No abstract

Re-introduction and translocation are conservation strategies often employed to circumvent declining wild orchid populations but their efficacy as conservation strategies is widely debated. The aim of this study was to investigate the long-term efficacy of re-introduction and translocation strategies for an endangered orchid as its climate changed. Vital rates of the wild, re-introduced and translocated populations of an endangered terrestrial orchid Caladenia amoena were compared from 2008 to 2019. Emergence and flowering declined at significantly faster rates in the translocated and re-introduced populations than in the wild population. Emergence and flowering declined as mean maximum temperatures rose, whereas flowering increased with rainfall. Both emergence and flowering were positively correlated with the length of the growing period, which decreased by >33% during the study. The relevant orchid mycorrhizal fungi (OMF) (Serendipita sp.) were more abundant in soil at the wild population than at the translocated or re-introduced populations. However, the limited soil sampling used to minimise disturbance may not have detected true fungal heterogeneity. This study suggests that translocation and re-introduction may not be effective long-term solutions for C. amoena. Reduction in above-ground growing period length was probably the over-riding influence in the decline of all populations. Greater OMF abundance in the soil may be the critical factor that renders the wild population more able to withstand the influences of climate change. Future research should consider methods to reduce the impacts of increased temperature and reduced rainfall on threatened orchid taxa.

Context. Maximising seed germination and seedling development is critical for conservation of endangered plants around the world. Orchidaceae is one of the most threatened plant families and can be one of the most difficult to propagate ex situ. Three critical, but potentially limiting, factors are important for orchid germination, namely, conducive conditions, 'ready-to-germinate' seed and effective mycorrhizal fungi. Aims. Our aim was to improve poor germination in vitro of a recalcitrant Australian endangered orchid, Caladenia robinsonii, and to predict the potential impacts of climate change on this species. Methods. Three experiments were conducted to optimise germination in C. robinsonii, with a focus on temperature. In Experiment 1, on the basis of meteorological data, three constant temperatures (15°C, 20°C and 27°C) were tested. In Experiment 2, the optimal constant temperature was compared with diurnally varying temperatures of 22°C/18°C (12/12 h), with and without warm stratification at 30°C/27°C (12/12 h) for 1 week. In Experiment 3, the same diurnally varying temperature and warm stratification were tested using multiple orchid mycorrhizal fungal isolates cultured from wild and re-introduced populations of C. robinsonii. Key results. Without warm stratification, germination was greatest at 20°C (21%), but only 4% of seedlings developed to the green-leaf stage, whereas fungal growth was greatest at 27°C. Stratification increased germination (79%) and development to the green-leaf stage (47%), but more so with subsequent incubation under constant 20°C than diurnal 22°C/18°C. Fungal isolate affected total germination (53-69%) and development to the green-leaf stage (26-41%); isolates from the wild population were less effective than were those from re-introductions. Conclusions. Warm stratification and specific seasonal temperatures significantly improved germination, both factors being typical of seeds with physiological dormancy. Implications. Mimicking in situ conditions can provide a strong basis for ex situ germination strategies and predicting future outcomes. Winter-spring flowering orchid seedlings are commonly observed in autumn, and warm stratification should be considered for improving germination of similar orchid species. However, future climate warming may reduce in situ seedling recruitment.