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Leaf Carbon Exchange of Two Dominant Plant Species Impacted by Water and Nitrogen Application in a Semi-Arid Temperate Steppe
No full textPhotosynthetic characteristics are widely used as indicators of plant responses to global environmental changes such as precipitation change and nitrogen (N) deposition increase. How different plant species respond physiologically to the future precipitation change combined with increasing N availability is largely unclear. A field experiment was conducted to study responses in seasonal and interannual leaf carbon (C) exchange of two dominant plant species, Leymus chinensis and Stipa grandis, to additional water (either as spring snow or as summer water) and N application in a semi-arid temperate steppe of China. Our results showed that spring snow and summer water addition both increased the maximum photosynthetic rate (A(max)) of two dominant species. Such effect was likely caused by raised light saturation point, the maximum apparent quantum yield, stomatal conductance, and transpiration rate. The N application combined with spring snow or summer water addition both enhanced A(max) of S. grandis in both experimental years, whereas N application only increased A(max) of L. chinensis combined with summer water addition. Their responses were attributed to a concurrent increase in leaf N concentration (N-leaf) and decrease in leaf phosphorus (P) concentration (P-leaf), indicating that N-leaf and P-leaf affect photosynthetic characteristics to regulate leaf C exchange. Our results suggest that differentiated responses among different species in photosynthetic characteristics may lead to changes in ecosystem structure and functioning under increasing precipitation and N deposition
Land-use change reduces soil nitrogen retention of both particulate and mineral-associated organic matter in a temperate grassland
No full textSoil organic matter (SOM) fractions vary in formation and microbial activities, thus playing different roles in exogenous nitrogen (N) retention in terrestrial ecosystems. However, it remains unclear how land-use and environmental changes affect the behavior of SOM fractions in retaining exogenous N. Here, we investigated N distribution among four SOM fractions and how soil N retention capacity responds to tillage and increased snowfall. We monitored N retention in SOM fractions by adding (NH4NO3)-N-15-N-15 isotope in the field in a temperate grassland in Inner Mongolia. Our results showed that the fine mineral-associated organic matter (MOM 20 mu m) represented the fewer N pool with the largest mass. MOM 90% of the N-15 tracer in soil. Deepened snow did not affect N-15 retention in SOM fractions, while tillage decreased N-15 retention in MOM < 20 mu m, fPOM, and occluded particulate organic matter within aggregates (oPOM). We suggested that the reduction in soil total N retention under tillage conditions was mainly due to the reduced N retention in fPOM and MOM < 20 mu m. Structural equation modeling analysis revealed that tillage-induced decrease in N-15 retention of MOM < 20 mu m was regulated by both decreased microbial N-15 retention and reduced clay and silt contents. The decrease in N-15 retention of fPOM was probably due to the decreased microbial N-15 retention along with the increased plant N-15 uptake. This research reveals divergent pathways of N-15 retention among different SOM fractions in response to land-use change and provides novel insights into the estimation of soil N retention capacity with SOM fractions taken into consideration
Extending a canopy reflectance model for mangroves: A case study in south east queensland, Australia
No full textMangroves are essential coastal wetland vegetation and their extent and leaf area index (LAI) have been mapped using remotely sensed Earth Observation images. However, the physics-based relationship between biophysical properties of mangroves, tidal height, and their spectral values remains underexplored. In order to quantitatively evaluate the impact of woody material on mangrove spectra from optical imagery, a canopy reflectance model (CRM) was extended to simulate and analyse the reflectance of mangroves. The fractional cover, leaf-to-total area ratio and water depth were included as model parameters, increasing the fidelity of the canopy architecture in the CRM. A mangrove study area in South East Queensland, Australia, was chosen for model parameterisation and verification using field and satellite data. Simulated Sentinel-2 reflectance spectra of the mangrove plots closely matched the observed pixel reflectance spectra, with their coefficient of determination (R2) values higher than 0.98 and root mean square error values lower than 0.01, which was better than the performance of the original CRM omitting the fractional cover and woody material. The inverted plant area index and fractional cover values from the satellite imagery closely matched the field-derived reference values (R2 = 0.78 and 0.97, respectively). Simulation results revealed that a higher proportion of woody material in crowns reduced the canopy reflectance of mangroves in the near infrared region and increased the reflectance in the shortwave infrared region. Moreover, the simulated reflectance of the Sentinel-2 red edge 1 (695-714 nm) was not sensitive to the wood proportion for the examined cases. The modelling framework may be used to evaluate the impact of woody material for estimating mangrove LAI from optical imagery. The model may also be used to quantitatively analyse the mangrove reflectance spectra when including other important factors such as tidal height
