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- Biological soil crusts (3)
- Fe-Al-hydroxide mixtures (1)
- Mode of photosynthesis (1)
- desorption (1)
- histidine (1)
- malic acid (1)
- phosphorus kinetics (1)
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In the context of ongoing climate change and increasing population, there is an urgent need to optimize the water consumption of surface and groundwater in agricultural production. In recent years, intensive irrigated viticulture and horticulture have faced increasing demand pressure in many water-limited areas including the Western Cape Province in South Africa. Shelterbelts of trees are often used to reduce wind speed and water demands as an eco-engineering measure directly influencing soil evaporation and crop transpiration. Objectives are (i) to evaluate the extent of impacts of wind speed from shelterbelts at canopy level in citrus orchards and vineyards (ii) to assess the wind effects at leaf level including leaf temperature and related ecophysiological performance in irrigated vineyards.
Biological soil crusts (BSCs) develop when various combinations of diminutive cyanobacteria, eukaryotic algae, non-lichenized fungi, lichens, and/or bryophytes occupy the upper few millimeters of the soil and raw material. They can be present in a wide range of ecological, including successional, and climatic conditions when and where disturbance and/or aridity have resulted in opportunities for colonization. However, they are most prevalent in arid, semiarid and polar ecosystems where vascular plant cover and diversity are characteristically low, leaving large areas available for colonization by some combination of the organismal groups mentioned above. The ecological roles of BSCs are numerous and diverse, and include the collection, accumulation and cycling of essential airborne and soil nutrients, redistribution of precipitated water, and soil formation and stabilization.
The generally accepted assumption that CAM is an important adaptation to the drought conditions in arid deserts is mainly based on studies in controlled environments comparing the respective photosynthetic pathways in plants of different morphology. Comparative long-term field studies on the ecophysiology of C3- and CAM succulents co-occurring in the same desert habitat are too rare to satisfactorily answer the old question whether the metabolic pathway or the succulence is more important to guarantee survival in such a harsh habitat. Thus, relevant ecophysiological parameters were repeatedly monitored on plants of the leaf succulents Augea capensis (C3) and Malephora purpureo-crocea (CAM), which commonly dominate a habitat in the Knersvlakte, Namaqualand, South Africa. Under identical conditions in the same habitat, carbon gain of the C3 species was higher than that of the CAM plant, but their WUE lower and maximum photosynthetic activity nearly the same. In M. purpureo-crocea, irrigation induced rapid whole day stomatal opening at drastically increased daytime but decreased night-time CO2-uptake, while respective responses of the C3 species were delayed. These different response dynamics were due to different rooting depth, root morphology and water acquisition strategy of the flat rooting CAM and the deep-rooting C3 species. This, however, may not explain the highly similar growth success. Anyway, the results verify that CAM provides no advantage over C3 for long-term survival in the same desert environment in morphologically similar succulents.
In recent years, the importance of soil health for ecosystem functions has come further into the scientific focus (Lehmann et al., 2020). Especially after severe ecosystem disturbances, soil formation has to start anew. Such disturbances, which reset ecosystem development to the starting point, can be of natural (volcanoes, mobile sand dunes, floods, glaciers) (La Farge et al., 2013; Lan et al., 2014) or human origin (post-mining landscapes, military training areas, agricultural lands) (Belnap et al., 2007; Schaaf et al., 2011). In these young ecosystems, the interactions between the initial colonizers, the inorganic matter, and the subsequent biogeochemical processes are an important prerequisite for the development of elemental fluxes, soil genesis, and thus for further ecosystem development.
Biological soil crusts (BSCs) are thin microbiological vegetation layers that naturally develop in unfavorable higher plant conditions (i.e., low precipitation rates and high temperatures) in global drylands. They consist of poikilohydric organisms capable of adjusting their metabolic activities depending on the water availability. However, they, and with them, their ecosystem functions, are endangered by climate change and land-use intensification. Remote sensing (RS)-based studies estimated the BSC cover in global drylands through various multispectral indices, and few of them correlated the BSCs’ activity response to rainfall. However, the allocation of BSCs is not limited to drylands only as there are areas beyond where smaller patches have developed under intense human impact and frequent disturbance. Yet, those areas were not addressed in RS-based studies, raising the question of whether the methods developed in extensive drylands can be transferred easily. Our temperate climate study area, the ‘Lieberoser Heide’ in northeastern Germany, is home to the country’s largest BSC-covered area. We applied a Random Forest (RF) classification model incorporating multispectral Sentinel-2 (S2) data, indices derived from them, and topographic information to spatiotemporally map the BSC cover for the first time in Central Europe. We further monitored the BSC response to rainfall events over a period of around five years (June 2015 to end of December 2020). Therefore, we combined datasets of gridded NDVI as a measure of photosynthetic activity with daily precipitation data and conducted a change detection analysis. With an overall accuracy of 98.9%, our classification proved satisfactory. Detected changes in BSC activity between dry and wet conditions were found to be significant. Our study emphasizes a high transferability of established methods from extensive drylands to BSC-covered areas in the temperate climate. Therefore, we consider our study to provide essential impulses so that RS-based biocrust mapping in the future will be applied beyond the global drylands
Phosphorus (P) fixation is a global problem for soil fertility and negatively impacts agricultural productivity. This study characterizes P desorption of already fixed P by using KCl, KNO3, histidine, and malic acid as inorganic and organic compounds, which are quite common in soil.
Goethite, gibbsite, and ferrihydrite, as well as hydroxide mixtures with varying Fe- and Al-ratio were selected as model substances of crystalline and amorphous Fe- and Al-hydroxides. Especially twoand multi-component hydroxide systems are common in soils, but they have barely been included in desorption studies. Goethite showed the highest desorption in the range from 70.4 to 81.0%, followed by gibbsite with values in the range from 50.7 to 42.6%. Ferrihydrite had distinctive lower desorption in the range from 11.8 to 1.9%. Within the group of the amorphous Fe-Al-hydroxide mixtures, P desorption was lowest at the balanced mixture ratio for 1 Fe: 1 Al, increased either with increasing Fe or Al amount. Precipitation and steric effects were concluded to be important influencing factors.
More P was released by crystalline Fe-hydroxides, and Al-hydroxides of varying crystallinity, but
desorption using histidine and malic acid did not substantially influence P desorption compared to
inorganic constituents.