Interannual and seasonal relationships between photosynthesis and summer soil moisture in the Ili River basin, Xinjiang, 2000-2018

Green Pak Choi is better in suitable environment but the purple ones more resist to drought and shading

BACKGROUND

Studying how economic vegetable adapt to stressful environment is important not only for plant biology application but also to agronomy. In this study, we selected two commonly used genotypes of pak choi, i.e., larger green pak choi (Brassica rapa ssp. chinensis) and smaller purple pak choi (Brassica rapa var. chinensis, 'Rubi F1') to examine the divergent response of the two genotypes to drought and shading in the semi-arid region of Xinjiang. We compared the differences in biomass accumulation and plant morphological traits of the two pak choi in response to the interaction effects of drought (55-70% of field water capacity) and shading (24% reduction of canopy light radiation).

RESULTS

The results showed drought and shading significantly reduced the aboveground and belowground biomass of the two pak choi, with a particularly pronounced decrease in shoot biomass under the combined effect of shading + drought. The decline in shoot biomass was mostly resulted from decreasing in the number of leaves rather than in plant height and crown width in response to drought and shading. In terms of morphological traits, green pak choi sensitively responded to increased drought and shading, with aboveground biomass mostly determined by leaf number and root mass. In contrast, purple pak choi likely more resistant to the stressful environment, as its aboveground biomass was also influenced by plant height and crown width.

CONCLUSIONS

Hence it is important to consider not only the effects of drought but also the role of adequate light, which plays a key part in promoting the cultivation and growth of pak choi in stressful environments. The research and application of plant biology and agronomy in the region also need to consider the diversity of key economic plants to promote sustainability of vegetable farming in adapting to changing environmental stresses.

Exploring the multifaceted reason for deficits in soil water within different soil layers in China's drylands

Soil water regulates the hydrological cycle and provides the water required for vegetation growth in drylands. However, existing studies have rarely investigated the reason for changes in soil water within different layers and compared differences in the contribution of driving factors from spatial and inter-annual perspectives. This study analyzed the dynamics of soil water content (SWC) at shallow (0-28 cm), intermediate (28-100 cm), and deep (100-289 cm) layers. The individual and interactive effects of different environmental factors on the spatial heterogeneity of SWC were investigated using the geographical detector. By selecting evapotranspiration (ET), precipitation, air temperature, land surface temperature (LST), and the Normalized Difference Vegetation Index (NDVI), we determined the influences of these factors on SWC dynamics for each layer as well as their contributions using ridge regression. Meanwhile, we also analyzed the influence of extreme events and lag effects of climatic factors on SWC. The results showed that SWC in each layer primarily exhibited a downward trend. In different layers, all interactive factors (two factors) had stronger effects on the spatial heterogeneity of SWC compared to any individual factor. Precipitation was the largest contributor (25.03 ± 20.66%) to SWC dynamics in shallow layer but its contribution decreased with increasing soil depth. NDVI mainly controlled the SWC in intermediate and deep layers with the largest contribution and exerted a dual effect on SWC. The contributions of air temperature and LST were the smallest. The lagged months of precipitation and air temperature on SWC increased with soil depth. Precipitation extremes with long duration and warm temperature extremes had large contributions and exceeded that of the average climate changes. These findings can provide a deeper insight into soil water dynamics and their environmental factors and scientific guidance for maintaining the hydrological cycle and sustainable development of vegetation in drylands.

Spatiotemporal patterns, sustainability, and primary drivers of NDVI-derived vegetation dynamics (2003-2022) in Nepal

Understanding the vegetation dynamics and their drivers in Nepal has significant scientific reference value for implementing sustainable ecological policies. This study provides a comprehensive analysis of the spatio-temporal variations in vegetation cover in Nepal from 2003 to 2022 using MODIS NDVI data and explores the effects of climatic factors and anthropogenic activities on vegetation. Mann-Kendall test was used to assess the significant trend in NDVI and was integrated with the Hurst exponent to predict future trends. The driving factors of NDVI dynamics were analyzed using Pearson's correlation, partial derivative, and residual analysis methods. The results indicate that over the last 20 years, Nepal has experienced an increasing trend in NDVI at 0.0013 year-1, with 80% of the surface area (vegetation cover) showing an increasing vegetation trend (~ 28% with a significant increase in vegetation). Temperature influenced vegetation dynamics in the higher elevation areas, while precipitation and human interventions influenced the lower elevation areas. The Hurst exponent analysis predicts an improvement in the vegetation cover (greening) for a larger area compared to vegetation degradation (browning). A significantly increased area of NDVI residuals indicates a positive anthropogenic influence on vegetation cover. Anthropogenic activities have a higher relative contribution to NDVI variation followed by temperature and then precipitation. The results of residual trend and Hurst analysis in different regions of Nepal help identify degraded areas, both in the present and future. This information can assist relevant authorities in implementing appropriate policies for a sustainable ecological environment.

