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Stand and leaf scale responses of loess grassland swards to elevated air CO 2 concentration had been investigated in a mini FACE system during 1998–2000. The study concentrated on biomass, leaf area index (LAI) and vegetation surface temperature (stand scale) and on diurnal carbohydrate pattern and gas-exchange responses (leaf scale). Leaf net CO 2 uptake under prolonged exposure to elevated CO 2 showed an upward response in the dicotyledonous and a downward one in the monocotyledonous species. Dawn and evening carbohydrate levels in leaves suggested growth stimulation of the dicot under elevated CO 2 and the opposite for the grass species and indicated sink limitation as a major factor determining photosynthetic acclimation at the species level. The smaller LAI as well as the insignificant biomass response to elevated air CO 2 was a compounded response by multi-species stands. Under mild water shortage, elevated air CO 2 concentration partly alleviated the drought effect shown by the higher relative growth rate of LAI. Canopy surface temperatures of the vegetation in the CO 2 enriched rings were higher than those in the ambient rings suggesting that decreased leaf conductance and transpiration were responsible for the temperature difference between the treatments. Increased canopy surface temperature under elevated air CO 2 concentration will probably lead to increased sensible heat flux and therefore enhanced convection at larger spatial scales.

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This brief overview decribes some structural and functional (including carbon cycling) aspects of grassland ecosystems, in particular with regard to the effects of global climate change and changes in land use. Afterward the papers briefly introduce the papers devoted to the above mentioned topics, which were selected for this special volume. As we can see, authors studied different kinds of management (including abandonment) and different parameters of climate change (CO 2 , temperature, rainfall, etc.). They consider predominately vegetation parameters, including the various plant traits, carbon cycling, soil respiration and different ecophysiological traits in simulated climate change. Dealing with different impacts of climate and/or land-use changes on multi-species systems, that grassland communities certainly are, is exceeding merely experimental synthesized-community or single-species approach on one side and classical vegetation studies on the other. The complex responses of natural communities, including those under FACE systems, are not easy to interpret and understand. The importance of non-linear dynamics during climate changes is emphasized by Bartha et al. (2008). In these selected papers, grasslands appear to be a very dynamic and plastic ecosystem. Grasslands are highlighted from a new, much more topical point of view. Linking ecophysiology and vegetation science, which is characteristic for our selection of papers, is a promising tool to deal with problems on the ecosystem level in general, not only addressing the global climate change and land-use issues.

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The aim of the present work was to study the soil seed bank of the semiarid sandy grassland community using the nested sampling procedure. The samples consisted of six concentric cores with diameters ranging from 5 to 22 cm and surface area ratio of the outermost to the innermost ring of 19. Investigations were directed to establish the minimum core diameter to find the dominant and less frequent species in the seed bank and also to have an insight on distribution patterns of species. The smallest core (diameter: 5 cm) employed in 20 repetitions was adequate to find the dominant species in the seed bank, while increasing the sample area to 19 times resulted in doubling the number of species found. The seeds of the dominant species had clustered distribution even at the smallest applied sample scale, while patterns of seed clumps followed different (uniform, contagious, random) distributions.

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The survey was carried out on the seed bank of several patches of an open, semiarid sandy grassland (Festucetum vaginatae Rapaics ex Soó 1929 (Borhidi 1996)). We chose four, approximately 20 m × 20 m large, adjacent patches, different in their species composition and total cover. Soil samples were taken in early spring and at the end of summer, in two consecutive years. We determined the seed bank of the samples with the seedling emergence method. The fact that we found the seeds of only two species that were not present in the vegetation indicates the isolated and without artificial disturbed state of the grassland. The vegetation and the seed bank of the patches showed a low degree of similarity in the same period, while the composition of the spring aspect reflected clearly in the seed bank of late summer in all four patches. Results showed that mosaic-like appearance is not only characteristic of the vegetation, but also the seed bank of the soil. Differentiation of the seed bank manifested mostly after the period of seed-fall, at the end of summer, while in early spring it was less expressed. On the basis of the differentiation of the seed bank we can conclude that not the dispersion of seeds, but natural vicinity of mother plants was decisive in forming the spatial variation of the seed bank.

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With the aim to obtain information about atmospheric deposition of metals all over the western Himalayas (Kumaon region) using moss as bioaccumulator, a biomonitoring program was setup by financial aid of the Department of Biotechnology, Ministry of Science and Technology, Govt. of India. Present study is a part of the same monitoring program. The moss Racomitrium crispulum was sampled from 24 localities of Nainital of the Kumaon Hills to indicate relative level of four metals: Pb, Zn, Cu and Cd. In summation of undertaken metals the highest 70% concentration of metals was observed in centre of the city. A gradient of decrease in metal was recorded while projecting away from city centre (zero km). A trend of metal precipitation was observed amongst seasons, viz. summer > winter > monsoon. The accumulation level of metals in the moss also varies amongst themselves, i.e. Zn > Pb > Cu > Cd. The moss metal-metal regression analysis correlation (R) exhibits that it gives significance for Pb-Zn (0.8088), Cu-Zn (0.6186) and Cu-Pb (0.5611).

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Community Ecology
Authors:
K. Pintér
,
Z. Barcza
,
J. Balogh
,
Sz. Czóbel
,
Zs. Csintalan
,
Z. Tuba
, and
Z. Nagy

Interannual variation of carbon fluxes of grasslands on sandy (5 years data) and heavy clay soils (4 years data) have been analysed. The sandy grassland was carbon sink in 3 (2004, 2005, 2006) out of the investigated 5 years. Its annual C-balance is precipitation limited, the relation seems strongly conservative, with r 2 of 0.83. More than half of the net source activity fell to the summer droughts. The heavy clay grassland was net source of carbon in one year (2007) only with no whole year record from 2003, a drought and heat wave year. Dependence of the C-balance on precipitation was somewhat weaker (r 2 =0.57) than in the sandy grassland. Length of growing period showed less variation here compared to the sandy grassland. Recovery of sink activity after rains was much slower for the heavy clay grassland than for the sandy grassland. The reason behind is that the amount of water required to reach optimal soil water content for plant functioning is several times larger for the mountain grassland. This fact and the low conductivity of the clay soil for water decrease the heavy clay grassland’s recovery potential after droughts. Owing to these soil characteristics, the clay grassland may be more vulnerable to droughts in terms of decreased C-assimilation and (soil) carbon losses under the predicted drier summers even if the annual precipitation sum was higher by 10.7% on average for the mountain compared to the sandy grassland. The annual precipitation sum is close to the threshold, below which the grasslands may turn into source of carbon. While in one hand this can be viewed as an example of ecosystem scale adaptation to available water, drought events also involve loss of soil carbon and a potential positive feedback between source activity and decreasing net primary production, on the other.

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