Experiments were conducted to study the effect of time of planting on the performance of Chinese water chestnut in the Mekong Delta in Vietnam over a single investigation. Plants of a local clone were planted in early January, March, May, July, September, or November and grown for four months. During the experiments, the photoperiod ranged from 11.2 to 12.6 h. The average daily mean temperature across the different cropping periods ranged from 27.70C to 29.10C. Information was collected on chlorophyll fluorescence, plant growth, and yield. Chlorophyll fluorescence (Fv/Fm) was greater than 0.7 in all the treatments (non-stressed), except for the first time of planting and at the end of growing. Corm yield was higher with a planting in May (525 g/plant), November (440 g/plant), and March (325 g/plant), intermediate with a planting in July (196 g/plant), and lower with a planting in January (116 g/plant) and September (55 g/plant). There were strong correlations between yield and the number of stems/plant (r = 0.84), and between yield and stem weight (r = 0.84). These results indicate that acceptable commercial yields can be achieved with water chestnut planted in May in this area.

Trabajo presentado en el International Conference on Integrative Plant Physiology, celebrado en Sitges (Espana), del 27 al 29 de octubre de 2019

The Chinese water pine Glyptostrobus pensilis is the sole surviving species of the genus Glyptostrobus. It is endemic to southern China, central Vietnam, and eastern Laos, and today it is nearly extinct in the wild. Forest community characteristics and population structure of G. pensilis in China have remained unknown up to now. We investigated six swamp forest stands and analyzed their forest community characteristics (i.e. vertical stratification, species composition, and diversity) and population structure, including the frequency distribution of DBH (diameter at breast height) and age-classes as found in Fujian Province, southeastern China. The vertical stratifications of all the forest stands were rather simple. The remaining wild specimens ranged from roughly 15 to some 357 years for an average of ca. 85 years, with only a few individuals less than 20 years old. Compared with the stands and populations of G. pensilis in Vietnam, the taxonomic compositions of the stands in the two regions were different, except for the dominant species-G. pensilis. The Shannon-Wiener index showed the overstory of each stand had much lower diversity (0.26 on average) in Fujian Province than that (1.97 on average) in Vietnam, whereas the diversity indices were about the same (around 2.41) for the understories in the two regions. Furthermore, we discovered 18 G. pensilis seedlings at the study sites in Fujian Province. This discovery demonstrates that G. pensilis regeneration is extremely poor and its populations are declining, although these populations are relatively healthier than those in Vietnam. Copyright (C) 2019 Kunming Institute of Botany, Chinese Academy of Sciences. Publishing services by Elsevier B.V.

Using eco‐physiological parameters, a quick assessment of the invasiveness of non‐native plant species was conducted in Tram Chim National Park, a Ramsar site that is located in the Mekong River Delta region of Vietnam. An investigation of non‐native species and a vegetation analysis were carried out along 25 line transects and in 50 quadrats by using the Braun–Blanquet method. The researchers identified 84 non‐native plant species but only 31 species were naturalized in the wetland ecosystems. Twenty of those 31 species with a high importance value index were screened by using a parameter that was obtained from chlorophyll a fluorescence measurement, the performance index. Five species were identified as invasive and five others were predicted to be potentially invasive. The first group of five species were: M imosa pigra, P anicum repens, E ichhornia crassipes, S alvinia cucullata and L eersia hexandra, which already had been confirmed as important weeds in the national park by previous studies. From the second group, two species ( L udwigia hyssopifolia and S accharum spontaneum) already are becoming prominent species in some locations. The three remaining species ( M onochoria hastata, I sachne globosa and M arsilea quadrifolia) are likely to become invasive in the future.

Comparative physiological attributes, obtained by chlorophyll fluorescence and gas exchange techniques, of restricted Dipterocarpus cf. condorensis and widespread Shorea roxburghii species that are actually co-located in Ta Kou Nature Reserve - Binh Thuan Province, provided essential information for understanding rarity of D. condorensis. The narrowly endemic D. condorensis had similar photosynthetic performance to the locally abundant S. roxburghii in more common habitats in which ground water tables are deep (>20m), but had significantly higher photosynthetic activities in its specific habitat, where the ground water level is shallow (<10m). These differences are probably the consequence of evolutionary trade-offs, and represent specializations of the endemic D. condorensis which is only successful in habitat where the ground water is accessible. However, while adaptive in this habitat, these traits may reduce success in other more common habitats in this region.

Causes for rarity in plants are poorly understood. Graptophyllum reticulatum is an endangered endemic species, and it has three close relatives with different conservation status: the vulnerable G. ilicifolium , the rare G. excelsum , and the common G. spinigerum . Applied to the chlorophyll a fluorescence transient of leaves, the JIP test provides a Performance Index (PI) which quantifies the main steps in photosystem II (PSII) photochemistry including light energy absorption, excitation energy trapping, and conversion of excitation energy into electron flow. The PI is calculated from three components which depend on the reaction center density, the trapping efficiency, and the electron transport efficiency. PI was measured in the natural habitats of the four species and under artificially imposed environmental stresses in the glasshouse to determine whether conservation status was related to stress resilience. The results showed that soil type is unlikely to restrict the endangered G. reticulatum , vulnerable G. ilicifolium , or rare G. excelsum because PI was similar in plants grown in diverse soils in the glasshouse. Photoinhibition is likely to restrict the endangered G. reticulatum to shade habitats because PI was significantly reduced when plants were exposed to more than 15% ambient light in controlled experiments. Water availability may determine the location and distribution of the vulnerable G. ilicifolium and common G. spinigerum because PI was reduced more than 60% when plants were exposed to water stress. While the characteristics of their natural habitats correspond to and explain the physiological responses, there was no obvious relationship between conservation status and environmental resilience. PI can be used to monitor vigor and health of populations of plants in the natural habitat. In cultivation experiments PI responds to key environmental variables that affect the distribution of species with conservation significance.