| 1. |
- Ali, Liaqat
(författare)
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Pre-harvest factors affecting quality and shelf-life in raspberries and blackberries (Rubus spp. L.)
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Fruit including berries have been demonstrated to exhibit a broad spectrum of benefits including protection against cardiovascular, neurological, and lung diseases, as well as having antioxidant, antimicrobial, anti-inflammatory, anti- diabetic and anti-aging properties. These protective effects are reported to be due to their high content of bioactive compounds, such as vitamin C, vitamin E, phenolic acids, ellagitannins, flavonoids and carotenoids. This thesis investigated the effect of pre- and postharvest factors on the concentrations of bioactive compounds in raspberries and blackberries. The factors studied included genetic variability, organic and synthetic fertilizers, seasonal variation (harvest-to-harvest and annual variation) in greenhouse, high tunnel and open field production, and post-harvest storage. Concentrations of bioactive compounds (anthocyanins, vitamin C, ellagic acid, carotenoids) in the berries, or in the leaves, were quantitatively analysed by high-performance liquid chromatography, and total phenolics were analysed by a spectrophotometric method. Generative parameters (yield, fruit size) investigated for the cultivar difference and organic nitrogen, responded differently to the nitrogen level within cultivars and varied significantly in primocane raspberries. Taste compounds, such as total acidity and different sugars, varied during the season and with nutrient regimes. Time of harvest also affected the ellagic acid content, which was high in early season, and the vitamin C content, which was high in late season in primocane raspberries. Significant changes were also found between different years. Vitamin C decreased significantly with high synthetic N and with low K application, but the application of high N with high K showed positive influence in the level of nutrients and bioactive compounds in blackberries except for ellagic acid. Increased level of organic fertilization (12-17 g N/plant) in primocane raspberries caused only minor changes in the analysed compounds. The post-harvest performance of raspberries regarding the levels of bioactive compounds was less dynamic than in blackberries. In addition, raspberries harvested in late season showed comparatively less changes in sugar content during storage as compared to early harvest, indicating less enzymatic activity in the late season.
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| 2. |
- Montelius, Malin
(författare)
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Chlorine Cycling in Terrestrial Environments
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Chlorinated organic compounds (Clorg) are produced naturally in soil. Formation and degradation of Clorg affect the chlorine (Cl) cycling in terrestrial environments and chlorine can be retained or released from soil. Cl is known to have the same behaviour as radioactive chlorine-36 (36Cl), a long-lived radioisotope with a half-life of 300,000 years. 36Cl attracts interest because of its presence in radioactive waste, making 36Cl a potential risk for humans and animals due to possible biological uptake. This thesis studies the distribution and cycling of chloride (Cl–) and Clorg in terrestrial environments by using laboratory controlled soil incubation studies and a forest field study. The results show higher amounts of Cl– and Clorg and higher chlorination rates in coniferous forest soils than in pasture and agricultural soils. Tree species is the most important factor regulating Cl– and Clorg levels, whereas geographical location, atmospheric deposition, and soil type are less important. The root zone was the most active site of the chlorination process. Moreover, this thesis confirms that bulk Clorg dechlorination rates are similar to, or higher than, chlorination rates and that there are at least two major Clorg pools, one being dechlorinated quickly and one remarkably slower. While chlorination rates were negatively influenced by nitrogen additions, dechlorination rates, seem unaffected by nitrogen. The results implicate that Cl cycling is highly active in soils and Cl– and Clorg levels result from a dynamic equilibrium between chlorination and dechlorination. Influence of tree species and the rapid and slow cycling of some Cl pools, are critical to consider in studies of Cl in terrestrial environments. This information can be used to better understand Cl in risk-assessment modelling including inorganic and organic 36Cl.
