Semiarid Loess Plateau Of China Research Articles

Transition from opportunistic to conservative water use strategy with the growth of Robinia pseudoacacia in a typical watershed in the semiarid Loess Plateau

Understanding water use strategy is essential to evaluate plant adaptability in water-limited regions, but whether this strategy changes with plant growth needs further investigation. Robinia pseudoacacia is an exotic pioneer plantation species widely planted in the semiarid Loess Plateau of China to restore degraded ecosystems. Plant water uptake proportion from different soil layers and the water uptake pattern calculated through soil water uptake niche breadth (B index) were determined for R. pseudoacacia in 11-, 25-, 33–, and 43-yr plantations. Leaf physiological parameters and carbon stable isotopic composition (δ13C) were measured concurrently to calculate short-term and long-time integrated water use efficiency (WUE). Then, the water use strategy for R. pseudoacacia at different plantation ages was assessed through water uptake patterns, stomatal conductance (gs), and WUE variation under varied soil water conditions. Results showed that R. pseudoacacia maintained high gs and low short-term WUE and δ13C through a relative equal water uptake pattern and absorbed water within 0 − 400 cm soil depths in 11- and 25-yr plantations. However, this species exhibited an exclusive water uptake pattern and absorbed water mainly from 50 − 400 cm soil depth, adopted low gs and high short-term WUE and δ13C in 33– and 43-yr plantations. Therefore, R. pseudoacacia transited from an opportunistic to a conservative water use strategy with plant growth. The short-term WUE and δ13C were mainly and significantly influenced by gs and specific leaf area, respectively. Furthermore, the significant influence of B index on gs, δ18OΔ, short-term WUE, and δ13C indicated that R. pseudoacacia coordinated both water uptake pattern and water use behavior to contend with varied soil water conditions. This study suggested that changes in age-related water use strategy were essential for the adaptability of R. pseudoacacia in water-limited conditions.

Differences in plant water use between check-dam land and slope land on the Loess Plateau: Significance for vegetation restoration

Check dam lands (DLs) and hillslope lands (SLs) are two typical landscape units in the semi-arid Loess Plateau of China (CLP). Knowledge of the water resource distribution and water use characteristics of plant species used for revegetation in SL and DL has profound implications for understanding plant–water relations and guiding revegetation strategies in water-limited ecosystems. To assess the spatiotemporal characteristics of water resource and investigate water use strategies of two widely used species for revegetation (i.e., Medicago sativa and Caragana korshinskii) in the SL and DL, numerous types of water samples (including rain-, soil-, plant-, and groundwater) were collected from a watershed in the semi-arid CLP for analysis. The oxygen and hydrogen stable isotopic ratios (δ18O and δD) of the water samples were estimated for three consecutive hydrological years (2018−2020). The soil water storage in the unsaturated zone of 0–600cm in the DL (mean 1008mm) was estimated to be 64% higher than that in the SL (mean 613mm). Below 600cm, soil was saturated with water (i.e. groundwater) in the DL and remained unsaturated in the SL. The Bayesian mixing model was applied to the stable isotopic ratios of H and O, which revealed significant differences (p < 0.05) in the proportional contributions of water resources between the two revegetated species. Although M. sativa (mean 76% for SL and 61% for DL) and C. korshinskii (mean 72% for SL and 47% for DL) relied on water from the upper 100-cm soil layer during the observation period, C. korshinskii generally utilised more water from the deep soil layer (>100cm) than M. sativa. Furthermore, the mean water uptake fractions of C. korshinskii in both the SL and DL for the deep soil layers and groundwater significantly increased with decreasing annual rainfall, whereas this was not observed for M. sativa, suggesting that the environmental adaptability of C. korshinskii may be more ecologically plastic than that of M. sativa. Additionally, the contribution of groundwater (>600cm) to root water uptake in M. sativa (mean, 21%) and C. korshinskii (mean, 28%) was comparable in the DL, indicating the importance of groundwater in combating possible water stress for revegetated plants. These results indicate that natural and engineering measure-induced water resource distributions result in different plant water-use characteristics and responses to variations in precipitation. Therefore, engineering measures and species are essential factors in ecological restoration management for enhancing the effectiveness of vegetation restoration strategies.

