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ABSTRACT In this paper, we discuss the adaptation mechanisms of desert riparian forest vegetation's responses to drought stress. Ecological and physiological parameters are presented, including coverage, density and species diversity. Also investigated are the photosynthesis, fluorescent parameters, leaf water potential, leaf proline (PRO), soluble sugar, malondialdehyde, superoxide dismutase (SOD), peroxidase (POD) and abscisic acid (ABA) of the main constructive species at various buried groundwater depths of the Tarim River's lower reaches. The results reveal a close relationship between vegetation and groundwater depth and show that the most appropriate groundwater depths for the optimal composition and structure of plant communities is 2-6 m. For the main constructive species, Populus euphratica and Tamarix spp., the most appropriate groundwater depths and the critical depths are 4 and 8 m for P. euphratica and 6 and 10 m for Tamarix spp., respectively. However, when groundwater depths exceed 4 m for P. euphratica or 6 m for Tamarix spp., the plants suffer drought stress. During moderate or extreme drought stress, P. euphratica and Tamarix spp. rapidly accumulate PRO, soluble sugar, SOD and ABA in their leaves, thereby reducing leaf water potential and stomatal conductance, enhancing osmoregulation and alleviating the esterification of cell membranes. Such a response decreases the yield as well as the photosynthetic and electron transport rate, thus improving the efficiency of water utilization. Complementary actions in resisting drought stress likewise occurred between SOD activity and POD activity, and between the contents of PRO and soluble sugar in P. euphratica and Tamarix spp. leaf cells. In the main, P. euphratica accumulated a large amount of soluble sugar for osmoregulation to counter drought stress, whereas Tamarix spp. accumulated a large volume of PRO. When suffering extreme drought stress, Tamarix spp. enhanced its POD activity. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

ABSTRACT Riparian plants in the lower reaches of the Tarim River (Tikanlik) and Heihe River (Ulan Tug) were selected as study objects, where they suffered from different drought stresses. The differences of root and twig xylem hydraulic conductivity and embolism of the typical riparian plants, including Populus euphratica, Tamarix spp., Alhagi sparsifolia and Karelinia caspica, and their responses to drought stress were analysed. The results showed that (1) the riparian plants in the lower Tarim River suffered from more severe drought stress than those in the lower Heihe River because of their lower xylem hydraulic conductivity, and the fundamental reason resulted in different degrees of drought stresses in the two regions was groundwater depth; (2) the drought resistance of Tamarix spp. was the strongest, which could exist in a broad habitat with different degrees of water stresses, whereas A. sparsifolia and K. caspica only exist in a narrow habitat with groundwater depth less than 4 m because of their weak drought resistance; and (3) the main resistance part of water transportation of riparian plants was twig xylem when they encountered the mild drought stress, whereas it was root xylem when the riparian plants encountered severe drought stress, and riparian plants adapted the mild drought stress through limiting twig xylem hydraulic conductivity to coordinate the plant growth, while they adapted the severe drought stress through enhancing xylem hydraulic conductivity of dominant branches with strong competitiveness of sap flow and sacrificing non-dominant branches to improve the plant survival chance. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

ABSTRACT On the basis of the characteristics of the oasis hydrological recycling processes in the lower reaches of the Tarim River, the impacts of surface water and groundwater on soil salt content were analyzed to determine how these processes affect soil salinization. The results showed that the relationship between surface water quality and soil salt content in the 0-50 cm layer of soil was significantly positive, with soil salt content declining as groundwater depths increased. However, there was no clear correlation between surface water and salt content in the 50-100 cm layer of soil. When the groundwater depth was <6 m, the soil salt content showed a high-surface concentration, exhibiting a 'T' distribution and decreased with increasing soil depth in the order of 0-20 cm > 20-50 cm > 50-100 cm. However, with increasing groundwater depth (>6 m), soil salt loads were reduced and showed a 'rhombus' distribution, mainly accumulating in the middle layer in the order of 20-50 cm > 0-20 cm > 50-100 cm. When groundwater depth was greater than 6 m, the hardness, total dissolved solids (TDS), and conductance of the groundwater underwent a radical change. Thus, the critical threshold groundwater depth for condensing salt content in groundwater and changing soil salt load distributions was deemed to be 6 m. Salt accumulation in the 0-50 cm layer of soil was determined by the TDS volume in the groundwater when groundwater depth was shallow, which accounted for more than 90% of salt accumulation. However, salt accumulation was determined by the volume of TDS in irrigation water when groundwater depth increased. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

