Institute of Soil and Water Conservation,Chinese Academy of Sciences and Ministry of Water Resources
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Galactolipid remodeling is involved in drought-induced leaf senescence in maize
No full textDrought triggers leaf senescence, leading to a critical decrease in crop yield. The membrane lipid composition generally undergoes major changes during drought. However, little is known about the role of galactolipid remodeling in the drought-induced senescence response in crops. Here, a comparative study of alterations in galactolipid and fatty acid composition during drought and recovery was carried out using two maize cultivars differing in drought-induced leaf senescence. Under drought condition, the monogalactosyldiacylglycerol (MGDG) content was decreased by 18.3% and 25.9% in the cultivar with retarded leaf senescence and the senescent cultivar, respectively, while digalactosyldiacylglycerol (DGDG) was enhanced by 43.2% and 22.9%. Compared with the senescent cultivar, the DGDG content and the DGDG/MGDG ratio were 29.8% and 20.7% higher in the cultivar with retarded leaf senescence, which also maintained stable chloroplast ultrastructure under drought stress. The expressions of key galactolipid biosynthesis genes in both cultivars were up-regulated by the drought stress. In addition, the expression levels were higher in the cultivar with retarded leaf senescence than that in the senescent cultivar. These results suggests that a profound modification of galactolipid composition with high DGDG content and DGDG/MGDG ratio is associated with the alleviation of leaf senescence in response to drought. The regulation of galactolipid remodeling could be a promising strategy for alleviating the leaf senescence and improving drought adaptation in crops
Estimates of carbon storage in grassland ecosystems on the Loess Plateau
No full textGrassland ecosystems play an important role in the carbon (C) balance of arid and semi-arid regions. These ecosystems provide C for grass growth and soil microbial activities and represent one of the main sources of atmospheric C. In this study, we estimated the C density and storage of 223 sampling sites in grassland ecosystems on the Loess Plateau using elevation, vegetation indexes, precipitation, air temperature, day and night land surface temperature (LSTd and LSTn, respectively), evapotranspiration (ET), percent tree cover and the non-vegetated area to build decision regression tree and generalized linear regression models (GLMs). The results showed that the C density decreased from south to north and ranged from 0.22 to 29.29 kg C/m(2). The average amount of C stored in the ecosystems was 1.46 Pg. The typical steppe and forest steppe stored the most C, and the steppe desert stored the least. The soil (0-1 m) stored most of the organic C, accounting for > 90%, and the belowground biomass (BGB) contained > 3 times the amount of C as the aboveground biomass (AGB). This study provides reference information for the loss of C and associated mitigation strategies on the Loess Plateau
Ecosystem carbon and nitrogen storage following farmland afforestation with black locust (Robinia pseudoacacia) on the Loess Plateau, China
No full textAlthough afforestation of farmlands has been proposed as an effective method of carbon (C) sequestration, there remain uncertainties that deter us from developing a clear picture of C stocks in plantation ecosystems. This study investigated the dynamics of stand structure and plant diversity, and C and nitrogen (N) pools in trees, herbs, litter, and soil (0-100 cm depth) in black locust plantations aged 9, 17, 30, and 37 years, and in newly abandoned farmlands as pre-afforestation sites, on the Loess Plateau, China. Stand density decreased significantly, while tree diameter at breast height and height increased during stand development. The dominant species of the herb layer differed with age. Afforestation resulted in slight increases in tree C and N storage in plantations from 9 to 30 years of age, and then significantly increased from 30 to 37 years. Compared to pre-afforestation, C and N storage in soil decreased to minimum values in stands aged 17 and 9 years, respectively. The soil re-accumulated C and N during stand development, attaining equilibrium levels similar to those in pre-afforestation when stands reached about 30 years of age. Soil C and N storage in 37-year stands were 29 and 16% higher, respectively, than in pre-afforestation levels. However, C and N concentrations in the subsoil (20-40 cm) were still less than the pre-afforestation levels for stands of all ages (from 9 to 37 years). The relative contribution to the total ecosystem C and N pools increased in trees and decreased in soil during the observed period. Our results indicate that afforestation reduced soil C and N storage during the early stages of stand development. We conclude that the growing phase of an afforested stand over its initial 30 years is important for C and N sequestration by black locust due to the C and N storage that result from recovered soil quality and an increase in tree biomass
A laboratory study of channel sidewall expansion in upland concentrated flows