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| 3. |
- Oyewole, Olusegun Ayodeji
(författare)
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Soil nitrogen fluxes and root uptake in the boreal forest : key processes to plant nitrogen nutrition
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Nitrogen (N) is essential for growth and net primary production of plants. However, N acquisition by plants is influenced by movement of soil N compounds from bulk soil to plant roots and uptake of N by roots. This thesis is aimed at deepening our knowledge on these key processes involved in plant N acquisition in the N-limited boreal forest. To address this aim, a novel, non-invasive microdialysis technique was employed. Amino acids dominated N fluxes in the boreal forest soils. Further, plant roots were shown to have the capacity to absorb organic and inorganic N present in the measured soil fluxes, but these soil fluxes, rather than root uptake, may limit plant N acquisition. The microdialysis technique was further developed to enable simultaneous estimation of diffusion and mass flow of N in soil. Applying this refinement of the technique in the field showed that mass flow significantly increased flux rates of soil N in the boreal forest ecosystem, and that it also altered the chemical composition of the N fluxes. The results from the studies presented in this thesis highlight the potential of the microdialysis technique to improve our understanding of the intrinsic processes involved in N acquisition by plant roots. They also suggest that amino acids might comprise an important source of N for plants in the boreal forest ecosystem. The results suggest that mass flow plays an important role for plant N acquisition in the boreal forest, and mass flow might increase the share of nitrate, particularly in nutrient-rich ecosystems. This finding opens a discussion on the role of transpiration in plant N nutrition, with implications for our understanding of how plant N nutrition will be affected by, among other things, elevated CO2, increased temperatures, and N fertilization.
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| 4. |
- Lv, Yanrong
(författare)
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Triterpenes and phenolic compounds in apple fruit (Malus domestica Borkh.) : variation due to cultivar, sun exposure, rootstock, harvest maturity, bruising, fungi inoculation, ozone treatment and storage conditions
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Apple (Malus × domestica Borkh.), a popular and widely cultivated fruit world-wide, contains bioactive triterpenes and phenolic compounds with potentially valuable pharmacological functions. This thesis investigated the effects of pre-harvest and postharvest factors on concentrations of these bioactive compounds in apples. It also studied the effect of ozone treatment, before or during storage, combined with cold storage on triterpene and phenolic compound concentrations in apples and the antifungal activity of triterpene-enriched crude extract. Concentrations of two major triterpenes, oleanolic acid and ursolic acid, in apple peel varied significantly between cultivars, with the late-ripening cultivar ‘Gloster’ having higher concentrations than the earlier ripening ‘Discovery’ and ‘Aroma’. The concentrations were higher in peel from the shaded side than from the sun-exposed side of both ‘Discovery’ and ‘Gloster’ apples. Harvest time and storage methods had minor effects on the concentrations, although some between-cultivar variation was observed. Inoculation with Penicillium expansum decreased oleanolic acid concentration in ‘Discovery’ and ‘Gloster’ at harvest in one study year and decreased ursolic acid concentration in ‘Aroma’ after cold storage. Oleanolic acid and ursolic acid concentrations in apple peel showed non-consistent changes in different cultivars after bruising. On four of six harvest occasions during a two-year study of ‘Aroma’, the concentrations were higher in peel of apples from rootstock ‘MM106’ than from ‘M9’. Total polyphenolics concentration was higher in ‘Amorosa’ peel than in ‘Santana’ peel at harvest and after four months of storage. Ursolic acid concentration in apple peel was almost unaffected by ozone treatment, but oleanolic acid concentration showed differing responses to varying ozone application. The concentrations of different bioactive compounds both increased and decreased after ozone treatment, but the changes were within the range of fluctuations observed in untreated apples during storage. Low-dose ozone treatment (0.5 ppm gaseous ozone one hour per day) during four months of cold storage did not affect total polyphenolics in ‘Amorosa’ and ‘Santana’ flesh, but increased total polyphenolics in ‘Amorosa’ peel and decreased them in ‘Santana’. Short-term ozone treatment (2.5 ppm gaseous ozone and ozonated water, alone or combined) before one month of cold storage reduced total polyphenolics content in apple peel, while inconsistent responses were observed in apple flesh. Triterpene-enriched water significantly inhibited mycelial growth of all pathogens studied, but inhibited conidia production differently in each pathogen.
