Schume, HelmutHailu, ZerfuHailu, TenawGodbold, Douglas L....
15页
查看更多>>摘要：Growth depressions in crops grown adjacent to Eucalyptus stands are often reported. The reasons for this observation range from competition for the resources light, nutrients and water to allelopathic effects. We investigated the effect of a Eucalyptus camaldulensis stand on soil water relations of an adjacent field of Zea mays. We used a geostatistical network spanning the Eucalyptus camaldulensis stand and the maize field. We measured changes in soil water storage in high spatial resolution (356 sample points over 3700 m(2)) in weekly to monthly intervals. In addition, an intensive root inventory of the Eucalyptus, covering a depth of 3.1 m, as well as aboveground biomass inventories in both land use forms were carried out. The majority of the fine root biomass of the Eucalyptus (70.5%) was found in the first 60 cm soil depth, which corresponded to the depth of the soil moisture measurements. Soil water depletion in the maize field was greatest up to 20 m from the forest edge, which coincided with the zone of least maize biomass production. In contrast, the water depletion across the first 6 m into the forest was 34% lower than in the border zone on the field side. Growth of the Eucalyptus was greatest at the forest edge, and the increased biomass production of the Eucalyptus balanced the decrease in maize production found in the first 20 m of the field. These changes in spatial growth patterns are explained by intense competition for soil water between the Eucalyptus and the maize.
查看更多>>摘要：Plant competition is a determinant of plant community formation, while resource partitioning is regarded as a critical factor for maintaining species coexistence under competition. However, how resource partitioning varies with species richness remains unclear; additionally, empirical studies of the dynamic processes involved in plant resource competition, especially that for belowground resources, are urgently needed. Here, we used the stable isotope approach to study the temporal dynamics of plant hydrological niches from species-poor to species-rich communities (including monocultural plantations, agroforestry systems and more diverse tropical rainforests) in a tropical area of southwestern China. We found that plant species in multispecies communities could be divided into two groups by comparison of their hydrological niches: deep-resource users and shallow-resource users. Resource partitioning was obvious between these two groups. However, resource partitioning was narrower within deep and shallow-resource users. In addition, with an increase in species richness, the general tendency of resource partitioning among all species became not just increasingly narrow but also uniform and stable. When we combined this information with data on belowground resource distribution and its correlations with plant resource use, we also found that the greater the species diversity and the smaller the resource use advantages among species, the easier it was for the species to achieve "competitive reversals". This study confirmed the generality of the seasonal segregation of the plant hydrological niche and demonstrated that variations in both environmental resources and plant resource partitioning weaken the resource use advantages of species, representing an important mechanism that helps maintain the coexistence of competing species in a species-rich community. These findings therefore provide novel insights for understanding species combinations and plant belowground interactions in complex communities and will be beneficial for seeking solutions to some important ecological issues, such as reconstruction of tropical rainforests.
查看更多>>摘要：The legacy effects of precipitation, defined as the impact of precipitation from previous years on current-year net primary productivity (NPP), have been well recognized in field experiments and site-level observational studies. However, it remains unclear how consecutive dry or wet years influence the directions and magnitude of legacies and broad-scale patterns of NPP. Here, we quantified the spatial and temporal patterns of legacy effect across different numbers of consecutive wet and dry years from 2000 to 2020 in the Inner Mongolia grassland. Spatially, the response of legacies to precipitation transitions was asymmetric along the mean annual precipitation gradient. The positive response of legacies to precipitation decrease was found for desert steppe and typical steppe after preceding wetness. In contrast, the response of legacies to precipitation increase was negative for desert steppe and meadow steppe after preceding drought. Moreover, legacies were more sensitive in desert steppe than that in typical steppe and meadow steppe for both the preceding wetness and preceding drought. However, the meadow steppe showed the highest response to the inter-annual precipitation change among the three grassland types. Furthermore, the legacies responded more strongly to precipitation decrease (preceding consecutive wet years) than the increase (preceding consecutive dry years) for meadow steppe and typical steppe. Yet, the desert steppe showed the opposite response to precipitation change. Temporally, the legacy effects lasted for only one year and could be transmitted year by year. Our findings highlight that consecutive wet and dry years play essential roles in controlling the NPP responses to climate fluctuations in arid and semi-arid grasslands. Understanding ecosystem responses to climatic periods can provide insights into the effects of directional changes in rainfall associated with climate change.
