Xinwen Xu

Research on chemical characteristics of soil salt crusts with saline groundwater drip-irrigation in the Tarim Desert Highway Shelterbelt.

Soil salt crusts are special layers at soil surface which are widely distributed in the Trim Desert Highway Shelterbelt under drip-irrigation with high salinity groundwater. In order to reveal annual variation of their chemical characteristics, soil salt crusts in shelterbelt of different ages in hinterland of the Taklimakan Desert were sampled. SOM, total salt, inions and pH were analyzed. Following results were obtained. SOM of salt crusts increased with the shelterbelt ages, but increasing trend became lower gradually. Total salt, ions, and pH of salt crusts reduced gradually with the shelterbelt ages. Total salt of salt crusts in shelterbelt of different ages was much higher than shifting sandy land. Ions were higher than shifting sandy land, Cl-, Na+, and SO42- increased more obvious, then Mg2+, K+, Ca2+ and HCO3-, CO32- was little and nearly had no change. pH was all alkaline, pH of salt crusts in shelterbelt of 11 years was even lower than shifting sandy land. We can include that the quality of shallow soil (0~30 cm) in the Trim Desert Highway Shelterbelt becomes better gradually.

Chlorophyll a fluorescence responses of Haloxylon ammodendron seedlings subjected to progressive saline stress in the Tarim desert highway ecological shelterbelt

In order to assess the long-term impacts of saline groundwater irrigation to Haloxylon ammodendron, one of the main shrubs in the Tarim desert highway ecological shelterbelt, we irrigated the H. ammodendron seedlings with progressive saline groundwater (3–30 g L−1, simulation environment in the Tarim desert highway ecological shelterbelt) and investigated the diurnal variations of chlorophyll a (Chl a) fluorescence parameters, such as maximal quantum yield of photosystem II (PSII) photochemistry (Fv/Fm), quantum yield of photochemical energy conversion in PSII (YII), the apparent rate of electron transport at the PSII level (ETR), photochemical quenching coefficient (qP), non-photochemical quenching (NPQ), quantum yield of nonregulated non-photochemical energy loss in PSII (YNO) and quantum yield of regulated non-photochemical energy loss in PSII (YII), at approximately 2-h intervals. Fv/Fm with 5 g L−1 (S2) was lower than that with 2 g L−1 (S1) but a little higher than 20 g L−1 (S5), respectively. Under the low light [photosyntheticallyactive radiation (PAR) ≤ 250 μmol m−2 s−1, at 08:00, 10:00 and 20:00 h of the local time], S1 kept the lowest YII and the highest YNPQ; while under the high light (PAR ≥ 1500 μmol m−2 s−1), the YII performed S1>S2>S5, and the reverse YNPQ; under mild light (250 μmol mt-2 s−1 ≤ PAR ≤ 1500 μmol m−2 s−1), S1 remained the highest YII, no matter the light and the salinity, the similar YNO almost occurred basically. The results showed that the sand-binding plant H. ammodendron could regulate its energy-utilizing strategies. The S2 might be the most suitable salinity of the irrigation water for H. ammodendron in the Tarim desert highway ecological shelterbelt in the northwest of China.

The effects of soil salt crusts on soil evaporation and chemical changes in different ages of Taklimakan Desert Shelterbelts

Abstract Understanding soil evaporation in reforestation processes in an area of extreme drought is important. We examined the effects of drip-irrigated, high-salinity groundwater on the formation of soil salt crusts and subsequent soil evaporation in the Taklimakan Desert Highway Shelterbelt. Soil evaporation was measured using micro-lysimeters (MLS, 20 cm in length × 10 cm in diameter), and chemical characteristics, including SOM, total salts, ion composition and pH, were analyzed. The results showed that the inhibition efficiency of salt crusts on soil evaporation decreased from the surface to the lower soil layers. Following irrigation, the inhibition efficiency was 33.0% in the shelterbelt, which was much higher than the 13.8% observed for the bare soil. Total salt content and ion contents (Cl - , Na + , and SO 42- ) were much higher for the soil salt crusts than for shifting sandy soils, while the contents of other ions (Mg 2+ , K + , Ca 2+ , HCO 3- , and CO 32- ) were very similar. The total salt content and ion composition of the salt crusts increased during the first 2 years of shelterbelt age, and decreased from 2 to 5 years. With the increasing age of the shelterbelts, the SOM of the salt crusts increased, whereas the total salts and pH decreased. We concluded that the formation of soil salt crusts results in reduced soil evaporation and the soil chemical condition functioned better for growth of the Taklimakan Desert Highway Shelterbelt.

