Leaf senescence of common bean plants as affected by soil phosphorus supply.

As respostas da senescência foliar ao suprimento de P podem constituir estratégias adaptativas para o crescimento vegetal sob condições limitantes do nutriente. O objetivo deste trabalho foi avaliar os efeitos do suprimento de P no solo na senescência foliar do feijoeiro (phaseolus vulgaris L.). Oito doses de P, variando entre 5 e 640 mg kg-l de P, foram aplicadas em vasos com 10 kg de Argissolo Óxico, onde foram crescidas quatro plantas da cultivar Carioca. As folhas presas as plantas foram contadas semanalmente; as folhas senescidas, coletadas em intervalos de dois dias; e as sementes colhidas na maturação. O número de folhas vivas aumentou ate 48 dias após emergência (DAE) e decresceu após, independentemente da dose de P aplicada ao solo. Nas doses mms baixas de P, o aumento inicial e o decréscimo final do número de folhas foram pouco intensos, enquanto nas maiores doses desse nutriente a número de folhas aumentou intensamente no inicio e decresceu rapidamente após 48 DAE. A acumulação de massa seca e de P nas folhas senescentes aumentou com a acréscimo das doses de nutriente ate 61 DAE; posteriormente, reduziram-se as diferenças entre as doses de P. As maiores quantidades de massa seca e de P depositadas pelas folhas senescentes foram observadas aos 48-54 DAE nas maiores doses de P; aos 62-68 DAE, nas doses intermediárias; e aos 69-76 DAE, nas menores doses. Os resultados indicam que a suprimento de P no solo nlIo afetou a estádio de máxima numero de folhas e a inicio da senêscencia foliar de plantas de feijoeiro; contudo, a estádio de máxima deposição de folhas senescentes ocorreu mais cedo durante a cicio de crescimento com o aumento do suprimento de P no solo. Responses of leaf senescence to P supply could constitute adaptive mechanisms for plant growth under P-limiting conditions. The aim of this study was to evaluate the effects of soil P supply on leaf senescence of common bean (Phaseolus vulgaris L.). Eight P levels, ranging from 5 to 640 mg kg-1 P, were applied to pots containing four bean plants of cultivar Carioca in 10 kg of an Oxic Haplustult soil. Attached leaves were counted weekly, abscised leaves were collected every other day, and seeds were harvested at maturity. The number of live leaves increased until 48 days after emergence (DAE) and decreased afterwards, irrespective of applied P levels. At lower applied P levels, the initial increase and the final decrease ofleaf number was weak, whereas at higher applied P levels the leaf number increased intensively at the beginning of the growth cycle and decreased strongly after 48 DAE. Dry matter and P accumulated in senesced leaves increased as soil P levels increased until 61 DAE, but differences between P treatments narrowed thereafter. The greatest amounts of dry mass and P deposited by senesced leaves were observed at 48-54 DAE for high P levels, at 62-68 DAE for intermediate P levels and at 69-76 DAE for low P levels. These results indicate that soil P supply did not affect the stage of maximal leaf number and the beginning of leaf senescence of common bean plants, but the stage of greatest deposition of senesced leaves occurred earlier in the growth cycle as the soil P supply was raised.

Parceria: UFRRJ; INCRA.