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| 5. |
- Einarsson, Rasmus, 1988
(författare)
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Agricultural nutrient budgets in Europe: data, methods, and indicators
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Agricultural production systems feed humanity but also cause a range of adverse environmental effects, including climate change, loss of biodiversity, and pollution of air and water. A main cause of these effects is the emissions of nitrogen (N) and phosphorus (P) that occur as a side effect of nutrient cycling in agriculture. One of the things that is needed to mitigate N and P pollution is a quantitative understanding of N and P flows in agricultural systems. A common tool for this is the nutrient budget. A nutrient budget quantifies inputs and outputs of nutrients in a system and can be used to understand how the system functions as well as to calculate quantitative environmental indicators for farms, regions, or products. This thesis aims to explore and expand the limits of how agricultural N and P budgets can be used to support environmental research and decision-making, focusing on European agriculture. To this end, the thesis looks into two broad research questions: (1) What are the limits to the accuracy and level of detail that can be attained in N and P budgets of European agricultural systems? (2) How are present and proposed uses of agricultural N and P budgets and derived indicators limited by (a) the inherent property that agricultural nutrient budgets do not account for environmental impacts, and (b) by uncertainties and lack of data in the estimation of nutrient budgets? This thesis builds on five appended research papers that explore various aspects of data sources, uncertainties, and possible uses of N and P budgets in Europe. International and national data sources are scrutinized and used to estimate N and P budgets. Novel ways to combine existing data sources are explored. The use of nutrient budgets with various system boundaries, with different degrees of spatial resolution, and in different time periods is discussed, emphasizing that the best approach is not only a question of data supply but also of intended audience and purpose.
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| 6. |
- Abubaker, Jamal
(författare)
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Effects of fertilisation with biogas residues on crop yield, soil microbiology and greenhouse gas emissions : recycling of plant nutrients from bioenergy production
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The amount of residues generated by biogas production has increased dramatically due to worldwide interest in using renewable energy. Biogas residues (BRs) originate from anaerobic degradation of different types of rural and urban organic wastes and have been proposed as organic fertilisers because of their high content of ammonium and other valuable macro- and micro-nutrients. However, application of BRs to agricultural soils may be accompanied by environmental risks, since they may contain heavy metals and organic pollutants. Therefore the effects of BRs on crop production and on the soil ecosystem and environment urgently need to be investigated before their wider use. This thesis evaluated and compared different types of BRs against cattle slurry, pig slurry, compost and mineral fertiliser with respect to their (1) ability to provide plants with necessary nutrients, (2) impact on the soil microbial ecosystem and (3) effects on emissions of the greenhouse gas nitrous oxide (N₂O). The results from short-term laboratory experiments and a long-term field trial showed that BRs increased crop yield to the same extent or more than conventional mineral fertiliser and compost, but less than pig slurry. BRs generated from source-separated organic household waste had a tendency to give higher crop yield and soil microbial activities than other BRs. BRs had no general negative effect on soil respiration, but substrate-induced respiration decreased significantly in organic soil on addition of BRs. Although all BRs initially inhibited potential ammonium oxidation and potential denitrification activity, no long-term negative effects were detected. BRs stimulated ammonium assimilation, which can temporarily decrease nitrogen availability to the plant. Furthermore, the bacterial community structure in the sandy soil was altered by BRs and cattle slurry, but no significant change was seen in the community structure of clay and organic soil. Application of BRs and animal slurry increased N₂O emissions, but the total losses and flux patterns were affected by fertiliser type and soil type. In conclusion, the fertiliser value of BRs should be regarded as high and they apparently have no long-term adverse effects on soil microbial functions and structures. Thus the problematic amounts of residues associated with expansion of biogas production could be turned to advantage, as these residues seem to be safe and competitive fertilisers.
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| 7. |
- Al-Azzawi, Zaenab
(författare)
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The role of biological processes in base cation supply in boreal forest podzols
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis describes experiments designed to improve understanding of biological processes contributing to supply of base cations and other nutrients in boreal forest podzols. We used microcosms containing tree seedlings growing in natural substrates, a combination of direct measurements, modelling, stable Mg isotope analysis, and 13CO2 pulse-labelling. Addition of 13C-labelled fungal necromass to soil resulted in rapid decomposition and active incorporation of 13C into RNA of Burkholderia, Streptacidophilus, Dyella, Herminiimonas, Granulicella and fungal species belonging mainly to the genera Mortierella and Umbelopsis. There was no evidence of 13C incorporation into RNA of ectomycorrhizal fungi supporting the idea that ectomycorrhizal fungi primarily play an active role in organic matter decomposition by releasing N from recalcitrant substrates, but do not use organic matter as a source of metabolic C. Selected ectomycorrhizal and nonmycorrhizal fungi were examined for their capacity to fractionate and assimilate stable Mg isotopes in vitro. Ectomycorrhizal fungi mobilised and accumulated significantly higher concentrations of Mg, K and P than nonmycorrhizal fungi, when grown on granite particles. Mycorrhizal fungi were significantly depleted in heavy isotopes compared with nonmycorrhizal fungi and there was a highly significant statistical relationship between δ26Mg tissue signature and mycelial concentration of Mg. Pinus sylvestris seedlings were grown in compartmentalised microcosms allowing their mycorrhizal mycelium, but not roots, to access different substrates, including granite particles. Root biomass and contents of Ca, K, Mg, and P in plants in granite treatments were significantly higher than in control roots. Carbon allocation by the ectomycorrhizal mycelium to soil solution was significantly and positively correlated with base cation and P content of the plants. A final experiment (using reconstructed boreal forest podzol layers) was conducted in which the relative amounts of organic and mineral substrates were manipulated to simulate different levels of intensification of the removal of organic matter. All plants were deficient in K and P but had above optimal levels of Ca and Mg. Total plant and fungal mycelial biomass was positively related to the amount of organic soil in each treatment. The δ26Mg values of soil solution samples in B horizon soil increased successively with increasing plant and fungal mycelial biomass, suggesting increased uptake of Mg from the B horizon, with discrimination against the heavier isotope resulting in higher enrichment of 26Mg.
