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Aims: Assuming the saturated, θs, and residual θr volumetric water contents of a seed as known inputs, we present a methodology to determine the hydraulic properties of a seed: α, n parameters and hydraulic conductivity Ks. Methods: The seed is considered as a porous material in which water flow is governed with the same hydraulic properties defined for soils. Using the HYDRUS-2D software, the hydraulic properties of a seed were estimated from the inverse analysis of several cumulative seed imbibition curves measured at different seed water potentials, h. The optimum number of h was evaluated on synthetic seeds. The theoretical analysis was validated in laboratory experiments on barley, wheat and vetch seeds, where imbibition curves were measured with germination tests at seven levels of h (from 0 to -2.50 MPa). Results: The theoretical analysis showed that accurate estimates of α, n and Ks can be obtained if the most negative h-values are included in the optimization. The sensitivity analysis showed that the method allows obtaining a unique solution of α, n and Ks. The optimization error on the theoretical α, n and Ks was less than 1%. A satisfactory validation was also obtained on the experimental seed imbibition curves, with robust fits between the measured and optimized data. A unique solution of α, n and Ks was also obtained in all cases. Conclusions: A new method to determine the hydraulic properties of a seed is presented. This methodology could be used in different areas involving seed imbibition and also to simulate seed imbibition in different scenarios. [ABSTRACT FROM AUTHOR]

Background and aims: Germination as a function of soil water potential (h) is modelled using polyethylene glycol (PEG). But, PEG would not consider soil properties. Our objective is to show the limitations of PEG to model germination in real soils. Using a new device, the tension germinator (TG), we show the interaction between soil type, h and seed characteristics on seed germination.TG (A Mariotte reservoir that supplies water at constant h to a porous substrate on which seeds are deposited). Barley (Hordeum vulgare L.) and vetch (Vicia sativa L.) seeds were placed on TG with loam (TG-loam) and sand (TG-sand), and h of 0, -0.002, -0.006 MPa. Then, the imbibition curves were monitored. PEG experiments (0 to -2.5 MPa) were performed to estimate the critical h, hPEG, or h from which the imbibition curve decreases compared with that at 0 MPa. PEG curves for 0 > h > -0.01 MPa were compared with TG.PEG and TG curves were not different at 0 MPa. hPEG for barley and vetch was within [0, -0.01] MPa. While no differences were observed between PEG at [0, -0.01] MPa and TG-loam curves, TG-sand curves at -0.002 and -0.006 MPa were different to those of PEG. Conversely to PEG at -0.01 MPa, no imbibition was observed in TG-sand (-0.006 MPa). A negligible influence of h in TG-loam was observed.PEG is not adequate to describe seed germination in soil. But the TG allows monitoring seed germination in real soils and controlled h.Methods: Germination as a function of soil water potential (h) is modelled using polyethylene glycol (PEG). But, PEG would not consider soil properties. Our objective is to show the limitations of PEG to model germination in real soils. Using a new device, the tension germinator (TG), we show the interaction between soil type, h and seed characteristics on seed germination.TG (A Mariotte reservoir that supplies water at constant h to a porous substrate on which seeds are deposited). Barley (Hordeum vulgare L.) and vetch (Vicia sativa L.) seeds were placed on TG with loam (TG-loam) and sand (TG-sand), and h of 0, -0.002, -0.006 MPa. Then, the imbibition curves were monitored. PEG experiments (0 to -2.5 MPa) were performed to estimate the critical h, hPEG, or h from which the imbibition curve decreases compared with that at 0 MPa. PEG curves for 0 > h > -0.01 MPa were compared with TG.PEG and TG curves were not different at 0 MPa. hPEG for barley and vetch was within [0, -0.01] MPa. While no differences were observed between PEG at [0, -0.01] MPa and TG-loam curves, TG-sand curves at -0.002 and -0.006 MPa were different to those of PEG. Conversely to PEG at -0.01 MPa, no imbibition was observed in TG-sand (-0.006 MPa). A negligible influence of h in TG-loam was observed.PEG is not adequate to describe seed germination in soil. But the TG allows monitoring seed germination in real soils and controlled h.Results: Germination