No full textGully erosion contributes large amounts of sediment within watersheds around the world. Gully widening constitutes about 80% of total soil loss, especially in the presence of a plow pan which manifests a less or non erodible soil layer. Current knowledge on sidewall toe scour (scour arcs) and tension crack processes in gully widening is limited. Thus, simulated channel sidewall expansion tests, where the channel bed was fixed to represent a non-erodible layer, were designed to investigate how inflow rate, slope gradient and initial channel width affect channel widening processes. Soil boxes (2.0 m-long, 0.3 m-wide and 0.5 m-deep) with two slope gradients (15 degrees and 20 degrees), four inflow rates (1.0, 2.0, 3.0 and 4.0 L min(-1)) and two initial channel widths (4 and 8 cm) were subjected to clear-water overland flow. Photogrammetry was used to detect tension crack and width variations of channels. The results show that sediment delivery and channel width increase with the increase of inflow rate, bed slope and the decrease of initial channel width. Exponential equations were used to predict the channel width time series. Time lag occurred between sediment peak and soil block failure. Toe scour, crack development, sidewall failure and block detachment and transport, in sequence, were the four main processes of channel widening. Basal scour arc length, tension crack length and width decreased with initial channel width and increased with time, flow discharge and bed slope. Basal scour arcs were divided into three patterns according to different shapes in comparison to the failure arcs. Sediment delivery equations based on the disaggregation of concentrated flow entrainment and mass failure were also fitted. This study provides new insight on improving gully erosion measurements and prediction technology
Soil C:N:P stoichiometry in plantations of N-fixing black locust and indigenous pine, and secondary oak forests in Northwest China
No full textSoil nutrient concentrations and stoichiometry are important indicators of plant growth, terrestrial productivity, and ecosystem functioning. Nevertheless, little is known about the vertical distribution and the environmental factors influencing the spatial patterns of different forest types under the "Grain for Green" program and the "Natural Forest Resources Protection" project in Northwest of China. We collected 114 soil profile samples within a 0-100-cm depth from black locust and Chinese pine plantations, and secondary oak forests. We determined the vertical distributions of soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), and their ratios along environmental gradients in Shaanxi Province, Northwest China. The results showed that both SOC and TN concentrations decreased exponentially within the soil profiles of the three forest types, but there was minimal change in TP. Significant differences in SOC, TN, and TP were found in the surface soil layers among the forest types. Both SOC and TN were relatively low in the N-fixing black locust plantations and TP was comparatively low in the Chinese pine plantations. The C:N:P ratios decreased with increasing soil depth for the three forest types. These ratios were comparatively high in the Chinese pine plantations, relatively low in the black locust plantations, and moderate in the oak forests. The differences in the ratios among the three forest types were more significant in surface soil than in deep soil. Precipitation was positively correlated with the concentrations of SOC and TN and the ratios of C:N:P. Temperature was negatively correlated with concentrations of SOC and TN and the ratios of C:N:P across all soil depths. A log-transformed linear C-N relationship was found for all three forest types, suggesting a well-constrained coupling between the levels of the two elements. Our results demonstrated the effect of different tree species on soil C:N:P ratios and their controlling factors within soil profiles along environmental gradients. The secondary oak forest accumulated soil C and N more effectively than the plantations. The Chinese pine plantations were relatively more susceptible to P limitation. Therefore, the mechanism of different plant species on soil biogeochemical processes at the whole soil profile level must be considered when developing forest management strategies and implementing vegetation restoration projects
Effects of straw mulching and plastic film mulching on improving soil organic carbon and nitrogen fractions, crop yield and water use efficiency in the Loess Plateau, China
No full textA field experiment was conducted in the Loess Plateau of Northwest China to study the effects of plastic film mulching and straw mulching on soil water, soil organic carbon (SOC), total nitrogen (TN), microbial biomass carbon (MBC) and nitrogen (MBN), dissolved organic carbon (DOC) and nitrogen (DON), crop yield and water use efficiency under winter wheat (Tricicwn aestivum L.)-summer maize (Zea mays L.) double-cropping system conditions using the following three cultural practices: (i) traditional plough with no mulching (CK), (ii) traditional plough with plastic film mulching (PM), and (iii) traditional plough with straw mulching (SM). Soil water contents were measured by the gravimetric method. SOC was determined using the dichromate oxidation method. TN was analyzed by the Kjeldahl method. MBC and MBN were determined using the chloroform fumigation extraction method. DOC and TDN were determined following Jones' procedures proposed by Jones and Willett (2006). The results showed that soil water was higher under the PM treatment than under the SM treatment and mainly changed in the upper 60 cm soil layer. Compared with the CK treatment, the concentrations of SOC and TN under the SM treatment were increased by 16.9% and 7.7% at the 0-10 cm soil depth, respectively, and the PM treatment had the similar SOC and TN concentrations. Compared with the CK treatment, soil C:N ratio was increased under the SM treatment by 6.2% (P < 0.05), and that under the