Water Sorption Isotherm Characteristics of Seeds of Six Indigenous Forest Tree Species in Ghana

The relationship between storage temperature, relative humidity and seed water content was investigated for six indigenous forest tree seed species, namely Garcinia kola, Terminalia superba, Terminalia ivorensis, Mansonia altissima, Entandrophragma angolense and Khaya anthotheca in Ghana. Seeds were equilibrated over a series of lithium chloride solutions with relative humidities ranging from 12 to 93% and silica gel with relative humidity of 3% at 20 ºC. Seeds reached equilibrium with different days depending on seed size and structure, ranging from 13 days for E. angolense to 91 days for G. kola. When seeds equilibrated, moisture contents were determined gravimetrically, and values of moisture contents were then plotted against relative humidity to construct moisture sorption isotherms for the species. Seeds of T. superba, T. ivorensis, M. altissima, E. angolense and K. anthotheca, exhibited a sigmoidal relationship between seed water content and relative humidity indicative of three regions of water binding. Contrarily to other reports, the shape of the isotherm curve for G. kola – a desiccation sensitive species – also showed the reversed sigmoid pattern similar to isotherm curves of orthodox species rather than the monotonic shape. The isotherms showed that seed moisture content increased with increasing relative humidity. Seed samples of G. kola, placed at all relative humidities chambers, lost water(desorption) as the initial water content of 58% was very high and, therefore, possessed a higher water potential than the environments. Seeds of the other species either lost water (desorption) to the relative humidity chambers, or absorbed water from the chambers depending on the relative humidity of the environment they were placed

Membrane chemical stability and seed longevity

Here, we investigate the relationships between the chemical stability of the membrane surface and seed longevity. Dry embryos of long-lived tomato and short-lived onion seeds were labeled with 5-doxyl-stearic acid (5-DS). Temperature-induced loss of the electron spin resonance signal caused by chemical conversion of 5-DS to nonparamagnetic species was used to characterize the membrane surface chemical stability. No difference was found between temperature plots of 5-DS signal intensity in dry onion and tomato below 345 K. Above this temperature, the 5-DS signal remained unchanged in tomato embryos and irreversibly disappeared in onion seeds. The role of the physical state and chemical status of the membrane environment in the chemical stability of membrane surfaces was estimated for model systems containing 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) dried alone or in the presence of trehalose or glucose. Fourier transform infrared spectroscopy was used to follow temperature-induced structural changes in dry POPC. Spin-label technique was used to relate the chemical stability of 5-DS with the dynamic properties of the bilayer and 5-DS motion behavior. In all the models, the decrease in 5-DS signal intensity was always observed above Tm for the membrane surface. The 5-DS signal was irreversibly lost at high temperature when dry POPC was embedded in a glucose matrix. The loss of 5-DS signal was moderate when POPC was dried alone or in the presence of trehalose. Comparison of model and in vivo data shows that the differences in longevity between onion and tomato seeds are caused by differences in the chemical status of the membrane surface rather than the degree of its immobilization

Explore before you restore: Incorporating complex systems thinking in ecosystem restoration

Abstract The global movement for ecosystem restoration has gained momentum in response to the Bonn Challenge (2010) and the UN Decade on Ecosystem Restoration (UNDER, 2021–2030). While several science‐based guidelines exist to aid in achieving successful restoration outcomes, significant variation remains in the outcomes of restoration projects. Some of this disparity can be attributed to unexpected responses of ecosystem components to planned interventions. Given the complex nature of ecosystems, we propose that concepts from Complex Systems Science (CSS) that are linked to non‐linearity, such as regime shifts, ecological resilience and ecological feedbacks, should be employed to help explain this variation in restoration outcomes from an ecological perspective. Our framework, Explore Before You Restore, illustrates how these concepts impact restoration outcomes by influencing degradation and recovery trajectories. Additionally, we propose incorporating CSS concepts into the typical restoration project cycle through a CSS assessment phase and suggest that the need for such assessment is explicitly included in the guidelines to improve restoration outcomes. To facilitate this inclusion and make it workable by practitioners, we describe indicators and methods available for restoration teams to answer key questions that should make up such CSS assessment. In doing so, we identify key outstanding science and policy tasks that are needed to further operationalize CSS assessment in restoration. Synthesis and applications. By illustrating how key Complex Systems Science (CSS) concepts linked to non‐linear threshold behaviour can impact restoration outcomes through influencing recovery trajectories, our framework Explore Before You Restore demonstrates the need to incorporate Complex Systems thinking in ecosystem restoration. We argue that inclusion of CSS assessment into restoration project cycles, and more broadly, into international restoration guidelines, may significantly improve restoration outcomes. </jats:p

Desiccation Tolerance, Germination and Moisture Sorption Isotherm of Garcinia afzelii seeds

