Photosynthetic Rates and Chlorophyll Fluorescence of Nitraria tangutorum at Different Leaf Water Potentials

At different leaf water potentials,the photosynthetic rates and chlorophyll fluorscence parameter of Nitraria tangutorum distributing in Ulan Buh desert were measured with LI-COR 6400 Portable photosynthesis system.The results indicated that as its leaf water potential of Nitraria tangutorum declined,its net photosynthetic rate and stomatal conductance fast decreased;its leaf water potential dropped to a certain level,its net photosynthetic rate and stomatal conductance remained nearly unchanged.But the parametersof its chlorophyll fluorescence remained approximately unchanged as its leaf water potential decreased within its high limits and approximately linearly declined as its leaf water potential dropped to a certain level.With its leaves saturated,Nitraria tangutorum had a lihgt compensation point of(43.1±4.8) μmol·m~(-2)·s~(-1),and a light saturation point of(676±150) μmol·m~(-2)·s~(-1);In the early and mature stages of leaf growth,the photosynthetic water potential compensation points(the leaf water potential at zero net photosynthetic rate) was-3.65 MPa and-5.76 MPa respectively,and the NPQ initial water potentials were-2.20 MPa and-6.63 MPa,respectively.The study pointed out that photosynthetic water potential compensation point and NPQ initial water potential could be used in evaluating the adaptabilities of Nitraria tangutorum to arid environments.