土壤养分空间异质性与根系觅食作用:从个体到群落

摘要

Soil nutrients are distributed in a heterogeneous or patchy manner with different sizes.In order to adapt to the heterogeneous environment and enhance resource capture,plant roots have to respond to these nutrient patches from the morphological and physiological plasticity.When roots encounter a nutrient-rich patch they often proliferate within it,especially fine roots with higher specific root length.Meanwhile,their physiological ion-uptake capacities are also higher compared with roots outside the nutrient patch.The effect of the spatial nutrient heterogeneity on plant growth depends on nutrient patch attributes (size,strength,composition,location and so on)and plant intrinsic traits (sensibility and root foraging ability).These differences of the plant traits or nutrient patch attributes and the timing variation of the root encountering the patch can intensify inter-or intraspecific competition in plant populations or community.The root which encounters the patch firstly proliferates in the nutrient hotspots and thus leads to resource pre-emption.That might cause size-asymmetric root competition in spatial nutrient heterogeneity conditions.In populations,the intensive and size-asymmetric root competition caused by the nutrient patch can enhance the shoot size variation and influence the structure of the population.Also,the spatial nutrient heterogeneity can affect the diversity of species and productivity within community due to the diversity of root foraging precision and competitiveness between species.The plant species with the stronger foraging ability (e.g.clonal plant) may integrate and dominate over small-scale resource patches and improve their biomass,leading to reduce the positive effect of small-scale resource heterogeneity on plant species richness.%土壤中分布着许多大小不一的养分富集区域(也称之为养分斑块).植物为了适应环境最大限度地获取资源,会对这些养分斑块做出形态及生理上的响应.当根系接触到这些富集养分的区域就会大量的增生,尤其是比根长较大的细根,并且根系对养分的生理吸收能力也强于养分富集区域以外的根系.养分斑块的属性(大小、强度、组成和位置等)和植物体本身的属性(敏感性和觅食能力等)共同决定了养分空间异质性对于植物体生长的影响.由于不同物种的根系对于养分斑块的可塑性和养分斑块属性的差异及植物根系接触到养分斑块的时间和规模的不同会加剧种间或种内的竞争强度；先接触到养分斑块的植物根系可能在其他植物的根系到达之前将养分斑块内部的养分大部分吸收或耗尽,从而引起根系间的不对称性竞争.养分空间异质性造成的群体内部竞争强度的增加甚至不对称性会引起群体内植株大小变异性的增加,从而进一步影响群体结构.同时养分空间异质性对根系竞争的影响也会改变群落内部物种的多样性及整个体系的生产力,这与群落内物种之间觅食精度及竞争力的差异有关；觅食能力较强的物种可能会高效整合并占据大量的小养分斑块从而提高自身生长,进而降低了小养分斑块对群落物种丰度的正效应.