Desertification of the semi-arid steppe of Mongolia is advancing very rapidly, motivating afforestation efforts. The “Green Belt” joint project (Government of Mongolia and Republic of Korea), which aims to mitigate soil degradation and develop agroforestry activities through the planting of a forest shelterbelt, is one such response. In these plantations, tree growth has been supported by different watering regimes (no watering, 2, 4, and 8 L h⁻¹) and by two types of soil fertilization (NPK and Compost). The present paper analyses the effect of these techniques on soil chemistry and root biomass partitioning of Populus sibirica (Horth ex Tausch) and Ulmus pumila (L.) tree species. In July 2019, at the plantation site in Lun Soum, Tuv province (Mongolia), six trees were excavated by hand in each treatment, the root system was divided into taproot and five diameter classes (0–2; 2–5; 5–10; 10–20; > 20 mm), and the biomass was measured. Soil organic matter, macronutrients, and pH were also measured. The addition of fertilizers in the long-term did not enhance the soil chemical properties. The build-up of root biomass in both species correlated positively with increasing levels of the watering, while the application of fertilizers led to root growth suppression. For most of the root classes and both species, an irrigation level of 4 L h⁻¹ was sufficient to yield the highest biomass and could be recommended for afforesting the semi-arid steppe of Mongolia. The root biomass of P. sibirica was more dependent on the watering regimes and of U. pumila was more negatively influenced by the application of fertilizers, indicating that U. pumila, due to the its lower water need, could be suitable for afforesting semi-arid environments. Our experiments suggest that afforestation practices in the semi-arid steppe of Mongolia should be supported by a prior analysis of plants' needs, soil type, dose, and type of fertilizers to be applied. Knowledge of the root response to the supporting techniques is necessary for choosing the best one for the plantation and, thus, to develop a sustainable and successful strategy to restore these degraded lands.

In this study, we assessed the functional and architectural traits in the coarse roots of Ulmus pumila trees, which are used for afforesting the semi-arid steppe of Mongolia. Tree growth was supported by different watering regimes (no watering, 2, 4, and 8 L h⁻¹) and by two types of soil fertilization (NPK and compost). In July, 2019, for each of these treatments six trees, outplanted in 2011 as 2-year-old seedlings from a container nursery, were randomly selected, excavated by hand, and digitized. The build-up of root length correlated positively with increasing levels of watering for both soil depths analyzed. The application of fertilizers led to root growth suppression resulting in a general reduction of root length in a lowered rooting depth. When root system characteristics were analyzed in relation to wind direction, unfertilized trees showed higher root diameter values in both soil layers of leeward quadrants, likely a response to mechanical forces to improve stability. On the contrary, fertilized trees did not show differences in root diameter among the different quadrants underscoring a strong reduction in root plasticity with a lack of morpho-architectural response to the mechanical forces generated by the two prevailing winds. Finally, the root branching density, another important trait for fast dissipation of mechanical forces, was significantly reduced by the fertilization, independently of the quadrants and watering regime. Our results suggest that knowledge of the root response to the afforestation techniques applied in the semi-arid steppe of Mongolia is a necessary step for revealing the susceptibility of this forest shelterbelt to the exacerbating environmental conditions caused by climate change and, thus, to the development of a sustainable and successful strategy to restore degraded lands.

Soil salinity is major threat to crop growth and reducing cultivated land areas and salt-resistant crops have been required to sustain agriculture in salinized areas. This original research was performed to determine the effectiveness of MgSO₄ (MS) and CaSO₄ (CS) for each species and assess changes in the physiology and growth of fodder crops after short and long-term salt stress. Six treatments (CON (control); NaCl (NaCl 100 mM); 1 MS (1 mM MgSO₄ + 100 mM NaCl); 2 MS (2 mM MgSO₄ + 100 mM NaCl); 7.5 CS (7.5 mM CaSO₄ + 100 mM NaCl); and 10 CS (10 mM CaSO₄ + 100 mM NaCl)) were applied to Red clover (Trifolium pratense) and Tall fescue (Festuca arundinacea) under greenhouse conditions. Cultivars were evaluated based on their dry weights, physiological parameters, forage quality, and ion concentrations. The biomass of both species decreased significantly under NaCl treatments and increased under the MS and CS treatments compared to solely salinity treatments. Salinity caused a decrease in the photosynthetic rate, but compared to CON, the MS and CS treatments yielded superior results. Moreover, the Na⁺/K⁺ ratio increased as Na⁺ concentration increased but crop quality (CP, NDF, ADF) did not show significant differences under salinity. Overall, we concluded that these T. pratense and F. arundinacea species demonstrated various responses to salinity, MS, and CS by different physiological and morphological parameters and it turned out to be efficient under salinity stress.