Comparative Microbial Nitrogen Functional Gene Abundances in the Topsoil vs. Subsoil of Three Grassland Habitats in Northern China
No full textThe microbial groups of nitrogen fixers, ammonia oxidizers, and denitrifiers play vital roles in driving the nitrogen cycle in grassland ecosystems. However, the understanding of the abundance and distribution of these functional microorganisms as well as their driving factors were limited mainly to topsoil. In this study, the abundances of nitrogen functional genes (NFGs) involved in nitrogen fixation (nifH), ammonia oxidation (amoA), and denitrification (nirK, nirS, and nosZ) were investigated in both topsoil (0-10 cm, soil layer with concentrated root) and subsoil (30-40 cm, soil layer with spare root) of three grassland habitats in northern China. The abundance of NFGs decreased with soil depth except for the archaeal amoA gene and the distribution of nifH, archaeal amoA, nirK, and nirS gene was significantly impacted by grassland habitats. Moreover, the distribution of NFGs was more responsive to the vertical difference than horizontal spatial heterogeneity. Redundancy analysis revealed that the distribution pattern of overall NFGs was regulated by grassland habitats, and these regulations were more obvious in the subsoil than in the topsoil. Variance partitioning analysis further indicated that soil resource supply (e.g., organic matter) may control the vertical distribution of NFGs. Taken together, the findings in this study could fundamentally improve our understanding of the distribution of N cycling-associated microorganisms across a vertical scale, which would be useful for predicting the soil N availability and guiding the soil N management in grassland ecosystems
Structural elucidation of vascular plant photosystem I and its functional implications
No full textIn vascular plants, bryophytes and algae, the photosynthetic light reaction takes place in the thylakoid membrane where two transmembrane supercomplexes PSII and PSI work together with cytochrome b(6)f and ATP synthase to harvest the light energy and produce ATP and NADPH. Vascular plant PSI is a 600-kDa protein-pigment supercomplex, the core complex of which is partly surrounded by peripheral light-harvesting complex I (LHCI) that captures sunlight and transfers the excitation energy to the core to be used for charge separation. PSI is unique mainly in absorption of longer-wavelengths than PSII, fast excitation energy transfer including uphill energy transfer, and an extremely high quantum ef?ciency. From the early 1980s, a lot of effort has been dedicated to structural and functional studies of PSI-LHCI, leading to the current understanding of how more than 200 cofactors are kept at the correct distance and geometry to facilitate fast energy transfer in this supercomplex at an atomic level. In this review, we review the history of studies on vascular plant PSI-LHCI, summarise the present research progress on its structure, and present some new and further questions to be answered in future studies
Unraveling the Biosynthesis of Carvacrol in Different Tissues of Origanum vulgare
No full textOriganum vulgare, belonging to the Lamiaceae family, is a principal culinary herb used worldwide which possesses great antioxidant and antibacterial properties corresponding to various volatile organic components (VOCs). However, the metabolite profiles and underlying biosynthesis mechanisms of elaborate tissues (stems, leaves, bracts, sepals, petals) of Origanum vulgare have seldom been reported. Here, solid-phase microextraction-gas chromatography/mass spectrometry results showed that Origanum vulgare 'Hot and Spicy' (O. vulgare 'HS') was extremely rich in carvacrol and had the tissue dependence characteristic. Moreover, a full-length transcriptome analysis revealed carvacrol biosynthesis and its tissue-specific expression patterns of 'upstream' MVA/MEP pathway genes and 'downstream' modifier genes of TPSs, CYPs, and SDRs. Furthermore, the systems biology method of modular organization analysis was applied to cluster 16,341 differently expressed genes into nine modules and to identify significant carvacrol- and peltate glandular trichome-correlated modules. In terms of these positive and negative modules, weighted gene co-expression network analysis results showed that carvacrol biosynthetic pathway genes are highly co-expressed with TF genes, such as ZIPs and bHLHs, indicating their involvement in regulating the biosynthesis of carvacrol. Our findings shed light on the tissue specificity of VOC accumulation in O. vulgare 'HS' and identified key candidate genes for carvacrol biosynthesis, which would allow metabolic engineering and breeding of Origanum cultivars
Plant C and N Pools Improved by N Addition Levels but Not Frequencies in a Typical Grassland of Northern China
