Tag: phenology
Fruiting patterns of macrofungi in tropical and temperate land use types in Yunnan Province, China
Evolution of soil chemical properties in the rotational agroforestry system with Acacia auriculiformis for 22 years, DRC
Near-infrared, mid-infrared or combined diffuse reflectance spectroscopy for assessing soil fertility in rice fields in sub-Saharan Africa
Assessment and monitoring of soil resources is needed for ensuring environmental sustainability of rice production in sub-Saharan Africa (SSA). Diffuse reflectance spectroscopy has the potential to offer means to evaluate and monitor soils at large scale in an efficient, affordable and timely manner. However, its accuracy for predicting chemical and physical properties of soils under rice cultivation is little known. The objectives of this study were to i) determine physical and chemical soil fertility properties which can be accurately analyzed using near infrared (NIR) (700–2500 nm), mid-infrared (MIR) (2500–16,670 nm), or a combination of both (NIR-MIR) (700–16,670 nm) spectral libraries, ii) compare their prediction potential for identifying the most suitable spectral range for simultaneous analysis of soil fertility properties, and iii) assess degrees of variation of 29 soil fertility properties for 2845 soil samples collected from 42 study sites in 20 SSA countries. Diffuse reflectance spectroscopy data were obtained using a Fourier-transform infrared spectrometer (FT-IR) Tensor 27 with a high-throughput screening (HTS-XT) extension unit. About 10% of the whole sample set was chosen for conventional wet chemistry soil analysis, and was used for developing best fitted models with partial least squares regression (PLSR) that can estimate soil fertility properties using infrared (IR) spectra. The prediction performances were evaluated by R2, RMSE and RPIQ. Good prediction models (0.75 < R2 ≤ 0.86 and 1.36 ≤ RPIQ ≤ 3.78) were obtained for 13 soil properties consisting of pH H2O 1:2, exchangeable Ca, exchangeable Mg, sum of exchangeable cations, CEC, ECEC, base saturation percentage, total N, total organic C, clay content, silt content, phosphorus sorption index (PSI) and extractable Al. Satisfactory predictions (0.53 ≤ R2 ≤ 0.75 and 0.59 ≤ RPIQ ≤ 2.56) were obtained for pH H2O 1:2.5, exchangeable K, extractable Mn, Cu, and B, and sand content. NIR, MIR, and combined NIR-MIR diffuse reflectance spectroscopy demonstrate the best prediction potential for 14, 21, and 76% of the studied soil fertility properties, respectively. Except soil pH, most of soil properties are moderate to highly variable (CV = 21–131%). On average, soils in rice fields are characterized by moderate acidity, and low total N, available P and B. In conclusion, the combined NIR-MIR diffuse reflectance spectroscopy can offer an alternative to conventional wet chemistry methods for assessing soil fertility properties in rice fields in SSA, except for those having poor prediction potentials.
Distribution margins as natural laboratories to infer species’ flowering responses to climate warming and implications for frost risk
The timing of flowering phenology in most temperate trees results from the interplay of winter chilling and spring heat. As global warming progresses, reduced chilling may gain increasing importance in regulating flowering dates, and eventually offset flowering advances in response to warmer springs. Later onset of flowering events may arise, with negative effects on plant fitness. However, delayed flowering in trees may also reduce the risk from late frosts. Different temperature conditions at both margins of the apple growing areas of Shaanxi in China provide a natural laboratory to examine the responses of trees’ flowering phenology and late frost risk to climate warming. We identified the chilling and heat accumulation periods for apples by Partial Least Squares regression of first flowering dates against daily chilling and heat accumulation rates during 2001–2016. We then analyzed the impacts of temperatures during these periods on flowering timing, and evaluated the frost risk for each site. Results indicated increasing importance of chilling temperatures from north to south, with greatest effects determined for the warmest site, where delayed blossom has been observed during the past 16 years. Since late frosts mostly occurred before tree flowering, only minor frost damage was detected for our study areas, with future delays in flowering likely to reduce the frost risk even further. The redistribution of apple trees to nearby locations with cold winters, either northward or uphill, could be a promising strategy to reduce the risk of insufficient chilling and ensure that production remains viable in a warming future.
