Savanna vegetation is characterized by tree-grass co-existence that can experience intense water limitation, yet the water relations of these savanna plants are poorly understood. We examined the water sources for trees and grasses in different seasons and investigated the importance of hydraulic redistribution in three tree species inhabiting a semi-arid savanna in South Africa. We used natural variation in H and O stable isotope composition of source waters to identify the principal water sources for these plants. We conducted an experiment by labelling deep-soil (2.5-m depth) with a deuterium tracer. Seasonal differences in the stable isotope composition of water in trees and grasses indicated that there was water-source use partitioning as well as overlap. Trees and grasses used water from the topsoil after rainfall indicating overlap of water-source use. All tree species shifted to groundwater or subsoil water use when there was no water in the topsoil indicating partitioning of water use. Grasses always used water from the topsoil. The seasonal changes in water-source use by trees and grasses indicated possible shifts in tree-grass interactions during different periods of the year. The tracer experiment confirmed hydraulic redistribution in all the three tree species and water transfer to grasses via the topsoil. However, this occurred only in the dry season. Our observations and experimental results indicate the potential for facilitation effects by trees to their understory grasses and show that dry season hydraulic redistribution from trees to grasses could be an important facilitative mechanism maintaining tree-grass co-existence in savannas.

A key question in savanna ecology is how trees and grasses coexist under N limitation. We used N stable isotopes and N content to study N source partitioning across seasons from trees and associated grasses in a semi-arid savanna. We also used (15)N tracer additions to investigate possible redistribution of N by trees to grasses. Foliar stable N isotope ratio (δ(15)N) values were consistent with trees and grasses using mycorrhiza-supplied N in all seasons except in the wet season when they switched to microbially fixed N. The dependence of trees and grasses on mineralized soil N seemed highly unlikely based on seasonal variation in mineralization rates in the Kruger Park region. Remarkably, foliar δ(15)N values were similar for all three tree species differing in the potential for N fixation through nodulation. The tracer experiment showed that N was redistributed by trees to understory grasses in all seasons. Our results suggest that the redistribution of N from trees to grasses and uptake of N was independent of water redistribution. Although there is overlap of N sources between trees and grasses, dependence on biological sources of N coupled with redistribution of subsoil N by trees may contribute to the coexistence of trees and grasses in semi-arid savannas.

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Seasonality poses significant nutritional constraints for ungulates. Consequently, most ungulates time their energy‐demanding events like calving and lactation to the availability of abundant and high‐quality nutritional resources. We investigated the reproductive phenology of blackbuck, Antilope cervicapra, in relation to resource seasonality, in a semi‐arid grassland in western India. We examined whether the body condition of females, forage abundance and forage quality influenced the timing of blackbuck reproduction. We also used a conceptual model to explore whether blackbuck use behavioural adaptations in maternal care as an adaptive strategy to buffer the high nutritional demands of lactation. Blackbuck showed biannual calving, which occurred before (pre‐monsoon) and after the rains (post‐monsoon). We found statistically significant relationships, albeit small effect sizes, of body condition, forage abundance (biomass) and moisture content of grasses on the proportion of lactating females. The biannual reproductive phenology seems more complex than a simple relationship of reproduction with body condition and optimal nutrition supply. In the conceptual model based on our data, we propose that blackbuck females shortened their lactation time and weaned their calves sooner during the pre‐monsoon calving to coincide with a period of optimal food quality, thus, ensuring sufficient nutrition for both weanlings and allowing the females to regain body reserves, whereas, resource availability during the post‐monsoon calving likely allowed females to invest in longer lactation, weaning the calves later, as compared to the pre‐monsoon calving season. Thereby, blackbuck may be maintaining biannual calving and thus increase their lifetime reproductive output.

Diabetes mellitus is a disease that is increasing globally and is a group of metabolic disorder, characterized by polyuria, polyphagia and polydypsia. By maintaining glycemic index levels in individuals diet aids in prevention of diabetes. Rice, millets and legumes are considered to be one of the staple food and play a vital role in human diet. In our study the glycemic index of varieties of rice, millets and legumes were determined in-vitro. Consumption of foods with high glycemic index is hypothesized to contribute to insulin resistance, which is associated with increased risk of diabetes mellitus, obesity and cardiovascular disease. It was seen that the legumes possess low glycemic index with comparison to rice and millets. Hence, it can be concluded that legumes are particularly good for preventing and managing diabetes.