沂蒙山区金银花光合效率对土壤水分的响应

为探索抗旱灌木光合作用效率对土壤水分的响应特征与阈值效应，以沂蒙山区优势灌木金银花为材料布设盆栽模拟试验，通过人工灌水与植物自然耗水的方法进行控水处理，在不同水分梯度下测定分析了金银花的光合作用参数，并对土壤水分有效性进行了分级。结果表明:1）金银花叶片净光合速率（P_n）和水分利用效率（WUE）对土壤相对含水量（RSWC）具有明显的阈值响应规律，当RSWC分别为79.59%和47.43%时，金银花P_n、WUE达到最大值。当RSWC=29.71%时，制约光合效率的主要因子由气孔限制转为非气孔限制。2）确定了金银花光合作用的5个特征水分阈值:P_n水分补偿点、P_n水分均值点、P_n水分饱和点、WUE水分均值点和WUE水分高效点。同时，将金银花的土壤水分有效性划分了5个等级:高产高效水、高产中效水、中产高效水、低产低效水和无产无效水。3）田间水分管理时，为维持金银花较高的光合作用水平，应维持的土壤水分范围为:42.38%≤RSWC≤96.05%，避免土壤水分低于29.71%。研究结果可为沂蒙山区干旱逆境下金银花的风险诊断和田间水分管理提供科学依据。

Response of Photosynthetic Efficiency in the Leaves of Lonicera japonica to Soil Moisture in Yimeng Mountainous Area

As climate change,soil drought in spring and summer in Yimeng mountainous area is becoming more and more frequent,which seriously restricts the growth and photosynthesis of plants.To explore the characteristics and threshold effects of photosynthetic efficiency in response to soil moisture,the potted experiment was carried out with Lonicera japonica seedlings in a green house.The photosynthesis parameters under different soil water contents were measured and analyzed,and the soil moisture grading based on photosynthetic productivity was investigated.Both net photosynthetic rate (P_n) and water use efficiency (WUE) showed threshold response to the relative soil water content (RSWC).When RSWCs were 79.59% and 47.43%,respectively,both parameters reached maximum values.The main reason for P_n decreasing was turned from stomatal limitation to non-stomatal limitation when RSWC was at 29.71%.Five key water thresholds,including the water compensation point of P_n,the water saturation point of P_n or WUE,the water point of average P_n or WUE,and the turning water point of stomatal mechanism,were determined.Meanwhile,the soil moisture based on photosynthetic productivity was graded into five categories,which were high productivity and high efficiency water,high productivity and middle efficiency water,middle productivity and high efficiency water,low productivity and low efficiency water,non-productivity and non-efficiency water.When the soil moisture was at 42.38% ≤RSWC≤96.05%,both P_n and WUE were higher than the average,and the soil water range was defined as high productivity and high efficiency water.Therefore,the field soil water content should be maintained in this range so that L.japonica can obtain higher productivity and efficiency.The conclusions could offer scientific basis for the risk diagnosis and field water management of L.japonica under drought conditions in Yimeng mountainous area.