Visokogorsko područje dinarskog krša obilježeno je raznolikošću reljefnih formi, koje su u kombinaciji s humidnom klimom i različitim odnosima dolomita i vapnenaca, posebice u pogledu brzine i načina trošenja, dodatni izvor varijabilnosti fiziografije tla. U Nacionalnom parku Risnjak dimenzijama se ističu dvije ponikve (Viljska ponikva - VIP i Velika ponikva - VP) gdje smo testirali hipotezu o postojanju značajnih razlika u fiziografiji površinskog dijela tla. Cilj je bio istražiti u kojoj se mjeri uzduž osojne i prisojne padine ponikve mijenjaju kemijske značajke površinskog dijela tla i očituje li se pri tomu i razlika između dviju ponikvi, s obzirom na postojanje razlike u njihovoj litološkoj građi i poziciji unutar gorskog masiva. Istraživanja su provedena tako da je u svakoj ponikvi postavljen transekt u pravcu ~sjever-jug preko dna ponikve, na komu je obavljeno uzorkovanje tla do dubine od 15 cm (ili do stijene, ako je tlo pliće). Pokazalo se da je u VIP izraženija diferencijacija prirode humusa u organičnom horizontu i da ona dobro korespondira s diferencijacijom vegetacije. U VP se fizička trošivost stijena (dolomitični supstrat) odražava na fiziografiji tla u obliku karbonatnosti i više pH-vrijednosti, koja u VIP raste od dna prema rubu ponikve, dok se u VP pH-vrijednost značajno ne mijenja uzduž padina. Na osojnoj ekspoziciji u VIP je udio organskog ugljika u tlu značajno veći (377 g kg–1) od udjela na prisojnoj ekspoziciji (97 g kg–1), pri čemu na osojnoj ekspoziciji udio organskog ugljika opada od dna prema rubu ponikve, a na prisojnoj ekspoziciji se očituje blagi rast. Za razliku od navedonoga, u VP udjel organskog ugljika ima obrnuti trend. Slične odnose i trendove pokazuje i udjel ukupnog dušika, osim pri dnu osojne padine u VIP, gdje je Ntot relativno nizak, a Corg relativno visok. Zaključno, fiziografija tla dubokih gorskih ponikvi krša pod snažnim je utjecajem prirode stijena u pogledu dolomitičnosti. Tlo povrh dolomita i dolomitičnih vapnenaca obilježeno je karbonatnošću. U ponikvama u masivima čvrstih vapnenaca može se očekivati na njihovim osojnim padinama karakteristične trendove pH-vrijednosti tla te udjela organskog ugljika i ukupnog dušika zbog vrlo izraženog hidrotermičkog, odnosno bioklimatskog trenda. Na prisojnim ekspozicijama takvih ponikvi analogni trendovi s karakterističnim gradijentima izostaju, što korespondira i s izostankom prepoznatljivog vegetacijskog slijeda. The high mountain area of ​​the Dinaric karst is characterized by a variety of relief forms, which in combination with humid climate and different relationships of dolomite and limestone, especially in terms of rate and nature of weathering, are an additional source of variability of soil physiography. In the Risnjak National Park, two sinkholes stand out in terms of dimensions (Viljska ponikva - VIP and Velika ponikva - VP), where we tested the hypothesis of the existence of significant differences in the physiography of the surface part of the soil. The aim was to investigate the extent to which the chemical characteristics of the surface part of the soil change along the shady and sunny slopes of the sinkhole and whether the difference between the two sinkholes is evident, given the difference in their lithological structure (VIP is sinkhole in limestone and VP is sinkhole in dolomitic limestones and calcite dolomites) and positions within the mountain massif. The research was carried out in such a way that in each sinkhole a transect was placed in the direction north-south over the bottom of the sinkhole, on which soil sampling was performed to a depth of 15 cm (or to the rock, if the soil is shallower). Sampling was performed on rows of profiles in 5 replicates, which were placed perpendicular to the transect with a height difference of 10 m (Fig. 1). In each sinkhole, 22 rows of profiles were set up, on which 110 soil samples were collected, and the pH value, carbonate content, organic carbon content and total nitrogen content were measured on them. The research showed that on the shady slope in VIP, in addition to vertical vegetation differentiation, there is also a differentiation of the nature of humus in the organic horizon (hemimor, modermor, sphagnomor). This differentiation is much less pronounced in the VP, and on the sunny slope in both sinkholes it is almost absent. In VP, the physical weathering of rocks (dolomitic substrate) is reflected in the physiography of the soil in the form of free carbonate and higher pH values ​​(Figs. 9 and 10). In VIP the pH rises from the bottom towards the edge of the sinkhole, both on the shady and sunny slope, while in VP the pH value does not change significantly, both along the shady and along the sunny slope. A recognizable factor in the spatial variability of carbonate content and pH value of this soil is phytopedoturbation in the form of tree felling and ejection of carbonate particles on the surface of the sinkhole slope, where they are exposed to gravitational and water erosion and further redistribution down the slope. At the shady slope in VIP, the share of organic carbon in the soil is significantly higher (377 g kg – 1) than the share at sunny slope (97 g kg – 1). At the shady slope the share of organic carbon decreases from the bottom to the edge of the sinkhole (Fig. 11), and a slight increase is evident on the sunny slope. In VP, the mean values ​​on the slopes and the trends of these shares on the slopes in relation to VIP have the opposite relationship (Fig. 12). Similar relatios and trends are shown by the share of total nitrogen (Fig. 13), except at the bottom of the shady slope in VIP. Here, the share of Ntot is relatively low, and the share of Corg is relatively high, so only in this part within both transects does C/N differ significantly from the remaining parts of the transects (Fig. 14). In conclusion, the soil physiography of deep karst sinkholes is strongly influenced by the nature of the rocks in terms of dolomiticity. The soil above the dolomite and dolomitic limestones is marked by carbonates. In deep sinkholes in solid limestone massifs, characteristic trends of soil pH and the content of organic carbon and total nitrogen can be expected on their shady slopes due to a very pronounced hydrothermal and bioclimatic trend. Analogous trends with characteristic gradients are absent on the sunny slopes of such sinkholes, which corresponds to the absence of a recognizable vegetation sequence.