The desiccation tolerance of Garcinia afzelii seeds was determined and  sensitive vigour tests for assessing seed deterioration of this species were identified. Matured fruits were harvested in March 2009 from a small  plantation at Ho in the Volta Region of Ghana. Depulped seeds were mixed with moistened sawdust and placed in white cotton sacks and quickly  transported by air to the Seed Conversation Department of the Royal  Botanic Gardens in the United Kingdom where a part of the experiment was carried out. The second season’s seeds was also harvested from the same plantation in April 2010 and used for another part of the studies in Ghana. Seed equilibrium relative humidity and moisture content on receipt in the United Kingdom were 93.3 % and 38.2 % respectively. Seed germination percentage decreased gradually with reduction in seed moisture content until after 25 % moisture content when germination percentage reduced drastically to 43 % at 23 % moisture content. The seeds of Garcinia afzelii are recalcitrant, with ‘critical moisture content’ about 25 %. Seedling dry weight, seed vigour index and speed of germination also decreased as seeds were dried. Electrical conductivity of leachate from seeds increased with desiccation of seeds. Water sorption isotherm curve for the species showed the typical sigmoid shape curve similar to that of orthodox species. Key words: Garcinia afzelii, vigour index, seedling dry weight, electrical conductivity, critical moisture content, moisture sorption isotherm

Germination résponses of Khaya anthotheca seeds to a range of alternating and constant températures provided by the 2-way Grant’s thermogradient plate

Khaya anthotheca seeds were placed in Petri dishes containing a gel of 1% water agar for germination over a period of 30 consecutive days. Petri dishes were arranged 8 units x 8 units on the 2-way Grant’s thermogradient plate (a bi-directional incubator). The goal of the study was to take a more comprehensive look at germination responses of seeds to a broad range of alternating or constant temperatures on the thermogradient plate. The instrument allows for germination testing of seeds over a wide range of single temperature and alternating temperature regimes over a time continuum, given 64 temperature combinations (regimes) (5 to 40°C). Conditions were 40/40°C (day/night temperature) on the high end of the plate and 5/5 ºC on the cool end. Two temperature gradients ranging from 5 to 40°C were used. The first gradient, progressing from left to right on the thermogradient plate in dark, was alternated every 12 hours with the second progressing from front to back of the thermogradient plate with light. The study was repeated twice. Fifteen (15) seeds were used in each replication. The various temperature combinations had significant effect on final germination percentage, mean germination time, time for first germination and rate of germination. Alternating temperatures improved overall germination. The best germination at a constant temperature was at 20/20°C and 30/30°C. The best temperature regimes for seed germination at alternating temperatures were at 5/30°C, 10/30°C,15/30°C, 20/25°C, 20/35°C, 25/15°C, 25/20°C, 25/30°C, 30/20°C, 35/10°C, and 35/15°C.Keywords: Khaya anthotheca, germination testing, thermogradient plate, temperature regimes, germination percentag

Viability loss of neem (Azadirachta indica) seeds associated with membrane phase behaviour

Storage of neem (Azadirachta indica) seeds is difficult because of their sensitivity to chilling stress at moisture contents (MC) 10␘r imbibitional stress below 10␖C. The hypothesis was tested that an elevated gel-to-liquid crystalline phase transition temperature (Tm) of membranes is responsible for this storage behaviour. To this end a spin probe technique, Fourier transform infrared microspectroscopy, and electron microscopy were used. The in situ Tm of hydrated membranes was between 10 °C and 15 °C, coinciding with the critical minimum temperature for germination. During storage, viability of fresh embryos was lost within two weeks at 5 °C, but remained high at 25 °C. The loss of viability coincided with an increased leakage of K from the embryos upon imbibition and with an increased proportion of cells with injured plasma membranes. Freeze–fracture replicas of plasma membranes from chilled, hydrated axes showed lateral phase separation and signs of the inverted hexagonal phase. Dehydrated embryos were sensitive to soaking in water, particularly at low temperatures, but fresh embryos were not. After soaking dry embryos at 5 °C (4 h) plus 1 d of further incubation at 25 °C, the axis cells were structurally disorganized and did not become turgid. In contrast, cells had a healthy appearance and were turgid after soaking at 35 °C. Imbibitional stress was associated with the loss of plasma membrane integrity in a limited number of cells, which expanded during further incubation of the embryos at 25 °C. It is suggested that the injuries brought about by storage or imbibition at sub-optimal temperatures in tropical seeds whose membranes have a high intrinsic Tm (10–15 °C), are caused by gel phase formation

Influence of freezable/non-freezable water and sucrose on the viability of Theobroma cacao somatic embryos following desiccation and freezing

Encapsulated cocoa (Theobroma cacao L.) somatic embryos subjected to 0.08-1.25 M sucrose treatments were analyzed for embryo soluble sugar content, non-freezable water content, moisture level after desiccation and viability after desiccation and freezing. Results indicated that the higher the sucrose concentration in the treatment medium, the greater was the extent of sucrose accumulation in the embryos. Sucrose treatment greatly assisted embryo post-desiccation recovery since only 40% of the control embryos survived desiccation, whereas a survival rate of 60-95% was recorded for embryos exposed to 0.5-1.25 M sucrose. The non-freezable water content of the embryos was estimated at between 0.26 and 0.61 g H2O g(-1)dw depending on the sucrose treatment, and no obvious relationship could be found between the endogenous sucrose level and the amount of non-freezable water in the embryos. Cocoa somatic embryos could withstand the loss of a fraction of their non-freezable water without losing viability following desiccation. Nevertheless, the complete removal of potentially freezable water was not sufficient for most embryos to survive freezing