Performance of pistachio (Pistacia vera L.) in warming Mediterranean orchards
Woody perennial species from temperate regions fall dormant during the cold winter season to avoid unfavourable conditions. To break out of dormancy and eventually flower, they must fulfil cultivar-specific chilling and heat requirements. Phenology analysis can clarify the climatic requirements of tree cultivars and thus provide critical information to ensure the future viability of orchards in warm growing regions, where warmer winters are expected as a result of climate change. We used Partial Least Squares (PLS) regression to correlate first bloom dates of 4 local and 3 foreign pistachio (Pistacia vera L.) cultivars with daily chill and heat accumulation (quantified with the Dynamic Model and Growing Degree Hours Model, respectively) for 18-year records (1997–2016) from Sfax, Tunisia. PLS outputs allowed delineation of the chilling phase, during which high chill accumulation was correlated to early bloom, and the forcing phase, when this was true for high heat accumulation. Both phases showed discontinuities. During September and October, high heat accumulation appeared to first have a bloom-delaying effect, followed by a bloom-advancing effect, indicating that temperature during dormancy induction may affect bloom dates. Chilling requirements were estimated between 32.1 ± 2.3 and 33.3 ± 2.2 Chill Portions and heat requirements between 9974 ± 198 and 12,738 ± 235 Growing Degree Hours. This study revealed limitations of the Dynamic Model, which is often considered the most accurate among commonly used models, in the warm Tunisian climate. High temperatures during the chilling phase had a significant bloom-delaying effect on all pistachio cultivars. Low chill accumulation was related to very low yields and associated with zero production in 1995, 2001 and 2007. Low flowering percentage, high bud fall percentage, long and inhomogeneous bloom, and co-occurrence of several phenological stages on the same branch were symptoms of lack of chill in 2016.
Sensitivity of Grapevine Phenology to Water Availability, Temperature and CO2 Concentration
In recent decades, mean global temperatures have increased in parallel with a sharp rise in atmospheric carbon dioxide (CO2) levels, with apparent implications for precipitation patterns. The aim of the present work is to assess the sensitivity of different phenological stages of grapevine to temperature and to study the influence of other factors related to climate change (water availability and CO2 concentration) on this relationship. Grapevine phenological records from 9 plantings between 42.75°N and 46.03°N consisting of dates for budburst, flowering and fruit maturity were used. In addition, we used phenological data collected from 2 years of experiments with grapevine fruit-bearing cuttings with two grapevine varieties under two levels of water availability, two temperature regimes and two levels of CO2. Dormancy breaking and flowering were strongly dependent on spring temperature, while neither variation in temperature during the chilling period nor precipitation significantly affected budburst date. The time needed to reach fruit maturity diminished with increasing temperature and decreasing precipitation. Experiments under semi-controlled conditions revealed great sensitivity of berry development to both temperature and CO2. Water availability had significant interactions with both temperature and CO2; however, in general, water deficit delayed maturity when combined with other factors. Sensitivities to temperature and CO2 varied widely, but higher sensitivities appeared in the coolest year, particularly for the late ripening variety, ‘White Tempranillo’. The knowledge gained in whole plant physiology and multi stress approaches is crucial to predict the effects of climate change and to design mitigation and adaptation strategies allowing viticulture to cope with climate change.
