Effects of short light/dark cycles on photosynthetic pathway switching and growth of medicinal Dendrobium officinale in aeroponic cultivation

Dendrobium officinale has high medicinal value but grows slowly in natural environment due to its special CAM photosynthetic pathway.In this study,D.officinale were grown aeroponically with light/dark cycles of 12 h/12 h,4 h/4 h,and 2 h/2 h for 150 d.The photosynthetic electron transfer characteristics,photosynthetic CO_(2) fixation pathways,and accumulations of biomass and soluble polysaccharides in D.officinale leaves were studied.The results showed that the photosynthetic apparatus states of D.officinale in aeroponic cultivation under short light/dark cycles of 4 h/4 h and 2 h/2 h were better than that under 12 h/12 h.The dark net CO_(2) exchange percentages of D.officinale were negative in short light/dark cycles of 4 h/4 h and 2 h/2 h,and the daily net CO_(2) exchange amount and dry/fresh weight increases were doubled compared with those in 12 h/12 h light/dark cycle.High soluble polysaccharides content and the soluble polysaccharides yield of D.officinale were obtained in the shorter light/dark cycle of 2 h/2 h.Therefore,the photosynthetic pathway of D.officinale could be switched from CAM to C3 by short light/dark cycles of 4 h/4 h and 2 h/2 h,and its higher biomass accumulation and soluble polysaccharides yield could be obtained by the shorter light/dark cycle of 2 h/2 h in aeroponic cultivation.

No C_4 Plants Found at the Haibei Alpine Meadow Ecosystem Research Station in Qinghai, China: Evidence from Stable Carbon Isotope Studies

Using the measurement of stable carbon isotopes in leaves as a tool to investigate photosynthetic pathway of 102 plant species grown at an alpine meadow ecosystem, at the foot of the Qilian Mountain, Qinghai, China. The results indicate that the delta C-13 values of plants have a narrow range from -28.24parts per thousand to -24.84parts per thousand, which means that none of the species examined belongs to C-4 and crassulaceous acid metabolism (CAM) photosynthetic pathway and all of these species perform photosynthesis through the C-3 pathway. This is likely due to a long-term adaptation to environments at the alpine meadow ecosystem.

The role of shaded cocoa plantations in the maintenance of epiphytic orchids and their interactions with phorophytes

Aims Habitat loss and fragmentation are the main threats to biodiversity in tropical forests.Agroecosystems such as shaded cocoa plantations(SCP)provide refuge for tropical forest biota.However,it is poorly known whether the interspecific ecological interactions are also maintained in these transformed habitats.We evaluated the diversity,reproductive status and photosynthetic metabolism(CAM or C3)of the epiphytic orchid community,and their interactions with host trees(phorophytes)in SCP compared to tropical rainforest(TRF).Methods In southeastern Mexico,three sites each in TRF and SCP were studied,with four 400 m2 plots established at each site to record all orchids and their phorophytes.We determined the reproductive(adult)or non-reproductive(juvenile)status of each orchid individual in relation to the presence or absence,respectively,of flowers/fruits(or remnants),and assigned the photosynthetic pathway of each orchid species based in literature.We used true diversity and ecological networks approaches to analyze orchid diversity and orchid–phorophyte interactions,respectively.Important Findings In total,607 individuals belonging to 47 orchid species were recorded.Orchid diversity was higher in TRF(19 effective species)than in SCP(11 effective species)and only seven species were shared between the two habitats.CAM orchid species were more frequent in SCP(53%)than in TRF(14%).At the community level the proportion of non-reproductive and reproductive orchid species and the nested structure and specialization level of the TRF orchid–phorophyte network were maintained in SCP.However,only a subset of TRF epiphytic orchids remains in SCP,highlighting the importance of protecting TRF.Despite this difference,shaded agroecosystems such as SCP can maintain some of the diversity and functions of natural forests,since the SCP epiphytic orchid community,mainly composed of CAM species,and its phorophytes constitute a nested interaction network,which would confer robustness to disturbances.

A photosynthesis continuous monitoring system for CAM plants

Diurnal CO_(2) exchanges in crassulacean acid metabolism(CAM)plants are significantly different from those in C3 and C4 plants.The instantaneous short-time CO_(2) exchange of a single leaf measured by commercial portable photosynthesis measuring systems with a small leaf chamber cannot reflect the plant photosynthetic capacity for CAM plants because of the CO_(2) fixation property.Therefore,a photosynthesis continuous monitoring system with two canopy cuvettes was developed for measuring diurnal net CO_(2) exchange rates for CAM plants.To evaluate stability and applicability of the photosynthesis continuous monitoring system,continuous measurement of net CO_(2) exchange rates of plants with different photosynthetic pathways were conducted.An obligate CAM plant(Kalanchoe daigremontiana),four facultative CAM plants(Dendrobium officinale,D.chrysotoxum,D.nobile,and D.primulinum),a C3 plant(Strawberry,Fragaria ananassa),and a C4 plant(Corn,Zea mays)were selected as model plants.K.daigremontiana had a significant CO_(2) absorption during the dark period and its net CO_(2) exchange rates fluctuated around 0μmol/(m^(2)·s)during the photoperiod in a growth chamber.Net CO_(2) exchange rates of F.ananassa and Z.mays in a greenhouse gradually increased after sunrise,reaching a maximum at about 12:00,and then gradually decreased to negative values during the night time.It is interesting to observe that D.officinale in the greenhouse and growth chamber absorbed CO_(2) during both day and night times.The photosynthetic pathways of D.chrysotoxum,D.nobile,and D.primulinum were also well distinguished by this photosynthesis continuous monitoring system.The results showed that the photosynthesis continuous monitoring system is capable for quantitative evaluation of diurnal net CO_(2) exchange characteristics not only in the CAM plants but also in small size C3 and C4 plants with low net photosynthetic rates for long-time and high-accuracy measurements.