Semi-arid China Research Articles

Climatic limitations of nearly endangered Juniperus rigida populations at their range edges in semiarid China

The treat of climate warming is expected to increase the frequency and severity of droughts and significantly affect tree growth and distribution ranges, particularly in regions without monsoons. The distribution limits of tree species are highly susceptible to climate change. A deeper understanding of how tree species respond to climate across their distribution ranges is crucial for accurately predicting forest dynamics in the face of climate warming. Using tree ring width data from 586 trees at 19 sites spanning the northernmost and southernmost limits of Juniperus rigida (near-threatened, IUCN: NT), we assessed the growth responses of J. rigida to climate at different distribution range limits. We observed significant differences in tree-growth variability between the southern and northern populations of J. rigida, characterized by an increasing growth trend at the southern range limit, but a decreasing trend at the northern limit since 1996. Moreover, tree growth at their northern limit was hindered by high temperatures and SPEI during summer months, whereas it was constrained by low temperatures in March and precipitation in June at the southern limit. Particularly noteworthy is the increased sensitivity of growth to SPEI and precipitation in recent decades (1996–2018) compared to previous decades (1961–1995), particularly at their northern distribution edge. We therefore conclude that the growth of J. rigida trees at the southern limit could benefit from climate warming, while increasing warming and drought could limit tree growth or even cause tree mortality at the northern range limits. These findings may serve as an early warning for the growth and survival of J. rigida trees in open forests at their northern distribution edges in the face of future climate warming.

Decline in tree-ring growth of Picea mongolica and its intra-annual eco-physiological responses to drought and CO2 enrichment in semi-arid China

Decline in tree-ring growth of Picea mongolica and its intra-annual eco-physiological responses to drought and CO2 enrichment in semi-arid China

Comparison of Xylem Anatomy and Hydraulic Properties in Black Locust Trees at Two Growth Stages in Semiarid China

Tree species transitioning between different developmental phases requires homeostatic adjustments in order to maintain the integrity of the tree hydraulic system. Hence, adjustments related to hydraulic traits (e.g., xylem conduit diameter) are of key functional significance. However, critical information on the differences between different developmental stages is rare. Using sapwood samples from 36 black locust trees with different growth stages (actively growing and declining stages) and a soil water gradient along a hillslope, xylem conduits at stem apexes and breast height (1.3 m above ground) stems were measured. The results showed marked differences in vascular traits between actively growing and declining trees. In contrast to actively growing trees, declining trees exhibited a reduction in conduit diameters accompanied by increased frequency with a positively skewed distribution and a subsequent decline in cumulative theoretical hydraulic conductivity. Across all sampled trees, the hydraulically weighted mean conduit diameter tapered acropetally from breast height to the stem apex. The extent of conduit tapering in actively growing trees (0.244, 95% CI 0.201–0.287) aligned with predictions from the hydraulic optimality model. Conversely, trees in a declining status displayed significantly reduced conduit tapering (0.175, 95% CI 0.146–0.198), indicating an elevation in hydraulic resistance with increasing tree height. Variations in hydraulic properties predominantly resulted from differences in tree height rather than variations in stem diameter or soil water content. The correlation between conduit diameter and soil water content in both actively growing and declining trees stemmed indirectly from variations in tree height rather than presenting a direct response to drought stress.

Loss and conservation of soil organic carbon and nutrients in arid and semiarid China during aeolian dust emissions

