Comparative synphysiological studies on Brachypodium pinnatum dominated forest- and steppe-type grasslands

The lack of community-level, synphysiological investigations inspired us to plan a study on Brachypodium pinnatum grasslands, well-known objects of local long-term coenological and dynamical examinations in Hungary. After removing every species but B. pinnatum, CO2 gas exchange responses by the grass stands indicated the difference in the degree of water-stress between the two investigated habitats. However, in intact community measurements these responses are masked by the presence of other species, by the change of species coexistence patterns and by different light conditions. We conclude that to understand the physiological performance of a dominant species in a plant community and also the photosynthetic behaviour of the whole community, considering the coenological aspect and examining the intensity of photosynthesis at a level of organization higher than the population level are essential

Variability of synphysiological processes in three non-arborescent temperate grasslands

Three plan t communities, a loess, a sand and an old-field grassland showed considerable differences in synphysiological variability during an investigation at the same spatial scale in 2000. The two former are widely distributed in the Carpathian Basin and with the latter the Hungarian non-arborescent, herbaceous vegetation is well represented. To arrive at conclusions on the causes of variability of synphysiological characteristics can be difficult when allowing for both physiological and abiotic variability. On the other hand it was also obvious that stands' or vegetation types' physiological processes reflect changes of abiotic conditions in coefficients of variation which could not be demonstrated in parallel coenological investigations. Coenological responses are much slower than the synphysiological ones. When considering synphysiological data under conditions of good water supply and under severe drought stress a decrease of variability was found in all types in the latter case. This trait seems to be independent of any coenological characteristic

Florális diverzitás mintázatok: egy komparativ funkcionális megközelités = Fine-scale neighborhoods in plant communities: a comparative functional approach

Munkánk alapgondolata, hogy a növényfajok együttélésének értelmezéséhez a térbeli függőség mellett a fajok találkozási valószínűségeit leíró finom térléptékű diverzitási relációk ismerete is szükséges. Standard mintavételi módszereket fejlesztettük és számos hazai gyeptársulásban végeztünk összehasonlító mikrocönológiai vizsgálatot. Null-modellekkel kimutattuk, hogy a fajok találkozási valószínűségei az átlagtér közelítéssel becsült értéktől az egyensúlytól távoli társulásokban térnek el jobban. A diverzitásmintázatok funkcionális értelmezéséhez növényi tulajdonságokat használtunk, amelyek egy részét terepen mértük. Leírtuk ezek szukcessziós trendjeit és segítségükkel társulási szabályokat állapítottunk meg. A florális diverzitást, mint a béta diverzitás egy új mérőszámát értelmeztük és leírtuk a homoki gyepek klímaváltozás hatására várható differenciálódási trendjét. Löszgyepek és homoki gyepek összehasonlító elemzésével kimutattuk, hogy a diverzebb állományok rezíliensebbek és a florális diverzitás időbeli fluktuációja az átlagos florális diverzitással forditottan arányos. Terepi és szimulációs vizsgálatok összekapcsolásával bizonyítottuk, hogy a domináns faj az egymáshoz hasonló szubordinált fajokat térben elszigetelheti és ezzel hozzájárul a közösség diverzitásának a fennmaradásához. Eredményeink szerint a gyepállományon belüli szerkezeti komplexitást a domináns, ill. a gyakori fajok alakítják ki, míg a többiek ehhez az alapszerkezethez asszociálódnak. | Plant neighborhood diversity (PnD) relationships provide important complementary information for assembly rules. Fine-scale diversity patterns and assembly rules were assessed in various Hungarian grasslands using a standard sampling protocol. Null-models showed that deviance from the mean field approximation was stronger in non-equilibrium communities. Several plant traits were measured in the field and used for interpreting community structure. The relative importance of different plant traits were estimated in contrasting grassland habitats and in different stages of forest succession. Expected differentiation of sand grasslands due to climate changes were described by a new PnD based beta diversity index. By analyzing long-term data sets, the average PnD we found to be in inverse ratio to the CV% of PnD. We used spatially explicit individual based simulation models for demonstrating that similar subordinate species can coexist within the matrix of dominant species under specific conditions. Using information theory models for analyzing fine-scale patterns in various grasslands we showed that fine-scale structural complexity was created mainly by the dominant species and subordinates were associated to this matrix structure

Soil CO2 efflux and production rates as influenced by evapotranspiration in a dry grassland

Aims Our aim was to study the effect of potential biotic drivers, including evapotranspiration (ET) and gross primary production (GPP), on the soil CO2 production and efflux on the diel time scale. Methods Eddy covariance, soil respiration and soil CO2 gradient systems were used to measure the CO2 and H2O fluxes in a dry, sandy grassland in Hungary. The contribution of CO2 production from three soil layers to plot-scale soil respiration was quantified. CO2 production and efflux residuals after subtracting the effects of the main abiotic and biotic drivers were analysed. Results Soil CO2 production showed a strong negative correlation with ET rates with a time lag of 0.5 hours in the two upper layers, whereas less strong, but still significant time-lagged and positive correlations were found between GPP and soil CO2 production. Our results suggest a rapid negative response of soil CO2 production rates to transpiration changes, and a delayed positive response to GPP. Conclusions We found evidence for a combined effect of soil temperature and transpiration that influenced the diel changes in soil CO2 production. A possible explanation for this pattern could be that a significant part of CO2 produced in the soil may be transported across soil layers via the xylem

