A UAV-Based Eddy Covariance System for Measurement of Mass and Energy Exchange of the Ecosystem: Preliminary Results.

Airborne eddy covariance (EC) measurement is one of the most effective methods to directly measure the surface mass and energy fluxes at the regional scale. It offers the possibility to bridge the scale gap between local- and global-scale measurements by ground-based sites and remote-sensing instrumentations, and to validate the surface fluxes estimated by satellite products or process-based models. In this study, we developed an unmanned aerial vehicle (UAV)-based EC system that can be operated to measure the turbulent fluxes in carbon dioxides, momentum, latent and sensible heat, as well as net radiation and photosynthetically active radiation. Flight tests of the developed UAV-based EC system over land were conducted in October 2020 in Inner Mongolia, China. The in-flight calibration was firstly conducted to correct the mounting error. Then, three flight comparison tests were performed, and we compared the measurement with those from a ground tower. The results, along with power spectral comparison and consideration of the differing measurement strategies indicate that the system can resolve the turbulent fluxes in the encountered measurement condition. Lastly, the challenges of the UAV-based EC method were discussed, and potential improvements with further development were explored. The results of this paper reveal the considerable potential of the UAV-based EC method for land surface process studies.

Dynamics of Phosphorus Content in the Water-Sediment Interface of Wetlands in a Mid-Temperature Steppe.

In order to reveal dynamics changes in phosphorus release from the sediments of wetlands in a mid-temperature steppe without external phosphorus input, the relationship between phosphorus content in the overlying water, sediment, and interstitial water was studied using the variables control method. The results showed that, during the incubation period, the content of total phosphorus in the overlying water and the content of total phosphorus in interstitial water both presented in the order of August > September > July. Furthermore, the correlation relationships between phosphorus content in the overlying water, total phosphorus in the interstitial water, and the ratios of sediment Olsen-P to total phosphorus in the interstitial water, indicated that Olsen-P might be a kind of release form of phosphorus - from the sediment to the overlying water of the wetlands in Hulunbeier steppe, without external phosphorus input.

Analysis of factors controlling sediment phosphorus flux potential of wetlands in Hulun Buir grassland by principal component and path analysis method.

Phosphorus (P) flux potential can predict the trend of phosphorus release from wetland sediments to water and provide scientific parameters for further monitoring and management for phosphorus flux from wetland sediments to overlying water. Many studies have focused on factors affecting sediment P flux potential in sediment-water interface, but rarely on the relationship among these factors. In the present study, experiment on sediment P flux potential in sediment-water interface was conducted in six wetlands in Hulun Buir grassland, China and the relationships among sediment P flux potential in sediment-water interface, sediment physical properties, and sediment chemical characteristics were examined. Principal component analysis and path analysis were used to discuss these data in correlation coefficient, direct, and indirect effects on sediment P flux potential in sediment-water interface. Results indicated that the major factors affecting sediment P flux potential in sediment-water interface were amount of organophosphate-degradation bacterium in sediment, Ca-P content, and total phosphorus concentrations. The factors of direct influence sediment P flux potential were sediment Ca-P content, Olsen-P content, SOC content, and sediment Al-P content. The indirect influence sediment P flux potential in sediment-water interface was sediment Olsen-P content, sediment SOC content, sediment Ca-P content, and sediment Al-P content. And the standard multiple regression describing the relationship between sediment P flux potential in sediment-water interface and its major effect factors was Y = 5.849 - 1.025X 1 - 1.995X 2 + 0.188X 3 - 0.282X 4 (r = 0.9298, p < 0.01, n = 96), where Y is sediment P flux potential in sediment-water interface, X 1 is sediment Ca-P content, X 2 is sediment Olsen-P content, X 3 is sediment SOC content, and X 4 is sediment Al-P content. Therefore, future research will focus on these sediment properties to analyze the interrelation among sediment properties factors, main vegetable factors, and environment factors which influence the sediment P flux potential in sediment-water interface.

The effects of litter input and increased precipitation on soil microbial communities in a temperate grassland.