Satellite-observed increasing coupling between vegetation productivity and greenness in the semiarid Loess Plateau of China is not captured by process-based models

Global vegetation has experienced notable changes in greenness and productivity since the early 1980s. However, the changes in the relationship between productivity and greenness, i.e., the coupling, and its underlying mechanisms, are poorly understood. The Loess Plateau (LP) is one of China's most significant areas for vegetation greening. Yet, it remains poorly documented what changes in the coupling between productivity and greenness are and how environmental and anthropogenic factors affect this coupling in the LP over the past four decades. We investigated the interannual trend of coupling between Gross Primary Productivity (GPP) and Leaf Area Index (LAI), i.e., the GPP-LAI coupling, and its response to climate factors and afforestation in the LP using long-term remote-sensed LAI, GPP and Solar-induced Chlorophyll Fluorescence (SIF). We found a monotonically increasing trend in the GPP-LAI coupling in the LP from 1982 to 2018 (0.0043 yr−1, p < 0.05), in which the significant trend in the northwest LP was driven by increasing soil water and landcover change, e.g., increased grassland and afforestation. An ensemble of 11 state-of-the-art ecosystem models from the TRENDY project failed to capture the observed monotonically increasing trend of the GPP-LAI coupling in the LP. The consistent projection of a decreasing GPP-LAI coupling in LP during 2019–2100 by 22 Earth System Models (ESMs) under various future scenarios should be treated with caution due to the identified inherent uncertainties in the ecosystem component in ESMs and the notable biases in the simulation of future climate conditions. Our study highlights the need to enhance the key mechanisms that regulate the coupling relationships between photosynthesis and canopy structure in indigenized ecosystem models to accurately estimate the ecosystem change in drylands under global climate change.

Nematode Community Characteristics Indicate Soil Restoration under Different Revegetation Approaches in the Semiarid Area of the Chinese Loess Plateau

Soil nematode communities can offer valuable indicators for monitoring the status of soil ecosystems. However, their potential for assessing soil restoration under revegetation has been neglected in temperate arid and semiarid areas. This study examined the characteristics of soil nematode communities and their relationships with soil physicochemical properties under five typical revegetation approaches in the semiarid Loess Plateau of China. The results showed that planting an artificial Caragana korshinskii forest led to the recovery of the soil food web, which significantly increased soil nematode abundance (138.10 ± 11.60 inds./100 g dry soil) and community diversity (Shannon-Wiener diversity: 2.48 ± 0.13; trophic diversity: 3.08 ± 0.02), associated with the high contents of SOC and NH4+-N. However, establishing an artificial Prunus sibirica forest improved neither soil properties nor nematode community characteristics, reflecting poor soil ecosystem restoration. After establishing an artificial Prunus davidiana forest (PD) and an artificial Medicago sativa grassland (MS), substantial increases in herbivorous and fungivorous nematodes were observed, respectively, likely due to the accumulation of particular genera that fed on roots (e.g., Pratylenchus) or their symbiotic fungi (e.g., Tylencholaimus), which might result in the deterioration (in MS) or restoration (in PD) of the soil food webs. Natural grassland restoration greatly improved soil properties (i.e., SOC, NH4+-N, microbial biomass carbon) but did not change the nematode community obviously, probably due to top-down predation in natural habitats. In conclusion, the characteristics of nematode communities can effectively indicate the restoration of soil food webs and identify their possible driving forces under revegetation, which have important implications for vegetation restoration in arid and semiarid regions.

Water stress memory in wheat/maize intercropping regulated photosynthetic and antioxidative responses under rainfed conditions

Drought is a most prevalent environmental stress affecting the productivity of rainfed wheat and maize in the semiarid Loess Plateau of China. Sustainable agricultural practices such as intercropping are important for enhancing crop performance in terms of better physiological and biochemical characteristics under drought conditions. Enzymatic and non-enzymatic antioxidant enzyme activities are associated with improved abiotic tolerance in crop plants, however, its molecular mechanism remains obscure. A 2-year field study was conducted to evaluate the influence of intercropping treatment viz. wheat mono-crop (WMC), maize mono-crop (MMC), intercropping maize (IM) and wheat (IW) crops, and nitrogen (N) application rates viz. control and full-dose of N (basal application at 150 and 235 kg ha−1 for wheat and maize, respectively) on chlorophyll fluorescence, gas exchange traits, lipid peroxidation, antioxidative properties and expression patterns of six tolerance genes in both crops under rainfed conditions. As compared with their respective monocropping treatments, IW and IM increased the Fo/Fm by 18.35 and 14.33%, PS-11 efficiency by 7.90 and 13.44%, photosynthesis by 14.31 and 23.97%, C-capacity by 32.05 and 12.92%, and stomatal conductance by 41.40 and 89.95% under without- and with-N application, respectively. The reductions in instantaneous- and intrinsic-water use efficiency and MDA content in the range of 8.76–26.30% were recorded for IW and IM treatments compared with WMC and MMC, respectively. Compared with the WMC and MMC, IW and IM also triggered better antioxidant activities under both N rates. Moreover, we also noted that intercropping and N addition regulated the transcript levels of six genes encoding non-enzymatic antioxidants cycle enzymes. The better performance of intercropping treatments i.e., IW and IM were also associated with improved osmolytes accumulation under rainfed conditions. As compared with control, N addition significantly improved the chlorophyll fluorescence, gas exchange traits, lipid peroxidation, and antioxidant enzyme activities under all intercropping treatments. Our results increase our understanding of the physiological, biochemical, and molecular mechanisms of intercropping-induced water stress tolerance in wheat and maize crops.

