Reclamation during oasification is conducive to the accumulation of the soil organic carbon pool in arid land

Soil organic carbon(SOC)and its stable isotope composition reflect key information about the carbon cycle in ecosystems.Studies of carbon fractions in oasis continuous cotton-cropped fields can elucidate the SOC stability mechanism under the action of the human-land relationship during the oasification of arid land,which is critical for understanding the carbon dynamics of terrestrial ecosystems in arid lands under global climate change.In this study,we investigated the Alar Reclamation Area on the northern edge of the Tarim Basin,Xinjiang Uygur Autonomous Region of China,in 2020.In original desert and oasis farmlands with different reclamation years,including 6,10,18,and 30 a,and different soil depths(0-20,20-40,40-60 cm),we analyzed the variations in SOC,very liable carbon(C_(VL)),liable carbon(C_(L)),less liable carbon(C_(LL)),and non-liable carbon(C_(NL))using the method of spatial series.The differences in the stable carbon isotope ratio(δ^(13)C)and beta(β)values reflecting the organic carbon decomposition rate were also determined during oasification.Through redundancy analysis,we derived and discussed the relationships among SOC,carbon fractions,δ^(13)C,and other soil physicochemical properties,such as the soil water content(SWC),bulk density(BD),pH,total salt(TS),total nitrogen(TN),available phosphorus(AP),and available potassium(AK).The results showed that there were significant differences in SOC and carbon fractions of oasis farmlands with different reclamation years,and the highest SOC was observed at the oasis farmland with 30-a reclamation year.C_(VL),C_(L),C_(LL),and C_(NL) showed significant changes among oasis farmlands with different reclamation years,and C_(VL) had the largest variation range(0.40-4.92 g/kg)and accounted for the largest proportion in the organic carbon pool.The proportion of C_(NL) in the organic carbon pool of the topsoil(0-20 cm)gradually increased.δ^(13)C varied from-25.61‰to-22.58‰,with the topsoil showing the most positive value at the oasis farmland with 10-a reclamation year;while theβvalue was the lowest at the oasis farmland with 6-a reclamation year and then increased significantly.Based on the redundancy analysis results,the soil physicochemical properties,such as TN,AP,AK,and pH,were significantly correlated with C_(L),and TN and AP were positively correlated with C_(VL).However,δ^(13)C was not significantly influenced by soil physicochemical properties.Our analysis advances the understanding of SOC dynamics during oasification,revealing the risk of soil carbon loss and its contribution to terrestrial carbon accumulation in arid lands,which could be useful for the sustainable development of regional carbon resources and ecological protection in arid ecosystem.

The Driving Mechanism of Oasificationdesertification in Hotan River Basin

[Objective] The main purpose is to reveal the laws and driving mechanism of oasification and desertification in Hotan River Basin during the period of 1972-2010. [Method] The visual interpretation method was used to process TM/ETM＋ image based on field work and investigation of Hotan Oasis. These interpretation dates have been reclassified to desert and oasis. Then, the driving mechanism of desertification and oasification was analyzed. [Result] The analysis indicated that the oasification velocity（91.24 km^2/year） was faster than the desertification’s（77.78 km^2/year）,with a rapid growth of 5.59 km^2/year in oasis area in the mid-lower reaches of the Hotan River. [Coclusion] There existed spatial coupling linked by water consumption between oasification in the middle reaches and desertification in the lower reaches.And the changing trends were opposite not only for the oasis area, but also for the oasification area and oasification velocity between the middle and the lower reaches of the Hotan River Basin. With climatic warming, population growth, economical development, scientific and technological progress, and in particular the implementation of national policies, the cropland area increased and oasis expanded, speeding up the oasification and water consumption in the middle reaches. Hence it is urgent to prevent the Hotan Oasis from exacerbating the current water supply-demand imbalance and prohibit the expansion of arable land to transitional belt between oasis and desert.