Global warming has contributed to shifts in precipitation patterns and increased plant productivity, resulting in a significant increase in litter input into the soils. The enhanced litter input, combined with higher levels of precipitation, may potentially affect soil microbial communities. This study aims to investigate the effects of litter input and increased precipitation on soil microbial biomass, community structure, and diversity in a temperate meadow steppe in northeastern China. Different levels of litter input (0%, +30%, +60%) and increased precipitation (0%, +15%, +30%) were applied over a three-year period (2015-2017). The results showed that litter input significantly increased the biomass of bacteria and fungi without altering their diversity, as well as the ratio of bacterial to fungal biomass. Increased precipitation did not have a notable effect on the biomass and diversity of bacteria and fungi, but it did increase the fungal-to-bacterial biomass ratio. However, when litter input and increased precipitation interacted, bacterial diversity significantly increased while the fungal-to-bacterial biomass ratio remained unchanged. These findings indicate that the projected increases in litter and precipitation would have a substantial impact on soil microbial communities. In energy-and water-limited temperate grasslands, the additional litter inputs and increased precipitation contribute to enhanced nutrient and water availability, which in turn promotes microbial growth and leads to shifts in community structure and diversity.

Flooding Length Mediates Fencing and Grazing Effects on Soil Respiration in Meadow Steppe.

Grassland management affects soil respiration (Rs, consists of heterotrophic respiration and autotrophic respiration) through soil micro-ecological processes, such as hydrothermal, plant root, organic carbon decomposition and microbial activity. Flooding, an irregular phenomenon in grasslands, may strongly regulate the response of soil respiration and its components to grassland management, but the regulatory mechanism remains unclear. We conducted a 3-year experiment by grassland management (fencing and grazing) and flooding conditions (no flooding (NF), short-term flooding (STF) and long-term flooding (LTF)) to study their effects on Rs and its components in a meadow steppe in the Hui River basin of Hulunbuir. We found differences in the patterns of Rs and its components under grassland management and flooding conditions. In 2021-2023, the temporal trends of Rs, heterotrophic respiration (Rh) and autotrophic respiration (Ra) were generally consistent, with peaks occurring on days 190-220, and the peaks of grazing were higher than that of fencing. In NF, Rs of grazed grassland was significantly higher than that of fenced grassland in 2021-2022 (p < 0.05). In STF and LTF, there was no significant difference in Rs between fenced and grazed grassland (p > 0.05). The dependence of Rs on soil temperature (ST) decreased with increasing flooding duration, and the dependence of Rs on ST of grazed grassland was higher than fenced grassland under NF and STF, but there was no difference between fenced grassland and grazed grassland under LTF. In addition, Rh was more sensitive to ST than Ra. This may be due to the different pathways of ST effects on Rs under grazing in different flooding conditions. Our study indicates that the effect of flooding on Rs is the key to the rational use of grassland under future climate change. To reduce regional carbon emissions, we recommend grazing on flooding grassland and fencing on no-flooding grassland.

Effect of temperature variation on phosphorus flux at the sediment-water interface of the steppe wetlands.

Environmental factors are generally considered to be important factors affecting the release process of phosphorus (P) in sediments. However, little is known about the effect of temperature increased at first and then decreased with the season change on the P flux rate and flux amount at the sediment-water interface in the steppe wetlands. The effects of the temperature variation on P flux at the sediment-water interface in the steppe wetlands during the vegetation growing season under simulated wetland habitat were studied. The results showed that the release of P from sediments to overlying water was greatly affected by temperature changes. When the temperature rose, P was released from the sediment into the overlying water, while P was precipitated from the water into the sediment with the temperature dropped. During simulation period, the total P in water flux rates between sediment and overlying water (FP) was ranged from - 4.51 to 4.99 mg·m-2·day-1, while the dissolved reactive P in water flux rates between sediment and overlying water (FDP) was changed from - 5.37 to 5.14 mg·m-2·day-1. The FP and FDP were negatively correlated with the content of total P in water (WTP), dissolved reactive P in water (WDRP), pH of sediment (pH), and microbial biomass P (MBP), but increased with temperature (T), aluminum phosphate (Al.P), and occluded phosphate (Oc.P). The P flux rates were affected by temperature variation both directly and indirectly; the mechanism of how temperature influenced the fate of P in the wetland is still not clear. Therefore, the physicochemical properties and kinetic, thermodynamic, and microbiology characteristics should be combined together to clarify the mechanism in future research.

