21 research outputs found
Auswirkungen der Landwirtschaft auf physikalische und chemische Funktionen EuropÀischer Torfböden
Torfböden bieten zahlreiche Funktionen: sie bilden den weltweit gröĂten terrestrischen Kohlenstoffspeicher, stellen wichtige NĂ€hrstofffilter dar und erhöhen hydrologische PufferkapazitĂ€ten. Torfböden sind in Mittel- und Nordeuropa zum ĂŒberwiegenden Teil landwirtschaftlich genutzt. Kultivierung fĂŒhrt zu extremen Mineralisierungsraten der organischen Substanz und hohen THG-Emissionen. Die AnfĂ€lligigkeit fĂŒr Bodensackung, Boden- und WasserqualitĂ€tsverschlechterung und folglich Ernteausfall steigt. Das Ziel dieser Studie ist es, Auswirkungen des Agrarmanagements auf Funktionen von Torfböden in Europa zu analysieren. In Deutschland, den Niederlanden, DĂ€nemark, Estland, Finnland und Schweden wurden standardisierte Bodenkartierungen, bodenphysikalische und -chemische Analysen, Grundwassermonitoring und Betriebsdatenerhebungen durchgefĂŒhrt. Die Ergebnisse belegen einen starken Einfluss der bisherigen Bewirtschaftung auf die Funktionen von Torfböden in Europa. Torfböden unter intensiver Ackernutzung bieten im Vergleich zu extensiver und intensiver GrĂŒnlandnutzung die niedrigste TragfĂ€higkeit in den oberen 10 cm, welche eine erfolgreiche landwirtschaftliche Praxis auf Torfböden stark einschrĂ€nkt. Der Unterschied lĂ€sst sich allein durch Wurzelstabilisierung erklĂ€ren, da die Bodenverdichtung in den oberen 25cm unter Ackernutzung am höchsten ist. Hieraus folgt eine starke Verringerung der nutzbaren FeldkapazitĂ€t und der gesĂ€ttigten hydraulischen LeitfĂ€higkeit, wodurch sich hydrologische Probleme wie StaunĂ€sse und Trockenstress, die hĂ€ufig auf kultivierten Torfböden vorkommen, weiter intensivieren. BodenkohlenstoffvorrĂ€te sinken deutlich mit steigender NutzungsintensitĂ€t und sind im Vergleich auf extensivem GrĂŒnland am höchsten. Dies wird bestĂ€tigt durch den Zersetzungsgrad, der hier am niedrigsten ist. Die Ergebnisse deuten auf eine starke Auswirkung des Managements auf Bodenkohlenstoffverluste und Torfkonservierung auf europĂ€ischer Ebene hin
Synergy of extreme drought and shrub invasion reduce ecosystem functioning and resilience in water-limited climates
Extreme drought events and plant invasions are major drivers of global change that can critically affect ecosystem functioning and alter ecosystem-atmosphere exchange. Invaders are expanding worldwide and extreme drought events are projected to increase in frequency and intensity. However, very little is known on how these drivers may interact to affect the functioning and resilience of ecosystems to extreme events. Using a manipulative shrub removal experiment and the co-occurrence of an extreme drought event (2011/2012) in a Mediterranean woodland, we show that native shrub invasion and extreme drought synergistically reduced ecosystem transpiration and the resilience of key-stone oak tree species. Ecosystem transpiration was dominated by the water use of the invasive shrub Cistus ladanifer, which further increased after the extreme drought event. Meanwhile, the transpiration of key-stone tree species decreased, indicating a competitive advantage in favour of the invader. Our results suggest that in Mediterranean-type climates the invasion of water spending species and projected recurrent extreme drought events may synergistically cause critical drought tolerance thresholds of key-stone tree species to be surpassed, corroborating observed higher tree mortality in the invaded ecosystems. Ultimately, this may shift seasonally water limited ecosystems into less desirable alternative states dominated by water spending invasive shrubs
A proposed methodology for the correction of the Leaf Area Index measured with a ceptometer for pinus and eucalyptus forests = Proposta de uma methodologia para a correcao do indice de area foliar medido pelo ceptometro em provoamentos de pinus e eucalyptus
Leaf area index (LAI) is an important parameter controlling many biological and physiological processes associated with vegetation on the Earth's surface, such as photosynthesis, respiration, transpiration,
carbon and nutrient cycle and rainfall interception. LAI can be measured indirectly by sunfleck ceptometers in an easy and non-destructive way but this practical methodology tends to underestimated when measured
by these instruments. Trying to correct this underestimation, some previous studies heave proposed the multiplication of the observed LAI value by a constant correction factor. The assumption of this work is LAI obtained from the allometric equations are not so problematic and can be used as a reference LAI to develop a new methodology to correct the ceptometer one. This new methodology indicates that the bias (the difference between the ceptometer and the reference LAI) is estimated as a function of the basal area per unit ground area and that bias is summed to the measured value. This study has proved that while the measured Pinus LAI needs a correction, there is no need for that correction for the Eucalyptus LAI. However, even for this last specie the proposed methodology gives closer estimations to the real LAI values
Soil water content effects on net ecosystem CO2 exchange and actual evapotranspiration in a Mediterranean semiarid savanna of Central Chile
Biosphere-atmosphere water and carbon fluxes depend on ecosystem structure, and their magnitudes
and seasonal behavior are driven by environmental and biological factors. We studied the seasonal
behavior of net ecosystem CO2 exchange (NEE), Gross Primary Productivity (GPP), Ecosystem
