conduct reverse transcription (RT)–qPCR., in which the Log2 (fold change) was significantly consistent with the qPCR results. The analysis of chloroplast transcription under drought provided clues for understanding chloroplast function under drought. The phylogenetic position of "Shanxinyang" within Populus was analysed by using the chloroplast genome sequences of 23 Populus plants, showing that "Shanxinyang" belongs to Sect. Populus and is sister to Populus davidiana. Further, mVISTA analysis showed that the variation in non-coding (regulatory) regions was greater than that in coding regions, which suggests that further attention should be paid to the chloroplast in order to obtain new evolutionary or functional insights related to aspects of plant biology. Conclusions: Our findings indicate that complex prokaryotic genome regulation occurs when processing transcripts under drought stress. The results not only offer clues for understanding the chloroplast genome and transcription features in woody plants but also serve as a basis for future molecular studies on poplar species. [ABSTRACT FROM AUTHOR]

The soils in karst regions, with carbonate rocks as the background material, are characterized by two main factors, drought and high calcium levels. Handeliodendron bodinieri (Levl.) Rehd is an endemic plant species in this area of China. However, few studies have been carried out on the adaptation mechanism of H. bodinieri to drought and high calcium soil. To reveal the physiological responses of H. bodinieri to exogenous calcium under drought stress, 10% PEG-6000 was used to simulate drought stress, and the effects of exogenous calcium at different concentrations on the physiology of H. bodinieri seedlings under drought stress were studied. The results showed that drought stress significantly reduced the relative water content and water potential of H. bodinieri seedlings. Malondialdehyde (MDA) content, O2– and H2O2 production rates significantly increased under drought stress. The addition of exogenous calcium significantly reduced MDA content and O2– and H2O2 production rates. Moreover, peroxidase (POD), superoxide dismutase (SOD), catalase (CAT), ascorbic acid peroxidase (APX) and glutathione peroxidase (GPX) activities increased significantly under drought stress. At the same time, the accumulation of osmotic regulators such as soluble sugar, betaine and free proline also increased significantly. The addition of exogenous calcium further increased the activity of antioxidant enzymes and the accumulation of osmotic regulatory substances. Consequently, the oxidative stress and osmotic stress induced by drought decreased. Finally, exogenous calcium enhanced the photosynthetic rate (Pn), stomatal conductance (Gs) and transpiration rate (Tr) of H. bodinieri under drought stress and significantly improved water use efficiency (WUE). This study confirmed that the application of exogenous calcium can enhance the water condition, photosynthetic capacity, osmotic regulation and antioxidant capacity of H. bodinieri under drought stress. Of the treatments, the 10 mmol·L-1 CaCl2 treatment is more likely to improve survival of H. bodinieri under drought tolerance. This study provides an important reference for describing the adaptation mechanism and appropriate conservation of H. bodinieri under drought and high calcium conditions. [ABSTRACT FROM AUTHOR]

Background and aims: Variations in plant nitrogen (N) and phosphorus (P) concentrations and ratios have great implications for primary productivity and nutrient cycling. Here, we reported their changes at functional group and community levels along an aridity gradient. Methods: We carried out a field investigation and set up 26 sampling sites along a transect in the drylands of northern China to examine the responses of plant nutrient status to increasing aridity and the relationships between plant and soil nutrients. Results: The responses of N and P concentrations to increasing aridity differed between woody (sub-) shrubs and herbaceous species (including annual/biennial forbs and grasses, perennial forbs and perennial grasses). Nitrogen and P concentrations of shrubs decreased while those of herbs generally increased with increasing aridity. Plant N:P ratios increased significantly with increasing aridity for the plant functional groups and at the community level. At both organizational levels, nutrient concentrations in plants were negatively related to those in soils. Conclusion: Our results indicated that the responses of plant nutrition to aridity were dependent on plant functional group. Plant growth appeared increasingly limited by P, and plant and soil nutrients become increasingly decoupled at large spatial scale with increasing aridity. [ABSTRACT FROM AUTHOR]

