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Seed biology in the annual herbaceous flora of ecologically stressful, seasonally wet habitats remains largely unexplored. Temporal and spatial species turnover between these habitats is often high, yet little is known about how fine-scale habitat variation drives intraspecific variability in seed dormancy depth and seed germination requirements.This study characterised seed dormancy and investigated the germination biology of six closely-related herbaceous annual species of Byblis from northern Australia. We assessed variation in the response of seeds of all species to temperature cues, as well as light and the naturally occurring germination stimulants KAR1 and ethylene. We also examined intraspecific variation in germination response and seed dormancy depth for three widely-distributed species with overlapping distribution occurring in habitats with differing soil thermal and hydrological conditions. Seed germination in all six species was significantly increased by exposure to either KAR1 or ethylene with this effect amplified in two species (B. filifolia and B. rorida) following a period of warm, dry afterripening. Seed dormancy depth and the germination response of seeds to both KAR1 and ethylene was partitioned more strongly between habitats than between species. Populations on shallow (<20 cm soil depth) sandy soils produced less dormant seeds than populations of the same species on deeper sandy soils (40+ cm) or on heavy cracking clays. The upper soil profile of shallow soil habitats was exposed to higher average temperatures, greater diurnal temperature fluctuation and greatly reduced moisture persistence compared to deeper soils. Fine-scale differences in the thermal and hydrological conditions of seasonally wet habitats appear to be strong drivers of dormancy depth in seeds of tropical Byblis.Widely-distributed species exhibit high levels of plasticity in seed dormancy depth and germination response between different habitats, with similar responses observed for sympatric species. In order to fully understand species turnover in tropical ephemerals, future studies should examine phenotypic plasticity and the rate of local adaptation of seed traits in greater detail.

Relevance. The article is devoted to the topical problem of studying the influence of soil conditions and the relief of an agricultural landscape on the yield of clover-timothy herbage on drained soils, knowledge of which makes it possible to optimize the production process of crops in the mode of adaptive landscape farming.Methods and results. The studies were carried out in 1998–2020 at the test site of the All-Russian Research Institute of Reclaimed Lands (VNIIMZ) – a branch of the Federal Research Centre Soil Science Institute named after V.V. Dokuchaev (Tver region), located within the end-moraine hill. The purpose of the research is to study the influence of soil conditions and the relief of the agricultural landscape on the yield of clover-timothy herbage of 1 year of use. Grass productivity monitoring was carried out on a transect – a field crossing the main microlandscape positions (relief elements) and elementary soil combinations of the agrolandscape. Crop productivity and other parameters of the vegetation and soil cover on the transect were taken into account on 30 systematically located plots, within which there are 4 replicates, 23 m2 in area, spaced 10 m from each other.Results of studies on productivity were processed by correlation and multivariate analysis of variance. Studies have shown that the relief and soil features of the agricultural landscape have almost the same effect on the crop yield. Each of these factors, on average, determined 18–16% of the spatial variability in productivity. About 2/3 of the variability in the yield of herbs depends on factors that are difficult to take into account. It was found that the degree of influence of the relief and soils on the yield of grasses is not constant over time and ranges from 2 to 33%. In the time series of observations, periods of synchronous and asynchronous fluctuations in the degrees of influence of soil and relief on the yield were distinguished. Synchronization of temporal fluctuations in the degrees of impact on the productivity of grasses of different elements of the landscape occurs with a decrease in the amount of precipitation and active temperatures. On the basis of the revealed patterns, it is possible to develop measures to adapt technologies for growing perennial grasses to the natural conditions of farms in the mode of adaptive landscape fodder production.

Yield monitoring of a five-component grass stand in a breeding field within a moraine hill was carried out in 2003- 2018 in order to find patterns of its dynamics in the agrolandscape. The grass was used in the conditions of the Tver region without fertilizers in a single-cut mode in a field crossing all microlandscape positions of the hill (transcct) and divided into 30 plots. Annual data on productivity of grass mixture on each plot are presented in the form of: 1) absolute yield (specific hay yield); 2) relative yield (expressed as a percentage to maximum yield on a transect in a definite year). It was revealed that the yield of grasses is maximum in the central parts (≈ 6.5 t/ha) and minimal in the upper parts of the hillsides and at the top (≈ 5.2 t/ha). Time variability of yield depends on the geological structure of the soils ‒ increases with the transition from powerful binomials (≈ 40 %) to low-powerful ones (≈ 65 %). Correlation analysis showed that the transition to relative units (% of the yield) can significantly reduce the impact of climate on data variability. The maximum coincidence of temporal dynamics of different yield indicators is noted at the upper elevations ‒ here climatic conditions do not have a significant impact on the yield, as on slopes. Changes in the sum of the active temperatures have the greatest influence on the yield. Average indicators of correlation coefficients of yield and temperature sums are negative on the plots of soil distribution on powerful and medium-powerful binomials and positive on soils of low-powerful binomials. There has been found an inversely proportional dependence of the absolute yield of grasses on the sums of active temperatures in the pre-cut periods and in September and directly proportional in the second half of summer. Increasing the sum of temperatures contributes to a decrease in relative yields on sandy soils and optimizes the production process on loams and light loams. Dispersion analysis has shown that the main influence of temperatures on absolute yield is exerted by soil hydromorphism. The degree of impact of temperatures on relative yield depends on the nature of water exchange in the agrolandscape, the exposure of slopes (energy) and granulometric composition of soils. The results will make it possible to adapt measures for the placement of grass stands, regulation of water and thermal regimes of soils to farm conditions.

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