Responses of sap flow density of two shrub species to rainfall classes on the semiarid Loess Plateau of China.

Rainfall events can determine a cascade of plant physiological and ecological processes, and there is considerable interest in the way that rainfall modifies plant water flux dynamics. The sap flow density (SF) of the planted species of Vitex negundo and Hippophae rhamnoides, on the Loess Plateau of China was monitored using the heat balance method from 2015 to 2017. The results showed that SF responded differently to rainfall classes because of the changing meteorological and soil water content (SWC) conditions. For class 1: 0.2-2 mm, SF increased by 14.36-42.93% for the two species, which were mainly attributable to the effect of solar radiation and vapor pressure deficit after rainfall. For class 2: 2-10 mm, SF remained nearly stable for V. negundo and decreased for H. rhamnoides because of the relative humidity's effect. For class 3: > 10 mm, SF increased significantly because of increased SWC and the increasing response to solar radiation. The increased percentage of SF was relatively higher for V. negundo when rainfall was less than 20 mm, while the value was higher for H. rhamnoides when rainfall was greater than 10 mm. Further, V. negundo's water potential increased at the soil-root interface (ψ0) and ψL, indicating that the plant, which has shallower roots and a coarser of leaf and bark texture, considered as anisohydric species and used precipitation-derived upper soil water to survive. The relatively consistent ψL and ψ0 for H. rhamnoides, which has deep roots and leathery leaves, indicated that this species was considered as isohydric species and insensitive to the slight change in the soil water status. The differed response patter and water use strategies between the two species showed that species as V. negundo are more susceptible to frequent, but small rainfall events, while larger, but less frequent rainfall events benefit such species as H. rhamnoides. This study quantified the effect of environmental factors for SF variation. The results could help formulate a selection process to determine which species are more suitable for sustainable management in the afforestation activities under the context of more frequent and intense rainfall events.

Long-Term Conservation Tillage Increases Yield and Water Use Efficiency of Spring Wheat (Triticum aestivum L.) by Regulating Substances Related to Stress on the Semi-Arid Loess Plateau of China

Improving the water-use efficiency (WUE) of crops is the most effective way to increase yields in semi-arid regions. Field research was carried out based on a long-term experiment initiated in 2001, aimed to explore the mechanisms of different tillage practices effects on grain yield and WUE of spring wheat. Tillage practices in the research including conventional tillage (CT), no tillage with no straw mulching (NT), conventional tillage with straw incorporation (TS), and no tillage with straw mulching (NTS). The effects of tillage practices on soil’s physical and chemical properties, dry matter accumulation, grain yield, dynamics of stress-related substances, and WUE were observed. Soil and plant samples in this research were collected in 2020 (wet year), 2021 (dry year), and 2022 (dry year). The results indicated that NTS improved the soil’s physical and chemical properties. The NTS treatment had the lowest soil bulk and pH and the highest total N, NO3--N, and available P. Throughout the whole growth stage, soil water content in the NTS and TS treatments were significantly higher than that of CT by 8.77–20.40% and 2.19–18.83, respectively. Averaged catalase (CAT), peroxidase (POD), and soluble protein across the three years with NTS and TS were significantly increased by 1.26–25.52% compared to CT. Meanwhile, the NTS treatment had the lowest malondialdehyde (MDA) content among the different tillage practices. NTS maintained the highest dry matter accumulation throughout the whole growth stage among different treatments; it was increased by 10.47–73.33% compared with CT. The average grain yields and WUE of NTS across the three years were 6.09–30.70% and 6.79–40.55% higher than other tillage practices, respectively. It is concluded that NTS influences dry matter accumulation and water-use efficiency during the whole growth stage of spring wheat by improving the soil’s physicochemical properties and modulating spring wheat substances related to stress, which in turn promotes yield formation.

