坡地桉树人工林蒸散作用与土壤水分功能演变研究

Eucalyptus plantation has been extending from southeast plain and lowland to west and north hill land/mountain in China. In the past decades, debate on the ecological effect on Eucalyptus has never been ended, as fast growth of Eucalyptus leads to a large amount of water consumption and an intense water competition and short harvest rotation of the silviculture might bring an integrated negative effect on ecosystem water function. Therefore, the attetion to the ecological processes of Eucalyptus ecosystem is greatly paid by scienties, governments and local people. Hill and mountain ecosystem due to its slope and thin soil stratum is likely fragile and inclined to water and soil loss. This project is to study the hydroecological processes of Eucalyptus under slope condition using integrated methodology including Grainer's sap flow, stable isotope δD and δ18O, scanning electron microscopy, Gerlach Trough and water infilation method, to probe into transpiration course and its response to soil water and slope gradient, and to illuminate water function evolvement response to age and generation of the ecosystem. As a result, this study will provide base data and theoretical support for plans of silviculture development in south China as well as other tropical and subtropical region in the world, and to maintain for regional ecological security.

我国桉树大面积人工林已由华南东南部平原和低地向北、向西山地迅速发展。近年来国内外学者对桉树人工林的生态问题一直争论不休，桉树快速生长消耗大量水分、桉树的强水分竞争力、短伐期的的营林模式可能对生态系统的水分功能产生负面影响。因此，桉树人工林的生态环境演化趋势成为学者、政府以及当地群众非常关心的问题。山地由于坡度以及土层的原因，使其十分脆弱，易于造成水土流失,人为的耕作扰动可能对土壤水分功能和生态系统持水功能产生影响。本研究针对坡地桉树人工林，采用树干液流、稳定氢氧同位素、电镜扫描、Gerlach Trough槽、土壤表面渗透性等多种技术方法,开展不同尺度的桉树人工林水分利用和土壤功能演变及水土涵养效应研究，探讨桉树在不同坡度和蒸腾过程的土壤水分效应、坡度效应，阐明桉树种植随着年龄和连栽的土壤水分功能演化特征,为探讨我国南方乃至世界热带亚热带地区林业产业生态可持续发展规划与区域生态安全提供基础

我国桉树大面积人工林已由华南东南部平原和低地向北、向西山地迅速发展。桉树人工林具有高强度的经营方式，而坡地具有易于水土流失的脆弱特性，这两种因素的叠加效应可能会对坡地桉树人工林的生态水文过程，尤其是其蒸散作用与土壤水分功能演变趋势产生重要影响，继而影响区域生态安全，但对这一问题的系统研究还十分缺乏。本项目应用热消散树干液流、稳定同位素等技术，结合环境因子监测和室内模拟控制实验，研究了不同尺度桉树的水分利用机理及其对环境驱动因子的响应规律。通过对不同经营方式、不同代际和林龄坡地桉树人工林土壤物理结构的取样测量和原位土壤入渗、蒸发实验，探求坡地桉树人工林种植对土壤物理结构与持水能力演化及其对蒸发、入渗等土壤水分过程的影响，并与地带性人工植被进行了对比。基于涡动相关和格拉槽技术，监测了坡地桉树人工林的蒸散发与地表径流过程，综合评价了坡地桉树人工林的水量平衡。结果表明：（1）桉树冠层叶片蒸腾存在异质性，桉树对土壤水分的适应能力高于本土植物青冈栎。（2）坡地桉树边材液流密度沿径向方向从外到内逐渐递减，并据此构建了新型桉树液流通量估算模型，提高了桉树人工林蒸腾耗水的估算精度；黄冕坡地桉树人工林三年平均日蒸腾耗水量为0.91 mm•d-1；（3）坡地桉树随林龄增加对土壤上层水的利用比例逐渐提高；研究期间，土壤水分不是桉树人工林水分利用的限制因素。（4）林龄增加（干扰减少）和桉树萌芽多代连续种植均会引起表土毛管孔隙率下降，为桉树蒸腾供水能力降低；（5）封育措施可以提高坡地桉树人工林的凋落物产量，并显著提高其蓄水能力。抚育经营坡地桉树人工林的凋落物产量和蓄水量与地带性人工植被差异不显著。（6）坡地桉树人工林地表径流高于次生阔叶林，接近马尾松林，但低于杉树林；（7）研究区域坡地桉树人工林年蒸散量为709.7mm，占年降雨量的53%，并没有引起系统水分过度耗散。