Arid Valley Research Articles

Enzyme stoichiometry reveals microbial nitrogen limitation in stony soils

Resource limitation for soil microorganisms is the crucial factor in nutrient cycling and vegetation development, which are especially important in arid climate. Given that rock fragments strongly impact hydrologic and geochemical processes in arid areas, we hypothesized that microbial resource (C and N) limitation will increase along the rock fragment content (RFC) gradient. We conducted a field experiment in Minjiang river arid valleys with four RFC content (0 %, 25 %, 50 %, and 75 %, V V−1) and four vegetation types (Artemisia vestita, Bauhinia brachycarpa, Sophora davidii, and the soil without plants). Activities of C (β-1,4-glucosidase, BG), N (β-1,4-N-acetyl-glucosaminidase, NAG; L-leucine aminopeptidase, LAP), and P (acid phosphatase, ACP) acquiring enzymes were investigated to assess the limitations by C, N or P. In unplanted soil, the C acquiring enzyme activity decreased by 43 %, but N acquiring enzyme activity increased by 72 % in 75 % RFC than those in rock-free soils (0 % RFC). Increasing RFC reduced C:N and C:P enzymatic ratios, as well as vector length and vector angle (< 45°). Plants increased the activities of C and N acquiring enzymes in soils, as well as C:P and N:P enzyme activities, as well as vector length (by 5.6 %–25 %), but decreased vector angle (by 13 %–21 %). Enzyme stoichiometry was dependent on biotic and abiotic factors, such as soil water content, soil C:N, and total content of phospholipid fatty acids, reflecting microbial biomass content. Increased RFC shifted enzymatic stoichiometry toward lower C but stronger N limitation for microorganisms. Vegetation increased microbial C and N limitation, and impacted the enzymatic activities and stoichiometry depending on shrub functional groups. Consequently, the direct effects of vegetation, nutrient availability and microbial biomass content, as well as indirect effects of soil properties collectively increased microbial resource limitations along the RFC gradient.

Shifting patterns in fine root distribution of four xerophytic species across soil structural gradients and years of growth.

Fine root (diameter < 2 mm) distribution influences the potential for resource acquisition in soil profiles, which defines how plants interact with local soil environments; however, a deep understanding of how fine root vertical distribution varies with soil structural variations and across growth years is lacking. We subjected four xerophytic species native to an arid valley of China, Artemisia vestita, Bauhinia brachycarpa, Sophora davidii, and Cotinus szechuanensis, to increasing rock fragment content (RFC) treatments (0%, 25%, 50%, and 75%, v v-1) in an arid environment and measured fine root vertical profiles over 4 years of growth. Fine root depth and biomass of woody species increased with increasing RFC, but the extent of increase declined with growth years. Increasing RFC also increased the degree of interannual decreases in fine root diameter. The limited supply of soil resources in coarse soils explained the increases in rooting depth and variations in the pattern of fine root profiles across RFC. Fine root depth and biomass of the non-woody species (A. vestita) in soil profiles decreased with the increase in RFC and growth years, showing an opposite pattern from the other three woody species. Within woody species, the annual increase in fine root biomass varied with RFC, which led to large interannual differences in the patterns of fine root profiles. Younger or non-woody plants were more susceptible to soil environmental changes than the older or woody plants. These results reveal the limitations of dry and rocky environments on the growth of different plants, with woody and non-woody plants adjusting their root vertical distribution through opposite pathways to cope with resource constraints, which has management implications for degraded agroforest ecosystems.

Indicator of climate variability: low treeline displacement in arid valleys of mountain areas, China

Indicator of climate variability: low treeline displacement in arid valleys of mountain areas, China

Ecosystem carbon sequestration of Zanthoxylum bungeanum plantations under the farmland conversion in the arid valley of the upper reaches of Yangtze River, China

Ecosystem carbon sequestration of Zanthoxylum bungeanum plantations under the farmland conversion in the arid valley of the upper reaches of Yangtze River, China

Research on Vegetation Ecological Security in Arid Region Mountain Front River Valleys Based on Ecological Water Consumption and Water Demand

