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Few studies have evaluated the effect of drought on the morpho‐physiological characteristics of African C4grasses. We investigated how drought affects leaf gas exchange characteristics, biomass partitioning, and water use efficiencies of Enteropogon macrostachyusand Cenchrus ciliaris. The grasses were grown in a controlled environment under optimum conditions, that is, 70% of the maximum water‐holding capacity (WHC) for the first 40 days. Thereafter, half of the columns were maintained under optimum or drought conditions (30% of maximum WHC) for another 20 days. Under optimum conditions, C. ciliarisshowed a significantly higher photosynthetic rate, stomatal conductance, and transpiration rate than E. macrostachyus. Drought decreased the photosynthetic rate, stomatal conductance and transpiration rate only in C. ciliaris. The net photosynthetic rate, stomatal conductance, and leaf transpiration of E. macrostachyusdid not differ significantly under optimum and drought conditions. E. macrostachyusshowed an increase in its water use efficiencies under drought to a greater extent than C. ciliaris. Our results demonstrate that C. ciliarisis more sensitive to drought than E. macrostachyus. The decrease in the intercellular CO2concentration and the increase in stomatal limitation with drought in C. ciliarisand E. macrostachyussuggest that stomatal limitation plays the dominant role in photosynthesis of the studied African C4grasses. The LI‐6400/XT Portable Photosynthesis System was used to measure leaf gas exchange characteristics of two C4 perennial grasses native to African rangelands, that is, Cenchrus ciliaris(African foxtail grass) and Enteropogon macrostachyus(Bush rye grass), under optimum and drought conditions.

Biochar showed additional C storage ability by preserving SOC from mineralization (negative priming) and stabilizing added labile organic substrateBiochar (30 Mg ha−1) significantly increased microbial carbon use efficiencyBiochar increased the formation of stable microbial residues (necromass) from a labile substrate (glucose) added to soil, as indicated by 13C recovery in amino sugars

Indigenous grasses have been effectively used to rehabilitate degraded African drylands. Despite their success, studies examining their effects on soil bioindicators such as microbial biomass carbon (C) and enzyme activities are scarce. This study elucidates the effects of drought stress and phenological stages of a typical indigenous African grass, Enteropogon macrostachyus, on microbial biomass and enzyme activities (β-glucosidase, cellobiohydrolase, and chitinase) in the rhizosphere soil. Enteropogon macrostachyuswas grown under controlled conditions. Drought stress (partial watering) was simulated during the last 10 d of plant growth, and data were compared with those from optimum moisture conditions. The rhizosphere soil was sampled after 40 d (seedling stage), 70 d (elongation stage), and 80 d (simulated drought stress). A high root:shoot ratio at seedling stage compared with elongation and reproduction stages demonstrated that E. macrostachyusinvested more on root biomass in early development, to maximise the uptake of nutrients and water. Microbial biomass and enzyme activities increased with root biomass during plant growth. Ten-day drought at reproduction stage increased the microbial biomass and enzyme activities, accompanying a decrease in binding affinity and catalytic efficiency. In conclusion, drought stress controls soil organic matter decomposition and nutrient mobilization, as well as the competition between plant and microorganisms for nutrient uptake.