A Síkfőkút DIRT parcellák létrehozása óta eltelt tizenkét év vizsgálati eredményei alapján megállapíthatjuk, hogy a talajba jutó avarinput mennyiségének és minőségének a megváltoztatása jelentős hatással van a talaj fizikai- kémiai tulajdonságaira, a talajban lejátszódó biológiai folyamatokra. Az avarmegvonásos kezelések hatására (NA, NGY, NI) a humuszfrakciók C–tartalma, továbbá a talaj CO2 kibocsátása, valamint a talajenzimek aktivitása csökkent. Az avarduplázásos kezelések (DA, DF) hatása nem volt olyan jelentős, mint az avarmegvonás hatása. Ha a jövőben növekedne az erdők avarprodukciója, az nem okozna jelentősebb változást a talajban, kedvező hatása csak több év múlva jelentkezne. Ha azonban az erdők avarprodukciója csökkenne, annak káros következményei lehetnek. A talaj hőingása növekedne, nedvességtartalma, pH-ja csökkenne, a talaj mikrobiális aktivitása csökkenne, ami a talaj termőképességének romlásához vezetne. Az ILTER DIRT Projectben való részvételünk kutatásaink hatékonyságát jelentős mértékben megnövelte, mivel eredményeinket összehasonlíthatjuk a többi DIRT kutatóhely azonos módszerekkel végzett kutatási eredményeivel, ezáltal szélesebb, általánosabb érvényű összefüggések feltárására nyílik lehetőségünk. Brant et al. (2006) három DIRT kutatóhelyen (Síkfőkút DIRT Project, Bousson Experimental Forest, H. J. Andrews Experimental Forest) a mikrobiális biomasszát és a mikrobaközösség összetételét vizsgálta és hasonlította össze. Kimutatták, hogy a föld alatti C input elvonásnak nagyobb hatása van a talaj mikrobiális közösségére, mint a föld feletti input elvonásnak. Mind a három kutatási területen a talaj mikrobiális közösségeit legjobban a gyökérmegvonásos kezelés befolyásolta. Ezt a mi kutatási eredményeink is igazolták. A talaj β-glükozidáz és dehidrogenáz aktivitásában az avar megvonásnak jóval nagyobb hatása volt, mint a megnövelt avar inputnak. A β-glükozidáz enzim esetében az aktivitás kezdetben nagyobb mértékben csökkent a gyökér megvonásos kezeléssel, mint a föld feletti avar megvonással. Sulzman et al. (2005) a H. J. Andrews Experimental Forest-en végzett vizsgálatai alapján kimutatta, hogy az avarmegvonás hatására a talajlégzés nem sokkal már a parcellák létesítését követően csökkent. Síkfőkúton az avarmegvonásnak ez a talajlégzést csökkentő hatása a parcellák létesítése után több év múlva jelentkezett. Az avarduplázásos kezelés hatása a talajlégzésre pedig még ennél is később jelentkezett. Ezek az eredmények jól mutatják, hogy a különböző erdő ökoszisztémák eltérő sebességgel reagálnak a talaj szerves anyag változásaira.

