Optimization of Groundwater Exploitation in an Irrigation Area in the Arid Upper Peacock River, NW China: Implications for Sustainable Agriculture and Ecology

Groundwater is the main irrigation water source in the Upper Peacock River. As fast enlargement of irrigation areas continues in recent years, the groundwater level declines continuously and has posed a threat to the sustainability of local agriculture and ecology. A numerical model was established with the code MODFLOW–2000 in order to predict the declining trend of groundwater level and formulate measures to counter the overexploitation, in which the river–aquifer interaction was elaborated and characterized by field survey. The results show that under current intensity of groundwater withdrawal, the levels of both unconfined and confined waters would decline continuously in 7 years from 2015. To stop the groundwater level from declining on the regional scale, the withdrawal rate should be compressed by 45% with respect to that in 2015. Moreover, taking consideration of the constraint of maintaining the ecological water level in the vicinity of the Euphrates Poplar forest in the study area, the withdrawal rate should be compressed 70% for seven towns around the forest.

Tree mortality and regeneration of Euphrates poplar riparian forests along the Tarim River, Northwest China

Background Tree mortality and regeneration (seedling and sapling recruitment) are essential components of forest dynamics in arid regions, especially where subjected to serious eco-hydrological problems. In recent decades, the mortality of the Euphrates poplar (Populus euphratica) along the Tarim River in Northwest China has increased. However, few studies have quantified the causes of mortality and regeneration in this azonal riparian forest type. Methods The present study describes the annual hydrological response of tree mortality and regeneration in forest gaps. A total of 60 canopy gaps were investigated in six replicate grid plots (50 m × 50 m) and the annual runoff and water consumption data during the period of 1955–2016 were collected from hydrological stations in the middle reaches of the Tarim River. We compared the regeneration density of seedlings and saplings within the canopy gap areas (CGAs), undercanopy areas (UCAs), and uncovered riverbank areas (RBAs) through detailed field investigation. Results Our study found that the mortality of young and middle-aged gap makers has increased remarkably over recent decades, particularly since the year 1996. The main results indicated that regional water scarcity was the primary limiting factor for long-term changes in tree mortality, as shown by a significant correlation between the diameter at breast height (DBH) of dead trees and the annual surface water. The average density (or regeneration rate) of seedlings and saplings was highest in the RBAs, intermediate in the CGAs, and lowest in the UCAs. Compared with the UCAs, the CGAs promote tree regeneration to some extent by providing favorable conditions for the survival and growth of seedlings and saplings, which would otherwise be suppressed in the understory. Furthermore, although the density of seedlings and saplings in the CGAs was not as high as in the RBAs, the survival rate was higher in the CGAs than in the RBAs. Conclusion Forest canopy gaps in floodplain areas can play a decisive role in the long-term germination and regeneration of plant species. However, as a typical phreatophyte in this hyper-arid region, the ecosystem structure, functions and services of this fragile P. euphratica floodplain forests are threatened by a continuous decrease of water resources, due to excessive water use for agricultural irrigation, which has resulted in a severe reduction of intact poplar forests. Furthermore, the survival of seedlings and saplings is influenced by light availability and soil water at the regional scale. Our findings suggest that policymakers may need to reconsider the restoration and regeneration measures implemented in riparian P. euphratica forests to improve flood water efficiency and create canopy gaps. Our results provide with valuable reference information for the conservation and sustainable development of floodplain forest ecosystems.

Tree Mortality and Regeneration in Euphrates Poplar Riparian Forests Along the Tarim River, Northwest China