Litter decomposition and nutrient dynamics of three woody halophytes in the Taklimakan Desert Highway Shelterbelt

ABSTRACT Litter decomposition is a crucial biogeochemical process for C and nutrient cycling in nutrient-constrained environments, but the controlling factors on litter decomposition in an extremely arid desert region such as the Taklimakan Desert are relatively unknown. To evaluate the litter decomposition and nutrient dynamic characteristics, five primary litter types of three woody halophytes (Haloxylon ammodendron, Calligonum arborescens, and Tamarix ramosissima) along the Taklimakan Desert Highway Shelterbelt were monitored in litterbags during 420 days, when placed on the soil surface and buried by sand, respectively. The results indicated that the decomposition rate decreased in the order of assimilative branches of H. ammodendron (HA, 0.94), branches of T. ramosissima (TB, 0.55), assimilative branches of C. arborescens (CA, 0.53), seeds of C. arborescens (CS, 0.41), and old branches of H. ammodendron (HB, 0.21) in the surface placement. In contrast, the litters buried by sand displayed a significantly accelerated decomposition rate (F = 12.28, P < 0.01), which were 1.3, 1.8, 1.3, 2.3, and 2.8 times of that at surface placement for HA, TB, CA, CS, and HB, respectively. Decomposition of the litters was primarily affected by initial content of C and K, lignin and cellulose in both placements, and varied among decomposition stages and conditions. The old branches of H. ammodendron and branches of T. ramosissima presented P accumulation in both placements, whereas nutrients (N, P, K) and C showed a release pattern during the litter decomposition process, which was influenced by initial litter contents and decomposition rate.

Soil microbial diversity, site conditions, shelter forest land, saline water drip-irrigation, drift desert

Soil microbes in forest land are crucial to soil development in extreme areas. In this study, methods of conventional culture, PLFA and PCR‐DGGE were utilized to analyze soil microbial quantity, fatty acids and microbial DNA segments of soils subjected to different site conditions in the Tarim Desert Highway forest land. The main results were as follows: the soil microbial amount, diversity indexes of fatty acid and DNA segment differed significantly among sites with different conditions (F < F0.05). Specifically, the values were higher in the middle and base of dunes than the top part of dunes and hardened flat sand, but all values for dunes were higher than for drift sand. Bacteria was dominant in the soil microbial community (>84%), followed by actinomycetes and then fungi (<0.05%). Vertical differences in the soil microbial diversity were insignificant at 0–35 cm. Correlation analysis indicated that the forest trees grew better as the soil microbial diversity index increased. Therefore, construction of the Tarim Desert Highway shelter‐forest promoted soil biological development; however, for enhancing sand control efficiency and promoting sand development, we should consider the effects of site condition in the construction and regeneration of shelter‐forest ecological projects.

Spatio-Temporal Dynamics of Soil Salt under Saline Irrigation in Taklimakan Desert Artificial Shelterbelt

Irrigation with saline water is in risk of soil salinity, which is a major threat for plant growth since salinity stored within the root zone. To determine the effects of saline irrigation on soil salinity, an experiment was carried out at the artificial shelterbelt in Taklimakan Desert Highway to examine soil salinity under different salt concentration irrigation. The rationale for conducting this study was to understand the movement for salinity in soil profile under saline irrigation. The results showed that topsoil (0-5 cm) salinity was greatly correlated with the mineralization of irrigation water, at temporal scale. During an irrigation cycle, the topsoil salinity increased at first four days, the largest soil salinity presented at the 4th day (11.7 dS m-1), and then presented a decreasing trend at the last ten days, while at the under layers (5-210 cm), soil salts were great less than the topsoil, and presented a decreasing trend within an irrigation cycle. During a growing season, topsoil salts presented a unimodal distribution under higher salinity irrigation (28 g L-1), from Apr to Jul it presented a rising trend, and then presented a decreasing trend to Oct, and the larger salinity presented from Jun to Aug, this phenomenon because great higher evaporation during Jun to Aug which lead to upward flux exceeding downward flux, while soil salinity did not change much throughout the soil profile of 5 cm to 200 cm. Yearly dynamics for topsoil salinity presented an increasing trend with the irrigation years, and also changed little at the under layers (5 cm to 210 cm) from 2002 to 2008. The spatial or profile distribution for soil salt showed salt not only accumulated at the topsoil, but also leached to the under layers (130 to 280 cm) and ground water (410 cm), but no salinity at the root zone(5 to 130 cm). These results documented that even with saline irrigation in Taklimakan Desert Highway artificial shelterbelt; it will lead no sodality for plants, since the content of soil salt at root zone was small (about 0.4 dS m-1). Therefore, saline groundwater should be used for protecting the Taklimakan Desert Highway. However, the impact of long-term irrigation with such salinity groundwater for vegetation should not be ignored; low saline water and also limiting irrigation quantities and frequency should be considered in future.