The central region of the Eurasian continent is widely affected by arid conditions, but the valleys in front of the mountains nurture ecosystems consisting of forests, shrubs, and grasslands. Preserving the ecological balance in these arid valley areas is an essential aspect of water resource planning and management. This study utilizes calculations of vegetation’s ecological water consumption and water requirements to quantitatively simulate groundwater levels. These simulated levels are then compared with the threshold depth suitable for vegetation, ultimately leading to the development of an ecological security assessment method for valley areas. The results show the following: (1) During 30 years, the water demand of river valley vegetation increased slowly, and the overall stability is about 4.82 × 108 m3. Among them, the ecological water demand of grassland is the largest. The water demand from June to August is about 68% of the whole year. (2) The results indicate that over a period of 30 years, the groundwater levels in the valley area have shown a gradual decline. The rate of decline in groundwater levels is approximately twice as fast in areas farther away from the river compared to areas closer to the river. The decline in groundwater levels typically begins in May each year. During the period of valley flooding in June, there is a temporary rise in water levels, followed by a continued decline afterwards. (3) The study area has a significant proportion of groundwater suitable areas, accounting for approximately 65% on average annually. Over the course of 30 years, the area experiencing groundwater deficiency has increased from 31% to 37%. (4) Over the past 30 years, the ratio of annual vegetation water consumption to water demand in the river valley has been slowly decreasing, and the vegetation growth status has changed from good growth to normal growth. (5) In the past 30 years, the area of ecological quality areas has decreased significantly, and most of them have been transformed into general areas. The area of ecologically fragile areas is increasing, and the area of fencing protected areas is slowly declining.

The Extraordinary Alkali Bee, Nomia melanderi (Halictidae), the World's Only Intensively Managed Ground-Nesting Bee.

Among the ground-nesting bees are several proven crop pollinators, but only the alkali bee (Nomia melanderi) has been successfully managed. In <80 years, it has become the world's most intensely studied ground-nesting solitary bee. In many ways, the bee seems paradoxical. It nests during the torrid, parched midsummer amid arid valleys and basins of the western United States, yet it wants damp nesting soil. In these basins, extensive monocultures of an irrigated Eurasian crop plant, alfalfa (lucerne), subsidize millions of alkali bees. Elsewhere, its polylectic habits and long foraging range allow it to stray into neighboring crops contaminated with insecticides. Primary wild floral hosts are either non-native or poorly known. Kleptoparasitic bees plague most ground nesters, but not alkali bees, which do, however, host other well-studied parasitoids. Building effective nesting beds requires understanding the hydraulic conductivity of silty nesting soils and its important interplay with specific soil mineral salts. Surprisingly, some isolated populations endure inhospitably cold climates by nesting amid hot springs. Despite the peculiarities and challenges associated with its management, the alkali bee remains the second most valuable managed solitary bee for US agriculture and perhaps the world.

Latitudinal patterns of soil nitrogen density across soil profiles and their driving factors in the arid valleys of southwest China

Latitudinal patterns of soil nitrogen density across soil profiles and their driving factors in the arid valleys of southwest China

Influences of rock fragment content and vegetation on soil microbial communities

Soil microbial communities are key drivers of ecosystem processes and can be strongly affected by soil properties. While the effects of soil texture and aggregate have been well studied, the effect of rock fragment content (RFC) on soil microbial communities is still poorly understood, particularly in arid ecosystem. We examined the responses of soil microbial biomass and communities to RFC gradients using a randomized block experiment with four RFCs (0 %, 25 %, 50 % and 75 %, V/V) and four planting treatments (Artemisia vestita, Bauhinia brachycarpa, Sophora davidii and no plants) in Minjiang arid valley. We explored soil community composition identified by total phospholipid fatty acids, and edaphic properties after two growth seasons. In most of current planting treatments, total phospholipid fatty acids, bacteria, saprotrophic fungi and arbuscular mycorrhizal fungi significantly decreased under 50–75 % RFCs versus 0–25 % RFCs. Compared to non-planted treatment, plants prominently increased soil microbial biomass and altered microbial communities only in 75% RFC. The ratio of gram-positive bacteria to gram-negative bacteria remarkably reduced in 75 % RFC of non-planted treatment, while significantly decreased in soil with 0 % RFC beneath A. vestita and S. davidii. These variations in soil microbial communities could be explained by the changes in soil water content, available nitrogen, total phosphorus and plant biomass allocation to fine root. These results indicated that both moderate and high RFC conditions inhibited soil microbial development, while plant can promote microbial biomass in high RFC by improving edaphic physiochemical properties and alleviating environmental stresses. Moreover, soil water content and nutrient levels explained much of the variation in soil microbial communities in these stony soils.