We found that the leaf-litter production of Quercus petraea trees during the 2003-2010 period was half of that measured earlier (1972-1976), and was significantly higher between 1972 and 1976 than between 2003 and 2010 (p<0.001). This could be explained by the considerable mortality of sessile oak (68%) during the past forty years. Despite of the 16% mortality of Quercus cerris, its leaf-litter production did not decrease. Leaf-litter production of Q. cerris not only compensated but significantly surpassed its former leaf-litter production in years 2003-2010. Leaf-litter production of Acer campestre is nearly five times as much as it was in the present period. In the earlier period A. campestre occurred only in the shrub layer, while now it forms a secondary canopy-layer. Leaf-litter production of Cornus mas did not differ significantly between the two periods (Kotroczó et al. 2007). Total leaf-litter production decreased as compared to the present period at Síkfőkút Project site, but differences between the two periods were not significant (p>0.05). The average leaf-litter production was 3532 kg ha-1year-1 between 2003 and 2010 which is close to the average data (4064 kg ha-1year-1) of the years 1972-1976. Total litter production was higher in the present period (with 1121 kg ha -1) than in the earlier period (1972-1976), but it was not significant. Total litter production includes the leaf-litter productions and branches, crops and debris, too. The quantity of total litter production did not change significantly, but we observed changes in litter quality. Q. cerris and A. campestre could partly compensate the deficiency of leaf-litter production which resulted from the significant mortality of Q. petraea. We found the soil temperature was higher in exclusion treatments (NL, NR, NI) than in the Control during the spring and summer. In these treatments the heat insulation litter layer (NL, NI) was missing and/or the shade effect of plant was also missing (NI, NR), so the soil’s warm up was quicker than in other treatments. The highest temperature was measured in NI and the lowest in DL. We found an opposite tendency during the winter. In exclusion treatments (NL, NI), where the heat insulation litter layer was missing, the soil cooled down very fast, the temperature decreased below zero. During the winter the lowest temperature was measured in NL and NI treatments, and the highest in DL. In DL treatments the temperature never fell below zero due to double heat insulation litter layer. The soil moisture of DL, NL and DW treatments were not different significantly from the Control plots. The soil moisture content was higher in NR and NI treatments, than the other treatments. In these plots, the biggest soil moisture content is a consequence of the missing plant transpiration and trench of plots. The higher moisture content is favorable to degradation of soil organic matter so in these plots the degradation of SOM was fast. Soil pH decreased in the litter removal plots (NL, NR, NI) presumably because litter removals reduced Ca2+ and Mg2+ inputs (Tóth et al. 2011, 2013). The decreased soil cation content and decreased SOM content decreased soil buffering capacity, making soils less able to neutralize acidic substances from decomposition (Fekete et al. 2011). Increased detrital inputs in DL and DW treatments increased Ca2+ and Mg2+ input, which resulted in a higher soil buffering capacity and soil pH (Kotroczó et al. 2014). Total humus carbon content was the highest in the DL treatments and the lowest in the NL treatments compared to the Control. Additional litter input increases the total humus carbon content of soil, while total humus carbon content of soil decreases as a consequence of litter removal. We observed the same pattern by the mobile humic acids fraction and mobile fulvic acids fraction. We found that season had significant effect on CO2 release with the highest rates in summer, while treatments had no significant effect. In 2010 CO2 release was the highest in DL treatments. In autumn 2010 CO2 release was in DL treatment significantly higher than in Control and all removal treatments. The lowest CO2 release was measured in the removal treatments as a consequence of the termination of litter input. Soil organic matter was not sufficient to maintain the decomposition processes (Sayer 2006, Fekete et al. 2012). In 2011 and 2012 there were no significant differences among treatments. The weather was extremely warm and dry in these years and the soil microbial activity also decreased. We found that soil moisture was a critical controller of soil respiration during the warm and dry periods. During dry periods, soil moisture was higher in the root exclusion plots than in the other treatments. Soil CO2 emissions during dry periods were larger in these treatments than it was in the other treatments, where both heterotrophic and autotrophic sources contributed to total soil respiration (Fekete et al. 2014, Veres et al. 2015a). There were significant differences in β-glucosidase activity among treatments. In general, activities were lower in removal treatments (NL, NR, NI) than in the Control or addition treatments (DL, DW). Litter removal had a stronger effect through time on β-glucosidase enzyme activities than did increased litter inputs. In contrast to our initial hypothesis, β-glucosidase activities did not increase significantly with either leaf litter or wood additions. These results together suggest that aboveground detritus, although a significant source of DOC from the O horizon, does not play as significant a role as roots in supplying labile C to the soil microbial community. There were no significant differences among treatments for soil phenol oxidase enzyme activities for the first 5 years after the establishment of the experimental plots. There were also no significant differences in mean values of phenol oxidase enzyme activities among treatments in the later (2010-2012) period, although the lowest activities were measured in the removal treatments. We did not expect phenol oxidase to respond to detrital manipulations as quickly as β-glucosidase, as the relatively stable nature of lignin should not differ immediately among treatments (Veres et al. 2015b). Dehydrogenase activities were lower in removal treatments than in the control or addition treatments, and the effect of detritus removal on dehydrogenase activities increased. Similar to our other enzyme activities results, dehydrogenase activities did not increase significantly with either leaf litter or wood additions (Veres et al. 2013).