Christoph Reisdorff

The importance of protein in leaf selection of folivorous primates.

Protein limitation has been considered a key factor in hypotheses on the evolution of life history and animal communities, suggesting that animals should prioritize protein in their food choice. This contrasts with the limited support that food selection studies have provided for such a priority in nonhuman primates, particularly for folivores. Here, we suggest that this discrepancy can be resolved if folivores only need to select for high protein leaves when average protein concentration in the habitat is low. To test the prediction, we applied meta‐analyses to analyze published and unpublished results of food selection for protein and fiber concentrations from 24 studies (some with multiple species) of folivorous primates. To counter potential methodological flaws, we differentiated between methods analyzing total nitrogen and soluble protein concentrations. We used a meta‐analysis to test for the effect of protein on food selection by primates and found a significant effect of soluble protein concentrations, but a non‐significant effect for total nitrogen. Furthermore, selection for soluble protein was reinforced in forests where protein was less available. Selection for low fiber content was significant but unrelated to the fiber concentrations in representative leaf samples of a given forest. There was no relationship (either negative or positive) between the concentration of protein and fiber in the food or in representative samples of leaves. Overall our study suggests that protein selection is influenced by the protein availability in the environment, explaining the sometimes contradictory results in previous studies on protein selection. Am. J. Primatol. 79:e22550, 2017.

Nighttime stomatal conductance differs with nutrient availability in two temperate floodplain tree species

Nighttime water flow varies between plant species and is a phenomenon for which the magnitude, purpose and consequences are widely discussed. A potential benefit of nighttime stomata opening may be increased nutrient availability during the night since transpiration affects the mass flow of soil water towards plant roots. We investigated how nitrogen (N) and phosphorus (P) fertilization, and short-term drought affected stomatal conductance of Fraxinus excelsior L. and Ulmus laevis Pallas during the day (gs) and night (gn), and how these factors affected growth for a period of 18 weeks. Both species were found to open their stomata during the night, and gn responded to nutrients and water in a different manner than gs. Under N-deficiency, F. excelsior had higher gn, especially when P was sufficient, and lower pre-dawn leaf water potential (Ψpd), supporting our assumption that nutrient limitation leads to increases in nighttime water uptake. Under P-deficiency, F. excelsior had higher relative root production and, thus, adjusted its biomass allocation under P shortage, while sufficient N but not P contributed to overall higher biomasses. In contrast, U. laevis had higher gn and lower root:shoot ratio under high nutrient (especially N) availability, whereas both sufficient N and P produced higher biomasses. Compared with well-watered trees, the drought treatment did not affect any growth parameter but it resulted in lower gn, minimum stomatal conductance and Ψpd of F. excelsior. For U. laevis, only gs during July was lower when drought-treated. In summary, the responses of gs and gn to nutrients and drought depended on the species and its nutrient uptake strategy, and also the timing of measurement during the growing season. Eutrophication of floodplain forests dominated by F. excelsior and U. laevis may, therefore, considerably change nighttime transpiration rates, leading to ecosystem-level changes in plant-water dynamics. Such changes may have more severe consequences in the future as a higher frequency of drought events is predicted under climate change.

Effects of elevated carbon dioxide and climate change on biomass and nutritive value of Kyasuwa ( Cenchrus pedicellatus Trin.)

Atmospheric carbon dioxide enrichment enhances plant growth and development and may alter the nutritive value of grasses. The objective of this study was to evaluate growth, biomass partitioning and nutritive value of Kyasuwa under combinations of atmospheric CO2 concentrations, watering and fertilization treatments. Plants were grown in two greenhouse chambers; with ambient (aCO2; 400 ppm) and elevated CO2 (eCO2; 950 ppm), two watering and three fertilization regimes. Elevated CO2 reduced stomatal conductance by 40%, root to shoot ratio by 8%, leaf to stem ratio (L:S) by 3%, protein content by 14% and Acid Detergent Lignin (ADL) by 23% with no significant changes in total biomass and C/N ratio however, slight increases in leaf area (2%) and Acid Detergent Fiber (ADF) by 4%. Higher fertilization resulted in increased biomass parameters only in well-watered plants while; a lower C/N ratio was recorded with higher fertilization. The L:S ratio was decreased with fertilization while ADL was increased at higher fertilization in well-watered plants. Interactive effects were recorded for ADF content and shoot height. Future eCO2 will be unfavorable to Kyasuwa growth and biomass production making them less competitive with a reduced nutritive value in drought prone and infertile soils.

Shea ( Vitellaria paradoxa C. F. Gaertn.) at the crossroads: current knowledge and research gaps

Shea (Vitellaria paradoxa C. F. Gaertn.) is arguably socio-economically and environmentally the most important plant species in the semi-arid and arid zones of Africa where it is widely distributed. Apart from the economic gains in international export markets where shea butter is valued for use in luxury cosmetic, pharmaceutical and confectionary industries, locally the fat (butter) is the main cooking oil for over 86 million inhabitants. Research during the past decades has acknowledged the chemical and nutritional composition as well as the ethnobotanical uses of shea which has resulted in its butter being used in a wide array of products. This review summarizes the current knowledge of the morphological and genetic diversity; propagation, initial growth, and management; ecology and population structure; chemical and nutritional composition as well as the socioeconomic and livelihood empowerment potential of shea. Little is known about the fruiting behaviour and the responses of shea to the inevitable changes in climate. We suggest ecophysiological and dendrochronological studies as an option to predict how the domestication of this multipurpose tree species can be sustained even under the prospects of global climate change.

Elevated CO 2 does not offset effects of competition and drought on growth of shea ( Vitellaria paradoxa C.F. Gaertn.) seedlings

The shea tree (Vitellaria paradoxa C. F. Gaertn.) is a major parkland species occurring across Africa from East to West. Its fruits, butter, and further products from shea butter play key roles in the Sustainable Development Goals of poverty eradication, hunger elimination, and gender equity in many African regions. The inter-play of abiotic conditions (e.g. rainfall patterns, drought periods) and biotic interactions (grazing by large herbivores) shape parklands because they influence vital processes like photosynthesis, transpiration and biomass production of common plant species including shea. We measured gas exchange of shea seedlings grown under ambient and elevated atmospheric CO2 (eCO2), with and without competition of the C4 grass Cenchrus pedicellatus, and under different water availabilities in greenhouse chambers. We hypothesized that eCO2 will generally increase seedling growth in shea via increases in photosynthesis. When growing together with C4 grass at low water availability, we expect an improved competitiveness of shea under eCO2, beacuse eCO2 is reported to augment water use efficiency (WUEi) of C3 plants more than C4 plants. Increased CO2 caused a 10% (p < 0.001) increase in maximum light-saturated photosynthesis (Amax), 22% (p < 0.001) increase in WUEi and 13% (p < 0.001) increase in stem mass fraction (SMF) of shea. Grass competition significantly reduced Amax by 9% (p < 0.001), SMF (p < 0.001) by 19%, with a corresponding reduction in all biomass parameters, but also significantly increased the C/N ratio (by 3%, p < 0.001). Interactive effects of eCO2 and competition were recorded for maximum electron transport rate, dark respiration, stomatal conductance, CO2 compensation point and the leaf area ratio. The control of grasses in the early stages of shea development is therefore recommended.