Data from: Shift from an extensive to an intensive root nutrient-acquisition mode with stand development of three Pinus species

Plant roots employ diverse strategies to acquire soil nutrients, including direct nutrient uptake through absorptive fine roots and root hairs, scavenging nutrients by forming symbioses with mycorrhizal fungi, and mining nutrients by releasing root exudates. However, whether these three strategies are differently coordinated among phylogenetically closely-related tree species and how this coordination shifts with stand development remains largely unclear. To fill these knowledge gaps, we measured 13 root morphological, architectural, physiological and mycorrhizal traits tightly related to nutrient-acquisition of three Pinus species (P. sylvestris var. mongolica, P. densiflora and P. tabuliformis) at young (20-year-old) and mature (50-year-old) stages planted in nutrient-impoverished sandy soils, in Northeast China. We found that young trees had thinner absorptive fine roots and a higher specific root length than mature trees across three Pinus species, indicating that roots become morphologically less efficient in “do it yourself” scavenging nutrients during stand development. Moreover, young stands had greater root length density and root area index, and mature stands had faster root-exudation rates, suggesting that young stands rely more on expanding soil volumes to scavenge nutrients and mature stands depend more on root exudation to ‘mine’ nutrients. The three Pinus species exhibited different nutrient-acquisition strategies at the mature stage; P. densiflora had higher root length density and root area index, and the other two Pinus species had greater ectomycorrhizal colonization rates. Synthesis. Our findings highlight that phylogenetically closely-related tree species may exhibit different nutrient-acquisition strategies, and suggest a shift from an extensive nutrient-acquisition mode depending more on absorptive fine roots to an intensive nutrient-acquisition mode relying more on root exudation during stand development.

植物根系可通过多种策略获取土壤养分，具体包括借助吸收性细根与根毛直接吸收养分、与菌根真菌建立共生关系以搜寻养分，以及通过释放根系分泌物来挖掘土壤养分。然而，在系统发育关系紧密的树木类群之间，这三种养分获取策略是否存在差异化协调模式，以及该协调模式如何随林分发育发生转变，目前仍不甚明确。为填补上述认知空白，本研究于中国东北养分贫瘠的沙质土壤中，对3个近缘松属物种（樟子松*P. sylvestris var. mongolica*、赤松*P. densiflora*与油松*P. tabuliformis*）的幼龄林（20年生）与成熟林（50年生）阶段的13项与养分获取紧密相关的根系形态、结构、生理及菌根性状进行了测定。研究发现，相较于成熟林个体，3个松属物种的幼龄林个体拥有更纤细的吸收性细根与更高的比根长，这表明随着林分发育，根系在"自力更生"式的养分搜寻过程中的形态学效率有所下降。此外，幼龄林的根长密度与根面积指数更高，而成熟林的根系分泌物释放速率更快，这表明幼龄林更依赖扩大土壤探查体积以搜寻养分，成熟林则更多依靠根系分泌物来"挖掘"土壤养分。3个松属物种在成熟林阶段展现出差异化的养分获取策略：赤松拥有更高的根长密度与根面积指数，其余两个松属物种则具有更高的外生菌根侵染率。综合而言，本研究结果表明，系统发育近缘的树木类群可能演化出差异化的养分获取策略，同时揭示了随着林分发育，养分获取模式会从更依赖吸收性细根的粗放型获取模式，向更依赖根系分泌物的集约型获取模式转变。