In this study, based on the application of the integrated wind erosion modeling system (IWEMS), we comprehensively simulated the loss and conservation of soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), and total potassium (TK) during aeolian dust emissions over 2001–2020 in the arid and semiarid areas of China (ASAC). It was found that the past two decades witnessed decreasing trends in nutrient losses over the central-eastern region of Inner Mongolia, most parts of Qinghai Province, the southern part of the Xinjiang Autonomous Region, and the northwestern part of the Tibet Autonomous Region. The results, being model-based estimates, showed that the ecosystems of the ASAC were crucial in preventing annual losses of SOC, TN, TP and TK: approximately 27318.25 Gg, 2311.18 Gg, 1077.28 Gg and 35780.10 Gg, respectively. Both the losses and conservation of SOC, TN, TP and TK were consistently greater in spring and winter than in summer and autumn. The losses of SOC and nutrients during aeolian dust emissions were more serious in the west of the ASAC than in the east, both in the actual situation and the potential degenerative status. The prevention rates of SOC, TN, TP and TK for different land cover types were all greater than 92%. Comparatively speaking, the prevention rates of SOC, TN, TP and TK were the lowest for barren or sparsely vegetated land (∼92.85%−93.12%), open shrublands (∼95.65%−96.10%) and grasslands (∼98.44%−98.50%). For other land cover types, the prevention rates of SOC, TN, TP and TK were all over 99.62%.

How does desertification combating affect vegetation cover and incomes of farmers and herdsmen in the arid and semi-arid China?

How does desertification combating affect vegetation cover and incomes of farmers and herdsmen in the arid and semi-arid China?

Understanding the traditional wisdom of harvesting rainwater in household yards: construction and rainwater usage patterns of settlement water cellars in semi-arid China

ABSTRACT This study focuses on the heritage users and artisans of water cellars – the principal source of potable water in semi-arid China for centuries – to examine their construction and rainwater usage patterns. The main advantages of water cellars are their low construction cost, user-friendly technology, and water usage stabilization features. The concrete impermeable layer was introduced by artisans in 1970, but residents’ and artisans’ preferences for raw material differ. Furthermore, the survey results showed that the daily average water-use per person was 28.5 L, when there was no drought and harvested rainwater was used for bathing. In contrast, about 14 L of water per person is required daily, when usage is kept to a minimum for bathing and laundry, in the event of a drought. The wisdom behind such adjustments is irrefutable, but it is inadequate to alleviate the discomfort of extreme water-saving. This evidence-based awareness of the advantages of water cellars – as well as the limitations of traditional wisdom – will facilitate their sustainable development.

Plastic film mulching with ridge planting alters soil chemical and biological properties to increase potato yields in semiarid Northwest China

BackgroundThe growth of potato (Solanum tuberosum L.) is severely affected by the complex and variable soil environment, and film mulching has been widely used for potato growth in semiarid areas of western China. However, there are few studies on the effects of film mulching on soil quality and tuber yield in potato fields.MethodsThe effects of four mulching patterns (flat plot without film mulching, FP; flat plot with film mulching, FPM; ridge planting with half mulch, RPHM; ridge planting with full mulch, RPFM) on soil chemical and biological properties and potato tuber yield were investigated during two growing seasons (2018 and 2019) in the field.ResultsThe results showed that compared with FP, the mulching treatments significantly increased the tuber yield of potato, with an increase of 3.7–20.77% and 7.89–26.35% in 2018 and 2019, respectively, and the yield of RPFM was higher than that of other treatments. In both growing seasons, RPFM significantly increased the contents of alkali-hydrolyzed N and available P, and the activities of soil urease, catalase, alkaline phosphatase, and sucrase. Bacterial and actinomycete counts were significantly higher in RPFM than those in the other treatments. Furthermore, RPFM significantly increased large potatoes and decreased small potatoes. Pearson’s correlation analysis revealed that soil alkaline dissolved nitrogen and actinomycete populations were the main factors affecting potato yield formation.ConclusionsThese results indicate that RPFM can improve the soil environment and further increase potato tuber yield, which is a viable option for potato production in semiarid areas.Graphical

Origin of Intra-annual Density Fluctuations in a Semi-arid Area of Northwestern China.