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| 8. |
- Andersson, Helena
(författare)
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The role of subsoil properties for phosphorus leaching in agricultural soils
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Phosphorus (P) leaching from agricultural land is a large contributor to eutrophication of many surface waters and the Baltic Sea. Better knowledge of P sorption and release in the subsoil could enable the development of effective mitigation strategies for P leaching. This thesis examined the impact of soil properties on P leaching from four Swedish agricultural soils (two clays, two sands), using intact soil columns extracted with (length 1.05 m) and without (length 0.77 m) topsoil. The role of the subsoil as a source or sink for P leaching was also investigated, and placement of quicklime (CaO) on top of the subsoil as a mitigation strategy for P leaching was evaluated. Leaching of dissolved reactive P (DRP) from subsoil lysimeters was 94% of that from full-length lysimeters in one of the clay soils, and 70% in the other. The higher contribution of the former clay subsoil was probably due to high P content deeper in the soil. Leaching of DRP was low from full-length and subsoil lysimeters (0.12 and 0.08 kg ha-1 yr-1, respectively) in one of the sandy soils, despite high topsoil P content, due to high P sorption capacity and low degree of P saturation in the subsoil. However, leaching of DRP was very high from full-length and subsoil lysimeters (3.33 and 3.29 kg ha-1 yr-1, respectively) from the other sandy soil with moderate topsoil P content, due to high P content and low P sorption capacity in the subsoil. These results indicate that the subsoil can function as both a source and sink for P leaching. Phosphorus leaching increased with increasing P content and DPS in subsoil and decreasing P sorption capacity in topsoil and subsoil, indicating that these parameters could be used for P leaching risk assessments. However, on soils with preferential flow in the subsoil, P leaching may be high despite high subsoil P sorption capacity. Hence, both chemical and physical properties of topsoil and subsoil must be considered in implementation of appropriate, cost-effective mitigation strategies for P loss reductions. Application of lime on top of the subsoil significantly reduced leaching of particulate P (PP) in both clay subsoils by 49 and 51%, respectively, compared with unlimed controls. This suggests that subsoil liming might be an appropriate method to reduce P leaching from clay soils.