The maize root stem cell niche: a partnership between two sister cell populations.

Using transcript profile analysis, we explored the nature of the stem cell niche in roots of maize (Zea mays). Toward assessing a role for specific genes in the establishment and maintenance of the niche, we perturbed the niche and simultaneously monitored the spatial expression patterns of genes hypothesized as essential. Our results allow us to quantify and localize gene activities to specific portions of the niche: to the quiescent center (QC) or the proximal meristem (PM), or to both. The data point to molecular, biochemical and physiological processes associated with the specification and maintenance of the niche, and include reduced expression of metabolism-, redox- and certain cell cycle-associated transcripts in the QC, enrichment of auxin-associated transcripts within the entire niche, controls for the state of differentiation of QC cells, a role for cytokinins specifically in the PM portion of the niche, processes (repair machinery) for maintaining DNA integrity and a role for gene silencing in niche stabilization. To provide additional support for the hypothesized roles of the above-mentioned and other transcripts in niche specification, we overexpressed, in Arabidopsis, homologs of representative genes (eight) identified as highly enriched or reduced in the maize root QC. We conclude that the coordinated changes in expression of auxin-, redox-, cell cycle- and metabolism-associated genes suggest the linkage of gene networks at the level of transcription, thereby providing additional insights into events likely associated with root stem cell niche establishment and maintenance.

Laboratory investigation of phosphorus loss with snowmelt and rainfall runoff from a Steppe wetland catchment.

Phosphorus (P) losses from terrestrial soils contribute to eutrophication of surface waters. As priority non-point source pollution ways, rainfall runoff (RS1) and snowmelt runoff (RS2) are the main carrier of P loss from terrestrial ecosystem. The aim of this study was to investigate the similarities and differences between P loss with RS1 and RS2 of the same soil type. Six types of soil were used in this experiment. Results have shown that 1), Different types of soil have different P loss with RS1 and RS2 under different slope, and the changes ranged from 0.003 to 0.370 mg L-1. 2), The effects of soil type, slope and runoff type on P loss with surface runoff was not independent, both individual effects of all factors and their interaction with the other two factors effected the P loss with runoff. 3), In our experiment, some soils showed no significant difference between P content in RS1 and RS2. In some soils, P loss with RS1 was higher than that with RS2 while the opposite conclusion was showed in Bog soil (BS) which with higher soil water content. 4), The P loss with RS1 and RS2 of different soils were both mainly affected by soil water content (SW), Olsen-P content (OP) and soil organic matter content (OM). These results can help us understand the P loss with different patterns of surface runoff better and are expected to provide pertinent opinions on the analysis of P loss with runoff and its influencing factors of grassland soils.

Organic carbon storage and its influencing factors under climate warming of sediments in steppe wetland, China.

The effect of climate warming on soil organic carbon (SOC) of sediment in wetlands is important for accurately projecting SOC content. Thus, understanding the mechanism influencing SOC content under climate warming is necessary. Field investigation and a laboratory incubation experiment were conducted in Hulunbeier steppe wetland during 2016 and 2017. Four types of wetland were selected to incubate with ambient temperature and temperature increased by 2.5 °C. The results showed that SOC content was negatively affected by temperature warming. The SOC content reduction in sediment caused by increasing temperature was ranged from - 2.34 to 39.52%. In addition, the content of sand, silt, total phosphorus (TP), calcium phosphate tribasic (Ca-P), total nitrogen (TN), and sediment moisture (MC) should be considered in models of SOC content in steppe wetland. However, it requires further validation, in particular how SOC content varies with warming temperatures, the duration of incubation, and other abiotic and biotic factors. These findings provide evidence that both climate warming and original characteristics of sediment can control the SOC storage dynamics in the steppe wetland. Graphical abstract.

Analysis of factors controlling soil phosphorus loss with surface runoff in Huihe National Nature Reserve by principal component and path analysis methods.

