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BTU
Manufacturing Simple and Inexpensive Soil Surface Temperature and Gravimetric Water Content Sensors
(2019)
Quantifying temperature and moisture at the soil surface is essential for understanding how soil surface biota responds to changes in its environment. However, at the soil surface these variables are highly dynamic and standard sensors do not explicitly measure temperature or moisture in the upper few millimeters of the soil profile. This manuscript describes methods for manufacturing simple, inexpensive sensors that simultaneously measure the temperature and moisture of the upper 5 mm of the soil surface. In addition to sensor construction, steps for quality control, as well as for calibration for various substrates, are explained. The sensors incorporate a Type E thermocouple to measure temperature
and assess soil moisture by measuring the resistance between two gold-plated metal probes at the end of the sensor at a depth of 5 mm. The methods presented here can be altered to customize probes for different depths or substrates. These sensors have been effective in a variety of environments and have endured months of heavy rains in tropical forests as well as intense solar radiation in deserts of the southwestern U.S. Results demonstrate the effectiveness of these sensors for evaluating warming, drying, and freezing of the soil surface in a global change experiment.
Top soils in temperate climates are regularly covered by cryptogames. Depending on the climatic and environmental conditions and their development stage, these biocrusts are built up by different species of cyanobacteria, bacteria, green algae, mosses, liverworts, lichens and fungi, which crosslink the uppermost soil particles. Biocrusts create a thin surface layer of high biotic activity, with high C and nutrient pools and fluxes to deeper soil layers, where the soil tends to be biotically and biogeochemically less active. Changes in soil structure, e.g. due to the accumulation of organic material and the ability of biological nitrogen fixation, result in significant feedback and control of biogeochemical processes. We analysed the response of photosynthesis and respiration to changing temperature and light in two moss-and lichen-dominated soil crusts from a dry acid grassland in the vicinity of a pine forest in Brandenburg, Germany. For the estimation of carbon fluxes, we combined lab-based CO2 gas exchange measurements and continuous determination of biocrust drying and rewetting cycles under field conditions. These experiments facilitated the development of an empirical photosynthesis model that allows for an estimation of the carbon dynamics of biological soil crusts based on their ecophysiological performance.
Initiale und nährstoffarme Ökosysteme wie Grasländer und Offenlandschaften haben aus Sicht des Naturschutzes einen hohen Wert für die Landschaft und sind in der intensiv genutzten Kulturlandschaft Mitteleuropas selten geworden. Gerade Bergbaufolgelandschaften, aber auch gestörte Binnendünen, bieten Potenzial für die Entwicklung von initialen Lebensräumen und Landschaften. Die obersten Millimeter der Bodenoberfläche dieser Ökosysteme werden durch Biokrusten besiedelt. Gebildet werden diese komplexen Lebensgemeinschaften aus einer Vielzahl von Cyanobakterien, Grünalgen, Moosen, Pilzen, Bakterien und Flechten. Diese Organismen „verkleben“ die Bodenoberfläche und beeinflussen als „Ökosystem en miniature“ maßgeblich die ökosystemaren Prozesse und die weitere Vegetationsentwicklung. Der Eintrag von C und N sowie die Akkumulation von organischem Material fördert die Bodenentwicklung in der initialen Phase.
Während der Sukzession der Biokrusten entwickeln sich die komplexen biotischen Prozesse des N-Kreislaufes mit Rückkopplungen auf die Nährstoffversorgung. Ausgeschiedene Exopolysaccharide, die eine Verbindung mit den Bodenpartikeln eingehen, verkleinern nach Regen den Porenraum der Bodenoberfläche und vermindern die Infiltration. Besonders Moos- und Flechten-Krusten unterbinden bei geringen Niederschlagsintensitäten die Infiltration in tiefere Bodenschichten. Konkurrenz und die großflächige Versiegelung der Bodenoberfläche haben zudem negative Auswirkungen auf die Keimung und Etablierung von höheren Pflanzen. Diese biotischen Interaktionen führen bei gesteuerten Sukzessionen auf Renaturierungsflächen zu Änderungen der Vegetationsentwicklung. Somit wird die Bedeutung der Biokrusten für die Renaturierungsökologie z.T. kontrovers diskutiert. Klein- und großräumige Störungen hingegen sind als integraler Bestandteil der Ökosystementwicklung einzuschließen.
