We studied water uptake variability at the plant scale using a three‐dimensional detailed model. Specifically, we investigated the sensitivity of the R‐SWMS model under different plant collar conditions by comparing computed water fluxes, flow variability, and soil water distributions for different case scenarios and different parameterizations. The relative radial root conductivity and soil hydraulic conductivity were shown to control the plant water extraction distribution. Highly conductive soils promote water uptake but at the same time decrease the variability of the soil water content. A large radial root conductivity increases the amount of water extracted by the root and generates very heterogeneous water extraction profiles. Increasing the xylem conductivity has less impact because the xylem is generally the most conductive part of the system. It was also determined that, due to the different magnitudes of soil and root conductivities, similar one‐dimensional sink‐term profiles can result in very different water content and flux distributions at the plant scale. Furthermore, an analysis based on soil texture showed that the ability of a soil to sustain high plant transpiration demand cannot be predicted a priori from the soil hydraulic properties only, as it depends on the evaporative demand and on the three‐dimensional distributions of the soil/root conductivity ratio and soil capacity, which continuously evolve with time. Combining soil and root hydraulic properties led to very complex one‐dimensional sink functions that are quite different from the simple reduction functions usually found in the literature. The R‐SWMS model could be used to develop more realistic one‐dimensional reduction functions.

This review focuses on more recent findings on the diapause in Monogonont rotifers, since the major reviews by Pourriot

Sexual reproduction in cyclically parthenogenetic rotifers results in the production of diapausing, fertilized (resting) eggs, which can survive for decades in sediment egg banks. Stem females hatching from these eggs can differ from genetically identical ones produced in subsequent parthenogenetic generations. Differences involve the inhibition of sexual reproduction, which may persist for many parthenogenetic generations; reduced morphology (apterous Polyarthra, shorter-spined Brachionus); and larger stores of lipid. These features of stem females may facilitate colonization by favoring population growth via female parthenogenesis and by decreasing food requirements for survival and reproduction. Fertilized eggs in dried sediments probably hatch soon after being flooded by rising water levels. Eggs in permanently submerged sediments may be in environments that inhibit hatching (e.g., darkness, low water temperature, low dissolved oxygen) and hatch only when brought to the sediment surface or resuspended into the water column by currents or bioturbation. Laboratory experiments show that the hatching of diapausing, fertilized eggs can require light and temperatures suitable for population development or specific changes in temperature consistent with a new growing season. The limited data that exist on their emergence from fertilized eggs in natural systems come from sediment traps, from the occurrence in the water column of apterous Polyarthra or empty egg shells, and from calculations of negative mortality rates of planktonic populations. Fertilized eggs often hatch at the beginning of the growth season but may continue to hatch intermittently thereafter. The extremely high genotypic diversity of some natural rotifer populations indicates extensive hatching of stem females from the sediment egg bank.

Summary 1.In monogonont rotifers parthenogenetic reproduction allows population growth, and mictic (sexual) reproduction leads to the production of diapausing eggs. When amictic females are exposed to a mixis stimulus, they produce mictic daughters, whose eggs develop into males or, if fertilized, into diapausing eggs. Experiments showed that mictic offspring production is initiated by crowding in females of angularis , E. senta and R. frontalis , the propensity of amictic females to respond to crowding by producing mictic female offspring is low in the stem female hatching from a diapausing egg, but then increases after some generations. In many cases, only few mictic offspring are produced by crowded females of the second to the fifth generation, but the maximal response occurs only in later generations. Delayed sexual reproduction in early generations from the resting egg may be advantageous, because it first favours rapid population growth and later on maximizes resting egg production. However, it may be disadvantageous, if unpredictable environmental variation causes a population decline when sexual reproduction is still suppressed. 3. The extent to which sexual reproduction is delayed varies among and within species. When strains from populations in temporary and permanent habitats were compared, sexual reproduction was significantly delayed in strains from temporary habitats in all species, whereas in B. calyciflorus and R. frontalis mixis was not significantly delayed in strains from permanent habitats. In E. senta mixis was significantly delayed in clones from both habitat types. 4. Within all strains there was significant variation among clones in the propensity to produce mictic offspring, the extent to which sexual reproduction was delayed in the first generations after the stem female hatched, or both.

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