Increased attention has been paid to effects of coal mining subsidence on the growth of plants. Studying the changes of plants photosynthetic physiology under the disturbance of coal mining subsidence is the basis for understanding dynamic exchanges of plant energy and water at that mining area. The 52302 working face of the Shendong mining area was selected as the experimental site, with Artemisia ordosica, Caragana korshinskii, and Populus spp. as the research targets. Changes in leaf photosynthesis were monitored in plants at a subsidence crack area. We showed collapse cracks decreased soil moisture and caused drought stress. The photosynthetic capacity of leaves was reduced. Compared with plants from the control area, stomatal conductance, photosynthetic CO2 assimilation, and transpiration rate were reduced in all three plant species. The activity of PSII reaction center and electron transport at the donor and acceptor sites significantly decreased. [ABSTRACT FROM AUTHOR]

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Chloris virgata is considered a useful grass species for grassland restoration in northern China. However, little information exists concerning the germination responses of this species to temperature and water potential caused by stress conditions. Experiments were conducted in growth chambers to assess the effect of temperature, salinity, alkalinity, drought and the interactions of temperature and stress on seed germination. Seeds were germinated at three diurnal temperature regimes, with four water potentials in NaCl, Na HCO3 and PEG solutions. Results showed that optimal germination under stress occurred at 15-25 °C, and germination percentages and rates were inhibited by either an increase or decrease in temperature from the optimal temperature. The inhibitory effects of the low water potential caused by salinity and drought on germination were greater at 25-35 °C, but seeds were subjected to more stress despite the relatively higher water potential because of the alkalinity at this temperature. The recovery percentage under salinity was highest at −1·2 MPa at 15-25 °C, and more than 80% of seeds also germinated at this water potential after they were transferred from drought stress. However, seeds lost their viability in higher alkalinities under all temperatures, and at 25-35 °C, there was lower recovery percentage under stress. Results suggest that salinity, alkalinity and drought stress have different impacts on seed germination, and the tolerance to stress of C. virgata seeds is affected by the interactions of temperature and water potential caused by salinity, alkalinity and drought. Chloris virgata shows potential utility as a promising grass species in salinity-alkalinity and drought-stressed environments. [ABSTRACT FROM AUTHOR]

Aquaporins are a specific type of membrane channel proteins that efficiently transport water molecules and other small molecular substrates in plants. In this study, we isolated the plasma membrane aquaporin gene EuPIP1;2 from Eucommia ulmoides, an important medicinal plant in China. The EuPIP1;2 protein was localized on the plasma membrane. Quantitative RT-PCR analysis revealed that EuPIP1;2 was constitutively expressed in all analyzed tissues, with the highest expression levels detected in the fruit and root. Overexpression of EuPIP1;2 in transgenic tobacco enhanced plant tolerance of drought and salinity. Under drought and salt stress, the transgenic lines exhibited higher percentage germination, longer roots, and enhanced percentage survival compared with wild-type plants. The contents of malonaldehyde and proline suggested that EuPIP1;2 improved drought and salt tolerance in transgenic lines by reducing damage to membranes and improving osmotic adjustment. We predict that EuPIP1;2 could be applied to improve drought and salt tolerance in transgenic plants. [ABSTRACT FROM AUTHOR]

Genotypic variations of alfalfa (Medicago sativa L.) to both phosphorus (P) deficiency and water deficiency are evident on the Loess Plateau of China. Here, we compare the adaptive mechanisms between an introduced cultivar (Arkaxiya) and a landrace (Longzhong) subjected to P- and water-limited conditions. The two genotypes were grown in a soil medium with 0, 4.2, 8.4 and 16.8 μg applied P per gram dry soil. Three water treatments were imposed (maintained at 75–90%, 45–55% and 30–35% of pot capacity (PC)) 28 days after sowing (DAS). At high soil P and high soil water content (SWC), high rates of net photosynthesis (Pn) contributed to greater plant growth and P-use efficiency (PUE) in the introduced Arkaxiya compared to the landrace Longzhong. However, at low SWC, Longzhong had enhanced antioxidative defense (mainly SOD and CAT) compared to Arkaxiya. In addition, shorter shoot length and greater branching in Longzhong than Arkaxiya may also facilitate adaptation to low SWC. The contrasting adaptive mechanisms of the two genotypes provide a number of early-screening parameters associated with plant growth for the selection and introduction of alfalfa targeted at different rainfall and available P environments. [ABSTRACT FROM AUTHOR]

