Eco-physiological studies on desert plants: germination of Halothamnus iraqensis Botsch. seeds under different conditions

With the aim to investigate if the halophyte Halothamnus iraqensis Botsch. can be suitable for re-vegetation and remediation of salt-affected lands, this study evaluated(1) the effects of photoperiod, thermoperiod, storage period and wings' presence on its seed germination, and(2) the ability of its seeds to have successful germination recovery after salt stress. Germination tests in different photoperiods(12 h light/12 h darkness and total darkness) and thermoperiods(15℃/20℃ and 20℃/25℃) were conducted for seeds collected in 2012, 2013, 2014, 2015 and 2016. The seeds collected in 2016 were sown under different salinity levels(0, 100, 200, 400 and 600 m M Na Cl) to assess the salinity tolerance during the germination. Wings' presence highly inhibited seed germination of this species in both photoperiods and thermoperiods under all salinity level treatments. In addition, the germination recovery occurred well when seeds were deprived of their wings. The photoperiod of 12 h light/12 h darkness and the thermoperiod of 15℃/20℃ were the best conditions for seed germination. Germination percentages of H. iraqensis seeds decreased with the increasing storage duration, especially after three years of the collection. In addition, H. iraqensis seeds were able to germinate under different salinity levels, and their germination percentages decreased with increasing salinity levels. H. iraqensis seeds have the ability to recover their germination after alleviating the salt stress, irrespective of photoperiod, highlighting the halophilous character of this species.

Effects of diurnal temperature range on adult size and emergence times from diapausing pupae in Papilio glaucus and R canadensis （Papilionidae）

With recent climate warming trends, both the increase in thermal variance （i.e., diurnal temperature range; DTR） as well as increased mean temperature may impact many different organisms, especially poikilothermic invertebrates. Predictions of insect developmental rates using degree-days （thermal unit accumulations above the developmental base threshold of the insect） are based on daily mean temperatures, regardless of DTR. However, non-linearity and variance in the means and extremes are often ignored. The role of thermal variance （e.g., daily temperature extremes and DTR） was evaluated experimentally for two swallowtail butterfly sister species using a common day/night photoperiod of 18 ： 6 h photo ： scoto-phase and corresponding daytime thermophase and nighttime cryophase periods of 22 ： 22℃ （constant 22℃）, 24 ： 16℃, and 26 ： 10℃（all three treatments had the same daily mean and the same degree-day accumulations）. Although developmental rates ofpost-diapause pupae were largely unaffected for both species, our results show that sizes in P canadensis females （but not males） were smaller in the treatments with more variance （26℃ ： 10℃） compared to constant 22℃. Such potentially significant impacts of size reduction in P canadensis females were not observed in P glaucus males or females under the same series ofthermo-period treatments.