Bouma Tjeerd J, Koutstaal Bas P, van Dongen Michel, Nielsen Kai L
Center for Estuarine and Coastal Ecology (NIOO-CEMO), Netherlands Institute of Ecology, P.O. Box 140, 4400 AC, Yerseke, The Netherlands.
Deparment of Horticulture, Danish Institute of Agricultural Sciences, Kirstinebjergvaj 10, 5792, Aarslev, Denmark.
Oecologia. 2001 Feb;126(4):472-481. doi: 10.1007/s004420000545. Epub 2001 Feb 1.
We describe the responses of three halophytic grass species that dominate the low (Spartina anglica), middle (Puccinellia maritima) and high (Elymus pycnanthus) parts of a salt marsh, to soil conditions that are believed to favour contrasting root-growth strategies. Our hypotheses were: (1) individual lateral root length is enhanced by N limitations in the soil but restricted by oxygen limitations, (2) the density of root branching within a species is inversely related to the length of the lateral roots, and (3) species from high elevations (i.e. the driest parts of a marsh) are the most responsive to changing soil conditions. Plant growth responses and soil parameters showed that the contrasting but uniformly applied soil treatments were effective. All three species showed a small but significant shift towards a finer root diameter distribution when N was limiting, partly because of the finer diameters of the laterals (Elymus and Spartina) and partly because of increased length of individual 1st-order laterals (Elymus and Puccinellia). The increased length of the 1st-order laterals of Elymus and Puccinellia grown under low N indicates that the first part of hypothesis 1 may be true. However, lack of effect of flooding and reduced soil conditions lead us to reject the second part of hypothesis 1. Hypothesis 2 was rejected for these three halophytes, as the branch density of 1st- and 2nd-order laterals appears to be controlled by other factors than length of individual laterals. Hypothesis 3 may be true for specific root characteristics (e.g. length of individual 1st-order laterals), but cannot be generalised (e.g. branch density and topological index). In conclusion, the present data on root growth in contrasting but homogeneous soil conditions indicate that morphological responsiveness of the root systems of these halophytic grass species is limited, regardless of their location along the elevational gradient.
我们描述了三种盐生草种对土壤条件的响应，这三种草种分别占据盐沼的低海拔区域（大米草）、中海拔区域（碱茅）和高海拔区域（密花披碱草），而这些土壤条件被认为有利于形成不同的根系生长策略。我们的假设是：（1）土壤中氮素限制会增加单个侧根长度，但氧气限制会抑制侧根长度；（2）一个物种内根系分支密度与侧根长度呈负相关；（3）高海拔区域（即盐沼最干燥的部分）的物种对土壤条件变化最为敏感。植物生长响应和土壤参数表明，对比明显但统一施加的土壤处理是有效的。当氮素受到限制时，所有这三个物种都出现了向更细根径分布的微小但显著的转变，部分原因是侧根更细（披碱草属和大米草属），部分原因是单个一级侧根长度增加（披碱草属和碱茅属）。在低氮条件下生长的披碱草属和碱茅属一级侧根长度增加，这表明假设1的第一部分可能是正确的。然而，水淹和土壤条件变差没有产生影响，这使我们否定了假设1的第二部分。对于这三种盐生植物，假设2被否定，因为一级和二级侧根的分支密度似乎受单个侧根长度以外的其他因素控制。假设3对于特定的根系特征（如单个一级侧根长度）可能是正确的，但不能一概而论（如分支密度和拓扑指数）。总之，目前关于在对比明显但均匀的土壤条件下根系生长的数据表明，这些盐生草种根系的形态响应能力是有限的，无论它们在海拔梯度上的位置如何。
