种植密度对尾巨桉幼苗光合特性和生物量分配的影响

Effects of Planting Density on Photosynthetic Characteristics and Biomass Allocation of Eucalyptus urophylla×E.grandis Seedlings

本研究从光合特性及光合产物分配两个方面阐释种植密度促进植株径向生长的作用机制。以3月龄尾巨桉DH32-29无性系为研究对象,比较分析2个种植密度下幼苗的生长性状、叶片光合特性、生物量及其分配模式。结果表明:在低种植密度条件下,尾巨桉的直径、冠幅、冠长、茎生物量、单株总叶面积、叶片净光合速率和五种光合酶活性(Rubisco、RCA、SuSy、AGPase和SBPase)均显著增大,其中直径和茎生物量分别增大26.29%、75.84%,净光合速率、Rubisco、RCA、SuSy、AGPase和SBPase分别增大145.75%、44%、40.70%、24.94%、52.17%和58.06%;而根生物量比(RMR)、根冠比(R/C)分别减小18.0%、21.0%,表明低种植密度条件下植株具有较强的光合能力和向主茎输送光合产物的能力。因此,种植密度可通过影响植株总叶面积和光合酶活性,调节植株的光合能力;同时也可影响光合产物在各器官中的分配模式,在促进主茎径向生长方面尤为突出。这为揭示密度调控林木主茎径向生长的作用机制提供了依据。

To elucidate how planting density influences stem radial growth,aspects of photosynthetic characteristics and biomass allocation,we compared the growth characteristics,leaf photosynthetic characteristics,biomass and biomass allocation model of Eucalyptus urophylla×E.grandis clone DH32-29 at age 3-month under a high planting density and a low planting density.The plants grown at the low planting density showed markedly higher stem diameter,tree crown size and stem biomass.The low planting density also led to higher total leaf area per plant with increased net leaf photosynthetic rate(Pn)and also increased activities of five key photosynthesis enzymes(Rubisco,RAC,SBPase,SuSy and AGPase).Among the traits examined,stem diameter,stem biomass,net leaf photosynthetic rate and the photosynthesis enzyme activities of Rubisco,RCA,SuSy,AGPase and SBPase increased by 26.29%,75.84%,145.75%,44.0%,40.70%,24.94%,52.2%and 58.06%respectively,whilst under the high planting density the root mass ratio(RMR)and root to crown ratio(R/C)increased by 18.0%and 21.0%respectively.These results indicated that plants grown under low planting densities acquire stronger photosynthetic capacities and better abilities to transport photosynthetic products to their stems.Accordingly,we suggest that planting density regulates the photosynthetic capacity of the plant by affecting the total leaf area and activities of key photosynthesis enzymes,while increasing stem biomass by affecting the biomass allocation in organs which contribute to radial stem growth.These results provided insights to mechanisms of stem radial growth under varying planation densities.