Phosphorus (P) loss with surface runoff accounts for the P input to and acceleration of eutrophication of the freshwater. Many studies have focused on factors affecting P loss with surface runoff from soils, but rarely on the relationship among these factors. In the present study, rainfall simulation on P loss with surface runoff was conducted in Huihe National Nature Reserve, in Hulunbeier grassland, China, and the relationships between P loss with surface runoff, soil properties, and rainfall conditions were examined. Principal component analysis and path analysis were used to analyze the direct and indirect effects on P loss with surface runoff. The results showed that P loss with surface runoff was closely correlated with soil electrical conductivity, soil pH, soil Olsen P, soil total nitrogen (TN), soil total phosphorus (TP), and soil organic carbon (SOC). The main driving factors which influenced P loss with surface runoff were soil TN, soil pH, soil Olsen P, and soil water content. Path analysis and determination coefficient analysis indicated that the standard multiple regression equation for P loss with surface runoff and each main factor was Y = 7.429 - 0.439 soil TN - 6.834 soil pH + 1.721 soil Olsen-P + 0.183 soil water content (r = 0.487, p < 0.01, n = 180). Soil TN, soil pH, soil Olsen P, and soil water content and the interactions between them were the main factors affecting P loss with surface runoff. The effect of physical and chemical properties of undisturbed soils on P loss with surface runoff was discussed, and the soil water content and soil Olsen P were strongly positive influences on the P loss with surface runoff.

Study on sandstorm PM10 exposure assessment in the large-scale region: a case study in Inner Mongolia.

The current exposure-effect curves describing sandstorm PM10 exposure and the health effects are drawn roughly by the outdoor concentration (OC), which ignored the exposure levels of people's practical activity sites. The main objective of this work is to develop a novel approach to quantify human PM10 exposure by their socio-categorized micro-environment activities-time weighed (SCMEATW) in strong sandstorm period, which can be used to assess the exposure profiles in the large-scale region. Types of people's SCMEATW were obtained by questionnaire investigation. Different types of representatives were trackly recorded during the big sandstorm. The average exposure levels were estimated by SCMEATW. Furthermore, the geographic information system (GIS) technique was taken not only to simulate the outdoor concentration spatially but also to create human exposure outlines in a visualized map simultaneously, which could help to understand the risk to different types of people. Additionally, exposure-response curves describing the acute outpatient rate odds by sandstorm were formed by SCMEATW, and the differences between SCMEATW and OC were compared. Results indicated that acute outpatient rate odds had relationships with PM10 exposure from SCMEATW, with a level less than that of OC. Some types of people, such as herdsmen and those people walking outdoors during a strong sandstorm, have more risk than office men. Our findings provide more understanding of human practical activities on their exposure levels; they especially provide a tool to understand sandstorm PM10 exposure in large scale spatially, which might help to perform the different categories population's risk assessment regionally.

Effects of Sediment Chemical Properties on Phosphorus Release Rates in the Sediment-Water Interface of the Steppe Wetlands.

Rising temperature causes a process of phosphorus release, which can be characterized well using phosphorus release rates (VP). The objective of the present study was to investigate the major factors affecting sediment phosphorus release rates through a wetland habitat simulation experiment. The results showed that the VP of different wetland sediments were different and changed with the order of W-R (river wetland) > W-L (lake wetland) > W-M (grassy marsh wetland) > W-A (reservoir wetland). The main driving factors which influenced sediment phosphorus flux velocity in the sediment-water interface were sediment B-SO42-, B-MBN and A-MBP content. Path analysis and determination coefficient analysis indicated the standard multiple regression equation for sediment phosphorus release rates in the sediment-water interface, and each main factor was Y = -0.105 + 0.096X1 + 0.275X2 - 0.010X3 (r = 0.416, p < 0.01, n = 144), where Y is sediment phosphorus release rates; X1 is sediment B-SO42- content; X2 is sediment B-MBN; and X3 is sediment A-MBP content. Sediment B-SO42-, B-MBN and A-MBP content and the interaction between them were the main factors affecting sediment phosphorus release rates in the sediment-water interface. Therefore, these results suggest that soil chemical properties and microbial activities likely play an important role in phosphorus release rates in the sediment-water interface. We hope to provide effective scientific management and control methods for relevant environmental protection departments.