Temporal and Habitat Dynamics of Soil Fungal Diversity in Gravel-Sand Mulching Watermelon Fields in the Semi-Arid Loess Plateau of China.

Mulching is an important agricultural management tool for increasing watermelon productivity and land-use efficiency because it helps improve water use efficiency and reduce soil erosion. However, there is relatively little available information regarding the effects of long-term continuous monoculture farming on soil fungal communities and related fungal pathogens in arid and semiarid regions. In this study, we characterized the fungal communities of four treatment groups, including gravel-sand-mulched farmland, gravel-sand-mulched grassland, fallow gravel-sand-mulched grassland, and native grassland, using amplicon sequencing. Our results revealed that the soil fungal communities differed significantly between mulched farmland and mulched grassland as well as the fallow mulched grassland. Gravel-sand mulch significantly impaired the diversity and composition of soil fungal communities. Soil fungal communities were more sensitive to gravel-sand mulch in grassland than in other habitats. Long-term continuous monoculture (more than 10 years) led to decreased abundance of Fusarium species, which contains include agronomically important plant pathogens. In the gravel-mulched cropland, some Penicillium and Mortierella fungi were significantly enriched with increasing mulch duration, suggesting potential beneficial properties of those fungi that could be applied to disease control. We also found that long-term gravel mulching in continuous monoculture farming could potentially form disease-suppressive soils and alter soil microbial biodiversity and fertility. Our study provides insights into the exploration of novel agricultural management strategies along with continuous monoculture practice to control watermelon wilt disease by maintaining a more sustainable and healthier soil environment. IMPORTANCE Gravel-sand mulching is a traditional agricultural practice in arid and semiarid regions, providing a surface barrier for soil and water conservation. However, application of such practice in monocropping systems may lead to outbreaks of several devastating plant diseases, such as watermelon Fusarium wilt. Our results with amplicon sequencing suggest that soil fungal communities differ significantly between mulched farmland and mulched grassland and are more sensitive to gravel-sand mulch in grassland. Under continuous monoculture regimens, long-term gravel mulch is not necessarily detrimental and may result in decreased Fusarium abundance. However, some known beneficial soil fungi may be enriched in the gravel-mulch cropland as mulch duration increases. A possible explanation for the reduction in Fusarium abundance may be the formation of disease-suppressive soils. This study provides insight into the need to explore alternative strategies using beneficial microbes for sustainable watermelon wilt control in continuous monocropping system.

Modeling root water uptake patterns of oil crops grown on semiarid loess

Oil crops are often used as cover crops by smallholders managing orchards on drylands, because they have an economic return and help regulate ecosystem services. Improving the ability of models in root water uptake (RWU) simulation is important to find the right crop species and predict the dynamics of these oil crops in water-limited regions. In this study, two different process-based models were used to simulate the RWU of three oil crops, i.e. soybean (Glycine max L., SYB) and two canola cultivars (turnip type rape (Brassica campestris L.), TTR, and cabbage type rape (Brassica napus L.), CTR), grown on the semiarid Loess Plateau of China, based on two-year in-situ measurements. The first model, IM-SVD, was developed by inverse modeling (IM) of the Richards equation and incorporating singular value decomposition (SVD) parameter optimization algorithms, which simulated the RWU pattern (including soil evaporation and plant transpiration). The second model was the Feddes model implemented in one-dimensional HYDRUS (HYDRUS 1-D). Both models reliably predicted the soil water content (SWC) in different layers. However, the IM-SVD model showed better modeling accuracy of SWC, and produced higher simulated RWU values than the HYDRUS 1-D model irrespective of crop. The results from both models implied that SYB had a higher daily and seasonal RWU than TTR and CTR, and its water source was derived mainly from the top 30 cm soil layer. Additionally, the simulated RWU was positively and significantly (p<0.05) correlated with fine root length density (FRLD). The RWU showed lagged correlations with SWC, which varied between crop species and growth stages, but overall were more positively correlated with the SWC on preceding days and more negatively correlated with the SWC on subsequent days. Our study provides insights into the improving RWU simulation for oil crops and similar crops in drylands.

