First assessment of the plant phenology index (PPI) for estimating gross primary productivity in African semi-arid ecosystems

The importance of semi-arid ecosystems in the global carbon cycle as sinks for CO2 emissions has recently been highlighted. Africa is a carbon sink and nearly half its area comprises arid and semi-arid ecosystems. However, there are uncertainties regarding CO2 fluxes for semi-arid ecosystems in Africa, particularly savannas and dry tropical woodlands. In order to improve on existing remote-sensing based methods for estimating carbon uptake across semi-arid Africa we applied and tested the recently developed plant phenology index (PPI). We developed a PPI-based model estimating gross primary productivity (GPP) that accounts for canopy water stress, and compared it against three other Earth observation-based GPP models: the temperature and greenness model, the greenness and radiation model and a light use efficiency model. The models were evaluated against in situ data from four semi-arid sites in Africa with varying tree canopy cover (3 to 65 percent). Evaluation results from the four GPP models showed reasonable agreement with in situ GPP measured from eddy covariance flux towers (EC GPP) based on coefficient of variation, root-mean-square error, and Bayesian information criterion. The PPI-based GPP model was able to capture the magnitude of EC GPP better than the other tested models. The results of this study show that a PPI-based GPP model is a promising tool for the estimation of GPP in the semi-arid ecosystems of Africa.Comment: Accepted manuscript; 12 pages, 4 tables, 9 figure

Spatio-temporal analysis of North African forest cover dynamics using time series of vegetation indices – case of the Maamora forest (Morocco)

North African forest areas play several roles and functions and represent a heritage of great economic and ecological importance. As a result of global changes, that act independently or synergistically, these areas are currently undergoing a pronounced degradation and their productivity is decreasing due to several factors. This work aims to characterize spatio-temporal dynamics of vegetation within the Maamora forest. This forest is considered as the most extensive cork oak woodland in the world and is divided, from west to east, into five cantons A, B, C, D and E. The data, extracted between 2000–2021 from MODIS NDVI/EVI images of 250 m, were analyzed using statistical parameters with the Pettitt homogeneity and the Mann-Kendall trend tests, with their seasonal and spatial components, in order to better consider the vegetation distribution of this forest. Results show a clear temporal and spatial (inter-canton) variability of vegetation intensity, unrelated to the continental gradient. In fact, recorded mean values in cantons C and E are significantly higher than those of cantons B and D respectively. This is confirmed by both regressive and progressive trends, which were identified respectively from the months of March 2012 and October 2008, in the data series of cantons B and E successively. Spatially, the regressive dynamic remains generalized and affects more than 26.7% of the Maamora’s total area with extreme rates (46.1% and 14.0%) recorded respectively by the two aforementioned cantons. Similarly, all the stand types in canton B show the highest regressive rates, especially the cork oak regeneration strata (75.4%) and the bare lands (86.1%), which may explain the positive tendencies identified by the related series during the fall season. However, the cantons C and E record the lowest rates, respectively, for natural stands of cork oak and artificial plantations. These results highlight also the absence of a causal relationship between the contrasting vegetation dynamics of the Maamora and the climatic conditions, expressed here by the continental gradient. However, they do highlight the effects of other factors, particularly those of a technical nature

First assessment of the plant phenology index (PPI) for estimating gross primary productivity in African semi-arid ecosystems

The importance of semi-arid ecosystems in the global carbon cycle as sinks for CO 2 emissions has recently been highlighted. Africa is a carbon sink and nearly half its area comprises arid and semi-arid ecosystems. However, there are uncertainties regarding CO 2 fluxes for semi-arid ecosystems in Africa, particularly savannas and dry tropical woodlands. In order to improve on existing remote-sensing based methods for estimating carbon uptake across semi-arid Africa we applied and tested the recently developed plant phenology index (PPI). We developed a PPI-based model estimating gross primary productivity (GPP) that accounts for canopy water stress, and compared it against three other Earth observation-based GPP models: the temperature and greenness (T-G) model, the greenness and radiation (GöR) model and a light use efficiency model (MOD17). The models were evaluated against in situ data from four semi-arid sites in Africa with varying tree canopy cover (3–65%). Evaluation results from the four GPP models showed reasonable agreement with in situ GPP measured from eddy covariance flux towers (EC GPP) based on coefficient of variation (R 2 ), root-mean-square error (RMSE), and Bayesian information criterion (BIC). The GöR model produced R 2 = 0.73, RMSE = 1.45 g C m −2 d −1 , and BIC = 678; the T-G model produced R 2 = 0.68, RMSE = 1.57 g C m −2 d −1 , and BIC = 707; the MOD17 model produced R 2 = 0.49, RMSE = 1.98 g C m −2 d −1 , and BIC = 800. The PPI-based GPP model was able to capture the magnitude of EC GPP better than the other tested models (R 2 = 0.77, RMSE = 1.32 g C m −2 d −1 , and BIC = 631). These results show that a PPI-based GPP model is a promising tool for the estimation of GPP in the semi-arid ecosystems of Africa

