[Radial growth response of Populus euphratica to climate change in the Cele desert oasis ecotone, China]. / ç­–å‹’æ²™æ¼ ç»¿æ´²è¿‡æ¸¡å¸¦èƒ¡æ¨å¾„å‘ç”Ÿé•¿å¯¹æ°”å€™å˜åŒ–çš„å“åº”.

Populus euphratica is an important tree species in the arid regions of Northwest China, which is sensitive to climate changes. Climate of the Northwest China is changing to be "warm and humid", but how it would affect the regional forest growth is not clear. In this study, the radial growth response of P. euphratica to major climatic factors and their temporal changes during 1984-2021 were analyzed by using dendrochronology method in the desert oasis ecotone of Cele in the southern Tarim basin. The results showed that tree-ring width index of P. euphratica had a significant negative correlation with temperature in September of the previous year, and in February and May of current year, had significant positive correlation with precipitation in September of previous year and March and May of current year, and had significant positive correlations with SPEI in February and May of current year. The relationships between tree-ring width index and combined month climatic factors were more obvious. The results of moving correlation analysis showed that the correlation between tree-ring width index and temperature in the growing season tended to be strengthened in recent years, while the correlation between tree-ring width index and precipitation, SPEI tended to be declined or remain stable. The variations of the relationships between tree-ring width index and combined month climatic factors were more obvious compared that with single month. Current regional climate is conducive to the growth and development, as well as the improvement of ecological shelter function of P. euphratica forest in the desert oasis ecotone of Cele.

Long-term clipping causes carbohydrate accumulation and induced transition of Alhagi sparsifolia from herbs to shrubs.

A field experiment was conducted on Alhagi sparsifolia Shap. with a long-term clipping history (5-8 years) to investigate the adaptation strategy of A. sparsifolia to long-term clipping. The present study found that long-term clipping can reduce self-shading and increase the photosynthesis rate (Pn) in May. During the whole growth season, clipped plants can maintain a high Pn with less variation, which we denote as a 'stable photosynthesis strategy'. Although Pn in unclipped plants was higher than in the long-term clipping treatment in August, clipped plants accumulated more carbohydrates in shoots. The enhanced amount of carbohydrates could be correlated with the greater amount of lignin synthesis in stems. Therefore, long-term clipping induced the transition of A. sparsifolia from herbs to shrubs. After long-term clipping, plants allocated more resources to plant defence against stress, whereas the ratio of resources allocated to leaf growth decreased. Consequently, photosynthesis in long-term clipped plants decreased in August. In PSII, the energy used for both photochemical quenching and non-photochemical quenching decreased in the clipped plants during the early stage of the growth season. In addition, due to the lower stomatal conductance (gs), clipped plants retained more water in their leaves and suffered less water stress. Thus, clipped plants produced less reactive oxygen species (ROS), which in turn, delayed leaf senescence. Plants also exhibited over-compensatory growth after long-term clipping, but this phenomenon was not caused by the increase in specific leaf area (SLA). The stable photosynthesis strategy helped to extend the lifespan of plants in the growth season and improve their adaptation to light, temperature, and water stress.

[Ion distribution, absorption and translocation characteristics of Alhagi sparsifolia in adaptation to saline habitat.] / 疏叶骆驼刺适应盐渍生境的离子分布、吸收和运输特征.

In order to explore the adaptive capacity of Alhagi sparsifolia to soil salinity (mild, mo-derate, severe saline soil), the distribution, adsorption and translocation characteristics of Na+, K+, Ca2+, Mg2+ in different organs of A. sparsifolia, which is a dominant native vegetation in southern edge of Tarim basin, were investigated. The results showed that when grown on a mild and moderate saline soil, Na+ distribution in different organs of A. sparsifolia followed the order of stem≈thorn>leaf>root; when grown on a severe saline soil, Na+ distribution followed leaf>stem≈thorn>root. The distribution of Ca2+ and Mg2+ followed leaf >thorn>stem>root. With the increase of soil salt level, Na+ content in different organs of A. sparsifolia increased, while K+ content in leave decreased; meanwhile the increasing soil salt level significantly decreased the K+/Na+ ratio in both root and leave, as well as the Ca2+/Na+ and Mg2+/Na+ ratios in all organs. The selective transportation coefficients for Ca2+-Na+ and Mg2+-Na+ followed order of stem-leaf>stem-thorn>root-stem under saline habitats. Based on the integrated analysis, in order to adapt to salinity habitat, A. sparsifolia could use multiple organs to accumulate Na+, depending on soil salt level. Na+ could accumulate in stem and thorn at a relative low level, but in leaves at high levels. Besides, Ca2+ and Mg2+ could be the inorganic osmotic adjustment substances for A. sparsifolia to adapt the saline environment.

[Effects of salt stress on Nitraria roborowskii growth and physiological characteristics of stress resistance].

A pot experiment was conducted to study the influences of different NaCl concentrations (0, 50, 100, 200, 400 mmol x L(-1)) on the growth, leaf hydrogen peroxide (H2O2), malonaldehyde (MDA) content, superoxide dismutases (SOD), catalases (CAT), peroxidase (POD), ascorbate peroxidase (APX) enzymes activity, water potential, soluble sugar and proline contents of Nitraria roborowskii. The results showed that the growth of N. roborowskii was not affected at lower NaCl concentrations (< or = 50 mmol L(-1)), while the SOD, POD, CAT and APX activities in leaves of N. roborowskii were increased. However, higher NaCl concentrations (> 50 mmol x L(-1)) restrained the growth parameters of crown area, number of branches, dry mass of leaf, branch and lateral root, and remarkably reduced the SOD, POD and CAT activities, soluble sugar and proline contents in leaves of N. roborowskii. H2O2 and MDA contents in leaves were increased and water potential was reduced with increasing NaCl concentrations.

