Comparison of water consumption of three urban greening trees in a typical arid oasis citiy, northwest China

In order to ensure sustainable development of arid oasis cities, close attention must be paid to the rational use of limited water resources. Since urban vegetation is one important user of water, urban greening activities should be adapted to local environmental conditions. In this study, one native (Morus alba L.) and two introduced urban greening tree species (Fraxinus sogdiana Bunge and Platanus acerifolia Willd.) were selected in Aksu – a typical oasis city in northwest China. Their stem sap flow velocity (SFV) was determined and diel water consumption was calculated. In the meantime, meteorological variables were recorded to analyze the water consumption strategy of these tree species. The results show that the average SFV of M. alba, F. sogdiana and P. acerifolia were 4.1±0.3 cm h-1, 10.5±0.7 cm h-1 and 22.3±2.6 cm h-1, respectively. SFV was positively correlated with solar radiation (Rs), air temperature (Ta), vapor pressure deficit (VPD) and wind speed (Ws), and negatively correlated with air humidity (RH). Stepwise analysis showed that VPD had the highest impact on SFV of F. sogdiana (R²=0.987) and M. alba (R²=0.887), while the impact of RH was highest on P. acerifolia (R²=0.937). P. acerifolia had the highest sap flow daily accumulation (104±7 L tree-1), F. sogdiana was second (52±4 L tree-1), and third was M. alba (16±2 L tree-1). The water use efficiency (WUE) was M. alba (3.61 mmol mol-1) > F. sogdiana (3.33 mmol mol-1) > P. acerifolia (2.90 mmol mol-1). This study showed that native tree species developed certain adaptation strategies to the arid environment and thus consumed less water. Therefore, we recommend that in tree species selection by landscape planners as well as other decision makers, native tree species should be given priority in future urban greening projects

Phosphorous Supplementation Alleviates Drought-Induced Physio-Biochemical Damages in Calligonum mongolicum

This work was supported by the National Natural Science Foundation of China (No. 41977050, 32250410301), the Key Program of Joint Funds of the National Natural Science Foundation of China, and the Government of Xinjiang Uygur Autonomous Region of China (Nos. U1903102). This research was further supported by the Ministry of Science and Technology, China (QN2022045005).Calligonum mongolicum is a phreatophyte playing an important role in sand dune fixation, but little is known about its responses to drought and P fertilization. In the present study, we performed a pot experiment to investigate the effects of P fertilization under drought or well-watered conditions on multiple morpho-physio-biochemical attributes of C. mongolicum seedlings. Drought stress leads to a higher production of hydrogen peroxide (HO) and malondialdehyde (MDA), leading to impaired growth and metabolism. However, C. mongolicum exhibited effective drought tolerance strategies, including a higher accumulation of soluble sugars, starch, soluble protein, proline, and significantly higheractivities of peroxidase (POD) and catalase (CAT) enzymes. P fertilization increased the productivity of drought-stressed seedlings by increasing their growth, assimilative shoots relative water content, photosynthetic pigments, osmolytes accumulation, mineral nutrition, N assimilation, and reduced lipid peroxidation. Our findings suggest the presence of soil high P depletion and C. mongolicum high P requirements during the initial growth stage. Thus, P can be utilized as a fertilizer to enhance the growth and productivity of Calligonum vegetation and to reduce the fragility of the hyper-arid desert of Taklamakan in the context of future climate change

Relating Water Use to Tree Vitality of Populus euphratica Oliv. in the Lower Tarim River, NW China

This study aimed to compare the hydraulic characteristics of different vitalities of Populus euphratica to reveal the differences in their water use strategies and water consumption to provide useful data to scale water use of riparian poplar forests in the lower reaches of the Tarim River, Northwestern China. Our results showed that the sapwood area of P. euphratica could be estimated based on its correlation with tree biometric parameters. The sapwood area of vital poplars tended to be larger than the senesced poplar despite both having the same diameter at breast height. This indicates that poplar vitality should be taken into account when estimating its sapwood area. Therefore, we established two different sapwood area estimation models for vital and senesced poplar (sapwood area = 1.452 × DBH1.553, R2 = 0.891; sapwood area = 0.915 × DBH1.618, R2 = 0.718; DBH: diameter at breast height). The sap flow process of vital and senesced poplar had certain differences and similarities; the average diurnal sap flow velocity and water consumption of vital poplar were 15.85 cm/h and 45.95 L, respectively; for the senesced poplar, it was 9.64 cm/h and 18.17 L, respectively, which were smaller than that of vital poplars. The influence of environmental factors on the sap flow velocity of two different P. euphratica was similar; the sap flow of both vital and senesced poplar had positive correlation with air temperature (R2 = 0.800 and 0.851), solar radiation (R2 = 0.732 and 0.778), vapor pressure deficit (R2 = 0.508 and 0.643) and groundwater depth (R2 = 0.301 and 0.171), while negative correlation with air humidity (R2 = −0.313 and −0.478)

Evidence of Differences in Covariation Among Root Traits Across Plant Growth Forms, Mycorrhizal Types, and Biomes

Fine roots play an important role in plant ecological strategies, adaptation to environmental constraints, and ecosystem functions. Covariation among root traits influence the physiological and ecological processes of plants and ecosystems. Root trait covariation in multiple dimensions at the global scale has been broadly discussed. How fine-root traits covary at the regional scale and whether the covariation is generalizable across plant growth forms, mycorrhizal types, and biomes are largely unknown. Here, we collected six key traits – namely root diameter (RD), specific root length (SRL), root tissue density (RTD), root C content (RCC), root N content (RNC), and root C:N ratio (RCN) – of first- and second-order roots of 306 species from 94 sampling sites across China. We examined the covariation in root traits among different plant growth forms, mycorrhizal types, and biomes using the phylogenetic principal component analysis (pPCA). Three independent dimensions of the covariation in root traits were identified, accounting for 39.0, 26.1, and 20.2% of the total variation, respectively. The first dimension was represented by SRL, RNC, RTD, and RCN, which was in line with the root economics spectrum (RES). The second dimension described a negative relationship between RD and SRL, and the third dimension was represented by RCC. These three main principal components were mainly influenced by biome and mycorrhizal type. Herbaceous and ectomycorrhizal species showed a more consistent pattern with the RES, in which RD, RTD, and RCN were negatively correlated with SRL and RNC within the first axis compared with woody and arbuscular mycorrhizal species, respectively. Our results highlight the roles of plant growth form, mycorrhizal type, and biome in shaping root trait covariation, suggesting that root trait relationships in specific regions may not be generalized from global-scale analyses.</jats:p

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

Abstract 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. </jats:sec