Simonin K, Kolb T E, Montes-Helu M, Koch G W
School of Forestry, Northern Arizona University, Flagstaff AZ, 86011-5018, USA.
Tree Physiol. 2006 Apr;26(4):493-503. doi: 10.1093/treephys/26.4.493.
Ponderosa pine (Pinus ponderosa Dougl. ex P. Laws) forest stand density has increased significantly over the last century (Covington et al. 1997). To understand the effect of increased intraspecific competition, tree size (height and diameter at breast height (DBH)) and leaf area to sapwood area ratio (A(L):A(S)) on water relations, we compared hydraulic conductance from soil to leaf (kl) and transpiration per unit leaf area (Q(L)) of ponderosa pine trees in an unthinned plot to trees in a thinned plot in the first and second years after thinning in a dense Arizona forest. We calculated kl and Q(L) based on whole- tree sap flux measured with heat dissipation sensors. Thinning increased tree predawn water potential within two weeks of treatment. Effects of thinning on kl and Q(L) depended on DBH, A(L):A(S) and drought severity. During severe drought in the first growing season after thinning, kl and Q(L) of trees with low A(L):A(S) (160-250 mm DBH; 9-11 m height) were lower in the thinned plot than the unthinned plot, suggesting a reduction in stomatal conductance (g(s)) or reduced sapwood specific conductivity (K(S)), or both, in response to thinning. In contrast kl and Q(L) were similar in the thinned plot and unthinned plot for trees with high A(L):A(S) (260-360 mm DBH; 13-16 m height). During non-drought periods, kl and Q(L) were greater in the thinned plot than in the unthinned plot for all but the largest trees. Contrary to previous studies of ponderosa pine, A(L):A(S) was positively correlated with tree height and DBH. Furthermore, kl and Q(L) showed a weak negative correlation with tree height and a strong negative correlation with A(S) and thus A(L):A(S) in both the thinned and unthinned plots, suggesting that trees with high A(L):A(S) had lower g(s). Our results highlight the important influence of stand competitive environment on tree-size-related variation in A(L):A(S) and the roles of A(L):A(S) and drought on whole-tree water relations in response to thinning.
在过去的一个世纪里，黄松（Pinus ponderosa Dougl. ex P. Laws）林分密度显著增加（科温顿等人，1997年）。为了了解种内竞争加剧对水分关系的影响，我们比较了亚利桑那州一片茂密森林中，在间伐后的第一年和第二年，未间伐地块与间伐地块的黄松树从土壤到叶片的导水率（kl）和单位叶面积蒸腾量（Q(L)），同时研究了树体大小（树高和胸径（DBH））以及叶面积与边材面积比（A(L):A(S)）对水分关系的影响。我们基于用热消散传感器测量的整树液流通量计算了kl和Q(L)。间伐在处理后的两周内提高了树木的黎明前水势。间伐对kl和Q(L)的影响取决于DBH、A(L):A(S)和干旱严重程度。在间伐后的第一个生长季节的严重干旱期间，A(L):A(S)较低的树木（DBH为160 - 250毫米；树高9 - 11米）在间伐地块的kl和Q(L)低于未间伐地块，这表明气孔导度（g(s)）降低或边材比导率（K(S)）降低，或两者兼而有之，是对间伐的响应。相比之下，A(L):A(S)较高的树木（DBH为260 - 360毫米；树高13 - 16米）在间伐地块和未间伐地块的kl和Q(L)相似。在非干旱时期，除最大的树木外，间伐地块的kl和Q(L)均高于未间伐地块。与之前对黄松的研究相反，A(L):A(S)与树高和DBH呈正相关。此外。在间伐地块和未间伐地块中，kl和Q(L)与树高呈弱负相关，与A(S)以及因此与A(L):A(S)呈强负相关，这表明A(L):A(S)较高的树木g(s)较低。我们的研究结果突出了林分竞争环境对与树体大小相关的A(L):A(S)变化的重要影响，以及A(L):A(S)和干旱对整树水分关系响应间伐的作用。
