雷州半岛粗皮桉蒸腾耗水特征及其与土壤水吸力的关系

Transpiration characteristics of Eucalyptus pellitain Leizhou Peninsula and its relationship with soil water suction

【目的】正确认识桉树旱雨季蒸腾耗水规律及其与土壤水分的关系,为桉树栽培抚育提供指导。【方法】在广东雷州半岛地区选择11a生桉树林设置20m×20m样地,根据每木检尺结果按径阶选择生长状况良好的粗皮桉样木3株,于2017年6-10月(雨季)和2017年11月至2018年1月(旱季),采用热扩散茎流计(德国,SF-G)对样木的蒸腾速率进行连续监测,并同步观测林分气象因子、林内降雨及土壤水吸力动态,分析0～100cm土层土壤水吸力与降雨量及粗皮桉蒸腾耗水与日潜在蒸散量和土壤水吸力的关系。【结果】各土层(0～100cm土层每20cm为一个土层)土壤水吸力与降雨量均呈极显著负相关,受降雨影响,雨季平均土壤水吸力(21.28kPa)显著小于旱季(510.44kPa);不同土层水吸力在观测期内变化趋势相同,但变化幅度差异较大。粗皮桉蒸腾速率存在明显的季节变化特征,雨季是桉树蒸腾耗水的主要时期,日平均蒸腾速率是旱季的1.8倍,各月平均单株蒸腾耗水量9月>8月>7月>6月>10月>11月>12月>1月,雨季显著大于旱季;无论是旱季还是雨季,日潜在蒸散量均与蒸腾速率呈极显著正相关。雨季蒸腾速率与各层土壤水吸力无显著相关性,但旱季与土壤水吸力呈极显著线性负相关,土壤水分在旱季成为粗皮桉蒸腾耗水的主要限制因子;旱季不同土层土壤水吸力与蒸腾速率相关性差异较大,相关系数大小为40～60cm>20～40cm>60～80cm>80～100cm>0～20cm。20～80cm土层是11a生粗皮桉的主要水分利用层。【结论】在雷州半岛地区,旱季土壤水分是限制粗皮桉蒸腾的主要因子,与潜在蒸散共同决定粗皮桉蒸腾;在无法改变光热的条件下,旱季适当补充水分,可有效提高桉树林分蒸腾,进而提高林分生产力。

【Objective】 This study investigated the transpiration and water consumption of Eucalyptus in dry and rainy seasons and its relationship with soil moisture to provide guidance for Eucalyptus cultivation.【Method】 In the Leizhou Peninsula area of Guangdong,an 11-year-old Eucalyptus forest was selected to set up a 20 m×20 m plot.According to sample-plot survey,3 sample trees with good growth were selected.From June to October 2017 (rainy season) and November 2017 to January 2018 (dry season),the transpiration rates were continuously monitored using a thermal diffusion shale flow meter (Germany,SF-G),and the meteorological factors, forest rainfall and soil water suction dynamics were simultaneously observed.The relationship between soil water suction in 0-100 cm soil layer and rainfall, the relationship between transpiration water consumption and daily evapotranspiration,and the relationship between transpiration water consumption and soil water suction were then studied.【Result】 The soil water suction of each soil layer (every 20 cm as a soil layer in the depth of 0-100 cm) had significantly negative correlation with rainfall.Affected by rainfall,the average soil water suction in the rainy season (21.28 kPa) was significantly lower than that in the dry season (510.44 kPa).The changing trend was same for water suction in different soil layers during the observation period,but the variation ranges were quite different.The transpiration rates of E. pellita had seasonal variations.The rainy season was the main period of transpiration and water consumption of Eucalyptus with daily average transpiration rate of 1.8 times that of the dry season.The average individual transpiration water consumption was in the order of September>August> July> June>October> November>December>January and the values in rainy season were significantly greater than in the dry season.The daily potential evapotranspiration had significantly positive correlation with transpiration rate in both seasons.There was no significant correlation between transpiration rate of the rainy season and soil water suction in each layer,but there was very significant negative linear correlation between dry season transpiration rate and soil water suction.Soil moisture was the major limiting factor for transpiration and water consumption of the Eucalyptus in the dry season.The relationships between dry season transpiration rate and water suction of different soil layers were quite different.The correlation coefficient was in the order of 40-60 cm>20-40 cm>60-80 cm>80-100 cm>0-20 cm.The soil layer of 20-80 cm was the main water use layer of the 11-year-old E. pellita.【Conclusion】 In the dry season of the Leizhou Peninsula,soil moisture was the main factor limiting the transpiration of the E. pellita, and it determined the transpiration together with potential evapotranspiration.With constant light and heat condition,proper water supplement measures in the dry season can effectively increase the transpiration and forest productivity of the Eucalyptus forest.