The difference in soil organic carbon distribution between natural and planted forests: A case study on stony soils mountainous area in the Upper Min River Arid Valley, China

AbstractFew studies have been conducted on the factors and distribution of soil organic carbon (SOC) in plantation forests in arid mountainous regions, especially in orchards. We aimed to unravel the SOC distribution among land‐use types and the effects of altitude gradients and rock fragment content (RFC) on SOC accumulation and sequestration in the Upper Min River Arid Valley, China. The differences in SOC distribution among land‐use types were quantified. The correlation analysis of SOC with various factors, such as altitude and RFC, was conducted. The variation percentage in SOC content and stocks was explained by the factors' contribution using mixed‐effects models. SOC distribution was characterized by high content and low stocks in native forests and shrubs, high content and high stocks in eco‐forest, and low content and high stocks in orchards. At the surface (0–30 cm), SOC content and stocks in orchards (cherry, plum, and apple) were significantly lower than those in eco‐forests. There was a significant positive correlation between altitude and SOC content at the surface but not at the subsoil (30–60 cm). With RFC increased, the surface SOC content decreased in native forests, shrubs, and eco‐forests, while it increased in orchards. Our results suggest that land management is the main factor controlling the variation in SOC distribution. Enhancing the surface SOC stability in orchards by land management is a priority for soil carbon pool management in the Arid Valleys.

Post‐farmland conversion spatio‐temporal dynamics of net soil nitrogen mineralization and availability in a chronosequence of Zanthoxylum bungeanum plantations

AbstractAfforestation on cultivated farmlands causes major shifts in the nitrogen (N) cycle. The consequences of large‐scale Zanthoxylum bungeanum afforestation on spatio‐temporal patterns of soil N mineralization and inorganic N (ION) availability have not been reported. Moreover, the regulatory roles of microbial biomass and soluble organic N (MBN and SON) in the N cycle are poorly characterized in soils below 20 cm. To investigate the long‐term effects of afforestation on the governing mechanism of vertical N dynamics, a 0–100 cm soil profile was collected from a chronosequence of Z. bungeanum plantations aged 8‐year (H8), 15‐year (H15), 20‐year (H20) and 28‐year (H28), as well as adjacent farmland and abandoned‐land (28‐year) as controls in an arid valley in Southwest China. With increasing stand age, conversion of farmland to Z. bungeanum plantations significantly improved soil organic carbon, available nutrients, and all N forms. These impacts were more evident in the topsoil (0–20 cm) than in the subsoil layers. MBN and SON contents improved by 1.42‐fold and 1.34‐fold in H28, respectively, compared to H8. Net N mineralization (1.31‐fold), net nitrification rates (1.30‐fold), and total ION (1.31‐fold) content followed similar trends of increase along with the stand age. Correlation and redundancy analysis also established a positive relationship and demonstrated that increased ION availability is due to improved MBN, SON, and urease activity with the plantations age. Although the nitrate‐N content was highest in abandoned‐land, its content also increased steadily in Z. bungeanum plantations with the stand age. A relatively low ammonium/nitrate ratio (0.331) in H28 advocated improved N supply via nitrification as well as low N leaching risks from plantations. The spatial investigation provided novel insights into controls of N cycle and suggested converting farmland to Z. bungeanum plantations is a suitable approach for restoring soil N.

Conservation genetics of Firmiana major, a threatened tree species with potential for afforestation of hot, arid climates

Firmiana major (Malvaceae) is a dominant tree species in hot, arid valleys with savanna vegetation in southwest China. Due to severe human disturbance, the populations of F. major declined sharply and was once considered extinct in the wild. Until 2020, eight populations of F. major were found by our investigation and it was listed as a Plant Species of Extremely Small Populations (PSESP) in Yunnan Province, China, for urgent rescuing during the next decade. To guide its conservation, the genetic structure, demographic history, and distribution model were studied. Four genetic groups of F. major were revealed and their divergence times coincided with warming periods during the last glacial stage. The distribution model showed a narrow habitat for F. major around the hot, arid areas of Yuanmou Basin, Jingsha arid-hot valleys and their adjacent areas, which enhanced its endangered situation. Based on the study, several conservation suggestions for F. major were proposed including adopting its germplasms with better drought tolerance for afforestation in this area. • Firmiana major is an endangered yet dominant tree that has potential to be a native greening species in savanna vegetation. • We found four genetic groups of F. major and one group showed climatic differentiation from other groups. • Divergence time of F. major was related to the warm periods in the last glacial stage. • The study predicted a relatively narrow distribution of F. major in hot, arid areas which enhanced its endangered situation. • We provided population recovery goals and conservation strategies for F. major based on the results.

