Topa M A, Cheeseman J M
Department of Plant Biology, 505 S. Goodwin Avenue, 265 Morrill Hall, University of Illinois, Urbana, IL 61801, USA.
Tree Physiol. 1992 Mar;10(2):195-207. doi: 10.1093/treephys/10.2.195.
Ten-week-old pond pine (Pinus serotina Michx.) seedlings were grown in solution culture at 5 or 100 microM P and under aerobic or hypoxic solution conditions. After 6 and 10 weeks in the treatments, changes in relative growth rate (RGR), P acquisition and allocation, and carbohydrate partitioning were determined by analyzing tissue for total P, soluble sugars and starch. Six weeks of low-P growth conditions decreased seedling dry weight and the ratio of shoot dry weight to root dry weight (S/R) by 39 and 51%, respectively, in comparison to seedlings from the aerobic, high-P (control) treatment. Mean RGRs of shoots in the low-P treatment were reduced by 33%, whereas root growth was unaffected. After 10 weeks of low-P growth conditions, however, both shoot and root RGRs were significantly reduced, and plants had lower S/R ratios than in any other treatment. Slowed shoot growth was accompanied by starch and nonstructural carbohydrate accumulation in needles, indicating that needle growth was not limited by carbohydrate supply. Six weeks of low-P growth conditions decreased total seedling P by 75%, reflecting a 97% reduction in the net uptake rate (NUR). Shoot NUR as a fraction of seedling NUR was also greatly reduced in the low-P treatment, indicating that low-P growth conditions affected P translocation to the shoot more than P accumulation by roots. In contrast, 6 weeks of hypoxic growth conditions decreased total dry weight of seedlings in the high-P treatment by 41% relative to their aerobic counterparts. Root growth was affected more than shoot growth, however, and S/R ratios increased. After 10 weeks, S/R ratios doubled, primarily because of the reduction in root RGR. Nevertheless, roots of hypoxic seedlings contained a higher percentage of total seedling P than their aerobic counterparts. Net P acquisition per seedling decreased by more than 50% under hypoxic growth conditions, as a result of reductions in both root RGR and seedling NUR. Starch accumulation in shoots of hypoxic seedlings reflected reductions both in root growth and in transport of carbohydrates to nonwoody roots. Carbohydrate availability did not appear to be limiting growth of hypoxic woody roots, which are well-aerated internally, but it may have limited metabolic processes in nonwoody roots of seedlings from the high-P treatment.
十周龄的池松（Pinus serotina Michx.）幼苗在5或100微摩尔/升磷的溶液培养中生长，并处于好氧或缺氧的溶液条件下。在处理6周和10周后，通过分析组织中的总磷、可溶性糖和淀粉来测定相对生长速率（RGR）、磷的获取和分配以及碳水化合物分配的变化。与好氧、高磷（对照）处理的幼苗相比，六周的低磷生长条件分别使幼苗干重和地上部干重与根部干重之比（S/R）降低了39%和51%。低磷处理中地上部的平均RGR降低了33%，而根部生长未受影响。然而，在低磷生长条件下10周后，地上部和根部的RGR均显著降低，且植株的S/R比低于其他任何处理。地上部生长减缓伴随着针叶中淀粉和非结构性碳水化合物的积累，这表明针叶生长不受碳水化合物供应的限制。六周的低磷生长条件使幼苗总磷含量降低了75%，反映出净吸收速率（NUR）降低了97%。低磷处理中地上部NUR占幼苗NUR的比例也大幅降低，这表明低磷生长条件对磷向地上部的转运影响大于根系对磷的积累。相比之下，六周的缺氧生长条件使高磷处理的幼苗总干重相对于好氧对照降低了41%。然而，根部生长比地上部生长受影响更大，且S/R比增加。10周后，S/R比翻倍，主要是由于根部RGR降低。尽管如此，缺氧幼苗的根部所含总磷占幼苗总磷的百分比高于好氧对照。在缺氧生长条件下，由于根系RGR和幼苗NUR均降低，每株幼苗的净磷获取量减少了50%以上。缺氧幼苗地上部的淀粉积累反映出根系生长以及碳水化合物向非木质根运输的减少。碳水化合物的可利用性似乎并未限制内部通气良好的缺氧木质根的生长，但可能限制了高磷处理幼苗非木质根中的代谢过程。