Rainfall Partitioning by Evergreen and Deciduous Broad-Leaved Xerophytic Tree Species: Influence of Rainfall, Canopy Characteristics, and Meteorology

Understanding how rainfall is partitioned into throughfall, stemflow, and interception losses by xerophytic trees is important for evaluating afforestation projects and modeling hydrological budgets in semi-arid regions. However, information regarding rainfall partitioning by xerophytic trees and the controlling factors in semi-arid regions remains underrepresented in the literature. We examined whether plant functional groups have a significant impact on rainfall partitioning in two xerophytic trees (evergreen species: Pinus tabuliformis (Pinales:Pinaceae) hereafter called P. tabuliformis, deciduous species: Robinia pseudoacacia L. (Fabales:Fabaceae) hereafter called R. pseudoacacia) commonly used for afforestation on the semi-arid Loess Plateau of China, and evaluated the effects of rainfall, canopy characteristics and meteorological variables on rainfall partitioning. The event-based gross rainfall, throughfall and stemflow were measured during both growing (May–October) and dormant (January–April and November–December) seasons in 2015 and 2016 within an afforested watershed in semi-arid Loess Plateau of China. During our study period, the average rainfall depth for growing season and dormant season was 8.4 mm (varied from 0.2 to 57.6 mm) and 5.6 mm (varied from 0.2 to 41.6 mm), respectively. On average, the measured throughfall, stemflow and interception loss for R. pseudoacacia accounted for 81.8%, 1.4% and 16.8% of gross rainfall, respectively. Corresponding values for P. tabuliformis were 75.1%, 0.7% and 24.1%, respectively. Significant differences (p &lt; 0.05) in stemflow were detected between R. pseudoacacia and P. tabuliformis during both the growing and dormant seasons. The rainfall partitioning components were significantly positively correlated with individual rainfall amounts. The minimum rainfall required to generate stemflow was 5.2 mm for R. pseudoacacia and 5.9 mm for P. tabuliformis during the growing season, and 3.1 mm for R. pseudoacacia and 6.0 mm for P. tabuliformis during the dormant season. Smaller rainfall events contributed to a lower percentage of rainfall amount, throughfall and stemflow but higher percentage of canopy interception loss. The percentage of throughfall and stemflow showed an increased tendency with increasing rain-fall characteristics, while the increasing rainfall characteristics resulted in a decrease in relative interception loss. During the growing season, leaf area index is significantly correlated with throughfall and interception loss of R. pseudoacacia, while there were no significant correlation between meteorological variables and rainfall partitioning. In general, the depth of rainfall partitioning can be predicted reasonably well by using the developed multiple regression models, but the proportions of rainfall partitioning had a relative lower accuracy using the developed models, especially for relative interception loss. To better predict canopy interception loss, other plant morphological and meteorological variables should be considered.

Straw mulching for enhanced water use efficiency and economic returns from soybean fields in the Loess Plateau China

Water shortages threaten agricultural sustainability in the semi-arid areas of the Loess Plateau. Judicious mulching management can improve water conservation practices to alleviate this issue while increasing crop productivity. We investigated the effect of straw strip mulching and film mulching on soil water consumption, temperature, growth, grain yield, and economic income of soybean [Glycine max(Linn.) Merr.] from 2017 to 2018 in Qingyang on the semi-arid Loess Plateau in China using four treatments: (a) alternating ridges and furrows with ridges mulched with white polyethylene film (PMP), (b) alternating flat and bare land with only the plat mulched by white polyethylene film (PMF), (c) alternating strips mulched with maize (Zea mays L.) straw (SM), and (d) traditional land planting without mulching (CK). The mulching treatments (PMP, PMF, and SM) increased soil water consumption and soil water use efficiency. The SM, PMF, and PMP treatments had 12.3–12.5, 16.8–22.1, and 23.2–24.2 mm higher soil water consumption (0–120 cm depth) than CK, most of which occurred in the 60–120 cm soil layer. Compared with CK, PMP and PMF significantly increased soil temperature by 1.30–1.31 °C and 0.76–1.00 °C, soybean grain yield by 38.6–39.0 % and 38.8–44.2 %, and water use efficiency (WUE) by 27.7–32.8 % and 30.8–37.5 %, respectively, while SM significantly decreased soil temperature by 0.96–1.15 °C, and increased grain yield by 21.8–25.4 % and WUE by 16.9–21.9 %. PMP and PMF did not significantly change soil water consumption, WUE, or grain yield. The SM treatment increased net income by 501.3–691.7 and 1914.5–2244.9 CNY ha−1 relative to PMP and CK, respectively, but PMF and SM did not significantly differ. Therefore, the SM system could help increase grain yields and economic returns in dryland soybean production, avoiding the adverse effects of the increasingly popular plastic mulching approach.

