Interactive effects between nitrogen fertilization and elevated CO2 on growth and gas exchange of papaya seedlings.

Elevated atmospheric CO2 will change the requirements plants have for minerals, mainly nitrogen, altering the relationship between nutrient demand and plant growth. Here, we evaluated the interacting effects between two concentrations of CO2 (390 or 750 µL L-1) and two nitrogen (N) levels (3 mM or 8 mM) on gas exchange, N use efficiency (NUE), and dry mass responses of papaya seedlings. The study was conducted in a climate controlled greenhouse using 3.5 L pots and six replicates for 62 days. No significant effects from N or CO2 were noticed for leaf conductance to water vapor and transpiration. However, CO2 elevation to 750 µL L-1 increased assimilation rate for both N levels. Elevated CO2 resulted in an increase of 52% and 16% of instantaneous water-use efficiency under high and low N, respectively, as compared to ambient CO2 (390 µL L-1). Lower N concentrations were observed for all the organs for plants grown under higher concentrations of CO2, regardless of the N level used. However, plants grown under elevated CO2 reached the highest NUEs. There was an N × CO2 interactive effect on the leaf, stem plus petiole, and root dry mass. However, no significant CO2 effect on the root:shoot ratio was observed. Our results revealed that elevated CO2 stimulated total dry mass accumulation of papaya plants, with the results being greatest for plants grown under lower levels of N

Elevated CO2 concentrations alleviate the inhibitory effect of drought on physiology and growth of cassava plants.

Due to the rise in anthropogenic greenhouse gas concentrations, the earth's climate is expected to change, with precipitation being reduced in some areas resulting in growth-limiting drought and, as a consequence, reduced plant productivity. We investigated the physiological and growth responses of cassava (Manihot esculenta Crantz) to approximate present-day ambient (390 µL L-1) and elevated (750 µL L-1) atmospheric CO2 concentrations under well-watered and water deficit conditions, aiming at understanding how cassava would face those problems. Water deficits led to reductions in the Leaf Elongation Rate of plants grown at ambient as well as CO2-enriched concentrations. However, plants grown at 750 µL L-1 of CO2 maintained leaf growth two days longer than plants grown at 390 µL L-1. Three Days After Withholding Water (DAWW), photosynthesis and stomatal conductance were reduced in plants grown under ambient CO2, while in plants under an elevated CO2 concentration, these physiological functions remained similar to that of control plants grown under good water availability. Five DAWW plants grown with 750 µL L-1 continued to have enhanced gas exchange compared with plants grown under 390 µL L-1. Under drought stress, the instantaneous transpiration efficiency was always greatest for plants grown under elevated CO2. The positive response of elevated CO2 levels on total dry mass was 61% in the water-stressed plants and only 20% for the plants grown under good water availability. Stomatal limitation was an important factor reducing CO2 assimilation in cassava growing under drought conditions

Conceito de ideotipo e seu uso no aumento do rendimento potencial de cereais The ideotipe concept and its use to increase cereal's yield potential

A presente revisão tem por objetivo apresentar algumas características consideradas interessantes de serem incorporadas em plantas de cereais quando cultivadas em comunidade, através da integração de conhecimentos de fisiologia, bioquímica e melhoramento. No melhoramento de diferentes espécies verifica-se que várias características de planta foram modificadas no processo de seleção para rendimento de grãos. Neste enfoque, propõe-se discutir a validade de incorporar estas características em cultivares e perguntar se as cultivares antigas tivessem sido melhoradas através destas características qual resultado teria sido alcançado. A discussão de ideotipo aumenta de importância com a rápida evolução das técnicas de avaliação da variabilidade genética, pois caso não seja definido um modelo de planta para aumentar o rendimento potencial estas técnicas podem ter uma utilização restrita. Na discussão de ideotipo para aumentar o rendimento potencial, é necessário formular um novo modelo baseado em algumas características já amplamente analisadas deforma isolada. As principais, são o maior crescimento inicial e maior fitomassa da comunidade, o que lhe permite aumentar a capacidade de aproveitamento da radiação, principalmente no início do ciclo da cultura. Somado a isto, o aumento da capacidade fotossintética através do aumento da força de demanda, com provável efeito sobre o índice de colheita. A ação conjunta das características individuais necessita ser testada quando incorporadas sobre um mesmo genótipo, para analisar o seu grau de resposta.<br>This review has the purpose of presenting some important traits to be incorporated in cereals through the integration of physiology, biochemistry and plant breeding. Several plant attributes were modified during the selection process to improve grain yield of different plant species. This paper intends to discuss the validity of aggregating some of the se traits in new cultivars and to pinpoint the possible consequences of using those individual characteristics rather than grain yield per se to bred the old genotypes. Discussion about crop ideotipes grows in importance with the fast evolution of genetic variability techniques because if a model plant to increase grain yield is not defined all the new genetic technology available may have a narrow practical utilization. This ideotipe was formulated integrating severa! characteristics that have been analyzed individually in the past. Its main proposed features are: (a) higher initial growth and greater communal phytomass, which are both important to improve solar radiation use, particularly during early stages of development, (b) an increase in photosynthetic capacity through the enhancement of sink strength with a probable effèct on harvest index. The collective influence of the suggested traits must be evaluated on different genotypes to analyze the response level obtained