Although afforestation is one of the best solutions for combating desertification, it requires intensive management. To minimize management efforts in plantations in arid area, it is crucial to select suitable tree species, i.e. those with a high adaptability to xeric environments. In this study, we investigated key tree traits related to drought adaptation in Populus sibirica Hort. ex Tausch and Ulmus pumila L., planted in the Korea-Mongolia Green Belt Plantation in Lun soum, Mongolia. We found that U. pumila had a smaller leaf size and smaller specific leaf area (SLA) than P. sibirica. In addition, the water use efficiency (WUE) of U. pumila (carbon isotope-based) was significantly higher than that of P. sibirica. Although biomass production was ∼2.5 times higher in P. sibirica than in U. pumila due to the differences in leaf area, there were no statistically significant differences in the photosynthetic characteristics on an area basis. These results indicate that U. pumila has a higher adaptive potential to dry conditions than P. sibirica due to its small leaf size, low SLA, and high WUE.

The environmental restoration of the semi-arid steppe of Mongolia is currently being addressed by creating new plantations able to protect the soil from the advancement of desertification and to improve the economy of the population living there. The success of these interventions relies on a high survival rate and good long-term growth performance of the transplanted trees. In the present work we analyzed stem height and root collar diameter (RCD) over 10 years for two native tree species (Populus sibirica and Ulmus pumila) grown with different water regimes and fertilizers. The investigated duration is sufficiently long to provide a reliable indication of the adaptation of these tree species to the steppe’s harsh environmental conditions. Results suggest that both species could be used for environmental restoration projects, although P. sibirica requires the support of additional irrigation to achieve the best growth performance. U. pumila, on the other hand, shows good growth performance even with rainfall as the only water source. However, the higher water use by P. sibirica trees seems to be compensated by a more rapid ground cover compared to U. pumila. The addition of fertilizers to the soil before transplantation does not improve the growth performance of either species.

Long-term studies on plant response mechanisms to different irrigation regimes will provide a better understanding of the survivability and establishment of plant communities in a desert environment. Thus, across 10 years, we regularly investigated the effects of the rainfall (control), rainfall + 4 L h⁻¹, rainfall + 8 L h⁻¹, and rainfall + 12 L h⁻¹ irrigation regimes on the growth and leaf morpho-physiology of Tamarix ramosissima Ledeb., Ulmus pumila L., Elaeagnus moorcroftii Wall. ex Schltdl., and Hippophae rhamnoides L. to suggest an optimal irrigation regime for each woody species for effective and sustainable afforestation in Mongolia. We measured the root collar diameter (RCD), annual height growth, survivability, leaf area (LA), specific leaf area (SLA), leaf biomass (LB), total chlorophyll concentration, and predawn (ψ_p) and midday (ψ_m) leaf water potentials across the treatments and species. Results showed that trees grown at 12 L h⁻¹ grew taller per year and generally resulted in a higher SLA, but generally resulted in a lower survival rate compared with those in the other treatments in all species. Total chlorophyll content was higher in trees grown under 4 and/or 8 L h⁻¹, particularly for T. ramosissima and E. moorcroftii. Lastly, leaf water potentials were found more negative for trees subjected to 4 L h⁻¹, especially in T. ramosissima and U. pumila, but still resulted in a higher survival rate and LB compared with 12 L h⁻¹. H. rhamnoides showed higher survivability at 8 and/or 12 L h⁻¹ than at 4 L h⁻¹. Therefore, we suggest 4 L h⁻¹ to be the optimal irrigation regime for irrigating T. ramosissima, U. pumila and E. moorcroftii, and 8 and/or 12 L h⁻¹ for H. rhamnoides. Our findings are relevant to ensuring the sustainability of afforestation programs in arid and semiarid landscapes in Mongolia.