Homoki gyep CO2-kibocsátásának vizsgálata új, nyílt rendszerű automata mérőeszközzel

Az utóbbi évtizedben zajló kutatások kimutatták, hogy a talajok CO2- kibocsátása jelentős napi és szezonális változékonyságot mutat. A manuális mérőrendszerekkel azonban ez nehezen követhető nyomon. Éppen ezért megjelent az igény a nagyobb időbeli felbontású automata mérőrendszerekre, több gyártó készítette el saját fejlesztésű műszerét. Ezeknek a rendszereknek a hátránya, hogy drágák és többnyire zárt rendszerben működnek, ahol a bonyolult kamranyitó-záró mechanika csökkentheti a működésbiztonságot. További hátrányt jelent a kamrák meglehetősen nagy mérete, ami miatt gyepállományokban nehezen alkalmazhatók. Az általunk kifejlesztett nyílt rendszerű mérőeszköz alkalmasnak bizonyult ezen problémák kiküszöbölésére: a kisméretű kamrák (d = 5 cm) könnyen elhelyezhetők a növények között, nyílt rendszerben nem szükséges kamranyitó-záró mechanikát építeni, és a rendszer olcsón kivitelezhető. A kifejlesztett 10 kamrás mérőrendszer kalibrálását laboratóriumi körülmények között végeztük el, valamint összehasonlítottuk terepi mérések segítségével egy nemzetközileg is hitelesnek számító mérőrendszerrel. A kapott eredmények szerint a kifejlesztett mérőrendszer alkalmas hosszú időtartamú automata-mérésekre, segítségével nagy mennyiségű adat nyerhető

Higher soil respiration under mowing than under grazing explained by biomass differences

Different management practices may change the rate of soil respiration, thus affecting the carbon balance of grasslands. Therefore, we investigated the effect of grazing and mowing on soil respiration along with its driving variables (soil water content, soil temperature, above and below ground biomass, vegetation indices and soil carbon) in adjacent treatments (grazed and mowed) at a semi-arid grassland in Hungary (2011-2013). The average soil respiration over three years was higher in the mown (6.03±4.07 µmol CO2 m-2 s-1) than in the grazed treatment (5.29±3.50 µmol CO2 m-2 s-1). While soil water content and soil temperature did not differ between treatments, mowing resulted in 20 % higher soil respiration than grazing, possibly due to 17% higher average above ground biomass in the mowed than in the grazed treatment. Inclusions of vegetation index VIGreen in the soil respiration model in addition to abiotic drivers improved the explained Rs variance by 16% in the mowed and by 5% in the grazed site, respectively. VIGreen alone proved to be a simple and fast indicator of soil respiration (r2=0.31 at grazed, r2=0.44 at mowed site). We conclude that soil respiration is responsive to the combined effect soil water content, soil temperature, biomass and soil carbon content as affected by the management (grazing vs. mowing) practice

Temporal variability of CO2 and N2O flux spatial patterns at a mowed and a grazed grassland

Spatial patterns of ecosystem processes constitute significant sources of uncertainty in greenhouse gas flux estimations partly because the patterns are temporally dynamic. The aim of this study was to describe temporal variability in the spatial patterns of grassland CO2 and N2O flux under varying environmental conditions and to assess effects of the grassland management (grazing and mowing) on flux patterns. We made spatially explicit measurements of variables including soil respiration, aboveground biomass, N2O flux, soil water content, and soil temperature during a four-year study in the vegetation periods at grazed and mowed grasslands. Sampling was conducted in 80×60 m grids of 10 m resolution with 78 sampling points in both study plots. Soil respiration was monitored nine times, and N2O flux was monitored twice during the study period. Altitude, soil organic carbon, and total soil nitrogen were used as background factors at each sampling position, while aboveground biomass, soil water content, and soil temperature were considered as covariates in the spatial analysis. Data were analyzed using variography and kriging. Altitude was autocorrelated over distances of 40–50 m in both plots and influenced spatial patterns of soil organic carbon, total soil nitrogen, and the covariates. Altitude was inversely related to soil water content and aboveground biomass and positively related to soil temperature. Autocorrelation lengths for soil respiration were similar on both plots (about 30 m), whereas autocorrelation lengths of N2O flux differed between plots (39 m in the grazed plot vs. 18 m in the mowed plot). Grazing appeared to increase heterogeneity and linkage of the spatial patterns, whereas mowing had a homogenizing effect. Spatial patterns of soil water content, soil respiration, and aboveground biomass were temporally variable especially in the first 2 years of the experiment, whereas spatial patterns were more persistent (mostly significant correlation at p<0.05 between location ranks) in the second 2 years, following a wet year. Increased persistence of spatial patterns after a wet year indicated the recovery potential of grasslands following drought and suggested that adequate water supply could have a homogenizing effect on CO2 and N2O fluxes