Response Of The Fine Root Morphology Of Two Kinds Of Poplar Plantations To Different Water And Fertilizer Measures

This study is based on triploid Populus tomentosa pulpwood on Shandong Yellow River flood plain and Populus xeuramericana fast growing and high yielding plantation at Beijing sandy land, where two field experiments were respectively conducted to investigate the fine root morphology of the two kinds of poplar plantation in0--30cm soil layers under different subsurface drip irrigation and surface drip irrigation and fertigation treatments by using soil cores method, aimed at inquiring into the mechanism how the fine root responded different treatments, revealing the mechanism how water and fertilizer management measures promoted woods growth from the angle of root distribution, and providing irrigation and fertigation decisions with theoretical basis. The main results and conclusions are as follows.1. Results based on triploid Populus tomentosa pulpwood on Shandong Yellow River flood plain showed that in the vertical direction, fine root biomass, length density, surface area and volume significantly decreased with more depth under the four treatments, subsurface drip irrigation did not change the vertical distribution pattern of fine root, subsurface drip irrigation significantly raised fine root biomass and volume in20-30cm soil layer, which was one of the main reasons why subsurface drip irrigation improved forest productivity. For example, in20～30cm soil layer, fine root biomass and volume under T2treatment were respectively0.29mg·cm-3and0.62mm3·cm-3, which were significantly112.31%and91.64%higher than CK treatment, subsurface drip irrigation significantly reduced fine specific root length in0～10cm and20～30cm soil layer and fine root tissue density in10～20cm soil layer, made both indices above in all soil layers roughly the same, in order to contribute to bringing into play the function of absorption and stretching of fine root in each soil layer. For example, under T1treatment, fine specific root length in20～30cm soil layer and fine root tissue density in10-20cm soil layer were respectively2799.1cm·g-1and0.411g·cm-3, which were significantly44.79%and17.28% lower than CK treatment. In each soil layer, the difference of each morphological index of fine root among the three subsurface drip irrigation treatments was not significant.2. Results based on Populus euramericana fast growing and high yielding plantation at Beijing sandy land showed that in the vertical direction, fine root biomass, length density, surface area and volume significantly decreased with more depth under the ten treatments, and the vertical distribution pattern of fine root has not been altered with the water and fertilizer treatments. For middle-(652g/plant) and high-(978g/plant) level of fertilizer, all treatments exerted an increase effect on fine root biomass, length density, surface area and volume. Meanwhile, fine root length density and surface area within the whole soil horizon, fine root biomass and volume in the soil layer of10-20cm and20-30cm among two levels of fertilizer decreased significantly with surface drip irrigation level. However, there was no significant change in all indices of the three soil layers for low-Ievel(326g/plant) of fertilizer. For three surface drip irrigation levels, all indices showed a significant increase with the progressive level of fertilizer. The treatment with high level of water and fertilizer(the third treatment) caused adistinct effect on the growth of fine root. The value of fine root biomass(0.248mg-cm’3), length density(0.526cm·cm-3), surface area(0.060cm2·cm-3) and volume(0.533mm3·cm-3) was386.18%,176.49%,212.82%and234.53%respectively higher relative to CK. Water and fertilizer treatments exerted no influence on fine specific root length in0～10cm soil layer. The specific root length in10-20cm soil layer significantly decreased under middle-(-50kPa) and high-(-25kPa) level of water and no significant change was found in10～20cm and20-30cm soil layer, however the specific root length in the two soil layers both declined with increasing level of fertilizer under low level(-75kPa) of water. Fine specific root length in10-20cm and20～30cm soil layer showed a significant increase with decreased surface drip irrigation level. Fine root tissue density in three soil layers appeared to increase in general with up-regulated fertilizer level but decrease in general with down-regulated water level and no significant change was found in0～10cm soil layer. An apparent decrease in specific root length and increase in root tissue density occurred with the treatment of high water and fertilizer. The fine specific root length and tissue density in20～30cm soil layer was2373.7cm·g-1and0.427g-cm-3, which was respectively45.69%lower and48.70%higher than CK.To sum up, water and fertilizer management measures can improve the effectiveness of soil resources of forest land, so as to promote fine root proliferation and enhance the absorption ability of soil water and nutrients, which is an important mechanism how the fine root morphology respond to different treatments, which is also the main mechanism how water and fertilizer management measures enhance the productivity of forest land. On the whole, except the low-level(326g/plant) of fertilizer, three kinds of irrigation level and two kinds of fertilizer level set for Beijing sand poplar were within the suitable range in this study. Therefore, water and fertilizer management measures, including subsurface drip irrigation, surface drip irrigation and fertigation, play an important role in promoting the plantation fine root growth and reasonable distribution.