Effect of different vegetation restoration on soil properties in the semi-arid Loess Plateau of China

Vegetation restoration on the Loess Plateau has decreased soil erosion. However, the comprehensive effects of different vegetation restoration types on soil properties are not clear. Evaluating the soil properties of the main economic and ecological tree species on the Loess Plateau can provide crucial guidance for regional ecological environment restoration. Therefore, we compared soil water content (SWC), soil particle composition, root distribution, soil organic carbon (SOC) content, soil bulk density (BD), total porosity (TP), saturated hydraulic conductivity (Ks), soil water retention curves (SWRCs), and soil aggregate stability of peach (Prunus persica), walnut (Juglans regia L.), and apple (Malus pumila) orchards, black locust (Robinia pseudoacacia), and grassland of similar age on the semi-arid Loess Plateau. Forestland, especially black locust, had significantly lower SWC than grassland. The different vegetation restoration types altered the soil texture; grassland had the highest clay content, while black locust had the lowest. Afforestation promoted deep root formation, reaching>10 m, with>50 % of the roots below 2 m. Compared with grassland, forestland did not increase SOC content in the soil profile. Soil BD increased with increasing soil depth from 0 to 80 cm for the five vegetation types but was relatively stable below 80 cm; grassland had the greatest BD, while black locust had the lowest. The walnut orchard had the lowest Ks in the 0–80 cm soil layer. The apple orchard had the highest residual soil water content and field capacity. The apple orchard had significantly lower mean weight diameter (MWD) than the others, indicating low surface soil stability due to tillage management, increasing the risk of soil erosion. Overall, these results suggested that black locust had greater negative effects on soil properties than economic trees. Therefore, black locust establishment or planting density should be reduced in future vegetation restoration processes.

Understanding Sustainable Livelihoods with a Framework Linking Livelihood Vulnerability and Resilience in the Semiarid Loess Plateau of China

Regional climate is complicated and unpredictable in the context of global climate change. Farmers on the Loess Plateau, who rely on agriculture and natural resources for subsistence, are one of the groups feeling the early effects of climate change. Their vulnerability is determined by their degree of connection with the natural environment. Frequent droughts on the Loess Plateau have severely challenged farmers’ livelihoods, although some actions have been taken to adapt to these changes. To enable farmers to find sustainable livelihood strategies in challenging natural conditions, we established a research framework to link livelihood vulnerability and resilience and applied it to Jiaxian County, a specific research area in the Loess Plateau of China. To validate previous research, we studied the fluctuation trends of farmers’ livelihood vulnerability and livelihood resilience in the past 30 years and the interrelationships between these two trends and their influencing factors. The results are as follows: since 1990, livelihood vulnerability has been polarized; however, moderate vulnerability has always been dominant. Livelihood resilience shows a trend of continuous enhancement. The relationship between livelihood vulnerability and resilience is complex, and the direction of change between the two can be both similar and different. The topography, arable land conditions, soil quality, and irrigation conditions in different areas impact vulnerability and resilience, and the degree of impact is different in different periods. Farmers’ livelihood strategies depend on their cognitive decision making and livelihood assets, which are critical vulnerability and resilience factors. Most farmers in the study area have undergone significant livelihood strategy changes, while some maintain their original livelihood strategies. These findings provide policy implications for reducing vulnerability, enhancing resilience, and helping smallholder farmers find sustainable livelihood strategies to avoid poverty traps.

Comparison of Different Methods to Estimate Canopy Water Storage Capacity of Two Shrubs in the Semi-Arid Loess Plateau of China

The canopy water storage capacity of vegetation has great significance for the hydrological cycle. We used the Pereira regression analysis method, scale-up method, and simulated rainfall method to determine canopy water storage capacity from 2014 to 2018. The Pereira regression analysis was affected mainly by the seasonal variation in the leaf area index and the observation method of throughfall. The canopy water storage capacity was 0.68 mm and 0.72 mm for C. korshinskii and H. rhamnoides, respectively. The canopy water storage capacity of C. korshinskii and H. rhamnoides was 0.73 mm and 0.76 mm, respectively, using the scale-up method. The scale-up method showed that water storage capacity per area of the canopy components was in the order of branches (0.31 mm) &gt; leaves (0.27 mm) &gt; trunks (0.15 mm) for C. korshinskii, and trunks (0.33 mm) &gt; branches (0.29 mm) &gt; leaves (0.14 mm) for H. rhamnoides. We used eight simulated rainfall intensities to determine the canopy water storage capacity for C. korshinskii and H. rhamnoides, which was 0.63 mm and 0.59 mm, respectively.