[Effects of different disturbance modes on the morphological characteristics and aboveground biomass of Alhagi sparsifolia in oasis-desert ecotone].

Taking Cele oasis at the southern fringe of Taklimakan Desert as a case, this paper studied the effects of different disturbances (burning in spring, cutting in spring, and cutting in fall) on the morphological characteristics and aboveground biomass of natural vegetation Alhagi sparsifolia in the ecotone of oasis-desert. Burning in spring decreased the A. sparsifolia plant height, crown width, and biomass significantly, being harmful to the regeneration and growth of the vegetation. Cutting in spring decreased the A. sparsifolia plant height, crown width, and biomass but increased the leaf biomass, thorn length, and thorn diameter, whereas cutting in fall decreased the plant height and crown width but increased the ramification amount and biomass of A. sparsifolia. Moderate cutting in fall could benefit the protection of A. sparsifolia at the southern fringe of Taklimakan Desert.

[Influence of different concentration Ni and Cu on the photosynthesis and chlorophyll fluorescence characteristics of Peganum harmala].

A pot experiment was conducted to study the influence of different concentration (0, 50, 100, 200, and 400 mg kg(-1)) Ni and Cu on the growth, photosynthesis, and chlorophyll fluorescence characteristics of Peganum harmala seedlings. With increasing concentration Ni in the medium, the seedlings growth parameters, photosynthetic pigment content, net photosynthetic rate (P(n)), stomatal conductance (G(s)), transpiration rate (T(r)), maximal photochemical efficiency of PS II (F(v)/F(m)), quantum efficiency of electric transport of PS II (phi (PS II)), and coefficient of photochemical quenching (q(P)) of P. harmala decreased significantly, while the intercellular CO2 concentration (C(i)) and the coefficient of non-photochemical quenching (q(N)) were in adverse. The decrease of P(n) under Ni stress was mainly caused by non-stomatal limitation. At 50 mg kg(-1) Cu, the growth parameters, photosynthetic pigment content, P(n), G(s), T(r), C(i), F(v)/F(m), phi(PS II), and q(P) reached their peak values; at 100 mg kg(-1) Cu, the growth parameters, chlorophyll a and b contents, P(n), G(s), T(r), C(i), and F(v)/F(m) were still slightly higher than the control; while with the further increasing Cu concentration in the medium, all the test indices except q(N) tended to decrease. The decrease of P(n) under Cu stress was mainly caused by stomatal limitation.

[Changes and analysis of soil quality under different land use types in oasis rim].

The aggravation process of oasisization leads to changes of land use type in oasis rim. In order to discuss the effects of different land use types on soil properties and soil quality, the four land use types located Cele oasis rim in south margin of Tarim Basin, which are the cotton field, orchard, and Caligonum mongolicum Turcz land use type reclaimed by people and nature state land use type covered by Alhagi sparsifolia SHAP, were selected as study object. The relative soil quality index (RI) and the soil quality synthesis index (SQI) were used to analyse the changes of soil quality between four land use types within 0-20 cm, 2040 cm, 40-60 cm soil depth, respectively. Meantime, the fractal theory was used to analyse the particle-size distribution (PSD) property of top soil under different land use types. The results indicated that there was a significant difference in the soil organic matter and total nitrogen in same soil depth between four land use types; the order ranked according to RI was same to the order ranked according to SQI in each soil depth between four land use types. The cotton field and orchard have an obviously positive effect on soil quality of the top soil, however, the soil quality of Alhagi sparsifolia SHAP land use type was gradually increasing along with the increasing soil depth. The soil properties and soil quality of Caligonum mongolicum Turcz land use type were at the lowest level according to the comparison results among all land use types, and the calculation results of PSD fractal dimension also indicated the Caligonum mongolicum Turcz land use type had the worst ability on maintaining soil fine fractions.

[Assessment of farmland soil quality under different utilization intensity in arid area].

Based on the 2005-2007 experimental data in Cele oasis in the southern margin of Tarim Basin of Xinjiang, the soil quality of four typical types of farmland with different utilization intensity, i.e., farmland with high input, farmland with normal input, newly reclaimed farmland, and farmland in oasis' interior, was analyzed and assessed by using sustainable yield index, soil improvement index, and soil quality synthesis index. Among the farmlands, there were significant differences in the contents of soil organic matter, available nitrogen, and available phosphorus. Newly reclaimed farmland had the lowest level of soil quality, while the farmland in oasis' interior had relatively higher soil quality. This study could help the reasonable exploitation and utilization of farmlands in Cele oasis, and the protection of local farmland eco-environment.

[Water physiological characteristics of four perennial plant species around Cele Oasis in Xinjiang].

The water physiological characteristics of four perennial plant species (Populus euphratica, Tamarix ramosissima, Calligonum caput-medusae, and Alhagi sparsifolia) around Cele Oasis in Xinjiang were studied through their vegetation growth period. No signs of serious drought stress were observed in any of the test perennial species during their vegetation growth, and irrigation had little effects on the water status of the plants (P > 0.05). The seasonal variation characteristics of water physiological parameters differed with the plants. A. sparsifolia had the highest predawn water potential (PWP) and daily mean sap flow, but the lowest mean water use efficiency (WUE); C. caput-medusae had the highest mean WUE, and its PWP and sap flow were stable and had less seasonal change; T. ramosissima had the lowest PWP during its growth, and had better adaptation ability to the environment; and P. euphratica had relatively stable water physiological characteristics during its growth. The four perennial plant species had deep root systems to access underground water to satisfy their large demands for water, and thus, well adapted to the harsh environmental conditions around Cele Oasis.