In the process of biological invasion, hybridization between invasive species and native species is very common, which may lead to the formation of hybrids with a stronger adaptability. The hybrid of Wedelia trilobata (an alien invasive species) and Wedelia chinensis (an indigenous congener) has been found in South China. In our previous study, we found that the hybrid showed heterosis under cadmium stress. However, the results of this experiment demonstrated that the leaves of the hybrid had no heterosis in controlling water loss. The results showed that the water loss rate of W. trilobata was the slowest, that of W. chinensis was the fastest, and that of the hybrid was in the middle. Compared with W. chinensis and the hybrid, W. trilobata accumulated more abscisic acid (ABA) in leaves to control water loss. After the leaves were detached, W. chinensis leaves suffered the most serious damage, the lowest maximum photochemical efficiency, the most serious membrane lipid peroxidation, and the largest accumulation of malondialdehyde and reactive oxygen species. Compared with W. chinensis and its hybrid, the leaves of W. trilobata could accumulate more antioxidant enzymes and antioxidants, and the total antioxidant capacity was the strongest. The results demonstrate that the ability of the hybrid to reduce water loss was lower than that of W. trilobata, but higher than that of W. chinensis. They showed that the drought resistance of the hybrid may be higher than that of W. chinensis, and it might threaten the survival of W. chinensis. [ABSTRACT FROM AUTHOR]

Drought stress, especially during the seedling stage, seriously limits the growth of maize and reduces production in the northeast of China. To investigate the molecular mechanisms of drought response in maize seedlings, proteome changes were analyzed. Using an isotopic tagging relative quantitation (iTRAQ) based method, a total of 207 differentially accumulated protein species (DAPS) were identified under drought stress in maize seedlings. The DAPS were classified into ten essential groups and analyzed thoroughly, which involved in signaling, osmotic regulation, protein synthesis and turnover, reactive oxygen species (ROS) scavenging, membrane trafficking, transcription related, cell structure and cell cycle, fatty acid metabolism, carbohydrate and energy metabolism, as well as photosynthesis and photorespiration. The enhancements of ROS scavenging, osmotic regulation, protein turnover, membrane trafficking, and photosynthesis may play important roles in improving drought tolerance of maize seedlings. Besides, the inhibitions of some protein synthesis and slowdown of cell division could reduce the growth rate and avoid excessive water loss, which is possible to be the main reasons for enhancing drought avoidance of maize seedlings. The incongruence between protein and transcript levels was expectedly observed in the process of confirming iTRAQ data by quantitative real-time polymerase chain reaction (qRT-PCR) analysis, which further indicated that the multiplex post-transcriptional regulation and post-translational modification occurred in drought-stressed maize seedlings. Finally, a hypothetical strategy was proposed that maize seedlings coped with drought stress by improving drought tolerance (via. promoting osmotic adjustment and antioxidant capacity) and enhancing drought avoidance (via. reducing water loss). Our study provides valuable insight to mechanisms underlying drought response in maize seedlings. [ABSTRACT FROM AUTHOR]

The drought resistance mechanism of Matteuccia struthiopteris (L.) Todar. and Athyrium multidentatum (Doll.) Ching were measured under natural drought exposure. The results showed that the two edible fern species showed stronger resistance in the early stages of drought, mainly expressed as the decrease of relative leaf water content (RLWC), increase of osmotic substances, secondary metabolites such as flavonoids (FC), total phenols (TPC), proantho cyanidins (PCC) content and enzyme activity (superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX)). The higher RLWC, FC, TPC, PCC and abscisic acid (ABA) content and lower H2O2 content indicates the stronger non-enzymatic antioxidant system and drought resistance of A. multidentatum. However, the proline (Pro) content changed slowly, and the synthesis of soluble protein (SP), total phenols, proantho cyanidins and ABA, SOD activity of two fern species were inhibited in the late stages of drought stress. This study can provide a scientific basis for the cultivation and utilization of edible fern species under forest in Northeast China. [ABSTRACT FROM AUTHOR]