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International audience; The photosynthetic, optical and morphological characteristics of a chlorophyll-deficient (Chldeficient) “yellow” soybean mutant (MinnGold) were examined in comparison with two green varieties (MN0095 and Eiko). Despite the large difference in Chl content, similar leaf photosynthesis rates were maintained in the Chl-deficient mutant by offsetting the reduced absorption of red photons by a small increase in photochemical efficiency and lower non-photochemical quenching (NPQ). When grown in the field, at full canopy cover, the mutants reflected a significantly larger proportion of incoming shortwave radiation, but the total canopy light absorption was only slightly reduced, most likely due to a deeper penetration of light into the canopy space. As a consequence, canopy-scale grossprimary production and ecosystem respiration were comparable between the Chl-deficient mutant and the green variety. However, total biomass production was lower in the mutant, which indicates that processes other than steady state photosynthesis, caused a reduction in biomass accumulation over time. Analysis of NPQ relaxation and gas exchange in Chl-deficient and green leaves after transitions from high to low light conditions suggested that dynamic photosynthesis might be responsible for the reduced biomass production in the Chl-deficient mutant under field conditions.

Within the framework of the European Union project CADSES "Carbon-Pro" and with the help of Croatian Forests Ltd. on 21 September 2007 a station for continuous monitoring of forest carbon and energy fluxes has been put into operation. The station is located within a lowland oak forest complex, in the Forest Mnagement Unit "Jastrebarski lugovi", forest compartment 37a. It is a 35-years old Pedunculate oak (Quercus robur L.) stand with significant share of other tree spcies (Black alder, Field ash, Hornbeam etc). Acquired data should enable us to better understand the processes, causes and effects that environmental factors have on Pedunculate oak stands and lowland forest in general. The station is first of such kind in Croatia and wider in South-European Region and as such has already become invaluable source of new data. At the station a wide range of meteorological and ecological variables is continuously measured and recorded. The fluxes of CO2, sensible and latent heat are estimated using eddy covariance method. In this work we present the preliminary results of the first year of our research. We illustrate changes with time of tatal precipitation (P), daily evapotranspiration (ET) of the stand and surface soil water content (SWC) during period January - August 2008. Comparison of aboveground biomass growth estimated with dendrometer bands and Net Ecosystem Productivity (NEP) measured with eddy covariance showed good correlation in the first half of the growing season. Negative NEE (i.e. CO2 assimilation) in summer still has to be explained in terms of biomass growth. High rate of soil respiration in summer could be an indicator of increased root respriration and root growth, but further research is necessary before conclusions could be made.

Deviations in amounts and patterns of precipitation caused by climate change will, to a certain extent, affect all ecosystems and Pedunculate oak (Quercus robur L.) forest are one of them. Negative aspects of climate changes particularity reflect in older Pedunculate oak stands with reduced mast or increase in tree dieback. Sufficient water supply, but also nutrient availability is of vital importance for stand growth. Dynamics of processes in soil, particularly decomposition of litter and other organic matter, is therefore very important. Soil water content and temperature are key environmental variables that affect processes in soil such as root respiration and rate of decomposition of organic material. Dynamics of those processes can be explored by research of soil respiration (SR), or more precisely, measurement of CO2 efflux from soil into the atmosphere. Aim of our research is to present the preliminary quantitative estimates of soil respiration for the period May – August of 2008. In our measurements of soil respiration we used a closed dynamic system with two chambers described by Delle Vedove et al. (2007). SR was performed in two modes: quasi-continuous (every 4 hours) on a fixed plot near the existing CO2 flux station (Marjanović et al. 2008) and periodically (2 times per month) on four different plots within the footprint of the station. Station within which the SR system was installed was established within the framework of an international project Carbon-Pro located within a lowland forest complex, in a 35-years old Pedunculate oak stand with significant share of other tree species (Black alder, Field ash, Hornbeam etc). Results indicate that SR strongly depends on soil temperature and soil water content (SWC). Observed daily CO2 efflux from soil ranges from 10 kgC ha-1 d-1, when SWC is high and soil temperature lower, up to 60 kgC ha-1 d-1, when the soil temperature is high and soil sufficiently dry. Further research is necessary to understand SR dynamics during the whole vegetation period and to better estimate spatial variability of SR.