查看更多>>摘要：Heatwaves cause severe adverse effects on urban human life. Green spaces that cool the urban environment through shading and transpiration can improve the urban thermal environment. However, there is currently a lack of quantitative evaluation of the transpirational cooling effect and physiological response of trees to heat. Therefore, this exploratory study investigated two pairs of trees (Cinnamomum camphora and Cedrus deodara), which are commonly used for urban greening in Nanjing, China. Transpirational cooling was estimated using the heat diffusion method for xylem sap flow in four trees. The morphological characteristics and environmental factors of each forest land were measured, and the transpirational cooling of the four trees was analyzed statistically. The results indicated that the canopy transpriation of C. deodara samples decreased substantially during extreme heat days. At the unit leaf area scale, the transpirational cooling effect of C. camphora samples was more pronounced than that of C. deodara samples during extreme heat days. Water vapor pressure and soil heat flux at 20 cm underground were the main drivers affecting the canopy transpiration of C. camphora samples, whereas air temperature and soil temperature at 5 cm underground were the main drivers affecting the canopy transpiration of C. deodara samples. To analyze the physiological cooling effects of trees, a new index (Transpirational Cooling Efficiency, TCE) is proposed to quantitatively evaluate the relationship between tree transpirational cooling and sap flow. The findings of this study may enrich the response patterns of trees to transpiration under extreme heat and provide guidance for the planning and designing of green spaces to improve thermal environments.
查看更多>>摘要：Forest tree growth plays an important role in forest ecosystem carbon cycle and carbon sequestration, and tree growth is affected by many factors. However, information on the contribution rate of different factors to tree growth is still limited. Thus, we hypothesized that increased regional competition has a significant negative impact on tree growth in plantations. In order to ascertain this hypothesis, tree-rings width for developing chronologies and competition data of the Larix kaempferi in Chinese plantations were sampled. Using tree-ring climatology method and non-linear models based on maximum likelihood analysis etc., the relationship between the tree-ring growth and competition index and climatic factors and their relative importance were evaluated in different years-interval and climate-zone. The results showed that the competitive effect for trees growth was always much stronger than the climatic or size effect. Competitive effects change over time, with drought effects (vapor pressure deficit (VPD) and standardized precipitation-evapotranspiration index (SPEI)) on tree growth exacerbated. The significant negative effects of neighborhood competition gradually increased over time. Climate moderates competitive effects during stand development, especially the negative effects of drought index on trees. Trees decline in growth due to climate warming with temperature and precipitation changes, and mainly, increased competition. Overall, these results constitute important new information, which not only further deepens our understanding of important theoretical issues related to plantation tree growth, but also helps to formulate new guidelines to make larch plantations adapt to global changes. Therefore, thinning measures are valuable suggestions to change forest density can promote trees growth, it provides highly valuable information for estimating future forest dynamics and changes in carbon storage and carbon neutrality under climate change.
查看更多>>摘要：The green leaf area index (GLAI) has been widely used in agriculture, forestry, and environmental sciences for the analysis and modeling of many biophysical processes of vegetation, including the attenuation of light through the canopy, transpiration, photosynthesis, and carbon and nutrient cycles. Nevertheless, its usefulness is hampered by the uncertainty introduced through the lack of quantitative information on leaf biochemistry, particularly leaf chlorophyll content, in its computation. Thus far, this uncertainty has not been properly recognized nor quantified. The main goal of this study was to quantify the uncertainty of GLAI as used in the estimation of key photosynthetic canopy traits, namely canopy chlorophyll content (CCC). This uncertainty was assessed through the evaluation of the relationship between GLAI and CCC in structurally and functionally contrasting crop species (Zea mays L., Glycine max (L.) Merr., and Oryza sativa L). Results show that for the same GLAI value, CCC varied 2- to 3-fold due mainly to the variability of leaf chlorophyll content. Therefore, we suggest using the absorption coefficient in the red-edge region of the electromagnetic spectrum as an alternative to GLAI for the evaluation of CCC and other important photosynthetic canopy traits. The absorption coefficient in this spectral region is particularly suitable as it has been successfully related with the gross primary productivity of vegetation canopies, the quantum yield of photosynthesis, and is sensitive to the repositioning of chloroplasts within leaf cells in response to water stress.
Verstraeten, Willem W.Kouznetsov, RostislavHoebeke, LucieBruffaerts, Nicolas...
12页
查看更多>>摘要：Airborne birch pollen may elicit allergies and affect the public health badly. Timely spatially distributed information on current and forecasted pollen levels may help people with pollen allergies to take preventive measures. This requires a modelling approach. Here we reconstruct multi-decadal (1982-2019) daily spatially distributed airborne birch pollen levels by ingesting seasonal dynamic birch pollen emission source maps into the pollen transport model SILAM (System for Integrated modeLling of Atmospheric coMposition) in a bottom-up approach. We introduce seasonal variations in the birch pollen emission maps by combining a forest inventory based areal birch fraction map with four decades of spaceborne Normalized Difference Vegetation Index (NDVI) in a Random Forest statistical framework. The approach of combining the transport model with NDVI based pollen emission maps is applied and evaluated with birch pollen observations by Hirst method from the Belgian aerobiological surveillance network that go back to 1982. Transport in SILAM is driven by ECMWF ERA5 meteorological data. The mean seasonal R2 values between modelled and observed time series of airborne birch pollen levels in the period 1982-2019 range between 0.35 and 0.63, but can go up to 0.86 for individual seasons, indicating good performance of SILAM for Belgium. Here we show that the predicted amount of birch pollen in the air in Belgium has been increasing on average by 13.1% per decade based on the Sen slopes computed on the Seasonal Pollen Integral for the period 1982-2019. Analysis of the SILAM runs shows that this increase over time is mainly climate-induced (8.2% per decade), but it is amplified by the spatiotemporal variations of the birch pollen emission sources with 4.9% per decade.