BackgroundTree mortality and seedling and sapling recruitment are essential components of forest dynamics in arid regions, especially those with serious eco-hydrological problems. In recent decades, the mortality of the Euphrates poplar ( Populus euphratica ) along the Tarim River in Northwest China has increased. However, few studies have quantified the causes of mortality and regeneration in this azonal riparian forest type. MethodsThe present paper describes the annual hydrological response of tree mortality and regeneration in forest gaps. A total of 60 canopy gaps were investigated in six replicate grid plots (50 m × 50 m) and the annual runoff and water consumption data during the period of 1955–2016 were collected from hydrological stations along the middle reaches of the Tarim River. In addition, we compared the regeneration density of seedlings and saplings within the canopy gap areas (CGAs), undercanopy areas (UCAs), and uncovered riverbank areas (RBAs) through detailed field investigation. ResultsOur study found that the mortality of young and middle aged gap makers has increased markedly over recent decades, particularly since 1996. The main results indicated that regional water scarcity was the primary limiting factor for long-term changes in tree mortality, as shown by a significant correlation between the diameter at breast height (DBH) of dead trees and the annual surface water. The average density (or regeneration rate) of seedlings and saplings was highest in the RBAs, intermediate in the CGAs, and lowest in the UCAs. Compared with the UCAs, the CGAs promote tree regeneration to some extent by providing favorable conditions for the survival and growth of seedlings and saplings, which would otherwise be suppressed in the understory. Furthermore, although the density of seedlings and saplings in the CGAs was not as high as in the RBAs, the survival rate was higher in the CGAs than in the RBAs. ConclusionThis study shows that forest canopy gaps can play a decisive role in the long-term germination and regeneration of plant species. However, as a typical phreatophyte in this hyper-arid region, the ecosystem structure, functions and services of this fragile P. euphratica , floodplain forests are threatened by a continuous decrease of water resources, due to excessive water use for monocultural cotton irrigation, which has resulted in a severe reduction in intact poplar forests. Furthermore, the survival of seedlings and saplings is influenced by light availability and soil water at the regional scale. Our findings suggest that policymakers may need to reconsider the restoration and regeneration measures implemented in riparian P. euphratica forests to improve flood water efficiency and create canopy gaps. Our results provide valuable reference information for the conservation and sustainable development of floodplain forest ecosystems.

The Preliminary Study on Bare Spots Under Populus Euphratica Canopy

Land degradation and desertification are the great concern of arid and semiarid areas. In Euphrates poplar forest, there exists large number of bare spots which have been considered as representative of desertification. In this study, Unmanned Aerial Vehicle (UAV) technology was used to determine the spatial distribution and extract the bare spots area and morphological characteristics of Populus euphratica stands. Besides, the physical and chemical properties between soils inside and outside of these spots were compared. We found that: (1) the UAV method could be reliably used to extract the area of bare spots and the morphological characteristics of Populus euphratica stands;(2) with Pearson correlation coefficients of 0.673 and 0.894, there were a strong correlation relationship between bare spots area and canopy area in both measured and estimated data rather than other morphological characteristics;(3) electrical conductivity, pH, soil water content, total nitrogen, total phosphorus and soil organic matter has great differences between soils inside and outside of bare spots. These results not only could contribute to further understanding of spatial distribution of bare spots, but also helps to the sustainable management of Populus euphratica forest in arid regions.

Genetic diversity of marginal populations of Populus euphratica Oliv. from highly fragmented river ecosystems

Populus euphratica Oliv. (Euphrates poplar) is one of the naturally distributed poplar species and limited to south and southwestern Turkey. The species possesses great importance for both renewable energy resources and persistence of a healthy river ecosystem. Due to increased habitat destructions and fragmentation by human activities, the distribution area of this species has become narrower. Hence, searching for potential genetic diversity present in species’ genetic resources is of great importance in terms of its resilience to changing environment as well as breeding and use. To explore genetic structure and diversity of Euphrates poplar, natural populations in the Göksu and Euphrates river ecosystems were studied with 21 microsatellite DNA loci. Results demonstrated reduced level of genetic diversity (Ho:0.44, uHe:0.45) and low differentiation among two river populations (FST= 0.07), suggesting a common origin. It appears that severe past reductions in population sizes have resulted in loss of genetic variation in the species. Native populations of this species in two rivers seemed to be marginal with continued gene pool shrinkage. Therefore, they are in great danger of collapsing, mainly because of continued habitat loss and fragmentation. Genetic data generated with the current study provide important information which could be useful for future restoration and conservation studies of the species.