Physiology and Biochemistry of Cold-hardy Table Grapevines

Grapes are grown worldwide to produce wine, grape juice and are also popular as fresh table grapes or dried raisins. Due to their nutritional value and importance in the multibillion-dollar wine industry, grapes are considered the most commercially important berry crop. Grape production has primarily concentrated on European wine grapes, Vitis vinifera, in the dry, hot Mediterranean and Central Asian climates. V. vinifera is not cold tolerant enough to endure winter temperatures below -15°C. The introduction of several interspecific hybrids (of both wine and table grape) cultivars in the 20th century and selection of a training system has helped propel the expansion of grapevine cultivation in cooler climates such as the Northeastern US and upper midwestern US states. Training and trellising systems are part of viticultural practices that influence many aspects of grapevine growth and productivity. Especially in cool climates like New Hampshire, choosing an appropriate training system will provide the grapevines with good exposure of leaves and berries to sunlight leading to fruits with improved berry composition and higher levels of sugar accumulation as well as increased concentrations of anthocyanins and phenolic compounds. However, there is limited research on the impact of training systems on cold-hardy table grapevine physiology and biochemistry. To address these knowledge gaps research was conducted at the UNH Woodman Horticultural Research Farm in Durham, NH, where cold-hardy grape varieties are growing on two different training systems. Mars and Canadice grape varieties grown on vertical shoot positioning (VSP) and Munson (M) training systems were used. Grapevine physiology and biochemistry were followed throughout three growing seasons using destructive and non-destructive methods to monitor grapevine health. Additionally, considering the current need for alternative environmentally friendly fungicides, plant material from these cold-hardy grape cultivars was tested for their putative antifungal properties. The objectives of this study were to: (1) Determine the physiological and biochemical parameters of Canadice and Mars cold-hardy grape varieties growing on vertical shoot positioning (VSP) and Munson training systems, and (2) Investigate the putative antifungal activity of field-collected grapevine leaves and cell suspension cultures obtained from Canadice and Mars grapevines against Botrytis cinerea. I hypothesized that the training system would influence the SPAD measurements, spectral indices (normalized difference vegetation index, red edge inflection point, moisture stress index, and phenology index), and gas exchange measurements (intercellular carbon dioxide concentration, stomatal conductance, net photosynthesis, transpiration rate, vapor pressure deficit, and water use efficiency) of Mars and Canadice leaves growing on two different training systems. I also hypothesized that the training system would have an effect on the amount of leaf photosynthetic pigments, leaf, juice, and skin metabolomes, titratable acidity and soluble solid contents of Canadice and Mars growing on two different training systems (Chapter 2). I hypothesized that field-collected leaves and cell suspension cultures established from Canadice and Mars grape varieties would contain compounds with antifungal activity against B. cinerea (Chapter 3). For objective 1, physiological parameters were measured with SPAD, spectral analysis, and gas exchange analysis on grapevine leaves throughout three growing seasons (2019, 2020, and 2021). Specifically, I determined the SPAD measurements, the spectral indices normalized difference vegetation index (NDVI), red edge inflection point (REIP), moisture stress index (MSI) and phenology index, and gas exchange measurements to determine intercellular carbon dioxide concentration (Ci), stomatal conductance (gs), vapor pressure deficit (VPD), net photosynthesis (A), transpiration (E), and water use efficiency (WUE). While no differences were found regarding training systems alone, there was a significant interaction of training system with time, suggesting that training system had different effects at different times. For the biochemical parameters, the same leaves that were used to perform SPAD measurements were used to analyze photosynthetic pigments and proton based nuclear magnetic resonance (1H-NMR spectroscopy)-based metabolomics. Consistent with the results of physiological parameters, no differences were found for photosynthetic pigments - chlorophyll a, chlorophyll b, total chlorophyll, and carotenoids - between training systems, but the training system had different effects at different time points. The leaf metabolites studied using 1H-NMR spectroscopy coupled with multivariate statistical analysis did not distinguish samples based on training systems, but sample separation occurred based on phenological stages. The compounds identified showed variations between flowering, veraison, and harvest. Namely, sucrose gradually increased from flowering to harvest. Additionally, the 1H-NMR spectroscopy-based metabolome of grape juice was investigated in grape berries collected from veraison to harvest. Various kinds of metabolites were identified. Fructose, glucose, alanine, threonine, myo-Inositol, and 3-hydroxybutyrate were all shown to increase from veraison to harvest. The amount of fructose and glucose increased over time (between veraison and harvest) and are indicators of berry ripeness. Furthermore, at harvest, grape titratable acidity and total soluble solid content were determined, and berry skin composition was investigated using ultra performance liquid chromatography-mass spectrometry (UPLC-MS) analysis. Distinct sets of metabolites were identified in Mars and Canadice skin samples and were dependent on the training system. For my objective 2, I investigated the putative antifungal activity of Mars- and Canadice-derived products, specifically field-collected grapevine senescent leaves and cell suspension cultures, against B. cinerea. The aim was to gather knowledge that could lead to the development of new botanical fungicides that could be used as an alternative to synthetic fungicides for disease management in vineyards. This approach could contribute to sustainable management practices in the long term. Using grapevine debris (such as canes, wood, and leaves) from V. vinifera to suppress B. cinerea and other plant pathogens has been successfully demonstrated. However, there is limited research evaluating secondary metabolites with antifungal properties from cold-hardy grapevines. Our results show that grapevine-derived extracts have antifungal activity in vitro and in detached berry experiments when challenged with B. cinerea, but the antifungal activity was not translated to in planta experiments. The metabolic profiling of senescent leaves and cell suspension cultures of Mars and Canadice identified an array of compounds, including some reported to have antimicrobial properties. Given the list of compounds that have been identified in cold-hardy grapevine-derived products, future work should examine these unique compounds present in the senescent leaves and cell cultures under controlled experimental conditions. While our results indicated that Mars- and Canadice-derived products have antifungal activity, the materials used in this study were crude extracts. Future studies should focus on using finer grapevine-products to test the efficacy against B. cinerea, not only in vitro, but also using pilot-scale greenhouse trials, and vineyard trials