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Photosynthetic performance of a canopy plant results from the activity of the present photosynthetizing organs, which are under a strong influence of their environmental history and age. In this framework, we determined diurnal changes of photochemical activity (using rapid light curves of chlorophyll α fluorescence parameters) in the three uppermost leaves of spring barley. Along the photosynthetic photon flux density (PPFD) and air temperature (AT) courses, a significant acclimatory process was observed. Although there was only a little difference in the photochemical efficiency (ΦPSII) among leaves, probably a limited capacity of the electron transport rate (ETR) in the lowest (third) senescing one caused the most pronounced disturbances on the PS II level (the largest decrease of maximal photochemical efficiency, FV/FM). On the other hand, the penultimate leaf exhibited almost no damage, suggesting the effect of reduced light absorption (lower photosynthetic pigment concentration).
The aim of this study was to establish a simple and cost-effective method to monitor the effects of harmful algal blooms as exemplified in Lake Powsinkowskie, and to link the monitoring results to potential health risks on the basis of established Alert Level Frameworks. An assessment of the severity of cyanobacterial development in Lake Powsinkowskie (52°9'27"N, 21°5'55"E), located in the Wilanów region, Warsaw, Poland, was performed to illustrate this. An Alert Level Framework based on cyanobacterial chlorophyll-a measurements was applied. Measurements of cyanobacterial chlorophyll-a in Lake Powsinkowskie were performed once per week at 10 locations on each side of the lake from May to July 2012. The highest algal densities were expected at the eastern side of the lake due to the use of fertilizers on the fields along the eastern shore, however, the opposite was observed. It seems that the conditions on the west side of the lake were more favourable for cyanobacterial growth. This study shows that an indication of the overall effects of eutrophication on algal growth and the potential risk of the presence of toxic cyanobacteria can easily be obtained using relatively simple, simultaneous measurements of total and cyanobacterial chlorophyll-a. The Alert Level Framework based on cyanobacterial chlorophyll-a levels is a rapid and easily applicable method for determining the severity of cyanobacterial developments. The findings of this study indicate that a reduction in nutrient loading to protect Lake Powsinkowskie’s unique species richness can be achieved by informing the local residents about the effects of draining cesspools directly into the lake. Studies such as this one can thus help to support awareness-raising among lake-side residents.
There is large area of saline abandoned and lowyielding land distributed in coastal zone in the world. Soil salinity which inhibits plant growth and decreases crop yield is a serious and chronic problem for agricultural production. Improving plant salt tolerance is a feasible way to solve this problem. Plant physiological and biochemical responses under salinity stress become a hot issue at present, because it can provide insights into how plants may be modified to become more tolerant. It is generally known that the negative effects of soil salinity on plants are ascribed to ion toxicity, oxidative stress and osmotic stress, and great progress has been made in the study on molecular and physiological mechanisms of plant salinity tolerance in recent years. However, the present knowledge is not easily applied in the agronomy research under field environment. In this review, we simplified the physiological adaptive mechanisms in plants grown in saline soil and put forward a practical procedure for discerning physiological status and responses. In our opinion, this procedure consists of two steps. First, negative effects of salt stress are evaluated by the changes in biomass, crop yield and photosynthesis. Second, the underlying reasons are analyzed from osmotic regulation, antioxidant response and ion homeostasis. Photosynthesis is a good indicator of the harmful effects of saline soil on plants because of its close relation with crop yield and high sensitivity to environmental stress. Particularly, chlorophyll a fluorescence transient has been accepted as a reliable, sensitive and convenient tool in photosynthesis research in recent years, and it can facilitate and enrich photosynthetic research under field environment.
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