Desertibacter xinjiangensis sp. nov., isolated from the soil of a Euphrates poplar forest, and emended description of the genus Desertibacter

A pale pink and strictly aerobic bacterium, designated strain M71T, was isolated from the soil of a Euphrates poplar forest in Xingjiang, PR China. Cells of the strain were Gram-reaction-negative, rod-shaped and motile by means of a single polar flagellum. Growth occurred at 10–37 °C (optimum 30 °C), at pH 6.0–9.0 (optimum pH 7.0–8.0) and with 0–2.0 % NaCl (w/v, optimum 0 %). Phylogenetic analysis, based on 16S rRNA gene sequences, indicated that strain M71T belongs to the genus Desertibacter in the family Rhodospirillaceae . The 16S rRNA gene sequence of this strain showed 96.2 % sequence similarity with the type strain of Desertibacter roseus 2262T. The respiratory quinone was Q-10 and the predominant cellular fatty acids were C18 : 1ω7c (53.2 %), C16 : 1ω5c (11.0 %), summed feature 3 (C16 : 1ω7c and/or C16 : 1ω6c, 10.2 %) and C16 : 0 (8.5 %). The DNA G+C content was 71.2 mol% (HPLC). The strain contained phosphatidylcholine and phosphatidylethanolamine as the predominant polar lipids. On the basis of the phenotypic, chemotaxonomic and phylogenetic data, strain M71T is considered to represent a novel species of the genus Desertibacter , for which the name Desertibacter xinjiangensis sp. nov. is proposed. The type strain is M71T ( = CCTCC AB 209291T = CIP 110127T).

Pontibacter populi sp. nov., isolated from the soil of a Euphrates poplar (Populus euphratica) forest

A Gram-negative-staining, rod-shaped, non-motile and pink bacterial strain was isolated from the soil of a Populus euphratica forest located in Xinjiang, China. The strain, designated strain HYL7-15T, was subjected to a taxonomic analysis using a polyphasic approach. 16S rRNA gene sequence analyses indicated that the isolate belonged to the phylum Bacteroidetes and was related to the genus Pontibacter, with sequence similarities ranging from 93.1 to 95.0 % with other species of the genus Pontibacter. Strain HYL7-15T contained MK-7 as the predominant menaquinone and its DNA G+C content was 44.9 mol%. The major cellular fatty acids of the novel strain were iso-C15 : 0 (16.49 %), iso-C17 : 0 3-OH (10.96 %) and summed feature 4 (comprising anteiso-C17 : 1 B and/or iso-C17 : 1 I, 18.46 %). The major polar lipids were phosphatidylethanolamine (PE) and phosphatidylglycerol (PG); diphosphatidylglycerol (DPG), three unknown aminophospholipids (APLs) and two unknown phospholipids (PLs) were also detected. On the basis of the evidence presented, it is concluded that strain HYL7-15T represents a novel species of the genus Pontibacter, for which the name Pontibacter populi sp. nov. is proposed. The type strain is HYL7-15T ( = CCTCC AB 206239T = NRRL B-59488T).

Flavitalea populi gen. nov., sp. nov., isolated from soil of a Euphrates poplar (Populus euphratica) forest

A novel strain, designated HY-50RT, isolated from soil of a Euphrates poplar (Populus euphratica) forest in Xinjiang, China, was characterized using a polyphasic taxonomic approach. Cells of the isolate were Gram-reaction-negative, strictly aerobic, rod-shaped, non-motile, oxidase-negative and catalase-positive. Phylogenetic analysis based on 16S rRNA gene sequences showed that the isolate was a member of the phylum Bacteroidetes, its closest relatives being Niastella populi THYL-44T (93.6 % similarity), Flavisolibacter ginsengisoli Gsoil 643T (93.5 %), Terrimonas ferruginea IAM 15098T (93.3 %) and Flavisolibacter ginsengiterrae Gsoil 492T (93.2 %). The major fatty acids were iso-C15 : 1 G (11.7 %), iso-C15 : 0 (19.6 %) and iso-C17 : 0 3-OH (19.3 %). The predominant menaquinone of strain HY-50RT was MK-7 and the genomic DNA G+C content was 46.8 mol%. Flexirubin-type pigments were not produced. Based on phylogenetic evidence and the results of phenotypic, genotypic and chemotaxonomic analysis, strain HY-50RT represents a novel species of a novel genus, for which the name Flavitalea populi gen. nov., sp. nov. is proposed. The type strain is HY-50RT ( = CCTCC AB 208255T = NRRL B-59222T).