Fluxo de seiva e condutância estomática de duas espécies lenhosas sempre-verdes no campo sujo e cerradão

Revista Brasileira de Fisiologia Vegetal 08/2000; 12(2). DOI: 10.1590/S0103-31312000000200003
Source: DOAJ


No presente estudo, comparou-se o curso diário de fluxo de seiva, condutância estomática e potencial hídrico (psi) de duas espécies sempre-verdes, Rapanea guianensis e Roupala montana. Os dados foram obtidos no final da estação seca, quando os efeitos do déficit hídrico seriam mais acentuados. As medidas foram realizadas no campo sujo, onde predomina gramíneas com sistemas radiculares superficiais, e no cerradão, em que a maior densidade de elementos lenhosos com sistemas radiculares profundos poderia levar a um esgotamento das reservas de água do subsolo na estação seca. Valores máximos de psinão diferiram para as duas espécies nas duas fisionomias estudadas. Os valores mínimos de potencial hídrico foliar de R. guianensis foram mais negativos (P<0,05) para as plantas do cerradão, enquanto os valores para R. montana não apresentaram diferenças entre as duas fisionomias. Os resultados indicaram que não existem diferenças significativas (P > 0,05) entre os valores de fluxo máximo e de fluxo total entre o campo sujo e cerradão. Os valores máximos de fluxo de seiva variaram entre 0,13 e 0,22 l. h-1 para R. guianensis e entre 0,15 e 0,54 l. h-1 para R. montana. Entretanto, as duas espécies, tanto no campo sujo quanto no cerradão, apresentaram um rígido controle estomático em relação à alta demanda evaporativa da atmosfera. O fluxo de seiva aumentou bruscamente pela manhã, alcançando rapidamente valores máximos entre 8 e 10 horas, e logo após decresceu severamente, apesar do crescente aumento da radiação solar e da demanda evaporativa da atmosfera.

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