Mitchell, Patrick J.Waldner, FrancoisHoran, HeidiBrown, Jaclyn N....
12页
查看更多>>摘要：National and regional yield forecasts can provide important insights into agribusiness beyond the farm gate. The incorporation of dynamical climate models into these forecasting systems strengthen their predictive performance in many cases but may contribute inherent biases to the final yield estimates. Downscaling the native climate model output so that is suitable for crop simulation modelling can also present challenges in representing realistic conditions for plant growth from a climate model. This study evaluated the performance of an operational national wheat yield forecast system for the Australian wheatbelt using climatology and seasonal climate model-based input data, and introduces an alternative approach using a data fusion method. The crop forecasting system uses the APSIM wheat model to estimate water-limited potential yield. The climatology-based forecast tended to over predict national yield (high yield bias; 1.5 to 7% across forecast months), while the model-based method (using ACCESS-S1 dynamical model) tended to under predict yield (low yield bias; -5.9 to -0.5% across forecast months) and had a lower spread than climatology (10 to 50% lower across forecast months). The modelbased forecast had skill in terms of accuracy and reliability during the second half of the season. The newly developed data fusion method used a weighting method calibrated for separate forecast locations (stations) to remove bias in the mean forecast yield and reduce ensemble spread. This resulted in improvements in the Australia-wide yield forecasts across all forecast start dates. This study provides a demonstration of how a datadriven approach can be applied to a crop forecast to improve accuracy and resolution of crop yield forecasts without the need for more computationally intensive downscaling approaches.
查看更多>>摘要：Understanding the long-term variations of stand water balance and carbon stocks under different water inputs is crucial for sustainable forest management under climate change. However, due to the lack of in-situ data, how forest plantations respond to variation in water inputs during stand development remains poorly understood. We varied water inputs with distinct irrigation amounts and measured the water-balance components, carbon stock growth, and water productivity during a whole rotation (2015-2019) in poplar plantations. Furthermore, in 2020, soil water contents in our stand and an adjacent 37-year-old poplar plantation were measured. Under rainfed conditions, soil water storage of different layers decreased greatly year by year, especially at the 2-3 m depth, such that transpiration was curtailed in 2019, a dry year. By 2019, the 0-2 m depth layer became periodically dried, and the 2-3 m was persistently dried, which was further confirmed by observations in 2020. Additionally, serious soil desiccation occurred throughout the 0-6 m soil depth in the 37-year-old poplar stand. Increasing the water inputs avoided stand water stress and decreased the drying rate of the deep soil. Furthermore, the highest water inputs treatment brought great increases in groundwater recharge, carbon stock growth, and water productivity. This treatment also led to 67% higher soil water storage in the 0-1 m soil layer and 23% higher soil water storage in the 1-6 m layer by the end of 2019, as compared to the rainfed treatment. However, these advantages were small or disappeared if the water inputs were insufficient. Our findings will be helpful to predict water relations and facilitate sustainable forest management under climate change in water-limited regions.
Baker, Jeffrey T.Lascano, Robert J.Yates, CharlesGitz III, Dennis C....
5页
查看更多>>摘要：The ongoing rise of atmospheric carbon dioxide concentration ([CO2]) has spurred the development of several experimental approaches for studying the effects of elevated [CO2] on crop plants. Some experimental designs enriched [CO2] only during the daytime hours and lacked [CO2] enrichment at night. Previous reports indicate that [CO2] enrichment at night can result in increased plant leaf area and shoot biomass. We developed [CO2] enrichment chambers suitable for greenhouse experiments in order to test whether [CO2] enrichment at night affected plant leaf area and shoot biomass in cotton seedlings. We imposed four [CO2] treatments: 1) ambient control with no [CO2] enrichment (Amb); 2) [CO2] enrichment from 1800 hours in the evening to 0600 hours of the next day (Night); 3) [CO2] enrichment from 0600 to 1800 hours (Day); and 4) [CO2] enrichment continuously 24 hours day-1 (24-h). Mean and standard deviation for the [CO2] enriched periods were approximately 799.7 +/- 3.4 mu mol mol-1. Our results indicate that nighttime [CO2] enrichment did not result in increased cotton seedling leaf area or growth. Comparing our results with previous reports suggests that the effects of nighttime [CO2] enrichment may be species or even cultivar dependent.
NSTL
Elsevier