Characterization of carbon fluxes, stock and nutrients in the sacred forest groves and invasive vegetation stands within the human dominated landscapes of a tropical semi-arid region

In the semi-arid plains of Southern India, outside the protected area network, sacred groves forests and the barren lands invaded by Prosopis juliflora are reckoned to be the major greenery, but have homogenous and heterogeneous vegetation respectively. This study attempted to compare 50 Sacred Groves Stands (SGS) and 50 monodominant Prosopis juliflora Stands (PJS) for the functional diversity, evenness, floral diversity, carbon stock and dynamics, carbon-fixing traits, dendrochronology of trees, soil nutrient profiles, and soil erosion. Quadrat sample survey was adopted to record stand density, species richness, abundance, basal area and leaf area index; composite soil samples were collected at depths 0-30 cm for nutrient profiling (N, P, K, and OC). Photosynthesis rate (µmole co2 m2/sec), air temperature (°c), leaf intracellular co2 concentration (ppm), ambient photosynthetic active radiation (µmole m2/sec), transpiration rate (m. mole H2O m2/sec) were determined for the 51 tree species existed in SGS and PJS using Plant Photosynthesis system. Structural Equation Model (SEM) was applied to derive the carbon sequestering potential and photosynthetic efficiency of eight dominant tree species using vital input parameters, including eco-physiological, morphological, and biochemical characterization. The Revised Universal Soil Loss Equation (RUSLE) model, in conjunction with ArcGIS Pro and ArcGIS 10.3, was adopted to map soil loss. Carbon source/sink determinations inferred through Net Ecosystem Productivity (NEP) assessments showed that mature SGS potentially acted as a carbon sink (0.06 ± 0.01 g C/m2/day), while matured PJS acted as a carbon source (-0.34 ± 0.12 g C/m2/day). Soil erosion rates were significantly greater (29.5 ± 13.4 ton/ha/year) in SGS compared to PJS (7.52 ± 2.55 ton/ha/year). Of the eight selected tree species, SEM revealed that trees belonging to the family Fabaceae [Wrightia tinctoria (estimated coefficient: 1.28, p = 0.02) > Prosopis juliflora (1.22, p = 0.01) > Acacia nilotica (1.21, p = 0.03) > Albizia lebbeck (0.97, p = 0.01)] showed comparatively high carbon sequestering ability.

Comparison, validation and improvement of empirical soil moisture models for conditions in Colombia

Modeling soil moisture as a function of meteorological data is necessary for agricultural applications, including irrigation scheduling. In this study, empirical water balance models and empirical compartment models are assessed for estimating soil moisture, for three locations in Colombia. The daily precipitation and average, maximum and minimum air temperatures are the input variables. In the water balance type models, the evapotranspiration term is based on the Hargreaves model, whereas the runoff and percolation terms are functions of precipitation and soil moisture. The models are calibrated using field data from each location. The main contributions compared to closely related studies are: i) the proposal of three models, formulated by combining an empirical water balance model with modifications in the precipitation, runoff, percolation and evapotranspiration terms, using functions recently proposed in the current literature and incorporating new modifications to these terms; ii) the assessment of the effect of model parameters on the fitting quality and determination of the parameters with higher effects; iii) the comparison of the proposed empirical models with recent empirical models from the literature in terms of the combination of fitting accuracy and number of parameters through the Akaike Information Criterion (AIC), and also the Nash-Sutcliffe (NS) coefficient and the root mean square error. The best models described soil moisture with an NS efficiency higher than 0.8. No single model achieved the highest performance for the three locations.