PM treatment was decreased by 5.2% (P < 0.05) after three years. The concentrations of MBC under the PM and SM treatments were significantly increased by 42.0% and 24.1%, respectively, and MBN under the PM treatment was significantly increased by 5.6% at 0-10 cm soil depth after the maize season. Compared with the CK treatment, DOC was significantly increased by 21.0% under the SM treatment and decreased by 13.1% under the PM treatment, and DON was significantly increased by 10.5% under the SM treatment and decreased by 4.3% under the PM treatment at the 0-10 cm soil depth after the maize season. Relative changes of labile soil organic carbon and nitrogen fractions were more sensitive than that of SOC and TN. The relative decline or increase of labile soil organic carbon and nitrogen fractions was on average almost 13.6% for the mulching practices. Compared with the CK treatment, the average maize yields under the PM and SM treatments were increased by 26.4% and 9.8%, and the average wheat yields under the PM and SM treatments were increased by 21.3% and 7.4%, respectively. The average water use efficiencies under the PM and SM treatments were 24.5%, 8.8% in winter wheat and 22.9%, 6.3% in summer maize higher than that under the CK treatment, respectively. Our results suggested that plastic film mulching could be used as an effective practice to improve low soil quality with adequate nitrogen and increase crop yield and water use efficiency in the Loess Plateau, China
Preliminary experiments to assess the effectiveness of magnetite powder as an erosion tracer on the Loess Plateau
No full textSoil water erosion monitoring is essential for long-term soil conservation and ecological restoration on the Loess Plateau region of China. Traditional approaches, such as runoff plots and water weirs in a watershed, provide reliable spatially averaged soil erosion data but cannot validate process-based erosion prediction models for dynamic soil erosion evaluation. Erosion tracer techniques are capable of quantitatively determining spatial distribution of soil erosion. Ideal tracers are expected to provide highly contrasting values compared with background ones, and be analyzed efficiently and acquired cost-effectively. In this laboratory study, magnetite powder was selected as an erosion tracer to test. The tracer was implanted into loessial soils from the Loess Plateau using a wet soil-tracer mixing procedure. The effectiveness of magnetite powder as an erosion tracer was evaluated in aspects of basic magnetic features between the tracer and soils, distribution under different soil aggregate sizes, mobility along soil profiles, and detachment of tracer-labeled loessial soils by shallow surface flow along a slope. Results showed that magnetite powder was bound tightly to loessial soil aggregates, with no noticeable vertical mobility under long-term leaching conditions, and almost synchronous detachment with the eroded soils. Furthermore, the tracer is an inexpensive tracer (approximately 0.08 US.kg(-1)), which has higher magnetic susceptibility over two or three orders of magnitude than ordinary soils and high sensitivity of analysis ( < 1% measuring error). It can also provide quick measurement ( < 15 s) with equipment expenditure at relatively low price (approximately 5000 US$). The work demonstrates that magnetite powder as a promising erosion tracer will be great potential on the Loess Plateau region. Effectiveness of the magnetite powder tracer under simulated and natural rainfall conditions in this region still need to be testified in the future studies
Responses of Vegetation Cover to Environmental Change in Large Cities of China
No full textVegetation cover is crucial for the sustainability of urban ecosystems; however, this cover has been undergoing substantial changes in cities. Based on climate data, city statistical data, nighttime light data and the Normalized Difference Vegetation Index (NDVI) dataset, we investigate the spatiotemporal variations of climate factors, urban lands and vegetation cover in 71 large cities of China during 1998-2012, and explore their correlations. A regression model between growing-season NDVI (G-NDVI) and urban land proportion (PU) is built to quantify the impact of urbanization on vegetation cover change. The results indicate that the spatiotemporal variations of temperature, precipitation, PU and G-NDVI are greatly different among the 71 cities which experienced rapid urbanization. The spatial difference of G-NDVI is closely related to diverse climate conditions, while the inter-annual variations of G-NDVI are less sensitive to climate changes. In addition, there is a negative correlation between G-NDVI trend and PU change, indicating vegetation cover in cities have been negatively impacted by urbanization. For most of the inland cities, the urbanization impacts on vegetation cover in urban areas are more severe than in suburban areas. But the opposite occurs in 17 cities mainly located in the coastal areas which have been undergoing the most rapid urbanization. Overall, the impacts of urbanization on G-NDVI change are estimated to be -0.026 per decade in urban areas and -0.015 per decade in suburban areas during 1998-2012. The long-term developments of cities would persist and continue to impact on the environmental change and sustainability. We use a 15-year window here as a case study, which implies the millennia of human effects on the natural biotas and warns us to manage landscapes and preserve ecological environments properly
Why does oriental arborvitae grow better when mixed with black locust: Insight on nutrient cycling?
