The amount of carbon dioxide (CO 2 ) of the Earth´s atmosphere is increasing, which has the potential of increasing greenhouse effect and air temperature in the future. Plants respond to environment CO 2 and temperature. Therefore, climate change may affect agriculture. The purpose of this paper was to review the literature about the impact of a possible increase in atmospheric CO 2 concentration and temperature on crop growth, development, and yield. Increasing CO 2 concentration increases crop yield once the substrate for photosynthesis and the gradient of CO 2 concentration between atmosphere and leaf increase. C3 plants will benefit more than C4 plants at elevated CO 2 . However, if global warming will take place, an increase in temperature may offset the benefits of increasing CO 2 on crop yield.

Resumo -O objetivo deste trabalho foi avaliar o efeito dos métodos de cálculo de graus-dia e de datas de semeadura na determinação do filocrono de cultivares de trigo (Triticum aestivum). Foi conduzido um experimento em campo, com 13 datas de semeadura, durante três anos (2005)(2006)(2007), em Santa Maria, RS, usando-se seis cultivares de trigo: BRS Louro, CEP 52, CEP 51, BRS 177, Nova Era e BRS Tarumã. O filocrono (°C dia folha -1 ) foi estimado pelo inverso do coeficiente angular da regressão linear entre o estádio de Haun e a soma térmica acumulada calculada por seis métodos. O método de cálculo da soma térmica afeta as estimativas do filocrono em trigo.O uso das três temperaturas cardinais de emissão de folhas e a comparação das temperaturas cardinais com a temperatura mínima e máxima do ar melhora a precisão na simulação do desenvolvimento vegetativo dessa cultura, em comparação aos demais métodos. O filocrono varia com a cultivar de trigo e com a data de semeadura, e cultivares mais precoces (BRS Louro e CEP 51) têm menor filocrono do que cultivares tardias (Nova Era e BRS Tarumã). Em semeaduras no outono ou inverno, o filocrono é maior do que em semeaduras de primavera ou verão.Termos para indexação: Triticum aestivum, aparecimento de folhas, desenvolvimento vegetal, fotoperíodo, temperatura. Thermal time methods and sowing dates in phyllochron determination in wheat cultivarsAbstract -The objective of this work was to evaluate the effect of degree-days and sowing dates calculation methods on phyllochron determination in wheat (Triticum aestivum) cultivars. A three-year field experiment with 13 sowing dates was conducted for three years (2005)(2006)(2007) in Santa Maria, RS, Brazil, using six wheat cultivars: BRS Louro, CEP 52, CEP 51, BRS 177, Nova Era and BRS Tarumã. The phyllochron (°C day leaf -1 ) was estimated by the inverse of the slope of the linear regression of the Haun stage against the accumulated thermal time calculated using six methods. The thermal time calculation method affects wheat phyllochron estimates. The use of the three cardinal temperatures for leaf emission and cardinal temperatures compared to the minimum and maximum air temperatures improves the precision of the vegetative development simulation of this crop, in comparison to the other methods. The phyllochron varies with wheat cultivar and sowing date, and early cultivars (BRS Louro and CEP 51) have lower phyllochron than late cultivars (Nova Era and BRS Tarumã). The phyllochron is greater in sowings carried out during fall and winter than in the ones carried out during spring and summer.

The prediction of leaf appearance rate (LAR) is an important part of many crop simulation models. Most wheat simulations models assume that LAR is affected by temperature and photoperiod. This assumption ignores the fact that seed reserves contribute to a greater LAR of the first two leaves and that the LAR of subsequent leaves decreases as a result of an increase in the distance that each leaf primordium must extend before it appears. The objective of this study was to develop a generalized LAR chronology response function [f(C)] for wheat that takes into account seed reserves and the increasing distance from the meristem to the whorl for later appearing leaves. This chronology response function was then incorporated into an existing LAR model [Wang and Engel (WE) model; Wang and Engel, 1998, Agricultural Systems 58: 1-24]. This function varied from 0 to 1, being equal to 1 for the first two leaves due to seed reserves, and decreasing (taking the form of a power law) for subsequent leaves. Data from a growth chamber (two cultivars) and several field experiments (four cultivars, two years and eight sowing dates) at Lincoln, Nebraska, USA, were used as independent data to test three LAR models (Miglietta model, Miglietta, 1991, Climate Research 1: 145-150; WE model; and modified WE model). Predictions of the main stem Haun stage, both in the growth chamber and in the field, were greatly improved by incorporating f(C) into the Wang and Engel model. The root mean square error for the field data was 1.1, 0.7, and 0.3 leaves for the Miglietta model, the Wang and Engel model, and the modified Wang and Engel model, respectively.

O desenvolvimento, incluindo a emissão de folhas, de culturas agrícolas e florestais depende fortemente da temperatura do ar. A emissão de folhas pode ser estimada e quantificada utilizando-se o conceito do filocrono, definido como o intervalo de tempo, em graus dia, entre o aparecimento de duas folhas sucessivas em uma haste, com unidade °C dia folha-1. O objetivo deste trabalho foi estimar a temperatura-base para a emissão de folhas e o filocrono em Eucalyptus grandis (Hill ex Maiden) e Eucalyptus saligna (Smith), em fase de muda. Foram realizados dois experimentos, um no campo e outro em casa de vegetação na área experimental do Departamento de Fitotecnia da Universidade Federal de Santa Maria, RS. A semeadura foi realizada em cinco épocas diferentes em campo e em 03/10/2005 na casa de vegetação. A temperatura-base foi estimada pelo menor valor do quadrado médio do erro da regressão entre o número de folhas acumuladas na haste principal (NF) e a soma térmica acumulada (STa), e o filocrono foi estimado pelo inverso do coeficiente angular da regressão entre NF e STa. A temperatura-base estimada foi de 8,0 °C para Eucalyptus saligna e 10 °C para Eucalyptus grandis. O filocrono em Eucalyptus grandis foi de 32,0 ºC dia folha-1 e em Eucalyptus saligna, 30,7 ºC dia folha-1, sendo essa diferença de filocrono entre as duas espécies não estatisticamente diferente.

4DF, CCR, UFSM, Santa Maria, RS, Brasil. 5Programa de Pós-graduação em Agronomia, CCR, UFSM, Santa Maria, RS, Brasil. RESUMO O meloeiro (Cucumis melo L.) é uma hortaliça de alto valor econômico. A emissão de nós é um componente

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The objective of this study was to adapt a nonlinear model (Wang and Engel - WE) for simulating the phenology of maize (Zea mays L.), and to evaluate this model and a linear one (thermal time), in order to predict developmental stages of a field-grown maize variety. A field experiment, during 2005/2006 and 2006/2007 was conducted in Santa Maria, RS, Brazil, in two growing seasons, with seven sowing dates each. Dates of emergence, silking, and physiological maturity of the maize variety BRS Missões were recorded in six replications in each sowing date. Data collected in 2005/2006 growing season were used to estimate the coefficients of the two models, and data collected in the 2006/2007 growing season were used as independent data set for model evaluations. The nonlinear WE model accurately predicted the date of silking and physiological maturity, and had a lower root mean square error (RMSE) than the linear (thermal time) model. The overall RMSE for silking and physiological maturity was 2.7 and 4.8 days with WE model, and 5.6 and 8.3 days with thermal time model, respectively.