Due to disturbances of soils after open-cast lignite mining activities in the Lusatian mining district, Northeast Germany, large areas covered with excavated and dumped material. These initial soils are characterized by a lack of nutrients and organic matter which is why Robinia pseudoacacia was established during reclamation of those marginal sites. As a pioneer species, Robinia is well suitable for the establishment on reclaimed forest ecosystems due to the N fixation capability and its ability to grow on a nutrient-poor sandy substrate with low water holding capacity. Since the N requirement of the Robinia can be covered by symbiotic nodule bacteria, P is important as a growth-limiting nutrient. Even though the total and available P in soils increased with the age of the plantings (planted between 1995 and 2007), the ratio of available to total P decreased relative to younger plantings. Despite the accumulation of organic matter and the decomposition of organic bound P, the bioavailability is affected by ad- and desorption processes, especially on Fe- and Al-hydroxides. It was hypothesized that the P demand of young trees, initially provided by a one-time fertilizer application, exceeds the P supply by mineralization over time. As a first step, kinetics of P desorption from synthetic Fe- and Al-hydroxides were characterized by using humic acid as a model organic compound, to detect fast and slow releasable P over time. At the Robinia sites, soil samples were examined at different depth with regard to their C, N and P concentrations. From the first results, we can conclude that the P availability and its limitation influences the growth performance of Robinia as well as the N-fixing symbiotic bacteria and, thus, the C:N:P ratio as a long-term effect on an ecosystem scale.
Biological soil crusts (biocrusts) play an important role as pioneering organisms on initial soils and in open landscapes after natural and human disturbances. Even though they only cover the topsoil, biocrusts are key drivers for biogeochemical and ecological processes and influencing ecosystem development. Microclimatic conditions, texture, water holding capacity, and chemical soil properties lead to the formation of spatial patterns. Sandy nutrient-poor soils in pine forests in the open-cast lignite mining district in Brandenburg are covered by biocrust, dominated by different functional types and species (e.g. algae, mosses, lichens). The photosynthetic activity of these poikilohydric organisms, strongly depending on moisture, affects biocrust function and their impact on soil C pools and dynamics. Therefore, the evaluation of photosynthesis in relation to the spatial distribution pattern variation is fundamental. For this purpose, we combined different remote sensing techniques, spectral reflectance sensors, and chlorophyll fluorescence imaging to analyze the photosynthetic dynamics in relation to biocrust species composition and wetness. Desiccation of the biocrusts was detected with a miniature moisture sensor and related to their activity. A low-cost consumer grade camera was used to determine NDVI and to map the distribution and heterogeneity of chlorophyll for a comprehensive characterization of spatial photosynthetic activity pattern. Basic as well as maximum fluorescence, the maximum photochemical efficiency, and NDVI decreased during desiccation of the biocrusts, whereby moss and moss/lichen biocrusts showed higher water holding capacities relative to green algae biocrusts. The combination of different sensor technologies is a powerful tool for monitoring long-term biocrust development and their implication for soil C dynamics.
Background and aims: Betony (Betonica officinalis L.) is one of the rarest and most spectacular plants in the Scandinavian flora. A long-term question has been whether it is spontaneous or introduced, or whether it comprises both spontaneous and introduced populations. This study aimed to answer this question by analyzing sequence data from the nuclear external transcribed spacer (ETS) region and three regions of the plastid genome, the trnT–trnL intergenic spacer (IGS) region, tRNA-Leu (trnL) intron, and the trnS–trnG IGS. Materials and methods: Altogether 41 samples from 11 European countries were analyzed. A unique duplication in the trnT–trnL IGS was detected in material from Skåne (southern Sweden), the “Skåne-duplication.” Populations with this duplication are united on a moderately supported branch in the phylogeny based on plastid sequences. A distinct heath genotype from Yorkshire was discovered in the phylogeny based on plastid sequences and in a comparative cultivation. Results: Phylogeny based on ETS sequences does not support any Scandinavian group, whereas a principal coordinates analysis ordination based on variable ETS positions indicated a spontaneous origin for all Scandinavian populations, which comprise a genetically well-defined subgroup of the species, most closely related to other spontaneous populations from adjacent parts of continental parts of Northern Europe. Discussion: Seven possible naturally occurring localities remain in Scandinavia, five in central Skåne, southernmost Sweden, and two on the southwestern part of the Danish island of Lolland.