Soil aggregation formation in relation to planting time, water salinity, and species in the Taklimakan Desert Highway shelterbelt

PurposeSoil formation and development can play an important role in the control of desertification in artificially forested desert areas. Here, we aimed to investigate soil aggregate formation in the Taklimakan Desert Highway shelterbelt (TDHS), China.Materials and methodsWe evaluated the topsoil aggregate stability and its fractal characteristics in relation to time from planting and irrigation water salinity.Results and discussionThe results showed that (1) regardless of soils investigated, the soil dry aggregate (SDA) content was higher than the soil water-stable aggregate (WSA) content. The > 0.25-mm SDA content ranged from 3.35 to 28.04%, whereas the > 0.25-mm WSA content ranged from 0.02 to 7.25%; (2) the > 0.25-mm SDA content, as well as the mean weight diameter (MWD) and geometric mean diameter (GMD) of soil aggregates increased with increasing planting time, indicating that plant growth accelerated soil formation; (3) the > 2-mm SDA content was considered to better characterize the soil mechanical stability against wind erosion, whereas the > 1-mm WSA content to better indicate the soil aggregate ability against water dispersion; and (4) the fractal dimension (D) of soil aggregates significantly increased with the increasing of shelterbelt ages, the total N and organic matter contents, and decreased with the increasing bulk density. Therefore, the D value was viewed as an indicator for quantifying the degree of sandy soil development.ConclusionsWe concluded that the artificial construction of TDHS prevents desertification by accelerating aggregate formation and consequently increasing soil stability.

Moderate irrigation intervals facilitate establishment of two desert shrubs in the Taklimakan Desert Highway Shelterbelt in China

Background Water influences various physiological and ecological processes of plants in different ecosystems, especially in desert ecosystems. The purpose of this study is to investigate the response of physiological and morphological acclimation of two shrubs Haloxylon ammodendron and Calligonum mongolicunl to variations in irrigation intervals. Methodology/Principal findings The irrigation frequency was set as 1-, 2-, 4-, 8- and 12-week intervals respectively from March to October during 2012–2014 to investigate the response of physiological and morphological acclimation of two desert shrubs Haloxylon ammodendron and Calligonum mongolicunl to variations in the irrigation system. The irrigation interval significantly affected the individual-scale carbon acquisition and biomass allocation pattern of both species. Under good water conditions (1- and 2-week intervals), carbon assimilation was significantly higher than other treatments; while, under water shortage conditions (8- and 12-week intervals), there was much defoliation; and under moderate irrigation intervals (4 weeks), the assimilative organs grew gently with almost no defoliation occurring. Conclusion/Significance Both studied species maintained similar ecophysiologically adaptive strategies, while C. mongolicunl was more sensitive to drought stress because of its shallow root system and preferential belowground allocation of resources. A moderate irrigation interval of 4 weeks was a suitable pattern for both plants since it not only saved water but also met the water demands of the plants.

Is the Taklimakan Desert Highway Shelterbelt Sustainable to Long-Term Drip Irrigation with High Saline Groundwater?

Freshwater resources are scarce in desert regions. Highly saline groundwater of different salinity is being used to drip irrigate the Taklimakan Desert Highway Shelterbelt with a double-branch-pipe system controlling the irrigation cycles. In this study, to evaluate the dynamics of soil moisture and salinity under the current irrigation system, soil samples were collected to a 2-m depth in the shelterbelt planted for different years and irrigated with different groundwater salinities, and soil moisture and salinity were analyzed. The results showed that both depletion of soil moisture and increase of topsoil salinity occurred simultaneously during one irrigation cycle. Soil moisture decreased from 27.4% to 2.4% for a 15-day irrigation cycle and from 26.4% to 2.7% for a 10-day-cycle, respectively. Topsoil electrical conductivity (EC) increased from 0.64 to 3.32 dS/m and 0.70 to 3.99 dS/m for these two irrigation cycles. With increased shelterbelt age, profiled average soil moisture (0–200 cm) reduced from 12.8% (1-year) to 7.1% (10-year); however, soil moisture in 0–20-cm increased, while topsoil salinity decreased. In addition, irrigation salinity mainly affected soil salinity in the 0–20-cm range. We conclude that water supply with the double-branch-pipe is a feasible irrigation method for the Taklimakan Desert Highway Shelterbelt, and our findings provide a model for shelterbelt construction and sustainable management when using highly saline water for irrigation in analogous habitats.

Correlations of Soil Nutrients, Microbial Mass and Enzyme Activity in the Hinterland of the Taklimakan Desert, a Case Study

We explored the unique environmental conditions and management model of the Tarim Desert Highway shelter forest as well as the important roles of such shelter forest in development of the socio-economy of South Xinjiang. Experiments were conducted in the shelter forest lands drip-irrigated with underground saline water. Our results indicated that there are canonical correlations among soil nutrients, microbial amount and enzyme activity. The correlation between soil nutrients and soil microbial biomass was mainly attributed to total nitrogen, organic matter, total phosphate of nutrient factors, and amount of actinomycetes, carbon and phosphate content in microbe. The correlation between soil nutrients and soil enzyme activity was due to organic carbon, available potassium in soil and soil enzyme activities such as catalase activity and phosphatase activity. The correlation between soil microbial mass and activities of soil enzymes was due to phosphate and nitrogen contents in microbe and soil enzymes invertase and phosphatase activities. In addition to the correlations of soil nutrients and soil bio-activities, there is a vertical difference between these three factors in soil. We concluded that irrigation with saline groundwater had major effects on soil mineralization process. The release of soil nutrients in the process supported microbial mass colonization and soil enzyme activities in the Tarim Desert Highway shelter forest land. However, high level of salt in ground water adversely affected soil nutrient accumulation and microbe survival.