Visiting Scientists

Jailson Cruz

Associated to Labex Scientist Alfredo Augusto C. Alves

Response of cassava genotypes to elevated CO2, nitrogen sources, water deficit and temperature

Research team: Jailson Cruz – Embrapa Cassava & Fruits, Cruz das Almas BA; Alfredo Alves – Embrapa/LABEX, Fort Collins CO; David Ellis – NCGRP/ARS, Fort Collins CO; and Jack Morgan – CRL/ARS, Fort Collins CO.

Objective: To evaluate the effect of elevated CO2 concentration, water deficit, nitrogen source, and temperature on several physiological parameters in cassava.

Approach: Cassava variety COL 1468 was grown in greenhouse conditions in 12L pots in two experiments. Treatments: (1) two air CO2 concentrations, 390 (ambient) and 750 (elevated) ppm; (2) two water status: well watered (WW) and periodically water stress (WS), imposed by withholding irrigation; (3) three nitrogen treatments: (a) 12 mM NO3-, (b) 6 mM NO3- + 6 mM NH4+, and (c) 12 mM NH4+; and (4) two air temperatures (30 and 40oC). Parameters evaluated: leaf elongation, dry matter accumulation, and gas exchange parameters (photosynthesis, stomatal conductance, transpiration, and instantaneous water use efficiency-WUE). Plants were harvested 92 days after the initiation of treatments, separated into tubers (roots > 1 cm in diameter) and shoots and oven-dried at 70oC until there was no further change in dry weight.

Results: Water lost by transpiration was higher for plants grown under 390_WS in the first 2 days. As a result, these plants came quickly under stress, closed their stomata and began to transpire lesser than plants under 750_WS. Five days after water suspension (DAWS) plants grown under 390_WS paralyzed their leaf growth; for 750_WS plants this only occurred seven DAWS. Three DAWS plants 390_WS reduced their photosynthesis, while no effect was observed for plants 750_WS. Five DAWS photosynthesis of plants 750_WS was 165% greater than plants 390_WS. However, when 390_WS plants were evaluated with projected 750 μmol.mol-1 of CO2 on their leaves photosynthesis reached normal value. For every evaluation day, the instantaneous water use efficiency of 750_WS plants was higher than of 390_WS plants. For the same amount of applied water 750_WS plants produced more dry mass. One day after re-watering, photosynthesis of 390_WS and 750_WS plants reached value equal to their respective irrigate control, demonstrating the excellent ability of cassava to quickly recover its photosynthetic machinery after a prolonged period of water stress. High CO2 concentration reduced the negative effect of increasing temperature on the photosynthesis of cassava leaf, since 390_WS plants was more affected (Figure 01). 750_WS plants produced 62% more total dry mass and 111% more dry mass of tuberous roots than 390_WS plants (Figure 02). For both CO2 treatments, NH4+ fertilization reduced total and tuber root dry matter. However, the negative effect of NH4+ was lower under elevated CO2 concentrations, since plants fertilized with only NH4+ produced 37% and 71% more total and tuber root dry matter, respectively, when grown at 750 ppm of CO2 than to 390 ppm of CO2 (Figure 03). Publication of 2 abstracts and presentation of 2 posters at the ‘2nd Scientific Conference of the Global Cassava Partnership for 21st Century – GCP21-II’, in Kampala, Uganda, June 18-22, 2012.
(http://www.danforthcenter.org/GCP21-II). Also, submission and approval of 3 abstracts to be presented (as poster or oral presentation) at the ‘6th International Crop Science Congress – 6th ICSC’, in Bento Gonçalves-RS, Brazil, August 6-10, 2012 (http://www.6icsc.com.br).