Conversion effects of farmland to Zanthoxylum bungeanum plantations on soil organic carbon fractions in the arid valley of the upper reaches of the yangtze river, china

Farmland afforestation is an effective measure to sequester carbon (C) into soil, but the effects of different farmland conversion approaches on soil organic C (SOC) fractions in arid valley are still not clear. In this work, the concentrations of each SOC fraction in 0–100 cm soil depth, litter stock (LS) and fine root biomass (FRB) in farmland (FL), abandoned land (AL) and Zanthoxylum bungeanum plantations of different ages (with planting ages of 8, 15, 20 and 28 years, abbreviated as ZB8, ZB15, ZB20 and ZB28, respectively) were measured. The results showed that 1) the concentrations of each SOC fraction in the same soil layer increased after the farmland conversion, and these indices ranked as AL > ZB28 > ZB20 > ZB15 > ZB8 > FL, and all of them decreased with the soil depth; 2) the SOC stock, SOC sequestration and SOC sequestration rate increased by 120.1–158.9 Mg ha−1, 4.9–43.8 Mg ha−1 and 0.6–1.6 Mg ha−1 yr−1, respectively, after FL was converted to AL and Z. bungeanum plantations and ranked the same order as the SOC fractions with the land-use types; and 3) the C pool management index (CPMI), LS and FRB of different land-use types ranked as AL > Z. bungeanum plantations > FL, and LS and FRB were significantly (p < 0.05) correlated with each SOC fraction and CPMI, while CPMI was significantly (p < 0.05) correlated with each SOC fraction. This implies that the farmland conversion in arid valleys mediated by LS and FRB is helpful to improve the size and activity of soil C pools, and CPMI can be used as a useful index to estimate soil C pools in this region. In this sense, litter and roots should be emphasized in the process of farmland conversion to increase soil C sequestration.

Response of soil microbial community structure and function to different altitudes in arid valley in Panzhihua, China

BackgroundAltitude affects biodiversity and physic-chemical properties of soil, providing natural sites for studying species distribution and the response of biota to environmental changes. We sampled soil at three altitudes in an arid valley, determined the physic-chemical characteristics and microbial community composition in the soils, identified differentially abundant taxa and the relationships between community composition and environmental factors.ResultsThe low, medium and high altitudes were roughly separated based on the physic-chemical characteristics and clearly separated based on the microbial community composition. The differences in community composition were associated with differences in soil pH, temperature, and SOC, moisture, TN, TP, AN, AP and SMBC contents. The contents of organic and microbial biomass C, total and available N and available P, and the richness and diversity of the microbial communities were lowest in the medium altitude. The relative abundances of phyla Proteobacteria, Gemmatimonadetes, Actinobacteria and Acidobacteria were high at all altitudes. The differentially abundant amplified sequence variants (ASVs) were mostly assigned to Proteobacteria and Acidobacteria. The highest number of ASVs characterizing altitude were detected in the high altitude. However, the predicted functions of the communities were overlapping, suggesting that the contribution of the communities to soil processes changed relatively little along the altitude gradient.ConclusionsThe low, medium and high altitudes were roughly separated based on the physicochemical characteristics and clearly separated based on the microbial community composition. The differences in community composition were associated with differences in soil pH, temperature, and SOC, moisture, TN, TP, AN, AP and SMBC contents.

