Role of aquaporins in root water transport of ectomycorrhizal jack pine (Pinus banksiana) seedlings exposed to NaCl and fluoride

Effects of ectomycorrhizal (ECM) fungus Suillus tomentosus on water transport properties were studied in jack pine (Pinus banksiana) seedlings. The hydraulic conductivity of root cortical cells (L_pc) and of the whole root system (L_pr) in ECM plants was higher by twofold to fourfold compared with the non‐ECM seedlings. HgCl₂ had a greater inhibitory effect on L_pc in ECM compared with non‐ECM seedlings, suggesting that the mercury‐sensitive, aquaporin (AQP)‐mediated water transport was largely responsible for the differences in L_pc between the two groups of plants. L_pc was rapidly and drastically reduced by the 50 mm NaCl treatment. However, in ECM plants, the initial decline in L_pc was followed by a quick recovery to the pre‐treatment level, while the reduction of L_pc in non‐ECM seedlings progressed over time. Treatments with fluoride reduced L_pc by about twofold in non‐ECM seedlings and caused smaller reductions of L_pc in ECM plants. When either 2 mm KF or 2 mm NaF were added to the 50 mm NaCl treatment solution, the inhibitory effect of NaCl on L_pc was rapidly reversed in both groups of plants. The results suggest that AQP‐mediated water transport may be linked to the enhancement of salt stress resistance reported for ECM plants.     

Effects of ultraviolet-B radiation on growth, mycorrhizas and mineral nutrition of silver birch (Betula pendula Roth) seedlings grown in low-nutrient conditions

The effects of increased ultraviolet‐B (UV‐B) radiation on the growth, mycorrhizas and mineral nutrition of silver birch (Betula pendula Roth) seedlings were studied in greenhouse conditions. Seedlings—planted in a birch‐forest top soil and sand substrate—were grown without additional nutrient supply. Ultraviolet treatment started immediately after the seedlings emerged and the daily integrated biologically effective UV‐B irradiance on the UV‐B‐treated plants was equivalent to a 25% depletion of stratospheric ozone under clear sky conditions. Visible symptoms of UV‐B damage or nutrient deficiency were not observed throughout the experiment. Seedling height and dry weight (DW) (measured after 58 days and 76 days of treatment) were not affected by increased UV‐B. However, a significant shift in DW allocation toward roots resulted in a lower shoot/root ratio and leaf area ratio in UV‐B‐treated plants compared to control plants. At the first harvest (after 58 days of treatment), the percentage of various mycorrhizal morphotypes and the number of short roots per unit of root length or weight were not affected by increased UV‐B despite significantly increased DW allocation toward roots. Subtle reduction in the allocation of nitrogen (N) to leaves and increased allocation of phosphorus (P) to roots may suggest cumulative effects that could affect the plant performance over the long‐term.     

桑天牛产卵分泌物对其产卵刻槽含水量、pH值及微生物数量的影响

为探讨桑天牛Apriona germari产卵分泌物对其产卵刻槽微生境的作用, 选用构树树干设置野外接虫和人工封槽两种处理, 取样测定和分析了桑天牛产卵分泌物对其产卵刻槽微生境含水量、pH值和微生物数量的影响。结果表明: 产卵4日内每日的人工封槽刻槽含水量均显著低于对照（P<0.05）, 4日后均高于对照, 产卵刻槽含水量的日变化与对照相似。产卵5日内, 人工封槽刻槽和产卵刻槽处树皮的pH值波动与对照基本一致, 5日后, 二者均高于对照, 但同日的人工封槽刻槽与产卵刻槽pH值无明显差异（P>0.05）。产卵刻槽、人工封槽刻槽与对照细菌数量比较如下: 产卵后第2日人工封槽刻槽显著高于对照和产卵刻槽（P<0.05）; 新制作与产卵后第1, 6, 7和8日人工封槽刻槽均达到极显著水平（P<0.01）; 第3日对照组的细菌数量（1 320.0±189.0）极显著高于人工封槽刻槽和产卵刻槽（P<0.01）; 第4日人工封槽刻槽显著高于产卵刻槽（P<0.05）, 但与对照无显著差异（P>0.05）; 第5日三者差异不显著（P>0.05）。分析表明桑天牛产卵分泌物具有维持刻槽微生境含水量稳定的作用, 对刻槽处树皮pH值无明显影响, 对细菌数量的增加有一定抑制作用。