The article addresses the problem of nature of species which could be reduced to the question: Are species classes (universals) or individuals (particular things)? Reflecting on the discussion between traditionalist (e.g. Kitts and Kitts, Ruse) and proponents of a radical solution (Ghiselin, Hull) - by way of the S-A-I thesis (Species As Individuals) - we concentrate on the third possibility under which species are viewed as a hybrid category such as a ''complex particular,'' ''individualized class'' or ''event-entities'' (Supe, Ruse). My argument centers on an interchangeability of parts, and it concludes that we must distinguish three types of relation between parts and wholes: constructivist, emergent and reproductive. Thanks to this differentiation, I tend to view species as individuals, but not in the usual constructivist or emergent sense. In order to do justice to the individual character of species, a special logico-ontological structure or type-which I propose to call ''reproductive type''-needs to be devised. and Vladimír Havlík
Vegetation and biocrust play crucial roles in dune stability and mobility, and their interaction can lead to bistability, temporal oscillations, and hysteresis. We studied a two-dimensional (2D) mathematical model of vegetation and biogenic crust cover dynamics on sand dunes. Under a certain parameter range, the space-independent version of the model exhibited the bi-stability of an oscillatory state and a steady state, and we studied the 2D dynamics of the model under these parameters. The patterns developed by the 2D model showed a high degree of spatial heterogeneity and complexity depending on the initial conditions and on the state type across the front. The results suggest that spatial heterogeneity and complexity can evolve from the intrinsic dynamics between vegetation and biocrust, even without natural geodiversity and spatiotemporal climate fluctuations. In the real world, these two types of intrinsic and extrinsic heterogeneity processes interact such that it is difficult to distinguish between them.
Rainfall pulses can significantly drive the evolution of the structure and function of semiarid ecosystems, and understanding the mechanisms that underlie the response of semiarid plants to rainfall is the key to understanding the responses of semi-arid ecosystems to global climatic change. We measured sap flow in the branches and stems of shrubs (Caragana korshinskii Kom. and Hippophae rhamnoides Linn.) using sap flow gauges, and studied the response of sap flow density to rainfall pulses using the ''threshold-delay'' model in the Chinese Loess Plateau. The results showed that the sap flow began about 1 h earlier, and increased twofold after rainfall, compared to its pre-rainfall value. The sap flow increased significantly with increasing rainfall classes, then gradually decreased. The response of sap flow was different among rainfall, species, position (branch and stem) during the pulse period, and the interactive effects also differed significantly (P < 0.0001). The response pattern followed the threshold-delay model, with lower rainfall thresholds of 5.2, 5.5 mm and 0.7, 0.8 mm of stem and branch for C. korshinskii and H. rhamnoides, demonstrating the importance of small rainfall events for plant growth and survival in semi-arid regions.
Symmetrical temperature difference also known as the sap flow index (SFI) forms the basis of the Heat Field Deformation sap flow measurement and is simultaneously collected whilst measuring the sap flow. SFI can also be measured by any sap flow method applying internal continuous heating through the additional installation of an axial differential thermocouple equidistantly around a heater. In earlier research on apple trees SFI was found to be an informative parameter for tree physiological studies, namely for assessing the contribution of stem water storage to daily transpiration. The studies presented in this work are based on the comparative monitoring of SFI and diameter in stems of different species (Pseudotsuga menziesii, Picea omorika, Pinus sylvestris) and tree sizes. The ability of SFI to follow the patterns of daily stem water storage use was empirically confirmed by our data. Additionally, as the HFD multipointsensors can measure sap flow at several stem sapwood depths, their use allowed to analyze the use of stored water in different xylem layers through SFI records. Radial and circumferential monitoring of SFI on large cork oak trees provided insight into the relative magnitude and timing of the contribution of water stored in different sapwood layers or stem sectors to transpiration.
The influence of the size soil aggregates derived from loess, expressed by mean weight diameter of aggregates which build soil samples, on the saturated hydraulic conductivity was presented. It has been found that size of aggregates influenced the amount of large pores in soil samples. The relationship between the saturated hydraulic conductivity and the amount of large pores can be described by function: Ks = 0.356. Exp (6.852 PL). and Príspevok obsahuje výsledky výskumu vplyvu velkosti agregátov pôdy, z ktorých sú vytvorené vzorky pôdy, na hydraulickú vodivost vodou nasýtených vzoriek pôdy. Z výsledkov vyplýva, že velkost agregátov pôdy ovplyvnuje množstvo velkých pórov vo vzorkách pôdy. Závislost medzi hodnotami nasýtenej hydraulickej vodivosti pôdy a množstvom velkých pórov - udaným v percentách objemu všetkých pórov - môže byt vyjadrená exponenciálnou funkciou.