U sklopu međunarodnog projekta Carbon-Pro te uz pomoć Hrvatskih šuma d.o.o. Zagreb, u Odjelu 37a G. J. "Jastrebarski lugovi" postavljen je sustav za intenzivno praćenje kruženja ugljika. Riječ je o kiompleksnom sustavu temeljenom na metodi vrtložne kovarijance koji kontinuirano i automatizirano prati dvadesetak raznih klimatskih i ekoloških varijabli. Podaci se pohranjuju u razmacima od 30 min, a pritom se osnovni meteorološki podaci prenose u realnom vremenu u centar u Šumarskom institutu te se pobliciraju na internetu. Sustav je smješten i u 35 godišnjoj sastojini hrasta lužnjaka sa značajnijim udjelom crne johe, poljskog jasena i običnog graba. Cilj našeg rada jest prezentirati prve rezultate rada istraživačke stanice te dati pregled dinamike kruženja ugljika, poniranje ugljičnog dioksida u sastojinu i otpuštanje iz sastojine na dnevnoj, tjednoj i sezonskoj razini. Neto proiztvodnja cijelog ekosustava ovisi o nizu ekoloških parametara poput temperature zraka i tla ; količini oborina, odnosno dostupnoj vlazi u tlu ; doznačenom sunčevom zračenju, posebno onom dijelu spektra koje omogućuje fotosintezu (fotosintetski aktivno zračenje). Istraživanje je prvenstveno usmjereno na procese kruženja ugljika u lužnjakovoj sastojini, ali ujedno omogućuje bolje razumijevanje sezonske dinamike procesa unutar sastojine i njihovu povezanost s glavnim klimatskim varijablama.

Odstupanja u količini i rasporedu oborina i temperaturi, uzrokovana klimatskim promjenama, značajno utječu na lokalne ekosustave pa tako i na sastojine hrasta lužnjaka. Negativni aspekti tih promjena očituju se povećanim sušenjem lužnjakovih stabala te izostalim ili smanjenim urodom žira. Dovoljne količine vode, ali i mineralnih tvari od kojih se dio oslobađa raspadanjem organskih ostataka, od vitalnog su značaja za rast i razvoj hrastovih sastojina te je stoga važno dobiti bolji uvid u dinamiku procesa u tlu. Stupanj vlažnosti i temperatura su ključni parametri koji utječu na procese u tlu poput respiracije korijena i raspadanja organske tvari. Dinamiku tih procesa moguće je procijeniti praćenjem respiracije tla, odnosno tôka ugljičnog dioksida (CO2) iz tla u atmosferu. Cilj našeg rada jest dati prve kvantitativne pokazatelje dinamike respiracije tla za period proljeće – ljeto 2008. U istraživanju je korišten sustav s dvije komore, opisan u radu Delle Vedove et al (2007), pomoću kojeg se automatizirano, svakih 4 sata, vrši izmjera respiracije tla. Sustav je instaliran u svibnju 2008. u sklopu postojeće istraživačke stanice za praćenje tokova CO2, postavljene u okviru međunarodnog projekta Carbon-Pro. Istraživačka stanica se nalazi na području g. j. Jastrebarski lugovi (UŠP Karlovac, šumarija Jastrebarsko) u mješovitoj sastojini hrasta lužnjaka i velike žutilovke s drhtavim šašem drugog dobnog razreda sa značajnijim učešćem johe, jasena i graba. Respiracija u tlu korelirana je s temperaturom zraka, tla na 5 cm dubine i volumnim udjelom vlage u tlu te je dobiveno dobra korelacija. Pokazalo se da se količina CO2 oslobađanja iz tla kreće u rasponu od približno 10 kgC/ha na dan kada su temperature niže i kada je u tlu veći sadržaj vlage pa do 60 kgC/ha na dan kada je temperatura visoka i tlo ima dovoljnu količinu vlage. Daljnja istraživanja respiracije tla, u kombinaciji s ostalim varijablama koje se mjere u sklopu istraživačke stanice pomoći će nam u boljem razumijevanju povezanosti sezonske dinamike rasta promatrane lužnjakove sastojine s glavnim klimatskim varijablama.