Effect of vineyard row orientation on microclimate, phenolic compounds, individual anthocyanins, and free volatile compounds of Cabernet Sauvignon (Vitis vinifera L.) in a high-altitude arid valley

Effect of vineyard row orientation on microclimate, phenolic compounds, individual anthocyanins, and free volatile compounds of Cabernet Sauvignon (Vitis vinifera L.) in a high-altitude arid valley

Soil microbial biomass and community composition along a latitudinal gradient in the arid valleys of southwest China

Identifying the latitudinal patterns and drivers of soil microbial biomass and community composition helps to better understand the biogeochemical cycling of carbon and nutrients. However, little is known about how and to what extent biotic and abiotic factors influence soil microbial biomass and specific microbial groups along latitudinal gradients, especially in arid and semi-arid regions. In this study, we sampled the topsoil (0–10 cm) and subsoil (10–20 cm) from 105 natural shrubland sites across a latitudinal gradient (23.2 °N to 32.3 °N) in the arid valleys of southwest China. We measured the soil microbial biomass and community composition (using phospholipid fatty acid [PLFA] analysis) and their possible environmental drivers. The results showed that soil microbial biomass (expressed as total PLFAs) increased significantly with increasing latitude, independent of the soil layer. More specifically, in the two soil layers, the PLFAs of Gram-negative bacteria and fungi, and the fungi/bacteria (F/B) ratio increased significantly along with the latitude, while the PLFAs of Actinobacteria did not significantly change with latitude. Bacterial and Gram-positive bacterial PLFAs increased significantly with latitude only in the subsoil, but not in the topsoil. Soil microbial biomass and the PLFAs of specific groups were closely related to vegetation properties (fine root biomass and plant species richness) and soil nutrients (e.g., soil organic carbon), while the F/B ratio was mainly related to climate (e.g., mean annual precipitation) and soil pH. The relationships between soil microbial biomass and community composition and environmental factors were similar in the topsoil and subsoil. Overall, our study elucidated the latitudinal patterns in soil microbial biomass and community composition, and our findings highlight that climate, vegetation, and soil properties jointly drive changes in soil microbial communities with latitude in the arid valleys of southwest China.

Conversion effects of farmland to Zanthoxylum bungeanum plantations on soil organic carbon mineralization in the arid valley of the upper reaches of Yangtze River, China.

Farmland conversion to forest is considered to be one of the effective measures to mitigate climate change. However, the impact of farmland conversion to forest land or grassland on soil CO2 emission in arid areas is unclear due to the lack of comparative information on soil organic carbon (SOC) mineralization of different conversion types. The SOC mineralization in 0–100 cm soil layer in farmland (FL), abandoned land (AL) and different ages (including 8, 15, 20 and 28 years) of Zanthoxylum bungeanum plantations were measured by laboratory incubation. The size and decomposition rate of fast pool (Cf) and slow pool (Cs) in different land-use types and soil layers were estimated by double exponential model. The results showed that: 1) Farmland conversion increased the cumulative CO2-C release (Cmin) and SOC mineralization efficiency, and those indexes in AL were higher than that in Z. bungeanum plantations. The Cmin and SOC mineralization efficiency of 0–100 cm soil increased with the ages of Z. bungeanum plantation. Both Cmin and SOC mineralization efficiency decreased with the increase of soil depth; 2) Both soil Cf and Cs increased after farmland converted to Z. bungeanum plantations and AL. The Cs in the same soil layer increased with the ages of Z. bungeanum plantation, and the Cf showed a “V” type with the increased ages of Z. bungeanum plantation. The Cf and Cs decreased with the increase of soil depth in all land-use types; 3) Farmland conversion increased the decomposition rate of Cf (k1) in all soil layer by 0.008–0.143 d−1 and 0.082–0.148 d−1 in Z. bungeanum plantations and AL, respectively. The k1 was obviously higher in the 0−20 cm soil layer than that in other soil layers, while the decomposition rate of Cs (k2) was not affected by FL conversion and soil depth; and 4) The initial soil chemical properties and enzyme activity affected SOC mineralization, especially the concentrations of total organic nitrogen (TON), SOC, easily oxidizable organic carbon (EOC) and microbial biomass carbon (MBC). It indicated that the conversion of farmland to Z. bungeanum plantations and AL increases SOC mineralization, especially in deeper soils, and it increased with the ages. The conversion of farmland to Z. bungeanum plantation is the optimal measure when the potential C sequestration of plant-soil system were taken in consideration.