Ecohydrological advantage of young apple tree-based agroforestry and its response to extreme droughts on the semiarid Loess Plateau

Agroforestry is considered to be climate-smart; not only can it be profitable for smallholders, but also it represents a sustainable form of intensive agriculture that can help buffer the effects of extreme climate. However, its feasibility remains under dispute in semiarid regions, especially where there can be extreme droughts. We therefore investigated how intercropping with annual bioenergy crops, soybean (Glycine max) and canola (Brassica rapa), affects ecohydrology in young apple trees, and how the trees respond to droughts of varying degrees on the semiarid Loess Plateau of China. A monoculture orchard was used as a control, and the droughts were controlled by reducing natural precipitation by 15% (moderate drought) and 25% (severe drought). We found that, compared with the monoculture, the agroforestry system increased soil water storage (SWS) in the 80-280 cm by 5-8%, apple tree's daily water use (Q) by 76-118%, and transpiration per unit leaf area (TrL) by 33-71%; it also promoted tree growth. Both drought levels affected soil water availability and water use. Compared with agroforestry without an enforced drought, moderate drought conditions reduced SWS in the 80-180 cm by 11-15%, the Q value by 19-24%, and TrL value by 13-17%, and these apple trees still had higher Q and TrL levels than monoculture trees suffering no drought; and severe drought conditions caused the apple trees to absorb soil water from deeper soil layers, and reduced SWS in the 80-280 cm by 16-18%, Q by 50-60% and TrL by 12-38%. However, there were no significant difference in Q, TrL and aboveground growth parameters for trees between monoculture and severe drought treatments. These findings demonstrate that agroforestry has clear ecohydrological advantage to monoculture for young apple trees in semiarid regions.

A field test to investigate spatiotemporal distribution of soil moisture under different cropland covers in the semiarid Loess Plateau of China

A field test to investigate spatiotemporal distribution of soil moisture under different cropland covers in the semiarid Loess Plateau of China

Nitrogen Supply Affects Yield and Grain Filling of Maize by Regulating Starch Metabolizing Enzyme Activities and Endogenous Hormone Contents.

This study aimed to examine the effect of nitrogen (N) application rate and time on yield, grain filling, starch metabolizing enzymes, and hormones of maize based on a long-term field experiment initiated in 2012. The total N fertilizer dose [(0 (N0), 100 (N1), 200 (N2), and 300 (N3) kg N ha–1] was split into two (T1, one-third at sowing and two-thirds at the six-leaf stage) or three (T2, one-third each at sowing, six-leaf, and eleven-leaf stage) times application. The results showed that the highest yield was obtained under N3T2, N2T1, and N3T2 in 2018, 2019, and 2020, which was 222.49, 185.31, and 194.00% than that of N0 in each year, respectively. N2 and N3 significantly increased the yield through enhancing ears ha–1, grains per plant, and 100-grain weight; however, N2 and N3 did not show a significant difference in yield and above-yield components. In addition, N application time did not significantly change yield under the same N rate. N0 limited the activities of starch metabolizing enzymes, resulting in insufficient accumulation of sucrose and starch. The contents of indole-3-acetic acid, cytokinin, abscisic acid, and gibberellin were decreased under N0 during grain filling. The average grain-filling rate and maximum grain-filling rate (Gmax) and grain weight increment achieving Gmax increased under N2 and N3, and the grain-filling parameters were positively correlated with 100-grain weight. In conclusion, 200 kg N ha–1 with one-third application at sowing and two-thirds application at the six-leaf stage is a suitable N supply way to improve starch metabolizing enzymes, regulate hormone content, and enhance grain-filling rates, and thus increasing the maize yield in the semiarid Loess Plateau of China.

Phenology determines water use strategies of three economic tree species in the semi-arid Loess Plateau of China

Economic tree species growing in the semi-arid Loess Plateau of China are important for maintaining sound economic viability and protecting the fragile hydro-ecological environment. However, their water use strategies and ecological adaptation to dryland environments remain poorly understood. In this study, we measured variations in soil water content, root distribution, water isotopic signature for hydrogen (δ2H) and oxygen (δ18O) in xylem and soil water of peach (Prunus persica), walnut (Juglans regia L.), and apple (Malus pumila) trees, as well as carbon isotopic signature (δ13C) in their leaves during two consecutive growing seasons—2018 (normal year) and 2019 (wet year). The results showed all species consumed less deep soil water in 2019 than in 2018 due to the increased precipitation. Peach trees used more shallow soil water compared to walnut and apple trees that used more deep soil water during high water-demanding periods. Walnut trees depended more on deep soil water throughout the growing season, contributing 46.2% in 2018, compared to 26.0% for peach trees and 24.0% for apple trees. Moreover, walnut trees had lower deep soil water and leaf δ13C than peach and apple trees. The findings suggest differences in phenology periods of the three rainfed economic tree species to affect the water source used. The three tree species differed in their water use strategies: walnut trees had ecological plasticity for reducing water stress by absorbing deep soil water, and peach and apple trees had higher water use efficiencies. This study has significance for evaluating water use characteristics and drought stress responses of economic trees in water-limited environments.