Intra-annual density fluctuation (IADF) is a structural modification of the tree ring in response to fluctuations in the weather. The expected changes in monsoon flow would lead to heterogeneous moisture conditions during the growing season and increase the occurrence of IADF in trees of the arid ecosystems of continental Asia. To reveal the timings and physiological mechanisms behind IADF formation, we monitored cambial activity and wood formation in Chinese pine (Pinus tabuliformis) during 2017–2019 at three sites in semi-arid China. We compared the dynamics of xylem formation under a drought event, testing the hypothesis that drought affects the process of cell enlargement and thus induces the production of IADF. Wood microcores collected weekly from April to October were used for anatomical analyses to estimate the timings of cambial activity, and the phases of enlargement, wall thickening, and lignification of the xylem. The first cells started enlargement from late April to early May. The last latewood cells completed differentiation in mid-September. Trees produced IADF in 2018. During that year, a drought in June limited cell production in the cambium, only 36% of the xylem cells being formed in IADF trees, compared to 68% in normal tree rings. IADF cells enlarged under drought in early July and started wall thickening during the rainfall events of late July. The drought restricted cell enlargement and affected wall thickening, resulting in narrow cells with wide walls. Cambium and cell enlargement recovered from the abundant rainfall, producing a new layer with large earlywood tracheids. IADF is a specific adaptation of trees to cope with water deficit events occurring during xylem formation. Our findings confirmed the hypothesis that the June-July drought induces latewood-like IADFs by limiting the process of cell enlargement in the xylem. Our finding suggests a higher occurrence of IADF in trees of arid and semi-arid climates of continental Asia if the changes to monsoon flows result in more frequent drought events during the earlywood formation in June.

Tracheid development under a drought event producing intra-annual density fluctuations in the semi-arid China

Drought is the primary limiting factor for tree growth in arid and semi-arid regions, where it can greatly influence xylem anatomical traits and induce multiple responses to wood development. However, the mechanisms driving xylogenesis and intra-annual density fluctuations (IADFs), as well as the seasonal dynamics of wood development in water-limited environments, are still unclear. In this study, we assessed the kinetics of xylem development weekly in Chinese pine (Pinus tabuliformis) and Qinghai spruce (Picea crassifolia), at two altitudes in the Helan Mountains, semi-arid China. Results indicate that summer drought in June inhibited cambial division and reduced xylogenesis, resulting in only 40% of the xylem developing before August. The onset of abundant precipitation in mid-July reactivated radial growth. This second growth extended the growing season by one month and partly compensated for the negative effect of the drought on growth. E-type IADF were characterized by narrow cells with thick walls, formed during July and early August. The duration of cell enlargement explained 57% of variance in tracheid diameter, showing that it played an important role in determining cell size. In contrast, changes in the cell wall thickness were mainly driven by the rate of secondary wall thickening, which explained 65% of the variance. This study reveals the potential mechanisms for xylem development and E-IADF formation under summer drought in semi-arid China, provides evidence for the plasticity and resistance of Chinese pine and Qinghai spruce under varying environmental conditions, and contributes to our understanding of likely future trends in forest productivity under climate changes.

Effect of cloud condensation nuclei concentration on a hail event with weak warm rain process in a semi-arid region of China

Although there are several studies on the effects of cloud condensation nuclei (CCN) concentration on convection, it requires more attention. A hail event in semi-arid China is simulated with four different CCN concentration levels, which correspond to the marine area, mid-continental, continental, and polluted background CCN concentrations. It was found that the auto-conversion of cloud water to rainwater is not significant in the simulated convection. The increase in CCN concentration was accompanied by a large number of graupel particles of smaller size, which consequently induced smaller rain droplets. It is shown that increasing CCN concentration changed the dominant average mass-weighted diameters of the graupel, hail particles and rain droplet. The number concentration of rain droplets increased with CCN concentration, corresponding to the significant evaporation during the falling process. Consequently, the maximum of rainfall on the ground did not increase. Additionally, increasing the CCN concentration does not have the same apparent impact on the size of hail particles.

Time and space catch up with restoration programs that ignore ecosystem service trade-offs.