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| 9. |
- Bandau, Franziska, 1982-
(författare)
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Importance of tannins for responses of aspen to anthropogenic nitrogen enrichment
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Boreal forests are often strongly nitrogen (N) limited. However, human activities are leading to increased N inputs into these ecosystems, through atmospheric N deposition and forest fertilization. N input into boreal forests can promote net primary productivity, increase herbivore and pathogen damage, and shift plant species composition and community structure. Genetic diversity has been suggested as a key mechanism to promote a plant species’ stability within communities in response to environmental change. Within any plant population, specific traits (e.g. growth and defense traits) can vary substantially among individuals, and a greater variation in traits may increase chances for the persistence of at least some individuals of a population, when environmental conditions change. One aspect of plant chemistry that can greatly vary among different genotypes (GTs) are condensed tannin (CTs). These secondary metabolites have been suggested to affect plant performance in many ways, e.g. through influencing plant growth, the interactions of plants with herbivores and pathogens, and through affecting litter decomposition, and hence the return of nutrients to plants. To investigate how genotypic variation in foliar CT production may mediate the effects that anthropogenic N enrichment can have on plant performance and litter decomposition, I performed a series of experiments. For these experiments, aspen (Populus tremula) GTs with contrasting abilities to produce foliar CTs (i.e. low- vs. high-tannin producers) were grown under 3 N conditions, representing ambient N (+0 kg ha-1), upper level atmospheric N deposition (+15 kg ha-1), and forest fertilization rates (+150 kg ha-1). This general experimental set-up was once established in a field-like environment, from which natural enemies were excluded, and once in a field, in which enemies were present. In my first two studies, I investigated tissue chemistry and plant performance in both environments. I observed that foliar CT levels decreased in response to N in the enemy‑free environment (study I), but increased with added N when enemies were present (study II). These opposing responses to N may be explained by differences in soil N availability in the two environments, or by induction of CTs after enemy attack. Enemy damage generally increased in response to N, and was higher in low-tannin than in high-tannin plants across all N levels. Plant growth of high‑tannin plants was restricted under ambient and low N conditions, probably due to a trade-off between growth and defense. This growth constraint for high‑tannin plants was weakened, when high amounts of N were added (study I and II), and when enemy levels were sufficiently high, so that benefits gained through defense could outweigh the costs of defense production (study II). Despite those general responses of low- and high‑tannin producers to added N, I also observed a number of individual responses of GTs to N addition, which in some case were not connected to the intrinsic ability of the GTs to produce foliar CTs. In study III, gene expression levels in young leaves and phenolic pools of the plants that were grown in the enemy‑free environment were studied. This study revealed that gene control over the regulation of the phenylpropanoid pathway (PPP) was distributed across the entire pathway. Moreover, PPP gene expression was higher in high-tannin GTs than in low‑tannin GTs, particularly under ambient N. At the low N level, gene expressions declined for both low- and high-tannin producers, whereas at the high N level expression at the beginning and the end of the PPP was upregulated and difference between tannin groups disappeared. Furthermore, this study showed that phenolic pools were frequently uncorrelated, and that phenolic pools were only to some extent related to tannin production and gene expression. In study IV, I investigated the decomposability of litter from the field plants. I found that N enrichment generally decreased mass loss, but there was substantial genetic variation in decomposition rates, and GTs were differentially responsive to added N. Study IV further showed that CTs only had a weak effect on decomposition, and other traits, such as specific leaf area and the lignin:N ratio, could better explain genotypic difference in mass loss. Furthermore, N addition caused a shift in which traits most strongly influenced decomposition rates. Collectively, the result of these studies highlight the importance of genetic diversity to promote the stability of species in environments that experience anthropogenic change.
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| 10. |
- Bargues Tobella, Aida
(författare)
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The importance of tree cover for water resources in semiarid West Africa
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The current paradigm in forest hydrology implies that an increase in tree cover always leads to reduced water yields as a result of increased interception and transpiration (ET) losses. This trade-off theory, in which more trees mean less water, has led to concerns that the establishment of trees in drylands may jeopardize scarce water resources. But in the seasonally dry tropics relevant studies are scarce, and few have explored the impact of intermediate tree densities on water yields in degraded soils, which greatly limits the applicability of the trade-off theory in this region. Here, I propose an alternative optimum tree cover theory in which, under conditions typical of the seasonally dry tropics, groundwater recharge is maximized at an intermediate tree cover. At tree covers below this optimum, the gains from more trees on soil hydraulic properties exceed their additional ET losses, leading to increased groundwater recharge. The overall aim of this thesis is to test this hypothesis and to clarify the main processes influencing the relationship between tree cover and groundwater recharge. To do this, a number of measurements were taken in an agroforestry parkland in semiarid West Africa; these included soil infiltrability, soil water drainage, tree transpiration and degree of preferential flow, in combination with stable isotope data. Results from this thesis show that deep soil water drainage was minimal near the tree stem, reached a maximum close to the canopy edge and from there decreased linearly with increasing distance to the nearest tree. This pattern is probably the result of a combination of increased ET losses next to the tree and reduced infiltrability and preferential flow with increasing distance from the nearest tree. The combined increase in infiltrability and degree of preferential flow close to trees allows for enhanced soil and groundwater recharge. Tree transpiration data were used in combination with the observed pattern in soil water drainage and data on tree water sources to model groundwater recharge as a function of tree cover. Modelling results confirm that groundwater recharge was maximized under intermediate tree cover irrespective of the scenarios considered. That trees do not always reduce water yields but can substantially improve them suggests new opportunities for tree protection and tree-based restoration in the seasonally dry tropics, benefitting hundreds of millions of people.
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