as a function of soil water potential (h) is modelled using polyethylene glycol (PEG). But, PEG would not consider soil properties. Our objective is to show the limitations of PEG to model germination in real soils. Using a new device, the tension germinator (TG), we show the interaction between soil type, h and seed characteristics on seed germination.TG (A Mariotte reservoir that supplies water at constant h to a porous substrate on which seeds are deposited). Barley (Hordeum vulgare L.) and vetch (Vicia sativa L.) seeds were placed on TG with loam (TG-loam) and sand (TG-sand), and h of 0, -0.002, -0.006 MPa. Then, the imbibition curves were monitored. PEG experiments (0 to -2.5 MPa) were performed to estimate the critical h, hPEG, or h from which the imbibition curve decreases compared with that at 0 MPa. PEG curves for 0 > h > -0.01 MPa were compared with TG.PEG and TG curves were not different at 0 MPa. hPEG for barley and vetch was within [0, -0.01] MPa. While no differences were observed between PEG at [0, -0.01] MPa and TG-loam curves, TG-sand curves at -0.002 and -0.006 MPa were different to those of PEG. Conversely to PEG at -0.01 MPa, no imbibition was observed in TG-sand (-0.006 MPa). A negligible influence of h in TG-loam was observed.PEG is not adequate to describe seed germination in soil. But the TG allows monitoring seed germination in real soils and controlled h.Conclusions: Germination as a function of soil water potential (h) is modelled using polyethylene glycol (PEG). But, PEG would not consider soil properties. Our objective is to show the limitations of PEG to model germination in real soils. Using a new device, the tension germinator (TG), we show the interaction between soil type, h and seed characteristics on seed germination.TG (A Mariotte reservoir that supplies water at constant h to a porous substrate on which seeds are deposited). Barley (Hordeum vulgare L.) and vetch (Vicia sativa L.) seeds were placed on TG with loam (TG-loam) and sand (TG-sand), and h of 0, -0.002, -0.006 MPa. Then, the imbibition curves were monitored. PEG experiments (0 to -2.5 MPa) were performed to estimate the critical h, hPEG, or h from which the imbibition curve decreases compared with that at 0 MPa. PEG curves for 0 > h > -0.01 MPa were compared with TG.PEG and TG curves were not different at 0 MPa. hPEG for barley and vetch was within [0, -0.01] MPa. While no differences were observed between PEG at [0, -0.01] MPa and TG-loam curves, TG-sand curves at -0.002 and -0.006 MPa were different to those of PEG. Conversely to PEG at -0.01 MPa, no imbibition was observed in TG-sand (-0.006 MPa). A negligible influence of h in TG-loam was observed.PEG is not adequate to describe seed germination in soil. But the TG allows monitoring seed germination in real soils and controlled h. [ABSTRACT FROM AUTHOR]

Water redistribution from bare soil to vegetation patches is a key feature of semi-arid ecosystems, and is responsible for their patchy vegetation patterns. The magnitude of water redistribution depends on the properties of the bare soil (which determine the amount of water run-off) and the capacity of vegetation patches to trap water run-on. We examined the relationships between plant spatial patterns, water infiltration into bare soil, and plant community composition in semi-arid sites with different hydro-physical properties (silty and gypseous soils) in NE Spain. We also studied the effect of two stressors, aridity and grazing, on water infiltration and plant spatial patterns. Our results indicate a negative correlation of bare soil sorptivity (the capacity to absorb water by capillarity) and vegetation aggregation. There was a strong positive correlation between perennial grass cover and the spatial aggregation of vegetation, but aggregation was not associated with positive associations of different plant types. The aggregation of vegetation was positively correlated with species richness and the overall extent of vegetation cover. Grazing reduced water infiltration into silty soils, which are prone to compaction. In contrast, soil crust affected the hydrology of gypseous soils, especially in the most arid sites, where grazing increased infiltration, reducing surface sealing due to breaking of the soil crust. Together, our results suggest that biotic and abiotic factors affect the hydro-physical properties of soils in the semi-arid ecosystems of NE Spain, which is linked to the plant communities through the spatial distribution of plants. [ABSTRACT FROM AUTHOR]