Simulation of annual leaf carbon fluxes and analysis of stand structure of poplars and balck locusts in an alley-cropping system, Brandenburg, Germany

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IMPACT OF THERMAL STRESS AND HIGH VPD ON GAS EXCHANGE AND CHLOROPHYLL FLUORESCENCE OF CITRUS GRANDIS UNDER DESERT CONDITIONS

Additional index words: photosynthesis, photoinhibition, heat stress, temperature Abstract The photosynthetic response of Citrus grandis to high light intensities, low air humidity and high temperature stress was investigated under desert conditions in the southern AravaValley (Israel). During summer, a typical midday stomatal closure was observed even in well-watered trees due to the dramatic increase of the leaf-to-air water vapour deficit. As a result of the reduced transpirational cooling, leaf temperatures increased up to 11 °C above ambient air temperature. The combination of heat stress and photoinhibition resulted in a reversible decrease of photosynthetic activity of Citrus grandis under the extreme summer conditions

Dew formation on the surface of biological soil crusts in central European sand ecosystems

Dew formation was investigated in three developmental stages of biological soil crusts (BSC), which were collected along a catena of an inland dune and in the initial substrate. The Penman equation, which was developed for saturated surfaces, was modified for unsaturated surfaces and used for prediction of dewfall rates. The levels of surface saturation required for this approach were predicted using the water retention functions and the thicknesses of the BSCs. During a first field campaign (2–3 August 2011), dewfall increased from 0.042 kg m<sup>−2</sup> for the initial sandy substrate to 0.058, 0.143 and 0.178 kg m<sup>−2</sup> for crusts 1 to 3, respectively. During a second field campaign (17–18 August 2011), where dew formation was recorded in 1.5 to 2.75-h intervals after installation at 21:30 CEST, dewfall increased from 0.011 kg m<sup>−2</sup> for the initial sandy substrate to 0.013, 0.028 and 0.055 kg m<sup>−2</sup> for crusts 1 to 3, respectively. Dewfall rates remained on low levels for the substrate and for crust 1, and decreased overnight for crusts 2 and 3 (with crust 3 > crust 2 > crust 1 throughout the campaign). Dew formation was well reflected by the model response. The suggested mechanism of dew formation involves a delay in water saturation in near-surface soil pores and extracellular polymeric substances (EPS) where the crusts were thicker and where the water capacity was high, resulting in elevated vapor flux towards the surface. The results also indicate that the amount of dewfall was too low to saturate the BSCs and to observe water flow into deeper soil. Analysis of the soil water retention curves revealed that, despite the sandy mineral matrix, moist crusts clogged by swollen EPS pores exhibited a clay-like behavior. It is hypothesized that BSCs gain double benefit from suppressing their competitors by runoff generation and from improving their water supply by dew collection. Despite higher amounts of dew, the water availability to the crust community decreases with crust development, which may be compensated by ecophysiological adaptation of crust organisms, and which may further suppress higher vegetation or mosses

Biogenic crust dynamics on sand dunes

Sand dunes are often covered by vegetation and biogenic crusts. Despite their significant role in dune stabilization, biogenic crusts have rarely been considered in studies of dune dynamics. Using a simple model, we study the existence and stability ranges of different dune-cover states along gradients of rainfall and wind power. Two ranges of alternative stable states are identified: fixed crusted dunes and fixed vegetated dunes at low wind power, and fixed vegetated dunes and active dunes at high wind power. These results suggest a cross-over between two different forms of desertification

Desertification and Rehabilitation in Arid and Semi-Arid Regions. Proceedings International Symposium Beijing 2004

Gao J, Veste M, Sun B, Beyschlag W, eds. Desertification and Rehabilitation in Arid and Semi-Arid Regions. Proceedings International Symposium Beijing 2004. Beijing: Science Press; 2006

Performance and photosynthetic ecophysiology of three photo-types of Dioscorea zingiberensis under differing light intensities

Li HM, He P, Veste M, Neudorf K. Performance and photosynthetic ecophysiology of three photo-types of Dioscorea zingiberensis under differing light intensities. Plant Biology. 2002;4(3):384-391.The performance and photosynthetic ecophysiology of three photo-types of Dioscorea zingiberensis were studied. The three types are designated DzTL, DzTM and DzTH, according to their adaptation to low (LL), medium (ML) and high (HL) light intensities, respectively. Under LL (23-55 mumol m(-2) s(-1)) and simulated natural light (SNL), DzTM grows well with increased longevity, and green leaves which are unspotted; while its leaves became small, light yellow and short-lived under HL (550 - 850 mumol m(-2) s(-1)). In contrast, under LL the leaves of DzTH were very large, spotted, light yellow and short-lived; while they were small, green and long-lived under HL. Under HL, DzTH had a much higher chlorophyll content than DzTM. Under LL, DzTM and DzTL had a higher Chl content than DzTH. Among the three types, DzTM had the highest peroxidase activity. DzTL had a higher electron transport rate (ETR), maximal quantum yield (MQY) and effective quantum yield (EQY) than DzTH and DzTL under LL, while DzTH had higher ETR, MQY and EQY than the other two types under ML and HL. Therefore, three different photo-types can be characterized according to their adaptation to LL, ML and HL: DzTL, DzTM and DzTH, respectively

Evaluation of fast growing tree water use under different soil moisture regimes using wick lysimeters

The cultivation of fast growing trees has high potential for bioenergy production on marginal lands. Information about the water use efficiency in combination with the ecophysiological response to drought stress is still incomplete. For the study of the transpiration-biomass relations satisfactory results can be obtained under controlled conditions by using lysimeters. Nonetheless, several technical problems related to the manufacturing can bias the outcome. Pan lysimeters are economical and relatively easy to assemble, however, saturation at the lower boundary can happen. On the other hand tension lysimeters, where the suction is applied by a vacuum pump, are effective but expensive and need constant maintenance. To avoid stagnancy and reduce production costs we assembled a tension controlled wick lysimeter, where the tension at the bottom layer is actively exerted by a hanging water column through the wick material (rockwool). We aim to assess the performance of the wick lysimeter coupled with an automatic irrigation system for the study of water use-yield relation black locust (Robinia pseudoacacia L.) under different irrigation regimes. The volumetric soil content for each treatment, namely low water (LW), medium water (MW) and high water amount (HW), was maintained at 0.07, 0.14 and 0.2 m3 m-3 respectively. During the vegetation period (161 days) the plants growing at LW reduced their water use by 60%, their leaf area by 40% and the total above ground biomass by 46%. As a result, we found a linear correlation (R2 = 0.98) between the relative biomass produced and the relative water use. The calculated relative water use efficiency (RWUE) for black locust total above ground dry biomass is 0.96. Furthermore, after the harvest we evaluated the effectiveness of the lysimeter and irrigation system: the soil moisture of the treatments was kept up at the predefined values and an unsaturated condition at the boundary layer was maintained throughout the vegetation period. Because of the improved design no roots grew into the drainage extension and no unexpected change of the lysimeters hydraulic property occurred. Considering the relatively low-cost material used and the low maintenance needed, compared to other tension controlled lysimeters, wick lysimeters are effective tools for forestry studies of young trees