Respiration (RE), and actual evapotranspiration (ETa) obtained by eddy covariance measurements
during two years in a Mediterranean Acacia savanna ecosystem (Acacia caven) in Central Chile. The
annual carbon balance was â53 g C mâ2 in 2011 and â111 g C mâ2 in 2012, showing that the ecosystem
acts as a net sink of CO2, notwithstanding water limitations on photosynthesis observed in this
particularly dry period. Total annual ETa was of 128 mm in 2011 and 139 mm in 2012. Both NEE and ETa
exhibited strong seasonality with peak values recorded in the winter season (July to September), as a
result of ecosystem phenology, soil water content and rainfall occurrence. Consequently, the maximum
carbon assimilation rate occurred in wintertime. Results show that soil water content is a major driver
of GPP and RE, defining their seasonal patterns and the annual carbon assimilation capacity of the
ecosystem, and also modulating the effect that solar radiation and air temperature have on NEE
components at shorter time scales.This work was funded by FONDECYT projects 1120713 and 1170429, a grant from the Inter-American Institute
for Global Change Research (IAI) [grant number CRN3056], which is supported by the US National Science
Foundation [grant number GEO-1128040], and the Spanish Ministry of Economy and Competitiveness project
GEI Spain (CGL2014-52838-C2-1-R), including ERDF founds. F. Bravo-MartĂnez is grateful to CONICYT for the
grants âFormaciĂłn de Capital Humano Avanzado-2009âČâČ, âBeca de Apoyo al tĂ©rmino de la tesis doctoral-2012âČâČ,
and CORFO INNOVA Grant N° 09CN14-5704. We thank to Enrique PĂ©rez Sanchez-Cañete and Borja RuĂz-
Reverter for technical support. We also thank âCODELCOâDivisiĂłn Andinaâ for use of the site. C. Montes
acknowledges the NASA Postdoctoral Program and to Universities Space Research Association
Quantification of dynamic soilâvegetation feedbacks following an isotopically labelled precipitation pulse
The presence of vegetation alters hydrological cycles of ecosystems. Complex
plantâsoil interactions govern the fate of precipitation input and water
transitions through ecosystem compartments. Disentangling these interactions
is a major challenge in the field of ecohydrology and a pivotal foundation for
understanding the carbon cycle of semi-arid ecosystems. Stable water isotopes
can be used in this context as tracer to quantify water movement through
soilâvegetationâatmosphere interfaces.
The aim of this study is to disentangle vegetation effects on soil water
infiltration and distribution as well as dynamics of soil evaporation and
grassland water use in a Mediterranean cork oak woodland during dry
conditions. An irrigation experiment using ÎŽ18O labelled water was
carried out in order to quantify distinct effects of tree and herbaceous
vegetation on the infiltration and distribution of event water in the soil
profile. Dynamic responses of soil and herbaceous vegetation fluxes to
precipitation regarding event water use, water uptake depth plasticity, and
contribution to ecosystem soil evaporation and transpiration were quantified.
Total water loss to the atmosphere from bare soil was as high as from
vegetated soil, utilizing large amounts of unproductive evaporation for
transpiration, but infiltration rates decreased. No adjustments of main root
water uptake depth to changes in water availability could be observed during
the experiment. This forces understorey plants to compete with adjacent trees
for water in deeper soil layers at the onset of summer. Thus, understorey
plants are subjected to chronic water deficits faster, leading to premature
senescence at the onset of drought. Despite this water competition, the
presence of cork oak trees fosters infiltration and reduces
evapotranspirative water losses from the understorey and the soil, both due to
altered microclimatic conditions under crown shading. This study highlights
complex soilâplantâatmosphere and inter-species interactions controlling
rain pulse transitions through a typical Mediterranean savannah ecosystem,
disentangled by the use of stable water isotopes
França amplia estado de emergĂȘncia para 3 meses
Savannah-type ecosystems account for 26â30% of global gross primary productivity GPP with water being one of the major driving factors. In Europe, savannah-type woodlands cover an area of about 1.5 million ha. Here, the recent past has shown a significant 5 decrease of precipitation P in winter and spring as well as decrease of total annual precipitation. Strong effects on local water balance and carbon sink strength have thus been reported due to changes in precipitation regime. The objective of this study is to quantify the impact of the extreme drought event in 2012 on the water balance, gross primary productivity and carbon sink strength of 10 a typical Portuguese cork-oak woodland (montado) compared to the wet year 2011. Physiological responses of the dominant tree species Quercus suber (L.) are disentangled, employing combined photosynthesis and stomatal conductance modelling. Precipitation effectiveness ET/P increased from 86% in 2011 to 122% in the dry year 2012 due to deep soil or ground water access of the Q. suber trees leaving no 15 water for ground water replenishment. Understorey and overstorey GPP were strongly reduced by 53% and 28 %, respectively, in 2012 compared to 2011 due to the late onset of the autumn rains in 2011 and an additional severe winter/spring drought. However, the ecosystem was still a carbon sink in both years but with a 38% reduced sink strength under extreme drought in 2012 compared to 2011. The