No full textThe pools of plant community carbon (C) and nitrogen (N) are important sources of soil organic matter in terrestrial ecosystems and directly affect soil C and N cycling. A large amount of studies were manipulated with multiple N levels on soil C and N pools. However, how and whether the frequency of N addition can affect the plant C and N pools is still unclear. In order to comprehensively understand the N addition effects (including frequencies and levels) on C and N pools of the plant community, we executed a randomized complete block experiment with the addition of five levels of N, including 0, 2, 10, 20 and 50 g N m(-2) yr(-1) (designated as N-0, N-2, N-10, N-20 and N-50) and two N addition frequencies (twice a year vs. monthly, F-2, F-12) in August of 2008. After 5 years of treatment, the physical-chemical properties of the plants and soil were measured in 2013. The results indicated that with increasing N addition levels, the C and N pools of the plant community significantly increased, while N addition frequency had no significant effects. Moreover, significant interactions between N addition levels and the frequencies on the C and N pools of the plant community were also found in this typical grassland. Under different frequencies of N addition treatment, the plant community C and N pools showed different response patterns along with N addition levels in plants aboveground and belowground, respectively. Under different frequencies of N addition, the changes in the C and N pools of the plant community caused by N addition were regulated by different environmental factors. We highlight that long-term N deposition could affect the plant community C and N pools and would influence C and N cycling of terrestrial ecosystems based on global climate change in the future
Evaluation of the Perception and Experience of Rural Natural Landscape among Youth Groups: An Empirical Analysis from Three Villages around Hefei
No full textResearch on the perception and evaluation degree that the rural natural landscape plays an important role in improving rural sustainable development and construction. However, the views of young people, who play a key role in social development, on the natural landscape of the countryside have been neglected. Based on the perspective of the rural natural landscape in China, this study combines the field research of Ma Ying, San Shi Gang, and Shen Fu villages around Hefei, Anhui Province, and constructs a perception and experience evaluation index and questionnaire of the rural natural landscape from four dimensions of rural landscape ecology, water environment, climate, and sound. Through the online questionnaire, 316 questionnaires were distributed to young people aged 18 to 35 years old, and 283 valid questionnaires were recovered with an effective recovery rate of 89.56%. The Cronbach coefficient was 0.954, and the KMO value was 0.968. The reliability and validity were good. The analytic hierarchy process (AHP) combined with the entropy method was used to calculate the weight of each index and analyze the influencing factors of young people's perception evaluation of the rural landscape. Firstly, young people have a good perception of rural climate conditions, but the planning and layout of rural landscape ecology need to be improved. Secondly, sound comfort, air cleanliness, and landscape adaptation in a rural environment are the key factors that affect young people's perception and experience of rural areas. Thirdly, improving the adaptability of the rural natural landscape to the local environment and the richness of vegetation is conducive to improving young people's favorable understanding of the rural environment
Microtubules promote the non-cell autonomous action of microRNAs by inhibiting their cytoplasmic loading onto ARGONAUTE1 in Arabidopsis
No full textMobile microRNAs (miRNAs) serve as local and long-distance signals in the developmental patterning and stress responses in plants. However, mechanisms governing the non-cell autonomous activities of miRNAs remain elusive. Here, we show that mutations that disrupt microtubule dynamics are specifically defective for the non-cell autonomous actions of mobile miRNAs, including miR165/6 that is produced in the endodermis and moves to the vasculature to pattern xylem cell fates in Arabidopsis roots. We show that KTN1, a subunit of a microtubule-severing enzyme, is required in source cells to inhibit the loading of miR165/6 into ARGONUATE1 (AGO1), which is cell autonomous, to enable the miRNA to exit the cell. Microtubule disruption enhances the association of miR165/6 with AGO1 in the cytoplasm. These findings suggest that although cell-autonomous miRNAs load onto AGO1 in the nucleus, the cytoplasmic AGO1 loading of mobile miRNAs is a key step regulated by microtubules to promote the range of miRNA cell-to-cell movement
Enhanced precipitation offsets climate warming inhibition on Solidago canadensis growth and sustains its high tolerance
No full textInvasions encompass sequential climate-mediated stages, and the establishment stage of invaders is crucial for their spread and damage. Growth and tolerance are two key components determining plant invasions, and addressing climate change effects on them at an establishment stage is key to predicting invasions. To mimic the plant invasion process, we selected 16 native plant species and an invader (Solidago canadensis native to North America) to create experimental communities. Once S. canadensis monocultures established, they were exposed to four manipulations consisting of temperature and precipitation. Relative to the ambient condition, warming substantially inhibited S. canadensis growth, as measured by plant height and biomass, and greatly increased its tolerance to high temperatures, as indicated by stomatal conductance and leaf dry matter content. Relative to the ambient condition, warming plus precipitation enhancement failed to reduce the growth of S. canadensis but increased its tolerance. These findings suggest that enhanced precipitation could completely offset the inhibitory effects of climate warming on S. canadensis growth and sustain its high tolerance to heat stress. Accordingly, we tentatively proposed a prediction that climate warming and precipitation enhancement will facilitate plant invasions via eliminating warming stress effects and retaining high tolerance