Gum arabic production in Sudan has developed over the years in a well-established traditional bush-fallow system in which
the gum tree (Acacia senegal) is rotated with annual crops. Following the Sahel drought, the gum area has suffered from deforestation and gum production
has declined. Several programs have been developed to stimulate gum production; however, many original adopters have disadopted
gum production and the bush-fallow system. In this paper we apply a logit model to study the decision-making behavior of farmers
in west Sudan and to identify the socio-economic factors influencing disadoption of gum production and gum agroforestry system.
Variables that measure farmer’s wealth were found significant in explaining the disadoption behavior. Off-farm work was also
found to positively influence the disadoption decision. Results show that a higher level of income from annual crops decreases
the probability of disadoption, which suggests that annual crops and gum production do not compete but rather complement each
other within the farm household economy. Therefore, policy measures aiming to boost the production of annual crops in the
region might reduce seasonal labor migration and accordingly stimulate gum production.
The combined effect of drought and light on different physiological and biochemical traits was assessed in cork oak (Quercus suber L.) seedlings grown under two levels of light availability and submitted to a long-standing drought. Watering was withdrawn after germination and seedlings were allowed to dry to a water content of ca. 50% of field capacity. At this point, water-stressed seedlings were grown under moderate drought and two light regimes: high light (HL—50%) and low light (LL—2%). Soil water in control plants was kept close to field capacity (90–100%) for both light environments. Water-relations parameters derived from P–V curves, gas exchange and water status at predawn (Ψpd) were evaluated at twice during the experiment. Nitrogen and chlorophyll contents were determined in the same leaves used for the gas exchange measurements. In addition, maximum rate of carboxylation (Vcmax) and electronic transport (Jmax) were derived from A–Ci curves in well-watered seedlings.
The variation on moisture availability during the experiment was the same under both light environments. In control plants, Ψpd was over −0.3 MPa at the two harvests, while stressed seedlings decreased to −0.9 MPa, with no differences between light treatments. Water stress decreased osmotic potentials at full (Ψπ100) and zero turgor (Ψπ0). The regressions between both potentials and Ψpd showed a higher intercept in shade grown seedlings. This fact will point out the higher osmoregulation capacity in sun seedlings whatever water availability.
Nitrogen investment on a per leaf mass (Nmass), chlorophyll content (Chlmass) and SLA tended to show a typical pattern of sun-shade acclimation. Thus, the three parameters increased with shade. Only for Nmass there was a significant effect of watering, since water stress increased Nmass.
LL plants showed a lower photosynthetic capacity in terms of maximum net photosynthesis at saturating light (Amax), which was related to a decrease in Vcmax and Jmax. Both parameters varied with specific leaf area (SLA) in a similar way. The low-light environment brought about a higher nitrogen investment in chlorophyll, while under high-light environment the investment was higher in carboxylation (Vcmax) and electronic transport (Fmax).
Stomatal conductance to water vapour (gwv) and Amax were lower in low-light seedlings independently of watering. In addition, there was a trend to keep higher intrinsic water use efficiency (IWUE) under high light environment. The increase of IWUE under water stress was higher in HL seedlings. This was as consequence of the steeper decline in gwv as Ψpd decreased. The decrease of Amax with Ψpd occurred in a similar way in LL and HL seedlings. Thus, the HL seedlings tended to sustain a higher ability to increase IWUE than LL seedlings when they were submitted to the same water stress. 相似文献
Drought and heat are major abiotic stresses that significantly reduce crop yield and seed quality. In this study, we examined the impact of heat, drought and combined effect of heat and drought stress imposed during the grain filling stage in 18 US spring barley varieties. These impacts were assessed based on dry biomass, seed yield and six important malting quality traits, namely, beta-glucan, free amino nitrogen, soluble protein, refractive index, diastatic power and alpha-amylase activity. Singly applied heat or drought stress evoked a diverse set of responses among these varieties with respect to biomass, seed yield and malt quality traits suggesting these varieties can be exploited for enhancing barley production based on local conditions. Majority of the tested varieties performed poorly with reference to seed yield when the stresses were applied in combination, suggesting a lack of genetic diversity in the currently grown spring barley varieties to overcome co-occurring episodic drought and heat regimes, especially during heading stages. In the wake of global climate change, enhancing adaptive capacity of barley varieties by introducing novel germplasm into breeding programs or via new technologies is vital to sustain US barley production and meet the demands of the rapidly growing brewing industry. 相似文献
Winter rye (Secale cereale L.) will be especially affected by drought induced yield losses in Central and Eastern Europe in the future because it is predominantly cultivated on low-fertile soils with a poor water-holding capacity. In order to examine the performance of winter rye under different drought conditions, field experiments were carried out during the years 2011, 2012, and 2013 near Braunschweig, Germany. Two sets of genotypes were tested under severe, mild, pre-anthesis, and post-anthesis drought stress in rain-out shelters as well as under rainfed and well-watered conditions. The grain, straw, and total above ground biomass yields, harvest index, grain yield components, leaf area index (LAI), and phenological characteristics were examined, as well as phenotypic correlations between grain yield and further characteristics. Drought induced grain yield reduction ranged from 14 to 57%, while straw yield and harvest index were lesser affected by drought than the grain yield. Under drought conditions, fully ripe was reached up to twelve days earlier than under non water-limited conditions. Pre-anthesis drought mainly reduced spikes m−2 and kernels spike−1 while drought during grain filling reduced the 1000-kernel weight (TKW) only. The grain yield was positively associated with straw yield, spikes m−2, and kernels spike−1 under water limited conditions while the TWK was only positively associated with grain yield under drought during grain filling. Consequently, high pre-anthesis biomass as well as high numbers of spikes m−2 and kernels spike−1 are especially important for obtaining high grain yields under water-limited conditions. Focusing on these traits is, therefore, recommendable for developing drought tolerant rye genotypes. 相似文献