Former studies using the chlorophyll fluorescence technique on evergreen Ilex aquifolium L. showed that its photosynthetic potential for electron transport in winter recovers quickly when exposed to more favorable conditions. Since little is known, however, about its photosynthetic carbon gain in winter, we investigated its leaf gas exchange over an entire winter and spring period. Measurements were made rotationally in the field and in the laboratory to also investigate if I. aquifolium profits from warmer phases during winter in terms of net carbon gain. From the end of autumn until the end of spring, three different climate-driven phases of photosynthetic responses could be distinguished: first, an acclimation phase which lasted until February and was characterized by a gradually decreasing light-saturated gross photosynthesis (Amax(gross)), decreasing apparent quantum yield of CO₂-assimilation (ɸi) and a decreasing ability of these parameters to recover overnight inside the laboratory. At the same time, maximal quantum yield of PSII (Fv/Fm) could fully regenerate. In this phase, single warmer days had a positive effect on carbon assimilation. Second, a phase of relatively constant but low photosynthesis which was virtually unaffected by temperature, lasting for almost two months occurred. Here, Amax(gross) and ɸi had lost their ability to recover from winter conditions in the
field, while Fv/Fm was much less affected. I. aquifolium was still able to conduct positive light-saturated net photosynthesis at a leaf temperature of -0.5°C, but during this time it could not profit from milder temperatures in terms
of carbon gain. Third, a phase of increasing photosynthesis (spring recovery) occurred, starting in March when the 5-day average temperature was above 5°C and radiation in the field increased, and where all parameters slowly recovered from winter depressions. Our findings show that I. aquifolium is photosynthetically active over the whole winter, even at temperatures around 0°C. In terms of carbon gain, however, I. aquifolium does not profit from warmer phases during winter, despite the fast recovery seen in chlorophyll fluorescence measurements.
In Brandenburg, eastern Germany, prospective climate changes imply extreme weather events, increasing annual temperature, and decreasing summer precipitation. Since alley-cropping systems (ACS) have a broad planning horizon, appraising their sustainability and efficiency under changing climate conditions is crucial for forthcoming risk assessments and adaptation scenarios. Consequently, this combined experimental and simulation study investigated the growth vulnerability of poplar clone “Max I” (Populus nigra L. x P. maximowiczii Henry) and black locust (Robinia pseudoacacia L.) short rotation coppices in an ACS established in Brandenburg to a considerable spectrum of weather conditions and long term climate change, from 2015 to the end of 2054. The investigation employed (i) Yield-SAFE, a biophysical, process-based model to simulate the above-ground tree woody biomass and (ii) 100 realisations of the statistical regional climate model STAR 2K. In the most optimistic sequence of events pertaining to air temperature, precipitation, and global radiation, 35% more woody biomass would be achieved by poplar and 43% by black locust in the last period compared to the base period. Alternatively, in the most pessimistic circumstances, 54% less woody biomass would be rendered by poplar and 47% by black locust. Our findings corroborated the tree growth vulnerability to prospective climatic changes, particularly to changes in water availability.
Die Wintertemperaturen und insbesondere Frost sind wichtige Umweltfaktoren, die das Verbreitungsgebiet der Stechpalme (Ilex aquifolium L.) Mitteleuropa beschränken. Bereits heute profitiert diese Art von dem Klimawandel durch eine erweiterte Verbreitung in Mitteleuropa und an seiner nördlichen Verbreitungsgrenze in Skandinavien. In dieser Arbeit wird die Bedeutung der milder werdenden Wintertemperaturen für den Stoffwechsel von I. aquifolium untersucht, insbesondere die Akklimatisation der Photosynthese während des Winters. Dafür wurde die Photosynthese mit der Chlorophyllfluoreszenz-Methode gemessen. Während milder Wintertage bei Temperaturen wenig unter 0°C erholte sich die Photosynthese innerhalb von zwei Stunden, sobald die Pflanzen Raumtemperatur ausgesetzt wurden. Dagegen war die Photosynthese nach langanhaltenden Frostperioden und die gemessenen Elektronentransportraten der im Freiland wachsenden Ilex-Bäume um bis zu 50% niedriger als bei den Vergleichspflanzen im Gewächshaus. Somit wird die Photosynthese im Winter von der minimalen Temperatur und der Frostdauer beeinflusst. In der Regel war die immergrüne Stechpalme in der Lage ihre Photosynthese im Winter aufrecht zu erhalten und flexibel auf frostfreie Tage zu reagieren. Damit profitiert die Stechpalme während milder Tage im Winter und Frühjahr von dem im Vergleich zu den Sommermonaten hohem Lichtgenuss
im Unterwuchs, wenn die sommergrünen Bäume in der Baumschicht unbelaubt sind.