ABSTRACT The interactive relationships of ecological and hydrological processes on individual plant growth and development as well as community succession have been a main focus of research in plant ecohydrology. In this paper, we firstly explore the spatial difference of the desert riparian ecosystems as distance to the river in the arid inland Tarim River Basin and then investigate the response of vegetation communities to emergent ecological water conveyances. Results showed that the decreasing groundwater table is the main driving force for vegetation degradation. Herbs exhibit degradation when the groundwater table is 4-6 m below the surface, whereas trees do not exhibit degradation until the groundwater table exceeds 6 m from the soil surface, in the lower reaches of the Tarim River. In addition, the structure of the plant community is controlled by the depth of the groundwater table. The mixed trees/shrubs/herbs structure is distributed in areas where the groundwater table is between 2 and 4 m in depth, the trees/shrubs structure is distributed in areas where the groundwater depth is 4-8 m and the simple structure of degraded Populus euphratica/ Tamarix chinensis dominates the areas where the groundwater depth is >8 m. After ecological water conveyance, the Phraginites communis leaf weight, length and width decrease with the increasing distance from the river channel. The length of current-year twigs and average number of leaves of P. euphratica are significantly greater in the upstream section of the lower reach than in the downstream section of the lower reach. We concluded that the ecologically suitable groundwater depth for P. euphratica and T. chinensis is 2-4 m and the critical groundwater depth for drought stress is about 9 m. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Groundwater is becoming increasingly important in extremely arid areas due to climate change and human activities. Little is known, however, regarding the long‐term dynamics of groundwater due to the lack of long‐term historical records of groundwater depth data. In this study, we investigated the relationship between hydrometeorology and tree rings of Populus euphratica (P. euphratica) and the feasibility of reconstructing historical groundwater depths from these tree rings in the lower reaches of the Tarim River, an extremely arid area in China. Tree‐ring growth of P. euphratica mainly reflected historical changes in regional water environments (including runoff and shallow groundwater), rather than climatic variables (including temperature, precipitation, relative humidity, and sunshine hours). Groundwater depth constituted the key environmental factor for directly controlling P. euphratica growth. Linear regression models using tree rings were developed to reconstruct historical changes of groundwater depths in the calendar year (January–December) and the growing season (April–August) from 1950 to 2015. Results tracked well with the main hydrological events in the study area. Our findings demonstrate that tree rings of P. euphratica are a key and effective ecological indicator for quantitatively reconstructing and elucidating historical changes of groundwater depth in the lower reaches of the Tarim River. Additionally, the suitable sampling range for establishing tree‐ring chronologies of P. euphratica and reconstructing groundwater depth is 0–300 m from the river channel in the lower Tarim River. Taking into consideration the lagged effect between runoff of the Ecological Water Conveyance Project (EWCP), decrease in groundwater and tree growth, we recommend that the optimal implementation time of ecological water conveyance is between the previous September and November in the lower Tarim River. This application will effectively improve the groundwater environment in the current year and ensure the growth of riparian trees. [ABSTRACT FROM AUTHOR]

Background Hydrogen peroxide (H 2 O 2 ) is a critical molecular signal in the development of abdominal aortic aneurysm ( AAA ) formation. Vascular peroxidase 1 ( VPO 1) catalyzes the production of hypochlorous acid ( HOC l) from H 2 O 2 and significantly enhances oxidative stress. The switch from a contractile phenotype to a synthetic one in vascular smooth muscle cells ( VSMC s) is driven by reactive oxygen species and is recognized as an early and important event in AAA formation. This study aims to determine if VPO 1 plays a critical role in the development of AAA by regulating VSMC phenotypic switch. Methods and Results VPO 1 is upregulated in human and elastase-induced mouse aneurysmal tissues compared with healthy control tissues. Additionally, KLF 4, a nuclear transcriptional factor, is upregulated in aneurysmatic tissues along with a concomitant downregulation of differentiated smooth muscle cell markers and an increase of synthetic phenotypic markers, indicating VSMC phenotypic switch in these diseased tissues. In cultured VSMC s from rat abdominal aorta, H 2 O 2 treatment significantly increases VPO 1 expression and HOC l levels as well as VSMC phenotypic switch. In support of these findings, depletion of VPO 1 significantly attenuates the effects of H 2 O 2 and HOC l treatment. Furthermore, HOC l treatment promotes VSMC phenotypic switch and ERK 1/2 phosphorylation. Pretreatment with U0126 (a specific inhibitor of ERK 1/2) significantly attenuates HOC l-induced VSMC phenotypic switch. Conclusions Our results demonstrate that VPO 1 modulates VSMC phenotypic switch through the H 2 O 2 / VPO 1/ HOC l/ ERK 1/2 signaling pathway and plays a key role in the development of AAA . Our findings also implicate VPO 1 as a novel signaling node that mediates VSMC phenotypic switch and plays a key role in the development of AAA . Clinical Trial Registration URL : www.chictr.org.cn . Unique identifier: Chi CTR 1800016922.