Latitudinal patterns and underlying factors of component biomass in plant communities in the arid valley of southwest China

Latitudinal patterns and underlying factors of component biomass in plant communities in the arid valley of southwest China

Caring for water in Northern Peru: On fragile infrastructures and the diverse work involved in irrigation

The term control used to be central to the scholarship on modern water management. More recently, however, scholars have remarked that the world is too unstable and capricious for control to ever fully succeed. They propose that technologically facilitating water to flow depends instead on care. Building on this, we here propose that holding on to a single catch-all theoretical concept, even if it is ‘care’, does not suffice. Instead, analytical terms are better adapted – and re-adapted to local specificities. To exemplify this, we here present the case of the Huallabamba, a canal that makes horticulture possible in the arid valley of Motupe on the Pacific coast of northern Peru. In this case, while ‘control’ was hard to find, ‘care’ took different forms: the tinkering that compensates for the not-quite-modern character of the infrastructures; the adaptive managerial style necessary given the absence of information; the watchful, hands-on cuidar of the men who walk along the canal high up in the Andes, repairing what is broken, cautious lest they anger the spirits; the listening to and singing for water in the catchment area; and the activism that resists the invasion of mining companies. This open-ended list is not meant to travel as a theoretical grid, but rather to inspire others to propose locally salient analytical terms to explore the sites and situations in which they are involved.

Influence of alternated drying and wetting on the characteristics of soil preferential flow formation in Honghe Arid Valley.

To clarify the effects of alternation of drying and wetting on the formation of soil preferential flow in arid valley, taking the wasteland in the arid valley of Honghe River as the research object, we analyzed the soil preferential flow characteristics before and after the simulation of drying and wetting alternation based on dyeing tracer method, water breakthrough curve, and image processing technology. The results showed that, under the simulated alternation of drying and wetting, the matrix flow occurred in the 0-10 cm soil layer, the dyeing depth reached 35 cm, the horizontal width of the preferred path was only 3-10 cm, and the dyeing area curve fluctuated little. Simulated alternation of drying and wetting led to significant increases in the steady effluent, macropores number, and macroporosity. In the 0-20 cm soil layer, the steady effluent after alternation of drying and wetting was about 0.27 cm3·s-1 higher than that non-alternation of drying and wetting, macropores number in dyeing area was about 1.4 times higher, and the macroporosity was 13.4% higher. The macropores number was positively correlated with stable flow rate. After simulated alternation of drying and wetting, the number of macropores from large to small was 0.6-0.8 mm＞0.8-1.0 mm＞1.0-1.5 mm＞1.5-2.0 mm＞2.0-3.7 mm, while under non-alternation of drying and wetting, it was 0.8-1.0 mm＞0.6-0.8 mm＞1.0-1.5 mm＞2.0-3.7 mm＞1.5-2.0 mm. The macropores number in each pore size range was significantly correlated with the dyeing area ratio. After simulated alternation of drying and wetting, the correlation increased, and the dominant factor affecting the occurrence of preferential flow changed from the macropores number in the pore size range of 1.5-2.0 mm to that of 0.8-1.0 mm. Therefore, the alternation of drying and wetting would affect the characteristics of macropores, which caused the soil to be more prone to preferential flow and with higher magnitude.

Holocene paleosols and paleoclimate for the arid upper Minjiang River valley in the eastern Tibetan Plateau

The pedogenic features of Holocene paleosols and their paleoclimatic significance in the arid upper Minjiang River valley of the eastern Tibetan Plateau, southwest China, were investigated using elemental geochemistry, particle size distribution, and magnetic susceptibility indices in combination with the min–max normalization and paleoclimate reconstruction methods. Paleosols developed in a semi-humid environment and were classified as Inceptisols and Entisols. Pedogenic intensity of these paleosols was higher in the Middle Holocene and lower in the Early and Late Holocene. Mean annual precipitation (MAP) and mean annual temperature (MAT) inferred from the paleosols formed in the Middle Holocene are ~ 700 mm and ~ 13 °C, respectively. Modern climate is cooler and drier than that of the Middle Holocene and resembles that of the Early Holocene and the period after the last glacial maximum. Climatic changes in the study region were sensitive to the Asian monsoon evolution, which was controlled by orbital forcing. Relative warmer and wetter conditions perhaps triggered the ancient cultural immigration and prosperity at ~ 6000 cal. yr BP in the arid valley region.