No full textTo identify why tree growth differs by afforestation type is a matter of prime concern in forestry. A study was conducted to determine why oriental arborvitae (Platycladus orientalis) grows better in the presence of black locust (Robinia pseudoacacia) than in monoculture. Different types of stands (i.e., monocultures and mixture of black locust and oriental arborvitae, and native grassland as a control) were selected in the Loess Plateau, China. The height and diameter at breast height of each tree species were measured, and soil, shoot, and root samples were sampled. The arbuscular mycorrhizal (AM) attributes, shoot and root nutrient status, height and diameter of black locust were not influenced by the presence of oriental arborvitae. For oriental arborvitae, however, growing in mixture increased height and diameter and reduced shoot Mn, Ca, and Mg contents, AM fungal spore density, and colonization rate. Major changes in soil properties also occurred, primarily in soil water, NO3-N, and available K levels and in soil enzyme activity. The increase in soil water, N, and K availability in the presence of black locust stimulated oriental arborvitae growth, and black locust in the mixed stand seems to suppress the development of AM symbiosis in oriental arborvitae roots, especially the production of AM fungal spores and vesicles, through improving soil water and N levels, thus freeing up carbon to fuel plant growth. Overall, the presence of black locust favored oriental arborvitae growth directly by improving soil water and fertility and indirectly by repressing AM symbiosis in oriental arborvitae roots
The role of maize plants in regulating soil profile dynamics and surface emissions of nitrous oxide in a semiarid environment
No full textTo study the effects of maize plants on nitrous oxide (N2O) fluxes from a dryland experimental farm, in situ soil profiles of N2O concentrations and surface emissions were investigated in a field experiment from 2014 to 2015 in the semiarid areas of northwestern China. The experiment included four treatments: unplanted and N-unfertilized soil (C0), unplanted soil fertilized with 225 kg N ha(-1) (CN), maize-planted and N-unfertilized soil (P0), and maize-planted soil fertilized with 225 kg N ha(-1) (PN). Surface N2O emissions and soil N2O concentrations at depths of 0, 10, 20, 30, 40, and 50 cm were measured weekly. Nitrogen fertilization significantly increased the soil N2O concentrations and surface emissions. Compared to the unplanted soil, the presence of maize plants significantly decreased the N2O concentrations at depths of 10-40 cm during the maize growing season. The modeled N2O fluxes at a depth of 10 cm presented a similar pattern to the chamber measurements. However, there was a discrepancy between the concentration gradient and chamber methods when the fluxes were high, mainly because the gradient method could not detect N2O production and consumption process above the uppermost gas sampler (0-10 cm). Soil moisture and temperature were critical factors affecting the N2O concentrations and surface emissions. The respective cumulative surface emissions and effluxes at a depth of 10 cm during the maize growing season (PN treatment) were decreased by 8.9 and 17.9% in 2014 and by 14.7 and 17.5% in 2015 compared to values of the CN treatment. This was mainly due to the decrease in soil moisture caused by the growth of the maize plants, which resulted in a soil condition less suitable for N2O production