Responses of Biogeochemical Characteristics and Enzyme Activities in Sediment to Climate Warming under a Simulation Experiment in Geographically Isolated Wetlands of the Hulunbuir Grassland, China.

Climate warming generates a tremendous threat to the stability of geographically-isolated wetland (GIW) ecosystems and changes the type of evaporation and atmospheric precipitation in a region. The intrinsic balance of biogeochemical processes and enzyme activity in GIWs may be altered as well. In this paper, we sampled three types of GIWs exhibiting different kinds of flooding periods. With the participation of real-time temperature regulation measures, we assembled a computer-mediated wetland warming micro-system in June 2016 to simulate climate situation of ambient temperature (control group) and two experimental temperature differences (+2.5 °C and +5.0 °C) following a scientific climate change circumstance based on daily and monthly temperature monitoring at a two-minutes scale. Our results demonstrate that the contents of the total organic carbon (TOC), total nitrogen (TN), and total phosphorus (TP) in the warmed showed, roughly, a balance or a slight decrease than the control treatment. Warming obstructed the natural subsidence of sediment, but reinforced the character of the ecological source, and reduced the activity of urease (URE), but promoted the activity of alkaline phosphatase (AKP) and sucrase (SUC). Redundancy analysis showed that sucrase, urease, available phosphorus (AP), and pH were the major correlating factors under warming conditions in our research scope. Total organic carbon, total nitrogen, sucrase, catalase (CAT), and alkaline phosphatase were the principal reference factors to reflect the ambient temperature variations. Nutrient compositions and enzyme activities in GIW ecosystems could be reconstructed under the warming influence.

Molecular evolution of VEF-domain-containing PcG genes in plants.

Arabidopsis VERNALIZATION2 (VRN2), EMBRYONIC FLOWER2 (EMF2), and FERTILIZATION-INDEPENDENT SEED2 (FIS2) are involved in vernalization-mediated flowering, vegetative development, and seed development, respectively. Together with Arabidopsis VEF-L36, they share a VEF domain that is conserved in plants and animals. To investigate the evolution of VEF-domain-containing genes (VEF genes), we analyzed sequences related to VEF genes across land plants. To date, 24 full-length sequences from 11 angiosperm families and 54 partial sequences from another nine families were identified. The majority of the full-length sequences identified share greatest sequence similarity with and possess the same major domain structure as Arabidopsis EMF2. EMF2-like sequences are not only widespread among angiosperms, but are also found in genomic sequences of gymnosperms, lycophyte, and moss. No FIS2- or VEF-L36-like sequences were recovered from plants other than Arabidopsis, including from rice and poplar for which whole genomes have been sequenced. Phylogenetic analysis of the full-length sequences showed a high degree of amino acid sequence conservation in EMF2 homologs of closely related taxa. VRN2 homologs are recovered as a clade nested within the larger EMF2 clade. FIS2 and VEF-L36 are recovered in the VRN2 clade. VRN2 clade may have evolved from an EMF2 duplication event that occurred in the rosids prior to the divergence of the eurosid I and eurosid II lineages. We propose that dynamic changes in genome evolution contribute to the generation of the family of VEF-domain-containing genes. Phylogenetic analysis of the VEF domain alone showed that VEF sequences continue to evolve following EMF2/VRN2 divergence in accordance with species relationship. Existence of EMF2-like sequences in animals and across land plants suggests that a prototype form of EMF2 was present prior to the divergence of the plant and animal lineages. A proposed sequence of events, based on domain organization and occurrence of intermediate sequences throughout angiosperms, could explain VRN2 evolution from an EMF2-like ancestral sequence, possibly following duplication of the ancestral EMF2. Available data further suggest that VEF-L36 and FIS2 were derived from a VRN2-like ancestral sequence. Thus, the presence of VEF-L36 and FIS2 in a genome may ultimately be dependent upon the presence of a VRN2-like sequence.