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A greenhouse experiment was conducted to evaluate the effects of humic substances extracted from composted sewage sludge on growth, phenological development, and photosynthetic activity of pepper (Capsicum annuum L. cv. Piquillo) plants. Humic substances derived from composted sludge (HSS) were compared with those derived from leonardite (HSL). Two doses of both humic substances were assayed (200 and 500 mg C [L substrate]–1) and compared with a control (C). HSS showed higher nitrogen content and a higher percentage of aliphatic carbon, as well as a lower content of aromatic and phenolic carbon than HSL. HSS significantly increased plant dry‐matter production (up to 560%), plant height (86%–151%), and leaf area (436%–1397%) during the early stages of pepper development. Net photosynthesis and stomatal conductance increased in the treatments with HSS (up to 48% and 63%, respectively) at the vegetative stage. In addition, HSS accelerated the phenological development of pepper plants, reducing significantly the number of days to flowering and ripening, which occurred 12 and 14 d earlier than in control plants, respectively. In general, the treatments with HSS and HSL did not markedly affect chlorophyll and nutrient concentrations in the leaves. At maturity, only small differences in total fruit yield, number of fruits per plant, and fruit size were observed between amended and control plants. The results suggest that the mechanisms through which HSS affected plant growth and development were not associated with an improved nutrient uptake. Although the identity of the growth‐promoting factors remains to be found, the results suggest that they may be linked to the chemical structure of the humic substances.  相似文献   
2.
Long-term investigations of Scots pine (Pinus sylvestris L.) growth were carried out in the vicinity of one of the biggest air pollution sources in Lithuania—mineral fertilizers plant “Achema.” It is detected that initial stages of the dynamic tree response to the external stress factors in the polluted environment with an increased quantity of nitrogen compounds have started with a stimulation stage, followed by a gradual transition to a depression of growth. The recovery of the damaged stands took place along with the reduced environmental pollution, and the overdraft of the “normal” annual increment was a characteristic feature of all the investigated stands. This phase is still continuing for the most damaged stands. A very high individual variability of the tree growth response to the environmental impact is a characteristic feature of the damaged Scots pine stands. The homeostatic mechanisms of the survived trees stipulated reaching approximately the same or even higher growth rate as prior to the depression period, and the tree growth rate before the depression period can serve as the most powerful predictor of tree growth recovery capacity under the reduced environmental pollution. Crown defoliation is the next most important predictor of individual tree recovery capacity. Lower stand density and lower competition cause higher recovery capacity of damaged trees. The conclusion is made that a reduction in the environmental pollution on the local and regional scale and especially a decrease in emissions and deposition of sulfur and nitrogen compounds caused the recovery of damaged forests. These trends should be taken into account while analyzing and modeling forest dynamics. Interaction of environmental pollution and climatic factors is very important for the response of tree growth to the environmental stressors.  相似文献   
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The objective of this research was to study the levels of some organic solutes, such as total protein, total soluble sugars, starch and proline in leaves, as well as abscisic acid concentration in xylem of pepper plants inoculated with Verticillium dahliae Kleb. Healthy and inoculated plants were always kept well watered. Measurements were made at time intervals after inoculation. Leaf water potential rapidly decreased as a consequence of fungal infection. However, relative water content in leaves only changed significantly from day 20 after inoculation, and such decreases coincided with a sharp build up of proline and total soluble sugars in leaves. Starch and protein levels, as well as abscisic acid concentration in xylem, declined in healthy and inoculated peppers as they became older. However, such decreases were more pronounced in infected plants, especially soon after inoculation. Results suggest that proline and total soluble sugars accumulation could be sensors of the damage caused by the fungal infection.  相似文献   
4.
桉树人工林在全世界的发展迅速,没有比在中国南部地区更需要一种新的木材和木纤维产品的需求。在桉树迅猛的扩张过程中,人工林可持续的生产力和合理的生态系统管理将扮演至关重要的角色。以往非可持续的农业经营导致了东门林场的土地严重退化,东门项目期间,在这些立地上重新造林证明了土壤营养的缺乏严重影响了退化立地的潜在生产力。1988年在东门进行了一个巨桉(E.grandis)早期施肥试验林植株地上部分不同器官的生物量和养分库的研究,以便更好地了解一些经营管理措施的养分结论。另一方面,林木采伐过程中养分的丧失,枯枝落叶的收集和燃烧使得土壤表面裸露,并加剧了土壤侵蚀。目前,在东门第3代、第4代集约经营的人工林的高生产力证明是高标准的经营管理的结果,林地上枯枝落叶和采伐剩余物的保留,细致的整地,土壤侵蚀的控制以及科学的施肥是关键因素;另外加上改良的遗传材料增强了生产力和收益,也增强了东门桉树人工林土壤可持续经营。一个国际林业研究中心网络得以建立,为了调查研究在同一立地上是否有可能进行连续的种植速生丰产林而对立地土壤和水资源没有损害,研究提供了大量的热带人工林有关立地管理的信息。为了优化集约经营人工林的生产力、收益率及可持续性,在华南地区有必要继续进行土壤和养分研究。  相似文献   
5.
Verticillium dahliae alters water status and consequently, growth and production of pepper plants. On the other hand, arbuscular mycorrhizal fungi (AMF) can reduce damage caused by specific soil-borne plant pathogens and improve drought resistance of pepper. Therefore, one objective of this research was to assess if AMF can modify the development of Verticillium-wilt in pepper plants. A second objective was to study the influence of plant phenology at the moment when V. dahliae was inoculated on the possible biocontrol of the disease by AMF. Results suggested that AMF reduce the deleterious effect of V. dahliae on pepper growth and yield. However, bioprotection against Verticillium-wilt was conditioned by plant phenology at the moment of pathogen attack. The highest efficacy of AMF occurred when V. dahliae was inoculated during the vegetative stage of plants. AMF allowed leaf relative water content to be maintained for longer and delayed both the appearance of disease symptoms and the decrease of photosynthesis in Verticillium-inoculated plants. These benefits on plant physiology increased pepper yield.  相似文献   
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