combined 20 photosynthesis-stomatal conductance model yielded best results if it was allowed to adjust photosynthetic and stomatal parameters simultaneously. If stomatal response was modelled with the Leuning approach, which allows for a different sensitivity to vapour pressure deficit, the stomatal model parameters were highly coupled. A change in either of the parameters needed to be compensated by the other to guarantee a sta25 ble sensitivity of stomatal conductance to assimilation, independently from variations in vapour pressure deficit. The Q. suber trees showed a 31% reduced stomatal conductance during the drought period 2012 compared to 2011 due to water supply limitations. In response to reduced leaf internal CO2 availability, the trees strongly reduced appar-ent maximum carboxylation rate by 39% in 2012 compared to 2011. Unexpectedly, the optimum temperature Topt of maximum electron transport rate decreased during the drought period, enhancing the susceptibility of the trees to high temperature stress during the summer. 5 Our results suggest that, if the trend of decreasing annual precipitation and changed precipitation pattern on the Iberian Peninsula continues, sustained effects on local ground water reservoirs, understorey species composition and tree mortality have to be expected in the long term. To successfully model the effect of drought on the montado ecosystem, variable apparent maximum carboxylation rate Vc,max, stomatal con10 ductance parameter m and vapor pressure deficit sensitivity parameter D0 need to be incorporated in photosynthesis-stomatal conductance modelling
X-ray computed microtomography characterizes the wound effect that causes sap flow underestimation by thermal dissipation sensors
Insertion of thermal dissipation (TD) sap flow sensors in living tree stems causes damage of the wood tissue, as is the case with other invasive methods. The subsequent wound formation is one of the main causes of underestimation of tree water-use measured by TD sensors. However, the specific alterations in wood anatomy in response to inserted sensors have not yet been characterized, and the linked dysfunctions in xylem conductance and sensor accuracy are still unknown. In this study, we investigate the anatomical mechanisms prompting sap flow underestimation and the dynamic process of wound formation. Successive sets of TD sensors were installed in the early, mid and end stage of the growing season in diffuse-and ring-porous trees, Fagus sylvatica (Linnaeus) and Quercus petraea ((Mattuschka) Lieblein), respectively. The trees were cut in autumn and additional sensors were installed in the cut stem segments as controls without wound formation. The wounded area and volume surrounding each sensor was then visually determined by X-ray computed microtomography (X-ray microCT). This technique allowed the characterization of vessel anatomical transformations such as tyloses formation, their spatial distribution and quantification of reduction in conductive area. MicroCT scans showed considerable formation of tyloses that reduced the conductive area of vessels surrounding the inserted TD probes, thus causing an underestimation in sap flux density (SFD) in both beech and oak. Discolored wood tissue was ellipsoidal, larger in the radial plane, more extensive in beech than in oak, and also for sensors installed for longer times. However, the severity of anatomical transformations did not always follow this pattern. Increased wound size with time, for example, did not result in larger SFD underestimation. This information helps us to better understand the mechanisms involved in wound effects with TD sensors and allows the provision of practical recommendations to reduce biases associated with wounding in field sap flow measurements
Modelling COâ and CHâ emissions from drained peatlands with grass cultivation by the BASGRA-BGC model
Abstract
Cultivated peatlands under drainage practices contribute significant carbon losses from agricultural sector in the Nordic countries. In this research, we developed the BASGRA-BGC model coupled with hydrological, soil carbon decomposition and methane modules to simulate the dynamic of water table level (WTL), carbon dioxide (COâ) and methane (CHâ) emissions for cultivated peatlands. The field measurements from four experimental sites in Finland, Denmark and Norway were used to validate the predictive skills of this novel model under different WTL management practices, climatic conditions and soil properties. Compared with daily observations, the model performed well in terms of RMSE (Root Mean Square Error; 0.06â0.11 m, 1.22â2.43 gC/mÂČ/day, and 0.002â0.330 kgC/ha/day for WTL, COâ and CHâ, respectively), NRMSE (Normalized Root Mean Square Error; 10.3â18.3%, 13.0â18.6%, 15.3â21.9%) and Pearson's r (Pearson correlation coefficient; 0.60â0.91, 0.76â0.88, 0.33â0.80). The daily/seasonal variabilities were therefore captured and the aggregated results corresponded well with annual estimations. We further provided an example on the model's potential use in improving the WTL management to mitigate COâ and CHâ emissions while maintaining grass production. At all study sites, the simulated WTLs and carbon decomposition rates showed a significant negative correlation. Therefore, controlling WTL could effectively reduce carbon losses. However, given the highly diverse carbon decomposition rates within individual WTLs, adding indicators (e.g. soil moisture and peat quality) would improve our capacity to assess the effectiveness of specific mitigation practices such as WTL control and rewetting