In response to extreme societal consequences of ecosystem degradation and climate change, attention to ecological restoration is increasing globally. In China, investments in restoration exceeded USD 378.5 billion over the past decade. However, restoration programs are experiments that can cause marked unintended consequences, with trade-offs across space and time that have undergone little empirical examination. We quantified the long-term effects of large-scale afforestation for soil erosion and sandstorm prevention in semiarid China. We found that soil erosion was notably reduced by afforestation but surface runoff declined significantly, after a time lag of 18 years, limiting overall benefit. While forest area also increased, forest quality declined, interacting with reduced surface water runoff. Crucially, increased forest water consumption accelerated downstream groundwater depletion, thus intensifying conflicts over water use. The time lags and spatial trade-offs revealed by this case study provide critical lessons for large-scale restoration programs globally.

Regional characteristics of the point-like historical water supply facilities of traditional villages in semi-arid China

ABSTRACT In this study, we use the integrated concept of the “historical water supply facility” to advance the regional characterization of point-like facilities. Eighteen villages in eastern Shanxi Province, which has a typical semi-arid climate, were taken as the study area, and data were collected by field observations and in-depth interviews. The results reveal that the natural environment, specifically the terrain and river systems, influenced the formation of water cellars and water-logging pools, but had less direct effects on well construction. The formation of these facilities was eventually influenced by the residents pursuing stability and exhibiting a preference for water resources. Furthermore, under the pressure of survival, the types of facilities gradually diversified, while the numbers changed dynamically. Additionally, water cellars exhibited a minor correlation with the flood prevention, environmental sanitation, and yard drainage facilities of the village. These findings demonstrate that the core issue in the formation of diversified regional water supply characteristics is the attempt to find a balance between nature and water use/flood prevention, an embodiment of the explicit recognition of limited self-ability.

An Ammoniated Straw Incorporation Increased Biomass Production and Water Use Efficiency in an Annual Wheat-Maize Rotation System in Semi-Arid China

Water shortage and excessive chemical fertilizers application result in low soil water and nutrient availability and limit crop production in the Loess Plateau of Northwest China. Ammoniated straw incorporation with N fertilization may be an efficient strategy to maintain agricultural sustainability. However, the interactive effects of straw incorporation and N fertilizer on the biomass water use efficiency (WUE) in the winter wheat–summer maize rotation system remain unclear. A 3-year field experiment was conducted to evaluate the effects of combining ammoniated straw incorporation and N fertilizer on soil water, biomass yield and biomass water use efficiency (WUE) in an annual summer maize (Zea mays L.)—Winter wheat (Triticum aestivum L.) rotation system. There were three treatments: (i) long straw (5 cm) mulching with N fertilizer (CK), (ii) long straw with N fertilizer plowed into the soil (LP), and (iii) ammoniated long straw with N fertilizer plowed into the soil (ALP). Compared with the CK treatment, LP and ALP led to a similar soil water storage capacity. ALP improved summer maize biomass yield and winter wheat biomass yield at the jointing-maturity stage. ALP improved summer maize WUE at the ten-leaf collar-tasseling stage and winter wheat WUE from the tillering stage to the maturity stage. Also, the ALP treatment increased the total water use efficiency (TWUE) of winter wheat by 4.1–22.0%. Overall, ammoniated straw incorporation produced the most favorable biomass yield and WUE in the summer maize—Winter wheat rotation system in the Loess Plateau of China.

Reliability of the Artemisia/Chenopodiaceae pollen ratio in differentiating vegetation and reflecting moisture in arid and semi-arid China

The reliability of the ratio between Artemisia and Chenopodiaceae pollen percentage (i.e. A/ C) in differentiating vegetation and reflecting moisture conditions in arid and semi-arid regions has been disputed and this hindered its potential application in palaeoclimate reconstructions. In this paper, we investigated the A/ C ratios of lake-centre surface sediment from 45 lakes in the Inner Mongolia Plateau and the Qaidam Basin in arid and semi-arid China, and numerically studied the relationships of A/ C ratios with vegetation and moisture. We found that the A/ C ratio of lake-centre surface sediments can be used as an effective index to differentiate desert and steppe and also can be used as a valid indicator to infer mean annual precipitation (MAP) in the Inner Mongolia Plateau and the Qaidam Basin in arid and semi-arid China. Moreover, the A/ C ratio from lake-centre surface sediments is more reliable and robust than that of soil-surface samples in differentiating vegetation and reflecting moisture conditions, and this might be attributed to its larger pollen source area and regional representation. In addition, the ( A − C)/( A + C) index helps to overcome the inherent weakness of non-linearity of the A/ C ratio and may be useful in paleo-vegetation reconstruction. These findings provide useful references for pollen-based vegetation and climate reconstructions of lake cores in arid and semi-arid China.