Conservation tillage improves soil water storage, spring maize (Zea mays L.) yield and WUE in two types of seasonal rainfall distributions

Variations in the rainfall distribution during the growing season are a major limiting factor restricting the spring maize yield on the semiarid Loess Plateau of China. Conservation tillage can improve yield and water use efficiency but the specific effects of conservation tillage with differing rainfall distributions during the growing season remain unclear. Therefore, a 12-year experiment was conducted and the data were divided into two categories based on rainfall distribution type. If poor rainfall occurred during the jointing-tasseling stage of the maize growing season and adequate rainfall occurred in the filling-maturity stage, the rainfall was named type-A. In contrast, if adequate rainfall occurred in the jointing-tasseling stage and poor rainfall occurred in the filling-maturity stage during the maize growing season, the rainfall distribution was categorized as type-B. This research used conventional tillage (CT) as a control to study the productivity of no-tillage (NT) and subsoiling (ST) under the selected rainfall distributions. The results showed that the type-B rainfall distribution increased dry matter accumulation, yield, soil water use efficiency (WUE) and precipitation use efficiency (PUE) by 18.9%, 32.0%, 21.7% and 45.1%, respectively, when compared with the type-A rainfall distribution. However, under type-A rainfall distribution, NT increased soil water storage by 3.7% and 4.4% and ST increased the soil water storage by 6.0% and 7.0% in the tasseling and grain filling stages, respectively, compared with CT. Moreover, NT and ST increased the dry matter accumulation, yield, WUE and PUE. The relationships among the yield, soil water storage and precipitation showed that the water storage in the sowing stage indirectly affected the maize yield through soil water storage at the tasseling stage, and the increase in precipitation from the jointing to tasseling stages had a directly positive effect on the increase in yield. Based on soil water storage with a value of 202.3 mm in the 0–200 cm soil depth during the tasseling stage, the yield increased by 47.8 kg ha−1 as the soil water storage improved by 1 mm. In conclusion, no-tillage and subsoiling improved the soil water conditions, mitigated the soil drought stress caused by variable rainfall distribution and improved the yield. Therefore, no-tillage and subsoiling practices are recommended for agricultural production in semiarid areas.

Soil Water Availability Changes in Amount and Timing Favor the Growth and Competitiveness of Grass Than a Co-dominant Legume in Their Mixtures.

The grasslands on the semi-arid Loess Plateau of China are expected to be particularly responsive to the size and frequency changes of extreme precipitation events because their ecological processes are largely driven by distinct soil moisture pulses. However, the plant growth and competitiveness of co-dominant species in response to the changes in the amount and timing of soil water are still unclear. Thus, two co-dominant species, Bothriochloa ischaemum and Lespedeza davurica, were grown in seven mixture ratios under three watering regimes [80 ± 5% pot soil capacity (FC) (high watering), 60 ± 5% FC (moderate watering), and 40 ± 5% FC (low watering)] in a pot experiment. The soil water contents were rapidly improved from low to moderate water and from moderate to high water, respectively, at the heading, flowering, and maturity stages of B. ischaemum, and were maintained until the end of the growing season of each species. The biomass production of both species increased significantly with the increased soil water contents, particularly at the heading and flowering periods, with a more pronounced increase in B. ischaemum in the mixtures. The root/shoot ratio of both species was decreased when the soil water availability increased at the heading or flowering periods. The total biomass production, water use efficiency (WUE), and relative yield total (RYT) increased gradually with the increase of B. ischaemum in the mixtures. The relative competition intensity was below zero in B. ischaemum, and above zero in L. davurica. The competitive balance index calculated for B. ischaemum was increased with the increase of the soil water contents. Bothriochloa ischaemum responded more positively to the periodical increase in soil water availability than L. davurica, indicating that the abundance of B. ischaemum could increase in relatively wet seasons or plenty-rainfall periods. In addition, the mixture ratio of 10:2 (B. ischaemum to L. davurica) was the most compatible combination for the improved biomass production, WUE, and RYTs across all soil water treatments.