The alley-cropping systems (ACSs), which integrate parallel tree strips at varying distances on an agricultural field can result, complementarity of resource use, in an increased land-use efficiency. Practitioners’ concerns have been directed towards the productivity of such systems given a reduced area covered by agricultural crops. The land equivalent ratio (LER) serves as a valuable productivity indicator of yield performance and land-use efficiency in ACSs, as it compares the yields achieved in monocultures to those from ACSs. Consequently, the objective of this combined experimental and simulation study was to assess the tree- and crop-yields and to derive the LER and gross energy yield for two temperate ACSs in Germany under different design scenarios, i.e., tree arrangements (lee- or wind-ward) and ratios of tree area to crop area. Both LER and gross energy yields resulted in a convex curve where the maximum values were achieved when either the tree or crop component was dominant (>75% of the land area) and minimum when these components shared similar proportions of land area. The implications of several design scenarios have been discussed in order to improve the decision-making, optimization, and adaptation of the design of ACSs with respect to site-specific characteristics
Trees from drought deciduous forests (“bosque seco”) in northern Peru and southern Ecuador regularly shed their leaves at the onset of seven months-long periods without rain. This way they very effectively reduce the bulk water consumption by leaf transpiration, still loosing small amounts of water through their bark, but at the risk of too little or no carbon gain when leaf-less. Seven species studied here have good developed green cortex tissue on stems and axes, as especially evident for the “bottle tree” Ceiba trischistandra (A. Gray) Bakhuisen (Bombacaceae). In several leaf-less tree species at the end of summer drought, when xylem sap flows are very low, indications of higher xylem flows at night as compared to day-time were found, which led to the question of whether the trees are capable of performing CAM in their axes. However, although quite low in some cases, the pH of the cortex tissues did not fluctuate diurnally. In addition, no night-time carbon uptake could be observed. Although no net carbon gain was measured in C. trischistandra and Erythrina smithiana Krukoff (Fabaceae) photosynthetic activity of the green cortex was sufficient to re-assimilate between 50% to 60% of the carbon released by mitochondrial respiration. In contrast, the obligate CAM plant Cereus diffusus (Britton & Rose) Werdermann (Cactaceae), which was studied as a reference in the same environment, showed both diurnal pH-fluctuations in its green tissue with lowest values before sun rise, and net carbon fixation at night.
Biocrusts are vulnerable to large scale disturbances including trampling activities, and their recovery rates are highly variable with estimates fluctuating by more than one order of magnitude, from<5 years (very fast) to>250 years (very slow). Also, the development of microbial abundance and community diversity of biocrusts
after disturbances is poorly understood. In a semiarid climate of the Chinese Loess Plateau, we conducted a recovery experiment on well-developed moss biocrusts after a severe disturbance, during which the entire upper 3 cm of the surface was removed. In the following nine years, the general characteristics and microbial community
of the recovering and undisturbed biocrusts as well as a substrate with no crust (bare sand) were periodically determined. Through linear or logistic extrapolation of the observed recovery rates, the recovery time of the biocrusts after disturbance was estimated by both biocrust characteristics and microbial community. Recovery time yielded the following estimates: a) coverage within 3 years, b) thickness within 8 years, c) biomass
within 9–13 years, and d) cultivable microbial density within 11–13 years. More importantly, the recovery time of the disturbed moss-biocrusts estimated by the number of bacteria and fungi was ~10 and 20 years, respectively, and that estimated by the bacterial and fungal community diversity was 12–14 and 12–16 years,
respectively. In conclusion, moss biocrusts would take 15–20 years to achieve full recovery, which was shorter than many previously published estimates that regarded biocrusts and especially moss-dominated biocrusts to have a long recovery time of hundreds of years. However, it should be also kept in mind that very fast recovery
(< 5 years) of biocrusts was less reliable because such estimations are mostly based on visual cover only rather than on the multi-variables of the recovering biocrusts.
