Germino Matthew J, Wraith Jon M
PO Box 8007, Department of Biology, Idaho State University, Pocatello ID 83209.
Thermal Biology Institute, Montana State University, Bozeman MT 59717.
New Phytol. 2003 Feb;157(2):241-250. doi: 10.1046/j.1469-8137.2003.00663.x.
• The effects of supraoptimal soil temperatures on plants are not well known, despite their importance with fluctuating temperatures in many habitats. The effects of warm soils on carbon gain and water relations were evaluated for Dichanthelium lanuginosum , a grass that can persist in soils sustained at > 45°C by geothermal heating. • Microclimate, root and shoot biomass, photosynthetic gas exchange, and soil/plant water relations were measured under different root-zone temperatures in the field and glasshouse. • Carbon gain at midsummer decreased markedly for plants in 35-50°C vs c. 30°C soils, due to foliar necrosis and stomatal constraints to photosynthesis. Daily rates of dehydration, estimated from changes in leaf water potential, were also 30% greater for plants in the warmer soils. Soil water, evapotranspiration, and ratios of root : shoot biomass and area could not explain greater plant dehydration in warmer soils. • Reduced uptake of soil water may therefore lead to water stress and stomatal limitations to photosynthesis in warm soils, and may thereby influence the local-scale distribution of D. lanuginosum along steep gradients of soil-temperature within geothermal basins.
• 尽管超适宜土壤温度在许多栖息地的温度波动中具有重要性，但其对植物的影响尚不为人所知。对于绒毛鸭茅（一种能在地热加热维持在45°C以上的土壤中存活的草），评估了温暖土壤对碳获取和水分关系的影响。
• 在田间和温室中，在不同根区温度下测量了小气候、根和地上部生物量、光合气体交换以及土壤/植物水分关系。
• 与约30°C土壤中的植物相比，35 - 50°C土壤中的植物在仲夏时碳获取显著下降，这是由于叶片坏死和气孔对光合作用的限制。根据叶片水势变化估算的每日脱水速率，温暖土壤中的植物也要高出30%。土壤水分、蒸散以及根:地上部生物量和面积的比率无法解释温暖土壤中植物脱水加剧的现象。
• 因此，土壤水分吸收减少可能导致温暖土壤中的水分胁迫和气孔对光合作用的限制，进而可能影响绒毛鸭茅在地热盆地内沿土壤温度陡峭梯度的局部分布。
