Zhang Junling, George Eckhard
College of Resources and Environmental Sciences, China Agricultural University, Beijing 100094, P.R. China.
Tree Physiol. 2009 Feb;29(2):199-206. doi: 10.1093/treephys/tpn016. Epub 2008 Dec 5.
Nutrient sources in soils are often heterogeneously distributed. Although many studies have examined the root responses to local N and P enrichments in the soil, less research was conducted on root responses to Mg patches. New roots of pre-grown Mg-insufficient and Mg-sufficient plants of Norway spruce (Picea abies [L.] Karst.) and Scots pine (Pinus sylvestris L.) seedlings were allowed to grow into four other pots of equal size, which were placed under the tree-bearing pot. Soils in the lower pots were either unfertilised, or supplied with Mg, or NPK or a mixture of NPKMg sources. Plants were harvested after 9 months of growth. Compared to the corresponding controls (Mg versus unfertilised and NPKMg versus NPK), Mg additions did not have a significant effect on either root dry matter, total root length (TRL) or specific root length (SRL), irrespective of tree species and plant Mg nutritional status. In contrast, NPK and NPKMg additions significantly increased the root dry matter and TRL in the nutrient-rich soil patch, and decreased SRL in Norway spruce. However, the observed root morphological changes did not occur in Scots pine. Root Mg concentrations were increased in Mg-rich soil patches, but those accumulations varied with tree species. Mg accumulation in a marked patch was measured only in newly grown roots of Mg-sufficient Norway spruce, whereas a more homogenous distribution of Mg concentration was observed for all newly grown roots in Mg-insufficient trees in the four soil treatments. In Scots pine, Mg accumulations occurred in both Mg-insufficient and Mg-sufficient plants. These results suggest that Mg patches in the soil may not lead to a local increase in root growth, but to Mg uptake and root Mg accumulation. Tree roots react differently to Mg patches in comparison to their response to N or P patches in the soil.
土壤中的养分来源通常呈非均匀分布。尽管许多研究已考察了根系对土壤中局部氮和磷富集的响应，但针对根系对镁斑块的响应开展的研究较少。将预先培养的镁缺乏和镁充足的挪威云杉（Picea abies [L.] Karst.）和欧洲赤松（Pinus sylvestris L.）幼苗的新根，放入另外四个同样大小的花盆中生长，这些花盆放置在装有树木的花盆下方。下方花盆中的土壤要么不施肥，要么施镁，要么施氮磷钾，要么施氮磷钾镁源混合物。生长9个月后收获植株。与相应对照（镁与不施肥、氮磷钾镁与氮磷钾）相比，无论树种和植株的镁营养状况如何，添加镁对根系干物质、总根长（TRL）或比根长（SRL）均无显著影响。相比之下，添加氮磷钾和氮磷钾镁显著增加了富营养土壤斑块中的根系干物质和总根长，并降低了挪威云杉的比根长。然而，欧洲赤松未出现观察到的根系形态变化。富镁土壤斑块中根系镁浓度增加，但这些积累因树种而异。仅在镁充足的挪威云杉新生长的根系中测量到明显斑块中的镁积累，而在四种土壤处理中，镁缺乏树木的所有新生长根系中镁浓度分布更为均匀。在欧洲赤松中，镁缺乏和镁充足的植株中均出现了镁积累。这些结果表明，土壤中的镁斑块可能不会导致根系生长局部增加，但会导致镁吸收和根系镁积累。与根系对土壤中氮或磷斑块的响应相比，树木根系对镁斑块的反应不同。