Exploring the Dynamic Coupling Relationship between Agricultural Economy and Agro-Ecological Environment in Semi-Arid Areas: A Case Study of Yulin, China

The rapid expansion of agricultural areas in semi-arid China over the past decades has aggravated the imbalance of the agroeconomy and agroecological environment. To further understand the coupling relationship between the two, this paper, taking Yulin as a case, develops an integrated index system for evaluation of the agricultural economy and the agroecological environment, and a model of the coupling coordination degree for evaluation of the dynamic coupling relationship between the two. Based on that, we have investigated the coupling coordination by comparing the differences of the development index of the two sub-systems at different periods. Subsequently, we further clarified the internal interaction and coupling relationship between the two sub-systems with a cross-impact analysis. The results suggested that the weights of ecological environmental conditions and agricultural development input are respectively0.5908 and 0.3570. From 1997 to 2016, a high-level interactive coupling existed between the agroecological environment and agricultural economy, and the coupling coordination degree of the two sub-systems grew slowly. Overall, the degradation of the agroecological environment impeded the coordinated development of the agricultural economy and the level of coupling coordination improved from basic coordination in the beginning to superior coordination in the end. The agricultural economy grew rapidly, at the expense of the degradation of the agroecological environment. Furthermore, more attention should be paid to improving agricultural development input for promoting economic and ecological benefits, and coupling coordination degree of the two sub-systems. These findings are important for boosting sustainable development of the agricultural economy in semi-arid areas.

Forage nitrogen yield and soil nitrogen in artificial grasslands with varied Medicago seedling proportion

ABSTRACTThis study aimed to understand the effects of Medicago spp proportion on symbiotic and non-symbiotic nitrogen (N) utilization of plants, and subsequent forage production and soil N status in an artificial Leymus chinensis grassland. By a two-year field experiment conducted in semi-arid northern China, it was found that the corresponding biomass proportions of legume in swards were 0, 39, 63, 83 and 98% when legume seedling proportions at sowing were 0, 25, 50, 75 and 100%, respectively. Increased Medicago seedling proportion (from 25 to 100%) decreased legume N2 fixation capacity from 53 to 21%, as a consequence, this reduced total symbiotic N2 fixation and its contribution to forage production with Medicago seedling proportion increasing from 50 to 75% or more. However, as increased Medicago seedling proportion enhanced legume biomass and sward uptake to soil mineral N, higher legume stands still led to the greater biomass and N yield. The cultures with 50% seedling of legume had 4–13% greater soil N concentration than the cultures with 0, 25, 75 and 100% seedling of legume. We concluded that pure Medicago stands led to the greatest forage yield, while medium Medicago stands could lead to the greater symbiotic N fixation and soil N concentration.

Quantifying Farmers’ Initiatives and Capacity to Cope with Drought: A Case Study of Xinghe County in Semi-Arid China

Farmers living in a state of poverty in semi-arid areas are the main victims of drought. They suffer most from drought, which makes it particularly important to assess their capacity to cope with it. The present study developed a new approach for such assessment. Famers’ resources and initiatives to deal with drought were evaluated, and appropriate coping strategies are proposed by analyzing the differences between the coping capacities of two categories of farmers; tenants (with large holdings) and smallholders. Tenants’ capacity to cope with drought was 1.7 times that of smallholders. Also, tenants showed greater initiative during droughts, whereas smallholders made greater efforts in preparing for droughts. Farmers’ resources were positively correlated to the degree of their initiative (correlation coefficient = 0.49). Farmers showed greater initiative when they had larger holdings and were less dependent on agricultural income. The state should give more financial support to subsidy-dependent farmers and encourage smallholders—whose major income comes from crops—to augment their income through livestock husbandry. Such a policy would prove more conducive to increasing the capacity of not only local farmers but also of the entire region to cope with droughts and to promote sustainable development of local agriculture.

