1. Climate-smart Brachiaria grasses:
Progress in identifying the role of root traits in soil carbon accumulation
Juan A. Cardoso, Juan dC. Jiménez, Idupulapati Rao: International Center for Tropical Agriculture (CIAT), Cali, Colombia. Contact:
Elias M. Gichangi, Donald M.G. Njarui: Kenya Agricultural and Livestock Research Organization (KALRO), Machakos, Kenya
Mupenzi Mutimura: Rwanda Agriculture Board (RAB), Kigali, Rwanda
Introduction
Brachiaria spp. and Napier grass are perennial deep-rooting grasses widely used to sustain animal production in the tropics.
Perennial and deep-rooting grasses sequester large amounts of carbon in the soil.
Yet, root traits of tropical forage grasses that are involved in soil carbon accumulation are not well understood.
Identification of root traits (length at different soil profiles, root length turnover, carbon, nitrogen and lignin) in a number of commercial Brachiaria grasses and Napier grass (Pennsisetum purpureum) is underway.
Methods
Greenhouse studies are being performed at CIAT headquarters in Cali (Colombia), and field studies at the KALRO’s Katumani Research Station (Machakos, Kenya) and RAB’s Karama Research Station (Bugesera district, Rwanda).
Plants had been established for over 16 months on soils with low nutrient availability
Root length (RL) and root length turnover (RLT) studies are being monitored non-destructively in plants grown in plastic transparent cylinders of 120 cm length x 20 cm width under greenhouse conditions (Fig. 1) .
Differences in RL and RLT are being analyzed every 4 months using segmenting algorithms with Matlab (R2015, Mathworks USA) and Photoshop (CS5, Adobe USA) software (Fig. 1).
A suit of root chemical traits of plants grown under greenhouse and field conditions are being analyzed for lignin (histo-chemistry and acid digestion), and C and N concentrations with an elemental auto-analyzer.
Original image Segmented image Analysis
20 cm
Dead roots
120 cm
Live roots
RLT = total roots/live roots
Fig. 1. Non-destructive estimation root length and root length turnover
Results and Discussion
After a period of 16 months, Napier grass showed greater root length production and turnover (Table 1).
Brachiaria grasses showed greater lignin (Table 1, Fig. 2) and carbon contents in roots, but lower N content than Napier grass (Table 1).
Brachiaria grasses showed greater lignin accumulation in root tissue (reddish to goldish color) in inner cylinder and exodermis
Table 1. Total root length, root length turnover and root chemical composition of 6 Brachiaria grasses and Napier grass. Data shown are means of 4 replicates.
Fig. 2. Detection and localization of lignin in root tissue by phloroglucinoll staining.
Greater root length production, root length turnover in combination with lower C/N and Lignin/N ratios in roots of Napier grass (when compared to Brachiaria grasses) suggest that Napier grass favors the production of fast growing “cheap” root tissue that might decompose faster than roots of Brachiaria grasses.
Conclusions
Root chemical characteristics of Brachiaria grasses suggest greater recalcitrance to decomposition than roots of Napier grass, in turn greater potential for carbon sequestration.
Further research (root decomposition studies) in combination with soil carbon determination is underway to validate the aforementioned.
Acknowledgments
This work is supported by a SIDA funded program (Innovative programmatic approach to climate change in support of BecA´s mission: Climate-smart Brachiaria grasses for improving livestock production in East Africa