Domestication of Irvingia gabonensis: 1. Phenotypic variation in fruits and kernels in two populations from Cameroon
Twenty four fruits from each of 52 Irvingia gabonensis trees from two villages (Nko’ovos II and Elig Nkouma) of the humid lowland forest zone of Cameroon (West Africa) were assessed to determine the extent of variation in ten fruit, nut (endocarp), and kernel (cotyledon) characteristics. Highly significant differences were found in fruit length (Range = 46.2 to 77.3 mm), fruit width (45.1 to 72.5 mm), flesh (mesocarp) depth (11.2 to 21.8 mm), fruit mass (44.5 to 195.4 g), kernel mass (0.54 to 6.9 g) and shell mass (5.4 to 18.6 g). In each of these traits there was continuous variation. Differences were also observed in fruit taste and fibrosity. The most frequent skin and flesh color was yellow (Methuen Color Code 4A8). Mean fruit length, fruit width, fruit mass, shell mass and kernel mass differed significantly between villages, but did not differ between different landuses (homegardens, cocoa farms, crop fields or fallows). These results represent the first quantitative assessment of tree-to-tree variation in fruit traits for this species and are discussed with regard to the domestication potential of I. gabonensis.
Tree leafing phenology and crop productivity in semi-arid agroforestry systems in Kenya
The hypothesis that temporal separation of resource use between trees and crops minimises competition for wa ter in agroforestry systems during the cropping period and increases utilisation of annual rainfall was tested at Machakos in semi-arid Kenya. Four popular tree species were chosen to provide a range of leafing phenologies. These included Melia volkensii, which sheds its leaves twice a year, Senna spectabilis and Gliricidia sepium, which shed their leaves during the long dry season, and the evergreen Croton megalocarpus. All four species retained their foliage during the long rains, offering little scope for temporal separation of resource use. Maize (Zea mays) yields were reduced by 50–70% in the agroforestry treatments. Reductions in crop yield were strongly correlated with tree growth (r 2 =0.94) and available soil moisture (r 2 =0.88). G. sepium remained leafless for much of the short rains despite the presence of available soil water, and was least competitive with the bean crops (Phaseolus vulgaris) grown at this time. Reductions in crop yield in the agroforestry treatments were closely correlated with tree growth (r 2 =0.99) and available moisture (r 2 =0.79) during the 1996/97 short rains (158 mm), but not during the much wetter 1997/98 season (608 mm). Shading by trees or shade nets reduced crop yield, in contrast to previous studies in the semi-arid tropics. Low off-season rainfall during the study period (9% of annual rainfall compared to the long-term average of 20%) limited the potential for temporal separation of growing periods. Where the prospects for temporal or spatial separation in resource use are limited, shoot and/or root pruning may be necessary to manage competition between trees and crops.
Land cover characterization in West Sudanian savannas using seasonal features from annual landsat time series
With the increasing temporal resolution of medium spatial resolution data, seasonal features are becoming more readily available for land cover characterization. However, in the tropical regions, images can be severely contaminated by clouds during the rainy season and fires during the dry season, with possible effects to seasonal features. In this study, we evaluated the performance of seasonal features based on an annual Landsat time series (LTS) of 35 images for land cover characterization in West Sudanian savanna woodlands. First, the burnt areas were detected and removed. Second, the reflectance seasonality was modelled using a harmonic model, and model parameters were used as inputs for land cover classification and tree crown cover prediction using the random forest algorithm. Furthermore, to study the sensitivity of the approach to the burnt areas, we repeated the analyses without the first step. Our results showed that seasonal features improved classification accuracy significantly from 68.7% and 66.1% to 76.2%, and decreased root mean square error (RMSE) of tree crown cover predictions from 11.7% and 11.4% to 10.4%, in comparison to the dry and rainy season single date images, respectively. The burnt areas biased the seasonal parameters in near-infrared and shortwave infrared bands, and decreased the accuracy of classification and tree crown cover prediction, suggesting that burnt areas should be removed before fitting the harmonic model. We conclude that seasonal features from annual LTS improved land cover characterization performance, and the harmonic model, provided a simple method for computing annual seasonal features with burnt area removal. © 2016 by the authors.