The composition, richness, and evenness of seedlings from the soil seed bank of a semi-arid steppe in northern China are affected by long-term stocking rates of sheep and rainfall variation

The soil seed bank has a large influence on the potential for grassland restoration. This study aimed to characterise the composition, density, richness, and evenness of seedlings emerging from the soil seed bank under different sheep stocking rates, in a summer grazing system, in semi-arid China. Soil was sampled in 2015, a year with extreme drought conditions and in 2016, a normal rainfall year. The soil seed bank was assessed by measuring seedling emergence under laboratory conditions. Comprising 16 species, 85.4% of the seedlings were concentrated within a depth of 0–5cm. Drought significantly reduced the density and richness of the seedlings. Grazing increased the richness of seedlings by increasing the richness of aboveground species, and grazing significantly reduced the evenness of the seedlings by reducing the evenness of aboveground species. Drought significantly reduced the similarities between the seedlings and the aboveground species, whereas grazing increased similarities in both years. This study revealed that the density and richness of seedlings were higher in higher stocking rate in drought year. We conclude that negative effects on density, richness and evenness of the seedlings caused by drought can be overcome by rotational grazing especially at higher stocking rate.

Ecological role of physical dormancy in seeds of Oxytropis racemosa in a semiarid sandland with unpredictable rainfall

Seed dormancy and the soil seed bank are crucial to plant regeneration strategy, especially in semiarid ecosystems with unpredictable precipitation. The aim of this study was to investigate how seed dormancy is controlled by environmental factors and how it is correlated with the soil seed bank and regeneration of the perennial legume Oxytropis racemosa, a dominant perennial herb in Mu Us Sandland of semiarid China. Germination and imbibition experiments on fresh intact and scarified seeds of O. racemosa were used to identify physical dormancy (PY) in seeds of this species. Soil seed bank dynamics, timing of seedling emergence and the fate of buried seeds in the natural habitat were investigated. PY was broken by mechanical scarification or wet heat/ice water cycles but not solely by dry heat or wet heat treatment. The soil seed bank exhibited seasonal changes in the number of seeds, which was highest in September and lowest in July. Seeds buried at different sand depths gradually lost dormancy; 20–42% of the seeds remained dormant after 20 months of burial. Dormancy break occurs gradually throughout the year. Our results indicate that O. racemosa exhibits hardcoatedness heterogeneity that spreads germination of a seed cohort between seasons and years in the semiarid environment, where the amount of precipitation during the growing season is highly variable.

Ecological role of physical dormancy in seeds of Oxytropis racemosa in a semiarid sandland with unpredictable rainfall

Seed dormancy and the soil seed bank are crucial to plant regeneration strategy, especially in semiarid ecosystems with unpredictable precipitation. The aim of this study was to investigate how seed dormancy is controlled by environmental factors and how it is correlated with the soil seed bank and regeneration of the perennial legume Oxytropis racemosa, a dominant perennial herb in Mu Us Sandland of semiarid China. Germination and imbibition experiments on fresh intact and scarified seeds of O. racemosa were used to identify physical dormancy (PY) in seeds of this species. Soil seed bank dynamics, timing of seedling emergence and the fate of buried seeds in the natural habitat were investigated. PY was broken by mechanical scarification or wet heat/ice water cycles but not solely by dry heat or wet heat treatment. The soil seed bank exhibited seasonal changes in the number of seeds, which was highest in September and lowest in July. Seeds buried at different sand depths gradually lost dormancy; 20–42% of the seeds remained dormant after 20 months of burial. Dormancy break occurs gradually throughout the year. Our results indicate that O. racemosa exhibits hardcoatedness heterogeneity that spreads germination of a seed cohort between seasons and years in the semiarid environment, where the amount of precipitation during the growing season is highly variable.