This study investigates the spatial and temporal impact of microclimate conditions caused by poplar hedgerows in a short rotation alley cropping system (SRACS), and their effect on the atmospheric evaporative demand (AED) and the grain crop yield of winter wheat (Triticum aestivum var. Patras) in direct comparison to a common agricultural crop system. Microclimate was measured at nine positions distributed at the SRACS and an adjacent open field in Brandenburg State (Germany) from March to August 2016. Our hypothesis was that microclimate and AED was improved at SRACS, with traceable effects on the crop yield. The analysis of air temperature and water vapour deficit (VPD) data revealed significantly (p B 0.05) lower daytime values from June to August at the crop alley of the SRACS, which were generally most frequent at the poplar hedgerow and 3 m west positions. By contrast, wind speed was reduced at almost all the positions of our crop alley and during the entire measurement period during both day and night. The AED measured on sampling days in July was significantly (p B 0.001) reduced at the whole crop alley, with values from 24 to 32% in comparison to the open field. We observed a strong linear relationship (R2 & 0.78–0.99) between AED on one side and wind speed and VPD on the other side. The average grain yield within the SRACS was 16% higher than on the OF. However, our microclimate data were insufficient to explain this yield surplus.
Competition for above- and below-ground resources depends on their availability and results in varied growth partitioning. This becomes clear as the supply and limitation of the main resources influence the slope of the size-growth relationship in stands. Nevertheless, growth partitioning among trees, especially among black locust (R. pseudoacacia) trees is not understood in sufficient detail. To scrutinize and estimate the mode of competition of R. pseudoacacia, this research analyzed 1333 trees in Germany in 10 study sites, consisting in total 27 sample plots, with similar climate but varying soil conditions. The stand age ranged from 2 to 32 years, with a diameter at breast height ranging from 0.6 to 29.1 cm. The main focus of the study was to evaluate the impact of nitrogen, phosphorus, and water supply on the competition mode of R. pseudoacacia by varying growth partitioning. We applied the size–growth relationship in a mixed-effects model with a random intercept and slope. Fixed effects were the basal area, phosphorus, water, the sunlight competition index, and the interactions between below- and above-ground resources. Site specific effects of the analyzed stands were quantified with the aid of the random effects. Depending on the supply and limitation of phosphorus and water, this study determined how the competition mode as well as the growth partitioning among R. pseudoacacia trees were influenced. Hence, if phosphorus and water availability increased, then the competition for above-ground resources (primarily sunlight) and the slope of the size–growth relationship increased. Large trees grew disproportionately more than smaller trees. If the available phosphorus and water decreased, then the competition for the below-ground resources increased and the slope of the size–growth relationship decreased – to be more flattened. Moreover, it was found that available nitrogen as a below-ground resource had no influence on the mode of competition. In summary, phosphorus was the most important nutrient and, together with water, was the main driver of growth partitioning among R. pseudoacacia trees.
Transitioning towards agroforestry demands systematic productivity assessments of such systems under different climatic and edaphic conditions. In this regard, the Land Equivalent Ratio (LER) serves as a valuable productivity indicator of agroforestry since it evaluates yields from growing trees and crops together in comparison to yields from monocultures over the same period. Consequently, our objective was to evaluate the overall productivity of two agroforestry systems in Forst (Brandenburg) and Wendhausen (Lower Saxony) by means of LER. Our approach followed two assumptions: (i) the yields of trees and crops had equal economic importance and (ii) the economic importance was given solely by the annual crop, the yield of trees representing a supplementary profit. The resulted values for LER were consistently above their specific threshold, corroborating the greater efficiency of agroforestry systems rather than monoculture. Additionally, this study highlighted the importance of choosing the appropriate assumptions when calculating the LER.